Nonlinear Dynamics of the Nearshore Boundary Layer of a Large Lake (Lake Geneva)

NASA Astrophysics Data System (ADS)

Cimatoribus, Andrea A.; Lemmin, U.; Bouffard, D.; Barry, D. A.

2018-02-01

We examine nearshore and pelagic current variability in Lake Geneva, a large and deep lake in western Europe, using observations from several measurement locations and a three-dimensional numerical model for the period 2014-2016. Linear internal seiche modes excited by wind forcing clearly appear as peaks in the energy spectra for measurements in offshore locations. In contrast, spectra from the nearshore data, where currents interact with the lake bed, reveal a negligible contribution of internal seiches to the total kinetic energy. A similar contrast is seen in the spectra obtained from the numerical model at the same locations. Comparing the contribution of the different terms in the vertically averaged momentum equation from the modeling results shows that the nonlinear advective term dominates in the nearshore boundary layer. Its contribution decays with distance from shore. The width of this nearshore boundary layer, which may extend for several kilometers, seems to be mainly determined by local topography. Both field measurements and modeling results indicate that nonlinear dynamics are of primary importance in the nearshore boundary layer.

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Observing the Vertical Extent of the Urban Boundary Layer Over Jersey City, NJ: A Diurnal and Seasonal Analysis

NASA Astrophysics Data System (ADS)

Dempsey, M. J.; Booth, J.; Arend, M.; Melecio-Vazquez, D.; Gonzalez, J.

2015-12-01

The atmospheric boundary remains one of the more difficult components of the climate system to classify. One of the most important characteristics is the boundary layer height, especially in urban settings. The current study examines the boundary layer height using the the New York City Meteorological Network or NYCMetNet. NYCMetNet is a network of weather stations, which report meteorological conditions in and around New York City, as part of the Optical Remote Sensing Laboratory of The City College of New York (ORSL). Of interest to this study is the data obtained from wind profiler station LSC01. The 915 MHz wind profiler is located 30m above the ground on the roof of the Liberty Science Center in Jersey City, NJ. It is a Vaisala Wind Profiler LAP 3000 with a wavelength of ~34cm, which means that the instrument responds primarily to Bragg backscattering. Can a seasonal urban boundary layer climatology be extrapolated from the data obtained from the wind profiler? What is the timing of boundary layer evolution and collapse over Jersey City? How effective is the profiler under cloudy skies and even in light rain or snow? This study examines the entire time period covered by the wind profile (2007 to present) and selects a series of clear days and a series of cloudy days. The top of the urban boundary layer is subjectively located from each half hour time stamp of signal to noise values. The urban boundary layer heights are recorded for clear and then cloudy days. Then the days are sorted seasonally (DJF, MAM, JJA, SON). A seasonal mean is calculated for every half hour time step. Finally a time series of seasonal urban boundary layer heights is constructed, and the timing of the urban boundary layer height maximum and time evolution and collapse of the boundary layer are generalized. A comparison is made against urban boundary layer heights obtained from Modern-Era Retrospective Analysis For Research And Applications (MERRA).

Correlations for Boundary-Layer Transition on Mars Science Laboratory Entry Vehicle Due to Heat-Shield Cavities

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2008-01-01

The influence of cavities (for attachment bolts) on the heat-shield of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally in order to develop a criterion for assessing whether the boundary layer becomes turbulent downstream of the cavity. Wind tunnel tests were conducted on the 70-deg sphere-cone vehicle geometry with various cavity sizes and locations in order to assess their influence on convective heating and boundary layer transition. Heat-transfer coefficients and boundary-layer states (laminar, transitional, or turbulent) were determined using global phosphor thermography.

Fuselage boundary-layer refraction of fan tones radiated from an installed turbofan aero-engine.

PubMed

Gaffney, James; McAlpine, Alan; Kingan, Michael J

2017-03-01

A distributed source model to predict fan tone noise levels of an installed turbofan aero-engine is extended to include the refraction effects caused by the fuselage boundary layer. The model is a simple representation of an installed turbofan, where fan tones are represented in terms of spinning modes radiated from a semi-infinite circular duct, and the aircraft's fuselage is represented by an infinitely long, rigid cylinder. The distributed source is a disk, formed by integrating infinitesimal volume sources located on the intake duct termination. The cylinder is located adjacent to the disk. There is uniform axial flow, aligned with the axis of the cylinder, everywhere except close to the cylinder where there is a constant thickness boundary layer. The aim is to predict the near-field acoustic pressure, and in particular, to predict the pressure on the cylindrical fuselage which is relevant to assess cabin noise. Thus no far-field approximations are included in the modelling. The effect of the boundary layer is quantified by calculating the area-averaged mean square pressure over the cylinder's surface with and without the boundary layer included in the prediction model. The sound propagation through the boundary layer is calculated by solving the Pridmore-Brown equation. Results from the theoretical method show that the boundary layer has a significant effect on the predicted sound pressure levels on the cylindrical fuselage, owing to sound radiation of fan tones from an installed turbofan aero-engine.

Boundary-layer transition and displacement thickness effects on zero-lift drag of a series of power-law bodies at Mach 6

NASA Technical Reports Server (NTRS)

Ashby, G. C., Jr.; Harris, J. E.

1974-01-01

Wave and skin-friction drag have been numerically calculated for a series of power-law bodies at a Mach number of 6 and Reynolds numbers, based on body length, from 1.5 million to 9.5 million. Pressure distributions were computed on the nose by the inverse method and on the body by the method of characteristics. These pressure distributions and the measured locations of boundary-layer transition were used in a nonsimilar-boundary-layer program to determine viscous effects. A coupled iterative approach between the boundary-layer and pressure-distribution programs was used to account for boundary-layer displacement-thickness effects. The calculated-drag coefficients compared well with previously obtained experimental data.

Schlieren and OH* chemiluminescence imaging of combustion in a turbulent boundary layer over a solid fuel

NASA Astrophysics Data System (ADS)

Jens, Elizabeth T.; Miller, Victor A.; Cantwell, Brian J.

2016-03-01

Combustion in a turbulent boundary layer over a solid fuel is studied using simultaneous schlieren and OH* chemiluminescence imaging. The flow configuration is representative of a hybrid rocket motor combustor. Six different hydrocarbon fuels, including both classical hybrid rocket fuels and a high regression rate fuel (paraffin wax), are burned in an undiluted oxygen free-stream at pressures ranging from atmospheric to 1524.2 kPa (221.1 psi). A detailed explanation of methods for registering the schlieren and OH* chemiluminescence images to one another is presented, and additionally, details of the routines used to extract flow features of interest (like the boundary layer height and flame location) are provided. At atmospheric pressure, the boundary layer location is consistent between all fuels; however, the flame location varies for each fuel. The flame zone appears to be smoothly distributed over the fuel surface at atmospheric pressure. At elevated pressures and correspondingly increased Dahmköhler number (but at constant Reynolds number), flame morphology is markedly different, exhibiting large rollers in a shear layer above the fuel grain and finer structures in the flame. The chemiluminescence intensity is found to be roughly proportional to the fuel burn rate at both atmospheric and elevated chamber pressures.

Mars Science Laboratory Heatshield Aerothermodynamics: Design and Reconstruction

NASA Technical Reports Server (NTRS)

Edquist, Karl T.; Hollis, Brian R.; Johnston, Christopher O.; Bose, Deepak; White, Todd R.; Mahzari, Milad

2013-01-01

The Mars Science Laboratory heatshield was designed to withstand a fully turbulent heat pulse based on test results and computational analysis on a pre-flight design trajectory. Instrumentation on the flight heatshield measured in-depth temperatures in the thermal protection system. The data indicate that boundary layer transition occurred at 5 of 7 thermocouple locations prior to peak heating. Data oscillations at 3 pressure measurement locations may also indicate transition. This paper presents the heatshield temperature and pressure data, possible explanations for the timing of boundary layer transition, and a qualitative comparison of reconstructed and computational heating on the as-flown trajectory. Boundary layer Reynolds numbers that are typically used to predict transition are compared to observed transition at various heatshield locations. A uniform smooth-wall transition Reynolds number does not explain the timing of boundary layer transition observed during flight. A roughness-based Reynolds number supports the possibility of transition due to discrete or distributed roughness elements on the heatshield. However, the distributed roughness height would have needed to be larger than the pre-flight assumption. The instrumentation confirmed the predicted location of maximum turbulent heat flux near the leeside shoulder. The reconstructed heat flux at that location is bounded by smooth-wall turbulent calculations on the reconstructed trajectory, indicating that augmentation due to surface roughness probably did not occur. Turbulent heating on the downstream side of the heatshield nose exceeded smooth-wall computations, indicating that roughness may have augmented heating. The stagnation region also experienced heating that exceeded computational levels, but shock layer radiation does not fully explain the differences.

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Flow prediction over a transport multi-element high-lift system and comparison with flight measurements

NASA Technical Reports Server (NTRS)

Vijgen, P. M. H. W.; Hardin, J. D.; Yip, L. P.

1992-01-01

Accurate prediction of surface-pressure distributions, merging boundary-layers, and separated-flow regions over multi-element high-lift airfoils is required to design advanced high-lift systems for efficient subsonic transport aircraft. The availability of detailed measurements of pressure distributions and both averaged and time-dependent boundary-layer flow parameters at flight Reynolds numbers is critical to evaluate computational methods and to model the turbulence structure for closure of the flow equations. Several detailed wind-tunnel measurements at subscale Reynolds numbers were conducted to obtain detailed flow information including the Reynolds-stress component. As part of a subsonic-transport high-lift research program, flight experiments are conducted using the NASA-Langley B737-100 research aircraft to obtain detailed flow characteristics for support of computational and wind-tunnel efforts. Planned flight measurements include pressure distributions at several spanwise locations, boundary-layer transition and separation locations, surface skin friction, as well as boundary-layer profiles and Reynolds stresses in adverse pressure-gradient flow.

Experimental Results from a Flat Plate, Turbulent Boundary Layer Modified for the Purpose of Drag Reduction

NASA Astrophysics Data System (ADS)

Elbing, Brian R.

2006-11-01

Recent experiments on a flat plate, turbulent boundary layer at high Reynolds numbers (>10^7) were performed to investigate various methods of reducing skin friction drag. The methods used involved injecting either air or a polymer solution into the boundary layer through a slot injector. Two slot injectors were mounted on the model with one located 1.4 meters downstream of the nose and the second located 3.75 meters downstream. This allowed for some synergetic experiments to be performed by varying the injections from each slot and comparing the skin friction along the plate. Skin friction measurements were made with 6 shear stress sensors flush mounted along the stream-wise direction of the model.

Effect of Surface Waviness on Transition in Three-Dimensional Boundary-Layer Flow

NASA Technical Reports Server (NTRS)

Masad, Jamal A.

1996-01-01

The effect of a surface wave on transition in three-dimensional boundary-layer flow over an infinite swept wing was studied. The mean flow computed using interacting boundary-layer theory, and transition was predicted using linear stability theory coupled with the empirical eN method. It was found that decreasing the wave height, sweep angle, or freestream unit Reynolds number, and increasing the freestream Mach number or suction level all stabilized the flow and moved transition onset to downstream locations.

Boundary layer temperature measurements of a noctual urban boundary layer

NASA Astrophysics Data System (ADS)

Holloway, Simon; Ricketts, Hugo; Vaughan, Geraint

2018-04-01

A low-power lidar system based in Manchester, United Kingdom has been developed to measure temperature profiles in the nocturnal urban boundary layer. The lidar transmitter uses a 355nm diode-pumped solid state Nd:YAG laser and two narrow-band interference filters in the receiver filter out rotational Raman lines that are dependent on temperature. The spectral response of the lidar is calibrated using a monochromator. Temperature profiles measured by the system are calibrated by comparison to co-located radiosondes.

Effects of shock on hypersonic boundary layer stability

NASA Astrophysics Data System (ADS)

Pinna, F.; Rambaud, P.

2013-06-01

The design of hypersonic vehicles requires the estimate of the laminar to turbulent transition location for an accurate sizing of the thermal protection system. Linear stability theory is a fast scientific way to study the problem. Recent improvements in computational capabilities allow computing the flow around a full vehicle instead of using only simplified boundary layer equations. In this paper, the effect of the shock is studied on a mean flow provided by steady Computational Fluid Dynamics (CFD) computations and simplified boundary layer calculations.

F-16XL ship #1 wing close-up showing boundary layer detection Preston tubes

NASA Technical Reports Server (NTRS)

1995-01-01

This photo shows the boundary layer Preston tubes mounted on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Numerical investigation of an internal layer in turbulent flow over a curved hill

NASA Technical Reports Server (NTRS)

Kim, S-W.

1989-01-01

The development of an internal layer in a turbulent boundary layer flow over a curved hill is investigated numerically. The turbulence field of the boundary layer flow over the curved hill is compared with that of a turbulent flow over a symmetric airfoil (which has the same geometry as the curved hill except that the leading and trailing edge plates were removed) to study the influence of the strongly curved surface on the turbulence field. The turbulent flow equations are solved by a control-volume based finite difference method. The turbulence is described by a multiple-time-scale turbulence model supplemented with a near-wall turbulence model. Computational results for the mean flow field (pressure distributions on the walls, wall shearing stresses and mean velocity profiles), the turbulence structure (Reynolds stress and turbulent kinetic energy profiles), and the integral parameters (displacement and momentum thicknesses) compared favorably with the measured data. Computational results show that the internal layer is a strong turbulence field which is developed beneath the external boundary layer and is located very close to the wall. Development of the internal layer was more obviously observed in the Reynolds stress profiles and in the turbulent kinetic energy profiles than in the mean velocity profiles. In this regard, the internal layers is significantly different from wall-bounded simple shear layers in which the mean velocity profile characterizes the boundary layer most distinguishably. Development of such an internal layer, characterized by an intense turbulence field, is attributed to the enormous mean flow strain rate caused by the streamline curvature and the strong pressure gradient. In the turbulent flow over the curved hill, the internal layer begin to form near the forward corner of the hill, merges with the external boundary layer, and develops into a new fully turbulent boundary layer as the fluid flows in the downstream direction. For the flow over the symmetric airfoil, the boundary layer began to form from almost the same location as that of the curved hill, grew in its strength, and formed a fully turbulent boundary layer from mid-part of the airfoil and in the downstream region. Computational results also show that the detailed turbulence structure in the region very close to the wall of the curved hill is almost the same as that of the airfoil in most of the curved regions except near the leading edge. Thus the internal layer of the curved hill and the boundary layer of the airfoil were also almost the same. Development of the wall shearing stress and separation of the boundary layer at the rear end of the curved hill mostly depends on the internal layer and is only slightly influenced by the external boundary layer flow.

Asymmetric simple exclusion process with position-dependent hopping rates: Phase diagram from boundary-layer analysis.

PubMed

Mukherji, Sutapa

2018-03-01

In this paper, we study a one-dimensional totally asymmetric simple exclusion process with position-dependent hopping rates. Under open boundary conditions, this system exhibits boundary-induced phase transitions in the steady state. Similarly to totally asymmetric simple exclusion processes with uniform hopping, the phase diagram consists of low-density, high-density, and maximal-current phases. In various phases, the shape of the average particle density profile across the lattice including its boundary-layer parts changes significantly. Using the tools of boundary-layer analysis, we obtain explicit solutions for the density profile in different phases. A detailed analysis of these solutions under different boundary conditions helps us obtain the equations for various phase boundaries. Next, we show how the shape of the entire density profile including the location of the boundary layers can be predicted from the fixed points of the differential equation describing the boundary layers. We discuss this in detail through several examples of density profiles in various phases. The maximal-current phase appears to be an especially interesting phase where the boundary layer flows to a bifurcation point on the fixed-point diagram.

Asymmetric simple exclusion process with position-dependent hopping rates: Phase diagram from boundary-layer analysis

NASA Astrophysics Data System (ADS)

Mukherji, Sutapa

2018-03-01

In this paper, we study a one-dimensional totally asymmetric simple exclusion process with position-dependent hopping rates. Under open boundary conditions, this system exhibits boundary-induced phase transitions in the steady state. Similarly to totally asymmetric simple exclusion processes with uniform hopping, the phase diagram consists of low-density, high-density, and maximal-current phases. In various phases, the shape of the average particle density profile across the lattice including its boundary-layer parts changes significantly. Using the tools of boundary-layer analysis, we obtain explicit solutions for the density profile in different phases. A detailed analysis of these solutions under different boundary conditions helps us obtain the equations for various phase boundaries. Next, we show how the shape of the entire density profile including the location of the boundary layers can be predicted from the fixed points of the differential equation describing the boundary layers. We discuss this in detail through several examples of density profiles in various phases. The maximal-current phase appears to be an especially interesting phase where the boundary layer flows to a bifurcation point on the fixed-point diagram.

Results of tests on a Rockwell International space shuttle orbiter (-139 configuration) 0.0175-scale model (no. 29-0) in AEDC tunnel B to determine boundary layer characteristics

NASA Technical Reports Server (NTRS)

Quan, M.

1975-01-01

Results of wind tunnel tests were conducted to determine boundary layer characteristics on the lower surface of a space shuttle orbiter. Total pressure and temperature profile data at various model stations were obtained using a movable, four-degree-of-freedom probe mechanism and static pressure taps on the model surface. During a typical run, the probe was located over a preselected model location, then driven down through the bondary layer until contact was made with the model surface.

Experimental Investigation of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

NASA Technical Reports Server (NTRS)

Hultgren, Lennart S.; Volino, Ralph J.

2002-01-01

Modern low-pressure turbine airfoils are subject to increasingly stronger pressure gradients as designers impose higher loading in an effort to improve efficiency and to reduce part count. The adverse pressure gradients on the suction side of these airfoils can lead to boundary-layer separation, particularly under cruise conditions. Separation bubbles, notably those which fail to reattach, can result in a significant degradation of engine efficiency. Accurate prediction of separation and reattachment is hence crucial to improved turbine design. This requires an improved understanding of the transition flow physics. Transition may begin before or after separation, depending on the Reynolds number and other flow conditions, has a strong influence on subsequent reattachment, and may even eliminate separation. Further complicating the problem are the high free-stream turbulence levels in a real engine environment, the strong pressure gradients along the airfoils, the curvature of the airfoils, and the unsteadiness associated with wake passing from upstream stages. Because of the complicated flow situation, transition in these devices can take many paths that can coexist, vary in importance, and possibly also interact, at different locations and instances in time. The present work was carried out in an attempt to systematically sort out some of these issues. Detailed velocity measurements were made along a flat plate subject to the same nominal dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil ('Pak-B'). The Reynolds number based on wetted plate length and nominal exit velocity, Re, was varied from 50;000 to 300; 000, covering cruise to takeoff conditions. Low, 0.2%, and high, 7%, inlet free-stream turbulence intensities were set using passive grids. These turbulence levels correspond to about 0.2% and 2.5% turbulence intensity in the test section when normalized with the exit velocity. The Reynolds number and free-stream turbulence level do not have a significant effect on the location of boundary-layer separation unless they are high enough to induce transition upstream of separation. The location and extent of the transition zone, in contrast, depend strongly on Re and TI. The beginning of reattachment closely follows the onset of transition. Under low free-stream turbulence conditions the boundary layer is laminar at separation and then begins to exhibit fluctuations in a finite frequency band in the shear layer over the separation bubble. These fluctuations are due to instability waves. The fluctuations grow in magnitude, higher harmonics are generated, and finally lead to a breakdown to turbulence. Transition begins in the shear layer, but quickly spreads to the near wall region and causes the boundary layer to reattach. The transition is rapid and the resulting turbulence contains a full range of high and low frequencies. Under high free-stream turbulence conditions, slowly growing low-frequency fluctuations are induced in the pretransitional boundary layer by the free-stream. The separation bubbles are considerably thinner than in the low TI cases, resulting in thinner boundary layers at the end of the test wall. At Re=50,000 and 100,000, the pre-transitional boundary layer separates at about the same location as in the low TI cases. Transition occurs through a bypass mode, begins upstream of the corresponding low-TI location, and proceeds in a manner similar to that of an attached boundary layer. Under high TI at Re=200,000 and 300,000, transition begins before separation. The boundary layer may separate, but if it does the separation bubble is very short and does not significantly affect the downstream development of the boundary layer. A comparison is made to previous work in a simulated cascade.

The Effect of Aerosol on Gravity Wave Characteristics above the Boundary Layer over a Tropical Location

NASA Astrophysics Data System (ADS)

Rakshit, G.; Jana, S.; Maitra, A.

2017-12-01

The perturbations of temperature profile over a location give an estimate of the potential energy of gravity waves propagating through the atmosphere. Disturbances in the lower atmosphere due to tropical deep convection, orographic effects and various atmospheric disturbances generates of gravity waves. The present study investigates the gravity wave energy estimated from fluctuations in temperature profiles over the tropical location Kolkata (22°34' N, 88°22' E). Gravity waves are most intense during the pre-monsoon period (March-June) at the present location, the potential energy having high values above the boundary layer (2-4 km) as observed from radiosonde profiles. An increase in temperature perturbation, due to high ambient temperature in the presence of heat absorbing aerosols, causes an enhancement in potential energy. As the present study location is an urban metropolitan city experiencing high level of pollution, pollutant aerosols can go much above the normal boundary layer during daytime due to convection causing an extended boundary layer. The Aerosol Index (AAI) obtained from Global Ozone Monitoring Experiment-2 (GOME-2) on MetOp-A platform at 340 nm and 380 nm confirms the presence of absorbing aerosol particles over the present location. The Hysplit back trajectory analysis shows that the aerosol particles at those heights are of local origin and are responsible for depleting liquid water content due to cloud burning. The aerosol extinction coefficient obtained from CALIPSO data exhibits an increasing trend during 2006-2016 accompanied by a similar pattern of gravity wave energy. Thus the absorbing aerosols have a significant role in increasing the potential energy of gravity wave at an urban location in the tropical region.

SPATIAL VARIATION OF THE EVOLUTION AND STRUCTURE OF THE URBAN BOUNDARY LAYER

EPA Science Inventory

The spatial variation of the nocturnal urban boundary layer structure and the time variation of the mixing height, the nocturnal inversion top and strength after sunrise are presented for urban sites located upwind, downwind, and near the center of the heat island and for upwind ...

Improved boundary layer height measurement using a fuzzy logic method: Diurnal and seasonal variabilities of the convective boundary layer over a tropical station

NASA Astrophysics Data System (ADS)

Allabakash, S.; Yasodha, P.; Bianco, L.; Venkatramana Reddy, S.; Srinivasulu, P.; Lim, S.

2017-09-01

This paper presents the efficacy of a "tuned" fuzzy logic method at determining the height of the boundary layer using the measurements from a 1280 MHz lower atmospheric radar wind profiler located in Gadanki (13.5°N, 79°E, 375 mean sea level), India, and discusses the diurnal and seasonal variations of the measured convective boundary layer over this tropical station. The original fuzzy logic (FL) method estimates the height of the atmospheric boundary layer combining the information from the range-corrected signal-to-noise ratio, the Doppler spectral width of the vertical velocity, and the vertical velocity itself, measured by the radar, through a series of thresholds and rules, which did not prove to be optimal for our radar system and geographical location. For this reason the algorithm was tuned to perform better on our data set. Atmospheric boundary layer heights obtained by this tuned FL method, the original FL method, and by a "standard method" (that only uses the information from the range-corrected signal-to-noise ratio) are compared with those obtained from potential temperature profiles measured by collocated Global Positioning System Radio Sonde during years 2011 and 2013. The comparison shows that the tuned FL method is more accurate than the other methods. Maximum convective boundary layer heights are observed between 14:00 and 15:00 local time (LT = UTC + 5:30) for clear-sky days. These daily maxima are found to be lower during winter and postmonsoon seasons and higher during premonsoon and monsoon seasons, due to net surface radiation and convective processes over this region being more intense during premonsoon and monsoon seasons and less intense in winter and postmonsoon seasons.

Analysis and evaluation of an integrated laminar flow control propulsion system

NASA Technical Reports Server (NTRS)

Keith, Theo G., Jr.; Dewitt, Kenneth J.

1993-01-01

Reduction of drag has been a major goal of the aircraft industry as no other single quantity influences the operating costs of transport aircraft more than aerodynamic drag. It has been estimated that even modest reduction of frictional drag could reduce fuel costs by anywhere from 2 to 5 percent. Current research on boundary layer drag reduction deals with various approaches to reduce turbulent skin friction drag as a means of improving aircraft performance. One of the techniques belonging to this category is laminar flow control in which extensive regions of laminar flow are maintained over aircraft surfaces by delaying transition to turbulence through the ingestion of boundary layer air. While problems of laminar flow control have been studied in some detail, the prospect of improving the propulsion system of an aircraft by the use of ingested boundary layer air has received very little attention. An initial study for the purpose of reducing propulsion system requirements by utilizing the kinetic energy of boundary layer air was performed in the mid-1970's at LeRC. This study which was based on ingesting the boundary layer air at a single location, did not yield any significant overall propulsion benefits; therefore, the concept was not pursued further. However, since then it has been proposed that if the boundary layer air were ingested at various locations on the aircraft surface instead of just at one site, an improvement in the propulsion system might be realized. The present report provides a review of laminar flow control by suction and focuses on the problems of reducing skin friction drag by maintaining extensive regions of laminar flow over the aircraft surfaces. In addition, it includes an evaluation of an aircraft propulsion system that is augmented by ingested boundary layer air.

The Impact of Wet Soil and Canopy Temperatures on Daytime Boundary-Layer Growth.

NASA Astrophysics Data System (ADS)

Segal, M.; Garratt, J. R.; Kallos, G.; Pielke, R. A.

1989-12-01

The impact of very wet soil and canopy temperatures on the surface sensible heat flux, and on related daytime boundary-layer properties is evaluated. For very wet soils, two winter situations are considered, related to significant changes in soil surface temperature: (1) due to weather perturbations at a given location, and (2) due to the climatological north-south temperature gradient. Analyses and scaling of the various boundary-layer properties, and soil surface fluxes affecting the sensible beat flux, have been made; related evaluations show that changes in the sensible heat flux at a given location by a factor of 2 to 3 due to temperature changes related to weather perturbations is not uncommon. These changes result in significant alterations in the boundary-layer depth; in the atmospheric boundary-layer warming; and in the break-up time of the nocturnal surface temperature inversion. Investigation of the impact of the winter latitudinal temperature gradient on the above characteristics indicated that the relative increase in very wet soil sensible heat flux, due to the climatological reduction in the surface temperature in northern latitudes, moderates to some extent its reduction due to the corresponding decrease in solar radiation. Numerical model simulations confirmed these analytical evaluations.In addition, the impact of synoptic temperature perturbations during the transition seasons (fall and spring) on canopy sensible heal fluxes, and the related boundary-layer characteristics mentioned above, was evaluated. Analogous features to those found for very wet soil surfaces occurred also for the canopy situations. Likewise, evaluations were also carried out to explore the impact of high midlatitude foreste areas on the boundary-layer characteristics during the winter as compared to those during the summer. Similar impacts were found in both seasons, regardless of the substantial difference in the daily total solar radiation.

Boundary-layer and wake measurements on a swept, circulation-control wing

NASA Technical Reports Server (NTRS)

Spaid, Frank W.; Keener, Earl R.

1987-01-01

Wind-tunnel measurements of boundary-layer and wake velocity profiles and surface static pressure distributions are presented for a swept, circulation-control wing. The model is an aspect-ratio-four semispan wing mounted on the tunnel side wall at a sweep angle of 45 deg. A full-span, tangential, rearward blowing, circulation-control slot is located ahead of the trailing edge on the upper surface. Flow surveys were obtained at mid-semispan at freestream Mach numbers of 0.425 and 0.70. Boundary-layer profiles measured on the forward portions of the wing are approximately streamwise and two dimensional. The flow in the vicinity of the jet exit and in the near wake is highly three dimensional. The jet flow near the slot on the Coanda surface is directed normal to the slot. Near-wake surveys show large outboard flows at the center of the wake. At Mach 0.425 and a 5-deg angle of attack, a range of jet-blowing rates was found for which an abrupt transition from incipient separation to attached flow occurs in the boundary layer upstream of the slot. The variation in the lower-surface separation location with blowing rate was determined from boundary-layer measurements at Mach 0.425.

Investigation of Low-Pressure Turbine Endwall Flows: Simulations and Experiments (Postprint)

DTIC Science & Technology

2015-01-01

direction) minor semiaxis of 0.0417Cx (0.25in). Measured in the axial direction, the flat plate leading edge was located at x=-3.958Cx (23.75in) where...for public release; distribution unlimited. plate boundary layer is δ∗ = 1.721s/Re0.5s . For s = 4.833Cx, Reδ∗ = 1.721 √ s/CxRe = 1, 200. At this...boundary which was located at x=-1.4Cx. The following approximations hold for a turbulent flat plate boundary layer: δ99 = 0.37s Re0.2s , δ∗ = 0.046s

The velocity field created by a shallow bump in a boundary layer

NASA Technical Reports Server (NTRS)

Gaster, Michael; Grosch, Chester E.; Jackson, Thomas L.

1994-01-01

We report the results of measurements of the disturbance velocity field generated in a boundary layer by a shallow three-dimensional bump oscillating at a very low frequency on the surface of a flat plate. Profiles of the mean velocity, the disturbance velocity at the fundamental frequency and at the first harmonic are presented. These profiles were measured both upstream and downstream of the oscillating bump. Measurements of the disturbance velocity were also made at various spanwise and downstream locations at a fixed distance from the boundary of one displacement thickness. Finally, the spanwise spectrum of the disturbances at three locations downstream of the bump are presented.

Shuttle Return To Flight Experimental Results: Protuberance Effects on Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Horvath, Thomas J.

2006-01-01

The effect of isolated roughness elements on the windward boundary layer of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamic Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental effort was initiated to provide a roughness effects database for developing transition criteria to support on-orbit decisions to repair damage to the thermal protection system. Boundary layer transition results were obtained using trips of varying heights and locations along the centerline and attachment lines of 0.0075-scale models. Global heat transfer images using phosphor thermography of the Orbiter windward surface and the corresponding heating distributions were used to infer the state of the boundary layer (laminar, transitional, or turbulent). The database contained within this report will be used to formulate protuberance-induced transition correlations using predicted boundary layer edge parameters.

On the Creation of An Urban Boundary Layer Product Using The Radar Wind Profiler of the New York City Meteorological Network

NASA Astrophysics Data System (ADS)

Dempsey, M. J.; Booth, J.; Arend, M.; Melecio-Vazquez, D.

2016-12-01

The radar wind profiler (RWP) located on the Liberty Science Center in Jersey City, NJ is a part of the New York City Meteorological Network (NYCMetNet). An automatic algorithm based on those by Angevine [1] and Molod [2] is expanded upon and implemented to take RWP signal to noise ratio data and create an urban boundary layer (UBL) height product. Time series of the RWP UBL heights from clear and cloudy days are examined and compared to UBL height time series calculated from thermal data obtained from a NYCMetNet radiometer located on the roof of the Grove School of Engineering at The City College of New York. UBL data from the RWP are also compared to the MERRA (Modern Era Retrospective Analysis for Research and Applications) planetary boundary layer height time series product. A limited seasonal climatology is created from the available RWP data for clear and cloudy days and then compared to a limited seasonal climatology produced from boundary layer data obtained from MERRA and boundary layer data calculated from the CCNY radiometer. As with wind profilers in the NOAA wind profiler network, the signal return to the lowest range gates is not always the result of turbulent scattering, but from scattering from other targets such as the building itself, birds and insects. The algorithm attempts to address this during the daytime, when strong signal returns at the lowest range gates mask the SNR maxima above which are representative of the actual UBL height. Detecting the collapse and fall of the boundary layer meets with limited success, also, from the hours of 2:30pm to 5:00pm. Upper and lower range gates from the wind profiler limit observation of the nighttime boundary layer for heights falling below the lowest range gate and daytime convective boundary layer maxima rising above the highest. Due to the constraints of the instrument and the algorithm it is recommended that the boundary layer height product be constrained to the hours of 8am to 7pm.

New Boundary Layer Facility at Andøya, 69N 16E

NASA Astrophysics Data System (ADS)

Gausa, M. A.; Reuder, J.; Blindheim, S.

2016-12-01

The present presentation introduces an inative for a new boundary layer research facility on the island of Andøya (69N,16E) in Norway. The facility will appreciate international cooperation and contributions.Most boundary layer observatories (as e.g. the Lindenberg Observatory in Germany, the Cabauw facility in the Netherlands, or the Boulder Atmospheric Observatory in the US) are located in mid latitudes. Arctic or sub-arctic stations are rare or not representative due to their location in valleys (e.g. Ny Ålesund). In addition, most of the existing sites are representative for a continental boundary layer and do not allow to observe coupling processes to the free troposphere and the upper atmosphere. The island of Andøya has a unique location at 69N. To the West, Andøya is open to the Norwegian Sea. Its orology maintains an almost undisturbed marine boundary on the foreseen location under SW and W wind weather conditions. Due to rugged mountains, other wind directions provide a more transformed PBL. The understanding of the Planetary Boundary Layer (PBL), in particular with respect to turbulence and turbulent exchange processes, is crucial for a wide range of science fields and environmental monitoring tasks: To name a few: basic atmospheric science, monitoring of pollutants, weather forecast, and climate projection. The PBL is consequently research focus for several research groups, which investigate the empirical and theoretical description of this complex height region. In particular, in high latitudes this lowermost layer of the atmosphere the understanding is poor. The following research topics of the new facility are foreseen: present climate projections show their largest bias in polar regions; this is mostly attributed to inappropriate parameterization of PBL processes in the numerical models forecasts of extreme weather events at high latitudes, e.g. of Polar lows with their potential of hazards for infrastructure and traffic, are still poor for the same reason natural aerosols and anthropogenic pollutants form and change in the PBL due to chemical and coagulation processes upward transport of energy are gravity (buoyancy) waves, which in many cases originate from the PBL precise measurements of precipitation under difficult meteorological conditions

A method for coupling a parameterization of the planetary boundary layer with a hydrologic model

NASA Technical Reports Server (NTRS)

Lin, J. D.; Sun, Shu Fen

1986-01-01

Deardorff's parameterization of the planetary boundary layer is adapted to drive a hydrologic model. The method converts the atmospheric conditions measured at the anemometer height at one site to the mean values in the planetary boundary layer; it then uses the planetary boundary layer parameterization and the hydrologic variables to calculate the fluxes of momentum, heat and moisture at the atmosphere-land interface for a different site. A simplified hydrologic model is used for a simulation study of soil moisture and ground temperature on three different land surface covers. The results indicate that this method can be used to drive a spatially distributed hydrologic model by using observed data available at a meteorological station located on or nearby the site.

Natural laminar flow and airplane stability and control

NASA Technical Reports Server (NTRS)

Vandam, Cornelis P.

1986-01-01

Location and mode of transition from laminar to turbulent boundary layer flow have a dominant effect on the aerodynamic characteristics of an airfoil section. The influences of these parameters on the sectional lift and drag characteristics of three airfoils are examined. Both analytical and experimental results demonstrate that when the boundary layer transitions near the leading edge as a result of surface roughness, extensive trailing-edge separation of the turbulent boundary layer may occur. If the airfoil has a relatively sharp leading-edge, leading-edge stall due to laminar separation can occur after the leading-edge suction peak is formed. These two-dimensional results are used to examine the effects of boundary layer transition behavior on airplane longitudinal and lateral-directional stability and control.

Hypersonic Boundary Layer Instability Over a Corner

NASA Technical Reports Server (NTRS)

Balakumar, Ponnampalam; Zhao, Hong-Wu; McClinton, Charles (Technical Monitor)

2001-01-01

A boundary-layer transition study over a compression corner was conducted under a hypersonic flow condition. Due to the discontinuities in boundary layer flow, the full Navier-Stokes equations were solved to simulate the development of disturbance in the boundary layer. A linear stability analysis and PSE method were used to get the initial disturbance for parallel and non-parallel flow respectively. A 2-D code was developed to solve the full Navier-stokes by using WENO(weighted essentially non-oscillating) scheme. The given numerical results show the evolution of the linear disturbance for the most amplified disturbance in supersonic and hypersonic flow over a compression ramp. The nonlinear computations also determined the minimal amplitudes necessary to cause transition at a designed location.

Study of Unsteady Flows with Concave Wall Effect

NASA Technical Reports Server (NTRS)

Wang, Chi R.

2003-01-01

This paper presents computational fluid dynamic studies of the inlet turbulence and wall curvature effects on the flow steadiness at near wall surface locations in boundary layer flows. The time-stepping RANS numerical solver of the NASA Glenn-HT RANS code and a one-equation turbulence model, with a uniform inlet turbulence modeling level of the order of 10 percent of molecular viscosity, were used to perform the numerical computations. The approach was first calibrated for its predictabilities of friction factor, velocity, and temperature at near surface locations within a transitional boundary layer over concave wall. The approach was then used to predict the velocity and friction factor variations in a boundary layer recovering from concave curvature. As time iteration proceeded in the computations, the computed friction factors converged to their values from existing experiments. The computed friction factors, velocity, and static temperatures at near wall surface locations oscillated periodically in terms of time iteration steps and physical locations along the span-wise direction. At the upstream stations, the relationship among the normal and tangential velocities showed vortices effects on the velocity variations. Coherent vortices effect on the velocity components broke down at downstream stations. The computations also predicted the vortices effects on the velocity variations within a boundary layer flow developed along a concave wall surface with a downstream recovery flat wall surface. It was concluded that the computational approach might have the potential to analyze the flow steadiness in a turbine blade flow.

Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

2016-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

F-16XL ship #1 - CAWAP boundary layer hot film, left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. Hot film is used to measure temperature changes on a surface. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

EPA Facility Locations and Regional Boundaries - National Geospatial Data Asset (NGDA)

EPA Pesticide Factsheets

This downloadable package contains the following layers: EPA facility points, EPA region boundary polygons and EPA region boundary polygons extended to the 200nm Exclusive Economic Zone (EEZ). Included in this package are a file geodatabase (v. 10.0), Esri ArcMap map document (v. 10.0) and XML files for this record and the layer level metadata. This dataset was produced by EPA Office of Environmental Information (OEI).

Observations of the Summertime Boundary Layer over the Ross Ice Shelf, Antarctica Using SUMO UAVs

NASA Astrophysics Data System (ADS)

Nigro, M. A.; Cassano, J. J.; Jolly, B.; McDonald, A.

2014-12-01

During January 2014 Small Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe the boundary layer over the Ross Ice Shelf, Antarctica. A total of 41 SUMO flights were completed during a 9-day period with a maximum of 11 flights during a single day. Flights occurred as frequently as every 1.5 hours so that the time evolution of the boundary layer could be documented. On almost all of the flights the boundary layer was well mixed from the surface to a depth of less than 50 m to over 350 m. The depth of the well-mixed layer was observed to both increase and decrease over the course of an individual day suggesting that processes other than entrainment were altering the boundary layer depth. The well-mixed layer was observed to both warm and cool during the field campaign indicating that advective processes as well as surface fluxes were acting to control the temporal evolution of the boundary layer temperature. Only a small number of weakly stably stratified boundary layers were observed. Strong, shallow inversions, of up to 6 K, were observed above the top of the boundary layer. Observations from a 30 m automatic weather station and two temporary automatic weather stations 10 km south and west of the main field campaign location provide additional data for understanding the boundary layer evolution observed by the SUMO UAVs during this 9-day period. This presentation will discuss the observed evolution of the summertime boundary layer as well as comment on lessons learned operating the SUMO UAVs at a remote Antarctic field camp.

A numerical method for the prediction of high-speed boundary-layer transition using linear theory

NASA Technical Reports Server (NTRS)

Mack, L. M.

1975-01-01

A method is described of estimating the location of transition in an arbitrary laminar boundary layer on the basis of linear stability theory. After an examination of experimental evidence for the relation between linear stability theory and transition, a discussion is given of the three essential elements of a transition calculation: (1) the interaction of the external disturbances with the boundary layer; (2) the growth of the disturbances in the boundary layer; and (3) a transition criterion. The computer program which carried out these three calculations is described. The program is first tested by calculating the effect of free-stream turbulence on the transition of the Blasius boundary layer, and is then applied to the problem of transition in a supersonic wind tunnel. The effects of unit Reynolds number and Mach number on the transition of an insulated flat-plate boundary layer are calculated on the basis of experimental data on the intensity and spectrum of free-stream disturbances. Reasonable agreement with experiment is obtained in the Mach number range from 2 to 4.5.

Pressure-sensing performance of upright cylinders in a Mach 10 boundary-layer

NASA Technical Reports Server (NTRS)

Johnson, Steven; Murphy, Kelly

1994-01-01

An experimental research program to provide basic knowledge of the pressure-sensing performance of upright, flushported cylinders in a hypersonic boundary layer is described. Three upright cylinders of 0.25-, 0.5- and l.0-in. diameters and a conventional rake were placed in the test section sidewall boundary layer of the 31 Inch Mach 10 Wind Tunnel at NASA Langley Research Center, Hampton, Virginia. Boundary-layer pressures from these cylinders were compared to those measured with a conventional rake. A boundary-layer thickness-to-cylinder-diameter ratio of 8 proved sufficient to accurately measure an overall pressure profile and ascertain the boundary-layer thickness. Effects of Reynolds number, flow angularity, and shock wave impingement on pressure measurement were also investigated. Although Reynolds number effects were negligible at the conditions studied, flow angularity above 10 deg significantly affects the measured pressures. Shock wave impingement was used to investigate orifice-to-orifice pressure crosstalk. No crosstalk was measured. The lower pressure measured above the oblique shock wave impingement showed no influence of the higher pressure generated at the lower port locations.

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

NASA Astrophysics Data System (ADS)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

Transient Growth Analysis of Compressible Boundary Layers with Parabolized Stability Equations

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

2016-01-01

The linear form of parabolized linear stability equations (PSE) is used in a variational approach to extend the previous body of results for the optimal, non-modal disturbance growth in boundary layer flows. This methodology includes the non-parallel effects associated with the spatial development of boundary layer flows. As noted in literature, the optimal initial disturbances correspond to steady counter-rotating stream-wise vortices, which subsequently lead to the formation of stream-wise-elongated structures, i.e., streaks, via a lift-up effect. The parameter space for optimal growth is extended to the hypersonic Mach number regime without any high enthalpy effects, and the effect of wall cooling is studied with particular emphasis on the role of the initial disturbance location and the value of the span-wise wavenumber that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary layer equations, mean flow solutions based on the full Navier-Stokes (NS) equations are used in select cases to help account for the viscous-inviscid interaction near the leading edge of the plate and also for the weak shock wave emanating from that region. These differences in the base flow lead to an increasing reduction with Mach number in the magnitude of optimal growth relative to the predictions based on self-similar mean-flow approximation. Finally, the maximum optimal energy gain for the favorable pressure gradient boundary layer near a planar stagnation point is found to be substantially weaker than that in a zero pressure gradient Blasius boundary layer.

Techniques used in the F-14 variable-sweep transition flight experiment

NASA Technical Reports Server (NTRS)

Anderson, Bianca Trujillo; Meyer, Robert R., Jr.; Chiles, Harry R.

1988-01-01

This paper discusses and evaluates the test measurement techniques used to determine the laminar-to-turbulent boundary layer transition location in the F-14 variable-sweep transition flight experiment (VSTFE). The main objective of the VSTFE was to determine the effects of wing sweep on the laminar-to-turbulent transition location at conditions representative of transport aircraft. Four methods were used to determine the transition location: (1) a hot-film anemometer system; (2) two boundary-layer rakes; (3) surface pitot tubes; and (4) liquid crystals for flow visualization. Of the four methods, the hot-film anemometer system was the most reliable indicator of transition.

Effect of Protuberance Shape and Orientation on Space Shuttle Orbiter Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

King, RUdolph A.; Berry, Scott A.; Kegerise, Michael A.

2008-01-01

This document describes an experimental study conducted to examine the effects of protuberances on hypersonic boundary-layer transition. The experiment was conducted in the Langley 20-Inch Mach 6 Tunnel on a series of 0.9%-scale Shuttle Orbiter models. The data were acquired to complement the existing ground-based boundary-layer transition database that was used to develop Version 1.0 of the boundary-layer transition RTF (return-to-flight) tool. The existing ground-based data were all acquired on 0.75%-scale Orbiter models using diamond-shaped ( pizza-box ) trips. The larger model scale facilitated in manufacturing higher fidelity protuberances. The end use of this experimental database will be to develop a technical basis (in the form of a boundary-layer transition correlation) to assess representative protrusion shapes, e.g., gap fillers and protrusions resulting from possible tile repair concepts. The primary objective of this study is to investigate the effects of protuberance-trip location and geometry on Shuttle Orbiter boundary-layer transition. Secondary goals are to assess the effects of gap-filler orientation and other protrusion shapes on boundary-layer transition. Global heat-transfer images using phosphor thermography of the Orbiter windward surface and the corresponding streamwise and spanwise heating distributions were used to infer the state of the boundary layer, i.e., laminar, transitional, or turbulent.

Trip-Induced Transition Measurements in a Hypersonic Boundary Layer Using Molecular Tagging Velocimetry

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Danehy, Paul M.; Jones, Stephen B.; Johansen, Craig T.; Goyne, Christopher P.

2013-01-01

Measurements of mean streamwise velocity, fluctuating streamwise velocity, and instantaneous streamwise velocity profiles in a hypersonic boundary layer were obtained over a 10-degree half-angle wedge model. A laser-induced fluorescence-based molecular tagging velocimetry technique was used to make the measurements. The nominal edge Mach number was 4.2. Velocity profiles were measured both in an untripped boundary layer and in the wake of a 4-mm diameter cylindrical tripping element centered 75.4 mm downstream of the sharp leading edge. Three different trip heights were investigated: k = 0.53 mm, k = 1.0 mm and k = 2.0 mm. The laminar boundary layer thickness at the position of the measurements was approximately 1 mm, though the exact thickness was dependent on Reynolds number and wall temperature. All of the measurements were made starting from a streamwise location approximately 18 mm downstream of the tripping element. This measurement region continued approximately 30 mm in the streamwise direction. Additionally, measurements were made at several spanwise locations. An analysis of flow features show how the magnitude, spatial location, and spatial growth of streamwise velocity instabilities are affected by parameters such as the ratio of trip height to boundary layer thickness and roughness Reynolds number. The fluctuating component of streamwise velocity measured along the centerline of the model increased from approximately 75 m/s with no trip to +/-225 m/s with a 0.53-mm trip, and to +/-240 m/s with a 1-mm trip, while holding the freestream Reynolds number constant. These measurements were performed in the 31-inch Mach 10 Air Tunnel at the NASA Langley Research Center.

Hypersonic Boundary Layer Transition Measurements Using NO2 approaches NO Photo-dissociation Tagging Velocimetry

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Johansen, Craig T.; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Goyne, Christopher P.

2011-01-01

Measurements of instantaneous and mean streamwise velocity profiles in a hypersonic laminar boundary layer as well as a boundary layer undergoing laminar-to-turbulent transition were obtained over a 10-degree half-angle wedge model. A molecular tagging velocimetry technique consisting of a NO2 approaches?NO photo-dissociation reaction and two subsequent excitations of NO was used. The measurement of the transitional boundary layer velocity profiles was made downstream of a 1-mm tall, 4-mm diameter cylindrical trip along several lines lying within a streamwise measurement plane normal to the model surface and offset 6-mm from the model centerline. For laminar and transitional boundary layer measurements, the magnitudes of streamwise velocity fluctuations are compared. In the transitional boundary layer the fluctuations were, in general, 2-4 times larger than those in the laminar boundary layer. Of particular interest were fluctuations corresponding to a height of approximately 50% of the laminar boundary layer thickness having a magnitude of nearly 30% of the mean measured velocity. For comparison, the measured fluctuations in the laminar boundary layer were approximately 5% of the mean measured velocity at the same location. For the highest 10% signal-to-noise ratio data, average single-shot uncertainties using a 1 ?Es and 50 ?Es interframe delay were 115 m/s and 3 m/s, respectively. By averaging single-shot measurements of the transitional boundary layer, uncertainties in mean velocity as low as 39 m/s were obtained in the wind tunnel. The wall-normal and streamwise spatial resolutions were 0.14-mm (2 pixel) and 0.82-mm (11 pixels), respectively. These measurements were performed in the 31-inch Mach 10 Air Wind Tunnel at the NASA Langley Research Center.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1985-01-01

A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information. The data were analyzed by using a version of the STAN5 two-dimensional boundary layer code. The transition starting and ending points were determined by adjusting parameters in STAN5 until the calculations matched the data. The results are presented as a table of the deduced transition location and length as functions of the test parameters. The data sets reviewed cover a wide range of flow conditions, from low-speed, flat-plate tests to full-scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free-stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Diffusive boundary layers at the bottom of gaps and cracks

NASA Astrophysics Data System (ADS)

Etzold, Merlin A.; Landel, Julien R.; Dalziel, Stuart B.

2017-11-01

This work is motivated by the chemical decontamination of droplets of chemical warfare agents trapped in the gaps and cracks found in most man-made objects. We consider axial laminar flow within gaps with both straight and angled walls. We study the diffusive mass transfer from a source (e.g. a droplet surface) located at the bottom of the gap. This problem is similar to boundary layers and Graetz-type problems (heat transfer in pipe flow) with the added complication of a non-uniform lateral concentration profile due to the lateral variation of the velocity profile. We present 3D solutions for the diffusive boundary layer and demonstrate that a 2D mean-field model, for which we calculate series and similarity solutions, captures the essential physics. We demonstrate the immediate practical relevance of our findings by comparing decontamination of a droplet located in a gap and on an exposed surface.

First results of a study on turbulent boundary layers in oscillating flow with a mean adverse pressure gradient

NASA Technical Reports Server (NTRS)

Houdeville, R.; Cousteix, J.

1979-01-01

The development of a turbulent unsteady boundary layer with a mean pressure gradient strong enough to induce separation, in order to complete the extend results obtained for the flat plate configuration is presented. The longitudinal component of the velocity is measured using constant temperature hot wire anemometer. The region where negative velocities exist is investigated with a laser Doppler velocimeter system with BRAGG cells. The boundary layer responds by forced pulsation to the perturbation of potential flow. The unsteady effects observed are very important. The average location of the zero skin friction point moves periodically at the perturbation frequency. Average velocity profiles from different instants in the cycle are compared. The existence of a logarithmic region enables a simple calculation of the maximum phase shift of the velocity in the boundary layer. An attempt of calculation by an integral method of boundary layer development is presented, up to the point where reverse flow starts appearing.

A complex-lamellar description of boundary layer transition

NASA Astrophysics Data System (ADS)

Kolla, Maureen Louise

Flow transition is important, in both practical and phenomenological terms. However, there is currently no method for identifying the spatial locations associated with transition, such as the start and end of intermittency. The concept of flow stability and experimental correlations have been used, however, flow stability only identifies the location where disturbances begin to grow in the laminar flow and experimental correlations can only give approximations as measuring the start and end of intermittency is difficult. Therefore, the focus of this work is to construct a method to identify the start and end of intermittency, for a natural boundary layer transition and a separated flow transition. We obtain these locations by deriving a complex-lamellar description of the velocity field that exists between a fully laminar and fully turbulent boundary condition. Mathematically, this complex-lamellar decomposition, which is constructed from the classical Darwin-Lighthill-Hawthorne drift function and the transport of enstrophy, describes the flow that exists between the fully laminar Pohlhausen equations and Prandtl's fully turbulent one seventh power law. We approximate the difference in enstrophy density between the boundary conditions using a power series. The slope of the power series is scaled by using the shape of the universal intermittency distribution within the intermittency region. We solve the complex-lamellar decomposition of the velocity field along with the slope of the difference in enstrophy density function to determine the location of the laminar and turbulent boundary conditions. Then from the difference in enstrophy density function we calculate the start and end of intermittency. We perform this calculation on a natural boundary layer transition over a flat plate for zero pressure gradient flow and for separated shear flow over a separation bubble. We compare these results to existing experimental results and verify the accuracy of our transition model.

An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

NASA Technical Reports Server (NTRS)

Dittmar, J. H.; Burns, R. J.; Leciejewski, D. J.

1984-01-01

Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear.

Flight Demonstration of a Shock Location Sensor Using Constant Voltage Hot-Film Anemometry

NASA Technical Reports Server (NTRS)

Moes, Timothy R.; Sarma, Garimella R.; Mangalam, Siva M.

1997-01-01

Flight tests have demonstrated the effectiveness of an array of hot-film sensors using constant voltage anemometry to determine shock position on a wing or aircraft surface at transonic speeds. Flights were conducted at the NASA Dryden Flight Research Center using the F-15B aircraft and Flight Test Fixture (FTF). A modified NACA 0021 airfoil was attached to the side of the FTF, and its upper surface was instrumented to correlate shock position with pressure and hot-film sensors. In the vicinity of the shock-induced pressure rise, test results consistently showed the presence of a minimum voltage in the hot-film anemometer outputs. Comparing these results with previous investigations indicate that hot-film anemometry can identify the location of the shock-induced boundary layer separation. The flow separation occurred slightly forward of the shock- induced pressure rise for a laminar boundary layer and slightly aft of the start of the pressure rise when the boundary layer was tripped near the airfoil leading edge. Both minimum mean output and phase reversal analyses were used to identify the shock location.

Numerical modeling of the transitional boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Ivanov, Dimitry; Chorny, Andrei

2015-11-01

Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Special attention was paid to the near-wall region in order to capture all levels of the boundary layer. In this study, the numerical software package OpenFOAM has been used in order to solve the flow field. The results were used in a comparative study with data obtained from Large Eddy Simulation (LES). The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. Presently this model is extended to the LES of the zero-pressure gradient, flat-plate turbulent boundary layer. In current study the time discretization is based on a second order Crank-Nicolson/Adams-Bashforth method. LES solver using Smagorinsky and the one-equation LES turbulence models. The transition models significantly improve the prediction of the onset location compared to the fully turbulent models.LES methods appear to be the most promising new tool for the design and analysis of flow devices including transition regions of the turbulent flow.

Stability of hypersonic boundary-layer flows with chemistry

NASA Technical Reports Server (NTRS)

Reed, Helen L.; Stuckert, Gregory K.; Haynes, Timothy S.

1993-01-01

The effects of nonequilibrium chemistry and three dimensionality on the stability characteristics of hypersonic flows are discussed. In two-dimensional (2-D) and axisymmetric flows, the inclusion of chemistry causes a shift of the second mode of Mack to lower frequencies. This is found to be due to the increase in size of the region of relative supersonic flow because of the lower speeds of sound in the relatively cooler boundary layers. Although this shift in frequency is present in both the equilibrium and nonequilibrium air results, the equilibrium approximation predicts modes which are not observed in the nonequilibrium calculations (for the flight conditions considered). These modes are superpositions of incoming and outgoing unstable disturbances which travel supersonically relative to the boundary-layer edge velocity. Such solutions are possible because of the finite shock stand-off distance. Their corresponding wall-normal profiles exhibit an oscillatory behavior in the inviscid region between the boundary-layer edge and the bow shock. For the examination of three-dimensional (3-D) effects, a rotating cone is used as a model of a swept wing. An increase of stagnation temperature is found to be only slightly stabilizing. The correlation of transition location (N = 9) with parameters describing the crossflow profile is discussed. Transition location does not correlate with the traditional crossflow Reynolds number. A new parameter that appears to correlate for boundary-layer flow was found. A verification with experiments on a yawed cone is provided.

High sensitivity boundary layer transition detector

NASA Technical Reports Server (NTRS)

Azzazy, M.; Modarress, D.; Hoeft, T.

1985-01-01

A high sensitivity differential interferometer has been developed to locate the region where the boundary layer flow changes from laminar to turbulent. Two experimental configurations have been used to evaluate the performance of the interferometer, open shear layer configuration and wind tunnel turbulent spot configuration. In each experiment small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements have been compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of .001 the laser wavelength.

Deplacement effect of the laminar boundary layer and the pressure drag

NASA Technical Reports Server (NTRS)

Gortler, H

1951-01-01

The displacement effect of the boundary layer on the outer frictionless flow is discussed for both steady and unsteady flows. The analysis is restricted to cases in which the potential flow pressure distribution remains valid for the boundary-layer calculation. Formulas are given for the dependence of the pressure drag, friction drag, and total drag of circular cylinders on the time from the start of motion for cases in which the velocity varies as a power of the time. Formulas for the locations and for the time for the appearance of the separation point are given for two dimensional bodies of arbitrary shape.

Boundary layer separation on isolated boattail nozzles. M.S. Thesis; [conducted in the Langley 16-foot transonic wind tunnel

NASA Technical Reports Server (NTRS)

Abeyounis, W. K.

1977-01-01

The phenomenon of separated flow on a series of circular-arc afterbodies was investigated using the Langley 16-foot transonic tunnel at free-stream Mach numbers from 0.40 to 0.95 at 0 deg angle of attack. Both high-pressure air and solid circular cylinders with a diameter equal to the nozzle exit diameter were used to simulate jet exhausts. A detailed data base of boundary layer separation locations was obtained using oil-flow techniques. The results indicate that boundary layer separation is most extensive on steep boattails at high Mach numbers.

Numerical study of Reynolds stress in compressible flows

NASA Technical Reports Server (NTRS)

Vandromme, D.; Hamin, H.

1985-01-01

A second order closure has been implemented in an implicit Navier-Stokes solver to study the behavior of the Reynolds stresses under the influence of severe pressure gradients. In the boundary layer zone, the strongly sheared character of the mean flow dominates the turbulence generation mechanisms. However, the pressure gradients also play a very important role for these processes, but at different locations within the boundary layer.

Stability of the Boundary Layer and the Spot

NASA Technical Reports Server (NTRS)

Wygnanski, I.

2007-01-01

The similarity among turbulent spots observed in various transition experiments, and the rate in which they contaminate the surrounding laminar boundary layer is only cursory. The shape of the spot depends on the Reynolds number of the surrounding boundary layer and on the pressure gradient to which it and the surrounding laminar flow are exposed. The propagation speeds of the spot boundaries depend, in addition, on the location from which the spot originated and do not simply scale with the local free stream velocity. The understanding of the manner in which the turbulent manner in which the turbulent spot destabilizes the surrounding, vortical fluid is a key to the understanding of the transition process. We therefore turned to detailed observations near the spot boundaries in general and near the spanwise tip of the spot in particular.

Effects of resolved boundary layer turbulence on near-ground rotation in simulated quasi-linear convective systems (QLCSs)

NASA Astrophysics Data System (ADS)

Nowotarski, C. J.

2017-12-01

Though most strong to violent tornadoes are associated with supercell thunderstorms, quasi-linear convective systems (QLCSs) pose a risk of tornadoes, often at times and locations where supercell tornadoes are less common. Because QLCS low-level mesocyclones and tornado signatures tend to be less coherent, forecasting such tornadoes remains particularly difficult. The majority of simulations of such storms rely on horizontally homogeneous base states lacking resolved boundary layer turbulence and surface fluxes. Previous work has suggested that heterogeneities associated with boundary layer turbulence in the form of horizontal convective rolls can influence the evolution and characteristics of low-level mesocyclones in supercell thunderstorms. This study extends methods for generating boundary layer convection to idealized simulations of QLCSs. QLCS simulations with resolved boundary layer turbulence will be compared against a control simulation with a laminar boundary layer. Effects of turbulence, the resultant heterogeneity in the near-storm environment, and surface friction on bulk storm characteristics and the intensity, morphology, and evolution of low-level rotation will be presented. Although maximum surface vertical vorticity values are similar, when boundary layer turbulence is included, a greater number of miso- and meso-scale vortices develop along the QLCS gust front. The source of this vorticity is analyzed using Eulerian decomposition of vorticity tendency terms and trajectory analysis to delineate the relative importance of surface friction and baroclinicity in generating QLCS vortices. The role of anvil shading in suppressing boundary layer turbulence in the near-storm environment and subsequent effects on QLCS vortices will also be presented. Finally, implications of the results regarding inclusion of more realistic boundary layers in future idealized simulations of deep convection will be discussed.

Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models

NASA Technical Reports Server (NTRS)

Eastman, Timothy E.

1995-01-01

Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key theoretical issues have been discussed for over two decades. This is because plasma instruments deployed prior to the ISEE and AMPTE missions did not have the required time resolution and most ISEE investigations to-date have focused on tests of MHD plasma models, especially reconnection. More recently, many phenomenological and theoretical models have been developed to explain the existence and characteristics of the magnetospheric boundary layers with only limited success to date. The cases with no boundary layer treated in this study provide a contrary set of conditions to those observed with a boundary layer. For the measured parameters of such cases, a successful boundary layer model should predict no plasma penetration across the magnetopause. Thus, this research project provides the first direct observational tests of magnetopause models using pristine magnetopause crossings and provides important new results on magnetopause microstructure and associated kinetic processes.

Heat Shield Cavity Parametric Experimental Aeroheating for a Proposed Mars Smart Lander Aeroshell

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Hollis, Brian R.

2002-01-01

The proposed Mars Smart Lander is to be attached through its aeroshell to the main spacecraft bus, thereby producing cavities in the heat shield. To study the effects these cavities will have on the heating levels experienced by the heat shield, an experimental aeroheating investigation was performed at the NASA Langley Research Center in the 20-Inch Mach 6 Air Tunnel. The effects of Reynolds number, angle-of-attack, and cavity size and location on aero-heating levels and distributions were determined and are presented. To aid the discussion on the effects of the cavities, laminar, thin-layer Navier-Stokes flow field solutions were post-processed to calculate relevant boundary layer properties such as boundary layer height and momentum thickness, edge Mach number, and streamwise pressure gradient. It was found that the effect of the cavities varies with angle-of-attack, freestream Reynolds number, and cavity size and location. The presence of a cavity raised the downstream heating rates by as much as 325% as a result of boundary layer transition.

A Low-Speed Experimental Investigation of the Effect of a Sandpaper Type of Roughness on Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

Von Doenhoff, Albert E; Horton, Elmer A

1958-01-01

An investigation was made in the Langley low-turbulence pressure tunnel to determine the effect of size and location of a sandpaper type of roughness on the Reynolds number for transition. Transition was observed by means of a hot-wire anemometer located at various chordwise stations for each position of the roughness. These observations indicated that when the roughness is sufficiently submerged in the boundary layer to provide a substantially linear variation of boundary-layer velocity with distance from the surface up to the top of the roughness, turbulent "spots" begin to appear immediately behind the roughness when the Reynolds number based on the velocity at the top of the roughness height exceeds a value of approximately 600. At Reynolds numbers even slightly below the critical value (value for transition), the sandpaper type of roughness introduced no measurable disturbances into the laminar layer downstream of the roughness. The extent of the roughness area does not appear to have an important effect on the critical value of the roughness Reynolds number.

Dual polarization micropulse lidar observations of the diurnal evolution of atmospheric boundary layer over a tropical coastal station

NASA Astrophysics Data System (ADS)

Rajeev, K.; Mishra, Manoj K.; Sunilkumar, S. V.; Sijikumar, S.

2016-05-01

High-resolution dual polarized micropulse lidar (MPL) observations have been used to investigate the diurnal evolution of atmospheric boundary layer (ABL) during winter (2008-2011) over Thiruvananthapuram (8.5°N, 77°E), a tropical coastal station located at southwest Peninsular India, adjoining the Arabian Sea. The lidar observations are compared with the boundary layer characteristics derived from concurrent balloon-borne radiosonde observations. This study shows that the mixed layer height over this coastal station generally increases from <300 m in the morning to 1500 m by the afternoon. Growth rate of the mixed layer height is rapid ( 350 m/hr) during 09-11 IST and slows down with time to <150 m/hr during 11-14 IST and <90 m/hr during 14-16 IST. Thermal internal boundary layer during the afternoon, caused by sea breeze circulation, extends up to 500 m altitude and is characterized by highly spherical aerosols, while a distinctly non-spherical aerosol layer appear above this altitude, in the return flow arising from the landmass.

Persistent Structures in the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Palumbo, Dan; Chabalko, Chris

2005-01-01

Persistent structures in the turbulent boundary layer are located and analyzed. The data are taken from flight experiments on large commercial aircraft. An interval correlation technique is introduced which is able to locate the structures. The Morlet continuous wavelet is shown to not only locates persistent structures but has the added benefit that the pressure data are decomposed in time and frequency. To better understand how power is apportioned among these structures, a discrete Coiflet wavelet is used to decompose the pressure data into orthogonal frequency bands. Results indicate that some structures persist a great deal longer in the TBL than would be expected. These structure contain significant power and may be a primary source of vibration energy in the airframe.

Experimental Investigation of Normal Shock Boundary-Layer Interaction with Hybrid Flow Control

NASA Technical Reports Server (NTRS)

Vyas, Manan A.; Hirt, Stefanie M.; Anderson, Bernhard H.

2012-01-01

Hybrid flow control, a combination of micro-ramps and micro-jets, was experimentally investigated in the 15x15 cm Supersonic Wind Tunnel (SWT) at the NASA Glenn Research Center. Full factorial, a design of experiments (DOE) method, was used to develop a test matrix with variables such as inter-ramp spacing, ramp height and chord length, and micro-jet injection flow ratio. A total of 17 configurations were tested with various parameters to meet the DOE criteria. In addition to boundary-layer measurements, oil flow visualization was used to qualitatively understand shock induced flow separation characteristics. The flow visualization showed the normal shock location, size of the separation, path of the downstream moving counter-rotating vortices, and corner flow effects. The results show that hybrid flow control demonstrates promise in reducing the size of shock boundary-layer interactions and resulting flow separation by means of energizing the boundary layer.

Discrete Roughness Effects on Shuttle Orbiter at Mach 6

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Hamilton, H. Harris, II

2002-01-01

Discrete roughness boundary layer transition results on a Shuttle Orbiter model in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed with new boundary layer calculations to provide consistency for comparison to other published results. The experimental results were previously obtained utilizing the phosphor thermography system to monitor the status of the boundary layer via global heat transfer images of the Orbiter windward surface. The size and location of discrete roughness elements were systematically varied along the centerline of the 0.0075-scale model at an angle of attack of 40 deg and the boundary layer response recorded. Various correlative approaches were attempted, with the roughness transition correlations based on edge properties providing the most reliable results. When a consistent computational method is used to compute edge conditions, transition datasets for different configurations at several angles of attack have been shown to collapse to a well-behaved correlation.

Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

NASA Technical Reports Server (NTRS)

Obara, C. J.; Holmes, B. J.

1985-01-01

Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.

Visualization of boundary-layer development on turbomachine blades with liquid crystals

NASA Technical Reports Server (NTRS)

Vanzante, Dale E.; Okiishi, Theodore H.

1991-01-01

This report documents a study of the use of liquid crystals to visualize boundary layer development on a turbomachine blade. A turbine blade model in a linear cascade of blades was used for the tests involved. Details of the boundary layer development on the suction surface of the turbine blade model were known from previous research. Temperature sensitive and shear sensitive liquid crystals were tried as visual agents. The temperature sensitive crystals were very effective in their ability to display the location of boundary layer flow separation and reattachment. Visualization of natural transition from laminar to turbulent boundary layer flow with the temperature sensitive crystals was possible but subtle. The visualization of separated flow reattachment with the shear sensitive crystals was easily accomplished when the crystals were allowed to make a transition from the focal-conic to a Grandjean texture. Visualization of flow reattachment based on the selective reflection properties of shear sensitive crystals was achieved only marginally because of the larger surface shear stress and shear stress gradient levels required for more dramatic color differences.

Dryline on 22 May 2002 During IHOP: Convective Scale Measurements at the Profiling Site

NASA Technical Reports Server (NTRS)

Demoz, Belay; Flamant, Cyrille; Miller, David; Evans, Keith; Fabry, Federic; DiGirolamo, Paolo; Whiteman, David; Geerts, Bart; Weckwerth, Tammy; Brown, William

2004-01-01

A unique set of measurements of wind, water vapor mixing ratio and boundary layer height variability was observed during the first MOP dryline mission of 22 May 2002. Water vapor mixing ratio from the Scanning Raman Lidar (SRL), high-resolution profiles of aerosol backscatter from the HARLIE and wind profiles from the GLOW are combined with the vertical velocity derived from the NCAR/ISS/MAPR and the high-resolution FMCW radar to reveal the convective variability of the cumulus cloud-topped boundary layer. A combined analysis of the in-situ and remote sensing data from aircraft, radiosonde, lidars, and radars reveals moisture variability within boundary layer updraft and downdraft regions as well as characterizes the boundary layer height variability in the dry and moist sides of the dryline. The profiler site measurements will be tied to aircraft data to reveal the relative intensity and location of these updrafts to the dry line. This study provides unprecedented high temporal and spatial resolution measurements of wind, moisture and backscatter within a dryline and the associated convective boundary layer.

Trade cumulus clouds embedded in a deep regional haze: Results from Indian Ocean CARDEX experiment

NASA Astrophysics Data System (ADS)

Wilcox, E. M.; Thomas, R. M.; Praveen, P. S.; Pistone, K.; Bender, F.; Feng, Y.; Ramanathan, V.

2013-12-01

During the winter monsoon, trade cumulus clouds over the North Indian Ocean are embedded within a deep regional haze described as an atmospheric brown cloud. While the trade-cu clouds are largely confined to the marine boundary layer, the sooty brown cloud extends from the boundary layer to as high as 3 km; well above the tops of the cumulus. The boundary layer pollution is persistent and limits drizzle in the cumulus over a period of greater than a month at the Maldives Climate Observatory located at Hanimaadhoo Island. The elevated haze from 1 to 3 km altitude is episodic and strongly modulated by synoptic variability in the 700 hPa flow. The elevated plume enhances heating above the marine boundary layer through daytime absorption of sunlight by the haze particles. The interplay between the microphysical modification of clouds by boundary layer pollution and the episodic elevated heating by the atmospheric brown cloud are explored in in-situ observations from UAVs and surface remote sensing during the CARDEX field campaign of winter 2012 and supported by multi-year analysis of satellite remote sensing observations. These observations document the variability in pollution at the surface and above the marine boundary layer and the effects of pollution on the microphysics of the trade-cu clouds, the depth of the marine boundary layer, the liquid water path of trade-cu clouds, and the profile of turbulent moisture flux through the boundary layer. The consequences of these effects for the radiative forcing of regional climate will be discussed.

Measured Boundary Layer Transition and Rotor Hover Performance at Model Scale

NASA Technical Reports Server (NTRS)

Overmeyer, Austin D.; Martin, Preston B.

2017-01-01

An experiment involving a Mach-scaled, 11:08 f t: diameter rotor was performed in hover during the summer of 2016 at NASA Langley Research Center. The experiment investigated the hover performance as a function of the laminar to turbulent transition state of the boundary layer, including both natural and fixed transition cases. The boundary layer transition locations were measured on both the upper and lower aerodynamic surfaces simultaneously. The measurements were enabled by recent advances in infrared sensor sensitivity and stability. The infrared thermography measurement technique was enhanced by a paintable blade surface heater, as well as a new high-sensitivity long wave infrared camera. The measured transition locations showed extensive amounts, x=c>0:90, of laminar flow on the lower surface at moderate to high thrust (CT=s > 0:068) for the full blade radius. The upper surface showed large amounts, x=c > 0:50, of laminar flow at the blade tip for low thrust (CT=s < 0:045). The objective of this paper is to provide an experimental data set for comparisons to newly developed and implemented rotor boundary layer transition models in CFD and rotor design tools. The data is expected to be used as part of the AIAA Rotorcraft SimulationWorking Group

Feasibility of generating an artificial burst in a turbulent boundary layer, phase 2

NASA Technical Reports Server (NTRS)

Gad-El-hak, Mohamed

1989-01-01

Various drag accounts for about half of the total drag on commercial aircraft at subsonic cruise conditions. Two avenues are available to achieve drag reduction: either laminar flow control or turbulence manipulation. The present research deals with the latter approach. The primary objective of Phase 2 research was to investigate experimentally the feasibility of substantially reducing the skin-friction drag in a turbulent boundary layer. The method combines the beneficial effects of suction and a longitudinally ribbed surface. At a sufficiently large spanwise separation, the streamwise grooves act as a nucleation site causing a focusing of low-speed streaks over the peaks. Suction is then applied intermittently through longitudinal slots located at selected locations along those peaks to obliterate the low-speed regions and to prevent bursting. Phase 2 research was divided into two tasks. In the first, selective suction from a single streamwise slot was used to eliminate either a single burst-like event or a periodic train of artificially generated bursts in laminar and turbulent boundary layers that develop on a flat plate towed in a water channel. The results indicate that equivalent values of the suction coefficient as low as 0.0006 were sufficient to eliminate the artificially generated bursts in a laminar boundary layer.

Turbulent Output-Based Anisotropic Adaptation

NASA Technical Reports Server (NTRS)

Park, Michael A.; Carlson, Jan-Renee

2010-01-01

Controlling discretization error is a remaining challenge for computational fluid dynamics simulation. Grid adaptation is applied to reduce estimated discretization error in drag or pressure integral output functions. To enable application to high O(10(exp 7)) Reynolds number turbulent flows, a hybrid approach is utilized that freezes the near-wall boundary layer grids and adapts the grid away from the no slip boundaries. The hybrid approach is not applicable to problems with under resolved initial boundary layer grids, but is a powerful technique for problems with important off-body anisotropic features. Supersonic nozzle plume, turbulent flat plate, and shock-boundary layer interaction examples are presented with comparisons to experimental measurements of pressure and velocity. Adapted grids are produced that resolve off-body features in locations that are not known a priori.

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

2008-01-01

An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.

Thermal boundary layer profiles in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Tong, Penger; Wang, Yin; He, Xiaozhou

2015-11-01

We have studied the mean temperature boundary layer profile T(z) and root-mean-square (rms) temperature profile S(z) in turbulent Rayleigh-Benard convection along the central axis z of a convection cell, which has a thin vertical disk shape with an inner diameter D = 18 cm. The temperature measurements were made at fixed Prandtl numbers Pr = 4.3 and Pr = 7.6 and with the Rayleigh number Ra varied in the range between 1 ×109 and 1 ×1010 . The measured T(z) for different values of Pr and Ra can all be well described by the newly proposed boundary layer model with a parameter c varying from 1 to 2.1. The measured rms temperature profile S(z) is found to be a single-peaked function with the peak position located at z ~= 0 . 8 δ , where δ is the boundary layer thickness. The measured S(z) has two separate scaling lengths. Within the boundary layer, it scales with δ and can be fitted to a power law, S (z) ~(z / δ) α with α ~= 0 . 6 . Outside the boundary layer, it scales with the cell size D and follows a different power law, S (z) ~(z / D) β , with β = - 0 . 42 . This work was supported by the Research Grants Council of Hong Kong SAR.

Planetary Boundary Layer Patterns, Height Variability and their Controls over the Indian Subcontinent with respect to Monsoon

NASA Astrophysics Data System (ADS)

Sathyanadh, A.; Karipot, A.; Prabhakaran, T.

2016-12-01

Planetary boundary layer (PBL) height and its controlling factors undergo large variations at different spatio-temporal scales over land regions. In the present study, Modern Era Retrospective analysis for Research and Applications (MERRA) data products are used to investigate variations of PBL height and its controls in relation to different phases of Indian monsoon. MERRA PBL height validations carried out against those estimated from radiosonde and Global Positioning System Radio Occultation atmospheric profiles revealed fairly good agreement. Different PBL patterns are identified in terms of maximum height, its time of occurrence and growth rate, and they vary with respect to geographical locations, terrain characteristics and monsoon circulation. The pre-monsoon boundary layers are the deepest over the region, often exceeding 4 km and grow at a rate of approximately 400 m hr-1. Large nocturnal BL depths, possibly related to weakly convective residual layers, are another feature noted during dry conditions. Monsoon BLs are generally shallower, except where rainfall is scanty. The break-monsoon periods have slightly deeper BLs than the active monsoon phase. The controlling factors for the observed boundary layer behaviour are investigated using supplementary MERRA datasets. Evaporative fraction is found to have dominant control on the PBL height varying with seasons and regions. The characteristics and controls of wet and dry boundary layer regimes over inland and coastal locations are different. The fractional diffusion (ratio of non-local and total diffusion) coefficient analyses indicated that enhanced entrainment during monsoon contributes to reduction in PBLH unlike in the dry period. The relationship between controls and PBLH are better defined over inland than coastal regions. The wavelet cross spectral analysis revealed temporal variations in dominant contributions from the controlling factors at different periodicities during the course of the year.

Augmenting ejector endwall effects. [V/STOL aircraft

NASA Technical Reports Server (NTRS)

Porter, J. L.; Squyers, R. A.

1979-01-01

Rectangular inlet ejectors which had multiple hypermixing nozzles for their primary jets were investigated for the effects of endwall blowing on thrust augmentation performance. The ejector configurations tested had both straight wall and active boundary layer control type diffusers. Endwall flows were energized and controlled by simple blowing jets suitably located in the ejector. Both the endwall and boundary layer control diffuser blowing rates were varied to determine optimum performance. High area ratio diffusers with insufficient endwall blowing showed endwall separation and rapid degradation of thrust performance. Optimized values of diffuser boundary layer control and endwall nozzle blowing rates in an ejector augmenter were shown to achieve high levels of augmentation performance for maximum compactness.

Numerical investigations of shock wave interaction with laminar boundary layer on compressor profile

NASA Astrophysics Data System (ADS)

Piotrowicz, M.; Flaszyński, P.

2016-10-01

The investigation of shockwave boundary layer interaction on suction side of transonic compressor blade is one of main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to look more closely into the flow structure on suction side of a profile, a design of generic test section in linear transonic wind tunnel was proposed. The experimental and numerical results of flow structure on a suction side of the compressor profile investigations are presented. The numerical simulations are carried out for EARSM (Explicit Algebraic Reynolds Stress Model) turbulence model with transition model. The result are compared with oil flow visualisation, schlieren pictures, Pressure Sensitive Paint (PSP) and static pressure.

Assessment of an Euler-Interacting Boundary Layer Method Using High Reynolds Number Transonic Flight Data

NASA Technical Reports Server (NTRS)

Bonhaus, Daryl L.; Maddalon, Dal V.

1998-01-01

Flight-measured high Reynolds number turbulent-flow pressure distributions on a transport wing in transonic flow are compared to unstructured-grid calculations to assess the predictive ability of a three-dimensional Euler code (USM3D) coupled to an interacting boundary layer module. The two experimental pressure distributions selected for comparative analysis with the calculations are complex and turbulent but typical of an advanced technology laminar flow wing. An advancing front method (VGRID) was used to generate several tetrahedral grids for each test case. Initial calculations left considerable room for improvement in accuracy. Studies were then made of experimental errors, transition location, viscous effects, nacelle flow modeling, number and placement of spanwise boundary layer stations, and grid resolution. The most significant improvements in the accuracy of the calculations were gained by improvement of the nacelle flow model and by refinement of the computational grid. Final calculations yield results in close agreement with the experiment. Indications are that further grid refinement would produce additional improvement but would require more computer memory than is available. The appendix data compare the experimental attachment line location with calculations for different grid sizes. Good agreement is obtained between the experimental and calculated attachment line locations.

F-16XL ship #1 CAWAP flight

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Gas diffusion in and out of super-hydrophobic surface in transitional and turbulent boundary layers

NASA Astrophysics Data System (ADS)

Ling, Hangjian; Fu, Matthew; Hultmark, Marcus; Katz, Joseph

2017-11-01

The rate of gas diffusion in and out of a super-hydrophobic surface (SHS) located in boundary layers is investigated at varying Reynolds numbers and ambient pressures. The hierarchical SHS consists of nano-textured, 100 μm wide spanwise grooves. The boundary layers over the SHS under the Cassie-Baxter and Wenzel states as well as a smooth wall at same conditions are characterized by particle image velocimetry. The Reynolds number based on momentum thickness of the smooth wall, ReΘ0, ranges from 518 to 2088, covering transitional and turbulent boundary layer regimes. The mass diffusion rate is estimated by using microscopy to measure the time-evolution of plastron shape and volume. The data is used for calculating the Sherwood number based on smooth wall momentum thickness, ShΘ0. As expected, the diffusion rate increases linearly with the under- or super-saturation level, i.e., ShΘ0 is independent of ambient pressure. For the turbulent boundary layers, the data collapses onto ShΘ0 = 0.47ReΘ00.77 . For the transitional boundary layer, ShΘ0 is lower than the turbulent power law. When ShΘ0 is plotted against the friction Reynolds number (Reτ0) , both the transitional and turbulent boundary layer data collapse onto a single power law, ShΘ0 = 0.34Reτ00.913 . Results scaled based on Wenzel state momentum thickness show very similar trends. Sponsored by ONR.

The effect of acoustic forcing on an airfoil tonal noise mechanism.

PubMed

Schumacher, Karn L; Doolan, Con J; Kelso, Richard M

2014-08-01

The response of the boundary layer over an airfoil with cavity to external acoustic forcing, across a sweep of frequencies, was measured. The boundary layer downstream of the cavity trailing edge was found to respond strongly and selectively at the natural airfoil tonal frequencies. This is considered to be due to enhanced feedback. However, the shear layer upstream of the cavity trailing edge did not respond at these frequencies. These findings confirm that an aeroacoustic feedback loop exists between the airfoil trailing edge and a location near the cavity trailing edge.

Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm

PubMed Central

Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Owen, C. J.; Petrukovich, A. A.; Yao, Z.; Nakamura, T. K. M.; Kubyshkina, M. V.; Sotirelis, T.; Burch, J. L.; Genestreti, K. J.; Vörös, Z.; Andriopoulou, M.; Gershman, D. J.; Avanov, L. A.; Magnes, W.; Russell, C. T.; Plaschke, F.; Khotyaintsev, Y. V.; Giles, B. L.; Coffey, V. N.; Dorelli, J. C.; Strangeway, R. J.; Torbert, R. B.; Lindqvist, P.‐A.; Ergun, R.

2017-01-01

Abstract During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high‐energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X‐line was located relatively close to the Earth, approximately at 16–18 RE. PMID:29399431

Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm

NASA Astrophysics Data System (ADS)

Varsani, A.; Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Owen, C. J.; Petrukovich, A. A.; Yao, Z.; Nakamura, T. K. M.; Kubyshkina, M. V.; Sotirelis, T.; Burch, J. L.; Genestreti, K. J.; Vörös, Z.; Andriopoulou, M.; Gershman, D. J.; Avanov, L. A.; Magnes, W.; Russell, C. T.; Plaschke, F.; Khotyaintsev, Y. V.; Giles, B. L.; Coffey, V. N.; Dorelli, J. C.; Strangeway, R. J.; Torbert, R. B.; Lindqvist, P.-A.; Ergun, R.

2017-11-01

During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high-energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X-line was located relatively close to the Earth, approximately at 16-18 RE.

Observed bottom boundary layer transport and uplift on the continental shelf adjacent to a western boundary current

NASA Astrophysics Data System (ADS)

Schaeffer, A.; Roughan, M.; Wood, J. E.

2014-08-01

Western boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross-shelf transport and uplift through the bottom boundary layer. Four years of moored in situ observations on the narrow southeastern Australian shelf (in water depths of between 65 and 140 m) were used to investigate bottom cross-shelf transport, both upstream (30°S) and downstream (34°S) of the separation zone of the East Australian Current (EAC). Bottom transport was estimated and assessed against Ekman theory, showing consistent results for a number of different formulations of the boundary layer thickness. Net bottom cross-shelf transport was onshore at all locations. Ekman theory indicates that up to 64% of the transport variability is driven by the along-shelf bottom stress. Onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream, occurring 64% of the time at 30°S. Wind-driven surface Ekman transport estimates did not balance the bottom cross-shelf flow. At both locations, strong variability was found in bottom water transport at periods of approximately 90-100 days. This corresponds with periodicity in EAC fluctuations and eddy shedding as evidenced from altimeter observations, highlighting the EAC as a driver of variability in the continental shelf waters. Ocean glider and HF radar observations were used to identify the bio-physical response to an EAC encroachment event, resulting in a strong onshore bottom flow, the uplift of cold slope water, and elevated coastal chlorophyll concentrations.

Investigations of Compression Shocks and Boundary Layers in Gases Moving at High Speed

NASA Technical Reports Server (NTRS)

Ackeret, J.; Feldmann, F.; Rott, N.

1947-01-01

The mutual influences of compression shocks and friction boundary layers were investigated by means of high speed wind tunnels.Schlieren optics provided a clear picture of the flow phenomena and were used for determining the location of the compression shocks, measurement of shock angles, and also for Mach angles. Pressure measurement and humidity measurements were also taken into consideration.Results along with a mathematical model are described.

The structure of a three-dimensional turbulent boundary layer

NASA Technical Reports Server (NTRS)

Degani, A. T.; Smith, F. T.; Walker, J. D. A.

1993-01-01

The three-dimensional turbulent boundary layer is shown to have a self-consistent two-layer asymptotic structure in the limit of large Reynolds number. In a streamline coordinate system, the streamwise velocity distribution is similar to that in two-dimensional flows, having a defect-function form in the outer layer which is adjusted to zero at the wall through an inner wall layer. An asymptotic expansion accurate to two orders is required for the cross-stream velocity which is shown to exhibit a logarithmic form in the overlap region. The inner wall-layer flow is collateral to leading order but the influence of the pressure gradient, at large but finite Reynolds numbers, is not negligible and can cause substantial skewing of the velocity profile near the wall. Conditions under which the boundary layer achieves self-similarity and the governing set of ordinary differential equations for the outer layer are derived. The calculated solution of these equations is matched asymptotically to an inner wall-layer solution and the composite profiles so formed describe the flow throughout the entire boundary layer. The effects of Reynolds number and cross-stream pressure gradient on the crossstream velocity profile are discussed and it is shown that the location of the maximum cross-stream velocity is within the overlap region.

Skin Friction and Transition Location Measurement on Supersonic Transport Models

NASA Technical Reports Server (NTRS)

Kennelly, Robert A., Jr.; Goodsell, Aga M.; Olsen, Lawrence E. (Technical Monitor)

2000-01-01

Flow visualization techniques were used to obtain both qualitative and quantitative skin friction and transition location data in wind tunnel tests performed on two supersonic transport models at Mach 2.40. Oil-film interferometry was useful for verifying boundary layer transition, but careful monitoring of model surface temperatures and systematic examination of the effects of tunnel start-up and shutdown transients will be required to achieve high levels of accuracy for skin friction measurements. A more common technique, use of a subliming solid to reveal transition location, was employed to correct drag measurements to a standard condition of all-turbulent flow on the wing. These corrected data were then analyzed to determine the additional correction required to account for the effect of the boundary layer trip devices.

Transport of chemical tracers from the boundary layer to stratosphere associated with the dynamics of the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Pan, Laura L.; Honomichl, Shawn B.; Kinnison, Douglas E.; Abalos, Marta; Randel, William J.; Bergman, John W.; Bian, Jianchun

2016-12-01

Chemical transport associated with the dynamics of the Asian summer monsoon (ASM) system is investigated using model output from the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model run in specified dynamics mode. The 3-D day-to-day behavior of modeled carbon monoxide is analyzed together with dynamical fields and transport boundaries to identify preferred locations of uplifting from the boundary layer, the role of subseasonal-scale dynamics in the upper troposphere and lower stratosphere (UTLS), and the relationship of ASM transport and the stratospheric residual circulation. The model simulation of CO shows the intraseasonal east-west oscillation of the anticyclone may play an essential role in transporting convectively pumped boundary layer pollutants in the UTLS. A statistical analysis of 11 year CO also shows that the southern flank of the Tibetan plateau is a preferred location for boundary layer tracers to be lofted to the tropopause region. The vertical structure of a model tracer (E90) further shows that the rapid ASM vertical transport is only effective up to the tropopause level (around 400 K). The efficiency of continued vertical transport into the deep stratosphere is limited by the slow ascent associated with the zonal-mean residual circulation in the lower stratosphere during northern summer. Quasi-isentropic transport near the 400 K potential temperature level is likely the most effective process for ASM anticyclone air to enter the stratosphere.

Prediction of High-Lift Flows using Turbulent Closure Models

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; Gatski, Thomas B.; Ying, Susan X.; Bertelrud, Arild

1997-01-01

The flow over two different multi-element airfoil configurations is computed using linear eddy viscosity turbulence models and a nonlinear explicit algebraic stress model. A subset of recently-measured transition locations using hot film on a McDonnell Douglas configuration is presented, and the effect of transition location on the computed solutions is explored. Deficiencies in wake profile computations are found to be attributable in large part to poor boundary layer prediction on the generating element, and not necessarily inadequate turbulence modeling in the wake. Using measured transition locations for the main element improves the prediction of its boundary layer thickness, skin friction, and wake profile shape. However, using measured transition locations on the slat still yields poor slat wake predictions. The computation of the slat flow field represents a key roadblock to successful predictions of multi-element flows. In general, the nonlinear explicit algebraic stress turbulence model gives very similar results to the linear eddy viscosity models.

The Impact of Model Uncertainty on Spatial Compensation in Active Structural Acoustic Control

NASA Technical Reports Server (NTRS)

Cabell, Randolph H.; Gibbs, Gary P.; Sprofera, Joseph D.; Clark, Robert L.

2004-01-01

Turbulent boundary layer (TBL) noise is considered a primary factor in the interior noise experienced by passengers aboard commercial airliners. There have been numerous investigations of interior noise control devoted to aircraft panels; however, practical realization is a challenge since the physical boundary conditions are uncertain at best. In most prior studies, pinned or clamped boundary conditions have been assumed; however, realistic panels likely display a range of varying boundary conditions between these two limits. Uncertainty in boundary conditions is a challenge for control system designers, both in terms of the compensator implemented and the location of actuators and sensors required to achieve the desired control. The impact of model uncertainties, uncertain boundary conditions in particular, on the selection of actuator and sensor locations for structural acoustic control are considered herein. Results from this research effort indicate that it is possible to optimize the design of actuator and sensor location and aperture, which minimizes the impact of boundary conditions on the desired structural acoustic control.

Intra-retinal segmentation of optical coherence tomography images using active contours with a dynamic programming initialization and an adaptive weighting strategy

NASA Astrophysics Data System (ADS)

Gholami, Peyman; Roy, Priyanka; Kuppuswamy Parthasarathy, Mohana; Ommani, Abbas; Zelek, John; Lakshminarayanan, Vasudevan

2018-02-01

Retinal layer shape and thickness are one of the main indicators in the diagnosis of ocular diseases. We present an active contour approach to localize intra-retinal boundaries of eight retinal layers from OCT images. The initial locations of the active contour curves are determined using a Viterbi dynamic programming method. The main energy function is a Chan-Vese active contour model without edges. A boundary term is added to the energy function using an adaptive weighting method to help curves converge to the retinal layer edges more precisely, after evolving of curves towards boundaries, in final iterations. A wavelet-based denoising method is used to remove speckle from OCT images while preserving important details and edges. The performance of the proposed method was tested on a set of healthy and diseased eye SD-OCT images. The experimental results, compared between the proposed method and the manual segmentation, which was determined by an optometrist, indicate that our method has obtained an average of 95.29%, 92.78%, 95.86%, 87.93%, 82.67%, and 90.25% respectively, for accuracy, sensitivity, specificity, precision, Jaccard Index, and Dice Similarity Coefficient over all segmented layers. These results justify the robustness of the proposed method in determining the location of different retinal layers.

F-16XL ship #1 outboard rake #7

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the #7 outboard rake on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

High-Frequency Response of the Atmospheric Electric Potential Gradient Under Strong and Dry Boundary-Layer Convection

NASA Astrophysics Data System (ADS)

Conceição, Ricardo; Silva, Hugo Gonçalves; Bennett, Alec; Salgado, Rui; Bortoli, Daniele; Costa, Maria João; Collares Pereira, Manuel

2018-01-01

The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection.

Characteristics of Boundary Layer Transition in a Multi-Stage Low-Pressure Turbine

NASA Technical Reports Server (NTRS)

Wisler, Dave; Halstead, David E.; Okiishi, Ted

2007-01-01

An experimental investigation of boundary layer transition in a multi-stage turbine has been completed using surface-mounted hot-film sensors. Tests were carried out using the two-stage Low Speed Research Turbine of the Aerodynamics Research Laboratory of GE Aircraft Engines. Blading in this facility models current, state-of-the-art low pressure turbine configurations. The instrumentation technique involved arrays of densely-packed hot-film sensors on the surfaces of second stage rotor and nozzle blades. The arrays were located at mid-span on both the suction and pressure surfaces. Boundary layer measurements were acquired over a complete range of relevant Reynolds numbers. Data acquisition capabilities provided means for detailed data interrogation in both time and frequency domains. Data indicate that significant regions of laminar and transitional boundary layer flow exist on the rotor and nozzle suction surfaces. Evidence of relaminarization both near the leading edge of the suction surface and along much of the pressure surface was observed. Measurements also reveal the nature of the turbulent bursts occuring within and between the wake segments convecting through the blade row. The complex character of boundary layer transition resulting from flow unsteadiness due to nozzle/nozzle, rotor/nozzle, and nozzle/rotor wake interactions are elucidated using these data. These measurements underscore the need to provide turbomachinery designers with models of boundary layer transition to facilitate accurate prediction of aerodynamic loss and heat transfer.

Aerothermodynamic Testing and Boundary Layer Trip Sizing of the HIFiRE Flight 1 Vehicle

NASA Technical Reports Server (NTRS)

Berger, Karen T.; Greene, Frank A.; Kimmel, Roger; Alba, Christopher; Johnson, Heath

2008-01-01

An experimental wind tunnel test was conducted in the NASA Langley Research Center s 20-Inch Mach 6 Air Tunnel in support of the Hypersonic International Flight Research Experimentation Program. The information in this article is focused on the Flight 1 configuration, the first in a series of flight experiments. The article documents experimental measurements made over a Reynolds numbers range of 2.1x10(exp 6)/ft to 5.6x10(exp 6)/ft and angles of attack of -5 to +5 deg on several scaled ceramic heat transfer models of the Flight 1 configuration. Global heat transfer was measured using phosphor thermography and the resulting images and heat transfer distributions were used to infer the state of the boundary layer on the vehicle windside and leeside surfaces. Boundary layer trips were used to force the boundary layer turbulent and the experimental data highlighted in this article were used to size and place the boundary layer trip for the flight vehicle. The required height of the flight boundary layer trip was determined to be 0.079 in and the trip was moved from the design location of 7.87 in to 20.47 in to ensure that augmented heating would not impact the laminar side of the vehicle. Allowable roughness was selected to be 3.2x10(exp -3) in.

The Kinematics of Turbulent Boundary Layer Structure

NASA Technical Reports Server (NTRS)

Robinson, Stephen Kern

1991-01-01

The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.

The Influence of Hydrofoil Oscillation on Boundary Layer Transition and Cavitation Noise.

DTIC Science & Technology

1981-04-01

p., and V. are fluid density, reference free-stream AVERAGED static pressure and reference free-stream velocity, respec- ORSPL3. Lair tively. S3.1...of cavitation on a propeller in both uni- ly, the location of boundary layer transition with the foil in form and nonuniform flow. He concluded that...the presence of oscillation must be determined either theoretically or ex- sheet and bubble cavitation in nonuniform flow can be perimentally. Thirdly

Modeling interface shear behavior of granular materials using micro-polar continuum approach

NASA Astrophysics Data System (ADS)

Ebrahimian, Babak; Noorzad, Ali; Alsaleh, Mustafa I.

2018-01-01

Recently, the authors have focused on the shear behavior of interface between granular soil body and very rough surface of moving bounding structure. For this purpose, they have used finite element method and a micro-polar elasto-plastic continuum model. They have shown that the boundary conditions assumed along the interface have strong influences on the soil behavior. While in the previous studies, only very rough bounding interfaces have been taken into account, the present investigation focuses on the rough, medium rough and relatively smooth interfaces. In this regard, plane monotonic shearing of an infinite extended narrow granular soil layer is simulated under constant vertical pressure and free dilatancy. The soil layer is located between two parallel rigid boundaries of different surface roughness values. Particular attention is paid to the effect of surface roughness of top and bottom boundaries on the shear behavior of granular soil layer. It is shown that the interaction between roughness of bounding structure surface and the rotation resistance of bounding grains can be modeled in a reasonable manner through considered Cosserat boundary conditions. The influence of surface roughness is investigated on the soil shear strength mobilized along the interface as well as on the location and evolution of shear localization formed within the layer. The obtained numerical results have been qualitatively compared with experimental observations as well as DEM simulations, and acceptable agreement is shown.

Flow visualization of discrete hole film cooling for gas turbine applications

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.

1975-01-01

Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing neutrally buoyant helium filled soap bubbles which follow the flow field. The bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included.

Boundary Layer Flow Control by an Array of Ramp-Shaped Vortex Generators

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Hirt, S. M.; Bencic, T. J.

2012-01-01

Flow field survey results for the effect of ramp-shaped vortex generators (VG) on a turbulent boundary layer are presented. The experiments are carried out in a low-speed wind tunnel and the data are acquired primarily by hot-wire anemometry. Distributions of mean velocity and turbulent stresses as well as streamwise vorticity, on cross-sectional planes at various downstream locations, are obtained. These detailed flow field properties, including the boundary layer characteristics, are documented with the primary objective of aiding possible computational investigations. The results show that VG orientation with apex upstream, that produces a downwash directly behind it, yields a stronger pair of streamwise vortices. This is in contrast to the case with apex downstream that produces a pair of vortices of opposite sense. Thus, an array of VG s with the former orientation, usually considered for film-cooling application, may also be superior for mixing enhancement and boundary layer separation control. (See CASI ID 20120009374 for Supplemental CD-ROM.)

Boundary Layer Flow Control by an Array of Ramp-Shaped Vortex Generators

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Hirt, S. M.; Bencic, T. J.

2012-01-01

Flow field survey results for the effect of ramp-shaped vortex generators (VG) on a turbulent boundary layer are presented. The experiments are carried out in a low-speed wind tunnel and the data are acquired primarily by hot-wire anemometry. Distributions of mean velocity and turbulent stresses as well as streamwise vorticity, on cross-sectional planes at various downstream locations, are obtained. These detailed flow field properties, including the boundary layer characteristics, are documented with the primary objective of aiding possible computational investigations. The results show that VG orientation with apex upstream, that produces a downwash directly behind it, yields a stronger pair of streamwise vortices. This is in contrast to the case with apex downstream that produces a pair of vortices of opposite sense. Thus, an array of VG s with the former orientation, usually considered for film-cooling application, may also be superior for mixing enhancement and boundary layer separation control. The data files can be found on a supplemental CD.

A numerical method for computing unsteady 2-D boundary layer flows

NASA Technical Reports Server (NTRS)

Krainer, Andreas

1988-01-01

A numerical method for computing unsteady two-dimensional boundary layers in incompressible laminar and turbulent flows is described and applied to a single airfoil changing its incidence angle in time. The solution procedure adopts a first order panel method with a simple wake model to solve for the inviscid part of the flow, and an implicit finite difference method for the viscous part of the flow. Both procedures integrate in time in a step-by-step fashion, in the course of which each step involves the solution of the elliptic Laplace equation and the solution of the parabolic boundary layer equations. The Reynolds shear stress term of the boundary layer equations is modeled by an algebraic eddy viscosity closure. The location of transition is predicted by an empirical data correlation originating from Michel. Since transition and turbulence modeling are key factors in the prediction of viscous flows, their accuracy will be of dominant influence to the overall results.

Shuttle Damage/Repair from the Perspective of Hypersonic Boundary Layer Transition - Experimental Results

NASA Technical Reports Server (NTRS)

Horvath, Thomas J.; Berry, Scott A.; Merski, N. Ronald; Berger, Karen T.; Buck, Gregory M.; Liechty, Derek S.; Schneider, Steven P.

2006-01-01

An overview is provided of the experimental wind tunnel program conducted at the NASA Langley Research Center Aerothermodynamics Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for Return-to-Flight. The effect of an isolated protuberance and an isolated rectangular cavity on hypersonic boundary layer transition onset on the windward surface of the Shuttle Orbiter has been experimentally characterized. These experimental studies were initiated to provide a protuberance and cavity effects database for developing hypersonic transition criteria to support on-orbit disposition of thermal protection system damage or repair. In addition, a synergistic experimental investigation was undertaken to assess the impact of an isolated mass-flow entrainment source (simulating pyrolysis/outgassing from a proposed tile repair material) on boundary layer transition. A brief review of the relevant literature regarding hypersonic boundary layer transition induced from cavities and localized mass addition from ablation is presented. Boundary layer transition results were obtained using 0.0075-scale Orbiter models with simulated tile damage (rectangular cavities) of varying length, width, and depth and simulated tile damage or repair (protuberances) of varying height. Cavity and mass addition effects were assessed at a fixed location (x/L = 0.3) along the model centerline in a region of near zero pressure gradient. Cavity length-to-depth ratio was systematically varied from 2.5 to 17.7 and length-to-width ratio of 1 to 8.5. Cavity depth-to-local boundary layer thickness ranged from 0.5 to 4.8. Protuberances were located at several sites along the centerline and port/starboard attachment lines along the chine and wing leading edge. Protuberance height-to-boundary layer thickness was varied from approximately 0.2 to 1.1. Global heat transfer images and heating distributions of the Orbiter windward surface using phosphor thermography were used to infer the state of the boundary layer (laminar, transitional, or turbulent). Test parametrics include angles-of-attack of 30 deg and 40 deg, sideslip angle of 0 deg, freestream Reynolds numbers from 0.02x106 to 7.3x106 per foot, edge-to-wall temperature ratio from 0.4 to 0.8, and normal shock density ratios of approximately 5.3, 6.0, and 12 in Mach 6 air, Mach 10 air, and Mach 6 CF4, respectively. Testing to simulate the effects of ablation from a proposed tile repair concept indicated that transition was not a concern. The experimental protuberance and cavity databases highlighted in this report were used to formulate boundary layer transition correlations that were an integral part of an analytical process to disposition observed Orbiter TPS damage during STS- 114.

Category 5: Sound Generation In Viscous Problems. Problem 2: Sound Generation By Flow Over a Cavity

NASA Technical Reports Server (NTRS)

Henderson, Brenda S.

2004-01-01

The discrete frequency sound produced by the flow of air at low subsonic speeds over a deep cavity was investigated. A long aspect ratio rectangular cavity with a leading edge overhang that cut off of the cavity opening was placed flush with the top surface of a wind tunnel. The approach flow velocity was maintained at 50 m/s for the benchmark problem although results are also presented for other conditions. Boundary layer measurements conducted with a single element hotwire anemometer indicated that the boundary layer thickness just upstream of the cavity was equal to 17 mm. Sound pressure level measurements were made at three locations in the cavity: the center of the leading edge wall, the center of the cavity floor, and the center of the trailing edge wall. Three discrete tones were measured at all three locations with corresponding Strouhal numbers (based on cavity opening length and approach flow velocity) equal to 0.24, 0.26, and 0.41. The amplitudes of each tone were approximately equal at each measurement location in the cavity. Measurements made at other approach flow conditions indicated that the approach flow velocity and the boundary layer thickness affected the frequency characteristics of the discrete tones.

Routes to turbulence in the rotating disk boundary-layer of a rotor-stator cavity

NASA Astrophysics Data System (ADS)

Yim, Eunok; Serre, Eric; Martinand, Denis; Chomaz, Jean-Marc

2016-11-01

The rotating disk is an important classical problem, due to the similarities between the 3D boundary layers on a disk and a swept aircraft wing. It is nowadays admitted that a direct transition to turbulence may exist through a steep-fronted nonlinear global mode located at the boundary between the locally connectively and absolutely unstable regions (Pier 2003; Viaud et al. 2008, 2011; Imayama et al. 2014 and others). However, recent studies (Healey 2010; Harris et al. 2012; Imayama et al. 2013) suggest that there may be an alternative route starting at lower critical Reynolds number, based on convective travelling waves but this scenario is still not fully validated and proven. To better characterize such transition, direct numerical simulations are performed in a closed cylindrical rotor-stator cavity (without hub) up to Re = O (105) . All boundaries are no slip and for the stable region around the rotation axis prevents the disturbances coming from the very unstable stator boundary to disturb the rotor boundary layer. Different transition scenarii to turbulence are investigated when the rotor boundary layer is forced at different positions and forcing amplitude. The associated dynamics of coherent structures in various flow regions are also investigated when increasing Re .

Hypersonic Navier-Stokes Comparisons to Orbiter Flight Data

NASA Technical Reports Server (NTRS)

Candler, Graham V.; Campbell, Charles H.

2010-01-01

During the STS-119 flight of Space Shuttle Discovery, two sets of surface temperature measurements were made. Under the HYTHIRM program3 quantitative thermal images of the windward side of the Orbiter with a were taken. In addition, the Boundary Layer Transition Flight Experiment 4 made thermocouple measurements at discrete locations on the Orbiter wind side. Most of these measurements were made downstream of a surface protuberance designed to trip the boundary layer to turbulent flow. In this paper, we use the US3D computational fluid dynamics code to simulate the Orbiter flow field at conditions corresponding to the STS-119 re-entry. We employ a standard two-temperature, five-species finite-rate model for high-temperature air, and the surface catalysis model of Stewart.1 This work is similar to the analysis of Wood et al . 2 except that we use a different approach for modeling turbulent flow. We use the one-equation Spalart-Allmaras turbulence model8 with compressibility corrections 9 and an approach for tripping the boundary layer at discrete locations. In general, the comparison between the simulations and flight data is remarkably good

High-Speed Boundary-Layer Transition: Study of Stationary Crossflow Using Spectral Analysis

NASA Astrophysics Data System (ADS)

McGuire, Patrick Joseph

Crossflow instability is primary cause of boundary-layer transition on swept wings used in high-speed applications. Delaying the downstream location of transition would drastically reduce the viscous drag over the wing surface, and subsequently improves the overall aircraft efficiency. By studying the development of instability growth rates and how they interact with the surroundings, researchers can control the crossflow transition location. Experiments on the 35° swept-wing model were performed in the NASA Langley 20-Inch Supersonic Wind Tunnel with Mach 2.0 flow conditions and 20 μm tall discrete roughness elements (DRE) with varying spacing placed along the leading edge. Fluorene was used as the sublimating chemical in the surface flow visualization technique to observe the transition front and stationary crossflow vortex patterns in the laminar flow region. Spatial spectral decomposition was completed on high-resolution images of sublimating chemical runs using a newly developed image processing technique. Streamwise evolution of the vortex track wavelengths within the laminar boundary-layer region was observed. The spectral information was averaged to produce dominant modes present throughout the laminar region.

Optimal Growth in Hypersonic Boundary Layers

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

2016-01-01

The linear form of the parabolized linear stability equations is used in a variational approach to extend the previous body of results for the optimal, nonmodal disturbance growth in boundary-layer flows. This paper investigates the optimal growth characteristics in the hypersonic Mach number regime without any high-enthalpy effects. The influence of wall cooling is studied, with particular emphasis on the role of the initial disturbance location and the value of the spanwise wave number that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary-layer equations, mean flow solutions based on the full Navier-Stokes equations are used in select cases to help account for the viscous- inviscid interaction near the leading edge of the plate and for the weak shock wave emanating from that region. Using the full Navier-Stokes mean flow is shown to result in further reduction with Mach number in the magnitude of optimal growth relative to the predictions based on the self-similar approximation to the base flow.

Boundary-layer instability & transition on a flared cone in a Mach 6 quiet wind tunnel

NASA Astrophysics Data System (ADS)

Hofferth, Jerrod; Saric, William

2011-11-01

Measurements of boundary-layer transition location and instability growth on a sharp-tipped 5°-half-angle flared cone were conducted in a low-disturbance Mach 6 wind tunnel at a freestream unit Reynolds number of 10 × 106/m. Under quiet flow at these conditions, the boundary layer becomes transitional near the base of the cone, where significant second-mode instability growth is evident. Transition location is determined using an array of embedded thermocouples, and instability development is observed in mean and fluctuating mass flux data using hotwire anemometry. The present work seeks to reproduce and build upon previous experiments which used the same test article and similar diagnostics in the facility's former installation at NASA Langley. Together with comprehensive measurements of the freestream disturbance environment, these baseline cone data characterize the facility's performance relative to that in its previous installation. In addition, the current campaign establishes experimental readiness for future research, which will study the effects of periodic surface roughness and controlled-input disturbances. AFOSR/NASA National Center for Hypersonic Research in Laminar-Turbulent Transition; Grant FA9550-09-1-0341.

New Synthesis of Ocean Crust Velocity Structure From Two-Dimensional Profiles

NASA Astrophysics Data System (ADS)

Christeson, G. L.; Goff, J.; Carlson, R. L.; Reece, R.

2017-12-01

The velocity structure of typical oceanic crust consists of Layer 2, where velocities increase rapidly with depth from seafloor, and Layer 3, which is thicker and has a lower velocity gradient. Previous syntheses have found no correlation of velocity structure with spreading rate, even though we know that magmatic processes differ between slow-spreading and fast-spreading crust. We present a new synthesis of ocean crust velocity structure, compiling observations from two-dimensional studies in the Atlantic, Pacific, and Indian ocean basins. The Layer 2/3 boundary was picked from each publication at a change in gradient either on velocity-depth functions or contour plots (with at least 0.5 km/s contour interval), or from the appropriate layer boundary for layered models. We picked multiple locations at each seismic refraction profile if warranted by model variability. Preliminary results show statistically significant differences in average Layer 2 and Layer 3 thicknesses between slow-spreading and superfast-spreading crust, with Layer 2 thinner and Layer 3 thicker for the higher spreading rate crust. The thickness changes are about equivalent, resulting in no change in mean crustal thickness. The Layer 2/3 boundary is often interpreted as the top of the gabbros; however, a comparison with mapped magma lens depths at the ridge axis shows that the boundary is typically deeper than average axial melt lens depth at superfast-spreading crust, and shallower at intermediate-spreading crust.

Assessing Uncertainties in Boundary Layer Transition Predictions for HIFiRE-1 at Non-zero Angles of Attack

NASA Technical Reports Server (NTRS)

Marek, Lindsay C.

2011-01-01

Boundary layer stability was analyzed for the HIFiRE-1 flight vehicle geometry for ground tests conducted at the CUBRC LENS I hypersonic shock test facility and the Langley Research Center (LaRC) 20- inch Mach 6 Tunnel. Boundary layer stability results were compared to transition onset location obtained from discrete heat transfer measurements from thin film gauges during the CUBRC test and spatially continuous heat transfer measurements from thermal phosphor paint data during the LaRC test. The focus of this analysis was on conditions at non-zero angles of attack as stability analysis has already been performed at zero degrees angle of attack. Also, the transition onset data obtained during flight testing was at nonzero angles of attack, so this analysis could be expanded in the future to include the results of the flight test data. Stability analysis was performed using the 2D parabolized stability software suite STABL (Stability and Transition Analysis for Hypersonic Boundary Layers) developed at the University of Minnesota and the mean flow solutions were computed using the DPLR finite volume Navier-Stokes computational fluid dynamics (CFD) solver. A center line slice of the 3D mean flow solution was used for the stability analysis to incorporate the angle of attack effects while still taking advantage of the 2D STABL software suite. The N-factors at transition onset and the value of Re(sub theta)/M(sub e), commonly used to predict boundary layer transition onset, were compared for all conditions analyzed. Ground test data was analyzed at Mach 7.2 and Mach 6.0 and angles of attack of 1deg, 3deg and 5deg. At these conditions, the flow was found to be second mode dominant for the HIFiRE-1 slender cone geometry. On the leeward side of the vehicle, a strong trend of transition onset location with angle of attack was observed as the boundary layer on the leeward side of the vehicle developed inflection points at streamwise positions on the vehicle that correlated to angle of attack. Inflection points are a strong instability mechanism that lead to rapid breakdown and transition to turbulence. The transition onset location on the windward side of the vehicle displayed no trend with angle of attack or freestream Reynolds number and transition was observed farther down the vehicle than observed on the leeward side of the vehicle. In analysis of both windward and leeward sides of the vehicle, use of the N factor methodology to develop trends to predict boundary layer transition onset showed improvements over the Re(sub theta)/M(sub e) empirical correlation methodology. Stronger correlations and less scatter in the data were observed when using the N factor method for these cases.

The behaviour of turbulence anisotropy through shock waves and expansions

NASA Technical Reports Server (NTRS)

Minh, H. H.; Kollmann, W.; Vandromme, D.

1985-01-01

A second order closure has been implemented in an implicit Navier-Stokes solver to study the behavior of the Reynolds stresses under the influence of severe pressure gradients. In the boundary layer zone, the strongly sheared character of the mean flow dominates the turbulence generation mechanisms. However, the pressure gradients play also a very important role for these processes, but at different locations within the boundary layer. This aspect may be emphasized by the analysis of turbulence anisotropy through shock waves and expansions.

Color surface-flow visualization of fin-generated shock wave boundary-layer interactions

NASA Technical Reports Server (NTRS)

Lu, F. K.; Settles, G. S.

1990-01-01

Kerosene-lampblack mixtures with addition of a ground colored chalk were used in an experiment on visualizing surface flows of swept shock boundary-layer interactions. The results show that contrasting colors intensify the visualization of different regions of the interaction surface, and help the eye in following the fine streaks to locate the upstream influence. The study confirms observations of the separation occurring at shock strength below accepted values. The superiority of the reported technique over the previous monochrome technique is demonstrated.

Color surface-flow visualization of fin-generated shock wave boundary-layer interactions

NASA Astrophysics Data System (ADS)

Lu, F. K.; Settles, G. S.

1990-03-01

Kerosene-lampblack mixtures with addition of a ground colored chalk were used in an experiment on visualizing surface flows of swept shock boundary-layer interactions. The results show that contrasting colors intensify the visualization of different regions of the interaction surface, and help the eye in following the fine streaks to locate the upstream influence. The study confirms observations of the separation occurring at shock strength below accepted values. The superiority of the reported technique over the previous monochrome technique is demonstrated.

The light wave flow effect in a plane-parallel layer with a quasi-zero refractive index under the action of bounded light beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gadomsky, O. N., E-mail: gadomsky@mail.ru; Shchukarev, I. A., E-mail: blacxpress@gmail.com

2016-08-15

It is shown that external optical radiation in the 450–1200 nm range can be efficiently transformed under the action of bounded light beams to a surface wave that propagates along the external and internal boundaries of a plane-parallel layer with a quasi-zero refractive index. Reflection regimes with complex and real angles of refraction in the layer are considered. The layer with a quasi-zero refractive index in this boundary problem is located on a highly reflective metal substrate; it is shown that the uniform low reflection of light is achieved in the wavelength range under study.

Neural field model of memory-guided search.

PubMed

Kilpatrick, Zachary P; Poll, Daniel B

2017-12-01

Many organisms can remember locations they have previously visited during a search. Visual search experiments have shown exploration is guided away from these locations, reducing redundancies in the search path before finding a hidden target. We develop and analyze a two-layer neural field model that encodes positional information during a search task. A position-encoding layer sustains a bump attractor corresponding to the searching agent's current location, and search is modeled by velocity input that propagates the bump. A memory layer sustains persistent activity bounded by a wave front, whose edges expand in response to excitatory input from the position layer. Search can then be biased in response to remembered locations, influencing velocity inputs to the position layer. Asymptotic techniques are used to reduce the dynamics of our model to a low-dimensional system of equations that track the bump position and front boundary. Performance is compared for different target-finding tasks.

Neural field model of memory-guided search

NASA Astrophysics Data System (ADS)

Kilpatrick, Zachary P.; Poll, Daniel B.

2017-12-01

Many organisms can remember locations they have previously visited during a search. Visual search experiments have shown exploration is guided away from these locations, reducing redundancies in the search path before finding a hidden target. We develop and analyze a two-layer neural field model that encodes positional information during a search task. A position-encoding layer sustains a bump attractor corresponding to the searching agent's current location, and search is modeled by velocity input that propagates the bump. A memory layer sustains persistent activity bounded by a wave front, whose edges expand in response to excitatory input from the position layer. Search can then be biased in response to remembered locations, influencing velocity inputs to the position layer. Asymptotic techniques are used to reduce the dynamics of our model to a low-dimensional system of equations that track the bump position and front boundary. Performance is compared for different target-finding tasks.

F-16XL ship #1 CAWAP flight - alpha 5 degrees, altitude 10,000 feet

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. This photo shows the aircraft gathering data at an altitude of 10,000 feet, with an angle of attack of 5 degrees. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 - CAWAP outboard rakes #7 and inboard rack #3

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the #7 outboard rake and the #3 inboard rake on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 CAWAP flight

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 - CAWAP outboard rake #7

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the #7 outboard rake on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Calculation of oblique-shock-wave laminar-boundary-layer interaction on a flat plate

NASA Technical Reports Server (NTRS)

Goldberg, U.; Reshotko, E.

1980-01-01

A finite difference solution to the problem of the interaction between an impinging oblique shock wave and the laminar boundary layer on a flat plate is presented. The boundary layer equations coupled with the Prandtl-Meyer relation for the external flow are used to calculate the flow field. A method for the calculation of the separated flow region is presented and discussed. Comparisons between this theory and the experimental results of other investigators show fairly good agreement. Results are presented for the case of a cooled wall with an oncoming flow at Mach number 2.0 without and with suction. The results show that a small amount of suction greatly reduces the extent of the separated region in the vicinity of the shock impingement location.

The inner core thermodynamics of the tropical cyclone boundary layer

NASA Astrophysics Data System (ADS)

Williams, Gabriel J.

2016-10-01

Although considerable progress has been made in understanding the inner-core dynamics of the tropical cyclone boundary layer (TCBL), our knowledge of the inner-core thermodynamics of the TCBL remains limited. In this study, the inner-core budgets of potential temperature (θ), specific humidity ( q), and reversible equivalent potential temperature (θ _e) are examined using a high-resolution multilevel boundary layer model. The potential temperature budgets show that the heat energy is dominated by latent heat release in the eyewall, evaporative cooling along the outer edge of the eyewall, and upward surface fluxes of sensible and latent heat from the underlying warm ocean. It is shown that the vertical θ advection overcompensates the sum of radial advective warming from the boundary layer outflow jet and latent heating for the development of cooling in the eyewall within the TCBL. The moisture budgets show the dominant upward transport of moisture in the eyewall updrafts, partly by the boundary-layer outflow jet from the bottom eye region, so that the eyewall remains nearly saturated. The θ _e budgets reveal that the TCBL is maintained thermodynamically by the upward surface flux of higher-θ _e air from the underlying warm ocean, the radial transport of low-θ _e air from the outer regions of the TCBL, and the dry adiabatic cooling associated by eyewall updrafts. These results underscore the significance of vertical motion and the location of the boundary layer outflow jet in maintaining the inner core thermal structure of the TCBL.

Simultaneous measurement of aero-optical distortion and turbulent structure in a heated boundary layer

NASA Astrophysics Data System (ADS)

Saxton-Fox, Theresa; McKeon, Beverley; Smith, Adam; Gordeyev, Stanislav

2014-11-01

This study examines the relationship between turbulent structures and the aero-optical distortion of a laser beam passing through a turbulent boundary layer. Previous studies by Smith et al. (AIAA, 2014--2491) have found a bulk convection velocity of 0 . 8U∞ for aero-optical distortion in turbulent boundary layers, motivating a comparison of the distortion with the outer boundary layer. In this study, a turbulent boundary layer is developed over a flat plate with a moderately-heated section of length 25 δ . Density variation in the thermal boundary layer leads to aero-optical distortion, which is measured with a Malley probe (Smith et al., AIAA, 2013--3133). Simultaneously, 2D PIV measurements are recorded in a wall-normal, streamwise plane centered on the Malley probe location. Experiments are run at Reθ = 2100 and at a Mach number of 0.03, with the heated wall 10 to 20°C above the free stream temperature. Correlations and conditional averages are carried out between Malley probe distortion angles and flow features in the PIV vector fields. Aero-optical distortion in this study will be compared to distortion in higher Mach number flows studied by Gordeyev et al. (J. Fluid Mech., 2014), with the aim of extending conclusions into compressible flows. This research is made possible by the Department of Defense through the National Defense & Engineering Graduate Fellowship (NDSEG) Program and by the Air Force Office of Scientific Research Grant # FA9550-12-1-0060.

High Reynolds number rough wall turbulent boundary layer experiments using Braille surfaces

NASA Astrophysics Data System (ADS)

Harris, Michael; Monty, Jason; Nova, Todd; Allen, James; Chong, Min

2007-11-01

This paper details smooth, transitional and fully rough turbulent boundary layer experiments in the New Mexico State high Reynolds number rough wall wind tunnel. The initial surface tested was generated with a Braille printer and consisted of an uniform array of Braille points. The average point height being 0.5mm, the spacing between the points in the span was 0.5mm and the surface consisted of span wise rows separated by 4mm. The wavelength to peak ratio was 8:1. The boundary layer thickness at the measurement location was 190mm giving a large separation of roughness height to layer thickness. The maximum friction velocity was uτ=1.5m/s at Rex=3.8 x10^7. Results for the skin friction co-efficient show that this surface follows a Nikuradse type inflectional curve and that Townsends outer layer similarity hypothesis is valid for rough wall flows with a large separation of scales. Mean flow and turbulence statistics will be presented.

The effects of streamwise concave curvature on turbulent boundary layer structure

NASA Astrophysics Data System (ADS)

Jeans, A. H.; Johnston, J. P.

1982-06-01

Concave curvature has a relatively large, unpredictable effect on turbulent boundary layers. Some, but not all previous studies suggest that a large-scale, stationary array of counter-rotating vortices exists within the turbulent boundary layer on a concave wall. The objective of the present study was to obtain a qualitative model of the flow field in order to increase our understanding of the underlying physics. A large free-surface water channel was constructed in order to perform a visual study of the flow. Streamwise components of mean velocity and turbulence intensity were measured using a hot film anemometer. The upstream boundary was spanwise uniform with a momentum thickness to radius of curvature of 0.05. Compared to flat wall flow, large-scale, randomly distributed sweeps and ejections were seen in the boundary layer on the concave wall. The sweeps appear to suppress the normal mechanism for turbulence production near the wall by inhibiting the bursting process. The ejections appear to enhance turbulence production in the outer layers as the low speed fluid convected from regions near the wall interacts with the higher speed fluid farther out. The large-scale structures did not occur at fixed spanwise locations, and could not be called roll cells or vortices.

Laser transit anemometer measurements on a slender cone in the Langley unitary plan wind tunnel

NASA Technical Reports Server (NTRS)

Humphreys, William M., Jr.; Hunter, William W., Jr.; Covell, Peter F.; Nichols, Cecil E., Jr.

1990-01-01

A laser transit anemometer (LTA) system was used to probe the boundary layer on a slender (5 degree half angle) cone model in the Langley unitary plan wind tunnel. The anemometer system utilized a pair of laser beams with a diameter of 40 micrometers spaced 1230 micrometers apart to measure the transit times of ensembles of seeding particles using a cross-correlation technique. From these measurements, boundary layer profiles around the model were constructed and compared with CFD calculations. The measured boundary layer profiles representing the boundary layer velocity normalized to the edge velocity as a function of height above the model surface were collected with the model at zero angle of attack for four different flow conditions, and were collected in a vertical plane that bisected the model's longitudinal center line at a location 635 mm from the tip of the forebody cone. The results indicate an excellent ability of the LTA system to make velocity measurements deep into the boundary layer. However, because of disturbances in the flow field caused by onboard seeding, premature transition occurred implying that upstream seeding is mandatory if model flow field integrity is to be maintained. A description and results of the flow field surveys are presented.

Effects of Land Surface Heterogeneity on Simulated Boundary-Layer Structures from the LES to the Mesoscale

NASA Astrophysics Data System (ADS)

Poll, Stefan; Shrestha, Prabhakar; Simmer, Clemens

2017-04-01

Land heterogeneity influences the atmospheric boundary layer (ABL) structure including organized (secondary) circulations which feed back on land-atmosphere exchange fluxes. Especially the latter effects cannot be incorporated explicitly in regional and climate models due to their coarse computational spatial grids, but must be parameterized. Current parameterizations lead, however, to uncertainties in modeled surface fluxes and boundary layer evolution, which feed back to cloud initiation and precipitation. This study analyzes the impact of different horizontal grid resolutions on the simulated boundary layer structures in terms of stability, height and induced secondary circulations. The ICON-LES (Icosahedral Nonhydrostatic in LES mode) developed by the MPI-M and the German weather service (DWD) and conducted within the framework of HD(CP)2 is used. ICON is dynamically downscaled through multiple scales of 20 km, 7 km, 2.8 km, 625 m, 312 m, and 156 m grid spacing for several days over Germany and partial neighboring countries for different synoptic conditions. We examined the entropy spectrum of the land surface heterogeneity at these grid resolutions for several locations close to measurement sites, such as Lindenberg, Jülich, Cabauw and Melpitz, and studied its influence on the surface fluxes and the evolution of the boundary layer profiles.

Pressure gradient effects on heat transfer to reusable surface insulation tile-array gaps

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1975-01-01

An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer within space shuttle reusable surface insulation (RSI) tile-array gaps under thick, turbulent boundary-layer conditions. Heat-transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel-wall boundary layer at a nominal free-stream Mach number and free-stream Reynolds numbers. Transverse pressure gradients of varying degree were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel-wall boundary-layer flow was obtained by measurement of boundary-layer pitot pressure profiles, wall pressure, and heat transfer. Flat-plate heat-transfer data were correlated and a method was derived for prediction of heat transfer to a smooth curved surface in the highly three-dimensional tunnel-wall boundary-layer flow. Pressure on the floor of the RSI tile-array gap followed the trends of the external surface pressure. Heat transfer to the surface immediately downstream of a transverse gap is higher than that for a smooth surface at the same location. Heating to the wall of a transverse gap, and immediately downstream of it, at its intersection with a longitudinal gap is significantly greater than that for the simple transverse gap.

Laminar-Turbulent Transition Behind Discrete Roughness Elements in a High-Speed Boundary Layer

NASA Technical Reports Server (NTRS)

Choudhari, Meelan M.; Li, Fei; Wu, Minwei; Chang, Chau-Lyan; Edwards, Jack R., Jr.; Kegerise, Michael; King, Rudolph

2010-01-01

Computations are performed to study the flow past an isolated roughness element in a Mach 3.5, laminar, flat plate boundary layer. To determine the effects of the roughness element on the location of laminar-turbulent transition inside the boundary layer, the instability characteristics of the stationary wake behind the roughness element are investigated over a range of roughness heights. The wake flow adjacent to the spanwise plane of symmetry is characterized by a narrow region of increased boundary layer thickness. Beyond the near wake region, the centerline streak is surrounded by a pair of high-speed streaks with reduced boundary layer thickness and a secondary, outer pair of lower-speed streaks. Similar to the spanwise periodic pattern of streaks behind an array of regularly spaced roughness elements, the above wake structure persists over large distances and can sustain strong enough convective instabilities to cause an earlier onset of transition when the roughness height is sufficiently large. Time accurate computations are performed to clarify additional issues such as the role of the nearfield of the roughness element during the generation of streak instabilities, as well as to reveal selected details of their nonlinear evolution. Effects of roughness element shape on the streak amplitudes and the interactions between multiple roughness elements aligned along the flow direction are also investigated.

Skin friction drag reduction on a flat plate turbulent boundary layer using synthetic jets

NASA Astrophysics Data System (ADS)

Belanger, Randy; Boom, Pieter D.; Hanson, Ronald E.; Lavoie, Philippe; Zingg, David W.

2017-11-01

In these studies, we investigate the effect of mild synthetic jet actuation on a flat plate turbulent boundary layer with the goal of interacting with the large scales in the log region of the boundary layer and manipulating the overall skin friction. Results will be presented from both large eddy simulations (LES) and wind tunnel experiments. In the experiments, a large parameter space of synthetic jet frequency and amplitude was studied with hot film sensors at select locations behind a pair of synthetic jets to identify the parameters that produce the greatest changes in the skin friction. The LES simulations were performed for a selected set of parameters and provide a more complete evaluation of the interaction between the boundary layer and synthetic jets. Five boundary layer thicknesses downstream, the skin friction between the actuators is generally found to increase, while regions of reduced skin friction persist downstream of the actuators. This pattern is reversed for forcing at low frequency. Overall, the spanwise-averaged skin friction is increased by the forcing, except when forcing at high frequency and low amplitude, for which a net skin friction reduction persists downstream. The physical interpretation of these results will be discussed. The financial support of Airbus is gratefully acknowledged.

Atmospheric Turbulence Estimates from a Pulsed Lidar

NASA Technical Reports Server (NTRS)

Pruis, Matthew J.; Delisi, Donald P.; Ahmad, Nash'at N.; Proctor, Fred H.

2013-01-01

Estimates of the eddy dissipation rate (EDR) were obtained from measurements made by a coherent pulsed lidar and compared with estimates from mesoscale model simulations and measurements from an in situ sonic anemometer at the Denver International Airport and with EDR estimates from the last observation time of the trailing vortex pair. The estimates of EDR from the lidar were obtained using two different methodologies. The two methodologies show consistent estimates of the vertical profiles. Comparison of EDR derived from the Weather Research and Forecast (WRF) mesoscale model with the in situ lidar estimates show good agreement during the daytime convective boundary layer, but the WRF simulations tend to overestimate EDR during the nighttime. The EDR estimates from a sonic anemometer located at 7.3 meters above ground level are approximately one order of magnitude greater than both the WRF and lidar estimates - which are from greater heights - during the daytime convective boundary layer and substantially greater during the nighttime stable boundary layer. The consistency of the EDR estimates from different methods suggests a reasonable ability to predict the temporal evolution of a spatially averaged vertical profile of EDR in an airport terminal area using a mesoscale model during the daytime convective boundary layer. In the stable nighttime boundary layer, there may be added value to EDR estimates provided by in situ lidar measurements.

Influence of the characteristics of atmospheric boundary layer on the vertical distribution of air pollutant in China's Yangtze River Delta

NASA Astrophysics Data System (ADS)

Wang, Chenggang; Cao, Le

2016-04-01

Air pollution occurring in the atmospheric boundary layer is a kind of weather phenomenon which decreases the visibility of the atmosphere and results in poor air quality. Recently, the occurrence of the heavy air pollution events has become more frequent all over Asia, especially in Mid-Eastern China. In December 2015, the most severe air pollution in recorded history of China occurred in the regions of Yangtze River Delta and Beijing-Tianjin-Hebei. More than 10 days of severe air pollution (Air Quality Index, AQI>200) appeared in many large cities of China such as Beijing, Tianjin, Shijiazhuang and Baoding. Thus, the research and the management of the air pollution has attracted most attentions in China. In order to investigate the formation, development and dissipation of the air pollutions in China, a field campaign has been conducted between January 1, 2015 and January 28, 2015 in Yangtze River Delta of China, aiming at a intensive observation of the vertical structure of the air pollutants in the atmospheric boundary layer during the time period with heavy pollution. In this study, the observation data obtained in the field campaign mentioned above is analyzed. The characteristics of the atmospheric boundary layer and the vertical distribution of air pollutants in the city Dongshan located in the center of Lake Taihu are shown and discussed in great detail. It is indicated that the stability of the boundary layer is the strongest during the nighttime and the early morning of Dongshan. Meanwhile, the major air pollutants, PM2.5 and PM10 in the boundary layer, reach their maximum values, 177.1μg m-3 and 285μg m-3 respectively. The convective boundary layer height in the observations ranges from approximately 700m to 1100m. It is found that the major air pollutants tend to be confined in a relatively shallow boundary layer, which represents that the boundary layer height is the dominant factor for controlling the vertical distribution of the air pollutants. In the observations, several strong temperature inversion layers are also found in the surface layer and the middle part of the boundary layer, which lead to the suppression of the vertical mixing of the air pollutants. The jet stream occurring in the boundary layer also contributes to the prevention of the vertical dissipation of the air pollutants. It is also observed that the temporal and spatial evolution of the air pollutants and the hygroscopic growth of the aerosols in the boundary layer are heavily dependent on the humidity of the air.

Deleterious localized stress fields: the effects of boundaries and stiffness tailoring in anisotropic laminated plates

PubMed Central

Weaver, P. M.

2016-01-01

The safe design of primary load-bearing structures requires accurate prediction of stresses, especially in the vicinity of geometric discontinuities where deleterious three-dimensional stress fields can be induced. Even for thin-walled structures significant through-thickness stresses arise at edges and boundaries, and this is especially precarious for laminates of advanced fibre-reinforced composites because through-thickness stresses are the predominant drivers in delamination failure. Here, we use a higher-order equivalent single-layer model derived from the Hellinger–Reissner mixed variational principle to examine boundary layer effects in laminated plates comprising constant-stiffness and variable-stiffness laminae and deforming statically in cylindrical bending. The results show that zigzag deformations, which arise due to layerwise differences in the transverse shear moduli, drive boundary layers towards clamped edges and are therefore critically important in quantifying localized stress gradients. The relative significance of the boundary layer scales with the degree of layerwise anisotropy and the thickness to characteristic length ratio. Finally, we demonstrate that the phenomenon of alternating positive and negative transverse shearing deformation through the thickness of composite laminates, previously only observed at clamped boundaries, can also occur at other locations as a result of smoothly varying the material properties over the in-plane dimensions of the laminate. PMID:27843401

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 5: Propagation of propeller tone noise through a fuselage boundary layer

NASA Technical Reports Server (NTRS)

Magliozzi, B.; Hanson, D. B.

1991-01-01

An analysis of tone noise propagation through a boundary layer and fuselage scattering effects was derived. This analysis is a three dimensional and the complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The outer wave field is constructed analytically from an incident wave appropriate to the source and a scattered wave in the standard Hankel function form. For the incident wave, an existing function - domain propeller noise radiation theory is used. In the boundary layer region, the wave equation is solved by numerical methods. The theoretical analysis is embodied in a computer program which allows the calculation of correction factors for the fuselage scattering and boundary layer refraction effects. The effects are dependent on boundary layer profile, flight speed, and frequency. Corrections can be derived for any point on the fuselage, including those on the opposite side from the source. The theory was verified using limited cases and by comparing calculations with available measurements from JetStar tests of model prop-fans. For the JetStar model scale, the boundary layer refraction effects produce moderate fuselage pressure reinforcements aft of and near the plane of rotation and significant attenuation forward of the plane of rotation at high flight speeds. At lower flight speeds, the calculated boundary layer effects result in moderate amplification over the fuselage area of interest. Apparent amplification forward of the plane of rotation is a result of effective changes in the source directivity due to boundary layer refraction effects. Full scale effects are calculated to be moderate, providing fuselage pressure amplification of about 5 dB at the peak noise location. Evaluation using available noise measurements was made under high-speed, high-altitude flight conditions. Comparisons of calculations made of free field noise, using a current frequency-domain propeller noise prediction method, and fuselage effects using this new procedure show good agreement with fuselage measurements over a wide range of flight speeds and frequencies. Correction factors for the JetStar measurements made on the fuselage are provided in an Appendix.

Measurements in the near-wall region of a relaxing three-dimensional low speed turbulent air boundary layer

NASA Technical Reports Server (NTRS)

Hebbar, K. S.; Melnik, W. L.

1976-01-01

An experimental investigation was conducted at selected locations of the near-wall region of a three dimensional turbulent air boundary layer relaxing in a nominally zero external pressure gradient behind a transverse hump (in the form of a 30 deg swept, 5-foot chord wing-type model) faired into the side wall of a low speed wind tunnel. Wall shear stresses measured with a flush-mounted hot-film gage and a sublayer fence were in very good agreement with experimental data obtained with two Preston probes. With the upstream unit Reynolds number held constant at 325,000/ft. approximately one-fourth of the boundary layer thickness adjacent to the wall was surveyed with a single rotated hot-wire probe mounted on a specially designed minimum interference traverse mechanism. The boundary layer (approximately 3.5 in thick near the first survey station where the length Reynolds number was 5.5 million) had a maximum crossflow velocity ratio of 0.145 and a maximum crossflow angle of 21.875 deg close to the wall.

The dependence of the strength and thickness of field-aligned currents on solar wind and ionospheric parameters

PubMed Central

Johnson, Jay R.; Wing, Simon

2017-01-01

Sheared plasma flows at the low-latitude boundary layer (LLBL) correlate well with early afternoon auroral arcs and upward field-aligned currents. We present a simple analytic model that relates solar wind and ionospheric parameters to the strength and thickness of field-aligned currents (Λ) in a region of sheared velocity, such as the LLBL. We compare the predictions of the model with DMSP observations and find remarkably good scaling of the upward region 1 currents with solar wind and ionospheric parameters in region located at the boundary layer or open field lines at 1100–1700 magnetic local time. We demonstrate that Λ~nsw−0.5 and Λ ~ L when Λ/L < 5 where L is the auroral electrostatic scale length. The sheared boundary layer thickness (Δm) is inferred to be around 3000 km, which appears to have weak dependence on Vsw. J‖ has dependencies on Δm, Σp, nsw, and Vsw. The analytic model provides a simple way to organize data and to infer boundary layer structures from ionospheric data. PMID:29057194

Numerical investigation of hypersonic flat-plate boundary layer transition mechanism induced by different roughness shapes

NASA Astrophysics Data System (ADS)

Zhou, Yunlong; Zhao, Yunfei; Xu, Dan; Chai, Zhenxia; Liu, Wei

2016-10-01

The roughness-induced laminar-turbulent boundary layer transition is significant for high-speed aerospace applications. The transition mechanism is closely related to the roughness shape. In this paper, high-order numerical method is used to investigate the effect of roughness shape on the flat-plate laminar-to-turbulent boundary layer transition. Computations are performed in both the supersonic and hypersonic regimes (free-stream Mach number from 3.37 up to 6.63) for the square, cylinder, diamond and hemisphere roughness elements. It is observed that the square and diamond roughness elements are more effective in inducing transition compared with the cylinder and hemisphere ones. The square roughness element has the longest separated region in which strong unsteadiness exists and the absolute instability is formed, thus resulting in the earliest transition. The diamond roughness element has a maximum width of the separated region leading to the widest turbulent wake region far downstream. Furthermore, transition location moves backward as the Mach number increases, which indicates that the compressibility significantly suppresses the roughness-induced boundary layer transition.

Passive Flap Actuation by Reversing Flow in Laminar Boundary Layer Separation

NASA Astrophysics Data System (ADS)

Parsons, Chase; Lang, Amy; Santos, Leo; Bonacci, Andrew

2017-11-01

Reducing the flow separation is of great interest in the field of fluid mechanics in order to reduce drag and improve the overall efficiency of aircraft. This project seeks to investigate passive flow control using shark inspired microflaps in laminar boundary layer separation. This study aims to show that whether a flow is laminar or turbulent, laminar and 2D or turbulent and 3D, microflaps actuated by reversing flow is a robust means of controlling flow separation. In order to generate a controlled adverse pressure gradient, a rotating cylinder induces separation at a chosen location on a flat plate boundary layer with Re above 10000. Within this thick boundary layer, digital particle image velocimetry is used to map the flow. This research can be used in the future to better understand the nature of the bristling shark scales and its ability to passively control separation. Results show that microflaps successfully actuated due to backflow and that this altered the formation of flow separation. I would like to thank the NSF for REU Grant EEC 1659710 and the Army Research Office for funding this project.

Transition Prediction in Hypersonic Boundary Layers Using Receptivity and Freestream Spectra

NASA Technical Reports Server (NTRS)

Balakumar, P.; Chou, Amanda

2016-01-01

Boundary-layer transition in hypersonic flows over a straight cone can be predicted using measured freestream spectra, receptivity, and threshold values for the wall pressure fluctuations at the transition onset points. Simulations are performed for hypersonic boundary-layer flows over a 7-degree half-angle straight cone with varying bluntness at a freestream Mach number of 10. The steady and the unsteady flow fields are obtained by solving the two-dimensional Navier-Stokes equations in axisymmetric coordinates using a 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using a third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The calculated N-factors at the transition onset location increase gradually with increasing unit Reynolds numbers for flow over a sharp cone and remain almost the same for flow over a blunt cone. The receptivity coefficient increases slightly with increasing unit Reynolds numbers. They are on the order of 4 for a sharp cone and are on the order of 1 for a blunt cone. The location of transition onset predicted from the simulation including the freestream spectrum, receptivity, and the linear and the weakly nonlinear evolutions yields a solution close to the measured onset location for the sharp cone. The simulations over-predict transition onset by about twenty percent for the blunt cone.

Recycling inflow method for simulations of spatially evolving turbulent boundary layers over rough surfaces

NASA Astrophysics Data System (ADS)

Yang, Xiang I. A.; Meneveau, Charles

2016-01-01

The technique by Lund et al. to generate turbulent inflow for simulations of developing boundary layers over smooth flat plates is extended to the case of surfaces with roughness elements. In the Lund et al. method, turbulent velocities on a sampling plane are rescaled and recycled back to the inlet as inflow boundary condition. To rescale mean and fluctuating velocities, appropriate length scales need be identified and for smooth surfaces, the viscous scale lν = ν/uτ (where ν is the kinematic viscosity and uτ is the friction velocity) is employed for the inner layer. Different from smooth surfaces, in rough wall boundary layers the length scale of the inner layer, i.e. the roughness sub-layer scale ld, must be determined by the geometric details of the surface roughness elements and the flow around them. In the proposed approach, it is determined by diagnosing dispersive stresses that quantify the spatial inhomogeneity caused by the roughness elements in the flow. The scale ld is used for rescaling in the inner layer, and the boundary layer thickness δ is used in the outer region. Both parts are then combined for recycling using a blending function. Unlike the blending function proposed by Lund et al. which transitions from the inner layer to the outer layer at approximately 0.2δ, here the location of blending is shifted upwards to enable simulations of very rough surfaces in which the roughness length may exceed the height of 0.2δ assumed in the traditional method. The extended rescaling-recycling method is tested in large eddy simulation of flow over surfaces with various types of roughness element shapes.

Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Carpenter, Mark H.; Choudhari, Meelan; Li, Fei; Streett, Craig L.; Chang, Chau-Lyan

2010-01-01

The problem of crossflow receptivity is considered in the context of a canonical 3D boundary layer (viz., the swept Hiemenz boundary layer) and a swept airfoil used recently in the SWIFT flight experiment performed at Texas A&M University. First, Hiemenz flow is used to analyze localized receptivity due to a spanwise periodic array of small amplitude roughness elements, with the goal of quantifying the effects of array size and location. Excitation of crossflow modes via nonlocalized but deterministic distribution of surface nonuniformity is also considered and contrasted with roughness induced acoustic excitation of Tollmien-Schlichting waves. Finally, roughness measurements on the SWIFT model are used to model the effects of random, spatially distributed roughness of sufficiently small amplitude with the eventual goal of enabling predictions of initial crossflow disturbance amplitudes as functions of surface roughness parameters.

Development of a Rotating Rake Array for Boundary-Layer-Ingesting Fan-Stage Measurements

NASA Technical Reports Server (NTRS)

Wolter, John D.; Arend, David J.; Hirt, Stefanie M.; Gazzaniga, John A.

2017-01-01

The recent Boundary-Layer-Ingesting Inlet/Distortion Tolerant Fan wind tunnel experiment at NASA Glenn Research Center's 8- by 6-foot Supersonic Wind Tunnel (SWT) examined the performance of a novel inlet and fan stage that was designed to ingest the vehicle boundary layer in order to take advantage of a predicted overall propulsive efficiency benefit. A key piece of the experiment's instrumentation was a pair of rotating rake arrays located upstream and downstream of the fan stage. This paper examines the development of these rake arrays. Pre-test numerical solutions were sampled to determine placement and spacing for rake pressure and temperature probes. The effects of probe spacing and survey density on the repeatability of survey measurements was examined. These data were then used to estimate measurement uncertainty for the adiabatic efficiency.

Correlation of nosetip boundary-layer transition data measured in ballistics-range experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, D.C.

1980-01-01

Preablated nosetips of various carbonaceous materials were tested in a ballistics range. Surface-temperature contours, measured with image-converter cameras, were used to define boundary-layer transition-front contours. Measurements of surface roughness, surface temperature, average transition-front location, and freestream environment were combined with calculations of nosetip flowfields, and with calculations of laminar boundary-layer development in these flowfields, to transform all data into various dimensionless parameters. These parameters were defined by previous attempts to correlate existing wind-tunnel data for transition on rough/blunt bodies. Of the available correlating techniques, only one, based on the concept of a constant (critical) roughness Reynolds number for transition, wasmore » found to successfully describe both the wind-tunnel and ballistics-range data, thereby validating the extrapolation of this concept to actual reentry-vehicle materials and environments.« less

Development of a Rotating Rake Array for Boundary-Layer-Ingesting Fan-Stage Measurements

NASA Technical Reports Server (NTRS)

Wolter, John D.; Arend, David J.; Hirt, Stefanie M.; Gazzaniga, John A.

2017-01-01

The recent Boundary-Layer-Ingesting Inlet/Distortion Tolerant Fan wind tunnel experiment at NASA Glenn Research Center's 8-foot by 6-foot supersonic wind tunnel examined the performance of a novel inlet and fan stage that was designed to ingest the vehicle boundary layer in order to take advantage of a predicted overall propulsive efficiency benefit. A key piece of the experiment's instrumentation was a pair of rotating rake arrays located upstream and downstream of the fan stage. This paper examines the development of these rake arrays. Pre-test numerical solutions were sampled to determine placement and spacing for rake pressure and temperature probes. The effects of probe spacing and survey density on the repeatability of survey measurements was examined. These data were then used to estimate measurement uncertainty for the adiabatic efficiency.

Skin-Friction Measurements in Incompressible Flow

NASA Technical Reports Server (NTRS)

Smith, Donald W.; Walker, John H.

1959-01-01

Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.

Boundary-layer transition on a flared cone in a Mach 6 quiet wind tunnel

NASA Astrophysics Data System (ADS)

Hofferth, Jerrod; Saric, William

2010-11-01

The Mach 6 Quiet Tunnel at Texas A&M is a low-disturbance blowdown facility suitable for boundary-layer stability and transition research. Following its reactivation in 2009, initial testing confirmed the presence of low-disturbance (< 0.1% Pt^'/Pt) freestream flow at select locations on the centerline of the nozzle for settling chamber pressures up to 10 atm, and a fully-traversed freestream flow-quality assessment is currently underway. As a third performance benchmark to complement these direct measurements, the present work measures the transition location on the NASA Langley 93-10 flared-cone model. This model has a 0.5m length, beginning as a 5^o half-angle circular cone. At the X=254mm station, a flare of surface radius 2.35m begins which is intended to induce transition within the quiet test core. Boundary-layer transition is detected on the thin-walled model by an observed surface temperature rise using an array of 51 embedded thermocouples. Transition data are presented for a sharp (2.5 μm) nose-tip radius case for comparison with the Lachowicz & Chokani (1996 data). Data for larger-radius nose-tips are also presented.

Effect of Surface Roughness on Polymer Drag Reduction with a High-Reynolds-Number Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Elbing, Brian; Dowling, David; Solomon, Michael; Bian, Sherry; Ceccio, Steven

2007-11-01

A recent experiment at the U.S. Navy's Large Cavitation Channel (LCC) investigated the effect of wall roughness on wall-injection polymer drag reduction (PDR) within a high-Reynolds-number (10^7 to 2x10^8 based on downstream distance) turbulent boundary layer (TBL). Testing was performed in two parts: 1) PDR experiment on a 12.9 m long, 3.05 m wide hydro-dynamically smooth flat plate and 2) PDR experiment on the same model with the entire surface roughened. The roughness was produced by blowing glass beads into epoxy paint that was applied to the entire model. The roughened model had an average roughness height ranging between 307 and 1154 μm. Drag reduction was determined using six, stream-wise located integrated skin-friction balances. In addition to skin-friction measurements, sampling was performed at three stream-wise located ports. The sampling ports were used to determine the amount of degradation, if any, caused by the turbulent flow on the polymer. Both the skin-friction measurements and sampling analysis indicates that wall roughness in a turbulent boundary layer significantly increases degradation of the polymer solution.

Cloud Physics Lidar Optical Measurements During the SAFARI-2000 Field Campaign

NASA Technical Reports Server (NTRS)

Hlavka, Dennis L.; McGill, Matt; Hart, William D.; Spinhirne, James D.; Starr, David OC. (Technical Monitor)

2002-01-01

In this presentation, we will show new optical data processing results from the Cloud Physics War during SAFARI-2000. Retrieved products include aerosol and cloud layer location and identification, layer optical depths, vertical extinction profiles, and extinction-to-backscatter (S) ratios for 532 and 1064 nm. The retrievals will focus on the persistent and smoky planetary boundary layer and occasional elevated aerosol layers found in southern Africa during August and September 2000.

Fuel decomposition and boundary-layer combustion processes of hybrid rocket motors

NASA Technical Reports Server (NTRS)

Chiaverini, Martin J.; Harting, George C.; Lu, Yeu-Cherng; Kuo, Kenneth K.; Serin, Nadir; Johnson, David K.

1995-01-01

Using a high-pressure, two-dimensional hybrid motor, an experimental investigation was conducted on fundamental processes involved in hybrid rocket combustion. HTPB (Hydroxyl-terminated Polybutadiene) fuel cross-linked with diisocyanate was burned with GOX under various operating conditions. Large-amplitude pressure oscillations were encountered in earlier test runs. After identifying the source of instability and decoupling the GOX feed-line system and combustion chamber, the pressure oscillations were drastically reduced from +/-20% of the localized mean pressure to an acceptable range of +/-1.5% Embedded fine-wire thermocouples indicated that the surface temperature of the burning fuel was around 1000 K depending upon axial locations and operating conditions. Also, except near the leading-edge region, the subsurface thermal wave profiles in the upstream locations are thicker than those in the downstream locations since the solid-fuel regression rate, in general, increases with distance along the fuel slab. The recovered solid fuel slabs in the laminar portion of the boundary layer exhibited smooth surfaces, indicating the existence of a liquid melt layer on the burning fuel surface in the upstream region. After the transition section, which displayed distinct transverse striations, the surface roughness pattern became quite random and very pronounced in the downstream turbulent boundary-layer region. Both real-time X-ray radiography and ultrasonic pulse-echo techniques were used to determine the instantaneous web thickness burned and instantaneous solid-fuel regression rates over certain portions of the fuel slabs. Globally averaged and axially dependent but time-averaged regression rates were also obtained and presented.

Acoustic energy exchange through flow turning

NASA Astrophysics Data System (ADS)

Baum, Joseph D.

1987-01-01

A numerical investigation of the mechanisms of acoustic energy exchange between the mean and acoustic flow fields in resonance chambers, such as rocket engines, is reported. A noniterative linearized block implicit scheme was used to solve the time-dependent compressible Navier-Stokes equations. Two test cases were investigated: acoustic wave propagation in a tube with a coexisting sheared mean flow (the refraction test) and acoustic wave propagation in a tube where the mean sheared flow was injected into the tube through its lateral boundary (the flow turning study). For flow turning, significant excitation of mean flow energy was observed at two locations: at the edge of the acoustic boundary layer and within a zone adjacent to the acoustic boundary layer extending up to 0.1 radii away from the wall. A weaker streaming effect was observed for the refraction study, and only at the edge of the acoustic boundary layer. The total dissipation for the flow turning test was twice the dissipation for refraction.

Effect of nose shape on three-dimensional stagnation region streamlines and heating rates

NASA Technical Reports Server (NTRS)

Hassan, Basil; Dejarnette, Fred R.; Zoby, E. V.

1991-01-01

A new method for calculating the three-dimensional inviscid surface streamlines and streamline metrics using Cartesian coordinates and time as the independent variable of integration has been developed. The technique calculates the streamline from a specified point on the body to a point near the stagnation point by using a prescribed pressure distribution in the Euler equations. The differential equations, which are singular at the stagnation point, are of the two point boundary value problem type. Laminar heating rates are calculated using the axisymmetric analog concept for three-dimensional boundary layers and approximate solutions to the axisymmetric boundary layer equations. Results for elliptic conic forebody geometries show that location of the point of maximum heating depends on the type of conic in the plane of symmetry and the angle of attack, and that this location is in general different from the stagnation point. The new method was found to give smooth predictions of heat transfer in the nose region where previous methods gave oscillatory results.

Mineralogy of Cretaceous/Tertiary boundary clays in the Chicxulub structure in northern Yucatan

NASA Technical Reports Server (NTRS)

Ming, D. W.; Sharpton, Virgil L.; Schuraytz, B. C.

1991-01-01

The Cretaceous/Tertiary (K/T) boundary clay layer is thought to be derived from ejecta material from meteorite impact, based on the anomalous concentrations of noble metals in the layer. Because of recent findings of a half-meter thick ejecta deposit at the K/T boundary in Haiti, efforts have focused on locating a large impact feature in the Caribbean and the Gulf of Mexico. One of the leading candidates for the site of a large impact is the Chicxulub structure located on the northern Yucatan Peninsula in Mexico. The Chicxulub structure is a subsurface zone of upper Cretaceous igneous rocks, carbonates, and breccias. The structure has been interpreted to be a 200 km diameter; however, there is some question to the size of the structure or to the fact that it even is an impact feature. Little is known about the mineralogy of this structure; the objective of this study was to determine the clay mineralogy of core samples from within the Chicxulub structure.

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 2; Phase-Averages

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

We examine the influence of surface heterogeneity on boundary layers using a large-eddy simulation coupled to a land-surface model. Heterogeneity, imposed in strips varying from 2-30 km (1 less than lambda/z(sub i) less than 18), is found to dramatically alter the structure of the free convective boundary layer by inducing significant organized circulations. A conditional sampling technique, based on the scale of the surface heterogeneity (phase averaging), is used to identify and quantify the organized surface fluxes and motions in the atmospheric boundary layer. The impact of the organized motions on turbulent transport depends critically on the scale of the heterogeneity lambda, the boundary layer height zi and the initial moisture state of the boundary layer. Dynamical and scalar fields respond differently as the scale of the heterogeneity varies. Surface heterogeneity of scale 4 less than lamba/z(sub i) less than 9 induces the strongest organized flow fields (up, wp) while heterogeneity with smaller or larger lambda/z(sub i) induces little organized motion. However, the organized components of the scalar fields (virtual potential temperature and mixing ratio) grow continuously in magnitude and horizontal scale, as lambda/z(sub i) increases. For some cases, the organized motions can contribute nearly 100% of the total vertical moisture flux. Patch-induced fluxes are shown to dramatically impact point measurements that assume the time-average vertical velocity to be zero. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

Measurement of crossflow vortices, attachment-line flow, and transition using microthin hot films

NASA Technical Reports Server (NTRS)

Mangalam, S. M.; Agarwal, N. K.; Maddalon, D. V.; Saric, W. S.

1990-01-01

A flow diagnostic experiment was conducted on a 45-deg swept-wing model using surface-mounted, multielement, microthin, hot-film sensors. The cross-flow vortex spacing, the attachment-line flow characteristics, and the transition region were all determined using an advanced data acquisition and instrumentation system. In addition to the frequencies of traveling waves predicted by linear stability theory, amplified disturbances at much higher frequencies were observed. Simultaneous measurements from sensors located at a number of chord and span locations highlighted the strong three-dimensionality of the boundary-layer flow in the presence of cross-flow vortices. The state of the attachment-line boundary layer was determined using a multielement sensor wrapped around the wing leading edge. The transition region flow characteristics were also identified.

Three-Dimensional Navier-Stokes Simulations with Two-Equation Turbulence Models of Intersecting Shock-Waves/Turbulent Boundary Layer at Mach 8.3

NASA Technical Reports Server (NTRS)

Bardina, J. E.; Coakley, T. J.

1994-01-01

An investigation of the numerical simulation with two-equation turbulence models of a three-dimensional hypersonic intersecting (SWTBL) shock-wave/turbulent boundary layer interaction flow is presented. The flows are solved with an efficient implicit upwind flux-difference split Reynolds-averaged Navier-Stokes code. Numerical results are compared with experimental data for a flow at Mach 8.28 and Reynolds number 5.3x10(exp 6) with crossing shock-waves and expansion fans generated by two lateral 15 fins located on top of a cold-wall plate. This experiment belongs to the hypersonic database for modeling validation. Simulations show the development of two primary counter-rotating cross-flow vortices and secondary turbulent structures under the main vortices and in each corner singularity inside the turbulent boundary layer. A significant loss of total pressure is produced by the complex interaction between the main vortices and the uplifted jet stream of the boundary layer. The overall agreement between computational and experimental data is generally good. The turbulence modeling corrections show improvements in the predictions of surface heat transfer distribution and an increase in the strength of the cross-flow vortices. Accurate predictions of the outflow flowfield is found to require accurate modeling of the laminar/turbulent boundary layers on the fin walls.

Boundary-Layer Transition on a Slender Cone in Hypervelocity Flow with Real Gas Effects

NASA Astrophysics Data System (ADS)

Jewell, Joseph Stephen

The laminar to turbulent transition process in boundary layer flows in thermochemical nonequilibrium at high enthalpy is measured and characterized. Experiments are performed in the T5 Hypervelocity Reflected Shock Tunnel at Caltech, using a 1 m length 5-degree half angle axisymmetric cone instrumented with 80 fast-response annular thermocouples, complemented by boundary layer stability computations using the STABL software suite. A new mixing tank is added to the shock tube fill apparatus for premixed freestream gas experiments, and a new cleaning procedure results in more consistent transition measurements. Transition location is nondimensionalized using a scaling with the boundary layer thickness, which is correlated with the acoustic properties of the boundary layer, and compared with parabolized stability equation (PSE) analysis. In these nondimensionalized terms, transition delay with increasing CO2 concentration is observed: tests in 100% and 50% CO2, by mass, transition up to 25% and 15% later, respectively, than air experiments. These results are consistent with previous work indicating that CO2 molecules at elevated temperatures absorb acoustic instabilities in the MHz range, which is the expected frequency of the Mack second-mode instability at these conditions, and also consistent with predictions from PSE analysis. A strong unit Reynolds number effect is observed, which is believed to arise from tunnel noise. NTr for air from 5.4 to 13.2 is computed, substantially higher than previously reported for noisy facilities. Time- and spatially-resolved heat transfer traces are used to track the propagation of turbulent spots, and convection rates at 90%, 76%, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, centroid, and trailing edge of the spots. A model constructed with these spot propagation parameters is used to infer spot generation rates from measured transition onset to completion distance. Finally, a novel method to control transition location with boundary layer gas injection is investigated. An appropriate porous-metal injector section for the cone is designed and fabricated, and the efficacy of injected CO2 for delaying transition is gauged at various mass flow rates, and compared with both no injection and chemically inert argon injection cases. While CO2 injection seems to delay transition, and argon injection seems to promote it, the experimental results are inconclusive and matching computations do not predict a reduction in N factor from any CO2 injection condition computed.

Boundary Layer Characterization during Perdigão Field Campaign 2017

NASA Astrophysics Data System (ADS)

Leo, L. S.; Salvadore, J. J.; Belo-Pereira, M.; Menke, R.; Gomes, S.; Krishnamurthy, R.; Brown, W. O. J.; Creegan, E.; Klein, P. M.; Wildmann, N.; Oncley, S.; Fernando, J.; Mann, J.

2017-12-01

The depth and structure of the atmospheric boundary layer (ABL) significantly impact the performances of wind farms located in complex terrain environments, since low-level jets and other flow structures in the proximity of hills and mountains determine the weather extremes, such as shear layer instabilities, lee/internal wave breaking, etc. which in turn profoundly modify the turbulence profile at wind turbine relevant heights.A suite of instruments was deployed covering a double-ridge in central Portugal near the town of Perdigão in 2016-2017, and they are used here to characterize the ABL structure over complex terrain during the Intensive Observational Period (IOP, May 1- June 15, 2017) of the research field program dubbed "Perdigão". Firstly, the methodology adopted in this work to estimate the BL height will be discussed; secondly, an overview of the BL depth and characteristics during Perdigão-IOP campaign will be provided, with emphasis on case studies of interest for both the wind-power and boundary-layer communities.

F-16XL ship #1 CAWAP flight - alpha 15 degrees, altitude 5,000 feet

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. This photo shows the aircraft gathering data at an altitude of 5000 feet, with an angle of attack of 15 degrees. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Experimental Studies of Flow Separation of the NACA 2412 Airfoil at Low Speeds

NASA Technical Reports Server (NTRS)

Seetharam, H. C.; Rodgers, E. J.; Wentz, W. H., Jr.

1997-01-01

Wind tunnel tests have been conducted on an NACA 2412 airfoil section at Reynolds number of 2.2 x 10(exp 6) and Mach number of 0.13. Detailed measurements of flow fields associated with turbulent boundary layers have been obtained at angles of attack of 12.4 degrees, 14.4 degrees, and 16.4 degrees. Pre- and post-separated velocity and pressure survey results over the airfoil and in the associated wake are presented. Extensive force, pressure, tuft survey, hot-film survey, local skin friction, and boundary layer data are also included. Pressure distributions and separation point locations show good agreement with theory for the two layer angles of attack. Boundary layer displacement thickness, momentum thickness, and shape factor agree well with theory up to the point of separation. There is considerable disparity between extent of flow reversal in the wake as measured by pressure and hot-film probes. The difference is attributed to the intermittent nature of the flow reversal.

Heat transfer and fluid mechanics measurements in transitional boundary layer flows

NASA Technical Reports Server (NTRS)

Wang, T.; Simon, T. W.; Buddhavarapu, J.

1985-01-01

Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.

Boundary Layer Transition During the Orion Exploration Flight Test 1 (EFT-1)

NASA Technical Reports Server (NTRS)

Kirk, Lindsay C.

2016-01-01

Boundary layer transition was observed in the thermocouple data on the windside backshell of the Orion reentry capsule. Sensors along the windside centerline, as well as off-centerline, indicated transition late in the flight at approximately Mach 4 conditions. Transition progressed as expected, beginning at the sensors closest to the forward bay cover (FBC) and moving towards the heatshield. Sensors placed in off-centerline locations did not follow streamlines, so the progression of transition observed in these sensors is less intuitive. Future analysis will include comparisons to pre-flight predictions and expected transitional behavior will be investigated. Sensors located within the centerline and off-centerline launch abort system (LAS) attach well cavities on the FBC also showed indications of boundary layer transition. The transition within the centerline cavity was observed in the temperature traces prior to transition onset on the sensors upstream of the cavity. Transition behavior within the off centerline LAS attach well cavity will also be investigated. Heatshield thermocouples were placed within Avcoat plugs to attempt to capture transitional behavior as well as better understand the aerothermal environments. Thermocouples were placed in stacks of two or five vertically within the plugs, but the temperature data obtained at the sensors closest to the surface did not immediately indicate transitional behavior. Efforts to use the in depth thermocouple temperatures to reconstruct the surface heat flux are ongoing and any results showing the onset of boundary layer transition obtained from those reconstructions will also be included in this paper. Transition on additional features of interest, including compression pad ramps, will be included if it becomes available.

Boundary Layer Transition Flight Experiment Overview and In-Situ Measurements

NASA Technical Reports Server (NTRS)

Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.

2010-01-01

In support of the Boundary Layer Transition Flight Experiment (BLT FE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for the flights of STS-119, STS-128 and STS-131. Additional instrumentation was installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLT FE Project. Significant efforts were made to place the protuberance at an appropriate location on the Orbiter and to design the protuberance to withstand the expected environments. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that predictions for boundary layer transition onset time closely match the flight data, while predicted temperatures were significantly higher than observed flight temperatures.

Flight experiments measuring boundary-layer disturbances in laminar flow and correlation with stability analysis

NASA Technical Reports Server (NTRS)

Lee, Cynthia C.; Obara, Clifford J.; Vijgen, Paul M.; Wusk, Michael S.

1991-01-01

Flight test results are reported from an experiment designed to study the detailed growth of disturbances in the laminar boundary layer. A gloved wing section incorporating closely-spaced flush-mounted streamwise-located instrumentation for measuring instability frequencies and amplitude growths as well as pressure distributions was used. The growth of Tollmien-Schlichting (T-S) and crossflow instabilities is predicted by the linear e exp n method and compared to the measured boundary-layer disturbance frequencies. The predictions showed good agreement with the measured data. The results exhibited fair agreement with previous n(T-S) and n(CF) flight correlations for several of the conditions analyzed. It is inferred from the high n(T-S) values for these data that moderately swept wings at compressible speeds can withstand higher combinations of n(T-S) and n(CF) values and still remain laminar than previously thought.

An Approach to the Constrained Design of Natural Laminar Flow Airfoils

NASA Technical Reports Server (NTRS)

Green, Bradford E.

1997-01-01

A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.

An approach to the constrained design of natural laminar flow airfoils

NASA Technical Reports Server (NTRS)

Green, Bradford Earl

1995-01-01

A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integml turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the larninar flow toward the desired amounl An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.

The eigenvalue spectrum of the Orr-Sommerfeld problem

NASA Technical Reports Server (NTRS)

Antar, B. N.

1976-01-01

A numerical investigation of the temporal eigenvalue spectrum of the ORR-Sommerfeld equation is presented. Two flow profiles are studied, the plane Poiseuille flow profile and the Blasius boundary layer (parallel): flow profile. In both cases a portion of the complex c-plane bounded by 0 less than or equal to CR sub r 1 and -1 less than or equal to ci sub i 0 is searched and the eigenvalues within it are identified. The spectra for the plane Poiseuille flow at alpha = 1.0 and R = 100, 1000, 6000, and 10000 are determined and compared with existing results where possible. The spectrum for the Blasius boundary layer flow at alpha = 0.308 and R = 998 was found to be infinite and discrete. Other spectra for the Blasius boundary layer at various Reynolds numbers seem to confirm this result. The eigenmodes belonging to these spectra were located and discussed.

The Goertler vortex instability mechanism in three-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Hall, P.

1984-01-01

The two dimensional boundary layer on a concave wall is centrifugally unstable with respect to vortices aligned with the basic flow for sufficiently high values of the Goertler number. However, in most situations of practical interest the basic flow is three dimensional and previous theoretical investigations do not apply. The linear stability of the flow over an infinitely long swept wall of variable curvature is considered. If there is no pressure gradient in the boundary layer the instability problem can always be related to an equivalent two dimensional calculation. However, in general, this is not the case and even for small values of the crossflow velocity field dramatic differences between the two and three dimensional problems emerge. When the size of the crossflow is further increased, the vortices in the neutral location have their axes locally perpendicular to the vortex lines of the basic flow.

Investigation of Turbulent Boundary-Layer Separation Using Laser Velocimetry

NASA Technical Reports Server (NTRS)

Modarress, D.; Johnson, D. A.

1979-01-01

Boundary-layer measurements realized by laser velocimetry are presented for a Much 2.9, two-dimensional, shock-wave/turbulent boundary-layer interaction containing an extensive region of separated flow. Mean velocity and turbulent intensity profiles were obtained from upstream of the interaction zone to downstream of the mean reattachment point. The superiority of the laser velocimeter technique over pressure sensors in turbulent separated flows is demonstrated by a comparison of the laser velocimeter data with results obtained from local pilot and static pressure measurements for the same flow conditions. The locations of the mean separation and reattachment points as deduced from the mean velocity measurements are compared to oil-now visualization results. Representative velocity probability density functions obtained in the separated now region are also presented. Critical to the success of this investigation were: the use of Bragg cell frequency shifting and artificial seeding of the now with submicron light-scattering particles.

A nonlinear investigation of the stationary modes of instability of the three-dimensional compressible boundary layer due to a rotating disc

NASA Technical Reports Server (NTRS)

Seddougui, Sharon O.

1989-01-01

The effects of compressibility on a stationary mode of instability of the 3-D boundary layer due to a rotating disc are investigated. The aim is to determine whether this mode will be important in the finite amplitude destabilization of the boundary layer. This stationary mode is characterized by the effective velocity profile having zero shear stress at the wall. Triple-deck solutions are presented for an adiabatic wall and an isothermal wall. It is found that this stationary mode is only possible over a finite range of Mach numbers. Asymptotic solutions are obtained which describe the structure of the wavenumber and the orientation of these modes as functions of the local Mach number. The effects of nonlinearity are investigated allowing the finite amplitude growth of a disturbance close to the neutral location to be described.

Diffractive Hyperbola of a Skin Layer

NASA Astrophysics Data System (ADS)

Yakubov, V. P.; Vaiman, E. V.; Shipilov, S. È.; Prasath, A. K.

2018-03-01

Based on an analysis of physics of the phase transition from the quasistatic state field to the running wave field of elementary electric and magnetic dipoles located in absorbing media, it is concluded that the skin layer is formed at the boundary of this phase transition. The possibility is considered of obtaining the diffractive hyperbola of the skin layer and its subsequent application for sensing of objects in strongly absorbing media.

Measurements in a Transitional Boundary Layer Under Low-Pressure Turbine Airfoil Conditions

NASA Technical Reports Server (NTRS)

Simon, Terrence W.; Qiu, Songgang; Yuan, Kebiao; Ashpis, David (Technical Monitor); Simon, Fred (Technical Monitor)

2000-01-01

This report presents the results of an experimental study of transition from laminar to turbulent flow in boundary layers or in shear layers over separation zones on a convex-curved surface which simulates the suction surface of a low-pressure turbine airfoil. Flows with various free-stream turbulence intensity (FSTI) values (0.5%, 2.5% and 10%), and various Reynolds numbers (50,000, 100,000 200,000 and 300,000) are investigated. Reynold numbers in the present study are based on suction surface length and passage exit mean velocity. Flow separation followed by transition within the separated flow region is observed for the lower-Re cases at each of the FSTI levels. At the highest Reynolds numbers and at elevated FSn, transition of the attached boundary layer begins before separation, and the separation zone is small. Transition proceeds in the shear layer over the separation bubble. For both the transitional boundary layer and the transitional shear layer, mean velocity, turbulence intensity and intermittency (the fraction of the time the flow is turbulent) distributions are presented. The present data are compared to published distribution models for bypass transition, intermittency distribution through transition, transition start position, and transition length. A model developed for transition of separated flows is shown to adequately predict the location of the beginning of transition, for these cases, and a model developed for transitional boundary layer flows seems to adequately predict the path of intermittency through transition when the transition start and end are known. These results are useful for the design of low-pressure turbine stages which are known to operate under conditions replicated by these tests.

Airborne measurements of turbulent trace gas fluxes and analysis of eddy structure in the convective boundary layer over complex terrain

NASA Astrophysics Data System (ADS)

Hasel, M.; Kottmeier, Ch.; Corsmeier, U.; Wieser, A.

2005-03-01

Using the new high-frequency measurement equipment of the research aircraft DO 128, which is described in detail, turbulent vertical fluxes of ozone and nitric oxide have been calculated from data sampled during the ESCOMPTE program in the south of France. Based on airborne turbulence measurements, radiosonde data and surface energy balance measurements, the convective boundary layer (CBL) is examined under two different aspects. The analysis covers boundary-layer convection with respect to (i) the control of CBL depth by surface heating and synoptic scale influences, and (ii) the structure of convective plumes and their vertical transport of ozone and nitric oxides. The orographic structure of the terrain causes significant differences between planetary boundary layer (PBL) heights, which are found to exceed those of terrain height variations on average. A comparison of boundary-layer flux profiles as well as mean quantities over flat and complex terrain and also under different pollution situations and weather conditions shows relationships between vertical gradients and corresponding turbulent fluxes. Generally, NO x transports are directed upward independent of the terrain, since primary emission sources are located near the ground. For ozone, negative fluxes are common in the lower CBL in accordance with the deposition of O 3 at the surface. The detailed structure of thermals, which largely carry out vertical transports in the boundary layer, are examined with a conditional sampling technique. Updrafts mostly contain warm, moist and NO x loaded air, while the ozone transport by thermals alternates with the background ozone gradient. Evidence for handover processes of trace gases to the free atmosphere can be found in the case of existing gradients across the boundary-layer top. An analysis of the size of eddies suggests the possibility of some influence of the heterogeneous terrain in mountainous area on the length scales of eddies.

Thermocouple Rakes for Measuring Boundary Layer Flows Extremely Close to Surface

NASA Technical Reports Server (NTRS)

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Blaha, Charles A.

2001-01-01

Of vital interest to aerodynamic researchers is precise knowledge of the flow velocity profile next to the surface. This information is needed for turbulence model development and the calculation of viscous shear force. Though many instruments can determine the flow velocity profile near the surface, none of them can make measurements closer than approximately 0.01 in. from the surface. The thermocouple boundary-layer rake can measure much closer to the surface than conventional instruments can, such as a total pressure boundary layer rake, hot wire, or hot film. By embedding the sensors (thermocouples) in the region where the velocity is equivalent to the velocity ahead of a constant thickness strut, the boundary-layer flow profile can be obtained. The present device fabricated at the NASA Glenn Research Center microsystem clean room has a heater made of platinum and thermocouples made of platinum and gold. Equal numbers of thermocouples are placed both upstream and downstream of the heater, so that the voltage generated by each pair at the same distance from the surface is indicative of the difference in temperature between the upstream and downstream thermocouple locations. This voltage differential is a function of the flow velocity, and like the conventional total pressure rake, it can provide the velocity profile. In order to measure flow extremely close to the surface, the strut is made of fused quartz with extremely low heat conductivity. A large size thermocouple boundary layer rake is shown in the following photo. The latest medium size sensors already provide smooth velocity profiles well into the boundary layer, as close as 0.0025 in. from the surface. This is about 4 times closer to the surface than the previously used total pressure rakes. This device also has the advantage of providing the flow profile of separated flow and also it is possible to measure simultaneous turbulence levels within the boundary layer.

Control of unsteadiness of a shock wave/turbulent boundary layer interaction by using a pulsed-plasma-jet actuator

NASA Astrophysics Data System (ADS)

Narayanaswamy, Venkateswaran; Raja, Laxminarayan L.; Clemens, Noel T.

2012-07-01

A pulsed-plasma jet actuator is used to control the unsteady motion of the separation shock of a shock wave/boundary layer interaction formed by a compression ramp in a Mach 3 flow. The actuator is based on a plasma-generated synthetic jet and is configured as an array of three jets that can be injected normal to the cross-flow, pitched, or pitched and skewed. The typical peak jet exit velocity of the actuators is about 300 m/s and the pulsing frequencies are a few kilohertz. A study of the interaction between the pulsed-plasma jets and the shock/boundary layer interaction was performed in a time-resolved manner using 10 kHz schlieren imaging. When the actuator, pulsed at StL ≈ 0.04 (f = 2 kHz), was injected into the upstream boundary layer, the separation shock responded to the plasma jet by executing a rapid upstream motion followed by a gradual downstream recovery motion. Schlieren movies of the interaction showed that the separation shock unsteadiness was locked to the pulsing frequency of the actuator, with amplitude of about one boundary layer thickness. Wall-pressure measurements made under the intermittent region showed about a 30% decrease in the overall magnitude of the pressure fluctuations in the low-frequency band associated with unsteady large-scale motion of the separated flow. Furthermore, by increasing the pulsing frequency to 3.3 kHz, the amplitude of the separation shock oscillation was reduced to less than half the boundary layer thickness. Investigation into the effect of the actuator location on the shock wave/boundary layer interaction (SWBLI) showed qualitatively and quantitatively that the actuator placed upstream of the separation shock caused significant modification to the SWBLI unsteadiness, whereas injection from inside the separation bubble did not cause a noticeable effect.

New Predictions of the Jovian Aurora: Location, Latitudinal Width, and Intensity

NASA Technical Reports Server (NTRS)

Tsurutani, B. T.; Arballo, J. K.; Ho, C. M.; Lin, N. G.; Kellogg, P. J.; Cornileau-Wehrlin, N.; Krupp, N.

1995-01-01

A model/theory for the Jovian aurora is formed based on a similar model for the dayside aurora at Earth and recent Ulysses field and particle measurements at Jupiter. Items discussed are plasma boundary layer, wave-particle resonant interactions, and the model's prediction of the aurora's location, latitudinal width, and intensity.

An experimental investigation of shock wave-turbulent boundary layer interactions with and without boundary layer suction: A data summary report

NASA Technical Reports Server (NTRS)

Sun, C. C.; Childs, M. E.

1977-01-01

Tabulated data from a series of experimental studies of the interaction of a shock wave with a turbulent boundary layer in axisymmetric flow configurations is presented. The studies were conducted at the walls of circular wind tunnels and on the cylindrical centerbody of an annular flow channel. Detailed pitot pressure profiles and wall static pressure profiles upstream of, within and downstream of the interaction region are given. Results are presented for flows at nominal freestream Mach Numbers of 2, 3 and 4. For studies at the tunnel sidewalls, the shock waves were produced by conical shock generators mounted on the centerline of the wind tunnel at zero angle of attack. The annular ring generator was used to produce the shock wave at the centerbody of the annular flow channel. The effects of boundary layer bleed were examined in the investigation. Both bleed rate and bleed location were studied. Most of the bleed studies were conducted with bleed holes drilled normal to the wall surface but the effects of slot suction were also examined. A summary of the principal results and conclusions is given.

Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Free Flight

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Wilder, Michael C.; Prabhu, Dinesh K.

2010-01-01

Smooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.

Pulsating flow and boundary layers in viscous electronic hydrodynamics

NASA Astrophysics Data System (ADS)

Moessner, Roderich; Surówka, Piotr; Witkowski, Piotr

2018-04-01

Motivated by experiments on a hydrodynamic regime in electron transport, we study the effect of an oscillating electric field in such a setting. We consider a long two-dimensional channel of width L , whose geometrical simplicity allows an analytical study as well as hopefully permitting an experimental realization. The response depends on viscosity ν , driving frequency ω , and ohmic heating coefficient γ via the dimensionless complex variable L/2ν (i ω +γ ) =i Ω +Σ . While at small Ω , we recover the static solution, a different regime appears at large Ω with the emergence of a boundary layer. This includes a splitting of the location of maximal flow velocity from the center towards the edges of the boundary layer, an increasingly reactive nature of the response, with the phase shift of the response varying across the channel. The scaling of the total optical conductance with L differs between the two regimes, while its frequency dependence resembles a Drude form throughout, even in the complete absence of ohmic heating, against which, at the same time, our results are stable. Current estimates for transport coefficients in graphene and delafossites suggest that the boundary-layer regime should be experimentally accessible.

Wind-tunnel investigation of a full-scale canard-configured general aviation aircraft

NASA Technical Reports Server (NTRS)

Yip, L. P.; Coy, P. F.

1982-01-01

As part of a broad research program to provide a data base on advanced airplane configurations, a wind-tunnel investigation was conducted in the Langley 30-by 60-Foot Wind Tunnel to determine the aerodynamic characteristics of an advanced canard-configured general aviation airplane. The investigation included measurements of forces and moments of the complete configuration, isolated canard loads, and pressure distributions on the wing, winglet, and canard. Flow visualization was obtained by using surface tufts to determine regions of flow separation and by using a chemical sublimation technique to determine boundary-layer transition locations. Additionally, other tests were conducted to determine simulated rain effects on boundary layer transition. Investigation of configuration effects included variations of canard locations, canard airfoil section, winglet size, and use of a leading-edge droop on the out-board section of the wing.

Wall boundary layer development near the tip region of an IGV of an axial flow compressor

NASA Technical Reports Server (NTRS)

Lakshminarayana, B.; Sitaram, N.

1983-01-01

The annulus wall boundary layer inside the blade passage of the inlet guide vane (IGV) passage of a low-speed axial compressor stage was measured with a miniature five-hole probe. The three-dimensional velocity and pressure fields were measured at various axial and tangential locations. Limiting streamline angles and static pressures were also measured on the casing of the IGV passage. Strong secondary vorticity was developed. The data were analyzed and correlated with the existing velocity profile correlations. The end wall losses were also derived from these data.

Computational Study of Hypersonic Boundary Layer Stability on Cones

NASA Astrophysics Data System (ADS)

Gronvall, Joel Edwin

Due to the complex nature of boundary layer laminar-turbulent transition in hypersonic flows and the resultant effect on the design of re-entry vehicles, there remains considerable interest in developing a deeper understanding of the underlying physics. To that end, the use of experimental observations and computational analysis in a complementary manner will provide the greatest insights. It is the intent of this work to provide such an analysis for two ongoing experimental investigations. The first focuses on the hypersonic boundary layer transition experiments for a slender cone that are being conducted at JAXA's free-piston shock tunnel HIEST facility. Of particular interest are the measurements of disturbance frequencies associated with transition at high enthalpies. The computational analysis provided for these cases included two-dimensional CFD mean flow solutions for use in boundary layer stability analyses. The disturbances in the boundary layer were calculated using the linear parabolized stability equations. Estimates for transition locations, comparisons of measured disturbance frequencies and computed frequencies, and a determination of the type of disturbances present were made. It was found that for the cases where the disturbances were measured at locations where the flow was still laminar but nearly transitional, that the highly amplified disturbances showed reasonable agreement with the computations. Additionally, an investigation of the effects of finite-rate chemistry and vibrational excitation on flows over cones was conducted for a set of theoretical operational conditions at the HIEST facility. The second study focuses on transition in three-dimensional hypersonic boundary layers, and for this the cone at angle of attack experiments being conducted at the Boeing/AFOSR Mach-6 quiet tunnel at Purdue University were examined. Specifically, the effect of surface roughness on the development of the stationary crossflow instability are investigated in this work. One standard mean flow solution and two direct numerical simulations of a slender cone at an angle of attack were computed. The direct numerical simulations included a digitally-filtered, randomly distributed surface roughness and were performed using a high-order, low-dissipation numerical scheme on appropriately resolved grids. Comparisons with experimental observations showed excellent qualitative agreement. Comparisons with similar previous computational work were also made and showed agreement in the wavenumber range of the most unstable crossflow modes.

A sharp and flat section of the core-mantle boundary

USGS Publications Warehouse

Vidale, J.E.; Benz, H.M.

1992-01-01

THE transition zone between the Earth's core and mantle plays an important role as a boundary layer for mantle and core convection1. This zone conducts a large amount of heat from the core to the mantle, and contains at least one thermal boundary layer2,3; the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4. Here we investigate one region of the core-mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary. The use of this phase (known as ScP), the large number of receiving stations, and the large aperture of our array all provide higher resolution than has previously been possible5-7. For the 350-km-long section of the core-mantle boundary under the northeast Pacific sampled by the reflections, the local boundary topography has an amplitude of less than 500 m, no sharp radial gradients exist in the 400 km above the boundary, and the mantle-lo-core transition occurs over less than 1 km. The simplicity of the structure near and above the core-mantle boundary argues against chemical heterogeneity at the base of the mantle in this location.

F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis

NASA Technical Reports Server (NTRS)

Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

1984-01-01

An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.

Numerical simulation of transitional flow on a wind turbine airfoil with RANS-based transition model

NASA Astrophysics Data System (ADS)

Zhang, Ye; Sun, Zhengzhong; van Zuijlen, Alexander; van Bussel, Gerard

2017-09-01

This paper presents a numerical investigation of transitional flow on the wind turbine airfoil DU91-W2-250 with chord-based Reynolds number Rec = 1.0 × 106. The Reynolds-averaged Navier-Stokes based transition model using laminar kinetic energy concept, namely the k - kL - ω model, is employed to resolve the boundary layer transition. Some ambiguities for this model are discussed and it is further implemented into OpenFOAM-2.1.1. The k - kL - ω model is first validated through the chosen wind turbine airfoil at the angle of attack (AoA) of 6.24° against wind tunnel measurement, where lift and drag coefficients, surface pressure distribution and transition location are compared. In order to reveal the transitional flow on the airfoil, the mean boundary layer profiles in three zones, namely the laminar, transitional and fully turbulent regimes, are investigated. Observation of flow at the transition location identifies the laminar separation bubble. The AoA effect on boundary layer transition over wind turbine airfoil is also studied. Increasing the AoA from -3° to 10°, the laminar separation bubble moves upstream and reduces in size, which is in close agreement with wind tunnel measurement.

Flight, Wind-Tunnel, and Computational Fluid Dynamics Comparison for Cranked Arrow Wing (F-16XL-1) at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Lamar, John E.; Obara, Clifford J.; Fisher, Bruce D.; Fisher, David F.

2001-01-01

Geometrical, flight, computational fluid dynamics (CFD), and wind-tunnel studies for the F-16XL-1 airplane are summarized over a wide range of test conditions. Details are as follows: (1) For geometry, the upper surface of the airplane and the numerical surface description compare reasonably well. (2) For flight, CFD, and wind-tunnel surface pressures, the comparisons are generally good at low angles of attack at both subsonic and transonic speeds, however, local differences are present. In addition, the shock location at transonic speeds from wind-tunnel pressure contours is near the aileron hinge line and generally is in correlative agreement with flight results. (3) For boundary layers, flight profiles were predicted reasonably well for attached flow and underneath the primary vortex but not for the secondary vortex. Flight data indicate the presence of an interaction of the secondary vortex system and the boundary layer and the boundary-layer measurements show the secondary vortex located more outboard than predicted. (4) Predicted and measured skin friction distributions showed qualitative agreement for a two vortex system. (5) Web-based data-extraction and computational-graphical tools have proven useful in expediting the preceding comparisons. (6) Data fusion has produced insightful results for a variety of visualization-based data sets.

Detection and measurement of tubulitis in renal allograft rejection

NASA Astrophysics Data System (ADS)

Hiller, John B.; Chen, Qi; Jin, Jesse S.; Wang, Yung; Yong, James L. C.

1997-04-01

Tubulitis is one of the most reliable signs of acute renal allograft rejection. It occurs when mononuclear cells are localized between the lining tubular epithelial cells with or without disruption of the tubular basement membrane. It has been found that tubulitis takes place predominantly in the regions of the distal convoluted tubules and the cortical collecting system. The image processing tasks are to find the tubule boundaries and to find the relative location of the lymphocytes and epithelial cells and tubule boundaries. The requirement for accuracy applies to determining the relative locations of the lymphocytes and the tubule boundaries. This paper will show how the different sizes and grey values of the lymphocytes and epithelial cells simplify their identification and location. Difficulties in finding the tubule boundaries image processing will be illustrated. It will be shown how proximate location of epithelial cells and the tubule boundary leads to distortion in determination of the calculated boundary. However, in tubulitis the lymphocytes and the tubule boundaries are proximate.In these cases the tubule boundary is adequately resolved and the image processing is satisfactory to determining relativity in location. An adaptive non-linear anisotropic diffusion process is presented for image filtering and segmentation. Multi-layer analysis is used to extract lymphocytes and tubulitis from images. This paper will discuss grading of tissue using the Banff system. The ability to use computer to use computer processing will be argued as obviating problems of reproducability of values for this classification. This paper will also feature discussion of alternative approaches to image processing and provide an assessment of their capability for improving the identification of the tubule boundaries.

Experimental evaluation of heat transfer on a 1030:1 area ratio rocket nozzle

NASA Technical Reports Server (NTRS)

Kacynski, Kenneth J.; Pavli, Albert J.; Smith, Tamara A.

1987-01-01

A 1030:1 carbon steel, heat-sink nozzle was tested. The test conditions included a nominal chamber pressure of 2413 kN/sq m and a mixture ratio range of 2.78 to 5.49. The propellants were gaseous oxygen and gaseous hydrogen. Outer wall temperature measurements were used to calculate the inner wall temperature and the heat flux and heat rate to the nozzle at specified axial locations. The experimental heat fluxes were compared to those predicted by the Two-Dimensional Kinetics (TDK) computer model analysis program. When laminar boundary layer flow was assumed in the analysis, the predicted values were within 15 percent of the experimental values for the area ratios of 20 to 975. However, when turbulent boundary layer conditions were assumed, the predicted values were approximately 120 percent higher than the experimental values. A study was performed to determine if the conditions within the nozzle could sustain a laminar boundary layer. Using the flow properties predicted by TDK, the momentum-thickness Reynolds number was calculated, and the point of transition to turbulent flow was predicted. The predicted transition point was within 0.5 inches of the nozzle throat. Calculations of the acceleration parameter were then made to determine if the flow conditions could produce relaminarization of the boundary layer. It was determined that if the boundary layer flow was inclined to transition to turbulent, the acceleration conditions within the nozzle would tend to suppress turbulence and keep the flow laminar-like.

Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry

NASA Astrophysics Data System (ADS)

Squire, D. T.; Morrill-Winter, C.; Hutchins, N.; Marusic, I.; Schultz, M. P.; Klewicki, J. C.

2016-10-01

Two particle image velocimetry arrangements are used to make true spatial comparisons between smooth- and rough-wall boundary layers at high Reynolds numbers across a very wide range of streamwise scales. Together, the arrangements resolve scales ranging from motions on the order of the Kolmogorov microscale to those longer than twice the boundary layer thickness. The rough-wall experiments were obtained above a continuous sandpaper sheet, identical to that used by Squire et al. [J. Fluid Mech. 795, 210 (2016), 10.1017/jfm.2016.196], and cover a range of friction and equivalent sand-grain roughness Reynolds numbers (12 000 ≲δ+≲ 18000, 62 ≲ks+≲104 ). The smooth-wall experiments comprise new and previously published data spanning 6500 ≲δ+≲17 000 . Flow statistics from all experiments show similar Reynolds number trends and behaviors to recent, well-resolved hot-wire anemometry measurements above the same rough surface. Comparisons, at matched δ+, between smooth- and rough-wall two-point correlation maps and two-point magnitude-squared coherence maps demonstrate that spatially the outer region of the boundary layer is the same between the two flows. This is apparently true even at wall-normal locations where the total (inner-normalized) energy differs between the smooth and rough wall. Generally, the present results provide strong support for Townsend's [The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, 1956), Vol. 1] wall-similarity hypothesis in high Reynolds number fully rough boundary layer flows.

Experimental evaluation of heat transfer on a 1030:1 area ratio rocket nozzle

NASA Technical Reports Server (NTRS)

Kacynski, Kenneth J.; Pavli, Albert J.; Smith, Tamara A.

1987-01-01

A 1030:1 carbon steel, heat-sink nozzle was tested. The test conditions included a nominal chamber pressure of 2413 kN/sq m and a mixture ratio range of 2.78 to 5.49. The propellants were gaseous oxygen and gaseous hydrogen. Outer wall temperature measurements were used to calculate the inner wall temperature and the heat flux and heat rate to the nozzle at specified axial locations. The experimental heat fluxes were compared to those predicted by the Two-Dimensional Kinetics (TDK) computer model analysis program. When laminar boundary layer flow was assumed in the analysis, the predicted values were within 15% of the experimental values for the area ratios of 20 to 975. However, when turbulent boundary layer conditions were assumed, the predicted values were approximately 120% higher than the experimental values. A study was performed to determine if the conditions within the nozzle could sustain a laminar boundary layer. Using the flow properties predicted by TDK, the momentum-thickness Reynolds number was calculated, and the point of transition to turbulent flow was predicted. The predicted transition point was within 0.5 inches of the nozzle throat. Calculations of the acceleration parameter were then made to determine if the flow conditions could produce relaminarization of the boundary layer. It was determined that if the boundary layer flow was inclined to transition to turbulent, the acceleration conditions within the nozzle would tend to suppress turbulence and keep the flow laminar-like.

Applying Geospatial Techniques to Investigate Boundary Layer Land-Atmosphere Interactions Involved in Tornadogensis

NASA Astrophysics Data System (ADS)

Weigel, A. M.; Griffin, R.; Knupp, K. R.; Molthan, A.; Coleman, T.

2017-12-01

Northern Alabama is among the most tornado-prone regions in the United States. This region has a higher degree of spatial variability in both terrain and land cover than the more frequently studied North American Great Plains region due to its proximity to the southern Appalachian Mountains and Cumberland Plateau. More research is needed to understand North Alabama's high tornado frequency and how land surface heterogeneity influences tornadogenesis in the boundary layer. Several modeling and simulation studies stretching back to the 1970's have found that variations in the land surface induce tornadic-like flow near the surface, illustrating a need for further investigation. This presentation introduces research investigating the hypothesis that horizontal gradients in land surface roughness, normal to the direction of flow in the boundary layer, induce vertically oriented vorticity at the surface that can potentially aid in tornadogenesis. A novel approach was implemented to test this hypothesis using a GIS-based quadrant pattern analysis method. This method was developed to quantify spatial relationships and patterns between horizontal variations in land surface roughness and locations of tornadogenesis. Land surface roughness was modeled using the Noah land surface model parameterization scheme which, was applied to MODIS 500 m and Landsat 30 m data in order to compare the relationship between tornadogenesis locations and roughness gradients at different spatial scales. This analysis found a statistical relationship between areas of higher roughness located normal to flow surrounding tornadogenesis locations that supports the tested hypothesis. In this presentation, the innovative use of satellite remote sensing data and GIS technologies to address interactions between the land and atmosphere will be highlighted.

Downstream boundary effects on the frequency of self-excited oscillations in transonic diffuser flows

NASA Astrophysics Data System (ADS)

Hsieh, T.

1986-10-01

Investigation of downstream boundary effects on the frequency of self-excited oscillations in two-dimensional, separated transonic diffuser flows were conducted numerically by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equation with two equation turbulence models. It was found that the flow fields are very sensitive to the location of the downstream boundary. Extension of the diffuser downstream boundary significantly reduces the frequency and amplitude of oscillations for pressure, velocity, and shock. The existence of a suction slot in the experimental setpup obscures the physical downstream boundary and therefore presents a difficulty for quantitative comparisons between computation and experiment.

Experimental investigation of the micro-ramp based shock wave and turbulent boundary layer interaction control

NASA Astrophysics Data System (ADS)

Bo, Wang; Weidong, Liu; Yuxin, Zhao; Xiaoqiang, Fan; Chao, Wang

2012-05-01

Using a nanoparticle-based planar laser-scattering technique and supersonic particle image velocimetry, we investigated the effects of micro-ramp control on incident shockwave and boundary-layer interaction (SWBLI) in a low-noise supersonic wind-tunnel with Mach number 2.7 and Reynolds number Rθ = 5845. High spatiotemporal resolution wake structures downstream of the micro-ramps were detected, while a complex evolution process containing a streamwise counter-rotating vortex pair and large-scale hairpin-like vortices with Strouhal number Stδ of about 0.5-0.65 was revealed. The large-scale structures could survive while passing through the SWBLI region. Reflected shockwaves are clearly seen to be distorted accompanied by high-frequency fluctuations. Micro-ramp applications have a distinct influence on flow patterns of the SWBLI field that vary depending on spanwise locations. Both the shock foot and separation line exhibit undulations corresponding with modifications of the velocity distribution of the incoming boundary layer. Moreover, by energizing parts of the boundary flow, the micro-ramp is able to dampen the separation.

Investigating a 65-Ma-Old Smoking Gun: Deep Drilling of the Chicxulub Impact Structure

NASA Astrophysics Data System (ADS)

Dressler, B. O.; Sharpton, V. L.; Morgan, J.; Buffler, R.; Moran, D.; Smit, J.; Stöffler, D.; Urrutia, J.

The Phanerozoic paleontological record is marked by several biological extinction events. One of them, at the Cretaceous/Tertiary (K/T) boundary, was responsible for the demise of about 5% of genera and 75% of species, including the dinosaurs. These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to account for them, amongst them climate changes, disease, or overspecialization. About 20 years ago, Alvarez et al. [1980] discovered a high iridium concentration in an Italian K/T boundary clay layer. They proposed that the iridium was derived from an extra-terrestrial impact 65 Ma ago and that the impact was the cause for the K/T boundary extinctions. The iridium layer was subsequently found at K/T boundary locations worldwide. Further evidence for a K/T impact came from the discovery of shocked quartz, nano-diamonds, glass spherules, and nickel-rich spinels in microkrystites in the iridium-rich layer. There was evidence for an impact event, but no crater.

Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Intermittency Behavior Along the Suction Surface of a Low Pressure Turbine Blade

NASA Technical Reports Server (NTRS)

Schobeiri, M. T.; Ozturk, B.; Ashpis, David E.

2007-01-01

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.

Application of Shark Skin Flow Control Techniques to Airflow

NASA Astrophysics Data System (ADS)

Morris, Jackson Alexander

Due to millions of years of evolution, sharks have evolved to become quick and efficient ocean apex predators. Shark skin is made up of millions of microscopic scales, or denticles, that are approximately 0.2 mm in size. Scales located on the shark's body where separation control is paramount (such as behind the gills or the trailing edge of the pectoral fin) are capable of bristling. These scales are hypothesized to act as a flow control mechanism capable of being passively actuated by reversed flow. It is believed that shark scales are strategically sized to interact with the lower 5% of a boundary layer, where reversed flow occurs at the onset of boundary layer separation. Previous research has shown shark skin to be capable of controlling separation in water. This thesis aims to investigate the same passive flow control techniques in air. To investigate this phenomenon, several sets of microflaps were designed and manufactured with a 3D printer. The microflaps were designed in both 2D (rectangular) and 3D (mirroring shark scale geometry) variants. These microflaps were placed in a low-speed wind tunnel in the lower 5% of the boundary layer. Solid fences and a flat plate diffuser with suction were placed in the tunnel to create different separated flow regions. A hot film probe was used to measure velocity magnitude in the streamwise plane of the separated regions. The results showed that low-speed airflow is capable of bristling objects in the boundary layer. When placed in a region of reverse flow, the microflaps were passively actuated. Microflaps fluctuated between bristled and flat states in reverse flow regions located close to the reattachment zone.

Planetary Boundary Layer Dynamics over Reno, Nevada in Summer

NASA Astrophysics Data System (ADS)

Liming, A.; Sumlin, B.; Loria Salazar, S. M.; Holmes, H.; Arnott, W. P.

2014-12-01

Quantifying the height of the planetary boundary layer (PBL) is important to understand the transport behavior, mixing, and surface concentrations of air pollutants. In Reno, NV, located in complex, mountainous terrain with high desert climate, the daytime boundary layer can rise to an estimated 3km or more on a summer day due to surface heating and convection. The nocturnal boundary layer, conversely, tends to be much lower and highly stable due to radiative cooling from the surface at night and downslope flow of cool air from nearby mountains. With limited availability of radiosonde data, current estimates of the PBL height at any given time or location are potentially over or underestimated. To better quantify the height and characterize the PBL physics, we developed portable, lightweight sensors that measure CO2 concentrations, temperature, pressure, and humidity every 5 seconds. Four of these sensors are used on a tethered balloon system to monitor CO2 concentrations from the surface up to 300m. We will combine this data with Radio Acoustic Sounding System (RASS) data that measures vertical profiles of wind speed, temperature, and humidity from 40m to 400m. This experiment will characterize the diurnal evolution of CO2 concentrations at multiple heights in the PBL, provide insight into PBL physics during stability transition periods at sunrise and sunset, and estimate the nighttime PBL depth during August in Reno. Further, we expect to gain a better understanding of the impact of mixing volume changes (i.e., PBL height) on air quality and pollution concentrations in Reno. The custom portable sensor design will also be presented. It is expected that these instruments can be used for indoor or outdoor air quality studies, where lightness, small size, and battery operation can be of benefit.

Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-attachment along the Suction Surface of a Low Pressure Turbine Blade

NASA Technical Reports Server (NTRS)

Ozturk, B.; Schobeiri, M. T.; Ashpis, David E.

2005-01-01

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.

Receptivity of Hypersonic Boundary Layers to Distributed Roughness and Acoustic Disturbances

NASA Technical Reports Server (NTRS)

Balakumar, P.

2013-01-01

Boundary-layer receptivity and stability of Mach 6 flows over smooth and rough seven-degree half-angle sharp-tipped cones are numerically investigated. The receptivity of the boundary layer to slow acoustic disturbances, fast acoustic disturbances, and vortical disturbances is considered. The effects of three-dimensional isolated roughness on the receptivity and stability are also simulated. The results for the smooth cone show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves than to the fast acoustic waves. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that of the slow acoustic wave. Distributed roughness elements located near the nose region decreased the receptivity of the second mode generated by the slow acoustic wave by a small amount. Roughness elements distributed across the continuous spectrum increased the receptivity of the second mode generated by the slow and fast acoustic waves and the vorticity wave. The largest increase occurred for the vorticity wave. Roughness elements distributed across the synchronization point did not change the receptivity of the second modes generated by the acoustic waves. The receptivity of the second mode generated by the vorticity wave increased in this case, but the increase is lower than that occurred with the roughness elements located across the continuous spectrum. The simulations with an isolated roughness element showed that the second mode waves generated by the acoustic disturbances are not influenced by the small roughness element. Due to the interaction, a three-dimensional wave is generated. However, the amplitude is orders of magnitude smaller than the two-dimensional wave.

Analytical method for predicting the pressure distribution about a nacelle at transonic speeds

NASA Technical Reports Server (NTRS)

Keith, J. S.; Ferguson, D. R.; Merkle, C. L.; Heck, P. H.; Lahti, D. J.

1973-01-01

The formulation and development of a computer analysis for the calculation of streamlines and pressure distributions around two-dimensional (planar and axisymmetric) isolated nacelles at transonic speeds are described. The computerized flow field analysis is designed to predict the transonic flow around long and short high-bypass-ratio fan duct nacelles with inlet flows and with exhaust flows having appropriate aerothermodynamic properties. The flow field boundaries are located as far upstream and downstream as necessary to obtain minimum disturbances at the boundary. The far-field lateral flow field boundary is analytically defined to exactly represent free-flight conditions or solid wind tunnel wall effects. The inviscid solution technique is based on a Streamtube Curvature Analysis. The computer program utilizes an automatic grid refinement procedure and solves the flow field equations with a matrix relaxation technique. The boundary layer displacement effects and the onset of turbulent separation are included, based on the compressible turbulent boundary layer solution method of Stratford and Beavers and on the turbulent separation prediction method of Stratford.

The IMADA-AVER Boundary Layer Experiment in the Mexico City Area.

NASA Astrophysics Data System (ADS)

Doran, J. C.; Bian, X.; de Wekker, S. F. J.; Edgerton, S.; Fast, J. D.; Hubbe, J. M.; Shaw, W. J.; Whiteman, C. D.; Abbott, S.; King, C.; Leach, J.; Mulhearn, M.; Russell, C.; Templeman, B.; Wolfe, D.; Archuleta, J.; Elliott, S.; Fernandez, A.; Langley, D.; Lee, J. T.; Porch, W.; Tellier, L.; Chow, J.; Watson, J. G.; Coulter, R. L.; Martin, T. J.; Shannon, J. D.; White, R.; Martinez, D.; Martinez, J. L.; Mora, V.; Sosa, G.; Mercado, G.; Pena, J. L.; Salas, R.; Petty, R.

1998-11-01

A boundary layer field experiment in the Mexico City basin during the period 24 February-22 March 1997 is described. A total of six sites were instrumented. At four of the sites, 915-MHz radar wind profilers were deployed and radiosondes were released five times per day. Two of these sites also had sodars collocated with the profilers. Radiosondes were released twice per day at a fifth site to the south of the basin, and rawinsondes were flown from another location to the northeast of the city three times per day. Mixed layers grew to depths of 2500-3500 m, with a rapid period of growth beginning shortly before noon and lasting for several hours. Significant differences between the mixed-layer temperatures in the basin and outside the basin were observed. Three thermally and topographically driven flow patterns were observed that are consistent with previously hypothesized topographical and thermal forcing mechanisms. Despite these features, the circulation patterns in the basin important for the transport and diffusion of air pollutants show less day-to-day regularity than had been anticipated on the basis of Mexico City's tropical location, high altitude and strong insolation, and topographical setting.

Measurements of scalar released from point sources in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Talluru, K. M.; Hernandez-Silva, C.; Philip, J.; Chauhan, K. A.

2017-04-01

Measurements of velocity and concentration fluctuations for a horizontal plume released at several wall-normal locations in a turbulent boundary layer (TBL) are discussed in this paper. The primary objective of this study is to establish a systematic procedure to acquire accurate single-point concentration measurements for a substantially long time so as to obtain converged statistics of long tails of probability density functions of concentration. Details of the calibration procedure implemented for long measurements are presented, which include sensor drift compensation to eliminate the increase in average background concentration with time. While most previous studies reported measurements where the source height is limited to, {{s}z}/δ ≤slant 0.2 , where s z is the wall-normal source height and δ is the boundary layer thickness, here results of concentration fluctuations when the plume is released in the outer layer are emphasised. Results of mean and root-mean-square (r.m.s.) profiles of concentration for elevated sources agree with the well-accepted reflected Gaussian model (Fackrell and Robins 1982 J. Fluid. Mech. 117). However, there is clear deviation from the reflected Gaussian model for source in the intermittent region of TBL particularly at locations higher than the source itself. Further, we find that the plume half-widths are different for the mean and r.m.s. concentration profiles. Long sampling times enabled us to calculate converged probability density functions at high concentrations and these are found to exhibit exponential distribution.

Superpixel guided active contour segmentation of retinal layers in OCT volumes

NASA Astrophysics Data System (ADS)

Bai, Fangliang; Gibson, Stuart J.; Marques, Manuel J.; Podoleanu, Adrian

2018-03-01

Retinal OCT image segmentation is a precursor to subsequent medical diagnosis by a clinician or machine learning algorithm. In the last decade, many algorithms have been proposed to detect retinal layer boundaries and simplify the image representation. Inspired by the recent success of superpixel methods for pre-processing natural images, we present a novel framework for segmentation of retinal layers in OCT volume data. In our framework, the region of interest (e.g. the fovea) is located using an adaptive-curve method. The cell layer boundaries are then robustly detected firstly using 1D superpixels, applied to A-scans, and then fitting active contours in B-scan images. Thereafter the 3D cell layer surfaces are efficiently segmented from the volume data. The framework was tested on healthy eye data and we show that it is capable of segmenting up to 12 layers. The experimental results imply the effectiveness of proposed method and indicate its robustness to low image resolution and intrinsic speckle noise.

F-16XL ship #1 CAWAP flight - alpha 10 degrees, beta -5 degrees, altitude 10,000 feet

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. This photo shows the aircraft gathering data at an altitude of 10,000 feet, with an angle of attack of 10 degrees and a sideslip angle of -5 degrees. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 crew

NASA Technical Reports Server (NTRS)

1995-01-01

November 27, 1995 Photograph of the F-16XL Ship #1 Cranked-Arrow Wing Aerodynamic Project (CAWAP) Test Team; from left to right, Ron Wilcox; Operations Engineer, Art Cope; Aircraft Mechanic, Dave Fisher; Chief Project Engineer, Dick Denman; Aircraft Mechanic, Bob Garcia; A/C Crew Chief, Susan Ligon; Aircraft Mechanic, Rodger Tarango; Mobile Operations Facility (MOF) Staff, Jerry Cousins; Aircraft Mechanic, Bruce Gallmeyer; MOF Staff, and Mike Reardon; Aircraft Mechanic/Helper. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred at NASA's Dryden Flight Research Center, Edwards, California, on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 CAWAP flight - alpha 21 degrees, altitude 17,500 feet

NASA Technical Reports Server (NTRS)

1996-01-01

The single-seat F-16XL (ship #1) makes another run during the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing (visible here) has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. This photo shows the aircraft gathering data at an altitude of 17,500 feet, with an angle of attack of 21 degrees The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers

NASA Astrophysics Data System (ADS)

Fong, Kahei Danny

The current understanding and research efforts on surface roughness effects in hypersonic boundary-layer flows focus, almost exclusively, on how roughness elements trip a hypersonic boundary layer to turbulence. However, there were a few reports in the literature suggesting that roughness elements in hypersonic boundary-layer flows could sometimes suppress the transition process and delay the formation of turbulent flow. These reports were not common and had not attracted much attention from the research community. Furthermore, the mechanisms of how the delay and stabilization happened were unknown. A recent study by Duan et al. showed that when 2-D roughness elements were placed downstream of the so-called synchronization point, the unstable second-mode wave in a hypersonic boundary layer was damped. Since the second-mode wave is typically the most dangerous and dominant unstable mode in a hypersonic boundary layer for sharp geometries at a zero angle of attack, this result has pointed to an explanation on how roughness elements delay transition in a hypersonic boundary layer. Such an understanding can potentially have significant practical applications for the development of passive flow control techniques to suppress hypersonic boundary-layer transition, for the purpose of aero-heating reduction. Nevertheless, the previous study was preliminary because only one particular flow condition with one fixed roughness parameter was considered. The study also lacked an examination on the mechanism of the damping effect of the second mode by roughness. Hence, the objective of the current research is to conduct an extensive investigation of the effects of 2-D roughness elements on the growth of instability waves in a hypersonic boundary layer. The goal is to provide a full physical picture of how and when 2-D roughness elements stabilize a hypersonic boundary layer. Rigorous parametric studies using numerical simulation, linear stability theory (LST), and parabolized stability equation (PSE) are performed to ensure the fidelity of the data and to study the relevant flow physics. All results unanimously confirm the conclusion that the relative location of the synchronization point with respect to the roughness element determines the roughness effect on the second mode. Namely, a roughness placed upstream of the synchronization point amplifies the unstable waves while placing a roughness downstream of the synchronization point damps the second-mode waves. The parametric study also shows that a tall roughness element within the local boundary-layer thickness results in a stronger damping effect, while the effect of the roughness width is relatively insignificant compared with the other roughness parameters. On the other hand, the fact that both LST and PSE successfully predict the damping effect only by analyzing the meanflow suggests the mechanism of the damping is by the meanflow alteration due to the existence of roughness elements, rather than new mode generation. In addition to studying the unstable waves, the drag force and heating with and without roughness have been investigated by comparing the numerical simulation data with experimental correlations. It is shown that the increase in drag force generated by the Mach wave around a roughness element in a hypersonic boundary layer is insignificant compared to the reduction of drag force by suppressing turbulent flow. The study also shows that, for a cold wall flow which is the case for practical flight applications, the Stanton number decreases as roughness elements smooth out the temperature gradient in the wall-normal direction. Based on the knowledge of roughness elements damping the second mode gained from the current study, a novel passive transition control method using judiciously placed roughness elements has been developed, and patented, during the course of this research. The main idea of the control method is that, with a given geometry and flow condition, it is possible to find the most unstable second-mode frequency that can lead to transition. And by doing a theoretical analysis such as LST, the synchronization location for the most unstable frequency can be found. Roughness elements are then strategically placed downstream of the synchronization point to damp out this dangerous second-mode wave, thus stabilizing the boundary layer and suppressing the transition process. This method is later experimentally validated in Purdue's Mach 6 quiet wind tunnel. Overall, this research has not only provided details of when and how 2-D roughness stabilizes a hypersonic boundary layer, it also has led to a successful application of numerical simulation data to the development of a new roughness-based transition delay method, which could potentially have significant contributions to the design of future generation hypersonic vehicles.

Diffuser for augmenting a wind turbine

DOEpatents

Foreman, Kenneth M.; Gilbert, Barry L.

1984-01-01

A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

On the small angle twist sub-grain boundaries in Ti3AlC2.

PubMed

Zhang, Hui; Zhang, Chao; Hu, Tao; Zhan, Xun; Wang, Xiaohui; Zhou, Yanchun

2016-04-01

Tilt-dominated grain boundaries have been investigated in depth in the deformation of MAX phases. In stark contrast, another important type of grain boundaries, twist grain boundaries, have long been overlooked. Here, we report on the observation of small angle twist sub-grain boundaries in a typical MAX phase Ti3AlC2 compressed at 1200 °C, which comprise hexagonal screw dislocation networks formed by basal dislocation reactions. By first-principles investigations on atomic-scale deformation and general stacking fault energy landscapes, it is unequivocally demonstrated that the twist sub-grain boundaries are most likely located between Al and Ti4f (Ti located at the 4f Wyckoff sites of P63/mmc) layers, with breaking of the weakly bonded Al-Ti4f. The twist angle increases with the increase of deformation and is estimated to be around 0.5° for a deformation of 26%. This work may shed light on sub-grain boundaries of MAX phases, and provide fundamental information for future atomic-scale simulations.

Effect of concentration boundary layers on passive solute flows in a system of two polymeric membranes positioned in vertical planes.

PubMed

Slezak, Andrzej; Jasik-Slezak, Jolanta; Dworecki, Kazimierz

2003-01-01

The results of studies of influence of concentration boundary layers on passive diffusive transport in a double-membrane osmo-diffusive cell, containing a series of two (Ml and M(r)) vertically positioned, flat, microporous and symmetric polymer membranes (Nephrophane and Cellulose IMP-1) are presented in this paper. The membranes separated three compartments (l, m, r) containing binary, heterogeneous and non-ionic solutions (aqueous solutions of glucose or ethanol) or ternary non-electrolyte solutions (glucose solutions in 0.75 mol.l-1 solution of ethanol or ethanol solutions in 0.1 mol.l-1 aqueous solution of glucose). Solution concentrations fulfilled the condition C(k)l > C(k)m > C(k)r. The intermembrane compartment (m) was an infinitesimal solution layer. The volume of the m compartment and the volumes of the external (l and r) compartments fulfilled the condition Vl = Vr approximately 170 Vm. The tests were performed for configurations A and B of a double-membrane osmo-diffusive cell. In configuration A, the solution was located behind the M(r) membrane, and water was placed behind the Ml membrane, while in configuration B this sequence was reversed. The results obtained during experiment were interpreted in the categories of convective instability, which increased the value of diffusive permeability coefficient of the system: concentration boundary layer/membrane/concentration boundary layer.

Ram-recovery Characteristics of NACA Submerged Inlets at High Subsonic Speeds

NASA Technical Reports Server (NTRS)

Hall, Charles F; Frank, Joseph L

1948-01-01

Results are presented of an experimental investigation of the characteristics of NACA submerged inlets on a model of a fighter airplane for Mach numbers from 0.30 to 0.875. The effects on the ram-recovery ratio at the inlets of Mach number, angle of attack, boundary-layer thickness on the fuselage, inlet location, and boundary-layer deflectors are shown. The data indicate only a slight decrease in ram-recovery ratio for the inlets ahead of or just behind the wing leading edge as Mach number increased, but showed large decreases at high Mach numbers for the inlets aft of the point of maximum thickness of the wing.

Scaling and modeling of three-dimensional, end-wall, turbulent boundary layers. Ph.D. Thesis - Final Report

NASA Technical Reports Server (NTRS)

Goldberg, U. C.; Reshotko, E.

1984-01-01

The method of matched asymptotic expansion was employed to identify the various subregions in three dimensional, turbomachinery end wall turbulent boundary layers, and to determine the proper scaling of these regions. The two parts of the b.l. investigated are the 3D pressure driven part over the endwall, and the 3D part located at the blade/end wall juncture. Models are proposed for the 3d law of the wall and law of the wake. These models and the data of van den Berg and Elsenaar and of Mueller are compared and show good agreement between models and experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coulter, R.L.; Klazura, J.; Lesht, B.M.

The Argonne Boundary Layer Experiments (ABLE) facility, located in south central Kansas, east of Wichita, is devoted primarily to investigations of and within the planetary boundary layer (PBL), including the dynamics of the mixed layer during both day and night; effects of varying land use and landform; the interactive role of precipitation, runoff, and soil moisture; storm development; and energy budgets on scales of 10 to 100 km. With an expected lifetime of 10--15 years, the facility is well situated to observe the effects of gradual urbanization on PBL dynamics and structure as the Wichita urban area expands to themore » east and several small municipalities located within the study area expand. Combining the continuous measurements of ABLE with (1) ancillary continuous measurements of, for example, the Atmospheric Radiation Measurement (ARM) program and the Global Energy Water Cycle Experiment (GEWEX) programs and with (2) shorter, more intensive studies within ABLE, such as the Cooperative Atmosphere Surface Exchange Studies (CASES) Program, allows hypothesized features of urbanization, including heat island effects, precipitation enhancement, and modification of the surface energy budget partitioning, to be studied.« less

Response of the Atmospheric Boundary Layer and Soil Layer to a High Altitude, Dense Aerosol Cover.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pittock, A. B.; Walsh, K.

1990-01-01

The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

Using UAV's to Measure the Urban Boundary Layer

NASA Astrophysics Data System (ADS)

Jacob, R. L.; Sankaran, R.; Beckman, P. H.

2015-12-01

The urban boundary layer is one of the most poorly studied regions of the atmospheric boundary layer. Since a majority of the world's population now lives in urban areas, it is becoming a more important region to measure and model. The combination of relatively low-cost unmanned aerial vehicles and low-cost sensors can together provide a new instrument for measuring urban and other boundary layers. We have mounted a new sensor and compute platform called Waggle on an off-the-shelf XR8 octo-copter from 3DRobotics. Waggle consists of multiple sensors for measuring pressure, temperature and humidity as well as trace gases such as carbon monoxide, nitrogen dioxide, sulfur dioxide and ozone. A single board computer running Linux included in Waggle on the UAV allows in-situ processing and data storage. Communication of the data is through WiFi or 3G and the Waggle software can save the data in case communication is lost during flight. The flight pattern is a deliberately simple vertical ascent and descent over a fixed location to provide vertical profiles and so flights can be confined to urban parks, industrial areas or the footprint of a single rooftop. We will present results from test flights in urban and rural areas in and around Chicago.

Formation of the Dayside Magnetopause and Its Boundary Layers Under the Radial IMF

NASA Astrophysics Data System (ADS)

Pi, Gilbert; Němeček, Zdeněk.; Å afránková, Jana; Grygorov, Kostiantyn; Shue, Jih-Hong

2018-05-01

The global structure of magnetopause boundary layers under the radial interplanetary magnetic field (IMF) conditions is studied by a comparison of experimental and simulation results. In magnetohydrodynamic simulations, the hemispherical asymmetry of the reconnection locations was found. The draped field adjacent to the magnetopause points northward in the Northern Hemisphere, but it is oriented southward in the Southern Hemisphere at the beginning of the simulation for negative IMF Bx. The magnetopause region affected by the positive IMF Bz component enlarges over time, and the density profile exhibit a north-south asymmetry near the magnetopause. The experimental part of the study uses the Time History of Events and Macroscale Interactions during Substorm data. We analyze profiles of the plasma parameters and magnetic field as well as the ion pitch-angle distributions. The nonsimultaneous appearance of parallel and antiparallel aligned flows suggests two spatially separated sources of these flows. We have identified (1) the inner part of the low-latitude boundary layer (LLBL) on closed magnetic field lines; (2) the outer LLBL on open field lines; (3) the inner part of the magnetosheath boundary layer (MSBL) formed by dayside reconnection in the Southern Hemisphere; and (4) the outer MSBL resulting from lobe reconnection in the Northern Hemisphere.

Development of Prototype Micro-Lidar using Narrow Linewidth Semiconductor Lasers for Mars Boundary Layer Wind and Dust Opacity Profiles

NASA Technical Reports Server (NTRS)

Menzies, Robert T.; Cardell, Greg; Chiao, Meng; Esproles, Carlos; Forouhar, Siamak; Hemmati, Hamid; Tratt, David

1999-01-01

We have developed a compact Doppler lidar concept which utilizes recent developments in semiconductor diode laser technology in order to be considered suitable for wind and dust opacity profiling in the Mars lower atmosphere from a surface location. The current understanding of the Mars global climate and meteorology is very limited, with only sparse, near-surface data available from the Viking and Mars Pathfinder landers, supplemented by long-range remote sensing of the Martian atmosphere. The in situ measurements from a lander-based Doppler lidar would provide a unique dataset particularly for the boundary layer. The coupling of the radiative properties of the lower atmosphere with the dynamics involves the radiative absorption and scattering effects of the wind-driven dust. Variability in solar irradiance, on diurnal and seasonal time scales, drives vertical mixing and PBL (planetary boundary layer) thickness. The lidar data will also contribute to an understanding of the impact of wind-driven dust on lander and rover operations and lifetime through an improvement in our understanding of Mars climatology. In this paper we discuss the Mars lidar concept, and the development of a laboratory prototype for performance studies, using, local boundary layer and topographic target measurements.

Manipulation of Turbulent Boundary Layers Using Synthetic Jets

NASA Astrophysics Data System (ADS)

Berger, Zachary; Gomit, Guillaume; Lavoie, Philippe; Ganapathisubramani, Bharath

2015-11-01

This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x104, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. Funded Supported by Airbus.

Sensitivity of boundary layer variables to PBL schemes over the central Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, L.; Liu, H.; Wang, L.; Du, Q.; Liu, Y.

2017-12-01

Planetary Boundary Layer (PBL) parameterization schemes play critical role in numerical weather prediction and research. They describe physical processes associated with the momentum, heat and humidity exchange between land surface and atmosphere. In this study, two non-local (YSU and ACM2) and two local (MYJ and BouLac) planetary boundary layer parameterization schemes in the Weather Research and Forecasting (WRF) model have been tested over the central Tibetan Plateau regarding of their capability to model boundary layer parameters relevant for surface energy exchange. The model performance has been evaluated against measurements from the Third Tibetan Plateau atmospheric scientific experiment (TIPEX-III). Simulated meteorological parameters and turbulence fluxes have been compared with observations through standard statistical measures. Model results show acceptable behavior, but no particular scheme produces best performance for all locations and parameters. All PBL schemes underestimate near surface air temperatures over the Tibetan Plateau. By investigating the surface energy budget components, the results suggest that downward longwave radiation and sensible heat flux are the main factors causing the lower near surface temperature. Because the downward longwave radiation and sensible heat flux are respectively affected by atmosphere moisture and land-atmosphere coupling, improvements in water vapor distribution and land-atmosphere energy exchange is meaningful for better presentation of PBL physical processes over the central Tibetan Plateau.

A three-dimensional dual potential procedure with applications to wind tunnel inlets and interacting boundary layers

NASA Technical Reports Server (NTRS)

Rao, K. V.; Pletcher, R. H.; Steger, J. L.; Vandalsem, W. R.

1987-01-01

A dual potential decomposition of the velocity field into a scalar and a vector potential function is extended to three dimensions and used in the finite-difference simulation of steady three-dimensional inviscid rotational flows and viscous flow. The finite-difference procedure was used to simulate the flow through the 80 by 120 ft wind tunnel at NASA Ames Research Center. Rotational flow produced by the stagnation pressure drop across vanes and screens which are located at the entrance of the inlet is modeled using actuator disk theory. Results are presented for two different inlet vane and screen configurations. The numerical predictions are in good agreement with experimental data. The dual potential procedure was also applied to calculate the viscous flow along two and three dimensional troughs. Viscous effects are simulated by injecting vorticity which is computed from a boundary layer algorithm. For attached flow over a three dimensional trough, the present calculations are in good agreement with other numerical predictions. For separated flow, it is shown from a two dimensional analysis that the boundary layer approximation provides an accurate measure of the vorticity in regions close to the wall; whereas further away from the wall, caution has to be exercised in using the boundary-layer equations to supply vorticity to the dual potential formulation.

Experimental plasma studies

NASA Technical Reports Server (NTRS)

Dunn, M. G.

1972-01-01

The rate coefficients for the reactions C(+) + e(-) + e(-) yields C + e(-) and CO(+) + e(-) yields C + O were measured over the electron temperature range of approximately 1500 deg K to 7000 deg K. The measurements were performed in CO that had expanded from equilibrium reservoir conditions of 7060 deg K at 17.3 atm pressure and from 6260 deg K at 10.0 atm pressure. Two RAM flight probes were used to measure electron density and electron temperature in the expanding flow of a shock tunnel. Experiments were performed in the inviscid flow with both probes and in the nozzle-wall boundary layer with the constant bias-voltage probe. The distributions of electron density and electron temperature were independently measured using voltage-swept thin-wire probes. Thin-wire Langmuir probes were also used to measure the electron-density and electron-temperature distributions in the boundary layer of a sharp flat plate located on the nozzle centerline. Admittance measurements were performed with the RAM C and RAM C-C S-band antennas in the presence of an ionized boundary layer.

Simulating boundary layer transition with low-Reynolds-number k-epsilon turbulence models. I - An evaluation of prediction characteristics. II - An approach to improving the predictions

NASA Technical Reports Server (NTRS)

Schmidt, R. C.; Patankar, S. V.

1991-01-01

The capability of two k-epsilon low-Reynolds number (LRN) turbulence models, those of Jones and Launder (1972) and Lam and Bremhorst (1981), to predict transition in external boundary-layer flows subject to free-stream turbulence is analyzed. Both models correctly predict the basic qualitative aspects of boundary-layer transition with free stream turbulence, but for calculations started at low values of certain defined Reynolds numbers, the transition is generally predicted at unrealistically early locations. Also, the methods predict transition lengths significantly shorter than those found experimentally. An approach to overcoming these deficiencies without abandoning the basic LRN k-epsilon framework is developed. This approach limits the production term in the turbulent kinetic energy equation and is based on a simple stability criterion. It is correlated to the free-stream turbulence value. The modification is shown to improve the qualitative and quantitative characteristics of the transition predictions.

The innovative concept of three-dimensional hybrid receptor modeling

NASA Astrophysics Data System (ADS)

Stojić, A.; Stanišić Stojić, S.

2017-09-01

The aim of this study was to improve the current understanding of air pollution transport processes at regional and long-range scale. For this purpose, three-dimensional (3D) potential source contribution function and concentration weighted trajectory models, as well as new hybrid receptor model, concentration weighted boundary layer (CWBL), which uses a two-dimensional grid and a planetary boundary layer height as a frame of reference, are presented. The refined approach to hybrid receptor modeling has two advantages. At first, it considers whether each trajectory endpoint meets the inclusion criteria based on planetary boundary layer height, which is expected to provide a more realistic representation of the spatial distribution of emission sources and pollutant transport pathways. Secondly, it includes pollutant time series preprocessing to make hybrid receptor models more applicable for suburban and urban locations. The 3D hybrid receptor models presented herein are designed to identify altitude distribution of potential sources, whereas CWBL can be used for analyzing the vertical distribution of pollutant concentrations along the transport pathway.

Thermal Analysis and Design of Multi-layer Insulation for Re-entry Aerodynamic Heating

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran

2001-01-01

The combined radiation/conduction heat transfer in high-temperature multi-layer insulations was modeled using a finite volume numerical model. The numerical model was validated by comparison with steady-state effective thermal conductivity measurements, and by transient thermal tests simulating re-entry aerodynamic heating conditions. A design of experiments technique was used to investigate optimum design of multi-layer insulations for re-entry aerodynamic heating. It was found that use of 2 mm foil spacing and locating the foils near the hot boundary with the top foil 2 mm away from the hot boundary resulted in the most effective insulation design. A 76.2 mm thick multi-layer insulation using 1, 4, or 16 foils resulted in 2.9, 7.2, or 22.2 percent mass per unit area savings compared to a fibrous insulation sample at the same thickness, respectively.

Improved diffuser for augmenting a wind turbine

DOEpatents

Foreman, K.M.; Gilbert, B.L.

A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

Vane clocking effects in an embedded compressor stage

NASA Astrophysics Data System (ADS)

Key, Nicole Leanne

The objective of this research was to experimentally investigate the effects of vane clocking, the circumferential indexing of adjacent vane rows with similar vane counts, in an embedded compressor stage. Experiments were performed in the Purdue 3-Stage Compressor, which consists of an IGV followed by three stages. The IGV, Stator 1, and Stator 2 have identical vane counts of 44, and the effects of clocking were studied on Stage 2. The clocking configuration that located the upstream vane wake on the Stator 2 leading edge was identified with total pressure measurements at the inlet to Stator 2 and confirmed with measurements at the exit of Stator 2. For both loading conditions, the total temperature results showed that there was no measurable change associated with vane clocking in the amount of work done on the flow. At design loading, the change in stage efficiency with vane clocking was 0.27 points between the maximum and minimum efficiency clocking configurations. The maximum efficiency configuration was the case where the Stator 1 wake impinged on the Stator 2 leading edge. This condition produced a shallower and thinner Stator 2 wake compared to the clocking configuration that located the wake in the middle of the Stator 2 passage. By locating the Stator 1 wake at the leading edge, it dampened the Stator 2 boundary layer response to inlet fluctuations associated with the Rotor 2 wakes. At high loading, the change in Stage 2 efficiency increased to 1.07 points; however, the maximum efficiency clocking configuration was the case where the Stator 1 wake passed through the middle of the downstream vane passage. At high loading, the flow physics associated with vane clocking were different than at design loading because the location of the Stator 1 wake fluid on the Stator 2 leading edge triggered a boundary layer separation on the suction side of Stator 2 producing a wider and deeper wake. Vane clocking essentially affects the amount of interaction between the upstream vane wake and the boundary layer of the downstream vane. Whether this dampens the adverse effects of the rotor wakes or triggers boundary layer separation will depend on the flow conditions such as Reynolds number, turbulence intensity, and pressure gradient (vane loading), to name a few.

Enthalpy effects on hypervelocity boundary layers

NASA Astrophysics Data System (ADS)

Adam, Philippe H.

Shots with air and carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 1-meter long, 5-deg half-angle cone. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer. Transitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases. This stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. Normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with the maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code. The observation that reference conditions are more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel and flight data are around an order of magnitude apart. This is commonly attributed to high disturbance levels in tunnels that cause the boundary layer to transition early. However, when the reference conditions are used instead, the tunnel and flight data come within striking distance of one another although the trends with enthalpy are reversed. This difference could be due to the cone bending and nose blunting. Experimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the noncatalytic and frozen chemistry models. The results for carbon dioxide, however, are inconclusive. This is, perhaps, because of inadequate modeling of the reactions. Experimentally, an anomalous yet repeatable, rise in the laminar heat transfer level can be seen at medium enthalpies in carbon dioxide boundary layers.

Experimental Investigation of Soil and Atmospheric Conditions on the Momentum, Mass, and Thermal Boundary Layers Above the Land Atmosphere Interface

NASA Astrophysics Data System (ADS)

Trautz, A.; Smits, K. M.; Illangasekare, T. H.; Schulte, P.

2014-12-01

The purpose of this study is to investigate the impacts of soil conditions (i.e. soil type, saturation) and atmospheric forcings (i.e. velocity, temperature, relative humidity) on the momentum, mass, and temperature boundary layers. The atmospheric conditions tested represent those typically found in semi-arid and arid climates and the soil conditions simulate the three stages of evaporation. The data generated will help identify the importance of different soil conditions and atmospheric forcings with respect to land-atmospheric interactions which will have direct implications on future numerical studies investigating the effects of turbulent air flow on evaporation. The experimental datasets generated for this study were performed using a unique climate controlled closed-circuit wind tunnel/porous media facility located at the Center for Experimental Study of Subsurface Environmental Processes (CESEP) at the Colorado School of Mines. The test apparatus consisting of a 7.3 m long porous media tank and wind tunnel, were outfitted with a sensor network to carefully measure wind velocity, air and soil temperature, relative humidity, soil moisture, and soil air pressure. Boundary layer measurements were made between the heights of 2 and 500 mm above the soil tank under constant conditions (i.e. wind velocity, temperature, relative humidity). The soil conditions (e.g. soil type, soil moisture) were varied between datasets to analyze their impact on the boundary layers. Experimental results show that the momentum boundary layer is very sensitive to the applied atmospheric conditions and soil conditions to a much less extent. Increases in velocity above porous media leads to momentum boundary layer thinning and closely reflect classical flat plate theory. The mass and thermal boundary layers are directly dependent on both atmospheric and soil conditions. Air pressure within the soil is independent of atmospheric temperature and relative humidity - wind velocity and soil moisture effects were observed. This data provides important insight into future work of accurately modeling the exchange processes associated with evaporation under various turbulent atmospheric conditions.

A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.

2003-01-01

Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

Characteristics of Boundary Layer Structure during a Persistent Haze Event in the Central Liaoning City Cluster, Northeast China

NASA Astrophysics Data System (ADS)

Li, Xiaolan; Wang, Yangfeng; Shen, Lidu; Zhang, Hongsheng; Zhao, Hujia; Zhang, Yunhai; Ma, Yanjun

2018-04-01

The characteristics of boundary layer structure during a persistent regional haze event over the central Liaoning city cluster of Northeast China from 16 to 21 December 2016 were investigated based on the measurements of particulate matter (PM) concentration and the meteorological data within the atmospheric boundary layer (ABL). During the observational period, the maximum hourly mean PM2.5 and PM10 concentrations in Shenyang, Anshan, Fushun, and Benxi ranged from 276 to 355 μg m-3 and from 378 to 442 μg m-3, respectively, and the lowest hourly mean atmospheric visibility (VIS) in different cities ranged from 0.14 to 0.64 km. The central Liaoning city cluster was located in the front of a slowly moving high pressure and was mainly controlled by southerly winds. Wind speed (WS) within the ABL (< 2 km) decreased significantly and WS at 10-m height mostly remained below 2 m s-1 during the hazy episodes, which was favorable for the accumulation of air pollutants. A potential temperature inversion layer existed throughout the entire ABL during the earlier hazy episode [from 0500 Local Time (LT) 18 December to 1100 LT 19 December], and then a potential temperature inversion layer developed with the bottom gradually decreased from 900 m to 300 m. Such a stable atmospheric stratification further weakened pollutant dispersion. The atmospheric boundary layer height (ABLH) estimated based on potential temperature profiles was mostly lower than 400 m and varied oppositely with PM2.5 in Shenyang. In summary, weak winds due to calm synoptic conditions, strong thermal inversion layer, and shallow atmospheric boundary layer contributed to the formation and development of this haze event. The backward trajectory analysis revealed the sources of air masses and explained the different characteristics of the haze episodes in the four cities.

Response of a partially penetrating well in a heterogeneous aquifer: integrated well-face flux vs. uniform well-face flux boundary conditions

NASA Astrophysics Data System (ADS)

Ruud, N. C.; Kabala, Z. J.

1997-07-01

A two-dimensional integrated well-face flux (IWFF) model is developed for computing the drawdown at the well-face and around a fully or partially penetrating well with wellbore storage, situated in a layered confined aquifer. In this model, we calculate drawdown and well-face flux distributions by numerically solving a two-dimensional diffusion equation in cylindrical coordinates subject to appropriate initial and boundary conditions and to the well-face boundary constraint of an integrated well-face flux rather than the physically inconsistent uniform well-face flux boundary condition (the UWFF model). The differences between the IWFF and UWFF models in a partially penetrating well situated in a homogeneous isotropic aquifer are insignificant for wellbore drawdown (less than 3%) but are pronounced for the well-face flux. In fact, the latter strongly deviates from uniformity as the ratio of the screen length to the aquifer thickness decreases. For partially penetrating wells situated in multilayer aquifers, significant differences between the two models may arise, especially if the screen is not located in the most conductive layer. These differences depend on the hydraulic conductivity contrast of the adjacent layers. Consequently, the uniform well-face flux boundary condition should be used with extreme caution.

Thermal evolution of the high-pressure ice layers beneath a buried ocean within Titan and Ganymede

NASA Astrophysics Data System (ADS)

Choblet, G.; Tobie, G.

2015-12-01

Deep interiors of massive icy satellites such as Titan and Ganymede probably harbor a buried ocean above high-pressure (HP) ice layers. The nature and location of the lower interface of the ocean is ultimately controlled by the amount of heat transferred through the surface ice Ih layer but it also involves equilibration of heat and melt transfer in the HP ices. While the Rayleigh number associated to such HP ice layers is most probably supercritical, classical subsolidus convection might not be a viable mechanism as the radial temperature gradient in the cold boundary layer is likely to exceed the slope of the melting curve. A significant part of the heat transfer could be achieved via the mass flux of warm liquid through this cold boundary layer up to the global phase boundary, a phenomenon sometimes referred to as heat-pipe mechanism. We present 3D spherical simulations of thermal convection in these HP ice layers that address for the first time this complex interplay. First, scaling relationships are proposed to describe this configuration for a large range of Rayleigh numbers and solidus curves. We then focus on a more realistic set-up where a prescribed basal heat flux is considered in a plausible range for the thermal history of Ganymede or Titan together with the expected viscosity law for HP ices.

Boundary-Layer Phenomena in the Vicinity of an Isolated Mountain: A Climatography Based on an Operational High-Resolution Forecast System

NASA Astrophysics Data System (ADS)

Serafin, S.; De Wekker, S.; Knievel, J. C.

2013-12-01

Granite Peak, located in the Dugway Proving Ground (DPG) in western Utah, is an isolated mountain rising ~800 m above the surrounding terrain. It has an approximately ellipsoidal shape oriented in the NNW-SSE direction and its main axes are respectively ~10- and ~6-km long. A flat dry lake (playa) lies west and northwest of the peak, while a NW-sloping plain covered by herbaceous vegetation extends to the eastern part of DPG. Because of these topography and land-use features, a variety of different flow phenomena are expected to occur over and around Granite Peak. These include upslope and drainage winds, local breeze systems, gap flows, dynamically accelerated downslope winds and potentially boundary layer separation and the formation of wakes. Consequently, the area is an ideal location for studying the interaction between mountain flows and the atmospheric boundary layer. Since the 1990s, DPG has used a continuously operating meso-gamma-scale analysis and forecast system (4DWX) developed by the NCAR's Research Applications Laboratory (RAL). The system is based on WRF, runs with a grid spacing of 1.1-km in its innermost domain, applies observational nudging in a three-hour cycle, and provides weather analyses and forecasts at hourly intervals. In this study, model output from the 4DWX system is used to build a short-term climatography (2010-2012) of the prevailing boundary layer flow regimes in DPG. Measurements from the network of Surface Area Mesonet Stations (SAMS) operative at DPG are used to verify the quality of 4DWX simulations and their ability to reproduce the dominant flow patterns. The study then focuses on boundary-layer separation (BLS) events: near-surface wind, temperature and pressure fields from 4DWX are analysed in order to identify the most favorable regions for the onset of separation. A limited set of events, identified by means of an objective procedure, is then studied in detail in order to understand the preferred conditions for the development of the phenomenon. S-SW flows with considerable near-surface veering and an embedded low-level jet are found to be the most common scenario leading to leeside boundary-layer separation. Example of a BLS event in the lee of Granite Peak (near gridpoints x=12, y=15). Near-surface wind speed (in m/s) and vectors are displayed on the 4DWX model grid (Δx: 1.1 km).

Performance evaluation and bias correction of DBS measurements for a 1290-MHz boundary layer profiler.

PubMed

Liu, Zhao; Zheng, Chaorong; Wu, Yue

2018-02-01

Recently, the government installed a boundary layer profiler (BLP), which is operated under the Doppler beam swinging mode, in a coastal area of China, to acquire useful wind field information in the atmospheric boundary layer for several purposes. And under strong wind conditions, the performance of the BLP is evaluated. It is found that, even though the quality controlled BLP data show good agreement with the balloon observations, a systematic bias can always be found for the BLP data. For the low wind velocities, the BLP data tend to overestimate the atmospheric wind. However, with the increment of wind velocity, the BLP data show a tendency of underestimation. In order to remove the effect of poor quality data on bias correction, the probability distribution function of the differences between the two instruments is discussed, and it is found that the t location scale distribution is the most suitable probability model when compared to other probability models. After the outliers with a large discrepancy, which are outside of 95% confidence interval of the t location scale distribution, are discarded, the systematic bias can be successfully corrected using a first-order polynomial correction function. The methodology of bias correction used in the study not only can be referred for the correction of other wind profiling radars, but also can lay a solid basis for further analysis of the wind profiles.

Performance evaluation and bias correction of DBS measurements for a 1290-MHz boundary layer profiler

NASA Astrophysics Data System (ADS)

Liu, Zhao; Zheng, Chaorong; Wu, Yue

2018-02-01

Recently, the government installed a boundary layer profiler (BLP), which is operated under the Doppler beam swinging mode, in a coastal area of China, to acquire useful wind field information in the atmospheric boundary layer for several purposes. And under strong wind conditions, the performance of the BLP is evaluated. It is found that, even though the quality controlled BLP data show good agreement with the balloon observations, a systematic bias can always be found for the BLP data. For the low wind velocities, the BLP data tend to overestimate the atmospheric wind. However, with the increment of wind velocity, the BLP data show a tendency of underestimation. In order to remove the effect of poor quality data on bias correction, the probability distribution function of the differences between the two instruments is discussed, and it is found that the t location scale distribution is the most suitable probability model when compared to other probability models. After the outliers with a large discrepancy, which are outside of 95% confidence interval of the t location scale distribution, are discarded, the systematic bias can be successfully corrected using a first-order polynomial correction function. The methodology of bias correction used in the study not only can be referred for the correction of other wind profiling radars, but also can lay a solid basis for further analysis of the wind profiles.

High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.

PubMed

Winkel, Eric S; Elbing, Brian R; Ceccio, Steven L; Perlin, Marc; Dowling, David R

2008-05-01

The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.

Measurements in a Transitioning Cone Boundary Layer at Freestream Mach 3.5

NASA Technical Reports Server (NTRS)

King, Rudolph A.; Chou, Amanda; Balakumar, Ponnampalam; Owens, Lewis R.; Kegerise, Michael A.

2016-01-01

An experimental study was conducted in the Supersonic Low-Disturbance Tunnel to investigate naturally-occurring instabilities in a supersonic boundary layer on a 7 deg half- angle cone. All tests were conducted with a nominal freestream Mach number of M(sub infinity) = 3:5, total temperature of T(sub 0) = 299:8 K, and unit Reynolds numbers of Re(sub infinity) x 10(exp -6) = 9:89, 13.85, 21.77, and 25.73 m(exp -1). Instability measurements were acquired under noisy- ow and quiet- ow conditions. Measurements were made to document the freestream and the boundary-layer edge environment, to document the cone baseline flow, and to establish the stability characteristics of the transitioning flow. Pitot pressure and hot-wire boundary- layer measurements were obtained using a model-integrated traverse system. All hot- wire results were single-point measurements and were acquired with a sensor calibrated to mass ux. For the noisy-flow conditions, excellent agreement for the growth rates and mode shapes was achieved between the measured results and linear stability theory (LST). The corresponding N factor at transition from LST is N 3:9. The stability measurements for the quiet-flow conditions were limited to the aft end of the cone. The most unstable first-mode instabilities as predicted by LST were successfully measured, but this unstable first mode was not the dominant instability measured in the boundary layer. Instead, the dominant instabilities were found to be the less-amplified, low-frequency disturbances predicted by linear stability theory, and these instabilities grew according to linear theory. These low-frequency unstable disturbances were initiated by freestream acoustic disturbances through a receptivity process that is believed to occur near the branch I locations of the cone. Under quiet-flow conditions, the boundary layer remained laminar up to the last measurement station for the largest Re1, implying a transition N factor of N greater than 8:5.

Lidar Applications in Atmospheric Dynamics: Measurements of Wind, Moisture and Boundary Layer Evolution

NASA Technical Reports Server (NTRS)

Demoz, Belay; Whiteman, David; Gentry, Bruce; Schwemmer, Geary; Evans, Keith; DiGirolamo, Paolo; Comer, Joseph

2005-01-01

A large array of state-of-the-art ground-based and airborne remote and in-situ sensors were deployed during the International H2O Project (THOP), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. These instruments provided extensive measurements of water vapor mixing ratio in order to better understand the influence of its variability on convection and on the skill of quantitative precipitation prediction (Weckwerth et all, 2004). Among the instrument deployed were ground based lidars from NASA/GSFC that included the Scanning Raman Lidar (SRL), the Goddard Laboratory for Observing Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). A brief description of the three lidars is given below. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars during MOP at the MOP ground profiling site in the Oklahoma Panhandle (hereafter referred as Homestead). This presentation will focus on the evolution and variability of moisture and wind in the boundary layer when frontal and/or convergence boundaries (e.g. bores, dry lines, thunderstorm outflows etc) were observed.

Three-dimensional turbulent boundary layers; Proceedings of the Symposium, Berlin, West Germany, March 29-April 1, 1982

NASA Astrophysics Data System (ADS)

Fernholz, H. H.; Krause, E.

Papers are presented on recent research concerning three-dimensional turbulent boundary layers. Topics examined include experimental techniques in three-dimensional turbulent boundary layers, turbulence measurements in ship-model flow, measurements of Reynolds-stress profiles in the stern region of a ship model, the effects of crossflow on the vortex-layer-type three-dimensional flow separation, and wind tunnel investigations of some three-dimensional separated turbulent boundary layers. Also examined are three-dimensional boundary layers in turbomachines, the boundary layers on bodies of revolution spinning in axial flows, the effect on a developed turbulent boundary layer of a sudden local wall motion, three-dimensional turbulent boundary layer along a concave wall, the numerical computation of three-dimensional boundary layers, a numerical study of corner flows, three-dimensional boundary calculations in design aerodynamics, and turbulent boundary-layer calculations in design aerodynamics. For individual items see A83-47012 to A83-47036

Fluid Physics Under a Stochastic Acceleration Field

NASA Technical Reports Server (NTRS)

Vinals, Jorge

2001-01-01

The research summarized in this report has involved a combined theoretical and computational study of fluid flow that results from the random acceleration environment present onboard space orbiters, also known as g-jitter. We have focused on a statistical description of the observed g-jitter, on the flows that such an acceleration field can induce in a number of experimental configurations of interest, and on extending previously developed methodology to boundary layer flows. Narrow band noise has been shown to describe many of the features of acceleration data collected during space missions. The scale of baroclinically induced flows when the driving acceleration is random is not given by the Rayleigh number. Spatially uniform g-jitter induces additional hydrodynamic forces among suspended particles in incompressible fluids. Stochastic modulation of the control parameter shifts the location of the onset of an oscillatory instability. Random vibration of solid boundaries leads to separation of boundary layers. Steady streaming ahead of a modulated solid-melt interface enhances solute transport, and modifies the stability boundaries of a planar front.

The Effect of an Isogrid on Cryogenic Propellant Behavior and Thermal Stratification

NASA Technical Reports Server (NTRS)

Oliveira, Justin; Kirk, Daniel R.; Chintalapati, Sunil; Schallhorn, Paul A.; Piquero, Jorge L.; Campbell, Mike; Chase, Sukhdeep

2007-01-01

All models for thermal stratification available in the presentation are derived using smooth, flat plate laminar and turbulent boundary layer models. This study examines the effect of isogrid (roughness elements) on the surface of internal tank walls to mimic the effects of weight-saving isogrid, which is located on the inside of many rocket propellant tanks. Computational Fluid Dynamics (CFD) is used to study the momentum and thermal boundary layer thickness for free convection flows over a wall with generic roughness elements. This presentation makes no mention of actual isogrid sizes or of any specific tank geometry. The magnitude of thermal stratification is compared for smooth and isogrid-lined walls.

A viscous-inviscid interactive compressor calculations

NASA Technical Reports Server (NTRS)

Johnston, W.; Sockol, P. M.

1978-01-01

A viscous-inviscid interactive procedure for subsonic flow is developed and applied to an axial compressor stage. Calculations are carried out on a two-dimensional blade-to-blade region of constant radius assumed to occupy a mid-span location. Hub and tip effects are neglected. The Euler equations are solved by MacCormack's method, a viscous marching procedure is used in the boundary layers and wake, and an iterative interaction scheme is constructed that matches them in a way that incorporates information related to momentum and enthalpy thicknesses as well as the displacement thickness. The calculations are quasi-three-dimensional in the sense that the boundary layer and wake solutions allow for the presence of spanwise (radial) velocities.

Moisture convergence from a combined mesoscale moisture analysis and wind field for 24 April 1975

NASA Technical Reports Server (NTRS)

Negri, A. J.; Hillger, D. W.; Vonder Haar, T. H.

1977-01-01

Precipitable water values inferred from the Vertical Temperature Profile Radiometer data of the polar orbiting NOAA-4 satellite are used in conjunction with wind-field analyses obtained from Synchronous Meteorological Satellite visible-channel data to study the moisture convergence in the boundary layer immediately preceding a storm. This combination of data simulates the information that will be available from the Visible and Infrared Spin-Scan Radiometer on board the GOES-D satellite, which is scheduled to begin operation in the 1980s. Serviceable representations of boundary layer flow are developed through analysis of the satellite infrared cumulus velocities, although the flow representations are not exactly located in the vertical.

Assessment of Planetary-Boundary-Layer Schemes in the Weather Research and Forecasting Model Within and Above an Urban Canopy Layer

NASA Astrophysics Data System (ADS)

Ferrero, Enrico; Alessandrini, Stefano; Vandenberghe, Francois

2018-03-01

We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.

Transient interaction between a reaction control jet and a hypersonic crossflow

NASA Astrophysics Data System (ADS)

Miller, Warrick A.; Medwell, Paul R.; Doolan, Con J.; Kim, Minkwan

2018-04-01

This paper presents a numerical study that focuses on the transient interaction between a reaction control jet and a hypersonic crossflow with a laminar boundary layer. The aim is to better understand the underlying physical mechanisms affecting the resulting surface pressure and control force. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate with a laminar boundary layer, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251. The pressure distribution induced on the flat plate is unsteady and is influenced by vortex structures that form around the jet. A horseshoe vortex structure forms upstream and consists of six vortices: two quasi-steady vortices and two co-rotating vortex pairs that periodically coalesce. Shear-layer vortices shed periodically and cause localised high pressure regions that convect downstream with constant velocity. A longitudinal counter-rotating vortex pair is present downstream of the jet and is formed from a series of trailing vortices which rotate about a common axis. Shear-layer vortex shedding causes periodic deformation of barrel and bow shocks. This changes the location of boundary layer separation which also affects the normal force on the plate.

Developing Present-day Proxy Cases Based on NARVAL Data for Investigating Low Level Cloud Responses to Future Climate Change.

NASA Astrophysics Data System (ADS)

Reilly, Stephanie

2017-04-01

The energy budget of the entire global climate is significantly influenced by the presence of boundary layer clouds. The main aim of the High Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) project is to improve climate model predictions by means of process studies of clouds and precipitation. This study makes use of observed elevated moisture layers as a proxy of future changes in tropospheric humidity. The associated impact on radiative transfer triggers fast responses in boundary layer clouds, providing a framework for investigating this phenomenon. The investigation will be carried out using data gathered during the Next-generation Aircraft Remote-sensing for VALidation (NARVAL) South campaigns. Observational data will be combined with ECMWF reanalysis data to derive the large scale forcings for the Large Eddy Simulations (LES). Simulations will be generated for a range of elevated moisture layers, spanning a multi-dimensional phase space in depth, amplitude, elevation, and cloudiness. The NARVAL locations will function as anchor-points. The results of the large eddy simulations and the observations will be studied and compared in an attempt to determine how simulated boundary layer clouds react to changes in radiative transfer from the free troposphere. Preliminary LES results will be presented and discussed.

The Impact of Model Uncertainty on Spatial Compensation in Structural Acoustic Control

NASA Technical Reports Server (NTRS)

Clark, Robert L.

2005-01-01

Turbulent boundary layer (TBL) noise is considered a primary contribution to the interior noise present in commercial airliners. There are numerous investigations of interior noise control devoted to aircraft panels; however, practical realization is a potential challenge since physical boundary conditions are uncertain at best. In most prior studies, pinned or clamped boundary conditions were assumed; however, realistic panels likely display a range of boundary conditions between these two limits. Uncertainty in boundary conditions is a challenge for control system designers, both in terms of the compensator implemented and the location of transducers required to achieve the desired control. The impact of model uncertainties, specifically uncertain boundaries, on the selection of transducer locations for structural acoustic control is considered herein. The final goal of this work is the design of an aircraft panel structure that can reduce TBL noise transmission through the use of a completely adaptive, single-input, single-output control system. The feasibility of this goal is demonstrated through the creation of a detailed analytical solution, followed by the implementation of a test model in a transmission loss apparatus. Successfully realizing a control system robust to variations in boundary conditions can lead to the design and implementation of practical adaptive structures that could be used to control the transmission of sound to the interior of aircraft. Results from this research effort indicate it is possible to optimize the design of actuator and sensor location and aperture, minimizing the impact of boundary conditions on the desired structural acoustic control.

A two-layer multiple-time-scale turbulence model and grid independence study

NASA Technical Reports Server (NTRS)

Kim, S.-W.; Chen, C.-P.

1989-01-01

A two-layer multiple-time-scale turbulence model is presented. The near-wall model is based on the classical Kolmogorov-Prandtl turbulence hypothesis and the semi-empirical logarithmic law of the wall. In the two-layer model presented, the computational domain of the conservation of mass equation and the mean momentum equation penetrated up to the wall, where no slip boundary condition has been prescribed; and the near wall boundary of the turbulence equations has been located at the fully turbulent region, yet very close to the wall, where the standard wall function method has been applied. Thus, the conservation of mass constraint can be satisfied more rigorously in the two-layer model than in the standard wall function method. In most of the two-layer turbulence models, the number of grid points to be used inside the near-wall layer posed the issue of computational efficiency. The present finite element computational results showed that the grid independent solutions were obtained with as small as two grid points, i.e., one quadratic element, inside the near wall layer. Comparison of the computational results obtained by using the two-layer model and those obtained by using the wall function method is also presented.

Active constrained layer damping treatments for shell structures: a deep-shell theory, some intuitive results, and an energy analysis

NASA Astrophysics Data System (ADS)

Shen, I. Y.

1997-02-01

This paper studies vibration control of a shell structure through use of an active constrained layer (ACL) damping treatment. A deep-shell theory that assumes arbitrary Lamé parameters 0964-1726/6/1/011/img1 and 0964-1726/6/1/011/img2 is first developed. Application of Hamilton's principle leads to the governing Love equations, the charge equation of electrostatics, and the associated boundary conditions. The Love equations and boundary conditions imply that the control action of the ACL for shell treatments consists of two components: free-end boundary actuation and membrane actuation. The free-end boundary actuation is identical to that of beam and plate ACL treatments, while the membrane actuation is unique to shell treatments as a result of the curvatures of the shells. In particular, the membrane actuation may reinforce or counteract the boundary actuation, depending on the location of the ACL treatment. Finally, an energy analysis is developed to determine the proper control law that guarantees the stability of ACL shell treatments. Moreover, the energy analysis results in a simple rule predicting whether or not the membrane actuation reinforces the boundary actuation.

Experimental and theoretical investigation of three-dimensional turbulent boundary layers and turbulence characteristics inside an axial flow inducer passage. Final Report. Ph.D. Thesis, Jun. 1971

NASA Technical Reports Server (NTRS)

Anand, A. K.; Lakshminarayana, B.

1977-01-01

Analytical and experimental investigations of the characteristics of three dimensional turbulent boundary layers in a rotating helical passage of an inducer rotor are reported. Expressions are developed for the velocity profiles in the inner layer, where the viscous effects dominate, in the outer layer, where the viscous effects are small, and in the interference layer, where the end walls influence the flow. The prediction of boundary layer growth is based on the momentum integral technique. The equations derived are general enough to be valid for all turbomachinery rotors with arbitrary pressure gradients. The experimental investigations are carried out in a flat plate inducer 3 feet in diameter. The mean velocity profiles, turbulence intensities and shear stresses, wall shear stress, and limiting streamline angles are measured at various radial and chordwise locations by using rotating probes. The measurements are in general agreement with the predictions. The radial flows are well represented by an expression which includes the effect of stagger angle and radial pressure gradient. The radial flows in the rotor channel are higher than those on a single blade. The collateral region exists only very near the blade surface. The radial component of turbulence intensity is higher than the streamwise component because of the effect of rotation.

The Influence of Low Wall Temperature on Boundary-Layer Transition and Local Heat Transfer on 2-Inch-Diameter Hemispheres at a Mach Number of 4.95 and a Reynolds Number per Foot of 73.2 x 10(exp 6)

NASA Technical Reports Server (NTRS)

Cooper, Morton; Mayo, Edward E.; Julius, Jerome D.

1960-01-01

Measurements of the location of boundary-layer transition and the local heat transfer have been made on 2-inch-diameter hemispheres in the Langley gas dynamics laboratory at a Mach number of 4.95, a Reynolds number per foot of 73.2 x 10(exp 6), and a stagnation temperature of approximately 400 F. The transient-heating thin-skin calorimeter technique was used, and the initial values of the wall-to-stream stagnation- temperature ratios were 0.16 (cold-model tests) and 0.65 (hot-model test). During two of the four cold tests, the boundary-layer flow changed from turbulent to laminar over large regions of the hemisphere as the model heated. On the basis of a detailed consideration of the magnitude of roughness possibly present during these two cold tests, it appears that this destabilizing effect of low wall temperatures (cooling) was not caused by roughness as a dominant influence. This idea of a decrease in boundary-layer stability with cooling has been previously suggested. (See, for example, NASA Memorandum 10-8-58E.) For the laminar data obtained during the early part of the hot test, the correlation of the local-heating data with laminar theory was excellent.

Measurements of Skin Friction of the Compressible Turbulent Boundary Layer on a Cone with Foreign Gas Injection

NASA Technical Reports Server (NTRS)

Pappas, Constantine C.; Ukuno, Arthur F.

1960-01-01

Measurements of average skin friction of the turbulent boundary layer have been made on a 15deg total included angle cone with foreign gas injection. Measurements of total skin-friction drag were obtained at free-stream Mach numbers of 0.3, 0.7, 3.5, and 4.7 and within a Reynolds number range from 0.9 x 10(exp 6) to 5.9 x 10(exp 6) with injection of helium, air, and Freon-12 (CCl2F2) through the porous wall. Substantial reductions in skin friction are realized with gas injection within the range of Mach numbers of this test. The relative reduction in skin friction is in accordance with theory-that is, the light gases are most effective when compared on a mass flow basis. There is a marked effect of Mach number on the reduction of average skin friction; this effect is not shown by the available theories. Limited transition location measurements indicate that the boundary layer does not fully trip with gas injection but that the transition point approaches a forward limit with increasing injection. The variation of the skin-friction coefficient, for the lower injection rates with natural transition, is dependent on the flow Reynolds number and type of injected gas; and at the high injection rates the skin friction is in fair agreement with the turbulent boundary layer results.

Exploring uncertainty in the radiative budget of the Antarctic atmospheric boundary layer at Dome C

NASA Astrophysics Data System (ADS)

Veron, D. E.; Schroth, A.; Genthon, C.; Vignon, E.

2017-12-01

In the past two decades, significant advances have been made in observing and modeling the atmospheric boundary layer processes over the Eastern Antarctic plateau. However, there are gaps in understanding related to the radiative and moisture budgets in the very bottom of the ABL. Since 2009, continuous meteorological observations have been made at 6 heights in the bottom 40-m of the atmosphere as part of the CALibration and VAlidation of meteorological and climate models and satellite retrievals (C ALVA) campaign to improve understanding of the atmospheric state over Dome C. A recent case study that is part of the GEWEX Atmospheric Boundary Layer Study, GABLS4, has also focused on the ability of models to simulate stable summertime boundary layers at the same location. As part of the intercomparison, a model derived summertime climatology based on 10-years of PolarWRF simulations over the Eastern Antarctic plateau was developed. Comparisons between these simulations and data from the CALVA campaign suggest that PolarWRF is not capturing the small-scale variations in the longwave heating rate profile near the surface, and so predicts biased surface temperatures relative to observations. Additional work suggests that modifications of the surface snow representations may also be needed. Studies of the sensitivity of these results to changes in the moisture budget are ongoing.

Evidence for renoxification in the tropical marine boundary layer

NASA Astrophysics Data System (ADS)

Reed, Chris; Evans, Mathew J.; Crilley, Leigh R.; Bloss, William J.; Sherwen, Tomás; Read, Katie A.; Lee, James D.; Carpenter, Lucy J.

2017-03-01

We present 2 years of NOx observations from the Cape Verde Atmospheric Observatory located in the tropical Atlantic boundary layer. We find that NOx mixing ratios peak around solar noon (at 20-30 pptV depending on season), which is counter to box model simulations that show a midday minimum due to OH conversion of NO2 to HNO3. Production of NOx via decomposition of organic nitrogen species and the photolysis of HNO3 appear insufficient to provide the observed noontime maximum. A rapid photolysis of nitrate aerosol to produce HONO and NO2, however, is able to simulate the observed diurnal cycle. This would make it the dominant source of NOx at this remote marine boundary layer site, overturning the previous paradigm according to which the transport of organic nitrogen species, such as PAN, is the dominant source. We show that observed mixing ratios (November-December 2015) of HONO at Cape Verde (˜ 3.5 pptV peak at solar noon) are consistent with this route for NOx production. Reactions between the nitrate radical and halogen hydroxides which have been postulated in the literature appear to improve the box model simulation of NOx. This rapid conversion of aerosol phase nitrate to NOx changes our perspective of the NOx cycling chemistry in the tropical marine boundary layer, suggesting a more chemically complex environment than previously thought.

LES on Plume Dispersion in the Convective Boundary Layer Capped by a Temperature Inversion

NASA Astrophysics Data System (ADS)

Nakayama, Hiromasa; Tamura, Tetsuro; Abe, Satoshi

Large-eddy simulation (LES) is applied to the problem of plume dispersion in the spatially-developing convective boundary layer (CBL) capped by a temperature inversion. In order to generate inflow turbulence with buoyant forcing, we first, simulate the neutral boundary layer flow (NBL) in the driver region using Lund's method. At the same time, the temperature profile possessing the inversion part is imposed at the entrance of the driver region and the temperature field is calculated as a passive scalar. Next, the buoyancy effect is introduced into the flow field in the main region. We evaluate the applicability of the LES model for atmospheric dispersion in the CBL flow and compare the characteristics of plume dispersion in the CBL flow with those in the neutral boundary layer. The Richardson number based on the temperature increment across the inversion obtained by the present LES model is 22.4 and the capping effect of the temperature inversion can be captured qualitatively in the upper portion of the CBL. Characteristics of flow and temperature fields in the main portion of CBL flow are similar to those of previous experiments[1],[2] and observations[3]. Concerning dispersion behavior, we also find that mean concentrations decrease immediately above the inversion height and the peak values of r.m.s concentrations are located near the inversion height at larger distances from the point source.

Characterization of the Boundary Layer on Full-Scale Bluefin Tuna

NASA Astrophysics Data System (ADS)

Amaral, Brian; Cipolla, Kimberly; Henoch, Charles

2014-11-01

The physics that enable tuna to cross large expanses of ocean while feeding and avoiding predators is not presently understood, and could involve complex control of turbulent boundary layer transition and drag reduction. Typical swimming speeds of Bluefin tuna are 1-2 m/s, but can be higher during strong accelerations. The goal of this work is to experimentally determine the approximate lateral location at which transition to turbulence occurs on the tuna for various speeds. The question is whether laminar flow or an advanced propulsion mechanism (or both) allows them to swim at high speeds. Uncertainties include the surface roughness of the skin, local favorable and adverse pressure gradients, and discontinuities such as the open mouth or juncture at the fins. Historically, much of the fluid mechanics work in the area of fish locomotion has focused on vortex shedding issues rather than the boundary layer. Here, the focus is obtaining information on the boundary layer characteristics of a rigid tuna model. A full scale model of a Pacific Bluefin tuna was fabricated using a mold made from an actual deceased tuna, preserving the surface features and details of the appendages. The model was instrumented with 32 wall pressure sensors and experiments performed in a tow tank. Results from flow visualization, drag and wall pressure measurements over a range of speeds and varying angles of attack will be presented.

EBIC/TEM investigations of defects in solar silicon ribbon materials

NASA Technical Reports Server (NTRS)

Ast, D. G.

1981-01-01

Transmission electron microscopy was used to investigate the defect structure of edge defined film growth (EFG) material, web dentritic ribbons (WEB), and ribbon to ribbon recrystallized material (RTR). The most common defects in all these materials are coherent first order twin boundaries. These coherent twins can be very thin, a few atomic layers. Bundles of the twins which contain odd numbers of twins will in optical images appear as a seemingly single first twin boundary. First-order coherent twin boundaries are not electrically active, except at locations where they contain intrinsic (grain boundary) dislocations. These dislocations take up small deviations from the ideal twin relation and play the same role in twin boundaries as conventional and play the some role in twin boundaries as conventional edge and screw dislocations in small angle tilt and twist boundaries.

Numerical studies of porous airfoils in transonic flow. Ph.D. Thesis. Final Report, 1 Jun. 1985 - 31 Aug. 1986

NASA Technical Reports Server (NTRS)

Chow, C. Y.

1986-01-01

A numerical tool is constructed to examine the effects of a porous surface on transonic airfoil performance and to help understand the flow structure of passive shockwave/boundary layer interactions. The porous region is located near the shock with a cavity underneath it. This study is composed of two parts. Solved in the first part, with an inviscid-flow approach, is the transonic full-potential equation associated with transpiration boundary conditions which are obtained from porosity modeling. The numerical results indicate that a porous airfoil has a wave drag lower than that of a solid airfoil. The observed lambda-shock structure in the wind-tunnel testing can be predicted. Furthermore, the lift could be increased with an appropriate porosity distribution. In the second part of this work, the modified version of either an interactive boundary layer (IBL) algorithm or a thin-layer Navier-Stokes (TLNS) algorithm is used to study the outer flow, while a stream-function formulation is used to model the inner flow in the shallow cavity. The coupling procedure at the porous surface is based on Darcy's law and the assumption of a constant total pressure in the cavity. In addition, a modified Baldwin-Lomax turbulence model is used to describe the transpired turbulent boundary layer in the TLNS approach, while the Cebeci turbulence model is used in the IBL approach. According to the present analysis, a porous surface can reduce the wave drag appreciably, but can also increase the viscous losses. As has been observed experimentally, the numerical results indicate that the total drag is reduced at higher Mach numbers and increased at lower Mach numbers when the angles of attack are small. Furthermore, the streamline pattern of passive shock/boundary layer interaction are revealed.

Global stability behaviour for the BEK family of rotating boundary layers

NASA Astrophysics Data System (ADS)

Davies, Christopher; Thomas, Christian

2017-12-01

Numerical simulations were conducted to investigate the linear global stability behaviour of the Bödewadt, Ekman, von Kármán (BEK) family of flows, for cases where a disc rotates beneath an incompressible fluid that is also rotating. This extends the work reported in recent studies that only considered the rotating-disc boundary layer with a von Kármán configuration, where the fluid that lies above the boundary layer remains stationary. When a homogeneous flow approximation is made, neglecting the radial variation of the basic state, it can be shown that linearised disturbances are susceptible to absolute instability. We shall demonstrate that, despite this prediction of absolute instability, the disturbance development exhibits globally stable behaviour in the BEK boundary layers with a genuine radial inhomogeneity. For configurations where the disc rotation rate is greater than that of the overlying fluid, disturbances propagate radially outwards and there is only a convective form of instability. This replicates the behaviour that had previously been documented when the fluid did not rotate beyond the boundary layer. However, if the fluid rotation rate is taken to exceed that of the disc, then the propagation direction reverses and disturbances grow while convecting radially inwards. Eventually, as they approach regions of smaller radii, where stability is predicted according to the homogeneous flow approximation, the growth rates reduce until decay takes over. Given sufficient time, such disturbances can begin to diminish at every radial location, even those which are positioned outwards from the radius associated with the onset of absolute instability. This leads to the confinement of the disturbance development within a finitely bounded region of the spatial-temporal plane.

Interaction of two glancing, crossing shock waves with a turbulent boundary-layer at various Mach numbers

NASA Technical Reports Server (NTRS)

Hingst, Warren R.; Williams, Kevin E.

1991-01-01

A preliminary experimental investigation was conducted to study two crossing, glancing shock waves of equal strengths, interacting with the boundary-layer developed on a supersonic wind tunnel wall. This study was performed at several Mach numbers between 2.5 and 4.0. The shock waves were created by fins (shock generators), spanning the tunnel test section, that were set at angles varying from 4 to 12 degrees. The data acquired are wall static pressure measurements, and qualitative information in the form of oil flow and schlieren visualizations. The principle aim is two-fold. First, a fundamental understanding of the physics underlying this flow phenomena is desired. Also, a comprehensive data set is needed for computational fluid dynamic code validation. Results indicate that for small shock generator angles, the boundary-layer remains attached throughout the flow field. However, with increasing shock strengths (increasing generator angles), boundary layer separation does occur and becomes progressively more severe as the generator angles are increased further. The location of the separation, which starts well downstream of the shock crossing point, moves upstream as shock strengths are increased. At the highest generator angles, the separation appears to begin coincident with the generator leading edges and engulfs most of the area between the generators. This phenomena occurs very near the 'unstart' limit for the generators. The wall pressures at the lower generator angles are nominally consistent with the flow geometries (i.e. shock patterns) although significantly affected by the boundary-layer upstream influence. As separation occurs, the wall pressures exhibit a gradient that is mainly axial in direction in the vicinity of the separation. At the limiting conditions the wall pressure gradients are primarily in the axial direction throughout.

A closed-form analytical model for predicting 3D boundary layer displacement thickness for the validation of viscous flow solvers

NASA Astrophysics Data System (ADS)

Kumar, V. R. Sanal; Sankar, Vigneshwaran; Chandrasekaran, Nichith; Saravanan, Vignesh; Natarajan, Vishnu; Padmanabhan, Sathyan; Sukumaran, Ajith; Mani, Sivabalan; Rameshkumar, Tharikaa; Nagaraju Doddi, Hema Sai; Vysaprasad, Krithika; Sharan, Sharad; Murugesh, Pavithra; Shankar, S. Ganesh; Nejaamtheen, Mohammed Niyasdeen; Baskaran, Roshan Vignesh; Rahman Mohamed Rafic, Sulthan Ariff; Harisrinivasan, Ukeshkumar; Srinivasan, Vivek

2018-02-01

A closed-form analytical model is developed for estimating the 3D boundary-layer-displacement thickness of an internal flow system at the Sanal flow choking condition for adiabatic flows obeying the physics of compressible viscous fluids. At this unique condition the boundary-layer blockage induced fluid-throat choking and the adiabatic wall-friction persuaded flow choking occur at a single sonic-fluid-throat location. The beauty and novelty of this model is that without missing the flow physics we could predict the exact boundary-layer blockage of both 2D and 3D cases at the sonic-fluid-throat from the known values of the inlet Mach number, the adiabatic index of the gas and the inlet port diameter of the internal flow system. We found that the 3D blockage factor is 47.33 % lower than the 2D blockage factor with air as the working fluid. We concluded that the exact prediction of the boundary-layer-displacement thickness at the sonic-fluid-throat provides a means to correctly pinpoint the causes of errors of the viscous flow solvers. The methodology presented herein with state-of-the-art will play pivotal roles in future physical and biological sciences for a credible verification, calibration and validation of various viscous flow solvers for high-fidelity 2D/3D numerical simulations of real-world flows. Furthermore, our closed-form analytical model will be useful for the solid and hybrid rocket designers for the grain-port-geometry optimization of new generation single-stage-to-orbit dual-thrust-motors with the highest promising propellant loading density within the given envelope without manifestation of the Sanal flow choking leading to possible shock waves causing catastrophic failures.

Method of high speed flow field influence and restrain on laser communication

NASA Astrophysics Data System (ADS)

Meng, Li-xin; Wang, Chun-hui; Qian, Cun-zhu; Wang, Shuo; Zhang, Li-zhong

2013-08-01

For laser communication performance which carried by airplane or airship, due to high-speed platform movement, the air has two influences in platform and laser communication terminal window. The first influence is that aerodynamic effect causes the deformation of the optical window; the second one is that a shock wave and boundary layer would be generated. For subsonic within the aircraft, the boundary layer is the main influence. The presence of a boundary layer could change the air density and the temperature of the optical window, which causes the light deflection and received beam spot flicker. Ultimately, the energy hunting of the beam spot which reaches receiving side increases, so that the error rate increases. In this paper, aerodynamic theory is used in analyzing the influence of the optical window deformation due to high speed air. Aero-optics theory is used to analyze the influence of the boundary layer in laser communication link. Based on this, we focused on working on exploring in aerodynamic and aero-optical effect suppression method in the perspective of the optical window design. Based on planning experimental aircraft types and equipment installation location, we optimized the design parameters of the shape and thickness of the optical window, the shape and size of air-management kit. Finally, deformation of the optical window and air flow distribution were simulated by fluid simulation software in the different mach and different altitude fly condition. The simulation results showed that the optical window can inhibit the aerodynamic influence after optimization. In addition, the boundary layer is smoothed; the turbulence influence is reduced, which meets the requirements of the airborne laser communication.

Three-dimensional instability analysis of boundary layers perturbed by streamwise vortices

NASA Astrophysics Data System (ADS)

Martín, Juan A.; Paredes, Pedro

2017-12-01

A parametric study is presented for the incompressible, zero-pressure-gradient flat-plate boundary layer perturbed by streamwise vortices. The vortices are placed near the leading edge and model the vortices induced by miniature vortex generators (MVGs), which consist in a spanwise-periodic array of small winglet pairs. The introduction of MVGs has been experimentally proved to be a successful passive flow control strategy for delaying laminar-turbulent transition caused by Tollmien-Schlichting (TS) waves. The counter-rotating vortex pairs induce non-modal, transient growth that leads to a streaky boundary layer flow. The initial intensity of the vortices and their wall-normal distances to the plate wall are varied with the aim of finding the most effective location for streak generation and the effect on the instability characteristics of the perturbed flow. The study includes the solution of the three-dimensional, stationary, streaky boundary layer flows by using the boundary region equations, and the three-dimensional instability analysis of the resulting basic flows by using the plane-marching parabolized stability equations. Depending on the initial circulation and positioning of the vortices, planar TS waves are stabilized by the presence of the streaks, resulting in a reduction in the region of instability and shrink of the neutral stability curve. For a fixed maximum streak amplitude below the threshold for secondary instability (SI), the most effective wall-normal distance for the formation of the streaks is found to also offer the most stabilization of TS waves. By setting a maximum streak amplitude above the threshold for SI, sinuous shear layer modes become unstable, as well as another instability mode that is amplified in a narrow region near the vortex inlet position.

Boundary Layer Control for Hypersonic Airbreathing Vehicles

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.

2004-01-01

Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.

Transducer placement for robustness to variations in boundary conditions for active structural acoustic control

NASA Astrophysics Data System (ADS)

Sprofera, Joseph D.; Clark, Robert L.; Cabell, Randolph H.; Gibbs, Gary P.

2005-05-01

Turbulent boundary layer (TBL) noise is considered a primary contribution to the interior noise present in commercial airliners. There are numerous investigations of interior noise control devoted to aircraft panels; however, practical realization is a potential challenge since physical boundary conditions are uncertain at best. In most prior studies, pinned or clamped boundary conditions were assumed; however, realistic panels likely display a range of boundary conditions between these two limits. Uncertainty in boundary conditions is a challenge for control system designers, both in terms of the compensator implemented and the location of transducers required to achieve the desired control. The impact of model uncertainties, specifically uncertain boundaries, on the selection of transducer locations for structural acoustic control is considered herein. The final goal of this work is the design of an aircraft panel structure that can reduce TBL noise transmission through the use of a completely adaptive, single-input, single-output control system. The feasibility of this goal is demonstrated through the creation of a detailed analytical solution, followed by the implementation of a test model in a transmission loss apparatus. Successfully realizing a control system robust to variations in boundary conditions can lead to the design and implementation of practical adaptive structures that could be used to control the transmission of sound to the interior of aircraft. Results from this research effort indicate it is possible to optimize the design of actuator and sensor location and aperture, minimizing the impact of boundary conditions on the desired structural acoustic control.

Computational aspects of unsteady flows

NASA Technical Reports Server (NTRS)

Cebeci, T.; Carr, L. W.; Khattab, A. A.; Schimke, S. M.

1985-01-01

The calculation of unsteady flows and the development of numerical methods for solving unsteady boundary layer equations and their application to the flows around important configurations such as oscillating airfoils are presented. A brief review of recent work is provided with emphasis on the need for numerical methods which can overcome possible problems associated with flow reversal and separation. The zig-zag and characteristic box schemes are described in this context, and when embodied in a method which permits interaction between solutions of inviscid and viscous equations, the characteristic box scheme is shown to avoid the singularity associated with boundary layer equations and prescribed pressure gradient. Calculations were performed for a cylinder started impulsively from rest and oscillating airfoils. The results are presented and discussed. It is conlcuded that turbulence models based on an algebraic specification of eddy viscosity can be adequate, that location of translation is important to the calculation of the location of flow separation and, therefore, to the overall lift of an oscillating airfoil.

Flow visualization of discrete hole film cooling for gas turbine applications

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.

1975-01-01

Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied for three different hole angles: (1) normal, (2) slanted 30 deg to the surface in the direction of the mainstream, and (3) slanted 30 deg to the surface and 45 deg laterally to the mainstream. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing very small neutrally buoyant helium filled 'soap' bubbles which follow the flow field. Unlike smoke, which diffuses rapidly in the high turbulent mixing region associated with discrete hole blowing, the bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included.

Interference drag in a simulated wing-fuselage juncture

NASA Technical Reports Server (NTRS)

Kubendran, L. R.; Mcmahon, H.; Hubbartt, J. E.

1984-01-01

The interference drag in a wing fuselage juncture as simulated by a flat plate and a body of constant thickness having a 1.5:1 elliptical leading edge is evaluated experimentally. The experimental measurements consist of mean velocity data taken with a hot wire at a streamwise location corresponding to 16 body widths downstream of the body leading edge. From these data, the interference drag is determined by calculating the total momentum deficit (momentum area) in the juncture and also in the two dimensional turbulent boundary layers on the flat plate and body at locations sufficiently far from the juncture flow effect. The interference drag caused by the juncture drag as measured at this particular streamwise station is -3% of the total drag due to the flat plate and body boundary layers in isolation. If the body is considered to be a wing having a chord and span equal to 16 body widths, the interference drag due to the juncture is only -1% of the frictional drag of one surface of such a wing.

Investigation of corner shock boundary layer interactions to understand inlet unstart

NASA Astrophysics Data System (ADS)

Funderburk, Morgan

2015-11-01

Inlet unstart is a detrimental phenomenon in dual-mode ramjet/scramjet engines that causes severe loss of thrust, large transient structural load, and potentially a loss of the aircraft. In order to analyze the effects that the corner shock boundary layer interaction (SBLI) has on initiating and perpetuating inlet unstart, a qualitative and quantitative investigation into mean and dynamic features of corner SBLI at various Mach numbers is made. Surface streakline visualization showed that the corner SBLI is highly three-dimensional with a dominant presence of corner separation vortex. Further, the peak r.m.s. pressure was located at the periphery of corner separation vortex, suggesting that the unsteady loading is caused by the corner vortex. Power spectral densities of wall-pressure fluctuations in the peak r.m.s. location were analyzed in order to characterize the dominant frequencies of oscillation of the flow structures and to unravel the dynamic interactions between them in order to expand the operating margin of future hypersonic air breathing vehicles.

Analysis of Crossflow Transition Flight Experiment aboard the Pegasus Launch Vehicle

NASA Technical Reports Server (NTRS)

Malik, Mujeeb R.; Li, Fei; Choudhan, Meelan

2007-01-01

The Pegasus wing-glove flight experiment was designed to provide crossflow transition data at high Mach numbers, specifically to help validate stability based predictions for transition onset in a flight environment. This paper provides an analysis of the flight experiment, with emphasis on computational results for crossflow disturbances and the correlation of disturbance growth factors with in-flight transition locations via the e(sup N) method. Implications of the flight data for attachment line stability are also examined. Analysis of the thermocouple data reveals that transition (from turbulent to laminar flow) was first detected during the ascending flight of the rocket when the free stream Mach number exceeded about 4. Therefore, computations have been performed for flight Mach numbers of 4.13, 4.35, 4.56 and 4.99. Due to continually decreasing unit Reynolds number at higher altitudes, the entire wing-glove boundary layer became laminar at the highest flight Mach number computed above. In contrast, the boundary layer flow over the inboard tile region remained transitional up to and somewhat beyond the time of laminarization over the instrumented glove region. Linear stability predictions confirmed that the tile boundary layer is indeed more unstable to crossflow disturbances than the much colder stainless steel glove boundary layer. The transition locations based on thermocouple data from both the glove and the tile regions are found to correlate with stationary-crossflow N-factors within the range of 7 to 12.4 and with traveling mode N-factors between 7.6 and 14.1. Data from the thermocouples and hot film sensors indicates that transition from turbulent to laminar flow (i.e., laminarization) at a fixed point over the glove is generally completed within a flight time interval of 3 seconds. However, the times at which transition begins and ends as inferred from the hot film sensors are found to differ by about 2 seconds from the corresponding estimates based on the thermocouple data.

The atmospheric boundary layer evening transitions: an observational and numerical study from two different datasets

NASA Astrophysics Data System (ADS)

Sastre, Mariano; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio; Ander Arrillaga, Jon

2015-04-01

In this work we study the temporal evolution of the Atmospheric Boundary Layer (ABL) along the transition period from a diurnal typical convection to a nocturnal more frequently stable situation. This period is known as late afternoon or evening transition, depending on the specific definitions employed by different authors [1]. In order to obtain a proper characterization, we try to learn whether or not the behaviour of these transitional boundary layers is strongly dependent on local conditions. To do so, two sets of evening transitions are studied from data collected at two different experimental sites. These locations correspond to research facilities named CIBA (Spain) and CRA (France), which are the places where atmospheric field campaigns have been conducted during the last years, such as CIBA2008 and BLLAST 2011, respectively. In order to get comparable situations, we focus especially on transitions with weak synoptic forcing, and consider daily astronomical sunset as a reference time. A statistical analysis on main parameters related to the transition is carried out for both locations, and the average behaviour is shown as well as extreme values according to the timing. A similar pattern in the qualitative evolution of many variables is found. Nevertheless, several relevant differences in the progress of key variables are obtained too. Moisture, both from the soil and the air, is thought to have great relevance in explaining many of the differences found between the two sites. Some case studies are explored, focusing on the role played by the atmospheric turbulence. Complementary, numerical experiments are also performed using the Weather Research and Forecast (WRF) mesoscale model, in order to test the role of humidity, by artificially varying it in some of the simulations. [1] Lothon, M. and coauthors (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence. Atmos. Chem. Phys., 14, 10931-10960.

Correlation-based Transition Modeling for External Aerodynamic Flows

NASA Astrophysics Data System (ADS)

Medida, Shivaji

Conventional turbulence models calibrated for fully turbulent boundary layers often over-predict drag and heat transfer on aerodynamic surfaces with partially laminar boundary layers. A robust correlation-based model is developed for use in Reynolds-Averaged Navier-Stokes simulations to predict laminar-to-turbulent transition onset of boundary layers on external aerodynamic surfaces. The new model is derived from an existing transition model for the two-equation k-omega Shear Stress Transport (SST) turbulence model, and is coupled with the one-equation Spalart-Allmaras (SA) turbulence model. The transition model solves two transport equations for intermittency and transition momentum thickness Reynolds number. Experimental correlations and local mean flow quantities are used in the model to account for effects of freestream turbulence level and pressure gradients on transition onset location. Transition onset is triggered by activating intermittency production using a vorticity Reynolds number criterion. In the new model, production and destruction terms of the intermittency equation are modified to improve consistency in the fully turbulent boundary layer post-transition onset, as well as ensure insensitivity to freestream eddy viscosity value specified in the SA model. In the original model, intermittency was used to control production and destruction of turbulent kinetic energy. Whereas, in the new model, only the production of eddy viscosity in SA model is controlled, and the destruction term is not altered. Unlike the original model, the new model does not use an additional correction to intermittency for separation-induced transition. Accuracy of drag predictions are improved significantly with the use of the transition model for several two-dimensional single- and multi-element airfoil cases over a wide range of Reynolds numbers. The new model is able to predict the formation of stable and long laminar separation bubbles on low-Reynolds number airfoils that is not captured with conventional turbulence models. The validated transition model is successfully applied to rotating blade configurations in axial flow conditions to study the effects of transitional boundary layers on rotor thrust and torque. In helicopter rotors, inclusion of transition effects increased thrust prediction by 2% and decreased torque by as much as 8% at lower collective angles, due to reduced airfoil profile drag. In wind turbine rotors, transition model predicted a 7%--70% increase in generated shaft torque at lower wind speeds, due to lower viscous drag. This has important implications for CFD analysis of small wind turbines operating at low values of rated power. Transition onset locations along upper and lower surfaces of rotor blades are analyzed in detail. A new crossflow transition onset criterion is developed to account for crossflow instability effects in three-dimensional boundary layers. Preliminary results for swept wing and rotating blade flows demonstrate the need to account for crossflow transition in three-dimensional simulations of wings, rotating blades, and airframes. Inclusion of crossflow effects resulted in accelerated transition in the presence of favorable pressure gradients and yawed flow. Finally, a new correction to the wall damping function in the Spalart-Allmaras turbulence model is proposed to improve sensitivity of the model to strong adverse pressure gradients (APG). The correction reduces turbulence production in the boundary layer when the ratio of magnitudes of local turbulent stress to the wall shear stress exceeds a threshold value, therefore enabling earlier separation of boundary layer. Improved prediction of static and dynamic stall on two-dimensional airfoils is demonstrated with the APG correction.

The effect of small angle of attack on the laminar-turbulent transition in boundary layer on swept wing at Mach number M=2

NASA Astrophysics Data System (ADS)

Semionov, N. V.; Yermolaev, Yu. G.; Kosinov, A. D.; Semenov, A. N.; Smorodsky, B. V.; Yatskikh, A. A.

2017-10-01

The paper is devoted to an experimental and theoretical study of effect of small angle of attack on disturbances evolution and laminar-turbulent transition in a supersonic boundary layer on swept wing at Mach number M=2. The experiments are conducted at the low nose supersonic wind tunnel T-325 of ITAM. Model is a symmetrical wing with a 45° sweep angle, a 3 percent-thick circular-arc airfoil. The transition location is determined using a hot-wire anemometer. Confirmed monotonous growth of the transition Reynolds numbers with increasing of angle of attack from -2° to 2.5°. The experimental data on the influence of the angle of attack on the disturbances evolution in the supersonic boundary layer on the swept wing model are obtained. Calculations on the effect of small angles of attack on the development of perturbations are made in the framework of the linear theory of stability. A good qualitative correspondence of theoretical and experimental data are obtained.

Circulation Control Model Experimental Database for CFD Validation

NASA Technical Reports Server (NTRS)

Paschal, Keith B.; Neuhart, Danny H.; Beeler, George B.; Allan, Brian G.

2012-01-01

A 2D circulation control wing was tested in the Basic Aerodynamic Research Tunnel at the NASA Langley Research Center. A traditional circulation control wing employs tangential blowing along the span over a trailing-edge Coanda surface for the purpose of lift augmentation. This model has been tested extensively at the Georgia Tech Research Institute for the purpose of performance documentation at various blowing rates. The current study seeks to expand on the previous work by documenting additional flow-field data needed for validation of computational fluid dynamics. Two jet momentum coefficients were tested during this entry: 0.047 and 0.114. Boundary-layer transition was investigated and turbulent boundary layers were established on both the upper and lower surfaces of the model. Chordwise and spanwise pressure measurements were made, and tunnel sidewall pressure footprints were documented. Laser Doppler Velocimetry measurements were made on both the upper and lower surface of the model at two chordwise locations (x/c = 0.8 and 0.9) to document the state of the boundary layers near the spanwise blowing slot.

Boundary Layer Transition Flight Experiment Overview and In-Situ Measurements

NASA Technical Reports Server (NTRS)

Anderson, Brian P.; Campbell, Charles H.; Saucedo, Luis A.; Kinder, Gerald R.; Berger, Karen T.

2010-01-01

In support of the Boundary Layer Transition Flight Experiment (BLTFE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for the flights of STS-119 and STS-128. Additional instrumentation was also installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLTFE Project, including the project history, organizations involved, and motivations for the flight experiment. Significant efforts were made to place the protuberance at an appropriate location on the Orbiter and to design the protuberance to withstand the expected environments. Efforts were also extended to understand the as-fabricated shape of the protuberance and the thermal protection system tile configuration surrounding the protuberance. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that predictions for boundary layer transition onset time closely match the flight data, while predicted temperatures were significantly higher than observed flight temperatures.

Characterization of structural response to hypersonic boundary-layer transition

DOE PAGES

Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...

2016-05-24

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less

Supersonic flow visualization of a nacelle in close proximity to a simulated wing

NASA Technical Reports Server (NTRS)

Biber, Kasim; Ellis, David R.

1993-01-01

A flow visualization study was made in the 9 x 9 inch supersonic wind tunnel at Wichita State University to examine shock and boundary layer flow interaction for a nacelle in close proximity to the lower surface of a simulated wing. The test matrix included variations of angle of attack from -2 degrees to +4 degrees, nacelle-wing gap from 0.5 to 3-nacelle inlet diameter (0.12 inch), and Reynolds number based on nacelle length (1.164 inch) from 1.16 x 10(exp 6) to 1.45 x 10(exp 6) at a nominal Mach number of 2. Schlieren pictures of wing and nacelle flowfield were recorded by a video camera during each tunnel run. Results show that the nacelle inlet shock wave remains attached to the inlet lip and its impingement does not significantly affect the wing boundary layer. At the nacelle trailing edge location, the wing boundary layer thickness is approximately one nacelle inlet diameter at alpha = 0 degrees and it decreases with increase of angle of attack.

Thermal Mechanisms for High Amplitude Aerodynamic Flow Control (YIP 2012)

DTIC Science & Technology

2016-04-15

memorandum, master’s thesis, progress, quarterly, research , special, group study, etc. 3. DATES COVERED. Indicate the time during which the work...boundary layer ahead of the plasma. Since the ns-DBD flow control mechanism is primarily thermal, or least symmetric if associated with a quasi ...conditions with minimal experimental effort. The validity of probing a single location on the low speed side of the mixing layer to test for control

An Examination of the Effect of Boundary Layer Ingestion on Turboelectric Distributed Propulsion Systems

NASA Technical Reports Server (NTRS)

Felder, James L.; Kim, Huyn Dae; Brown, Gerald V.; Chu, Julio

2011-01-01

A Turboelectric Distributed Propulsion (TeDP) system differs from other propulsion systems by the use of electrical power to transmit power from the turbine to the fan. Electrical power can be efficiently transmitted over longer distances and with complex topologies. Also the use of power inverters allows the generator and motors speeds to be independent of one another. This decoupling allows the aircraft designer to place the core engines and the fans in locations most advantageous for each. The result can be very different installation environments for the different devices. Thus the installation effects on this system can be quite different than conventional turbofans where the fan and core both see the same installed environments. This paper examines a propulsion system consisting of two superconducting generators, each driven by a turboshaft engine located so that their inlets ingest freestream air, superconducting electrical transmission lines, and an array of superconducting motor driven fan positioned across the upper/rear fuselage area of a hybrid wing body aircraft in a continuous nacelle that ingests all of the upper fuselage boundary layer. The effect of ingesting the boundary layer on the design of the system with a range of design pressure ratios is examined. Also the impact of ingesting the boundary layer on off-design performance is examined. The results show that when examining different design fan pressure ratios it is important to recalculate of the boundary layer mass-average Pt and MN up the height for each inlet height during convergence of the design point for each fan design pressure ratio examined. Correct estimation of off-design performance is dependent on the height of the column of air measured from the aircraft surface immediately prior to any external diffusion that will flow through the fan propulsors. The mass-averaged Pt and MN calculated for this column of air determine the Pt and MN seen by the propulsor inlet. Since the height of this column will change as the amount of air passing through the fans change as the propulsion system is throttled, and since the mass-average Pt and MN varies by height, this capture height must be recalculated as the airflow through the propulsor is varied as the off-design performance point is converged.

Discussion of boundary-layer characteristics near the casing of an axial-flow compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mahoney, John J; Budinger, Ray E

1951-01-01

Boundary-layer velocity profiles on the casing of an axial-flow compressor behind the guide vanes and rotor were measured and resolved into two components: along the streamline of the flow and perpendicular to it. Boundary-layer thickness and the deflection of the boundary layer at the wall were the generalizing parameters. By use of these results and the momentum-integral equations, the characteristics of boundary on the walls of axial-flow compressor are qualitatively discussed. Important parameters concerning secondary flow in the boundary layer appear to be turning of the flow and the product of boundary-layer thickness and streamline curvature outside the boundary layer. Two types of separation are shown to be possible in three dimensional boundary layer.

Vertical Profiles of Light Scattering, Light Absorption, and Single Scattering Albedo during the Dry, Biomass Burning Season in Southern Africa and Comparisons of In Situ and Remote Sensing Measurements of Aerosol Optical Depths

NASA Technical Reports Server (NTRS)

Magi, Brian I.; Hobbs, Peter V.; Schmid, Beat; Redermann, Jens

2003-01-01

Airborne in situ measurements of vertical profiles of aerosol light scattering, light absorption, and single scattering albedo (omega (sub 0)) are presented for a number of locations in southern Africa during the dry, biomass burning season. Features of the profiles include haze layers, clean air slots, and marked decreases in light scattering in passing from the boundary layer into the free troposphere. Frequency distributions of omega (sub 0) reflect the strong influence of smoke from biomass burning. For example, during a period when heavy smoke was advected into the region from the north, the mean value of omega (sub 0) in the boundary layer was 0.81 +/- 0.02 compared to 0.89 +/- 0.03 prior to this intrusion. Comparisons of layer aerosol optical depths derived from the in situ measurements with those measured by a Sun photometer aboard the aircraft show excellent agreement.

Reynolds stress structures in a self-similar adverse pressure gradient turbulent boundary layer at the verge of separation.

NASA Astrophysics Data System (ADS)

Atkinson, C.; Sekimoto, A.; Jiménez, J.; Soria, J.

2018-04-01

Mean Reynolds stress profiles and instantaneous Reynolds stress structures are investigated in a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL) at the verge of separation using data from direct numerical simulations. The use of a self-similar APG-TBL provides a flow domain in which the flow gradually approaches a constant non-dimensional pressure gradient, resulting in a flow in which the relative contribution of each term in the governing equations is independent of streamwise position over a domain larger than two boundary layer thickness. This allows the flow structures to undergo a development that is less dependent on the upstream flow history when compared to more rapidly decelerated boundary layers. This APG-TBL maintains an almost constant shape factor of H = 2.3 to 2.35 over a momentum thickness based Reynolds number range of Re δ 2 = 8420 to 12400. In the APG-TBL the production of turbulent kinetic energy is still mostly due to the correlation of streamwise and wall-normal fluctuations, 〈uv〉, however the contribution form the other components of the Reynolds stress tensor are no longer negligible. Statistical properties associated with the scale and location of sweeps and ejections in this APG-TBL are compared with those of a zero pressure gradient turbulent boundary layer developing from the same inlet profile, resulting in momentum thickness based range of Re δ 2 = 3400 to 3770. In the APG-TBL the peak in both the mean Reynolds stress and the production of turbulent kinetic energy move from the near wall region out to a point consistent with the displacement thickness height. This is associated with a narrower distribution of the Reynolds stress and a 1.6 times higher relative number of wall-detached negative uv structures. These structures occupy 5 times less of the boundary layer volume and show a similar reduction in their streamwise extent with respect to the boundary layer thickness. A significantly lower percentage of wall-attached structures is observed in the present case when compared with a similar investigation of a rapidly decelerating APG-TBL, suggesting that these wall-attached features could be the remanent from the lower pressure gradient domain upstream.

Impact wave deposits provide new constraints on the location of the K/T boundary impact

NASA Technical Reports Server (NTRS)

Hildebrand, A. R.; Boynton, W. V.

1988-01-01

All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. Although much of this evidence is incompatible with an endogenic origin, some investigators still feel that a volcanic origin is possible for the Cretaceous/Tertiary (K/T) boundary clay layers. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region. The K/T boundary interval was investigated as preserved on the banks of the Brazos River, Texas. The K/T fireball and ejecta layers with associated geochemical anomalies were found interbedded with this sequence which apparently allows a temporal resolution 4 orders of magnitude greater than typical K/T boundary sections. A literature search reveals that such coarse deposits are widely preserved at the K/T boundary. Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. The coarse deposits preserved in Deep Sea Drilling Project (DSDP) holes 151-3 suggest the impact occurred nearby. Subsequent tectonism has complicated the picture.

Developments in flow visualization methods for flight research

NASA Technical Reports Server (NTRS)

Holmes, Bruce J.; Obara, Clifford J.; Manuel, Gregory S.; Lee, Cynthia C.

1990-01-01

With the introduction of modern airplanes utilizing laminar flow, flow visualization has become an important diagnostic tool in determining aerodynamic characteristics such as surface flow direction and boundary-layer state. A refinement of the sublimating chemical technique has been developed to define both the boundary-layer transition location and the transition mode. In response to the need for flow visualization at subsonic and transonic speeds and altitudes above 20,000 feet, the liquid crystal technique has been developed. A third flow visualization technique that has been used is infrared imaging, which offers non-intrusive testing over a wide range of test conditions. A review of these flow visualization methods and recent flight results is presented for a variety of modern aircraft and flight conditions.

Planetary boundary-layer wind model evaluation at a mid-Atlantic coastal site

NASA Technical Reports Server (NTRS)

Tieleman, H. W.

1980-01-01

Detailed measurements of the mean flow and turbulence were made with the use of a micrometeorological facility consisting of an instrumented 76-m tall tower located within a 100-m distance from the Atlantic Ocean at Wallops Island, Virginia. Under moderately strong wind conditions, the popular neutral boundary layer flow model fails to provide an adequate description of the actual flow. In addition to detailed flow information for all wind directions, averages of the important flow parameters used for design such as vertical distribution of mean velocity, turbulence intensities and turbulence integral scales were presented for wind direction sectors with near uniform upstream terrain. Power spectra of the three velocity components for the prevailing northwesterly and southerly winds are discussed.

A hot-wire surface gage for skin friction and separation detection measurements

NASA Technical Reports Server (NTRS)

Rubesin, M. W.; Okuno, A. F.; Mateer, G. G.; Brosh, A.

1975-01-01

A heated-element, skin-friction gage employing a very low thermal conductivity support is described. It is shown that the effective dimension of the gage in the stream direction in only 0.06 mm, including the effects of heat conduction in the supporting material. Because of its small size, the calibration of the gage is independent of the kind of boundary-layer flow (whether laminar or turbulent) and is insensitive to pressure gradients. Construction tolerances can be maintained so that a single universal calibration can be applied. Multiple gages, sufficiently closely spaced so as to interfere with each other, are shown to provide accurate determinations of the locations of the points of boundary-layer separation and reattachment.

Assessment of Turbulent CFD Against STS-128 Hypersonic Flight Data

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.; Hyatt, Andrew J.

2010-01-01

Turbulent CFD simulations are compared against surface temperature measurements of the space shuttle orbiter windward tiles at reentry flight conditions. Algebraic turbulence models are used within both the LAURA and DPLR CFD codes. The flight data are from temperature measurements obtained by seven thermocouples during the STS-128 mission (September 2009). The flight data indicate boundary layer transition onset over the Mach number range 13.5{15.5, depending upon the location on the vehicle. But the boundary layer flow appeared to be transitional down through Mach 12, based upon the flight data and CFD trends. At Mach 9 the simulations match the flight data on average within 20 F/11 C, where typical surface temperatures were approximately 1600 F/870 C.

Interface shapes during vertical Bridgman growth of (Pb, Sn)Te crystals

NASA Technical Reports Server (NTRS)

Huang, YU; Debnam, William J.; Fripp, Archibald L.

1990-01-01

Melt-solid interfaces obtained during vertical Bridgman growth of (Pb, Sn)Te crystals were investigated with a quenching technique. The shapes of these interfaces, revealed by etching longitudinally cut sections, were correlated with the composition variations determined by EMPA. These experiments demonstrated that the interface shape can be changed from concave to convex by moving its location from the edge of the cold zone into the hot zone. The metallography and microsegregation near the melt-solid interface were analyzed in detail. A sharp change in composition above the interface indicated the existence of a diffusion boundary layer 40-90 microns thick. This small diffusion boundary layer is consistent with strong convective mixing in the (Pb, Sn)Te melt.

The liquid fuel jet in subsonic crossflow

NASA Technical Reports Server (NTRS)

Nguyen, T. T.; Karagozian, A. R.

1990-01-01

An analytical/numerical model is described which predicts the behavior of nonreacting and reacting liquid jets injected transversely into subsonic cross flow. The compressible flowfield about the elliptical jet cross section is solved at various locations along the jet trajectory by analytical means for free-stream local Mach number perpendicular to jet cross section smaller than 0.3 and by numerical means for free-stream local Mach number perpendicular to jet cross section in the range 0.3-1.0. External and internal boundary layers along the jet cross section are solved by integral and numerical methods, and the mass losses due to boundary layer shedding, evaporation, and combustion are calculated and incorporated into the trajectory calculation. Comparison of predicted trajectories is made with limited experimental observations.

Study on resources and environmental data integration towards data warehouse construction covering trans-boundary area of China, Russia and Mongolia

NASA Astrophysics Data System (ADS)

Wang, J.; Song, J.; Gao, M.; Zhu, L.

2014-02-01

The trans-boundary area between Northern China, Mongolia and eastern Siberia of Russia is a continuous geographical area located in north eastern Asia. Many common issues in this region need to be addressed based on a uniform resources and environmental data warehouse. Based on the practice of joint scientific expedition, the paper presented a data integration solution including 3 steps, i.e., data collection standards and specifications making, data reorganization and process, data warehouse design and development. A series of data collection standards and specifications were drawn up firstly covering more than 10 domains. According to the uniform standard, 20 resources and environmental survey databases in regional scale, and 11 in-situ observation databases were reorganized and integrated. North East Asia Resources and Environmental Data Warehouse was designed, which included 4 layers, i.e., resources layer, core business logic layer, internet interoperation layer, and web portal layer. The data warehouse prototype was developed and deployed initially. All the integrated data in this area can be accessed online.

Magnetic field reversals, polar wander, and core-mantle coupling.

PubMed

Courtillot, V; Besse, J

1987-09-04

True polar wander, the shifting of the entire mantle relative to the earth's spin axis, has been reanalyzed. Over the last 200 million years, true polar wander has been fast (approximately 5 centimeters per year) most of the time, except for a remarkable standstill from 170 to 110 million years ago. This standstill correlates with a decrease in the reversal frequency of the geomagnetic field and episodes of continental breakup. Conversely, true polar wander is high when reversal frequency increases. It is proposed that intermittent convection modulates the thickness of a thermal boundary layer at the base of the mantle and consequently the core-to-mantle heat flux. Emission of hot thermals from the boundary layer leads to increases in mantle convection and true polar wander. In conjunction, cold thermals released from a boundary layer at the top of the liquid core eventually lead to reversals. Changes in the locations of subduction zones may also affect true polar wander. Exceptional volcanism and mass extinctions at the Cretaceous-Tertiary and Permo-Triassic boundaries may be related to thermals released after two unusually long periods with no magnetic reversals. These environmental catastrophes may therefore be a consequence of thermal and chemical couplings in the earth's multilayer heat engine rather than have an extraterrestrial cause.

Boundary layer turbulence in transitional and developed states

NASA Astrophysics Data System (ADS)

Park, George Ilhwan; Wallace, James M.; Wu, Xiaohua; Moin, Parviz

2012-03-01

Using the recent direct numerical simulations by Wu and Moin ["Transitional and turbulent boundary layer with heat transfer," Phys. Fluids 22, 85 (2010)] of a flat-plate boundary layer with a passively heated wall, statistical properties of the turbulence in transition at Reθ ≈ 300, from individual turbulent spots, and at Reθ ≈ 500, where the spots merge (distributions of the mean velocity, Reynolds stresses, kinetic energy production, and dissipation rates, enstrophy and its components) have been compared to these statistical properties for the developed boundary layer turbulence at Reθ = 1840. When the distributions in the transitional regions are conditionally averaged so as to exclude locations and times when the flow is not turbulent, they closely resemble the distributions in the developed turbulent state at the higher Reynolds number, especially in the buffer layer. Skin friction coefficients, determined in this conditional manner at the two Reynolds numbers in the transitional flow are, of course, much larger than when their values are obtained by including both turbulent and non-turbulent information there, and the conditional averaged values are consistent with the 1/7th power law approximation. An octant analysis based on the combinations of signs of the velocity and temperature fluctuations, u, v, and θ shows that the momentum and heat fluxes are predominantly of the mean gradient type in both the transitional and developed regions. The fluxes appear to be closely associated with vortices that transport momentum and heat toward and away from the wall in both regions of the flow. The results suggest that there may be little fundamental difference between the nonlinear processes involved in the formation of turbulent spots that appear in transition and those that sustain the turbulence when it is developed. They also support the view that the transport processes and the vortical structures that drive them in developed and transitional boundary layer turbulence are, in many dynamically important respects, similar.

Further studies of turbulence structure resulting from interactions between embedded vortices and wall jets at high blowing ratios

NASA Astrophysics Data System (ADS)

Doner, William D.

1989-12-01

Interactions of wall jets and vortices embedded in turbulent layers commonly occur near gas turbine blades and endwalls where film cooling is employed. These interactions frequently result in undesirable heat transfer effects at blade and endwall surfaces. In this thesis, a crossed hot-wire probe is used to measure the turbulence structure resulting from this type of interaction. The vortex is generated using a half delta-wing vortex generator mounted 12 deg with respect to a 10 m/s mean velocity flow over a flat plate. A single injection hole, 0.95 cm in diameter, inclined 30 deg to the horizontal, is positioned 59.3 cm downstream of the vortex generator. The vortex generator is positioned so that vortex upwash and downwash could be located over the injection hole. Streamwise development of the turbulent boundary layer was investigated for the following cases: (1) boundary layer with jet only (m = 1.5), and (2) boundary layer with vortex only. Measurement of interaction between the boundary layer, vortex upwash, and the wall jet was made at one station with various blowing ratios. At low blowing ratios (m = 0.5 and 1.5) the vortex dominates the flow. Significant alterations to the turbulent structure are seen in the Reynolds stress components, vorticity distributions and mean velocities. At higher blowing ratios (m = 2.5 and 3.5) the jet dominates the flow, the vortex is blown away from the wall, and its turbulence effects are dispersed over a larger area.

Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Hollis, Brian R.; Horvath, Thomas J.

2003-01-01

Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.

Thermodynamic and radiative structure of stratocumulus-topped boundary layers*

DOE PAGES

Ghate, Virendra P.; Miller, Mark A.; Albrecht, Bruce A.; ...

2015-01-05

Stratocumulus Topped Boundary Layers (STBL) observed in three different regions with distinctive environments are described in the context of their thermodynamic and radiative properties. Here, the primary data set consisted of 131 soundings from the South East Pacific (SEP), 90 soundings from the island of Graciosa (GRW) in the North Atlantic and 83 soundings from the US Southern Great Plains (SGP). A new technique that preserves the depths of the sub-layers within a STBL is proposed for averaging the profiles of thermodynamic and radiative variables. The STBL was deepest over SEP and had the strongest radiative cooling rates near cloudmore » top among the three locations. Although the radiative cooling rates were comparable over GRW and SGP, the STBL was deeper over GRW compared to that over SGP. On average the STBL inversion was strongest over SEP (11.7 k and -5.43 g kg -1) and weakest over the SGP (6.89 k and -0.41 g kg -1). Significantly larger liquid water path, integrated water vapor, and variability in these two properties was found over GRW and evidence presented suggests that conditions at cloud top may play a lesser role in determining the resident cloud structure over GRW than over SEP. A modal analysis revealed ~26% of the STBL to be well-mixed, ~20% of STBL to be stable and ~30% STBL having a stable layer in-between a surface mixed layer and the cloud layer. Over all the three locations, the STBL was shallowest in well-mixed mode and deepest in the stable mode.« less

Heat Transfer Due to Shock Wave Turbulent Boundary Layer Interactions on High Speed Weapon Systems

DTIC Science & Technology

1974-04-01

Thermocouple Location. ............ 20 8 Pressure Tap LoceL.lons ............ 23 9 Pitot Pressurp Rake Detail and Profile Measurement Stations... Pitot Pressure Profile Measurements - Pitot pressure measure- ments were made with a NASA Langley five-probe pitot pressure rake at the axial location...defined in Figure 6. Figure 9 is a schematic illustration providing the dimensions of the rake and the pitot pressure profile measure- ment stations. The

Establishing Accurate and Sustainable Geospatial Reference Layers in Developing Countries

NASA Astrophysics Data System (ADS)

Seaman, V. Y.

2017-12-01

Accurate geospatial reference layers (settlement names & locations, administrative boundaries, and population) are not readily available for most developing countries. This critical information gap makes it challenging for governments to efficiently plan, allocate resources, and provide basic services. It also hampers international agencies' response to natural disasters, humanitarian crises, and other emergencies. The current work involves a recent successful effort, led by the Bill & Melinda Gates Foundation and the Government of Nigeria, to obtain such data. The data collection began in 2013, with local teams collecting names, coordinates, and administrative attributes for over 100,000 settlements using ODK-enabled smartphones. A settlement feature layer extracted from satellite imagery was used to ensure all settlements were included. Administrative boundaries (Ward, LGA) were created using the settlement attributes. These "new" boundary layers were much more accurate than existing shapefiles used by the government and international organizations. The resulting data sets helped Nigeria eradicate polio from all areas except in the extreme northeast, where security issues limited access and vaccination activities. In addition to the settlement and boundary layers, a GIS-based population model was developed, in partnership with Oak Ridge National Laboratories and Flowminder), that used the extracted settlement areas and characteristics, along with targeted microcensus data. This model provides population and demographics estimates independent of census or other administrative data, at a resolution of 90 meters. These robust geospatial data layers found many other uses, including establishing catchment area settlements and populations for health facilities, validating denominators for population-based surveys, and applications across a variety of government sectors. Based on the success of the Nigeria effort, a partnership between DfID and the Bill & Melinda Gates Foundation was formed in 2017 to help other developing countries collect these geospatial reference layers, and to build capacity within the host governments to manage, use, and sustain them. This work will support, wherever possible, a national geo-referenced census, from which the reference layers can be extracted.

Effect of wall roughness on liquid oscillations damping in rectangular tanks

NASA Technical Reports Server (NTRS)

Bugg, F. M.

1970-01-01

Tests were conducted in two rectangular glass tanks using silicon carbide grit bonded to walls to determine effect of wall roughness for damping liquid oscillations. Tests included effects of roughness height, roughness location, roughness at various values, amplitude decay, Reynolds number, and boundary layer thickness.

Separation behavior of boundary layers on three-dimensional wings

NASA Technical Reports Server (NTRS)

Stock, H. W.

1981-01-01

An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.

Tribal Boundaries, U.S., 2014, EPA/OAR/OAQPS/AQAD

EPA Pesticide Factsheets

This web service contains a layer depicting the union of TigerWEB AIANNHA map service layers 2 (Federal American Indian Reservations) and 3 (Off-Reservation Trust Lands) located at https://tigerweb.geo.census.gov/arcgis/rest/services/TIGERweb/AIANNHA/MapServerFederal (federal AIRs) are areas that have been set aside by the United States for the use of tribes, the exterior boundaries of which are more particularly defined in the final tribal treaties, agreements, executive orders, federal statutes, secretarial orders, or judicial determinations. The Bureau of Indian Affairs maintains a list of all federally recognized tribal governments and makes final determination of the inventory federal AIRs. The Census Bureau recognizes federal reservations (and associated off-reservation trust lands) as territory over which American Indian tribes have primary governmental authority. American Indian reservations can be legally described as colonies, communities, Indian colonies, Indian communities, Indian rancheria, Indian reservations, Indian villages, pueblos, rancherias, ranches, reservations, reserves, settlements, or villages. The Census Bureau contacts representatives of American Indian tribal governments to identify the boundaries for federal reservations through its annual Boundary and Annexation Survey. Federal reservations may cross state and all other area boundaries.State (state AIRs) are reservations established by some state governments for tribes recognized by

3D LDV Measurements in Oscillatory Boundary Layers

NASA Astrophysics Data System (ADS)

Mier, J. M.; Garcia, M. H.

2012-12-01

The oscillatory boundary layer represents a particular case of unsteady wall-bounded flows in which fluid particles follow a periodic sinusoidal motion. Unlike steady boundary layer flows, the oscillatory flow regime and bed roughness character change in time along the period for every cycle, a characteristic that introduces a high degree of complexity in the analysis of these flows. Governing equations can be derived from the general Navier-Stokes equations for the motion of fluids, from which the exact solution for the laminar oscillatory boundary layer is obtained (also known as the 2nd Stokes problem). No exact solution exists for the turbulent case, thus, understanding of the main flow characteristics comes from experimental work. Several researchers have reported experimental work in oscillatory boundary layers since the 1960's; however, larger scale facilities and the development of newer measurement techniques with improved temporal and spatial resolution in recent years provides a unique opportunity to achieve a better understanding about this type of flows. Several experiments were performed in the Large Oscillatory Water and Sediment Tunnel (LOWST) facility at the Ven Te Chow Hydrosystems Laboratory, for a range of Reynolds wave numbers between 6x10^4 < Rew < 6x10^6 over a flat and smooth bottom. A 3D Laser Doppler Velocimetry (LDV) system was used to measure instantaneous flow velocities with a temporal resolution up to ~ 1,000 Hz. It was mounted on a 3-axis traverse with a spatial resolution of 0.01 mm in all three directions. The closest point to the bottom was measured at z = 0.2 mm (z+ ≈ 4), which allowed to capture boundary layer features with great detail. In order to achieve true 3D measurements, 2 probes were used on a perpendicular configuration, such that u and w components were measured from a probe on the side of the flume and v component was measured from a probe pointing down through and access window on top of the flume. The top probe was submerged in a water container, such that the focal length remained constant and coincidence in the measurement volume for all 3 components was maintained when traversing the probes along the measurement profiles. Results show the existence of high turbulence levels inside the boundary layer up to about 30 mm away from the bottom. The streamwise component u shows greater intensities closer to the bottom and ahead of the freestream velocity maximum. On the contrary, the vertical component w shows smaller values of turbulent intensity, located higher up in the profile and lagging with respect to the freestream velocity maximum. Meanwhile, the spanwise component v shows similar intensities than w, happening in phase with it, but distributed all along the boundary layer, overlapping the areas of greater intensity of u and w. In addition, wall shear stress and other turbulent magnitudes related to the boundary layer were analyzed from the experimental results obtained through this research.

Summary of experimentally determined facts concerning the behavior of the boundary layer and performance of boundary layer measurements. [considering sailing flight

NASA Technical Reports Server (NTRS)

Vanness, W.

1978-01-01

A summary report of boundary layer studies is presented. Preliminary results of experimental measurements show that: (1) A very thin layer (approximately 0.4 mm) of the boundary layer seems to be accelerated; (2) the static pressure of the outer flow does not remain exactly constant through the boundary layer; and (3) an oncoming boundary layer which is already turbulent at the suction point can again become laminar behind this point without being completely sucked off.

Mise en oeuvre et etalonnage d'une soufflerie de recherche sur les couches limites

NASA Astrophysics Data System (ADS)

Pioton, Julien

In order to reproduce a turbulent boundary layer separation bubble in a laboratory at the École de Technologie Supérieure of Montreal, an open-circuit wind tunnel equipped with a blow-down centrifugal fan has been implemented and calibrated for this research project. The methodology for the conception of the wind tunnel components, based on the results obtained from previous experiments, has been validated by the comparison between experimental and theoretical pressure losses along the wind tunnel. Dimensionless mean axial velocity measurements in the working section have showed an irrotational uniform flow zone at the contraction end, which demonstrates the satisfactory performance of the flowconditioning components located upstream from the working section. Mean axial velocity and total pressure measurements along the working section have allowed for estimates of the location of boundary between irrotational and rotational flow at the separation bubble. The maximum mean height of the boundary layer has been estimated at around 15 cm. Oil film visualisations have revealed a mean bubble separation length of approximately 52 cm. Theses oil visualisations, supported by mean lateral velocity measurements in the current configuration of the working section, have indicated important three-dimensional effects and significant dissymmetry in the vicinity of the separation and reattachment zones at the separation bubble.

Displacements of Metallic Thermal Protection System Panels During Reentry

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Blosser, Max L.; Wurster, Kathryn E.

2006-01-01

Bowing of metallic thermal protection systems for reentry of a previously proposed single-stage-to-orbit reusable launch vehicle was studied. The outer layer of current metallic thermal protection system concepts typically consists of a honeycomb panel made of a high temperature nickel alloy. During portions of reentry when the thermal protection system is exposed to rapidly varying heating rates, a significant temperature gradient develops across the honeycomb panel thickness, resulting in bowing of the honeycomb panel. The deformations of the honeycomb panel increase the roughness of the outer mold line of the vehicle, which could possibly result in premature boundary layer transition, resulting in significantly higher downstream heating rates. The aerothermal loads and parameters for three locations on the centerline of the windward side of this vehicle were calculated using an engineering code. The transient temperature distributions through a metallic thermal protection system were obtained using 1-D finite volume thermal analysis, and the resulting displacements of the thermal protection system were calculated. The maximum deflection of the thermal protection system throughout the reentry trajectory was 6.4 mm. The maximum ratio of deflection to boundary layer thickness was 0.032. Based on previously developed distributed roughness correlations, it was concluded that these defections will not result in tripping the hypersonic boundary layer.

Instability of fluid flow over saturated porous medium

NASA Astrophysics Data System (ADS)

Lyubimova, Tatyana; Kolchanova, Ekaterina; Lyubimov, Dmitry

2013-04-01

We investigate the stability of a fluid flow over a saturated porous medium. The problem is of importance due to the applications to washing out of contaminants from the bottom layer of vegetation, whose properties are similar to the properties of porous medium. In the case of porous medium with the relatively high permeability and porosity the flow involves a part of the fluid saturating the porous medium, with the tangential fluid velocity drop occurring because of the resistance of the solid matrix. The drop leads to the instability analogous to Kelvin-Helmholtz one accompanied by the formation of travelling waves. In the present paper we consider a two-layer system consisting of a pure fluid layer and a porous layer saturated by the fluid located underneath. The system is bounded by a rigid surface at the bottom and a non-deformable free surface at the top. It is under the gravity and inclined at a slight angle to the horizontal axis. The boundary conditions at the interface between the fluid and porous layers are the continuity of fluid velocities and the balance of normal and tangential stresses taking into account the resistance of the solid matrix with respect to the fluid flow near the interface [1-2]. The problem is solved in the framework of the Brinkman model applying the classical shooting algorithm with orthogonalization. The stability boundaries of the stationary fluid flow over the saturated porous medium with respect to the small oscillatory perturbations are obtained for the various values of the Darcy number and the ratio of the porous layer thickness to the full thickness of the system d. It was shown that at the d > 0.5 with increasing the porous layer thickness (or with decreasing of the fluid layer thickness) the stability threshold rises. This is because of the fact that the instability is primarily caused by perturbations located in the fluid layer. At the d < 0.5 the reduction of the porous layer thickness leads to the stability threshold growth. The numerical calculations were also conducted for nonlinear regimes of the flow applying the finite-element method. Flow characteristics are determined at supercritical values of parameters. The work was made under the financial support of Russian Foundation for Basic Research (Grant 12-01-00795). 1. Ochoa-Tapia J. A. and Whitaker S. Momentum transfer at the boundary between a porous medium and a homogeneous fluid-I. Theoretical development. Int. J. Heat Mass Transfer. 1995. N 38. P. 2635-2646. 2. Ochoa-Tapia J. A. and Whitaker S. Momentum transfer at the boundary between a porous medium and a homogeneous fluid-II. Comparison with experiment. Int. J. Heat Mass Transfer. 1995. N 38. P. 2647-2655.

Boundary-layer receptivity due to distributed surface imperfections of a deterministic or random nature

NASA Technical Reports Server (NTRS)

Choudhari, Meelan

1992-01-01

Acoustic receptivity of a Blasius boundary layer in the presence of distributed surface irregularities is investigated analytically. It is shown that, out of the entire spatial spectrum of the surface irregularities, only a small band of Fourier components can lead to an efficient conversion of the acoustic input at any given frequency to an unstable eigenmode of the boundary layer flow. The location, and width, of this most receptive band of wavenumbers corresponds to a relative detuning of O(R sub l.b.(exp -3/8)) with respect to the lower-neutral instability wavenumber at the frequency under consideration, R sub l.b. being the Reynolds number based on a typical boundary-layer thickness at the lower branch of the neutral stability curve. Surface imperfections in the form of discrete mode waviness in this range of wavenumbers lead to initial instability amplitudes which are O(R sub l.b.(exp 3/8)) larger than those caused by a single, isolated roughness element. In contrast, irregularities with a continuous spatial spectrum produce much smaller instability amplitudes, even compared to the isolated case, since the increase due to the resonant nature of the response is more than that compensated for by the asymptotically small band-width of the receptivity process. Analytical expressions for the maximum possible instability amplitudes, as well as their expectation for an ensemble of statistically irregular surfaces with random phase distributions, are also presented.

Observations of transitional tidal boundary layers and their impact on sediment transport in the Great Bay, NH

NASA Astrophysics Data System (ADS)

Koetje, K. M.; Foster, D. L.; Lippmann, T. C.

2017-12-01

Observations of the vertical structure of tidal flows obtained in 2016 and 2017 in the Great Bay Estuary, NH show evidence of transitional tidal boundary layers at deployment locations on shallow mudflats. High-resolution bottom boundary layer currents, hydrography, turbidity, and bed characteristics were observed with an acoustic Doppler current profiler (ADCP), an acoustic Doppler velocimeter (ADV), conductivity-depth-temperature (CTD) sensors, optical backscatter sensors, multibeam bathymetric surveys, and sediment grab samples and cores. Over the 2.5 m tidal range and at water depths ranging from 0.3 m to 1.5 m at mean lower low water, peak flows ranged from 10 cm/s to 30 cm/s and were primarily driven by the tides. A downward-looking ADCP captured the velocity profile over the lowest 1 m of the water column. Results consistently show a dual-log layer system, with evidence of a lower layer within 15 cm of the bed, another layer above approximately 30 cm from the bed, and a transitional region where the flow field rotates between that the two layers that can be as much as 180 degrees out of phase. CTD casts collected over a complete tidal cycle suggest that the weak thermohaline stratification is not responsible for development of the two layers. On the other hand, acoustic and optical backscatter measurements show spatial and temporal variability in suspended sediments that are dependant on tidal phase. Current work includes an examination of the relationship between sediment concentrations in the water column and velocity profile characteristics, along with an effort to quantify the impact of rotation and dual-log layers on bed stress.

Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions

NASA Technical Reports Server (NTRS)

Wood, William A.; Erickson, David W.; Greene, Francis A.

2007-01-01

Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.

Lidar Measurements of Wind, Moisture and Boundary Layer Evolution in a Dryline During IHOP2002

NASA Technical Reports Server (NTRS)

Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhien; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David

2003-01-01

Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air -mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents groundbased measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International BO Project (IHOP-2002), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. The chief goal of IHOP-2002 is to improve characterization of the four-dimensional (4-D) distribution of water vapor and its application to improving the understanding and prediction of convection

Lidar Measurements of Wind, Moisture, and Boundary Layer Evolution in a Dry Line during 1HOP 2002

NASA Technical Reports Server (NTRS)

Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhe-In; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David; Palm, Stephen

2002-01-01

Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These . variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air-mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International H2O Project (MOP-2002), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. The chief goal of MOP-2002 is to improve characterization of the four-dimensional (4-D) distribution of water vapor and its application to improving the understanding and prediction of convection

Calculation methods for compressible turbulent boundary layers, 1976

NASA Technical Reports Server (NTRS)

Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

1977-01-01

Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.

Preliminary Note on a Correlation of a Boundary-Layer Transition Results on Highly Cooled Blunt Bodies

NASA Technical Reports Server (NTRS)

Wisniewski, Richard J.

1957-01-01

Transition data on highly cooled blunt bodies are correlated in terms of the ratio of wall to local-stream enthalpy, Reynolds number based on displacement thickness, and location of transition. The proposed correlation, although not sensitive enough to predict the exact location of transition does predict the enthalpy ratio below which very early transition on blunt bodies is expected. The correlation is not altered by moderate amounts of surface roughness; however, the location of transition may well be affected by roughness.

Proterozoic crustal boundary in the southern part of the Illinois Basin

USGS Publications Warehouse

Heigold, P.C.; Kolata, Dennis R.

1993-01-01

Recently acquired COCORP and proprietary seismic reflection data in the southern part of the Illinois Basin, combined with other geological and geophysical data, indicate that a WNW-trending Proterozoic terrane boundary (40 km wide) lies within basement. The boundary is characterized by the termination of subhorizontal Proterozoic reflectors and associated diffraction patterns along a line coinciding with the major magnetic lineament in this region (South Central Magnetic Lineament). North of the boundary, where reflectors thought to represent a sequence of layered Proterozoic rocks in the upper crust are widespread and as much as 11 km thick, total magnetic intensity values are relatively high, suggesting layers of rock with high magnetic susceptibility. To the south, the Proterozoic rocks are acoustically transparent on seismic reflection sections and total magnetic intensity values are relatively low. Moreover, relatively high Bouguer gravity anomaly values to the south may be caused by a dense, altered, lower crustal layer similar to that interpreted from deep seismic refraction studies to underlie the northern Mississippi Embayment. The boundary lies along the projected trend of the northern margin of the Early Proterozoic Central Plains orogen and we suggest that it marks the convergent margin of this orogen. Reactivation of the boundary and the associated zone of weakness during late Paleozoic times apparently resulted in structural deformation in the southern part of the Illinois Basin, including movement along the Cottage Grove Fault System and Ste. Genevieve Fault Zone and igneous activity at Hicks Dome. In addition to the role played by this crustal boundary in the evolution of the Illinois Basin, its location between the Wabash Valley Seismic Zone to the northeast and the New Madrid Seismic Zone to the southwest may be a significant factor in present-day seismicity. ?? 1993.

A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers

NASA Technical Reports Server (NTRS)

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Microgravity Effects on Plant Boundary Layers

NASA Technical Reports Server (NTRS)

Stutte, Gary; Monje, Oscar

2005-01-01

The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

Boundary layer friction of solvate ionic liquids as a function of potential.

PubMed

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lillo, Thomas; Rooyen, Isabella Van

2015-05-01

Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory’s AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number ofmore » nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ~23 μm along a radial direction through the 35 μm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ~24 μm in the SiC layer. Also, Pd-rich, nano-precipitates (~10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not all grain boundaries and triple junctions contained precipitates with fission products and/or uranium, along with the differences in migration behavior between Pd, Ag and U, it was concluded that crystallographic grain boundary and triple junction parameters likely influence migration behavior.« less

Turbulent Combustion Study of Scramjet Problem

DTIC Science & Technology

2015-08-01

boundary layer model for 2D simulations of a supersonic flat plate boundary layer . The inflow O2 has an average density of...flow above the flat plate has a transition from a laminar boundary layer to a turbulent boundary layer at a position downstream from the inlet. The...δ. Chapman [13] estimated the number of cells need to resolve the outer layer is proportional to Re0.4 for flat plat boundary layer and

Experimental Study of Boundary Layer Behavior in a Simulated Low Pressure Turbine. Degree awarded by the University of Toledo, May 1998

NASA Technical Reports Server (NTRS)

Shyne, Rickey J.

1998-01-01

A detailed investigation of the flow physics occurring on the suction side of a simulated Low Pressure Turbine (LPT) blade was performed. A contoured upper wall was designed to simulate the pressure distribution of an actual LPT blade onto a flat plate. The experiments were carried out at Reynolds numbers of 100,000 and 250,000 with three levels of freestream turbulence. Freestream turbulence levels ranging from 0.8% to 3% was used in this experiment. Smoke-wire flow visualization data was used to confirm that the boundary layer was separated and formed a bubble. Hot-wires (single and x-wire) and surface mounted hot-film gases and static pressure taps were used to map the flowfield. The transition process over the separated flow region is observed to be similar to a laminar free shear layer flow with the formation of a large coherent eddy structure. For each condition, the locations defining the separation bubble were determined by careful examination of pressure and mean velocity profile data. Transition onset location and length determined from intermittency profiles decrease as freestream turbulence levels increase. Additionally, the length and height of the laminar separation bubbles were observed to be inversely proportional to the levels of freestream turbulence.

Diurnal and seasonal variation of mercury species at coastal-suburban, urban, and rural sites in the southeastern United States

NASA Astrophysics Data System (ADS)

Nair, Udaysankar S.; Wu, Yuling; Walters, Justin; Jansen, John; Edgerton, Eric S.

2012-02-01

Observations for the 2005-2008 time period from three Southeastern Aerosol Research and Characterization (SEARCH) air quality monitoring sites are examined for diurnal and seasonal variation in concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle bound mercury (HgP < 2.5 μm). The sites are located at 1) a suburban-coastal location near Pensacola, Florida (OLF), 2) an urban location in Birmingham, Alabama (BHM), and 3) a rural location west-northwest of Atlanta, Georgia (YRK). Average concentrations of GEM at both OLF and YRK are 1.35 ng m -3, whereas at BHM it is 2.12 ng m -3. All sites show increase in GEM concentration during the morning hours (0.023 and 0.011 ng m -3hr -1 at OLF and YRK between 6 and 10 AM, 0.038 ng m -3hr -1 at BHM between 5 and 10 AM) due to downward mixing of higher concentrations from the residual layer, after which OLF and YRK show negligible variation compared to decrease in concentration at BHM (2.3-1.9 ng m -3 from 10 AM to 6 PM). All sites show seasonal variation of GEM with enhanced concentrations found in winter and spring. Average GOM concentrations are 4.26, 8.55, and 78.2 pg m -3 at OLF, YRK, and BHM, respectively. Seasonally, GOM values are enhanced during fall and spring. All sites undergo a sinusoidal daytime variation of GOM that peaks in the afternoon, while BHM additionally exhibits an early morning enhancement likely caused by vertical mixing. The average HgP concentrations at OLF, YRK, and BHM are 2.49, 4.43, and 39.5 pg m -3, respectively. At OLF, vertical mixing causes an early morning increase in HgP concentration followed by an afternoon decline during all seasons. A daytime increase in HgP is found at YRK for all seasons, while at BHM, nocturnal accumulation followed by a daytime decline is also found for most seasons except winter. In winter, concentrations increase due to vertical mixing in the morning and then decline as the boundary layer grows. Boundary layer processes appear to play an important role in the seasonal and diurnal variation of Hg species and further investigation utilizing a boundary layer process model is warranted.

High-Fidelity PIV of a Naturally Grown High Reynolds Number Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Biles, Drummond; White, Chris; Klewicki, Joeseph

2017-11-01

High-fidelity particle image velocimetry data acquired in the Flow Physics Facility (FPF) at the University of New Hampshire is presented. Having a test section length of 72m, the FPF employs the ``big and slow'' approach to obtain well-resolved turbulent boundary layer measurements at high Reynolds number. We report on PIV measurements acquired in the streamwise-wall-normal plane at a downstream position 59m from the test-section inlet over the friction Reynolds number range 7000 < Reτ < 15000 . Local flow tracer seeding is employed through a wall-mounted slot fed by a large volume plenum located 13.4m upstream of the PIV measurement station. Both time-independent and time-dependent turbulent flow statistics are presented and compared to existing data.

Subsonic Investigation of a Leading-Edge Boundary Layer Control Suction System on a High-Speed Civil Transport Configuration

NASA Technical Reports Server (NTRS)

Campbell, Bryan A.; Applin, Zachary T.; Kemmerly, Guy T.; Coe, Paul L., Jr.; Owens, D. Bruce; Gile, Brenda E.; Parikh, Pradip G.; Smith, Don

1999-01-01

A wind tunnel investigation of a leading edge boundary layer control system was conducted on a High Speed Civil Transport (HSCT) configuration in the Langley 14- by 22-Foot Subsonic Tunnel. Data were obtained over a Mach number range of 0.08 to 0.27, with corresponding chord Reynolds numbers of 1.79 x 10(exp 6) to 5.76 x 10(exp 6). Variations in the amount of suction, as well as the size and location of the suction area, were tested with outboard leading edge flaps deflected 0 and 30 deg and trailing-edge flaps deflected 0 and 20 deg. The longitudinal and lateral aerodynamic data are presented without analysis. A complete tabulated data listing is also presented herein.

Boundary-Layer Transition on the N.A.C.A. 0012 and 23012 Airfoils in the 8-Foot High-Speed Wind Tunnel, Special Report

NASA Technical Reports Server (NTRS)

Becker, John V.

1940-01-01

Determinations of boundary-layer transition on the NACA 0012 and 2301 airfoils were made in the 8-foot high-speed wind tunnel over a range of Reynolds Numbers from 1,600,000 to 16,800,000. The results are of particular significance as compared with flight tests and tests in wind tunnels of appreciable turbulence because of the extremely low turbulence in the high-speed tunnel. A comparison of the results obtained on NACA 0012 airfoils of 2-foot and 5-foot chord at the same Reynolds Number permitted an evaluation of the effect of compressibility on transition. The local skin friction along the surface of the NACA 0012 airfoil was measured at a Reynolds Number of 10,000,000. For all the lift coefficient at which tests were made, transition occurred in the region of estimated laminar separation at the low Reynolds Numbers and approach the point of minimum static pressure as a forward limit at the high Reynolds Numbers. The effect of compressibility on transition was slight. None of the usual parameters describing the local conditions in the boundary layer near the transition point served as an index for locating the transition point. As a consequence of the lower turbulence in the 8-foot high-speed tunnel, the transition points occurred consistently farther back along the chord than those measured in the NACA full-scale tunnel. An empirical relation for estimating the location of the transition point for conventional airfoils on the basis of static-pressure distribution and Reynolds Number is presented.

Lagrangian large eddy simulations of boundary layer clouds on ERA-Interim and ERA5 trajectories

NASA Astrophysics Data System (ADS)

Kazil, J.; Feingold, G.; Yamaguchi, T.

2017-12-01

This exploratory study examines Lagrangian large eddy simulations of boundary layer clouds along wind trajectories from the ERA-Interim and ERA5 reanalyses. The study is motivated by the need for statistically representative sets of high resolution simulations of cloud field evolution in realistic meteorological conditions. The study will serve as a foundation for the investigation of biomass burning effects on the transition from stratocumulus to shallow cumulus clouds in the South-East Atlantic. Trajectories that pass through a location with radiosonde data (St. Helena) and which exhibit a well-defined cloud structure and evolution were identified in satellite imagery, and sea surface temperature and atmospheric vertical profiles along the trajectories were extracted from the reanalysis data sets. The System for Atmospheric Modeling (SAM) simulated boundary layer turbulence and cloud properties along the trajectories. Mean temperature and moisture (in the free troposphere) and mean wind speed (at all levels) were nudged towards the reanalysis data. Atmospheric and cloud properties in the large eddy simulations were compared with those from the reanalysis products, and evaluated with satellite imagery and radiosonde data. Simulations using ERA-Interim data and the higher resolution ERA5 data are contrasted.

Detailed Study of Moderately Swept Impinging Oblique Shock/Boundary-Layer Interaction in Mach 2.3 Flow

NASA Astrophysics Data System (ADS)

Threadgill, James; Doerhmann, Adam; Little, Jesse

2017-11-01

A detailed experimental investigation of an impinging oblique Shock/Boundary Layer Interaction (SBLI) with 30° sweep in Mach 2.3 flow has been conducted. Despite its non-dimensional form, this canonical SBLI configuration has attracted little attention and remains poorly understood. Using a 12 .5° shock generator mounted in the freestream over a turbulent boundary layer, the interaction has been characterized with oil flow visualization, fast-response pressure transducers, and particle image velocimetry. Velocity vectors are used to extract the 3D interaction structure. These data are compared to wall pressure measurements and surface skin-friction streamlines. A local collapse of data normal to separation indicates a swept equivalence to Free Interaction Theory, albeit at a lower angle of sweep than imposed by the shock generator. Conditions at reattachment align with the imposed shock. Low-frequency shock motion near separation is observed, analogous to unswept SBLIs, with significant correlations that indicate spanwise traveling ripples in the shock foot. However, the magnitude of wall-pressure unsteadiness in this location is lower and shifted to higher frequencies than observed in equivalent unswept SBLI counterparts. Supported by the Air Force Office of Scientific Research (FA9550-15-1-0430).

Flow Visualization by Elastic Light Scattering in the Boundary Layer of a Supersonic Flow

NASA Technical Reports Server (NTRS)

Herring, G. C.; Hillard, Mervin E., Jr.

2000-01-01

We demonstrate instantaneous flow visualization of the boundary layer region of a Mach 2.5 supersonic flow over a flat plate that is interacting with an impinging shock wave. Tests were performed in the Unitary Plan Wind Tunnel (UPWT) at NASA Langley Research Center. The technique is elastic light scattering using 10-nsec laser pulses at 532 nm. We emphasize that no seed material of any kind, including water (H2O), is purposely added to the flow. The scattered light comes from a residual impurity that normally exists in the flow medium after the air drying process. Thus, the technique described here differs from the traditional vapor-screen method, which is typically accomplished by the addition of extra H2O vapor to the airflow. The flow is visualized with a series of thin two-dimensional light sheets (oriented perpendicular to the streamwise direction) that are located at several positions downstream of the leading edge of the model. This geometry allows the direct observation of the unsteady flow structure in the spanwise dimension of the model and also allows the indirect observation of the boundary layer growth in the streamwise dimension.

Calibration of a γ- Re θ transition model and its application in low-speed flows

NASA Astrophysics Data System (ADS)

Wang, YunTao; Zhang, YuLun; Meng, DeHong; Wang, GunXue; Li, Song

2014-12-01

The prediction of laminar-turbulent transition in boundary layer is very important for obtaining accurate aerodynamic characteristics with computational fluid dynamic (CFD) tools, because laminar-turbulent transition is directly related to complex flow phenomena in boundary layer and separated flow in space. Unfortunately, the transition effect isn't included in today's major CFD tools because of non-local calculations in transition modeling. In this paper, Menter's γ- Re θ transition model is calibrated and incorporated into a Reynolds-Averaged Navier-Stokes (RANS) code — Trisonic Platform (TRIP) developed in China Aerodynamic Research and Development Center (CARDC). Based on the experimental data of flat plate from the literature, the empirical correlations involved in the transition model are modified and calibrated numerically. Numerical simulation for low-speed flow of Trapezoidal Wing (Trap Wing) is performed and compared with the corresponding experimental data. It is indicated that the γ- Re θ transition model can accurately predict the location of separation-induced transition and natural transition in the flow region with moderate pressure gradient. The transition model effectively imporves the simulation accuracy of the boundary layer and aerodynamic characteristics.

Most-Critical Transient Disturbances in an Incompressible Flat-Plate Boundary Layer

NASA Astrophysics Data System (ADS)

Monschke, Jason; White, Edward

2015-11-01

Transient growth is a linear disturbance growth mechanism that plays a key role in roughness-induced boundary-layer transition. It occurs when superposed stable, non-orthogonal continuous spectrum modes experience algebraic disturbance growth followed by exponential decay. Algebraic disturbance growth can modify the basic state making it susceptible to secondary instabilities rapidly leading to transition. Optimal disturbance theory was developed to model the most-dangerous disturbances. However, evidence suggests roughness-induced transient growth is sub-optimal yet leads to transition earlier than optimal theory suggests. This research computes initial disturbances most unstable to secondary instabilities to further develop the applicability of transient growth theory to surface roughness. The main approach is using nonlinear adjoint optimization with solutions of the parabolized Navier-Stokes and BiGlobal stability equations. Two objective functions were considered: disturbance kinetic energy growth and sinuous instability growth rate. The first objective function was used as validation of the optimization method. Counter-rotating streamwise vortices located low in the boundary layer maximize the sinuous instability growth rate. The authors would like to acknowledge NASA and the AFOSR for funding this work through AFOSR Grant FA9550-09-1-0341.

X-33 Hypersonic Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II

1999-01-01

Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.

Reversing flow development in a separating turbulent boundary layer

NASA Astrophysics Data System (ADS)

Santos, Leonardo; Lang, Amy; Wahidi, Redha; Bonacci, Andrew

2016-11-01

Fast swimming sharks have micro-structures on their skin consisting of bristling scales. These scales are hypothesized to bristle in response to backflow generated from the separated turbulent boundary layer (TBL) in regions of adverse pressure gradient (APG) on the shark body. Vortices are trapped in the cavities between the scales, which induce momentum exchange between the higher momentum fluid in the outer flow and that in the separated region. This momentum exchange causes reattachment of the separated TBL, causing the scales to return to the unbristled location, and the cycle continues. The rows of scales have widths that are comparable to the spanwise length scale of the intermittent backflow patches that appear in the region of incipient detachment of TBLs. In this experimental investigation, correlations between the shark scale's width and the spanwise size of the low backflow streaks are examined, as well as details of the incipient detachment region. The experiments are conducted in a water tunnel facility and the flow field is measured using PIV. Turbulent boundary layers are subjected to an APG via a rotating cylinder. Separated TBLs are investigated on a flat plate. The authors would like to greatfully acknowledge the Army Research Office for funding this project.

On the role of surface friction in tropical cyclone intensification

NASA Astrophysics Data System (ADS)

Wang, Yuqing

2017-04-01

Recent studies have debated on whether surface friction is positive or negative to tropical cyclone intensification in the view on angular momentum budget. That means whether the frictionally induced inward angular momentum transport can overcome the loss of angular momentum to the surface due to surface friction itself. Although this issue is still under debate, this study investigates another implicit dynamical effect, which modifies the radial location and strength of eyewall convection. We found that moderate surface friction is necessary for rapid intensity of tropical cyclones. This is demonstrated first by a simple coupled dynamical system that couples a multi-level boundary layer model and a shallow water equation model above with mass source parameterized by mass flux from the boundary layer model below, and then by a full physics model. The results show that surface friction leads to the inward penetration of inflow under the eyewall, shift the boundary layer mass convergence slightly inside the radius of maximum wind, and enhance the upward mass flux, and thus diabatic heating in the eyewall and intensification rate of a TC. This intensification process is different from the direct angular momentum budget previously used to explain the role of surface friction in tropical cyclone intensification.

Characteristic Lifelength of Coherent Structure in the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Palumbo, Daniel L.

2006-01-01

A characteristic lifelength is defined by which a Gaussian distribution is fit to data correlated over a 3 sensor array sampling streamwise sidewall pressure. The data were acquired at subsonic, transonic and supersonic speeds aboard a Tu-144. Lifelengths are estimated using the cross spectrum and are shown to compare favorably with Efimtsov's prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distribution, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data can be converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize coherent structure in the turbulent boundary layer.

Evolution of vortex-surface fields in transitional boundary layers

NASA Astrophysics Data System (ADS)

Yang, Yue; Zhao, Yaomin; Xiong, Shiying

2016-11-01

We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers. The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11472015, 11522215 and 11521091), and the Thousand Young Talents Program of China.

Observations of the Nocturnal Boundary Layer and Morning Transitional Periods in Houston, Texas during the TexAQS II Campaign

NASA Astrophysics Data System (ADS)

Day, B. M.; Clements, C. B.; Rappenglueck, B.

2007-12-01

High-temporal resolution tethersonde profiles taken during the TexAQS II field campaign in Houston were used to study the overnight development and progression of the nocturnal boundary layer (NBL) and the evolution of the convective boundary layer after sunrise. The measurements were made at the University of Houston campus, located approximately 4 km southeast of the downtown Houston central business district, and consisted of vertical profiles of potential temperature, water vapor mixing ratio, wind speed, wind direction, and ozone concentration. Profile heights averaged 250 m AGL with a few reaching 400 m AGL. Profiles were taken at approximately 30 min intervals throughout 4 nights during Intensive Observational Periods (IOPs), including both the evening and morning transitional periods. Tethersonde experiments also were performed during several additional morning break-up periods during the campaign. Preliminary results from the overnight experiments of Sept 7-8 and Sept 14-15, 2006 showed different NBL evolutions. Sept 7-8 exhibited a stronger and deeper inversion compared with Sept 14-15 when the inversion was weak with a fairly constant height throughout the night. The Sept 7-8 profiles showed elevated bluff-like structures in the virtual potential temperature profiles between 0300-0400 CDT, indicating neutral stability within the 40-90 m AGL level. And, just before sunrise a neutral layer with constant potential temperature developed between the surface and 75 m AGL reflecting horizontal cold air advection. Further analyses will be presented for other vertical profiles taken during the campaign, including the additional overnight profiles as well as the profiles taken during the morning transition to the convective boundary layer.

Full-Scale Wind-Tunnel Investigation of a Jet Flap in Conjunction with a Plain Flap with Blowing Boundary-Layer Control on a 35 deg Sweptback-Wing Airplane

NASA Technical Reports Server (NTRS)

Aoyagi, Kiyoshi; Hickey, David H.

1959-01-01

Previous investigations have shown that increased blowing at the hinge-line radius of a plain flap will give flap lift increases above that realized with boundary-layer control. Other experiments and theory have shown that blowing from a wing trailing edge, through the jet flap effect, produced lift increases. The present investigation was made to determine whether blowing simultaneously at the hinge-line radius and trailing edge would be more effective than blowing separately at either location. The tests were made at a Reynolds number of 4.5 x 10(exp 6) with a 35 deg sweptback-wing airplane. For this report, only the lift data are presented. Of the three flap blowing arrangements tested, blowing distributed between the trailing edge and the hinge-line radius of a plain flap was found to be superior to blowing at either location separately at the plain flap deflections of interest. Comparison of estimated and experimental jet flap effectiveness was fair.

The Gale Crater Mound in a Regional Geologic Setting

NASA Technical Reports Server (NTRS)

Allen, Carlton C.; Korn, L. K.

2012-01-01

The Mars Science Laboratory Rover Curiosity is commencing a two-year investigation of Gale crater and Mt. Sharp, the crater s prominent central mound. Gale is a 155 km, late Noachian / early Hesperian impact crater located near the dichotomy boundary separating the southern highlands from the northern plains. The central mound is composed of layered sedimentary rock, with upper and lower mound units separated by a prominent erosional unconformity (Milliken et al., 2010). The lower mound is of particular interest, as it contains secondary minerals indicative of a striking shift from water-rich to water-poor conditions on early Mars. A key unknown in the history of Gale is the relationship between the sedimentary units in the mound and sedimentary sequences in the surrounding region. We employed orbital remote sensing data to determine if areas within a 1,000 km radius of Gale match the characteristics of sedimentary units in Mt. Sharp. Regions of interest were defined based on: the mound s inferred age (late Noachian to early Hesperian), altitude range (-4,600 m to +400 m), and THEMIS nighttime brightness (a proxy for thermal inertia). This combination of characteristics is matched by two extensive units, the late Noachian subdued cratered unit Npl2 and Noachian / Hesperian undivided material HNu (Greeley and Guest, 1987), located along the dichotomy. Geomorphic units have been mapped within the Gale mound by Thomson et al. (2011) based on albedo, layering and erosional characteristics. Using orbital CTX, MOC and HiRISE images we examined all areas within our regions of interest for analogous geomorphic units in the same altitude ranges as the corresponding units in Mt. Sharp. The most convincing geomorphic analogs to lower mound units, dominated by fine-scale layering and prominent yardangs, were located approximately 200 km northeast and southeast of Gale in late Noachian unit Npl2. The most convincing geomorphic analogs to upper mound layered units are located 250 900 km northwest of Gale in unit HNu, estimated to span the Noachian / Hesperian boundary.

Wind-Turbine Wakes in a Convective Boundary Layer: A Wind-Tunnel Study

NASA Astrophysics Data System (ADS)

Zhang, Wei; Markfort, Corey D.; Porté-Agel, Fernando

2013-02-01

Thermal stability changes the properties of the turbulent atmospheric boundary layer, and in turn affects the behaviour of wind-turbine wakes. To better understand the effects of thermal stability on the wind-turbine wake structure, wind-tunnel experiments were carried out with a simulated convective boundary layer (CBL) and a neutral boundary layer. The CBL was generated by cooling the airflow to 12-15 °C and heating up the test section floor to 73-75 °C. The freestream wind speed was set at about 2.5 m s-1, resulting in a bulk Richardson number of -0.13. The wake of a horizontal-axis 3-blade wind-turbine model, whose height was within the lowest one third of the boundary layer, was studied using stereoscopic particle image velocimetry (S-PIV) and triple-wire (x-wire/cold-wire) anemometry. Data acquired with the S-PIV were analyzed to characterize the highly three-dimensional turbulent flow in the near wake (0.2-3.2 rotor diameters) as well as to visualize the shedding of tip vortices. Profiles of the mean flow, turbulence intensity, and turbulent momentum and heat fluxes were measured with the triple-wire anemometer at downwind locations from 2-20 rotor diameters in the centre plane of the wake. In comparison with the wake of the same wind turbine in a neutral boundary layer, a smaller velocity deficit (about 15 % at the wake centre) is observed in the CBL, where an enhanced radial momentum transport leads to a more rapid momentum recovery, particularly in the lower part of the wake. The velocity deficit at the wake centre decays following a power law regardless of the thermal stability. While the peak turbulence intensity (and the maximum added turbulence) occurs at the top-tip height at a downwind distance of about three rotor diameters in both cases, the magnitude is about 20 % higher in the CBL than in the neutral boundary layer. Correspondingly, the turbulent heat flux is also enhanced by approximately 25 % in the lower part of the wake, compared to that in the undisturbed CBL inflow. This study represents the first controlled wind-tunnel experiment to study the effects of the CBL on wind-turbine wakes. The results on decreased velocity deficit and increased turbulence in wind-turbine wakes associated with atmospheric thermal stability are important to be taken into account in the design of wind farms, in order to reduce the impact of wakes on power output and fatigue loads on downwind wind turbines.

Evaluation of WRF physical parameterizations against ARM/ASR Observations in the post-cold-frontal region to improve low-level clouds representation in CAM5

NASA Astrophysics Data System (ADS)

Lamraoui, F.; Booth, J. F.; Naud, C. M.

2017-12-01

The representation of subgrid-scale processes of low-level marine clouds located in the post-cold-frontal region poses a serious challenge for climate models. More precisely, the boundary layer parameterizations are predominantly designed for individual regimes that can evolve gradually over time and does not accommodate the cold front passage that can overly modify the boundary layer rapidly. Also, the microphysics schemes respond differently to the quick development of the boundary layer schemes, especially under unstable conditions. To improve the understanding of cloud physics in the post-cold frontal region, the present study focuses on exploring the relationship between cloud properties, the local processes and large-scale conditions. In order to address these questions, we explore the WRF sensitivity to the interaction between various combinations of the boundary layer and microphysics parameterizations, including the Community Atmospheric Model version 5 (CAM5) physical package in a perturbed physics ensemble. Then, we evaluate these simulations against ground-based ARM observations over the Azores. The WRF-based simulations demonstrate particular sensitivities of the marine cold front passage and the associated post-cold frontal clouds to the domain size, the resolution and the physical parameterizations. First, it is found that in multiple different case studies the model cannot generate the cold front passage when the domain size is larger than 3000 km2. Instead, the modeled cold front stalls, which shows the importance of properly capturing the synoptic scale conditions. The simulation reveals persistent delay in capturing the cold front passage and also an underestimated duration of the post-cold-frontal conditions. Analysis of the perturbed physics ensemble shows that changing the microphysics scheme leads to larger differences in the modeled clouds than changing the boundary layer scheme. The in-cloud heating tendencies are analyzed to explain this sensitivity.

Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition

NASA Technical Reports Server (NTRS)

Grosch, C. E.

1980-01-01

A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.

Space shuttle: Directional and lateral stability and interference effects of cruise engine location on a 0.015 scale space shuttle

NASA Technical Reports Server (NTRS)

Buchholz, R. E.

1972-01-01

The results are presented that were obtained from a wind tunnel tests to improve space shuttle booster baseline lateral-directional stability, control characteristics, and cruise engine location optimization. Tests were conducted in a 7 x 10-foot transonic wind tunnel. The model employed was a 0.015-scale replica of a space shuttle booster. The three major objectives of this test were to determine the following: (1) force, static stability, and control effectiveness characteristics for varying angles of positive and negative wing dihedral and various combinations of wing tip and centerline dorsal fins; (2) force and static stability characteristics of cruise engines location on the body below the high aerodynamic canard; and (3) control effectiveness for the low-mounted wing configuration. The wing dihedral study was conducted at a cruise Mach number of 0.40 and simulated altitude of 10,000 feet. Portions of the test were conducted to determine the control surfaces stability and control characteristics over the Mach number range of 0.4 to 1.2. The aerodynamic characteristics determined are based on a unit Reynolds number of approximately 2 million per foot. Boundary layer trip strips were employed to induce boundary layer transition.

Analysis of turbulent free-convection boundary layer on flat plate

NASA Technical Reports Server (NTRS)

Eckert, E R G; Jackson, Thomas W

1950-01-01

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

Using Vertical electrical sounding survey and refraction seismic survey for determining the geological layers depths, the structural features and assessment groundwater in Aqaba area in South Jordan.

NASA Astrophysics Data System (ADS)

Akawwi, Emad; Alzoubi, Abdallah; Ben Abraham, Zvi; Rahamn Abo Alades, Abdel; Alrzouq, Rami; Tiber, Gidon; Neimi, Tina

2010-05-01

The study area is the Aqaba region (Southern wadi Araba basin). Aqaba region area located at 87900 and 89000 North and 147000 and 158000 East (Palestine grid). Tectonically Aqaba area lies within the tectonic plate boundary along the Arabian and African plate slide. This plate boundary comprises numerous and shot fault segments. The main aims of this study are to assessing the groundwater potential and its quality, to explain the subsurface geological conditions and support the ongoing geological, environmental and hydrogeological studies. Therefore, it was anticipated that the results of the geophysical surveying will give many different important parameters as The subsurface geological features, thicknesses of the different lithological units, depth to the bed rocks and depth to the water table. The groundwater can apply an important role in ensuring sustainable water supply in the area. This study was carried out in order to assess groundwater condition, geological layers thicknesses and structural features in Aqaba area by using vertical electrical sounding (VES) surveys and refraction seismic techniques. There are three geoelectrical cross section were carried out at different sites by using the Schlumberger array. The first cross section indicated three layers of different resistivity. The second cross section indicated four layers of different resistivity. The third geoelectrical cross sections indicated three layers. The refraction seismic method also has been conducted in the same area as VES. About 12 refraction seismic profiles have been carried out in the study area. The length of the first profile was 745 m at the direction N-S. This profile indicated two different layers with a different velocities. The length of the second profile was 1320 m with E-W direction. This profile indicated two different layers. The length of the third profile was about 515 m with a direction SE-NW. It recognized two different layers with a different velocities. The fourth profile was N-S direction and the length of this profile was 950 m. Two different layers were recognized along this profile. The fifth profile was located N-S with length about 340 m. Two layers were recognized from this profile. The sixth profile was located N-S direction and the length about 575 m. Three layers were recognized from this profile. The direction of the seventh profile was N-S with a length of about 235 m. two different layers were recognized the top layer was unconsolidated alluvium. The profile number 8 was located N-S with length about 232 m. two layers were conducted from this profile. The direction of ninth profile was NW-SE with length about 565 m. two layers were conducted along this profile. The length of the tenth profile was 235 m and the direction was N-S. Two layers with a different velocities were detected along this profile. Profile number eleven was located SW-NE with length about 475 m. two layers were recognized from this profile. The length of the last profile was 375 m with direction SE-NW. Two layers were conducted from this profile. It was found that the shallow aquifers exist at a depths ranging from 4 to 19 m and the relatively deep aquifers from 24 to 60 m below the ground surface. Keywords: Vertical electrical sounding, Aqaba, Resistivity, Groundwater, Layer depth, Geoelectrical.

Measurements and Modeling of the Mean and Turbulent Flow Structure in High-Speed Rough-Wall Non-Equilibrium Boundary Layers

DTIC Science & Technology

2010-01-25

study builds on three basic bodies of knowledge: (1) supersonic rough wall boundary layers, (2) distorted supersonic turbulent boundary layers, and...with the boundary layer turbulence . The present study showed that secondary distortions associated with such waves significantly affect the transport...38080 14. ABSTRACT The response of a supersonic high Reynolds number turbulent boundary layer flow subjected to mechanical distortions was

Understanding the Fundamental Roles of Momentum and Vorticity Injections in Flow Control

DTIC Science & Technology

2016-09-02

production by pitched and skewed jets in a turbulent boundary layer . AIAA Journal 30, 640–647. DISTRIBUTION A: Distribution approved for public release...adverse pressure gradient along the suction surface, which ultimately results in a separated boundary layer . Such behavior of the boundary layer can... boundary layer either directly or by utilizing free stream momentum to energize the boundary layer (Gad-el-Hak, 2000a). Directly adding momentum to the

Effect of an isolated semi-arid pine forest on the boundary layer height

NASA Astrophysics Data System (ADS)

Brugger, Peter; Banerjee, Tirtha; Kröniger, Konstantin; Preisler, Yakir; Rotenberg, Eyal; Tatarinov, Fedor; Yakir, Dan; Mauder, Matthias

2017-04-01

Forests play an important role for earth's climate by influencing the surface energy balance and CO2 concentrations in the atmosphere. Semi-arid forests and their effects on the local and regional climate are studied within the CliFF project (Climate Feedbacks and benefits of semi-arid Forests). This requires understanding of the atmospheric boundary layer over semi-arid forests, because it links the surface and the free atmosphere and determines the exchange of momentum, heat and trace gases. Our study site, Yatir, is a semi-arid isolated pine forest in the Negev desert in Israel. Higher roughness and lower albedo compared to the surrounding shrubland make it interesting to study the influences of the semi-arid Yatir forest on the boundary layer. Previous studies of the forest focused on the energy balance and secondary circulations. This study focuses on the boundary layer structure above the forest, in particular the boundary layer height. The boundary layer height is an essential parameter for many applications (e.g. construction of convective scaling parameters or air pollution modeling). We measured the boundary layer height upwind, over and downwind of the forest. In addition we measured at two sites wind profiles within the boundary layer and turbulent fluxes at the surface. This allows us to quantify the effects of the forest on boundary layer compared to the surrounding shrubland. Results show that the forest increases the boundary layer height in absence of a strong boundary layer top inversion. A model of the boundary layer height based on eddy-covariance data shows some agreement to the measurements, but fails during anticyclonic conditions and the transition to the nocturnal boundary layer. More complex models accounting for large scale influences are investigated. Further influences of the forest and surrounding shrubland on the turbulent transport of energy are discussed in a companion presentation (EGU2017-2219).

A nonperturbing boundary-layer transition detection

NASA Astrophysics Data System (ADS)

Ohare, J. E.

1985-01-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Karman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

A Nonperturbing Boundary-Layer Transition Detector

NASA Astrophysics Data System (ADS)

O'Hare, J. E.

1986-01-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Kaman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

NASA Technical Reports Server (NTRS)

Hingst, W. R.; Towne, C. E.

1974-01-01

An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

Infrared Imaging of Boundary Layer Transition Flight Experiments

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J., Jr.; Schwartz, Richard; Ross, Martin; Anderson, Brian; Campbell, Charles H.

2008-01-01

The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASA-sponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.

Optimally growing boundary layer disturbances in a convergent nozzle preceded by a circular pipe

NASA Astrophysics Data System (ADS)

Uzun, Ali; Davis, Timothy B.; Alvi, Farrukh S.; Hussaini, M. Yousuff

2017-06-01

We report the findings from a theoretical analysis of optimally growing disturbances in an initially turbulent boundary layer. The motivation behind this study originates from the desire to generate organized structures in an initially turbulent boundary layer via excitation by disturbances that are tailored to be preferentially amplified. Such optimally growing disturbances are of interest for implementation in an active flow control strategy that is investigated for effective jet noise control. Details of the optimal perturbation theory implemented in this study are discussed. The relevant stability equations are derived using both the standard decomposition and the triple decomposition. The chosen test case geometry contains a convergent nozzle, which generates a Mach 0.9 round jet, preceded by a circular pipe. Optimally growing disturbances are introduced at various stations within the circular pipe section to facilitate disturbance energy amplification upstream of the favorable pressure gradient zone within the convergent nozzle, which has a stabilizing effect on disturbance growth. Effects of temporal frequency, disturbance input and output plane locations as well as separation distance between output and input planes are investigated. The results indicate that optimally growing disturbances appear in the form of longitudinal counter-rotating vortex pairs, whose size can be on the order of several times the input plane mean boundary layer thickness. The azimuthal wavenumber, which represents the number of counter-rotating vortex pairs, is found to generally decrease with increasing separation distance. Compared to the standard decomposition, the triple decomposition analysis generally predicts relatively lower azimuthal wavenumbers and significantly reduced energy amplification ratios for the optimal disturbances.

Exploratory Investigation of the Effects of Boundary-Layer Control on the Pressure-Recovery Characteristics of a Circular Internal-Contraction Inlet with Translating Centerbody at Mach Numbers of 2.00 and 2.35

NASA Technical Reports Server (NTRS)

Martin, Norman J.

1959-01-01

Exploratory tests of a circular internal-contraction inlet were made at Mach numbers of 2.00 and 2.35 to determine the effect of a cowl-type boundary-layer control located downstream of the inlet throat. The inlet was designed for a Mach number of 2.5. Tests were also made of the inlet modified to correspond to design Mach numbers of 2.35 and 2.25. Surveys near the minimum area section of the inlet without boundary-layer control indicated maximum averaged pressure recoveries between 0.90 and 0.92 at a free-stream Mach number, M(sub infinity), of 2.35 for the inlets. Farther downstream, after partial subsonic diffusion, a maximum pressure recovery of 0.842 was obtained with the inlet at M(sub infinity) = 2.35. The pressure recovery of the inlet was increased by 0.03 at a Mach number of 2.35 and decreased by 0.02 at a Mach number of 2.00 by the application of cowl-type boundary-layer control. Further investigation with the inlet without bleed demonstrated that an increase of angle of attack from 0 deg to 3 deg reduced the pressure recovery 0.04. The effect of Reynolds number was to increase pressure recovery 0.07 (from 0.785 to 0.855) with an increase in Reynolds number (based on inlet diameter) from 0.79 x 10(exp 6) to 3.19 x 10(exp 6).

Boundary layers in centrifugal compressors. [application of boundary layer theory to compressor design

NASA Technical Reports Server (NTRS)

Dean, R. C., Jr.

1974-01-01

The utility of boundary-layer theory in the design of centrifugal compressors is demonstrated. Boundary-layer development in the diffuser entry region is shown to be important to stage efficiency. The result of an earnest attempt to analyze this boundary layer with the best tools available is displayed. Acceptable prediction accuracy was not achieved. The inaccuracy of boundary-layer analysis in this case would result in stage efficiency prediction as much as four points low. Fluid dynamic reasons for analysis failure are discussed with support from flow data. Empirical correlations used today to circumnavigate the weakness of the theory are illustrated.

Receptivity of the compressible mixing layer

NASA Astrophysics Data System (ADS)

Barone, Matthew F.; Lele, Sanjiva K.

2005-09-01

Receptivity of compressible mixing layers to general source distributions is examined by a combined theoretical/computational approach. The properties of solutions to the adjoint Navier Stokes equations are exploited to derive expressions for receptivity in terms of the local value of the adjoint solution. The result is a description of receptivity for arbitrary small-amplitude mass, momentum, and heat sources in the vicinity of a mixing-layer flow, including the edge-scattering effects due to the presence of a splitter plate of finite width. The adjoint solutions are examined in detail for a Mach 1.2 mixing-layer flow. The near field of the adjoint solution reveals regions of relatively high receptivity to direct forcing within the mixing layer, with receptivity to nearby acoustic sources depending on the source type and position. Receptivity ‘nodes’ are present at certain locations near the splitter plate edge where the flow is not sensitive to forcing. The presence of the nodes is explained by interpretation of the adjoint solution as the superposition of incident and scattered fields. The adjoint solution within the boundary layer upstream of the splitter-plate trailing edge reveals a mechanism for transfer of energy from boundary-layer stability modes to Kelvin Helmholtz modes. Extension of the adjoint solution to the far field using a Kirchhoff surface gives the receptivity of the mixing layer to incident sound from distant sources.

Use of Ground Penetrating Radar to Study Gradient Media

NASA Astrophysics Data System (ADS)

Titov, A.

2016-12-01

Nowadays Ground Penetrating Radar (GPR) is often used to solve different problems of applied geophysics including the hydrological ones. This work was motivated by detection of weak reflections in the body of water observed during the surveys on the freshwater lakes using GPR. The same reflections were first analyzed by John Bradford in 2007. These reflections can arise from the thermal gradient layer or thermocline due to different dielectric permittivity of cold and warm water. We employed physical and mathematical modeling to identify the properties of such thermoclines. We have constructed a special GPR stand to study the gradient media in our laboratory. The stand consists of a water-filled plastic tank and plastic tubes, which gather the cold water under the warm water. Our stand allows for changing parameters of the gradient layer, such as limits of dielectric permittivity and the thickness of the gradient layer. GPR antenna was placed slightly under the water surface to remove the parasitic reflections. To visualize the thermal distribution, an infrared camera and thermal sensors were used. Analysis of the GPR traces after physical modeling, performed in the MATLAB environment, allows us to locate the weak reflection from the gradient layer. We observed that (i) the change of the gradient boundary values alters the amplitude of the signal, (ii) the arrival time of the impulse reflected from the gradient layer corresponds to the arrival time of the impulse reflected from the top boundary of this layer, and (iii) the shape of the signal reflected from the gradient layer coincides with the shape of the signal reflected from the non-gradient boundary between two bodies. The quantitative properties of thermocline can be determined using amplitude analysis of GPR signals. Finally, the developed methods were successfully applied to real field data.

Boundary-Layer Bypass Transition Over Large-Scale Bodies

DTIC Science & Technology

2016-12-16

shape of the streamwise velocity profile compared to the flat- plate boundary layer. The research showed that the streamwise wavenumber plays a key role...many works on the suppression of the transitional boundary layer. Most of the results in the literature are for the flat- plate boundary layer but the...behaviour of the velocity and pressure changes with the curvature. This work aims to extend the results of the flat- plate boundary layer to a Rankine

Is Chicxulub Too Small to be the Source of the K/Pg Boundary Layer and the Cause of the Dinosaur Extinction Event and would the Amazon Basin Considered as an Impact Feature fit the Evidence Better?

NASA Astrophysics Data System (ADS)

Burgener, J. A.

2016-12-01

The Chicxulub impact is well associated with the K/Pg boundary layer and extinction event [Schulte et al., 2010]. However, most agree that Chicxulub is considered to be too small to have caused the extinction in itself [Kring, 2007; Keller, 2014]. Keller [2014] discusses how the K/Pg extinction event may have been due to many factors, of which Chicxulub would be part, but global warming or volcanic fumes or other factors were the main killers. There are several features in the K/Pg layer that require a much higher energy impact than Chicxulub. The worldwide distribution of shocked crystals does not fit Chicxulub - Chicxulub would only send such granules 400 km away [Morgan et al, 2006]. The Fern Spore anomaly extends too far from Chicxulub indicating a much larger fireball and impact [Fleming 1990; Robertson, 2103]. Fireballs falling around the planet have been proposed and dismissed as not possible. [Goldin & Melosh, 2009] and [Adair,2010] rule out a firestorm from ejecta. One of the reasons that Chicxulub is convincingly attributed with the K/Pg boundary layer is the calculation that the size of the impacting asteroid should have been about 10 km in diameter, based on the thickness of the boundary layer and the amount of iridium in the boundary layer [Alvarez, 1980]. Alvarez used the factor from the Krakatoa eruption (0.22) as the amount of asteroid material that would stay in the atmosphere. More recent studies imply that far less than 0.22 of an asteroid would stay in the atmosphere after an impact. When a comet hits at 55 - 72 km/sec, the vast majority of the comet material will be buried deep into the Earth or ejected at speeds in excess of the escape velocity, and very little would remain [Jeffers et al.2001]. Therefore a comet impact should leave a relatively small boundary layer, requiring a much larger impact by a comet to form what Alvaraz calculated for a 10 km asteroid. If a much larger impact occurred at the end of the Cretaceous, it would resolve the challenges of Chicxulub as long as it was near the location of Chicxulub. If the Amazon Basin was considered as an impact, it would be large enough to fit the K/Pg boundary layer details much better than Chicxulub, and it would explain the extinction event without any need to rely on extenuating factors - the impact itself would have been sufficient to cause the extinction.

An experimental investigation of a two and a three-dimensional low speed turbulent boundary layer

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.; Melnik, W. L.

1976-01-01

Experimental studies of a two and a three-dimensional low speed turbulent boundary layer were conducted on the side wall of a boundary layer wind tunnel. The 20 ft. long test section, with a rectangular cross section measuring 17.5 in. x 46 in., produced a 3.5 in. thick turbulent boundary layer at a free stream Reynolds number. The three-dimensional turbulent boundary layer was produced by a 30 deg swept wing-like model faired into the side wall of the test section. Preliminary studies in the two-dimensional boundary layer indicated that the flow was nonuniform on the 46 in. wide test wall. The nonuniform boundary layer is characterized by transverse variations in the wall shear stress and is primarily caused by nonuniformities in the inlet damping screens.

Three Dimensional Viscous Flow Field in an Axial Flow Turbine Nozzle Passage

NASA Technical Reports Server (NTRS)

Ristic, D.; Lakshminarayana, B.

1997-01-01

The objective of this investigation is experimental and computational study of three dimensional viscous flow field in the nozzle passage of an axial flow turbine stage. The nozzle passage flow field has been measured using a two sensor hot-wire probe at various axial and radial stations. In addition, two component LDV measurements at one axial station (x/c(sum m) = 0.56) were performed to measure the velocity field. Static pressure measurements and flow visualization, using a fluorescent oil technique, were also performed to obtain the location of transition and the endwall limiting streamlines. A three dimensional boundary layer code, with a simple intermittency transition model, was used to predict the viscous layers along the blade and endwall surfaces. The boundary layers on the blade surface were found to be very thin and mostly laminar, except on the suction surface downstream of 70% axial chord. Strong radial pressure gradient, especially close to the suction surface, induces strong cross flow components in the trailing edge regions of the blade. On the end-walls the boundary layers were much thicker, especially near the suction corner of the casing surface, caused by secondary flow. The secondary flow region near the suction-casing surface corner indicates the presence of the passage vortex detached from the blade surface. The corner vortex is found to be very weak. The presence of a closely spaced rotor downstream (20% of the nozzle vane chord) introduces unsteadiness in the blade passage. The measured instantaneous velocity signal was filtered using FFT square window to remove the periodic unsteadiness introduced by the downstream rotor and fans. The filtering decreased the free stream turbulence level from 2.1% to 0.9% but had no influence on the computed turbulence length scale. The computation of the three dimensional boundary layers is found to be accurate on the nozzle passage blade surfaces, away from the end-walls and the secondary flow region. On the nozzle passage endwall surfaces the presence of strong pressure gradients and secondary flow limit the validity of the boundary layer code.

Interaction of Atmospheric Turbulence with Blade Boundary Layer Dynamics on a 5MW Wind Turbine using Blade-Boundary-Layer-Resolved CFD with hybrid URANS-LES.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vijayakumar, Ganesh; Brasseur, James; Lavely, Adam

We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.

Semiconductor P-I-N detector

DOEpatents

Sudharsanan, Rengarajan; Karam, Nasser H.

2001-01-01

A semiconductor P-I-N detector including an intrinsic wafer, a P-doped layer, an N-doped layer, and a boundary layer for reducing the diffusion of dopants into the intrinsic wafer. The boundary layer is positioned between one of the doped regions and the intrinsic wafer. The intrinsic wafer can be composed of CdZnTe or CdTe, the P-doped layer can be composed of ZnTe doped with copper, and the N-doped layer can be composed of CdS doped with indium. The boundary layers is formed of an undoped semiconductor material. The boundary layer can be deposited onto the underlying intrinsic wafer. The doped regions are then typically formed by a deposition process or by doping a section of the deposited boundary layer.

Near-optimal energy transitions for energy-state trajectories of hypersonic aircraft

NASA Technical Reports Server (NTRS)

Ardema, M. D.; Bowles, J. V.; Terjesen, E. J.; Whittaker, T.

1992-01-01

A problem of the instantaneous energy transition that occurs in energy-state approximation is considered. The transitions are modeled as a sequence of two load-factor bounded paths (either climb-dive or dive-climb). The boundary-layer equations associated with the energy-state dynamic model are analyzed to determine the precise location of the transition.

Acoustically excited heated jets. 2: In search of a better understanding

NASA Technical Reports Server (NTRS)

Lepicovsky, J.; Ahuja, K. K.; Brown, W. H.; Salikuddin, M.; Morris, P. J.

1988-01-01

The second part of a three-part report on the effects of acoustic excitation on jet mixing includes the results of an experimental investigation directed at resolving the question of poor excitability of some of the heated jets. The theoretical predictions discussed in Part 1 are examined to find explanations for the observed discrepancies between the measured and the predicted results. Additional testing was performed by studying the self excitation of the shock containing hot jets and also by exciting the jet by sound radiated through source tubes located externally around the periphery of the jet. The effects of nozzle-exit boundary layer conditions on jet excitability was also investigated. It is concluded that high-speed, heated jet mixing rates and consequently also the jet excitability strongly depends on nozzle exit boundary layer conditions.

High speed transition prediction

NASA Technical Reports Server (NTRS)

Gasperas, Gediminis

1993-01-01

The main objective of this work period was to develop, maintain and exercise state-of-the-art methods for transition prediction in supersonic flow fields. Basic state and stability codes, acquired during the last work period, were exercised and applied to calculate the properties of various flowfields. The development of a code for the prediction of transition location using a currently novel method (the PSE or Parabolized Stability Equation method), initiated during the last work period and continued during the present work period, was cancelled at mid-year for budgetary reasons. Other activities during this period included the presentation of a paper at the APS meeting in Tallahassee, Florida entitled 'Stability of Two-Dimensional Compressible Boundary Layers', as well as the initiation of a paper co-authored with H. Reed of the Arizona State University entitled 'Stability of Boundary Layers'.

Influence of ablation impurities on blunt body re-entry ionization

NASA Technical Reports Server (NTRS)

Schexnayder, C. J., Jr.; Evans, J. S.

1974-01-01

Electron density profiles which include the effect of an ablated sodium impurity were computed for the boundary layer on a blunt-nosed body re-entering the atmosphere at 7.62 km/sec. Profiles are computed from the nose to a distance of four diameters along the RAM C-payload. A finite-difference, laminar, nonequilibrium chemistry boundary-layer program was used. Comparison of theory with S-band diagnostic antenna results, electron concentration deduced from X- and C-band attenuation data, and Langmuir probe data at several different aft body locations show that agreement is good at high altitude. At the lower altitudes there is disagreement between theory and S-band antenna data where the apparent discrepancy is attributed to the three-body recombination rate constant used for deionization of sodium coupled with the effect of angle of attack.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1984-01-01

A symposium on transition in turbines was held at the NASA Lewis Research Center. One recommendation of the working groups was the collection of existing transition data to provide standard cases against which models could be tested. A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information from the heat transfer data. The data sets reviewed cover a wide range of flow conditions, from low speed, flat plate tests to full scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1985-01-01

A symposium on transition in turbines was held at the NASA Lewis Research Center. One recommendation of the working groups was the collection of existing transition data to provide standard cases against which models could be tested. A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information from the heat transfer data. The data sets reviewed cover a wide range of flow conditions, from low speed, flat plate tests to full scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Instrumentation development for study of Reynolds Analogy in reacting flows

NASA Technical Reports Server (NTRS)

Deturris, Dianne J.

1995-01-01

Boundary layers in supersonic reacting flows are not well understood. Recently a technique has been developed which makes more extensive surface measurements practical, increasing the capability to understand the turbulent boundary layer. A significant advance in this understanding would be the formulation of an analytic relation between the transfer of momentum and the transfer of heat for this flow, similar to the Reynolds Analogy that exists for laminar flow. A gauge has been designed and built which allows a thorough experimental investigation of the relative effects of heat transfer and skin friction in the presence of combustion. Direct concurrent measurements made at the same location, combined with local flow conditions, enable a quantitative analysis to obtain a relation between the surface drag and wall heating, as well as identifying possible ways of reducing both.

Practical calculation of laminar and turbulent bled-off boundary layers

NASA Technical Reports Server (NTRS)

Eppler, R.

1978-01-01

Bleed-off of boundary layer material is shown to be an effective means for reducing drag by conserving the laminar boundary layer and preventing separation of the turbulent boundary layer. The case in which the two effects of bleed-off overlap is examined. Empirical methods are extended to the case of bleed-off. Laminar and turbulent boundary layers are treated simultaneously and the approximation differential equations are solved without an uncertain error. The case without bleed-off is also treated.

Tables for correcting airfoil data obtained in the Langley 0.3-meter transonic cryogenic tunnel for sidewall boundary-layer effects

NASA Technical Reports Server (NTRS)

Jenkins, R. V.; Adcock, J. B.

1986-01-01

Tables for correcting airfoil data taken in the Langley 0.3-meter Transonic Cryogenic Tunnel for the presence of sidewall boundary layer are presented. The corrected Mach number and the correction factor are minutely altered by a 20 percent change in the boundary layer virtual origin distance. The sidewall boundary layer displacement thicknesses measured for perforated sidewall inserts and without boundary layer removal agree with the values calculated for solid sidewalls.

Discussion of Boundary-Layer Characteristics Near the Wall of an Axial-Flow Compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mohoney, John J; Budinger, Ray E

1952-01-01

The boundary-layer velocity profiles in the tip region of an axial-flow compressor downstream of the guide vanes and downstream of the rotor were measured by use of total-pressure and claw-type yaw probes. These velocities were resolved into two components: one along the streamline of the flow outside the boundary layer, and the other perpendicular to it. The affinity among all profiles was thus demonstrated with the boundary-layer thickness and the deflection of the boundary layer at the wall as the generalizing parameters. By use of these results and the momentum-integral equations, boundary-layer characteristics on the walls of an axial-flow compressor were qualitatively evaluated.

The atmospheric boundary layer in the CSIRO global climate model: simulations versus observations

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Rotstayn, L. D.; Krummel, P. B.

2002-07-01

A 5-year simulation of the atmospheric boundary layer in the CSIRO global climate model (GCM) is compared with detailed boundary-layer observations at six locations, two over the ocean and four over land. Field observations, in the form of surface fluxes and vertical profiles of wind, temperature and humidity, are generally available for each hour over periods of one month or more in a single year. GCM simulations are for specific months corresponding to the field observations, for each of five years. At three of the four land sites (two in Australia, one in south-eastern France), modelled rainfall was close to the observed climatological values, but was significantly in deficit at the fourth (Kansas, USA). Observed rainfall during the field expeditions was close to climatology at all four sites. At the Kansas site, modelled screen temperatures (Tsc), diurnal temperature amplitude and sensible heat flux (H) were significantly higher than observed, with modelled evaporation (E) much lower. At the other three land sites, there is excellent correspondence between the diurnal amplitude and phase and absolute values of each variable (Tsc, H, E). Mean monthly vertical profiles for specific times of the day show strong similarities: over land and ocean in vertical shape and absolute values of variables, and in the mixed-layer and nocturnal-inversion depths (over land) and the height of the elevated inversion or height of the cloud layer (over the sea). Of special interest is the presence climatologically of early morning humidity inversions related to dewfall and of nocturnal low-level jets; such features are found in the GCM simulations. The observed day-to-day variability in vertical structure is captured well in the model for most sites, including, over a whole month, the temperature range at all levels in the boundary layer, and the mix of shallow and deep mixed layers. Weaknesses or unrealistic structure include the following, (a) unrealistic model mixed-layer temperature profiles over land in clear skies, related to use of a simple local first-order turbulence closure, (b) a tendency to overpredict cloud liquid water near the surface.

Prediction of turbulent shear layers in turbomachines

NASA Technical Reports Server (NTRS)

Bradshaw, P.

1974-01-01

The characteristics of turbulent shear layers in turbomachines are compared with the turbulent boundary layers on airfoils. Seven different aspects are examined. The limits of boundary layer theory are investigated. Boundary layer prediction methods are applied to analysis of the flow in turbomachines.

Study of boundary-layer transition using transonic-cone preston tube data

NASA Technical Reports Server (NTRS)

Reed, T. D.; Moretti, P. M.

1980-01-01

The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones.

Stability of boundary layer flow based on energy gradient theory

NASA Astrophysics Data System (ADS)

Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

2018-05-01

The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

Wind and boundary layers in Rayleigh-Bénard convection. II. Boundary layer character and scaling.

PubMed

van Reeuwijk, Maarten; Jonker, Harm J J; Hanjalić, Kemo

2008-03-01

The scaling of the kinematic boundary layer thickness lambda(u) and the friction factor C(f) at the top and bottom walls of Rayleigh-Bénard convection is studied by direct numerical simulation (DNS). By a detailed analysis of the friction factor, a new parameterisation for C(f) and lambda(u) is proposed. The simulations were made of an L/H=4 aspect-ratio domain with periodic lateral boundary conditions at Ra=(10(5), 10(6), 10(7), 10(8)) and Pr=1. The continuous spectrum, as well as significant forcing due to Reynolds stresses, clearly indicates a turbulent character of the boundary layer, while viscous effects cannot be neglected, judging from the scaling of classical integral boundary layer parameters with Reynolds number. Using a conceptual wind model, we find that the friction factor C(f) should scale proportionally to the thermal boundary layer thickness as C(f) proportional variant lambda(Theta)/H, while the kinetic boundary layer thickness lambda(u) scales inversely proportionally to the thermal boundary layer thickness and wind Reynolds number lambda(u)/H proportional variant (lambda(Theta)/H)(-1)Re(-1). The predicted trends for C(f) and lambda(u) are in agreement with DNS results.

Unsteady transonic viscous-inviscid interaction using Euler and boundary-layer equations

NASA Technical Reports Server (NTRS)

Pirzadeh, Shahyar; Whitfield, Dave

1989-01-01

The Euler code is used extensively for computation of transonic unsteady aerodynamics. The boundary layer code solves the 3-D, compressible, unsteady, mean flow kinetic energy integral boundary layer equations in the direct mode. Inviscid-viscous coupling is handled using porosity boundary conditions. Some of the advantages and disadvantages of using the Euler and boundary layer equations for investigating unsteady viscous-inviscid interaction is examined.

Numerical Modeling of the Propagation Environment in the Atmospheric Boundary Layer over the Persian Gulf.

NASA Astrophysics Data System (ADS)

Atkinson, B. W.; Li, J.-G.; Plant, R. S.

2001-03-01

Strong vertical gradients at the top of the atmospheric boundary layer affect the propagation of electromagnetic waves and can produce radar ducts. A three-dimensional, time-dependent, nonhydrostatic numerical model was used to simulate the propagation environment in the atmosphere over the Persian Gulf when aircraft observations of ducting had been made. A division of the observations into high- and low-wind cases was used as a framework for the simulations. Three sets of simulations were conducted with initial conditions of varying degrees of idealization and were compared with the observations taken in the Ship Antisubmarine Warfare Readiness/Effectiveness Measuring (SHAREM-115) program. The best results occurred with the initialization based on a sounding taken over the coast modified by the inclusion of data on low-level atmospheric conditions over the Gulf waters. The development of moist, cool, stable marine internal boundary layers (MIBL) in air flowing from land over the waters of the Gulf was simulated. The MIBLs were capped by temperature inversions and associated lapses of humidity and refractivity. The low-wind MIBL was shallower and the gradients at its top were sharper than in the high-wind case, in agreement with the observations. Because it is also forced by land-sea contrasts, a sea-breeze circulation frequently occurs in association with the MIBL. The size, location, and internal structure of the sea-breeze circulation were realistically simulated. The gradients of temperature and humidity that bound the MIBL cause perturbations in the refractivity distribution that, in turn, lead to trapping layers and ducts. The existence, location, and surface character of the ducts were well captured. Horizontal variations in duct characteristics due to the sea-breeze circulation were also evident. The simulations successfully distinguished between high- and low-wind occasions, a notable feature of the SHAREM-115 observations. The modeled magnitudes of duct depth and strength, although leaving scope for improvement, were most encouraging.

Characteristics of sources and sinks of momentum in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Fiscaletti, D.; Ganapathisubramani, B.

2018-05-01

In turbulent boundary layers, the wall-normal gradient of the Reynolds shear stress identifies momentum sources and sinks (T =∂ [-u v ]/∂ y ). These motions can be physically interpreted in two ways: (1) as contributors to the turbulence term balancing the mean momentum equation, and (2) as regions of strong local interaction between velocity and vorticity fluctuations. In this paper, the space-time evolution of momentum sources and sinks is investigated in a turbulent boundary layer at the Reynolds number (Reτ) = 2700, with time-resolved planar particle image velocimetry in a plane along the streamwise and wall-normal directions. Wave number-frequency power spectra of T fluctuations reveal that the wave velocities of momentum sources and sinks tend to match the local streamwise velocity in proximity to the wall. However, as the distance from the wall increases, the wave velocities of the T events are slightly lower than the local streamwise velocities of the flow, which is also confirmed from the tracking in time of the intense momentum sources and sinks. This evidences that momentum sources and sinks are preferentially located in low-momentum regions of the flow. The spectral content of the T fluctuations is maximum at the wall, but it decreases monotonically as the distance from the wall grows. The relative spectral contributions of the different wavelengths remains unaltered at varying wall-normal locations. From autocorrelation coefficient maps, the characteristic streamwise and wall-normal extents of the T motions are respectively 60 and 40 wall units, independent of the wall distance. Both statistics and instantaneous visualizations show that momentum sources and sinks have a preferential tendency to be organized in positive-negative pairs in the wall-normal direction.

Flight Wing Surface Pressure and Boundary-Layer Data Report from the F-111 Smooth Variable-Camber Supercritical Mission Adaptive Wing

NASA Technical Reports Server (NTRS)

Powers, Sheryll Goecke; Webb, Lannie D.

1997-01-01

Flight tests were conducted using the advanced fighter technology integration F-111 (AFTI/F-111) aircraft modified with a variable-sweep supercritical mission adaptive wing (MAW). The MAW leading- and trailing-edge variable-camber surfaces were deflected in flight to provide a near-ideal wing camber shape for the flight condition. The MAW features smooth, flexible upper surfaces and fully enclosed lower surfaces, which distinguishes it from conventional flaps that have discontinuous surfaces and exposed or semi-exposed mechanisms. Upper and lower surface wing pressure distributions were measured along four streamwise rows on the right wing for cruise, maneuvering, and landing configurations. Boundary-layer measurements were obtained near the trailing edge for one of the rows. Cruise and maneuvering wing leading-edge sweeps were 26 deg for Mach numbers less than 1 and 45 deg or 58 deg for Mach numbers greater than 1. The landing wing sweep was 9 deg or 16 deg. Mach numbers ranged from 0.27 to 1.41, angles of attack from 2 deg to 13 deg, and Reynolds number per unit foot from 1.4 x 10(exp 6) to 6.5 x 10(exp 6). Leading-edge cambers ranged from O deg to 20 deg down, and trailing-edge cambers ranged from 1 deg up to 19 deg down. Wing deflection data for a Mach number of 0.85 are shown for three cambers. Wing pressure and boundary-layer data are given. Selected data comparisons are shown. Measured wing coordinates are given for three streamwise semispan locations for cruise camber and one spanwise location for maneuver camber.

Exploring the Contribution of Primary Marine Organic Matter to the Arctic Boundary Layer

NASA Astrophysics Data System (ADS)

Collins, D. B.; Chang, R. Y. W.; Boyer, M.; Abbatt, J.

2016-12-01

The ocean is a significant source of aerosol to the atmosphere, and contributes significantly to the aerosol population especially in remote locations. Both primary and secondary processes connect the ocean to ambient aerosol loadings, but the extent to which the ocean is a source of organic material to the atmosphere is a current topic of scientific debate. The contribution of primary marine aerosol to atmospheric organic matter may have an influence on the water uptake properties and chemical reactivity of primary marine aerosol particles, influencing their climate-relevant properties. In this study, we characterize the contribution of primary marine aerosol to the arctic marine boundary layer using coincident quantitative measurements of freshly-produced sea spray aerosol and ambient marine aerosol to the arctic boundary layer during an expedition aboard the CCGS Amundsen. Sea spray production experiments were conducted during the cruise using a tank fitted with a plunging waterfall apparatus, a technique which has been recently shown to closely mimic the aerosol production behavior of controlled breaking waves. Comparison of the chemical composition of sea spray particles generated from water samples in various locations throughout the Canadian Archipelago will be presented. A tracer analysis of specific compounds known to be important contributors to primary marine organic material are tracked using GC/MS, along with those known to be tracers of biological aerosol and other organic matter sources. Size-segregated trends in tracer concentrations and ratios with inorganic components will be discussed in the context of understanding the contribution of primary organics to the Arctic atmosphere and in comparison with other sources of organic material observed during the ship-board campaign.

A Nocturnal Boundary Layer Simulation over the ARM-CART Site

NASA Astrophysics Data System (ADS)

Werth, D.; Leclerc, M.; Duarte, H.; Fischer, M.; Kurzeja, R.; Parker, M.

2008-12-01

The nocturnal boundary layer (NBL) is characterized by strong inversions and weak turbulent motions. It is during this time that low-level jets (LLJs) often form as the winds aloft reach speeds approaching 15-25m/s at levels below 1000m. During the daytime, turbulent mixing quickly damps such organized motion, but at night the surface cooling establishes an inversion which reduces turbulence and allows jets to form uninhibited. A field project over the ARM-CART site during a period of several nights in September, 2007 was conducted to explore the jet evolution. Data was collected from a tower and analyzed for turbulent behavior. With data limited to a single location, however, the full range of NBL behavior is difficult to determine. The Regional Atmospheric Modeling System (RAMS) is therefore used to simulate the ARM-CART NBL field experiment and validated against the data collected from the site. This model was run at high resolution, and is ideal for calculating the interactions among the various motions within the boundary layer and their influence on the surface. The model can provide information throughout the NBL - with a larger domain, a simulation of the NBL can provide information over a large range of locations and heights. In particular, we are interested in the way that the simulated NBL eddies are affected by their height and proximity to the LLJ, and how this compares to the tower results. The eddy sizes that exist in the model are limited by its grid spacing, but a series of smaller, finer nests allow us to study eddy motion at the relevant scales for short periods.

The impact of water vapor assimilation on quantitative precipitation forecast over the Washington, DC metropolitan area

NASA Astrophysics Data System (ADS)

Walford, Segayle Cereta

Forecasting subtle, small-scale convective cases in both winter and summer time is an ongoing challenge in weather forecasting. Recent studies have shown that better structure of moisture within the boundary layer is crucial for improving forecasting skills, particularly quantitative precipitation forecasting (QPF). Lidars, which take high temporal observations of moisture, are able to capture very detailed structures, especially within the boundary layer where convection often begins. This study first investigates the extent to which an aerosol and a water vapor lidar are able to capture key boundary layer processes necessary for the development of convection. The results of this preliminary study show that the water vapor lidar is best able to capture the small scale water vapor variability that is necessary for the development of convection. These results are then used to investigate impacts of assimilating moisture from the Howard University Raman Lidar (HURL) for one mesoscale convective case, July 27-28, 2006. The data for this case is from the Water Vapor Validation Experiment-Satellite and Sondes (WAVES) field campaign located at the Howard University Beltsville Site (HUBS) in Beltsville, MD. Specifically, lidar-based water vapor mixing ratio profiles are assimilated into the Weather Research and Forecasting (WRF) regional model over a 4 km grid resolution over Washington, DC. Model verification is conducted using the Meteorological Evaluation Tool (MET) and the results from the lidar run are then compared to a control (no assimilation) run. The findings indicate that quantitatively conclusions cannot be draw from this one case study. However, qualitatively, the assimilation of the lidar observations improved the equivalent potential temperature, and water vapor distribution of the region. This difference changed location, strength and spatial coverage of the convective system over the HUBS region.

Identification of the Viscous Superlayer on the Low-Speed Side of a Single-Stream Shear Layer

NASA Astrophysics Data System (ADS)

Foss, John; Peabody, Jason

2010-11-01

Image pairs (elevation/plan views) have been acquired of a smoke streakline originating in the irrotational region on the low-speed side of a high Re single-stream shear layer of Morris and Foss (2003). The viscous superlayer (VSL) is identified as the terminus of the streak; 1800 such images provide VSL position statistics. Hot-wire data acquired concurrently at the shear layer edge and interior are used to investigate the relationship between these velocity magnitudes and the large-scale motions. Distinctive features (plumes) along the streakline are tracked between images to provide discrete irrotational region velocity magnitudes and material trajectories. A non-diffusive marker, introduced in the separating (high speed) boundary layer and imaged at x/θo=352, has revealed an unexpected bias in the streak-defined VSL locations. The interpretation of this bias clarifies the induced flow patterns in the entrainment region. The observations are consistent with a conception of the large-scale shear layer motions as "billows" of vortical fluid separated by re-entrant "wedges" of irrotational fluid, per Phillips (1972). Morris, S.C. and Foss, J.F. (2003). "Turbulent Boundary Layer to Single Stream Shear Layer: The Transition Region." Journal of Fluid Mechanics. Vol. 494, pp. 187-221. Phillips, O. M. (1972). "The Entrainment Interface." Journal of Fluid Mechanics. Vol. 51, pp. 97-118.

Inventory of File gfs.t06z.smartguam00.tm00.grib2

Science.gov Websites

boundary layer WDIR analysis Wind Direction (from which blowing) [degtrue] 013 planetary boundary layer WIND analysis Wind Speed [m/s] 014 planetary boundary layer RH analysis Relative Humidity [%] 015 planetary boundary layer DIST analysis Geometric Height [m] 016 surface 4LFTX analysis Best (4 layer) Lifted

Effect of vortical structures on velocity and turbulent fields in the near region of an impinging turbulent jet

NASA Astrophysics Data System (ADS)

Yadav, Harekrishna; Agrawal, Amit

2018-03-01

This experimental study pertains to the formation of a secondary peak in heat transfer distribution for an axisymmetric turbulent impinging submerged jet. The analysis of instantaneous fields is undertaken at various Reynolds numbers based upon the bulk velocity and nozzle diameter (Re = 1300-10 000) and surface spacings (L/D = 0.25-6). Our analysis shows that flow separation and reattachment correspond to decrease/increase in local pressure and are caused by primary vortices; these are further linked to the location of maxima in streamwise and cross-stream velocities. It is further observed that the locations of maxima and minima in velocities are linked to fluctuations in rms velocities and thickening/thinning of the boundary layer. The vortices transported along the surface either coalesce among themselves or combine with other eddies to form a primary vortex. The primary vortex while getting convected downstream makes multiple interactions with the inner shear layer and causes waviness in instantaneous flow fields. In their later stage, the primary vortex moves away from the wall and accelerates, while the flow decelerates in the inner shear layer. The accelerated fluid in the outer shear layer pulls the downstream fluid from the inner shear layer and leads to the formation of a secondary vortex. After a certain distance downstream, the secondary vortex rolling between the primary vortex and the wall eventually breaks down, while the flow reattaches to the wall. The behavior of time average and instantaneous velocity fields suggests that unsteadiness in the heat transfer is linked to the location of maximum streamwise velocity, location of flow attachment, location of rms velocity, and thickness of the boundary layer. The instantaneous velocity fields show that for a given surface spacing, the chances for the appearance of the secondary vortex reduce with an increase in Reynolds number because of the reduction in space available for the secondary vortex to develop. It is further deduced that the strength of the secondary vortex is primarily dependent upon the strength of the primary vortex. However, the velocity field estimated using the linear stochastic estimation technique shows a tendency for the formation of the secondary vortex at higher Reynolds number, suggesting that most measurements do not resolve them well. Our analysis explains the reason for the appearance of the secondary peak in heat transfer distribution and helps resolve the contradictions in the literature regarding this phenomenon.

INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

EPA Science Inventory

Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

Skin-Friction Measurements at Subsonic and Transonic Mach Numbers with Embedded-Wire Gages

DTIC Science & Technology

1981-01-01

Model ................................... 17 9. Boundary-Layer Rake Installation on EBOR Model...boundary-layer total pressure rake eliminates this bulky mechanism and the long data acquisition time, but it introduces interferences which affect the...its construction. Further, boundary-layer rakes are restricted to measurements in thick boundary layers. Surface pressure probes such as Stanton tubes

Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

NASA Technical Reports Server (NTRS)

Mack, L. M.

1967-01-01

The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.

Three dimensional flow field inside compressor rotor, including blade boundary layers

NASA Technical Reports Server (NTRS)

Galmes, J. M.; Pouagere, M.; Lakshminarayana, B.

1982-01-01

The Reynolds stress equation, pressure strain correlation, and dissipative terms and diffusion are discussed in relation to turbulence modelling using the Reynolds stress model. Algebraic modeling of Reynolds stresses and calculation of the boundary layer over an axial cylinder are examined with regards to the kinetic energy model for turbulence modelling. The numerical analysis of blade and hub wall boundary layers, and an experimental study of rotor blade boundary layer in an axial flow compressor rotor are discussed. The Patankar-Spalding numerical method for two dimensional boundary layers is included.

Boundary-layer effects in composite laminates. I - Free-edge stress singularities. II - Free-edge stress solutions and basic characteristics

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1982-01-01

The fundamental nature of the boundary-layer effect in fiber-reinforced composite laminates is formulated in terms of the theory of anisotropic elasticity. The basic structure of the boundary-layer field solution is obtained by using Lekhnitskii's stress potentials (1963). The boundary-layer stress field is found to be singular at composite laminate edges, and the exact order or strength of the boundary layer stress singularity is determined using an eigenfunction expansion method. A complete solution to the boundary-layer problem is then derived, and the convergence and accuracy of the solution are analyzed, comparing results with existing approximate numerical solutions. The solution method is demonstrated for a symmetric graphite-epoxy composite.

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

NASA Technical Reports Server (NTRS)

Corke, T. C.; Guezennec, Y.; Nagib, H. M.

1981-01-01

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code

NASA Technical Reports Server (NTRS)

Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.

2006-01-01

The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients

NASA Technical Reports Server (NTRS)

Hoffmann, J. A.; Kassir, S. M.; Larwood, S. M.

1989-01-01

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.

Study of mean- and turbulent-velocity fields in a large-scale turbine-vane passage

NASA Technical Reports Server (NTRS)

Bailey, D. A.

1979-01-01

Laser-Doppler velocimetry, and to a lesser extent hot-wire anemometry, were employed to measure three components of the mean velocity and the six turbulent stresses at four planes within the turbine inlet-guide-vane passage. One variation in the turbulent inlet boundary layer thickness and one variation in the blade aspect ratio (span/axial chord) were studied. A longitudinal vortex (passage vortex) was clearly identified in the exit plane of the passage for the three test cases. The maximum turbulence intensities within the longitudinal vortex were found to be on the order of 2 to 4 percent, with large regions appearing nonturbulent. Because a turbulent wall boundary layer was the source of vorticity that produced the passage vortex, these low turbulence levels were not anticipated. For the three test cases studied, the lateral velocity field extended significantly beyond the region of the longitudinal velocity defect. Changing the inlet boundary layer thickness produced a difference in the location, the strength, and the extent of the passage vortex. Changing the aspect ratio of the blade passage had a measurable but less significant effect. The experiment was performed in a 210 mm pitch, 272 mm axial chord model in low speed wind tunnel at an inlet Mach number of 0.07.

A Mesoscale Model-Based Climatography of Nocturnal Boundary-Layer Characteristics over the Complex Terrain of North-Western Utah.

PubMed

Serafin, Stefano; De Wekker, Stephan F J; Knievel, Jason C

Nocturnal boundary-layer phenomena in regions of complex topography are extremely diverse and respond to a multiplicity of forcing factors, acting primarily at the mesoscale and microscale. The interaction between different physical processes, e.g., drainage promoted by near-surface cooling and ambient flow over topography in a statically stable environment, may give rise to special flow patterns, uncommon over flat terrain. Here we present a climatography of boundary-layer flows, based on a 2-year archive of simulations from a high-resolution operational mesoscale weather modelling system, 4DWX. The geographical context is Dugway Proving Ground, in north-western Utah, USA, target area of the field campaigns of the MATERHORN (Mountain Terrain Atmospheric Modeling and Observations Program) project. The comparison between model fields and available observations in 2012-2014 shows that the 4DWX model system provides a realistic representation of wind speed and direction in the area, at least in an average sense. Regions displaying strong spatial gradients in the field variables, thought to be responsible for enhanced nocturnal mixing, are typically located in transition areas from mountain sidewalls to adjacent plains. A key dynamical process in this respect is the separation of dynamically accelerated downslope flows from the surface.

Investigation of Vortical Flow Patterns in the Near Field of a Dynamic Low-Aspect-Ratio Cylinder

NASA Astrophysics Data System (ADS)

Gildersleeve, Samantha; Amitay, Michael

2016-11-01

The flowfield and associated flow structures of a low-aspect-ratio cylindrical pin were investigated experimentally in the near-field as the pin underwent wall-normal periodic oscillations. Under dynamic conditions, the pin is driven at the natural wake shedding frequency with an amplitude of 33% of its mean height. Additionally, a static pin was also tested at various mean heights of 0.5, 1.0, and 1.5 times the local boundary layer thickness to explore the effect of the mean height on the flowfield. Three-dimensional flowfields were reconstructed and analyzed from SPIV measurements where data were collected along streamwise planes for several spanwise locations under static and dynamic conditions. The study focuses on the incoming boundary layer as it interacts with the pin, as well as two main vortical formations: the arch-type vortex and the horseshoe vortex. Under dynamic conditions, the upstream boundary layer is thinner, relative to the baseline, and the downwash in the wake increases, resulting in a reduced wake deficit. These results indicate enhanced strength of the aforementioned vortical flow patterns under dynamic conditions. The flow structures in the near-field of the static/dynamic cylinder will be discussed in further detail. Supported by The Boeing Company.

Hypersonic Boundary-Layer Stability Experiments on a Flared-Cone Model at Angle of Attack in a Quiet Wind Tunnel

NASA Technical Reports Server (NTRS)

Doggett, Glen P.; Chokani, Ndaona

1996-01-01

An experimental investigation of the effects of angle of attack on hypersonic boundary-layer stability on a flared-cone model was conducted in the low-disturbance Mach-6 Nozzle-Test Chamber Facility at NASA Langley Research Center. This unique facility provided a 'quiet' flow test environment which is well suited for stability experiments because the low levels of freestream 'noise' minimize artificial stimulation of flow-disturbance growth. Surface pressure and temperature measurements documented the adverse-pressure gradient and transition-onset location. Hot-wire anemometry diagnostics were applied to identify the instability mechanisms which lead to transition. In addition, the mean flow over the flared-cone geometry was modeled by laminar Navier-Stokes computations. Results show that the boundary layer becomes more stable on the windward ray and less stable on the leeward ray relative to the zero-degree angle-of-attack case. The second-mode instability dominates the transition process at a zero-degree angle of attack, however, on the windward ray at an angle of attack this mode was completely stabilized. The less-dominant first-mode instability was slightly destabilized on the windward ray. Non-linear mechanisms such as saturation and harmonic generation are identified from the flow-disturbance bispectra.

A Top-Down Pathway to Secondary Eyewall Formation in Simulated Tropical Cyclones

NASA Astrophysics Data System (ADS)

Tyner, Bryce; Zhu, Ping; Zhang, Jun A.; Gopalakrishnan, Sundararaman; Marks, Frank; Tallapragada, Vijay

2018-01-01

Idealized and real-case simulations conducted using the Hurricane Weather Research and Forecasting (HWRF) model demonstrate a "top-down" pathway to secondary eyewall formation (SEF) for tropical cyclones (TCs). For the real-case simulations of Hurricane Rita (2005) and Hurricane Edouard (2014), a comparison to observations reveals the timing and overall characteristics of the simulated SEF appear realistic. An important control of the top-down pathway to SEF is the amount and radial-height distribution of hydrometeors at outer radii. Examination into the simulated hydrometeor particle fall speed distribution reveals that the HWRF operational microphysics scheme is not producing the lightest hydrometeors, which are likely present in observed TCs and are most conducive to being advected from the primary eyewall to the outer rainband region of the TC. Triggering of SEF begins with the fallout of hydrometeors at the outer radii from the TC primary eyewall, where penetrative downdrafts resulting from evaporative cooling of precipitation promote the development of local convection. As the convection-induced radial convergence that is initially located in the midtroposphere extends downward into the boundary layer, it results in the eruption of high entropy air out of the boundary layer. This leads to the rapid development of rainband convection and subsequent SEF via a positive feedback among precipitation, convection, and boundary layer processes.

A Generalized Wall Function

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Povinelli, Louis A.; Liu, Nan-Suey; Potapczuk, Mark G.; Lumley, J. L.

1999-01-01

The asymptotic solutions, described by Tennekes and Lumley (1972), for surface flows in a channel, pipe or boundary layer at large Reynolds numbers are revisited. These solutions can be extended to more complex flows such as the flows with various pressure gradients, zero wall stress and rough surfaces, etc. In computational fluid dynamics (CFD), these solutions can be used as the boundary conditions to bridge the near-wall region of turbulent flows so that there is no need to have the fine grids near the wall unless the near-wall flow structures are required to resolve. These solutions are referred to as the wall functions. Furthermore, a generalized and unified law of the wall which is valid for whole surface layer (including viscous sublayer, buffer layer and inertial sublayer) is analytically constructed. The generalized law of the wall shows that the effect of both adverse and favorable pressure gradients on the surface flow is very significant. Such as unified wall function will be useful not only in deriving analytic expressions for surface flow properties but also bringing a great convenience for CFD methods to place accurate boundary conditions at any location away from the wall. The extended wall functions introduced in this paper can be used for complex flows with acceleration, deceleration, separation, recirculation and rough surfaces.

Near Continuum Velocity and Temperature Coupled Compressible Boundary Layer Flow over a Flat Plate

NASA Astrophysics Data System (ADS)

He, Xin; Cai, Chunpei

2017-04-01

The problem of a compressible gas flows over a flat plate with the velocity-slip and temperature-jump boundary conditions are being studied. The standard single- shooting method is applied to obtain the exact solutions for velocity and temperature profiles when the momentum and energy equations are weakly coupled. A double-shooting method is applied if these two equations are closely coupled. If the temperature affects the velocity directly, more significant velocity slip happens at locations closer to the plate's leading edge, and inflections on the velocity profiles appear, indicating flows may become unstable. As a consequence, the temperature-jump and velocity-slip boundary conditions may trigger earlier flow transitions from a laminar to a turbulent flow state.

Turbulence Statistics in the Coastal Ocean Bottom Boundary Layer

NASA Astrophysics Data System (ADS)

Nayak, A. R.; Hackett, E. E.; Luznik, L.; Katz, J.; Osborn, T. R.

2010-12-01

A submersible particle image velocimetry (PIV) system was deployed off the coast of New Jersey, near the LEO-15 site, to characterize the flow and turbulence in the inner part of the continental shelf bottom boundary layer. The measurement domain extended from 5 mm at the bottom up to an elevation of 51 cm in different datasets. The flow comprised of a mean current and wave-induced flow with a period of 10 s. The ratio of wave velocity amplitude to mean current magnitude varied over the tidal cycle and with elevation, with a maximum of 2.35. Their relative orientation also varied. Large databases of time-resolved, high resolution, 2D velocity distributions enabled us to calculate the instantaneous spatial velocity gradients, and from them, the statistically converged vertical dissipation rate profiles. Reynolds Stresses were estimated using the Shaw & Trowbridge technique outside of the wave boundary layer (WBL), and directly, using the instantaneous spatial variations in velocity, near the wall. Results were utilized for calculating the shear production profiles. Hilbert Transforms were utilized for calculating the wave phase of each velocity distribution, and performing conditional sampling of data to determine variations in flow and turbulence parameters during a wave cycle. The mean velocity profiles indicated the presence of a wave boundary layer, followed by a transition region, and a log layer above it. The datasets extending to the wall show that there is no clear log layer within the WBL, but, as expected, profiles vary substantially with location relative to the ripples. Phase dependent variations in mean flow and dissipation rate occurred only in the WBL and transition region, but vanished at higher elevations. The dissipation rate typically peaked during acceleration phases of wave-induced motion, especially near the wall, but it sometimes peaked during wave-crest phases. Below the transition region, the dissipation rate increased rapidly as the wall was approached all the way to the ripple crest, presumably due to the increasing presence of eddies with characteristic size of 1-3 times the ripple height that fell in the dissipation range of the energy spectra. Shear production also peaked at the ripple crest, consistent with laboratory data for rough wall boundary layers. Acknowledgements : NSF

Increased Jet Noise Due to a "Nominally Laminar" State of Nozzle Exit Boundary Layer

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

2017-01-01

A set of 2-in. diameter nozzles is used to investigate the effect of varying exit boundary layer state on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while nozzles involving a "nominally laminar" boundary layer are loud especially on the high-frequency side of the sound pressure level spectrum. The latter boundary layer state involves a "Blasius-like" mean velocity profile but higher turbulence intensities compared to those in the turbulent state. The higher turbulence in the initial region of the jet shear layer leads to increased high-frequency noise. The results strongly suggest that an anomaly noted with subsonic jet noise databases in the literature is due to a similar effect of differences in the initial boundary layer state.

Increased Jet Noise Due to a "Nominally Laminar" State of Nozzle Exit Boundary Layer

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

2017-01-01

A set of 2-inch diameter nozzles is used to investigate the effect of varying exit boundary layer state on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while nozzles involving a nominally-laminar boundary layer are loud especially on the high-frequency side of the sound pressure level spectrum. The latter boundary layer state involves a Blasius-like mean velocity profile but higher turbulence intensities compared to those in the turbulent state. The higher turbulence in the initial region of the jet shear layer leads to increased high-frequency noise. The results strongly suggest that an anomaly noted with subsonic jet noise databases in the literature is due to a similar effect of differences in the initial boundary layer state.

The role of boundary layer momentum advection in the mean location of the ITCZ

NASA Astrophysics Data System (ADS)

Dixit, Vishal; Srinivasan, J.

2017-08-01

The inter-tropical convergence zones (ITCZ) form closer to the equator during equinoxes while they form well away from the equator during the boreal summer. A simple three-way balance between the pressure gradients, Coriolis force and effective Rayleigh friction has been classically used to diagnose the location of maximum boundary layer convergence in the near equatorial ITCZ. If such a balance can capture the dynamics of off-equatorial convergence was not known. We used idealized aqua planet simulations with fixed, zonally symmetric sea surface temperature boundary conditions to simulate the near equatorial and off-equatorial ITCZ. As opposed to the convergence of inter-hemispheric flows in the near equatorial convergence, the off-equatorial convergence forms due to the deceleration of cross-equatorial meridional flow. The detailed momentum budget of the off-equatorial convergence zone reveals that the simple balance is not sufficient to capture the relevant dynamics. The deceleration of the meridional flow is strongly modulated by the inertial effects due to the meridional advection of zonal momentum in addition to the terms in the simple balance. The simple balance predicts a spurious near equatorial convergence and a consistent off-equatorial convergence of the meridional flow. The spurious convergence disappears when inertial effects are included in the balance. As cross equatorial meridional flow decelerates to form convergence, the inertial effects cancel the pressure gradient effects near the equator while they add away from the equator. The contribution to the off-equatorial convergence induced by the pressure gradients is significantly larger than the contribution due to the inertial effects and hence pressure gradients appear to be the primary factor in anchoring the strength and location of the off-equatorial convergence.

ANGULAR MOMENTUM TRANSPORT BY ACOUSTIC MODES GENERATED IN THE BOUNDARY LAYER. I. HYDRODYNAMICAL THEORY AND SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M., E-mail: rrr@astro.princeton.edu

The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification ofmore » three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.« less

Deterministic multi-zone ice accretion modeling

NASA Technical Reports Server (NTRS)

Yamaguchi, K.; Hansman, R. John, Jr.; Kazmierczak, Michael

1991-01-01

The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.

Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2015-11-01

In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.

Nonequilibrium chemistry boundary layer integral matrix procedure

NASA Technical Reports Server (NTRS)

Tong, H.; Buckingham, A. C.; Morse, H. L.

1973-01-01

The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

Vertical thermodynamic structure of the troposphere during the Norwegian young sea ICE expedition (N-ICE2015)

NASA Astrophysics Data System (ADS)

Kayser, Markus; Maturilli, Marion; Graham, Robert M.; Hudson, Stephen R.; Rinke, Annette; Cohen, Lana; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats A.

2017-10-01

The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively "clear" and "opaque" atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Ålesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Ålesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Ålesund generate great differences below. The long-term radiosonde record (1993-2014) from Ny-Ålesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1-3°C warmer than the climatology during winter.

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

2006-01-01

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

2006-01-01

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

Particle image velocimetry measurements of Mach 3 turbulent boundary layers at low Reynolds numbers

NASA Astrophysics Data System (ADS)

Brooks, J. M.; Gupta, A. K.; Smith, M. S.; Marineau, E. C.

2018-05-01

Particle image velocimetry (PIV) measurements of Mach 3 turbulent boundary layers (TBL) have been performed under low Reynolds number conditions, Re_τ =200{-}1000, typical of direct numerical simulations (DNS). Three reservoir pressures and three measurement locations create an overlap in parameter space at one research facility. This allows us to assess the effects of Reynolds number, particle response and boundary layer thickness separate from facility specific experimental apparatus or methods. The Morkovin-scaled streamwise fluctuating velocity profiles agree well with published experimental and numerical data and show a small standard deviation among the nine test conditions. The wall-normal fluctuating velocity profiles show larger variations which appears to be due to particle lag. Prior to the current study, no detailed experimental study characterizing the effect of Stokes number on attenuating wall-normal fluctuating velocities has been performed. A linear variation is found between the Stokes number ( St) and the relative error in wall-normal fluctuating velocity magnitude (compared to hot wire anemometry data from Klebanoff, Characteristics of Turbulence in a Boundary Layer with Zero Pressure Gradient. Tech. Rep. NACA-TR-1247, National Advisory Committee for Aeronautics, Springfield, Virginia, 1955). The relative error ranges from about 10% for St=0.26 to over 50% for St=1.06. Particle lag and spatial resolution are shown to act as low-pass filters on the fluctuating velocity power spectral densities which limit the measurable energy content. The wall-normal component appears more susceptible to these effects due to the flatter spectrum profile which indicates that there is additional energy at higher wave numbers not measured by PIV. The upstream inclination and spatial correlation extent of coherent turbulent structures agree well with published data including those using krypton tagging velocimetry (KTV) performed at the same facility.

Review of Research on Low-Profile Vortex Generators to Control Boundary-Layer Separation

NASA Technical Reports Server (NTRS)

Lin, John C.

2002-01-01

An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the boundary layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils-low-Reynolds number, high-lift, and transonic-as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall proturbances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well.

Infrared Images of Boundary Layer Transition on the D8 Transport Configuration in the LaRC 14- by 22-Foot Subsonic Tunnel

NASA Technical Reports Server (NTRS)

Mason, Michelle L.; Gatlin, Gregory M.

2015-01-01

Grit, trip tape, or trip dots are routinely applied on the leading-edge regions of the fuselage, wings, tails or nacelles of wind tunnel models to trip the flow from laminar to turbulent. The thickness of the model's boundary layer is calculated for nominal conditions in the wind tunnel test to determine the effective size of the trip dots, but the flow over the model may not transition as intended for runs with different flow conditions. Temperature gradients measured with an infrared camera can be used to detect laminar to turbulent boundary layer transition on a wind tunnel model. This non-intrusive technique was used in the NASA Langley 14- by 22-Foot Subsonic Tunnel to visualize the behavior of the flow over a D8 transport configuration model. As the flow through the wind tunnel either increased to or decreased from the run conditions, a sufficient temperature difference existed between the air and the model to visualize the transition location (due to different heat transfer rates through the laminar and the turbulent boundary layers) for several runs in this test. Transition phenomena were visible without active temperature control in the atmospheric wind tunnel, whether the air was cooler than the model or vice-versa. However, when the temperature of the model relative to the air was purposely changed, the ability to detect transition in the infrared images was enhanced. Flow characteristics such as a wing root horseshoe vortex or the presence of fore-body vortical flows also were observed in the infrared images. The images of flow features obtained for this study demonstrate the usefulness of current infrared technology in subsonic wind tunnel tests.

Differential analysis for the turbulent boundary layer on a compressor blade element (including boundary-layer separation)

NASA Technical Reports Server (NTRS)

Schmidt, J. F.; Todd, C. A.

1974-01-01

A two-dimensional differential analysis is developed to approximate the turbulent boundary layer on a compressor blade element with strong adverse pressure gradients, including the separated region with reverse flow. The predicted turbulent boundary layer thicknesses and velocity profiles are in good agreement with experimental data for a cascade blade, even in the separated region.

Low-latitude boundary layer near noon: An open field line model

NASA Technical Reports Server (NTRS)

Lyons, L. R.; Schulz, M.; Pridmore-Brown, D. C.; Roeder, J. L.

1994-01-01

We propose that many features of the cusp and low-latitude boundary layer (LLBL) observed near noon MLT can be explained by interpreting the LLBL as being on open lines with an inner boundary at the separatrix between open and closed magnetic field lines. This interpretation places the poleward boundary of the LLBL and equatorward boundary of the cusp along the field line that bifurcates at the cusp neutral point. The interpretation accounts for the abrupt boundary of magnetosheath particles at the inner edge of the LLBL, a feature that is inconsistent with LLBL formation by diffusion onto closed field lines, and for the distribution of magnetosheath particles appearing more as one continuous region than as two distinct regions across the noon cusp/LLBL boundary. Furthermore, we can explain the existence of energetic radiation belt electrons and protons with differing pitch angle distributions within the LLBL and their abrupt cutoff at the poleward boundary of the LLBL. By modeling the LLBL and cusp region quantitatively, we can account for a hemispherical difference in the location of the equatorial boundary of the cusp that is observed to be dependent on the dipole tilt angle but not on the interplanetary magnetic field (IMF) x component. We also find important variations and hemispherical differences in that the size of the LLBL that should depend strongly upon the x component of the IMF. This prediction is observationally testable. Finally, we find that when the IMF is strongly northward, the LLBL may include a narrow region adjacent to the magnetopause where field lines are detached (i.e., have both ends connected to the IMF).

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

NASA Technical Reports Server (NTRS)

Hoffert, M. I.; Sud, Y. C.

1976-01-01

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Assessment of a 3-D boundary layer code to predict heat transfer and flow losses in a turbine

NASA Technical Reports Server (NTRS)

Anderson, O. L.

1984-01-01

Zonal concepts are utilized to delineate regions of application of three-dimensional boundary layer (DBL) theory. The zonal approach requires three distinct analyses. A modified version of the 3-DBL code named TABLET is used to analyze the boundary layer flow. This modified code solves the finite difference form of the compressible 3-DBL equations in a nonorthogonal surface coordinate system which includes coriolis forces produced by coordinate rotation. These equations are solved using an efficient, implicit, fully coupled finite difference procedure. The nonorthogonal surface coordinate system is calculated using a general analysis based on the transfinite mapping of Gordon which is valid for any arbitrary surface. Experimental data is used to determine the boundary layer edge conditions. The boundary layer edge conditions are determined by integrating the boundary layer edge equations, which are the Euler equations at the edge of the boundary layer, using the known experimental wall pressure distribution. Starting solutions along the inflow boundaries are estimated by solving the appropriate limiting form of the 3-DBL equations.

Effects of boundary layer on flame propagation generated by forced ignition behind an incident shock wave

NASA Astrophysics Data System (ADS)

Ishihara, S.; Tamura, S.; Ishii, K.; Kataoka, H.

2016-09-01

To study the effects of the boundary layer on the deflagration to detonation transition (DDT) process, the mixture behind an incident shock wave was ignited using laser breakdown. Ignition timing was controlled so that the interaction of the resulting flame with a laminar or turbulent boundary layer could be examined. In the case of the interaction with a laminar boundary layer, wrinkling of the flame was observed after the flame reached the corner of the channel. On the other hand, interaction with the turbulent boundary layer distorted the flame front and increased the spreading rate of the flame followed by prompt DDT. The inner structure of the turbulent boundary layer plays an important role in the DDT process. The region that distorted the flame within the turbulent boundary layer was found to be the intermediate region 0.01< y/δ < 0.4, where y is the distance from the wall and δ is the boundary layer thickness. The flame disturbance by the turbulent motions is followed by the flame interaction with the inner layer near the wall, which in turn generates a secondary-ignition kernel that produced a spherical accelerating flame, which ultimately led to the onset of detonation. After the flame reached the intermediate region, the time required for DDT was independent of the ignition position. The effect of the boundary layer on the propagating flame, thus, became relatively small after the accelerating flame was generated.

Typhoon Impacts

DTIC Science & Technology

2014-09-30

and Rmax is the radius of maximum winds . Figure 1 compares two properties of the cold wake, its location and its strength , from 6 storms. The...dimensional response of the underlying ocean including strong surface currents, upwelling of the thermocline, intense mixing across the thermocline, the...mixing determining the rate and character of wake dissipation. The wake is also expected to modify the atmospheric boundary layer and the biology

Permanent-Change Thermal Paints for Hypersonic Flight-Test

DTIC Science & Technology

2010-09-24

thermochromic liquid crystals (Ireland et al. 1999, Ireland & Jones 2000), and temperature sensitive paints (Liu & Sullivan 2005), thermal paints are...surfaces and fin-fuselage junctions, shock boundary layer interactions, scramjet combustion chambers and around control thrusters. Thermal paints can...use of discrete wired sensors may also not practical on some locations on a hypersonic vehicle. Thermochromic liquid crystals Coatings of

Turbulent boundary layer in high Rayleigh number convection in air.

PubMed

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.

Experimental Study of Fillets to Reduce Corner Effects in an Oblique Shock-Wave/Boundary Layer Interaction

NASA Technical Reports Server (NTRS)

Hirt, Stefanie M.

2015-01-01

A test was conducted in the 15 cm x 15 cm supersonic wind tunnel at NASA Glenn Research Center that focused on corner effects of an oblique shock-wave/boundary-layer interaction. In an attempt to control the interaction in the corner region, eight corner fillet configurations were tested. Three parameters were considered for the fillet configurations: the radius, the fillet length, and the taper length from the square corner to the fillet radius. Fillets effectively reduced the boundary-layer thickness in the corner; however, there was an associated penalty in the form of increased boundary-layer thickness at the tunnel centerline. Larger fillet radii caused greater reductions in boundary-layer thickness along the corner bisector. To a lesser, but measureable, extent, shorter fillet lengths resulted in thinner corner boundary layers. Overall, of the configurations tested, the largest radius resulted in the best combination of control in the corner, evidenced by a reduction in boundary-layer thickness, coupled with minimal impacts at the tunnel centerline.

Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1973-01-01

An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

Generating Inviscid and Viscous Fluid Flow Simulations over a Surface Using a Quasi-simultaneous Technique

NASA Technical Reports Server (NTRS)

Sturdza, Peter (Inventor); Martins-Rivas, Herve (Inventor); Suzuki, Yoshifumi (Inventor)

2014-01-01

A fluid-flow simulation over a computer-generated surface is generated using a quasi-simultaneous technique. The simulation includes a fluid-flow mesh of inviscid and boundary-layer fluid cells. An initial fluid property for an inviscid fluid cell is determined using an inviscid fluid simulation that does not simulate fluid viscous effects. An initial boundary-layer fluid property a boundary-layer fluid cell is determined using the initial fluid property and a viscous fluid simulation that simulates fluid viscous effects. An updated boundary-layer fluid property is determined for the boundary-layer fluid cell using the initial fluid property, initial boundary-layer fluid property, and an interaction law. The interaction law approximates the inviscid fluid simulation using a matrix of aerodynamic influence coefficients computed using a two-dimensional surface panel technique and a fluid-property vector. An updated fluid property is determined for the inviscid fluid cell using the updated boundary-layer fluid property.

A nonperturbing boundary-layer transition detector

NASA Astrophysics Data System (ADS)

Ohare, J. E.

1985-11-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels. The boundary-layer transition detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Data which depict boundary-layer transition from laminar to turbulent flow are presented to provide comparisons of the BLTD with other measurement methods. Spectra from the BLTD reveals the presence of a high-frequency peak during transition which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

Distributed-Roughness Effects on Stability and Transition In Swept-Wing Boundary Layers

NASA Technical Reports Server (NTRS)

Carrillo, Ruben B., Jr.; Reibert, Mark S.; Saric, William S.

1997-01-01

Boundary-layer stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure distribution and test conditions are designed to suppress Tollmien-Schlichting disturbances and provide crossflow-dominated transition. The surface of the airfoil is finely polished to a near mirror finish. Under these conditions, submicron surface irregularities cause the naturally occurring stationary crossflow waves to grow to nonuniform amplitudes. Spanwise-uniform stationary crossflow disturbances are generated through careful control of the initial conditions with full-span arrays of micron-high roughness elements near the attachment line. Detailed hot-wire measurements are taken to document the stationary crossflow structure and determine growth rates for the total and individual-mode disturbances. Naphthalene flow visualization provides transition location information. Roughness spacing and roughness height are varied to examine the effects on transition location and all amplified wavelengths. The measurements show that roughness spacings that do not contain harmonics equal to the most unstable wavelength as computed by linear stability theory effectively suppress the most unstable mode. Under certain conditions, subcritical roughness spacing delays transition past that of the corresponding smooth surface.

Inverse structure functions in the canonical wind turbine array boundary layer

NASA Astrophysics Data System (ADS)

Viggiano, Bianca; Gion, Moira; Ali, Naseem; Tutkun, Murat; Cal, Raúl Bayoán

2015-11-01

Insight into the statistical behavior of the flow past an array of wind turbines is useful in determining how to improve power extraction from the overall available energy. Considering a wind tunnel experiment, hot-wire anemometer velocity signals are obtained at the centerline of a 3 x 3 canonical wind turbine array boundary layer. Two downstream locations are considered referring to the near- and far-wake, and 21 vertical points were acquired per profile. Velocity increments are used to quantify the ordinary and inverse structure functions at both locations and their relationship between the scaling exponents is noted. It is of interest to discern if there is evidence of an inverted scaling. The inverse structure functions will also be discussed from the standpoint of the proximity to the array. Observations will also address if inverted scaling exponents follow a power law behavior and furthermore, extended self-similarity of the second moment is used to obtain the scaling exponent of other moments. Inverse structure functions of moments one through eight are tested via probability density functions and the behavior of the negative moment is investigated as well. National Science Foundation-CBET-1034581.

Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980

USGS Publications Warehouse

Kieffer, S.W.; Sturtevant, B.

1988-01-01

Nearly horizontal, quasi-periodic erosional features of 7-m average transverse wavelength and of order 100-m length occur in scattered locations from 3.5 to 9 km from the crater at Mount St. Helens under deposits of the lateral blast of May 18, 1980. We attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography, namely, by streamline curvature in regions of reattachment downstream of sheltered regions, and by the cross-flow component of flow subparallel to ridge crests. The diameter of the vortices and their transverse spacing, inferred from the distance between furrows, are taken to be of the order of the boundary layer thickness. The inferred boundary layer thickness (???14 m at 9 km from the source of the blast) is consistent with the running length from the mountain to the furrow locations. The orientation of furrows induced by the cross-flow instability can be used to measure the upwash angle and estimate the flow Mach number: at the central ridge of Spirit Lake the Mach number is inferred to have been about 2.5, and the flow velocity approximately 235 m/s. -from Authors

Monte Carlo simulations of thermal comptonization process in a two-component advective flow around a neutron star

NASA Astrophysics Data System (ADS)

Bhattacharjee, Ayan; Chakrabarti, Sandip K.

2017-12-01

We explore spectral properties of a two-component advective flow around a neutron star. We compute the effects of thermal Comptonization of soft photons emitted from a Keplerian disc and the boundary layer of the neutron star by the post-shock region of a sub-Keplerian flow, formed due to the centrifugal barrier. The shock location Xs is also the inner edge of the Keplerian disc. We compute a series of realistic spectra assuming a set of electron temperatures of the post-shock region TCE, the temperature of the Normal BOundary Layer (NBOL) TNS of the neutron star and the shock location Xs. These parameters depend on the disc and halo accretion rates (\\dot{m}d and \\dot{m}h, respectively) that control the resultant spectra. We find that the spectrum becomes harder when \\dot{m}_h is increased. The spectrum is controlled strongly by TNS due to its proximity to the Comptonizing cloud since photons emitted from the NBOL cool down the post-shock region very effectively. We also show the evidence of spectral hardening as the inclination angle of the disc is increased.

Effect of Ply Orientation and Crack Location on SIFs in Finite Multilayers with Aligned Cracks

NASA Astrophysics Data System (ADS)

Chen, Linfeng; Pindera, Marek-Jerzy

2008-02-01

An exact elasticity solution is presented for arbitrarily laminated finite multilayers in a state of generalized plane deformation under horizontally pinned end constraints that are weakened by aligned cracks. Based on half-range Fourier series and the local/global stiffness matrix approach, the mixed boundary-value problem is reduced to Cauchy-type singular integral equations in the unknown displacement discontinuities. Solution to these equations is obtained using the approach developed by Erdogan and co-workers. Numerical results quantify the thus-far undocumented geometric and material effects on Mode I, II and III stress intensity factors in composite multilayers with interacting cracks under uniform vertical displacement. These effects include finite dimensions, crack location, material anisotropy due to a unidirectional fiber-reinforced layer/s orientation, and orientational grading.

Mean velocity and turbulence measurements in a 90 deg curved duct with thin inlet boundary layer

NASA Technical Reports Server (NTRS)

Crawford, R. A.; Peters, C. E.; Steinhoff, J.; Hornkohl, J. O.; Nourinejad, J.; Ramachandran, K.

1985-01-01

The experimental database established by this investigation of the flow in a large rectangular turning duct is of benchmark quality. The experimental Reynolds numbers, Deans numbers and boundary layer characteristics are significantly different from previous benchmark curved-duct experimental parameters. This investigation extends the experimental database to higher Reynolds number and thinner entrance boundary layers. The 5% to 10% thick boundary layers, based on duct half-width, results in a large region of near-potential flow in the duct core surrounded by developing boundary layers with large crossflows. The turbulent entrance boundary layer case at R sub ed = 328,000 provides an incompressible flowfield which approaches real turbine blade cascade characteristics. The results of this investigation provide a challenging benchmark database for computational fluid dynamics code development.

Assessment of planetary boundary layer and residual layer heights in the Northeastern U.S. using Lidar, a network of surface observations, and the WRF-STILT model

NASA Astrophysics Data System (ADS)

Barrera, Y.; Nehrkorn, T.; Hegarty, J. D.; Wofsy, S. C.; Gottlieb, E.; Sargent, M. R.; Decola, P.; Jones, T.

2015-12-01

Simulation of the planetary boundary layer (PBL) and residual layer (RL) are key requirements for forecasting air quality in cities and detecting transboundary air pollution events. This study combines information from a network of Mini Micropulse Lidar (MPL) instruments, the CALIOP satellite, meteorological and air pollution measuring sensors, and a particle-transport model to critically test mesoscale transport models at the regional level. Aerosol backscattering measurements were continuously taken with MPL units in various locations within the Northeastern U.S., between September 2012 to August 2015. Data is analyzed using wavelet covariance transforms and image processing techniques. Initial results for the city of Boston show a PBL growth rate between approx. 150 and 300 meters per hour, in the morning to early afternoon (~12-19 UTC). The RL was present throughout the night and day at approx. 1.3 to 2.0 km. Transboundary air pollution events were detected and quantified, and variations in concentrations of greenhouse gases and aerosols were also evaluated. Results were compared to information retrieved from Weather and Research Forecasting (WRF) model and the Stochastic Time-Inverted Lagrangian Transport (STILT) model.

Compressible Boundary Layer Investigation for Ramjet/scramjet Inlets and Nozzles

NASA Astrophysics Data System (ADS)

Goldfeld, M. A.; Starov, A. V.; Semenova, Yu. V.

2005-02-01

The results of experimental investigation of a turbulent boundary layer on compression and expansion surfaces are presented. They include the study of the shock wave and/or expansion fan action upon the boundary layer, boundary layer separation and its relaxation. Complex events of paired interactions and the flow on compression convex-concave surfaces were studied [M. Goldfeld, 1993]. The possibility and conditions of the boundary layer relaminarization behind the expansion fan and its effect on the relaxation length are presented. Different model configurations for wide range conditions were investigated. Comparison of results for different interactions was carried out.

Heat transfer through turbulent boundary layers - The effects of introduction of and recovery from convex curvature

NASA Technical Reports Server (NTRS)

Simon, T. W.; Moffat, R. J.

1979-01-01

Measurements have been made of the heat transfer through a turbulent boundary layer on a convexly curved isothermal wall and on a flat plate following the curved section. Data were taken for one free-stream velocity and two different ratios of boundary layer thickness to radius of curvature delta/R = 0.051 and delta/R = 0.077. Only small differences were observed in the distribution of heat transfer rates for the two boundary layer thicknesses tested, although differences were noted in the temperature distributions within the boundary layer

An Experimental Investigation of the Confluent Boundary Layer on a High-Lift System

NASA Technical Reports Server (NTRS)

Thomas, F. O.; Nelson, R. C.

1997-01-01

This paper describes a fundamental experimental investigation of the confluent boundary layer generated by the interaction of a leading-edge slat wake with the boundary layer on the main element of a multi-element airfoil model. The slat and airfoil model geometry are both fully two-dimensional. The research reported in this paper is performed in an attempt to investigate the flow physics of confluent boundary layers and to build an archival data base on the interaction of the slat wake and the main element wall layer. In addition, an attempt is made to clearly identify the role that slat wake / airfoil boundary layer confluence has on lift production and how this occurs. Although complete LDV flow surveys were performed for a variety of slat gap and overhang settings, in this report the focus is on two cases representing both strong and weak wake boundary layer confluence.

Damage localization and quantification of composite stratified beam Structures using residual force method

NASA Astrophysics Data System (ADS)

Behtani, A.; Bouazzouni, A.; Khatir, S.; Tiachacht, S.; Zhou, Y.-L.; Abdel Wahab, M.

2017-05-01

In this paper, the problem of using measured modal parameters to detect and locate damage in beam composite stratified structures with four layers of graphite/epoxy [0°/902°/0°] is investigated. A technique based on the residual force method is applied to composite stratified structure with different boundary conditions, the results of damage detection for several damage cases demonstrate that using residual force method as damage index, the damage location can be identified correctly and the damage extents can be estimated as well.

Numerical Modeling of Active Flow Control in a Boundary Layer Ingesting Offset Inlet

NASA Technical Reports Server (NTRS)

Allan, Brian G.; Owens, Lewis R.; Berrier, Bobby L.

2004-01-01

This investigation evaluates the numerical prediction of flow distortion and pressure recovery for a boundary layer ingesting offset inlet with active flow control devices. The numerical simulations are computed using a Reynolds averaged Navier-Stokes code developed at NASA. The numerical results are validated by comparison to experimental wind tunnel tests conducted at NASA Langley Research Center at both low and high Mach numbers. Baseline comparisons showed good agreement between numerical and experimental results. Numerical simulations for the inlet with passive and active flow control also showed good agreement at low Mach numbers where experimental data has already been acquired. Numerical simulations of the inlet at high Mach numbers with flow control jets showed an improvement of the flow distortion. Studies on the location of the jet actuators, for the high Mach number case, were conducted to provide guidance for the design of a future experimental wind tunnel test.

Computation of the turbulent boundary layer downstream of vortex generators

NASA Astrophysics Data System (ADS)

Chang, Paul K.

1987-12-01

The approximate analysis of three-dimensional incompressible turbulent boundary layer downstream of vortex generators is presented. Extensive numerical computations are carried out to assess the effectiveness of single-row, counter-rotating vane-type vortex generators to alleviate flow separation lines. Flow separation downstream of the vortex generators on a thick airfoil are determined in terms of size, location, and arrangement of the vortex generators. These lines are compared with the separation line without the vortex generators. High efficiency is obtained with the moderately slender rectangular blade of the generator. The results indicate that separations is alleviated more effectively in the region closer to the symmetry axis of the generator than in the outer region of the symmetry axis. No optimum conditions for the alleviation of flow separation are established in this investigation, and no comparisons are made with other analytical results and experimental data.

Aircraft measurement of ozone turbulent flux in the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Affre, Ch.; Carrara, A.; Lefebre, F.; Druilhet, A.; Fontan, J.; Lopez, A.

In May 1995, the "Chimie-Creil 95" experiment was undertaken in the north of France. The field data are first used to validate the methodology for airborne measurement of ozone flux. A certain number of methodological problems due to the location of the fast ozone sensor inside the airplane are, furthermore discussed. The paper describes the instrumentation of the ARAT (Avion de Recherche Atmosphérique et de Télédétection), an atmospheric research and remote-sensing aircraft used to perform the airborne measurements, the area flown over, the meteorological conditions and boundary layer stability conditions. These aircraft measurements are then used to determine ozone deposition velocity and values are proposed for aerodynamic, bulk transfer coefficients (ozone and momentum). The paper also establishes the relationship between the normalised standard deviation and stability parameters ( z/ L) for ozone, temperature, humidity and vertical velocity. The laws obtained are then presented.

Computation of turbulent flow in a thin liquid layer of fluid involving a hydraulic jump

NASA Technical Reports Server (NTRS)

Rahman, M. M.; Faghri, A.; Hankey, W. L.

1991-01-01

Numerically computed flow fields and free surface height distributions are presented for the flow of a thin layer of liquid adjacent to a solid horizontal surface that encounters a hydraulic jump. Two kinds of flow configurations are considered: two-dimensional plane flow and axisymmetric radial flow. The computations used a boundary-fitted moving grid method with a k-epsilon model for the closure of turbulence. The free surface height was determined by an optimization procedure which minimized the error in the pressure distribution on the free surface. It was also checked against an approximate procedure involving integration of the governing equations and use of the MacCormack predictor-corrector method. The computed film height also compared reasonably well with previous experiments. A region of recirculating flow was found to be present adjacent to the solid boundary near the location of the jump, which was caused by a rapid deceleration of the flow.

Theoretical and experimental studies of electric field distribution in N-polar GaN/AlGaN/GaN heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gladysiewicz, M., E-mail: marta.gladysiewicz@pwr.edu.pl; Janicki, L.; Kudrawiec, R.

2015-12-28

Electric field distribution in N-polar GaN(channel)/AlGaN/GaN(buffer) heterostructures was studied theoretically by solving Schrodinger and Poisson equations in a self-consistent manner for various boundary conditions and comparing results of these calculations with experimental data, i.e., measurements of electric field in GaN(channel) and AlGaN layers by electromodulation spectroscopy. A very good agreement between theoretical calculations and experimental data has been found for the Fermi-level located at ∼0.3 eV below the conduction band at N-polar GaN surface. With this surface boundary condition, the electric field distribution and two dimensional electron gas concentration are determined for GaN(channel)/AlGaN/GaN(buffer) heterostructures of various thicknesses of GaN(channel) and AlGaNmore » layers.« less

Spatial optimal disturbances in swept-wing boundary layers

NASA Astrophysics Data System (ADS)

Chen, Cheng

2018-04-01

With the use of the adjoint-based optimization method proposed by Tempelmann et al. (J. Fluid Mech., vol. 704, 2012, pp. 251-279), in which the parabolized stability equation (PSE) and so-called adjoint parabolized stability equation (APSE) are solved iteratively, we obtain the spatial optimal disturbance shape and investigate its dependence on the parameters of disturbance wave and wall condition, such as radial frequency ω and wall temperature Twall, in a swept-wing boundary layer flow. Further, the non-modal growth mechanism of this optimal disturbance has been also discussed, regarding its spatial evolution way in the streamwise direction. The results imply that the spanwise wavenumber, disturbance frequency and wall cooling do not change the physical mechanism of perturbation growth, just with a substantial effect on the magnitude of perturbation growth. Further, wall cooling may have enhancing or suppressing effect on spatial optimal disturbance growth, depending on the streamwise location.

Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

NASA Technical Reports Server (NTRS)

Nagamatsu, H. T.; Brower, W. B., Jr.; Bahi, L.; Ross, J.

1982-01-01

The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.

Cleanups In My Community (CIMC) - Brownfields Grant Jurisdictions, National Layer

EPA Pesticide Factsheets

This data layer provides access to Brownfields Grant Jurisdictions as part of the CIMC web service. The data represent polygonal boundaries that show different types of grants. Only properties benefiting from EPA Brownfields grant funding and technical assistance appear in Cleanups in My Community. There are different types of grants and each grant covers a specific area of geography. Grant areas can overlap, and often do. On the map, Brownfields jurisdictions will be shown as colored boundaries. Grant Jurisdictions have their own reports and fact sheet. For more information on Brownfields grants, see Brownfields Grants and Funding at https://www.epa.gov/brownfields/types-brownfields-grant-funding.The CIMC web service was initially published in 2013, but the data are updated on the 18th of each month. The full schedule for data updates in CIMC is located here: https://iaspub.epa.gov/enviro/data_update_v2.

Cloud Feedback Key to Marine Heatwave off Baja California

NASA Astrophysics Data System (ADS)

Myers, Timothy A.; Mechoso, Carlos R.; Cesana, Gregory V.; DeFlorio, Michael J.; Waliser, Duane E.

2018-05-01

Between 2013 and 2015, the northeast Pacific Ocean experienced the warmest surface temperature anomalies in the modern observational record. This "marine heatwave" marked a shift of Pacific decadal variability to its warm phase and was linked to significant impacts on marine species as well as exceptionally arid conditions in western North America. Here we show that the subtropical signature of this warming, off Baja California, was associated with a record deficit in the spatial coverage of co-located marine boundary layer clouds. This deficit coincided with a large increase in downwelling solar radiation that dominated the anomalous energy budget of the upper ocean, resulting in record-breaking warm sea surface temperature anomalies. Our observation-based analysis suggests that a positive cloud-surface temperature feedback was key to the extreme intensity of the heatwave. The results demonstrate the extent to which boundary layer clouds can contribute to regional variations in climate.

Towards Natural Transition in Compressible Boundary Layers

DTIC Science & Technology

2016-06-29

AFRL-AFOSR-CL-TR-2016-0011 Towards natural transition in compressible boundary layers Marcello Faraco de Medeiros FUNDACAO PARA O INCREMENTO DA...to 29-03-2016 Towards natural transition in compressible boundary layers FA9550-11-1-0354 Marcello A. Faraco de Medeiros Germán Andrés Gaviria...unlimited. 109 Final report Towards natural transition in compressible boundary layers Principal Investigator: Marcello Augusto Faraco de Medeiros

Inventory of File nam.t00z.smartconus00.tm00.grib2

Science.gov Websites

(Eta model reduction) [Pa] 014 planetary boundary layer WDIR analysis Wind Direction (from which blowing) [degtrue] 015 planetary boundary layer WIND analysis Wind Speed [m/s] 016 planetary boundary layer RH analysis Relative Humidity [%] 017 planetary boundary layer DIST analysis Geometric Height [m

Geographic Information System Incorporated into Earth Science Classrooms to Enhance Individual Learning Development with Interconnected Concepts

NASA Astrophysics Data System (ADS)

Garifo, Mary Anna

2017-04-01

Geographic Information System, GIS, is a powerful tool and when incorporated into Earth Science classrooms, can enhance and empower students' engagement in their learning. Through utilization of GIS, students can process what they are learning in a spatially orientated method, which allows them to make connections among different related concepts. For example, if students are given a map in a GIS software with multiple layers of data on earthquakes, plate technics, and volcanoes then they can manipulate this information to come up with their own patterns. Through allowing students to develop their spatial recognition of where the Earth's plate boundaries are and where earthquakes have occurred, students can see how these two concepts are connected. In a guided but exploratory activity, students would be given multiple different websites that they could explore to research what different type of plates there are while they are working simultaneously with the GIS software. Using a plate technics layer, including data on type of boundary, students can explore and estimate which direction the plates are moving. When they look up convergent boundaries and see that the oceanic plates submerge under continental plates they can see where volcanic chains might be. Once they understand this in a spatial way, students can predict where they think volcanoes could be, based on where convergent boundaries are. When they manipulate the volcanic layer and see abnormalities to what they just learned, it will cause them to have cognitive dissonance, which will force them into seeking further understanding. The concept of a hot spot can then be introduced to resolve the cognitive dissonance and emphasis the idea that plates we live on are moving. Concepts can further be developed through GIS by showing how the strength and frequency of earthquakes are related to the level of activity at the plate boundary. This can be done by manipulating the map layer that represents earthquakes so that students can visualize each earthquake based on depth, size, or just location. If it is more active, then students should predict which direction it is moving based on the different boundary types. Rather than a traditional lecture approach, GIS software enables students to explore and manipulate relevant variables in an interactive and stimulating environment. It can harness their sense of wonder and exploration by giving them the opportunity to be hands on with the technology. In addition, using GIS in an Earth Science classroom can foster empathy in students. When the students look at the dots on the map, the hope is that they can visualize what type of destruction that could happen, especially when they change the variable function based on location to magnitude. As a teacher in Virginia, U.S.A., most students here have not experienced an earthquake. Although their perspective is limited, by allowing them to explore different locations with GIS, they create connections with places where earthquakes occur. The data and information they use allows them to learn about how the earth's systems are not isolated events but are the reality people live in.

Holocene sedimentary processes in the Gemlik Gulf: a transtensional basin on the middle Strand of the North Anatolian Fault, Sea of Marmara

NASA Astrophysics Data System (ADS)

Özmaral, A.; Çagatay, M. N.; Imren, C.; Gasperini, L.; Henry, P.

2012-04-01

Gemlik Gulf is an oval-shaped transtensional basin with a maximum depth of 113 m, located on the middle strand of the North Anatolian Fault (NAF) in the eastern part of the Sea of Marmara (SOM). During the last glacial period until the Holocene marine transgression about 12 ka BP, the sea level was below the Çanakkale (Dardanelles) Strait's bedrock sill depth of -85 m, and the Gemlik Basin became a lake isolated lake from the rest of the Sea of Marmara "Lake" and the global ocean. The high resolution seismic profiles and the multi- beam bathymetric map of the basin show that the basin is characterized by NW-SE trending transtensional oblique faults, delta lobes of the Büyükdere (Kocadere) to the east and an erosional surface below an up to 15 m-thick Holocene mud drape. The Holocene mud drape was studied in up to 9.5 m-long gravity-piston and 0.84 m-long sediment/water interface cores located at -105 to -113 m in the basin's depocentre. The Holocene mud consists mainly of plastic gray green marine clayey mud that includes thick-red brown clay layers and a laminated organic-rich, dark olive green sapropel in the lower part, which was previously dated at 11.6-6.4 14Ckyr (uncalib) BP. Multi-proxy analyses of the Holocene mud drape in the sediment cores were carried out using Multisensor Core Logger, XRF Core Scanner equipped with digital X-Ray radiography, and laser particle size analyzer. Seismic-core correlation was made using seismic data of the chirp profiles at the core locations and the synthetic seismograms generated using the MSCL P-wave velocity and gamma density measurements. The long piston-gravity cores include five 20 to 100 mm-thick "red brown mud layers" in the top 2.5 m of the core. These layers have a sharp basal boundary and gradational upper boundary. The red brown layers consist of 55-75% clay-size material with an average grain size of 3-4 µm, and have relatively a high magnetic susceptibility. They are enriched in K, Fe, Ti and Zr that are the proxy of detrital mineral input, and depleted in Ca, Br, Fe and Mn. Manganese shows a sharp enrichment immediately below the base of the red brown layers. All these features strongly suggest that the red layers represent the distal edges mass flow deposits, possibly sourced from the delta to the east. The distinct Mn enrichments below the base of the red brown layers represent the diagenetic enrichment at the oxic/anoxic boundary near the seafloor, which was later covered by the mass flow deposit. C-14 and radionuclide datings of the mass flow layers and investigation of their possible relation to the past earthquakes are under progress.

Boundary Layer

NASA Technical Reports Server (NTRS)

Loitsianskii. L. G.

1956-01-01

The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

Supersonic turbulent boundary layers with periodic mechanical non-equilibrium

NASA Astrophysics Data System (ADS)

Ekoto, Isaac Wesley

Previous studies have shown that favorable pressure gradients reduce the turbulence levels and length scales in supersonic flow. Wall roughness has been shown to reduce the large-scales in wall bounded flow. Based on these previous observations new questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface roughness and favorable pressure gradients are combined? To answer these questions and to enhance the current experimental database, an experimental analysis was performed to provide high fidelity documentation of the mean and turbulent flow properties along with surface and flow visualizations of a high-speed (M = 2.86), high Reynolds number (Retheta ≈ 60,000) supersonic turbulent boundary layer distorted by curvature-induced favorable pressure gradients and large-scale ( k+s ≈ 300) uniform surface roughness. Nine models were tested at three separate locations. Three pressure gradient models strengths (a nominally zero, a weak, and a strong favorable pressure gradient) and three roughness topologies (aerodynamically smooth, square, and diamond shaped roughness elements) were used. Highly resolved planar measurements of mean and fluctuating velocity components were accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized using pressure sensitive paint. Finally flow visualization was accomplished using schlieren photographs. Roughness topology had a significant effect on the boundary layer mean and turbulent properties due to shock boundary layer interactions. Favorable pressure gradients had the expected stabilizing effect on turbulent properties, but the improvements were less significant for models with surface roughness near the wall due to increased tendency towards flow separation. It was documented that proper roughness selection coupled with a sufficiently strong favorable pressure gradient produced regions of "negative" production in the transport of turbulent stress. This led to localized areas of significant turbulence stress reduction. With proper roughness selection and sufficient favorable pressure gradient strength, it is believed that localized relaminarization of the boundary layer is possible.

Current status of validating operational model forecasts at the DWD site Lindenberg

NASA Astrophysics Data System (ADS)

Beyrich, F.; Heret, C.; Vogel, G.

2009-09-01

Based on long experience in the measurement of atmospheric boundary layer parameters, the Meteorological Observatory Lindenberg / Richard - Aßmann-Observatory is well qualified to validate operational NWP results for this location. The validation activities cover a large range of time periods from single days or months up to several years and include much more quantities than generally used in areal verification techniques. They mainly focus on land surface and boundary layer processes which play an important role in the atmospheric forc-ing from the surface. Versatility and continuity of the database enable a comprehensive evaluation of the model behaviour under different meteorological conditions in order to esti-mate the accuracy of the physical parameterisations and to detect possible deficiencies in the predicted processes. The measurements from the boundary layer field site Falkenberg serve as reference data for various types of validation studies: 1. The operational boundary-layer measurements are used to identify and to document weather situations with large forecast errors which can then be analysed in more de-tail. Results from a case study will be presented where model deficiencies in the cor-rect simulation of the diurnal evolution of near-surface temperature under winter con-ditions over a closed snow cover where diagnosed. 2. Due to the synopsis of the boundary layer quantities based on monthly averaged di-urnal cycles systematic model deficiencies can be detected more clearly. Some dis-tinctive features found in the annual cycle (e.g. near-surface temperatures, turbulent heat fluxes and soil moisture) will be outlined. Further aspects are their different ap-pearance in the COSMO-EU and COSMO-DE models as well as the effects of start-ing time (00 or 12 UTC) on the prediction accuracy. 3. The evaluation of the model behaviour over several years provides additional insight into the impact of changes in the physical parameterisations, data assimilation or nu-merics on the meteorological quantities. The temporal development of the error char-acteristics of some near-surface weather parameters (temperature, dewpoint tem-perature, wind velocity) and of the energy fluxes at the surface will be discussed.

Intermittent turbulence events observed with a sonic anemometer and minisodar during CASES99.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coulter, R. L.; Doran, J. C.

The Cooperative Air Surface Exchange Study 1999 (CASES99), designed to investigate in detail the nocturnal boundary layer (NBL) of the atmosphere with particular emphasis on turbulence and turbulence events, took place during October 1999, within the Atmospheric Boundary Layer Experiments (ABLE) region east of Wichita KS. The principal measurement site was a heavily instrumented 2-km square located near Leon (LE), KS, but additional sites at Smileyberg (SM) and Beaumont (BE) were also used. The authors augmented the normal ABLE measurements at Beaumont (radar wind profiler, minisodar, 10-m meteorological tower, precipitation gauge) with a sonic anemometer mounted on the tower, 7more » m above the surface. For this campaign, the minisodar data were saved in single-pulse mode with no averaging. The Beaumont site is within gently rolling rangeland used primarily for grazing. The site is on a flat plain rising gradually to the east.The Flint Hills escarpment, located approximately 2 km to the east, marks the highest point in, and the eastern boundary of, the Walnut River watershed. Although most terrain features are subtle, terrain effects on atmospheric flows are still possible, particularly in stable conditions. The intent was to observe turbulence and, hopefully, turbulence events with the sonic anemometer and minisodar. The horizontal extent of these occurrences can be studied by including the Beaumont data with those obtained at the Leon site. In this report the authors are concerned with the occurrence of intermittent turbulence.« less

Sound-turbulence interaction in transonic boundary layers

NASA Astrophysics Data System (ADS)

Lelostec, Ludovic; Scalo, Carlo; Lele, Sanjiva

2014-11-01

Acoustic wave scattering in a transonic boundary layer is investigated through a novel approach. Instead of simulating directly the interaction of an incoming oblique acoustic wave with a turbulent boundary layer, suitable Dirichlet conditions are imposed at the wall to reproduce only the reflected wave resulting from the interaction of the incident wave with the boundary layer. The method is first validated using the laminar boundary layer profiles in a parallel flow approximation. For this scattering problem an exact inviscid solution can be found in the frequency domain which requires numerical solution of an ODE. The Dirichlet conditions are imposed in a high-fidelity unstructured compressible flow solver for Large Eddy Simulation (LES), CharLESx. The acoustic field of the reflected wave is then solved and the interaction between the boundary layer and sound scattering can be studied.

Pitot-probe displacement in a supersonic turbulent boundary layer

NASA Technical Reports Server (NTRS)

Allen, J. M.

1972-01-01

Eight circular pitot probes ranging in size from 2 to 70 percent of the boundary-layer thickness were tested to provide experimental probe displacement results in a two-dimensional turbulent boundary layer at a nominal free-stream Mach number of 2 and unit Reynolds number of 8 million per meter. The displacement obtained in the study was larger than that reported by previous investigators in either an incompressible turbulent boundary layer or a supersonic laminar boundary layer. The large probes indicated distorted Mach number profiles, probably due to separation. When the probes were small enough to cause no appreciable distortion, the displacement was constant over most of the boundary layer. The displacement in the near-wall region decreased to negative displacement in some cases. This near-wall region was found to extend to about one probe diameter from the test surface.

Year-Long Vertical Velocity Statistics Derived from Doppler Lidar Data for the Continental Convective Boundary Layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berg, Larry K.; Newsom, Rob K.; Turner, David D.

One year of Coherent Doppler Lidar (CDL) data collected at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) site in Oklahoma is analyzed to provide profiles of vertical velocity variance, skewness, and kurtosis for cases of cloud-free convective boundary layers. The variance was scaled by the Deardorff convective velocity scale, which was successful when the boundary layer depth was stationary but failed in situations when the layer was changing rapidly. In this study the data are sorted according to time of day, season, wind direction, surface shear stress, degree of instability, and wind shear across the boundary-layer top. Themore » normalized variance was found to have its peak value near a normalized height of 0.25. The magnitude of the variance changes with season, shear stress, and degree of instability, but was not impacted by wind shear across the boundary-layer top. The skewness was largest in the top half of the boundary layer (with the exception of wintertime conditions). The skewness was found to be a function of the season, shear stress, wind shear across the boundary-layer top, with larger amounts of shear leading to smaller values. Like skewness, the vertical profile of kurtosis followed a consistent pattern, with peak values near the boundary-layer top (also with the exception of wintertime data). The altitude of the peak values of kurtosis was found to be lower when there was a large amount of wind shear at the boundary-layer top.« less

Towards a Viscous Wall Model for Immersed Boundary Methods

NASA Technical Reports Server (NTRS)

Brehm, Christoph; Barad, Michael F.; Kiris, Cetin C.

2016-01-01

Immersed boundary methods are frequently employed for simulating flows at low Reynolds numbers or for applications where viscous boundary layer effects can be neglected. The primary shortcoming of Cartesian mesh immersed boundary methods is the inability of efficiently resolving thin turbulent boundary layers in high-Reynolds number flow application. The inefficiency of resolving the thin boundary is associated with the use of constant aspect ratio Cartesian grid cells. Conventional CFD approaches can efficiently resolve the large wall normal gradients by utilizing large aspect ratio cells near the wall. This paper presents different approaches for immersed boundary methods to account for the viscous boundary layer interaction with the flow-field away from the walls. Different wall modeling approaches proposed in previous research studies are addressed and compared to a new integral boundary layer based approach. In contrast to common wall-modeling approaches that usually only utilize local flow information, the integral boundary layer based approach keeps the streamwise history of the boundary layer. This allows the method to remain effective at much larger y+ values than local wall modeling approaches. After a theoretical discussion of the different approaches, the method is applied to increasingly more challenging flow fields including fully attached, separated, and shock-induced separated (laminar and turbulent) flows.

Investigations on entropy layer along hypersonic hyperboloids using a defect boundary layer

NASA Technical Reports Server (NTRS)

Brazier, J. P.; Aupoix, B.; Cousteix, J.

1992-01-01

A defect approach coupled with matched asymptotic expansions is used to derive a new set of boundary layer equations. This method ensures a smooth matching of the boundary layer with the inviscid solution. These equations are solved to calculate boundary layers over hypersonic blunt bodies involving the entropy gradient effect. Systematic comparisons are made for both axisymmetric and plane flows in several cases with different Mach and Reynolds numbers. After a brief survey of the entropy layer characteristics, the defect boundary layer results are compared with standard boundary layer and full Navier-Stokes solutions. The entropy gradient effects are found to be more important in the axisymmetric case than in the plane one. The wall temperature has a great influence on the results through the displacement effect. Good predictions can be obtained with the defect approach over a cold wall in the nose region, with a first order solution. However, the defect approach gives less accurate results far from the nose on axisymmetric bodies because of the thinning of the entropy layer.

Effects of Blade Boundary Layer Transition and Daytime Atmospheric Turbulence on Wind Turbine Performance Analyzed with Blade-Resolved Simulation and Field Data

NASA Astrophysics Data System (ADS)

Nandi, Tarak Nath

Relevant to utility scale wind turbine functioning and reliability, the present work focuses on enhancing our understanding of wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and rotating blades of a GE 1.5 MW wind turbine using a unique data set from a GE field experiment and computer simulations at two levels of fidelity. Previous studies have shown that the stability state of the lower troposphere has a major impact on the coherent structure of the turbulence eddies, with corresponding differences in wind turbine loading response. In this study, time-resolved aerodynamic data measured locally at the leading edge and trailing edge of three outer blade sections on a GE 1.5 MW wind turbine blade and high-frequency SCADA generator power data from a daytime field campaign are combined with computer simulations that mimic the GE wind turbine within a numerically generated atmospheric boundary layer (ABL) flow field which is a close approximation of the atmospheric turbulence experienced by the wind turbine in the field campaign. By combining the experimental and numerical data sets, this study describes the time-response characteristics of the local loadings on the blade sections in response to nonsteady nonuniform energetic atmospheric turbulence eddies within a daytime ABL which have spatial scale commensurate with that of the turbine blade length. This study is the first of its kind where actuator line and blade boundary layer resolved CFD studies of a wind turbine field campaign are performed with the motivation to validate the numerical predictions with the experimental data set, and emphasis is given on understanding the influence of the laminar to turbulent transition process on the blade loadings. The experimental and actuator line method data sets identify three important response time scales quantified at the blade location: advective passage of energy-dominant eddies (≈25 - 50 s), blade rotation (1P, ≈3 s) and sub-1P scale (< 1 s) response to internal eddy structure. Large amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the airfoil plane, modulated by eddy passage at longer time scales. Generator power is found to respond strongly to large-eddy wind modulations. The experimental data show that internal dynamics of blade boundary layer near the trailing edge is temporally modulated by the nonsteady external ABL flow that was measured at the leading edge, as well as blade generated turbulence motions. A blade boundary layer resolved CFD study of a GE 1.5MW wind turbine blade is carried out using a hybrid URANS/LES framework to quantify the influence of transition on the blade boundary layer dynamics and subsequent loadings, and also to predict the velocity magnitude data set measured by the trailing edge rakes in the experiment. A URANS based transition model is used as the near-wall model, and its ability to predict nonsteady boundary layer dynamics is assessed for flow over an oscillating airfoil exhibiting varying extents of nonsteady behavior. The CFD study shows that, at rated conditions, the transition and separation locations on the blade surface can be quite dynamic, but the transitional flow has negligible influence on the determination of the separation location and the overall pressure distribution at various blade sections, and subsequently the power output. But this conclusion should be accepted with caution for wind turbines running in off-design conditions (e.g. with significant yaw error, off-design pitch or rapid changes in pitch), where massive separation and dynamic stall may occur. Analysis of the near-blade flow field shows strong three dimensional flow in the inboard regions, which can possibly weaken the chordwise flow in the relatively outboard regions and make them more prone to separation. The trailing edge velocity profiles show qualitative resemblance with some specific cycles observed in the field experiment. The factors leading to the observed differences from the experimental data are also mentioned.

Airborne observations of new particle formation events in the boundary layer using a Zeppelin

NASA Astrophysics Data System (ADS)

Lampilahti, Janne; Manninen, Hanna E.; Nieminen, Tuomo; Mirme, Sander; Pullinen, Iida; Yli-Juuti, Taina; Schobesberger, Siegfried; Kangasluoma, Juha; Kontkanen, Jenni; Lehtipalo, Katrianne; Ehn, Mikael; Mentel, Thomas F.; Petäjä, Tuukka; Kulmala, Markku

2014-05-01

Atmospheric new particle formation (NPF) is a frequent and ubiquitous process in the atmosphere and a major source of newly formed aerosol particles [1]. However, it is still unclear how the aerosol particle distribution evolves in space and time during an NPF. We investigated where in the planetary boundary layer does NPF begin and how does the aerosol number size distribution develop in space and time during it. We measured in Hyytiälä, southern Finland using ground based and airborne measurements. The measurements were part of the PEGASOS project. NPF was studied on six scientific flights during spring 2013 using a Zeppelin NT class airship. Ground based measurements were simultaneously conducted at SMEAR II station located in Hyytiälä. The flight profiles over Hyytiälä were flown between sunrise and noon during the growth of the boundary layer. The profiles over Hyytiälä covered vertically a distance of 100-1000 meters reaching the mixed layer, stable (nocturnal) boundary layer and the residual layer. Horizontally the profiles covered approximately a circular area of four kilometers in diameter. The measurements include particle number size distribution by Neutral cluster and Air Ion Spectrometer (NAIS), Differential Mobility Particle Sizer (DMPS) and Particle Size Magnifier (PSM) [2], meteorological parameters and position (latitude, longitude and altitude) of the Zeppelin. Beginning of NPF was determined from an increase in 1.7-3 nm ion concentration. Height of the mixed layer was estimated from relative humidity measured on-board the Zeppelin. Particle growth rate during NPF was calculated. Spatial inhomogeneities in particle number size distribution during NPF were located and the birthplace of the particles was estimated using the growth rate and trajectories. We observed a regional NPF event that began simultaneously and evolved uniformly inside the mixed layer. In the horizontal direction we observed a long and narrow high concentration plume of growing particles that moved over the measurement site. The particles of the regional event as well as the particles of the plume were uniformly distributed in the vertical direction and showed a similar growth rate of approximately 2 nm/h. The plume caused sharp discontinuities in the number size distribution of the growing particle mode. These kinds of discontinuities are seen quite often on SMEAR II data during NPF events and it is likely that they are caused by inhomogeneous NPF in the horizontal direction (possibly narrow long plumes). This work is supported by European Commission under the Framework Programme 7 (FP7-ENV-2010-265148) and by the Academy of Finland Centre of Excellence program (project no. 1118615). The Zeppelin is accompanied by an international team of scientists and technicians. They are all warmly acknowledged. References [1] Kulmala, M., et al., (2013), Direct Observations of Atmospheric Aerosol Nucleation, Science, 339, 943-946 [2] Kulmala, M., et al., (2012), Measurement of the nucleation of atmospheric aerosol particles, Nature Protocols, 7, 1651-1667

Inventory of File gfs.t06z.smartguam15.tm00.grib2

Science.gov Websites

hour fcst Visibility [m] 014 planetary boundary layer WDIR 15 hour fcst Wind Direction (from which blowing) [degtrue] 015 planetary boundary layer WIND 15 hour fcst Wind Speed [m/s] 016 planetary boundary layer RH 15 hour fcst Relative Humidity [%] 017 planetary boundary layer DIST 15 hour fcst Geometric

Physical modeling of the atmospheric boundary layer in the UNH Flow Physics Facility

NASA Astrophysics Data System (ADS)

Taylor-Power, Gregory; Gilooly, Stephanie; Wosnik, Martin; Klewicki, Joe; Turner, John

2016-11-01

The Flow Physics Facility (FPF) at UNH has test section dimensions W =6.0m, H =2.7m, L =72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPF's ability to experimentally simulate different types of the atmospheric boundary layer (ABL) using upstream roughness arrays. The American Society for Civil Engineers defines standards for simulating ABLs for different terrain types, from open sea to dense city areas (ASCE 49-12). The standards require the boundary layer to match a power law shape, roughness height, and power spectral density criteria. Each boundary layer type has a corresponding power law exponent and roughness height. The exponent and roughness height both increase with increasing roughness. A suburban boundary layer was chosen for simulation and a roughness element fetch was created. Several fetch lengths were experimented with and the resulting boundary layers were measured and compared to standards in ASCE 49-12: Wind Tunnel Testing for Buildings and Other Structures. Pitot tube and hot wire anemometers were used to measure average and fluctuating flow characteristics. Velocity profiles, turbulence intensity and velocity spectra were found to compare favorably.

Effect of Pulsed Plasma Jets on the Recovering Boundary Layer Downstream of a Reflected Shock Interaction

NASA Astrophysics Data System (ADS)

Greene, Benton; Clemens, Noel; Magari, Patrick; Micka, Daniel; Ueckermann, Mattheus

2015-11-01

Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic inlets including flow distortion and instability, structural fatigue, poor pressure recovery, and unstart. The current study investigates the effect of pulsed plasma jets on the recovering boundary layer downstream of a reflected shock wave-boundary layer interaction. The effects of pitch and skew angle of the jet as well as the heating parameter and discharge time scale are tested using several pulsing frequencies. In addition, the effect of the plasma jets on the undisturbed boundary layer at 6 mm and 11 mm downstream of the jets is measured. A pitot-static pressure probe is used to measure the velocity profile of the boundary layer 35 mm downstream of the plasma jets, and the degree of boundary layer distortion is compared between the different models and run conditions. Additionally, the effect of each actuator configuration on the shape of the mean separated region is investigated using surface oil flow visualization. Previous studies with lower energy showed a weak effect on the downstream boundary layer. The current investigation will attempt to increase this effect using a higher-energy discharge. Funded by AFRL through and SBIR in collaboration with Creare, LLC.

Optimal Control of Shock Wave Turbulent Boundary Layer Interactions Using Micro-Array Actuation

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Tinapple, Jon; Surber, Lewis

2006-01-01

The intent of this study on micro-array flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to determine optimal designs of micro-array actuation for controlling the shock wave turbulent boundary layer interactions within supersonic inlets and compare these concepts to conventional bleed performance. The term micro-array refers to micro-actuator arrays which have heights of 25 to 40 percent of the undisturbed supersonic boundary layer thickness. This study covers optimal control of shock wave turbulent boundary layer interactions using standard micro-vane, tapered micro-vane, and standard micro-ramp arrays at a free stream Mach number of 2.0. The effectiveness of the three micro-array devices was tested using a shock pressure rise induced by the 10 shock generator, which was sufficiently strong as to separate the turbulent supersonic boundary layer. The overall design purpose of the micro-arrays was to alter the properties of the supersonic boundary layer by introducing a cascade of counter-rotating micro-vortices in the near wall region. In this manner, the impact of the shock wave boundary layer (SWBL) interaction on the main flow field was minimized without boundary bleed.

Generalization of Boundary-Layer Momentum-Integral Equations to Three-Dimensional Flows Including Those of Rotating System

NASA Technical Reports Server (NTRS)

Mager, Arthur

1952-01-01

The Navier-Stokes equations of motion and the equation of continuity are transformed so as to apply to an orthogonal curvilinear coordinate system rotating with a uniform angular velocity about an arbitrary axis in space. A usual simplification of these equations as consistent with the accepted boundary-layer theory and an integration of these equations through the boundary layer result in boundary-layer momentum-integral equations for three-dimensional flows that are applicable to either rotating or nonrotating fluid boundaries. These equations are simplified and an approximate solution in closed integral form is obtained for a generalized boundary-layer momentum-loss thickness and flow deflection at the wall in the turbulent case. A numerical evaluation of this solution carried out for data obtained in a curving nonrotating duct shows a fair quantitative agreement with the measures values. The form in which the equations are presented is readily adaptable to cases of steady, three-dimensional, incompressible boundary-layer flow like that over curved ducts or yawed wings; and it also may be used to describe the boundary-layer flow over various rotating surfaces, thus applying to turbomachinery, propellers, and helicopter blades.

Control of vortical separation on conical bodies

NASA Technical Reports Server (NTRS)

Mourtos, Nikos J.; Roberts, Leonard

1987-01-01

In a variety of aeronautical applications, the flow around conical bodies at incidence is of interest. Such applications include, but are not limited to, highly maneuverable aircraft with delta wings, the aerospace plane and nose portions of spike inlets. The theoretical model used has three parts. First, the single line vortex model is used within the framework of slender body theory, to compute the outer inviscid field for specified separation lines. Next, the three dimensional boundary layer is represented by a momentum equation for the cross flow, analogous to that for a plane boundary layer; a von Karman Pohlhausen approximation is applied to solve this equation. The cross flow separation for both laminar and turbulent layers is determined by matching the pressure at the upper and lower separation points. This iterative procedure yields a unique solution for the separation lines and consequently for the position of the vortices and the vortex lift on the body. Lastly, control of separation is achieved by blowing tangentially from a slot located along a cone generator. It is found that for very small blowing coefficients, the separation can be postponed or suppressedy completely.

Modeling marine boundary-layer clouds with a two-layer model: A one-dimensional simulation

NASA Technical Reports Server (NTRS)

Wang, Shouping

1993-01-01

A two-layer model of the marine boundary layer is described. The model is used to simulate both stratocumulus and shallow cumulus clouds in downstream simulations. Over cold sea surfaces, the model predicts a relatively uniform structure in the boundary layer with 90%-100% cloud fraction. Over warm sea surfaces, the model predicts a relatively strong decoupled and conditionally unstable structure with a cloud fraction between 30% and 60%. A strong large-scale divergence considerably limits the height of the boundary layer and decreases relative humidity in the upper part of the cloud layer; thus, a low cloud fraction results. The efffects of drizzle on the boundary-layer structure and cloud fraction are also studied with downstream simulations. It is found that drizzle dries and stabilizes the cloud layer and tends to decouple the cloud from the subcloud layer. Consequently, solid stratocumulus clouds may break up and the cloud fraction may decrease because of drizzle.

Calculation of sidewall boundary-layer parameters from rake measurements for the Langley 0.3-meter transonic cryogenic tunnel

NASA Technical Reports Server (NTRS)

Murthy, A. V.

1987-01-01

Correction of airfoil data for sidewall boundary-layer effects requires a knowledge of the boundary-layer displacement thickness and the shape factor with the tunnel empty. To facilitate calculation of these quantities under various test conditions for the Langley 0.3 m Transonic Cryogenic Tunnel, a computer program was written. This program reads the various tunnel parameters and the boundary-layer rake total head pressure measurements directly from the Engineering Unit tapes to calculate the required sidewall boundary-layer parameters. Details of the method along with the results for a sample case are presented.

Studies on the influence on flexural wall deformations on the development of the flow boundary layer

NASA Technical Reports Server (NTRS)

Schilz, W.

1978-01-01

Flexural wave-like deformations can be used to excite boundary layer waves which in turn lead to the onset of turbulence in the boundary layer. The investigations were performed with flow velocities between 5 m/s and 40 m/s. With four different flexural wave transmissions a frequency range from 0.2 kc/s to 1.5 kc/s and a phase velocity range from 3.5 m/s to 12 m/s was covered. The excitation of boundary layer waves becomes most effective if the phase velocity of the flexural wave coincides with the phase velocity region of unstable boundary layer waves.

Viscous flow drag reduction; Symposium, Dallas, Tex., November 7, 8, 1979, Technical Papers

NASA Technical Reports Server (NTRS)

Hough, G. R.

1980-01-01

The symposium focused on laminar boundary layers, boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT aircraft, drag reduction of an oscillating flat plate with an interface film, electromagnetic precipitation and ducting of particles in turbulent boundary layers, large eddy breakup scheme for turbulent viscous drag reduction, blowing and suction, polymer additives, and compliant surfaces. Topics included influence of environment in laminar boundary layer control, generation rate of turbulent patches in the laminar boundary layer of a submersible, drag reduction of small amplitude rigid surface waves, and hydrodynamic drag and surface deformations generated by liquid flows over flexible surfaces.

RANS Based Methodology for Predicting the Influence of Leading Edge Erosion on Airfoil Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langel, Christopher M.; Chow, Raymond C.; van Dam, C. P.

The impact of surface roughness on flows over aerodynamically designed surfaces is of interested in a number of different fields. It has long been known the surface roughness will likely accelerate the laminar- turbulent transition process by creating additional disturbances in the boundary layer. However, there are very few tools available to predict the effects surface roughness will have on boundary layer flow. There are numerous implications of the premature appearance of a turbulent boundary layer. Increases in local skin friction, boundary layer thickness, and turbulent mixing can impact global flow properties compounding the effects of surface roughness. With thismore » motivation, an investigation into the effects of surface roughness on boundary layer transition has been conducted. The effort involved both an extensive experimental campaign, and the development of a high fidelity roughness model implemented in a R ANS solver. Vast a mounts of experimental data was generated at the Texas A&M Oran W. Nicks Low Speed Wind Tunnel for the calibration and validation of the roughness model described in this work, as well as future efforts. The present work focuses on the development of the computational model including a description of the calibration process. The primary methodology presented introduces a scalar field variable and associated transport equation that interacts with a correlation based transition model. The additional equation allows for non-local effects of surface roughness to be accounted for downstream of rough wall sections while maintaining a "local" formulation. The scalar field is determined through a boundary condition function that has been calibrated to flat plate cases with sand grain roughness. The model was initially tested on a NACA 0012 airfoil with roughness strips applied to the leading edge. Further calibration of the roughness model was performed using results from the companion experimental study on a NACA 63 3 -418 airfoil. The refined model demonstrates favorable agreement predicting changes to the transition location, as well as drag, for a number of different leading edge roughness configurations on the NACA 63 3-418 airfoil. Additional tests were conducted on a thicker S814 airfoil, with similar roughness configurations to the NACA 63 3-418. Simulations run with the roughness model compare favorably with the results obtained in the experimental study for both airfoils.« less

Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices

NASA Astrophysics Data System (ADS)

Lee, Yoju; Verstraete, Frank; Gendiar, Andrej

2016-08-01

The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field.

Sensitivity of shock boundary-layer interactions to weak geometric perturbations

NASA Astrophysics Data System (ADS)

Kim, Ji Hoon; Eaton, John K.

2016-11-01

Shock-boundary layer interactions can be sensitive to small changes in the inlet flow and boundary conditions. Robust computational models must capture this sensitivity, and validation of such models requires a suitable experimental database with well-defined inlet and boundary conditions. To that end, the purpose of this experiment is to systematically document the effects of small geometric perturbations on a SBLI flow to investigate the flow physics and establish an experimental dataset tailored for CFD validation. The facility used is a Mach 2.1, continuous operation wind tunnel. The SBLI is generated using a compression wedge; the region of interest is the resulting reflected shock SBLI. The geometric perturbations, which are small spanwise rectangular prisms, are introduced ahead of the compression ramp on the opposite wall. PIV is used to study the SBLI for 40 different perturbation geometries. Results show that the dominant effect of the perturbations is a global shift of the SBLI itself. In addition, the bumps introduce weaker shocks of varying strength and angles, depending on the bump height and location. Various scalar validation metrics, including a measure of shock unsteadiness, and their uncertainties are also computed to better facilitate CFD validation. Ji Hoon Kim is supported by an OTR Stanford Graduate Fellowship.

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients

NASA Technical Reports Server (NTRS)

Hoffmann, Jon A.

1988-01-01

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent bounday layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free stream, both of which act to improve the transmission of momentum from the free stream to the boundary layers.

Foliar trichomes, boundary layers, and gas exchange in 12 species of epiphytic Tillandsia (Bromeliaceae).

PubMed

Benz, Brett W; Martin, Craig E

2006-04-01

We examined the relationships between H2O and CO2 gas exchange parameters and leaf trichome cover in 12 species of Tillandsia that exhibit a wide range in trichome size and trichome cover. Previous investigations have hypothesized that trichomes function to enhance boundary layers around Tillandsioid leaves thereby buffering the evaporative demand of the atmosphere and retarding transpirational water loss. Data presented herein suggest that trichome-enhanced boundary layers have negligible effects on Tillandsia gas exchange, as indicated by the lack of statistically significant relationships in regression analyses of gas exchange parameters and trichome cover. We calculated trichome and leaf boundary layer components, and their associated effects on H2O and CO2 gas exchange. The results further indicate trichome-enhanced boundary layers do not significantly reduce transpirational water loss. We conclude that although the trichomes undoubtedly increase the thickness of the boundary layer, the increase due to Tillandsioid trichomes is inconsequential in terms of whole leaf boundary layers, and any associated reduction in transpirational water loss is also negligible within the whole plant gas exchange pathway.

Hydrodynamic structure of the boundary layers in a rotating cylindrical cavity with radial inflow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrmann-Priesnitz, Benjamín, E-mail: bherrman@ing.uchile.cl; Torres, Diego A.; Advanced Mining Technology Center, Universidad de Chile, Av. Tupper 2007, Santiago

A flow model is formulated to investigate the hydrodynamic structure of the boundary layers of incompressible fluid in a rotating cylindrical cavity with steady radial inflow. The model considers mass and momentum transfer coupled between boundary layers and an inviscid core region. Dimensionless equations of motion are solved using integral methods and a space-marching technique. As the fluid moves radially inward, entraining boundary layers develop which can either meet or become non-entraining. Pressure and wall shear stress distributions, as well as velocity profiles predicted by the model, are compared to numerical simulations using the software OpenFOAM. Hydrodynamic structure of themore » boundary layers is governed by a Reynolds number, Re, a Rossby number, Ro, and the dimensionless radial velocity component at the periphery of the cavity, U{sub o}. Results show that boundary layers merge for Re < < 10 and Ro > > 0.1, and boundary layers become predominantly non-entraining for low Ro, low Re, and high U{sub o}. Results may contribute to improve the design of technology, such as heat exchange devices, and turbomachinery.« less