Boundary layer response to wind gusts
Morland, Bruce Thomas
1968-01-01
is the qwsstioa of tba flew ower aa oscillatisS ~ irfoil. The dcwosash distrihutisa ?ad Che airlosds distributioa froa basic ?hoary ara iscorrect bocosse tha basic theory idaores the booadary layer sa tha airfoil ss weD as Che respoaso of tbe bossdary layer... percent of tha free stxesa velocity sad wss of high frequency. The saaLL sire sa4 wo?4 ?castructien of this tunnel facilitated the iastallation of tba sir La+?tice systeu. Ths tuanol airspeed control was bsse4 oa coaditkcns as?cured by a pitot...
Transitional boundary-layer response to wall vibrations
S. Y. Kim; X. Bonnardel; J. P. Guibergia; E. Brocher
1994-01-01
The effects of wall vibration on the development of Tollmien-Schlichting (T-S) waves in a transitional flat-plate boundary layer are considered. Theoretically, the dynamic interaction between T-S waves and velocity perturbations induced by the vibrating wall is demonstrated through the kinetic energy balance of velocity perturbations. For a compliant wall, the response of T-S waves to velocity perturbations induced by the
Wind tunnel measurement of boundary-layer response to sediment transport
Cheryl McKenna Neuman; Marianne Maljaars
1997-01-01
This paper presents an empirical analysis of theboundary-layer response to sediment transport in awind tunnel with working section 0.7 × 0.76 × 12.5 m.With equilibrium transport, both the boundary-layer depth anddisplacement thickness increase relativeto clean air. The logarithmic expression of the Lawof the Wall provides a good description of thevelocity profile within the lower 20% of theboundary-layer depth, at least.
Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance
Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing
2014-01-01
The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993
Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.
Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing
2014-01-01
The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993
NASA Technical Reports Server (NTRS)
Frendi, Abdelkader
1997-01-01
Using the model developed by the author for zero-pressure gradient turbulent boundary layers, results are obtained for adverse and favorable pressure gradients. It is shown that when a flexible plate is located in an adverse pressure gradient area, it vibrates more than if it were in a favorable pressure gradient one. Therefore the noise generated by the plate in an adverse pressure gradient is much greater than that due to the plate in a favorable pressure gradient. The effects of Reynolds number and boundary layer thickness are also analyzed and found to have the same effect in both adverse and favorable pressure gradient cases. Increasing the Reynolds number is found to increase the loading on the plate and therefore acoustic radiation. An increase in boundary layer thickness is found to decrease the level of the high frequencies and therefore the response and radiation at these frequencies. The results are in good qualitative agreement with experimental measurements.
Response of a panel to a supersonic turbulent boundary layer - Studies on a theoretical model
NASA Technical Reports Server (NTRS)
Yen, D. H. Y.; Maestrello, L.; Padula, S. L.
1980-01-01
A study of the response of a clamped panel to a supersonic turbulent boundary layer, based on a recently developed theoretical model, is presented. It is demonstrated that the model incorporates the effect of coupling between the panel motion and the flow of the surrounding fluid. Further, a Ritz-Galerkin method is used to obtain approximate solutions for the statistics of the panel response to the turbulence. The numerical results are compared with previous experimental data and the theoretical model is assessed.
Forced Response Analysis of a Fan with Boundary Layer Inlet Distortion
NASA Technical Reports Server (NTRS)
Bakhle, Milind A.; Reddy, T. S. R.; Coroneos, Rula M.
2014-01-01
Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn for future generations of commercial aircraft, but these systems must be designed to overcome the challenge of high dynamic stresses in fan blades due to forced response. High dynamic stresses can lead to high cycle fatigue failures. High-fidelity computational analysis of the fan aeromechanics is integral to an ongoing effort to design a boundary layer ingesting inlet and fan for a wind-tunnel test. An unsteady flow solution from a Reynoldsaveraged Navier Stokes analysis of a coupled inlet-fan system is used to calculate blade unsteady loading and assess forced response of the fan to distorted inflow. Conducted prior to the mechanical design of a fan, the initial forced response analyses performed in this study provide an early look at the levels of dynamic stresses that are likely to be encountered. For the boundary layer ingesting inlet, the distortion contains strong engine order excitations that act simultaneously. The combined effect of these harmonics was considered in the calculation of the forced response stresses. Together, static and dynamic stresses can provide the information necessary to evaluate whether the blades are likely to fail due to high cycle fatigue. Based on the analyses done, the overspeed condition is likely to result in the smallest stress margin in terms of the mean and alternating stresses. Additional work is ongoing to expand the analyses to off-design conditions, on-resonance conditions, and to include more detailed modeling of the blade structure.
Investigating Response from Turbulent Boundary Layer Excitations on a Real Launch Vehicle using SEA
NASA Technical Reports Server (NTRS)
Harrison, Phillip; LaVerde,Bruce; Teague, David
2009-01-01
Statistical Energy Analysis (SEA) response has been fairly well anchored to test observations for Diffuse Acoustic Field (DAF) loading by others. Meanwhile, not many examples can be found in the literature anchoring the SEA vehicle panel response results to Turbulent Boundary Layer (TBL) fluctuating pressure excitations. This deficiency is especially true for supersonic trajectories such as those required by this nation s launch vehicles. Space Shuttle response and excitation data recorded from vehicle flight measurements during the development flights were used in a trial to assess the capability of the SEA tool to predict similar responses. Various known/measured inputs were used. These were supplemented with a range of assumed values in order to cover unknown parameters of the flight. This comparison is presented as "Part A" of the study. A secondary, but perhaps more important, objective is to provide more clarity concerning the accuracy and conservatism that can be expected from response estimates of TBL-excited vehicle models in SEA (Part B). What range of parameters must be included in such an analysis in order to land on the conservative side in response predictions? What is the sensitivity of changes in these input parameters on the results? The TBL fluid structure loading model used for this study is provided by the SEA module of the commercial code VA One.
The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1989-01-01
The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.
Bravo, Teresa; Maury, Cédric
2011-01-01
Random wall-pressure fluctuations due to the turbulent boundary layer (TBL) are a feature of the air flow over an aircraft fuselage under cruise conditions, creating undesirable effects such as cabin noise annoyance. In order to test potential solutions to reduce the TBL-induced noise, a cost-efficient alternative to in-flight or wind-tunnel measurements involves the laboratory simulation of the response of aircraft sidewalls to high-speed subsonic TBL excitation. Previously published work has shown that TBL simulation using a near-field array of loudspeakers is only feasible in the low frequency range due to the rapid decay of the spanwise correlation length with frequency. This paper demonstrates through theoretical criteria how the wavenumber filtering capabilities of the radiating panel reduces the number of sources required, thus dramatically enlarging the frequency range over which the response of the TBL-excited panel is accurately reproduced. Experimental synthesis of the panel response to high-speed TBL excitation is found to be feasible over the hydrodynamic coincidence frequency range using a reduced set of near-field loudspeakers driven by optimal signals. Effective methodologies are proposed for an accurate reproduction of the TBL-induced sound power radiated by the panel into a free-field and when coupled to a cavity. PMID:21302997
Response of a two-layer ocean to typhoon passage in the western boundary region
Nobuo Suginohara
1973-01-01
Effect of the typhoon passage on the western boundary region of a two-layer ocean with bottom topography is studied. The ocean is initially at rest and is set in motion by a typhoon passing parallel to the west coast. Equations that represent barotropic and baroclinic modes of motions are solved numerically by means of the method of finite differences. Motions
On the response of skin friction and heat transfer to fluctuating boundary layers
D. P. Telionis; M. S. Romaniuk
1977-01-01
A method is described for integration of the incompressible laminar boundary layer equations with periodic fluctuating outer flow velocity and temperature distributions. The method is a combination of numerical analysis and perturbation techniques and is valid for small amplitude ratios, epsilon. It is demonstrated that a reduction by at least a factor of one hundredth in computer storage is accomplished
J. Y. Fu; Q. S. Li; J. R Wu; Y. Q. Xiao; L. L. Song
2008-01-01
This paper presents field measurement results of boundary layer wind characteristics over typical open country and urban terrains and wind-induced responses of two super-tall buildings during the passages of windstorms. The field data such as wind speed, wind direction and acceleration responses, etc., were measured from an observation tower with height of 17.5m at a coastal region in Lufeng and
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.
1984-01-01
High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.
Boundary layers in centrifugal compressors
R. C. Dean 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
Boundary layer transition studies
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1995-01-01
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.
Jupiter's deep magnetotail boundary layer
NASA Astrophysics Data System (ADS)
Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.
2015-06-01
In 2007 the New Horizons (NH) spacecraft flew by Jupiter for a gravity assist en route to Pluto. After closest approach on day of year (DOY) 58, 2007, NH followed a tailward trajectory that provided a unique opportunity to explore the deep jovian magnetotail and the surrounding magnetosheath. After DOY 132, 16 magnetopause crossings were observed between 1654 and 2429 Jupiter radii (Rj) along the dusk flank tailward of the planet. In some cases the crossings were identified as rapid transitions from the magnetotail to the magnetosheath and vice versa. In other cases a boundary layer was observed just inside the magnetopause. Solar Wind Around Pluto (SWAP) is an instrument on board NH that obtained spectra of low energy ions during the flyby period. We use a forward model including the SWAP instrument response to derive plasma parameters (density, temperature and velocity) which best reproduce the observations. We also vary the plasma parameters in our model in order to fit the observations more accurately on occasions where the measurements exhibit significant variability. We compare the properties of the plasma in the boundary layer with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the boundary layer assuming pressure balance between it and the magnetosheath. Finally, we investigate several possible scenarios to assess if magnetopause movement and structure could cause the variations seen in the data.
NASA Astrophysics Data System (ADS)
Costigliola, V.
2010-09-01
It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate matter for regional environmental agencies - Local forecast model evaluation support for local authorities and city bodies. Giving value to the above listed aspects, PASODOBLE objectives are following: - Evolution of existing and development of new sustainable air quality services for Europe on regional and local scales - Development and testing of a generic service framework for coordinated input data acquisition and customizable user-friendly access to services - Utilization of multiple cycles of delivery, use and assessment versus requirements and market planning in cooperation with users - Promotion and harmonisation of best practise tools for air quality communities. Further European multidisciplinary projects should be created to better understand the most prevalent atmospheric factors to be impacted in predictive, preventive and personalised medicine considered as the central concept for future medicine.
Boundary layer receptivity and control
NASA Technical Reports Server (NTRS)
Hill, D. C.
1993-01-01
Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three-dimensional motions of a non-parallel boundary layer was developed. The method makes use of the same computationally efficient formulation that makes the PSE currently so appealing. In the area of flow control, adjoint systems offer a powerful insight into the effect of control forces. One of the simplest control strategies for boundary layers involves the application of localized mean wall suction.
Minimalist turbulent boundary layer model.
Moriconi, L
2009-04-01
We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent intensity, skewness, and flatness) of the streamwise velocity fluctuations. As an application, we advance some heuristic considerations on the boundary layer underlying kinematics that could be associated with the phenomenon of drag reduction by polymers, finding a suggestive support from its experimental signatures. PMID:19518332
Vortex boundary-layer interactions
NASA Technical Reports Server (NTRS)
Bradshaw, P.
1985-01-01
The interaction of a turbulent boundary layer on a flat plate with a strong artificially generated longitudinal vortex which may or may not actually enter the boundary layer is studied. The vortices are generated by a delta wing suspended ahead of the test plate, so that the configuration is approximately that of a close coupled carnard with zero main-wing sweep and an invisible body. All necessary configuration and parametric checks are completed, and data acquisition and analysis on the first configuration chosen for detailed study, in which the vortex starts to merge with the boundary layer a short distance downstream of the leading edge of the test plate, are nearly complete.
Response of the atmospheric boundary layer to a mesoscale oceanic eddy in the northeast Atlantic
NASA Astrophysics Data System (ADS)
Bourras, Denis; Reverdin, Gilles; Giordani, Hervé; Caniaux, Guy
2004-09-01
Fields of air-sea turbulent fluxes and bulk variables were derived from satellite sensor data from February to April 2001, over a region of the northeast Atlantic where a field experiment, Programme Océan Multidisciplinaire Meso Echelle (POMME), was conducted. The satellite products are in good agreement with in situ data in terms of heat fluxes, sea surface temperature, and wind speed. The central part of the experimental domain presented a cyclonic eddy in the ocean, which corresponded to a cold sea surface temperature (SST) anomaly. Winds were weaker within the eddy than outside of it, with lower latent and sensible heat loss. In order to analyze the relationship between the SST and wind anomalies, three numerical experiments were conducted with a regional atmospheric model. Three 3-month runs of the model were performed, using a realistic SST field, a smoothed SST field in which the cold SST was not present (reference run), and an SST field where the cold anomaly was increased by two degrees, successively. The fields simulated with the realistic SST were consistent with satellite sensor derived observations. In particular, the weak wind area over the cold SST anomaly was successfully rendered, whereas it was not present in the forcing fields. Taken individually, the three runs did not reveal the presence of secondary circulations. However, anomalous secondary circulations were clearly identified with respect to the reference run. The origin of the latter circulations was investigated with the Giordani and Planton generalization of the Sawyer-Eliassen equations. According to our results, differential heating induced by the cold SST anomaly mostly altered the vertical wind through the effect of friction and only marginally through pressure gradient forces. In the upper part of the boundary layer, the wind speed increased (decreased) over (downstream) the cold SST. We found that stability was the main factor that induced the simulated patterns of the friction term in the diagnostic equations. Therefore our results show that mesoscale wind patterns were significantly affected by SST gradients through the effect of stability, in a region of low oceanic eddy activity.
Boundary Layer Control on Airfoils.
ERIC Educational Resources Information Center
Gerhab, George; Eastlake, Charles
1991-01-01
A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)
The plasma sheet boundary layer
NASA Technical Reports Server (NTRS)
Eastman, T. E.; Frank, L. A.; Peterson, W. K.; Lennartsson, W.
1984-01-01
A spatially distinct, temporally variable, transition region between the magnetotail lobes and the central plasma sheet designated the plasma sheet boundary layer has been identified from a survey of particle spectra and three-dimensional distributions as sampled by the ISEE 1 LEPEDEA. The instrumentation and data presentation are described, and the signatures of the magnetotail plasma regimes are presented and discussed for the central plasma sheet and lobe and the plasma sheet boundary layer. Comparisons of plasma parameters and distribution fucntions are made and the evolution of ion velocity distributions within the plasma sheet boundary layer is discussed. The spatial distribution of the plasma sheet boundary layer is considered and ion composition measurements are presented.
NASA Technical Reports Server (NTRS)
O'Brien, Walter F.; Ferrar, Anthony M.; Arend, David
2011-01-01
BWB Aircraft with embedded engines and BLI inlets offer attractive advantages in terms of reduced noise from engines and increased range and fuel economy. The BLI inlet produces inlet distortion patterns that can reduce fan performance and stall margin, and can produce undesirable forced responses. Knowledge of the dynamic response of fan flow when subjected to flow distortions of the type produced by BLI inlets is important for the design of distortion tolerant fans. This project is investigating fan response to flow distortion by measuring the response of the fan of a JT15D engine to a flow pattern following the results of the NASA Inlet A BLI wind tunnel tests.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
1995-01-01
This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.
Boundary layer control for airships
NASA Technical Reports Server (NTRS)
Pake, F. A.; Pipitone, S. J.
1975-01-01
An investigation is summarized of the aerodynamic principle of boundary layer control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the boundary layer development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing boundary-layer control to nonrigid airships.
Nonparallel stability of boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.
1987-01-01
The asymptotic formulations of the nonparallel linear stability of incompressible growing boundary layers are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing boundary layers is explained.
Laminar boundary layer over riblets
NASA Astrophysics Data System (ADS)
Djenidi, L.; Anselmet, F.; Liandrat, J.; Fulachier, L.
1994-09-01
Laser doppler anemometry (LDA) measurements and numerical calculations have been made for a laminar boundary layer on triangular riblets. Calculated mean velocity distributions along the riblet contour are in good agreement with the measured ones. The results show that no transversal motion exists above and within the riblet valleys (e.g., no secondary motion). It is found that despite the large wetted area increase, the frictional drag is not increased on riblets relative to a smooth wall. This result suggests that the viscous effects are at play in the drag reduction for a turbulent boundary layer, in the sense that they compensate for the increase in wetted area.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, I. H.
1993-01-01
The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.
Localized receptivity of boundary layers
J. D. Crouch
1992-01-01
The boundary-layer receptivity resulting from acoustic forcing over a flat plate with a localized surface irregularity is analyzed using perturbation methods. The length-scale reduction, essential to acoustic receptivity, is captured within the framework of the classical stability theory. At first order, two disturbances are calculated: an unsteady disturbance resulting from the acoustic forcing and a steady disturbance resulting from the
Boundary Layer Cloudiness Parameterizations Using ARM Observations
Bruce Albrecht
2004-09-15
This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.
Direct Numerical Simulation of a Quasilaminarized Boundary Layer
Luciano Castillo; Juan Guillermo Araya; Raul Bayoan Cal
2010-01-01
Direct Numerical Simulations of spatially-evolving turbulent boundary layers with strong favorable pressure gradients are performed. The driven force behind this investigation is elucidate the mechanisms responsible for the quasi-laminarization of the boundary layer. Budgets of the turbulent kinetic energy and the shear Reynolds stresses provide insight into the terms responsible for this phenomenon. The results also confirm the similarity analysis
Turbulent boundary layers over nonstationary plane boundaries
NASA Technical Reports Server (NTRS)
Roper, A. T.
1976-01-01
Methods of predicting integral parameters and skin-friction coefficients of turbulent boundary layers developing over moving-ground-planes are evaluated using test information from three different wind tunnel facilities at the NASA Langley Research Center. These data include test information from the VSTOL tunnel which is presented for the first time. The three methods evaluated were: (1) relative integral parameter method, (2) relative power law method, and (3) modified law of the wall method. Methods (1) and (2) can be used to predict moving-ground-plane shape factors with an expected accuracy of + or - 10%. They may also be used to predict moving-ground-plane displacement and momentum thicknesses with lower expected accuracy. This decrease in accuracy can be traced to the failure of approximations upon which these methods are based to prove universal when compared with VSTOL tunnel test results.
Unsteady boundary-layer injection
NASA Technical Reports Server (NTRS)
Telionis, D. P.; Jones, G. S.
1981-01-01
The boundary-layer equations for two-dimensional incompressible flow are integrated numerically for the flow over a flat plate and a Howarth body. Injection is introduced either impulsively or periodically along a narrow strip. Results indicate that injection perpendicular to the wall is transmitted instantly across the boundary layer and has little effect on the velocity profile parallel to the wall. The effect is a little more noticeable for flows with adverse pressure gradients. Injection parallel to the wall results in fuller velocity profiles. Parallel and oscillatory injection appears to influence the mean. The amplitude of oscillation decreases with distance from the injection strip but further downstream it increases again in a manner reminiscent of an unstable process.
Turbulent boundary layer of an airfoil
NASA Technical Reports Server (NTRS)
Fediaevsky, K
1937-01-01
A need has arisen for a new determination of the velocity profiles in the boundary layer. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the boundary layer, we shall consider the nature of the shear distribution for a boundary layer with a pressure gradient.
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.
Turbulent boundary layer behind a separation zone
P. Wauschkuhn; V. I. Vasanta Ram
1975-01-01
The turbulent boundary layer after reattachment following separation on a backward-facing step in incompressible flow has been studied experimentally. Hot-wire measurements of the velocity and shear-stress distribution in the boundary layer were made. Furthermore the local wall shear stress was measured by a sub-layer fence. For a considerable distance downstream of reattachment the boundary layer exhibits a region not obeying
Modelling the transitional boundary layer
NASA Technical Reports Server (NTRS)
Narasimha, R.
1990-01-01
Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.
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.
Vortex boundary-layer interactions
NASA Technical Reports Server (NTRS)
Bradshaw, P.
1986-01-01
Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.
Radiation-viscous boundary layer
NASA Technical Reports Server (NTRS)
Arav, Nahum; Begelman, Mitchell C.
1992-01-01
A viscous boundary layer (BL) is studied which is most likely to occur in astrophysical systems dominated by radiation pressure, in particular compact objects surrounded by a very optically thick envelope and radiating at close to the Eddington limit. Calculations are reported which show that a BL due to radiation viscosity behaves very differently from a 'classical' incompressible BL for flows with Mach number M much greater than unity far from the BL. In these flows the width of the BL is much larger than its incompressible value and scales as M-squared times the width of the imcompressible BL. The density inside the BL is much lower than that in the undisturbed fluid and scales as 1/M-squared with respect to the value far away from the BL. It is concluded that under certain circumstances a cocoon of low-density material will develop between a jet and its surrounding medium.
Development of perturbations in the boundary layer
NASA Technical Reports Server (NTRS)
Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.
1986-01-01
The transition of laminar flows into turbulent flows in a boundary layer is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the boundary layer, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the boundary layer; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed boundary layer by means of a focused effect.
Three-dimensional receptivity of boundary layers
Yury S. Kachanov
2000-01-01
The paper presents a review of results of some recent (mainly experimental) studies devoted to a quantitative investigation of the problem of receptivity of the 2D and 3D boundary layers with respect to various 3D (in general) external perturbations. The paper concentrates on the mechanisms of excitation and development of stationary and travelling instability modes in a 3D boundary layer
Stably stratified boundary layer over longitudinal ridges
L. Falcomer; V. Armenio; G. C. Carnevale
2003-01-01
It is well known that a boundary layer (BL) developing over a topography behaves very differently from an analogous, plane BL. On the other hand, in geophysical applications topographic effects are often predominant. We analyze the turbulent boundary layer developing over a longitudinally-ridged wall in presence of stable stratification. The analysis is performed numerically, using large eddy simulation (LES). A
Numerical simulation of a controlled boundary layer
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Hussaini, M. Yousuff
1986-01-01
The problem of interest is the boundary layer over a flat plate. The three standard laminar flow control (LFC) techniques are pressure gradient, suction, and heating. The parameters used to describe the amount of control in the context of the boundary layer equations are introduced. The numerical method required to find the mean flow, the linear eigenvalues of the Orr-Sommerfeld equation, and the full, nonlinear, 3-D solution of the Navier-Stokes equations are outlined. A secondary instability exists for the parallel boundary subject to uniform pressure gradient, suction, or heating. Selective control of the spanwise mode reduces the secondary instability in the parallel boundary layer at low Reynolds number.
Calculation methods for compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
1976-01-01
Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.
Boundary-layer control for drag reduction
NASA Technical Reports Server (NTRS)
Harvey, William D.
1988-01-01
Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.
Novel parameterisations in the boundary layer
Plant, Robert
Novel parameterisations in the boundary layer Bob Plant Department of Meteorology, University stochastic physics from perturbed tendencies: D Dt = (1+µ)P where P is parameterization tendency, is noise
Boundary-layer stability and airfoil design
NASA Technical Reports Server (NTRS)
Viken, Jeffrey K.
1986-01-01
Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.
Two-fluid boundary layer stability
S. Özgen; G. Degrez; G. S. R. Sarma
1998-01-01
The stability of a two-fluid boundary layer is investigated. A boundary layer shears a second fluid that is bounded by the wall and the shearing fluid. The eigenvalue problem governing the linear stability of the configuration is solved using an efficient shooting-search method. Besides the Tollmien-Schlichting mode (hard mode) found in the classical hydrodynamical stability theory an additional Yih-mode (interfacial
BUBBLE – an Urban Boundary Layer Meteorology Project
M. W. Rotach; R. Vogt; C. Bernhofer; E. Batchvarova; A. Christen; A. Clappier; B. Feddersen; S.-E. Gryning; G. Martucci; H. Mayer; V. Mitev; T. R. Oke; E. Parlow; H. Richner; M. Roth; Y.-A. Roulet; D. Ruffieux; J. A. Salmond; M. Schatzmann; J. A. Voogt
2005-01-01
Summary The Basel UrBan Boundary Layer Experiment (BUBBLE) was a year-long experimental effort to investigate in detail the boundary layer structure in the City of Basel, Switzerland. At several sites over different surface types (urban, sub-urban and rural reference) towers up to at least twice the main obstacle height provided turbulence observations at many levels. In addition, a Wind Profiler
Solute boundary layer on a rotating crystal
NASA Astrophysics Data System (ADS)
Povinelli, Michelle L.; Korpela, Seppo A.; Chait, Arnon
1994-11-01
A perturbation analysis has been carried out for the solutal boundary layer next to a rotating crystal. Our aim is to extend the classical results of Burton, Prim and Slicher [1] in order to obtain higher order terms in asymptotic expansions for the concentration field and boundary-layer thickness. Expressions for the effective segregation coefficient are directly obtained from the concentration solution in the two limits that correspond to weak and strong rotation.
Boundary layer variational principles: a case study.
Grmela, Miroslav; Karlin, Iliya V; Zmievski, Vladimir B
2002-07-01
Considering the model heat conduction problem in the setting of Grad's moment equations, we demonstrate a crossover in the structure of minima of the entropy production within the boundary layer. Based on this observation, we formulate and compare variation principles for solving the problem of boundary conditions in nonequilibrium thermodynamics. PMID:12241345
NASA Astrophysics Data System (ADS)
Sarlak, H.; Sørensen, J. N.; Mikkelsen, R.
2012-09-01
Large eddy simulation (LES) of flow in a wind farm is studied in neutral as well as thermally stratified atmospheric boundary layer (ABL). An approach has been practiced to simulate the flow in a fully developed wind farm boundary layer. The approach is based on the Immersed Boundary Method (IBM) and involves implementation of an arbitrary prescribed initial boundary layer (See [1]). A prescribed initial boundary layer profile is enforced through the computational domain using body forces to maintain a desired flow field. The body forces are then stored and applied on the domain through the simulation and the boundary layer shape will be modified due to the interaction of the turbine wakes and buoyancy contributions. The implemented method is capable of capturing the most important features of wakes of wind farms [1] while having the advantage of resolving the wall layer with a coarser grid than typically required for such problems.
Excitation of a Helmholtz resonator by a turbulent boundary layer
NASA Technical Reports Server (NTRS)
Panton, R. L.; Miller, J. M.
1975-01-01
A turbulent boundary layer on the fuselage of a glider is used to excite a Helmholtz resonator whose openings are comparable in size to the turbulent eddies in the boundary layer. The resonator was excited at both the Helmholtz frequency and a standing wave frequency. The level of the resonator response and the response frequency are the major results. A shift in the response frequency, compared to acoustic excitation, indicates an interaction of turbulent and acoustic motions and a modification of the orifice end correction. A strong excitation phenomenon occurs when the resonator and boundary layer are tuned, in which case turbulent eddies of about the orifice diameter in size flow past the orifice and impose a frequency equal to one of the resonant frequencies of the resonator.
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.
Vortex-induced boundary-layer separation
NASA Astrophysics Data System (ADS)
Peridier, Vellorie Jeanne
1989-12-01
Unsteady boundary-layer separation at high Reynolds numbers, Re, is considered on a theoretical and computational basis. Whenever an external inviscid flow induces a region of adverse pressure gradient near a wall, the development of recirculating eddies in the boundary layer is common. An unsteady viscous-inviscid interaction often follows in the form of a local boundary-layer eruption and abrupt ejection of near-wall vorticity into the external flow. The dynamics of this process, as it develops in an initially thin boundary layer, is considered. As interaction ensues, the flow focuses into a band which progressively narrows in the streamwise direction. The complex flow development is extremely difficult to resolve using conventional Eulerian methods; the boundary-layer solutions are obtained using Lagrangian methods, where trajectories of a large number of fluid particles are computed. The algorithms developed are general but are applied to the problem of the boundary-layer induced by a two-dimensional vortex above an infinite plane wall. Solutions are obtained for the limit problem Re yields infinity, and for Re large but finite using an interacting boundary-layer approach. For the limit problem Re yields infinity, the boundary-layer solution develops a singularity at finite time, t(subs)(infinity), as the flow focuses toward an eruption. The multi-sturctured terminal state is the same as reached for the impulsively-started circular cylinder and found in recent asymptotic analysis. The interacting boundary-layer solutions are also shown to develop a singularity at finite times t(subs) (Re) is less than t(subs) (infinity). Thus, conventional interacting boundary-layer concepts do not alleviate the evolution of a singularity, but promote breakdown at an earlier time that decreases with Reynolds number. The computed results are found to be in excellent agreement with the interactive lengths and time scales predicted by recent asymptotic theories. The present results describe the initial stages of a strong unsteady viscous-inviscid interaction.
Ground observations of magnetospheric boundary layer phenomena
NASA Technical Reports Server (NTRS)
Mchenry, Mark A.; Clauer, C. Robert; Friis-Christensen, Eigil; Newell, Patrick T.; Kelly, J. D.
1990-01-01
Several classes of traveling vortices in the dayside ionosphere convection have been detected and tracked using the Greenland magnetometer chain (Friis-Christensen et al., 1988, McHenry et al., 1989). One class observed during quiet times consists of a continuous series of vortices moving generally antisunward for several hours at a time. The vortices' strength is seen to be approximately steady and neighboring vortices rotate in opposite directions. Sondrestrom radar observations show that the vortices are located at the ionospheric convection reversal boundary. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, it is argued that this class of vortices is caused by the Kelvin-Helmholtz instability of the inner edge of the magnetospheric boundary layer.
Streamline curvature effects on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
1976-01-01
A theoretical tool has been developed for predicting, in a nonempirical manner, effects of streamline curvature and coordinate-system rotation on turbulent boundary layers. The second-order closure scheme developed by Wilcox and Traci has been generalized for curved streamline flow and for flow in a rotating coordinate system. A physically based straightforward argument shows that curvature/rotation primarily affects the turbulent mixing energy; the argument yields suitable curvature/rotation terms which are added to the mixing-energy equation. Singular-perturbation solutions valid in the wall layer of a curved-wall boundary layer and a fully developed rotating channel flow demonstrate that, with the curvature/rotation terms, the model predicts the curved-wall and the rotating coordinate system laws of the wall. Results of numerical computations of curved-wall boundary layers and of rotating channel flow show that curvature/rotation effects can be computed accurately with second-order closure.
Dynamics of Thin Astrophysical Boundary Layers
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail Alexander
We study the modal structure and angular momentum transport mechanisms of astrophysical boundary layers. We focus on the case where the accretion disk extends all the way to surface of the star and the boundary layer is thin in comparison with the stellar radius. Such a scenario is applicable, for example, to weakly magnetized neutron stars and white dwarfs, for which the strength of the magnetic field outside the star is too small to disrupt the disk and funnel matter to the poles. Within the boundary layer, material rotating at the Keplerian velocity within the disk slows down to the rotational velocity inside the star. This generates intense velocity gradients and makes the boundary layer susceptible to shear instabilities. By performing a linear stability analysis for the simplified case of a plane-parallel, compressible shear layer, we argue that astrophysical boundary layers are unstable to the sonic instability. This instability is part of a more general class of acoustic instabilities that includes the Papaloizou-Pringle instability. We confirm the predictions of our linear stability analysis by running a suite of simulations in 2D and 3D, with and without stratification, and with and without magnetic field. In our numerical experiments, we find that acoustic modes excited by the sonic instability persist even in the nonlinear regime. We explain the morphological properties and derive analytic formulas for the pattern speed of these acoustic modes. Our work has significant implications for semianalytic models describing the structure and spectral emission from boundary layers. Typically, these models adopt a local, effective viscosity prescription for the angular momentum transport. However, in our simulations we find that angular momentum transport in the boundary layer is facilitated by acoustic modes. In this scenario, accreting material inside the boundary layer loses angular momentum to sound waves that propagate into both the star and the disk. Since transport of angular momentum by waves is inherently nonlocal, our work invites the construction of new phenomenological models of the boundary layer in which angular momentum is transported by waves rather than by an anomalous viscosity.
Soot and radiation in combusting boundary layers
Beier, R.A.
1981-12-01
In most fires thermal radiation is the dominant mode of heat transfer. Carbon particles within the fire are responsible for most of this emitted radiation and hence warrant quantification. As a first step toward understanding thermal radiation in full scale fires, an experimental and theoretical study is presented for a laminar combusting boundary layer. Carbon particulate volume fraction profiles and approximate particle size distributions are experimentally determined in both free and forced flow for several hydrocarbon fuels and PMMA (polymethylmethacrylate). A multiwavelength laser transmission technique determines a most probable radius and a total particle concentration which are two unknown parameters in an assumed Gauss size distribution. A sooting region is observed on the fuel rich side of the main reaction zone. For free flow, all the flames are in air, but the free stream ambient oxygen mass fraction is a variable in forced flow. To study the effects of radiation heat transfer, a model is developed for a laminar combusting boundary layer over a pyrolyzing fuel surface. An optically thin approximation simplifies the calculation of the radiant energy flux at the fuel surface. For the free flames in air, the liquid fuel soot volume fractions, f/sub v/, range from f/sub v/ approx. 10/sup -7/ for n-heptane, a paraffin, to f/sub v/ approx. 10/sup -7/ for toluene, an aromatic. The PMMA soot volume fractions, f/sub v/ approx. 5 x 10/sup -7/, are approximately the same as the values previously reported for pool fires. Soot volume fraction increases monotonically with ambient oxygen mass fraction in the forced flow flames. For all fuels tested, a most probable radius between 20 nm and 80 nm is obtained which varies only slightly with oxygen mass fraction, streamwise position, or distance normal to the fuel surface. The theoretical analysis yields nine dimensionless parameters, which control the mass flux rate at the pyrolyzing fuel surface.
Boundary layers in dilute particle suspensions
NASA Astrophysics Data System (ADS)
Foster, M. R.; Duck, P. W.; Hewitt, R. E.
2005-11-01
Boundary layers in dilute particle suspensions have been found to have a number of interesting features. The development of a singularity at the wall has recently been found to be common to many of these flows, ootnotetextSee Foster, Duck & Hewitt, J. Fluid Mech. 474 (2003) and Duck, Hewitt & Foster, J. Fluid Mech. 514, (2004) and we note here that Falkner-Skan-type boundary layers (layers with `edge' velocity proportional to x^m) and the boundary layer under a linearly decelerating flow ootnotetextHowarth (1934) also break down at the wall in the absence of gravity, but can be singularity-free for heavy particles. In addition, we find that matching of the Falkner-Skan profile to an outer flow is problematic for some values of m, though the case most studied heretofore---the Blasius case (for m=0)---does not feature this difficulty. Finally, a boundary layer that does not develop a singularity takes on a the typical Falkner-Skan self-similarity far downstream, in the absence of gravity. For heavy particles, however, gravity causes a constant drift of particles toward the wall, and a constant-thickness far-downstream layer. The far-downstream behavior in a light-particle suspension is different, with a particle-free zone between the wall and a particle `shock' that grows like x^(1-m).
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.
Diverging boundary layers with zero streamwise pressure gradient
Wayne R. Pauley; John K. Eaton; Andrew D. Cutler
1989-01-01
The effects of spanwise divergence on the boundary layer forming between a pair of embedded streamwise vortices with the common flow between them directed toward the wall was studied. Measurements indicate that divergence controls the rate of development of the boundary layer and that large divergence significantly retards boundary layer growth and enhances skin friction. For strongly diverging boundary layers,
Thermal boundary condition effects on compressible turbulent boundary layers
NASA Astrophysics Data System (ADS)
Beekman, Izaak; Martin, Pino
2013-11-01
Numerous questions about the physics of compressible boundary layers, and their modeling remain open. While Morkovin's hypothesis has proven remarkably robust for zero pressure gradient, smooth wall, compressible, turbulent boundary layers, accounting correctly for thermal energy transport and its impact on the density and momentum fields remains challenging. We use spatially developing DNS data over strongly and weakly adiabatic walls at Mach 3 and Mach 7. The strongly adiabatic boundary condition further stresses common assumptions of weak direct compressibility and weak total temperature fluctuations. We observe non-trivial differences between the two cases. The simulations are performed at Re? ~ 500 on very large domains in the streamwise and spanwise directions, approximately 50 by 10?inlet , with a rescaling method providing the inflow. We examine the effects of this boundary condition on common scaling laws, temperature-velocity relations, and suggest improvements, where possible. A dimensionless parameter is proposed, the ``fluctuation Nusselt number,'' to quantify the impact of the wall material for laboratory and engineering flows and relate it to these idealized, numerical boundary conditions. Numerous questions about the physics of compressible boundary layers, and their modeling remain open. While Morkovin's hypothesis has proven remarkably robust for zero pressure gradient, smooth wall, compressible, turbulent boundary layers, accounting correctly for thermal energy transport and its impact on the density and momentum fields remains challenging. We use spatially developing DNS data over strongly and weakly adiabatic walls at Mach 3 and Mach 7. The strongly adiabatic boundary condition further stresses common assumptions of weak direct compressibility and weak total temperature fluctuations. We observe non-trivial differences between the two cases. The simulations are performed at Re? ~ 500 on very large domains in the streamwise and spanwise directions, approximately 50 by 10?inlet , with a rescaling method providing the inflow. We examine the effects of this boundary condition on common scaling laws, temperature-velocity relations, and suggest improvements, where possible. A dimensionless parameter is proposed, the ``fluctuation Nusselt number,'' to quantify the impact of the wall material for laboratory and engineering flows and relate it to these idealized, numerical boundary conditions. Supported by AFOSR grant AF/9550-10-1-0535 STW 21 - Revitalization of the hypersonics testing and evaluation workforce.
Boundary lubrication by an adsorption layer
I. A. Buyanovskii
2010-01-01
Some key directions of study of the friction and wear of solids under conditions of boundary lubrication by an adsorption\\u000a layer are analyzed. The ideas and methods of the studies are considered in sequence starting from works of the founder of\\u000a the boundary lubrication concept W. Hardy and proceeding to the results of the outstanding scientists of the following generations—F.P.
The structure of APG turbulent boundary layers
NASA Astrophysics Data System (ADS)
Gungor, Ayse G.; Maciel, Yvan; Simens, Mark P.; Soria, Julio
2013-11-01
A boundary layer under influence of a strong APG is studied using DNS. Transition to turbulence is triggered using a trip wire which is modelled using the immersed boundary method. The Reynolds number close to the exit of the numerical domain is Re? = 2175 and the shape-factor H = 2 . 5 . Two dimensional two-point spatial correlation functions are obtained in this region and close to the transition region. Cvu with a reference point close to the transition region shows a flow periodicity until Re? ~ 1600 . This periodicity is related to the shear layer instability of the separation bubble created as a result of the APG. The Cvv and Cww correlations obtained far from the transition region at Re? = 2175 and at y / ? = 0 . 4 coincide with results obtained for a ZPG boundary layer. Implying that the structure of the v , w fluctuations is the same as in ZPG. However, Cuu indicates that the structure of the u fluctuation in an APG boundary layer is almost twice as short as the ZPG structures. The APG structures are also less correlated with the flow at the wall. The near wall structure of strong APG flows is different from ZPG flows in that streaks are much shorter or absent. A boundary layer under influence of a strong APG is studied using DNS. Transition to turbulence is triggered using a trip wire which is modelled using the immersed boundary method. The Reynolds number close to the exit of the numerical domain is Re? = 2175 and the shape-factor H = 2 . 5 . Two dimensional two-point spatial correlation functions are obtained in this region and close to the transition region. Cvu with a reference point close to the transition region shows a flow periodicity until Re? ~ 1600 . This periodicity is related to the shear layer instability of the separation bubble created as a result of the APG. The Cvv and Cww correlations obtained far from the transition region at Re? = 2175 and at y / ? = 0 . 4 coincide with results obtained for a ZPG boundary layer. Implying that the structure of the v , w fluctuations is the same as in ZPG. However, Cuu indicates that the structure of the u fluctuation in an APG boundary layer is almost twice as short as the ZPG structures. The APG structures are also less correlated with the flow at the wall. The near wall structure of strong APG flows is different from ZPG flows in that streaks are much shorter or absent. Funded in part by ITU, NSERC of Canada, ARC Discovery Grant, and Multiflow program of the ERC.
Boundary layer blockage in expansion tube nozzles
NASA Technical Reports Server (NTRS)
Sudnitsin, Olga; Morgan, Richard G.
1995-01-01
The results of a first order perfect gas correction for the effects of the boundary layer formation within expansion tubes with nozzles are presented. The analytical model developed to describe the boundary layer formation within the expansion tube and an expansion nozzle located at the end of the acceleration tube is based on the Karman integral equations. The results of this analytical model are compared with experimental data from an expansion diffuser. The model provides a useful tool for the preliminary design of nozzles for such facilities.
An interacting boundary layer model for cascades
NASA Technical Reports Server (NTRS)
Davis, R. T.; Rothmayer, A. P.
1983-01-01
A laminar, incompressible interacting boundary layer model is developed for two-dimensional cascades. In the limit of large cascade spacing these equations reduce to the interacting boundary layer equations for a single body immersed in an infinite stream. A fully implicit numerical method is used to solve the governing equations, and is found to be at least as efficient as the same technique applied to the single body problem. Solutions are then presented for a cascade of finite flat plates and a cascade of finite sine-waves, with cusped leading and trailing edges.
NASA Technical Reports Server (NTRS)
Parmar, D. S.
1991-01-01
A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength of the incident light. Application of a step input shear stress results in a liquid crystal time response that can be described as consisting of an initial delay, a shear induced helix deformation, and a relaxation to the initial state through diffusion processes. The method has been used for quantitative calibration of a shear sensitive liquid crystal by observing the peak in reflected light intensity, at a given wavelength, as a function of the shear stress.
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.
Hairpins et al. in Turbulent Boundary Layers
Schlatter, Philipp; Chevalier, Mattias; Brethouwer, Geert; Johansson, Arne V; Henningson, Dan S
2011-01-01
A new set of three-dimensional visualisations of a large-scale direct numerical simulations (DNS) of a turbulent boundary layer is presented. The Reynolds number ranges from $Re_\\theta=180$ to 4300, based on the momentum-loss thickness $\\theta$ and the free-stream velocity $U_\\infty$. The focus of the present fluid dynamics video is on analysing the coherent vortical structures in the boundary layer: It is clearly shown that the initial phases are dominated by coherent so-called hairpin vortices which are characteristic remainders of the laminar-turbulent transition at lower Reynolds numbers. At higher $Re$ (say $Re_\\theta>2000$), these structures are no longer seen as being dominant; the coherence is clearly lost, both in the near-wall region as well as in the outer layer of the boundary layer. Note, however, that large-scale streaks in the streamwise velocity, which have their peak energy at about half the boundary-layer thickness, are unambiguously observed. In addition to visualisation with classical thre...
INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT
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...
Secondary Görtler Instability in Hypersonic Boundary Layers
NASA Astrophysics Data System (ADS)
Whang, C. W.; Zhong, X.
2000-11-01
In general, boundary layer flows become turbulent in three steps: 1) receptivity, 2) linear growth of disturbance, and 3) nonlinear effects in which the flow breaks down to turbulence. Görtler instability is one of the many B-L instability mechanisms. Görtler vortices appear in boundary layer flow along concave surfaces due to the imbalance between the pressure and centrifugal force. Many practical engineering designs, such as engine inlet, involve concave surfaces. Therefore, Görtler instability is an important subject in fluid mechanics. In this paper, Görtler instability is investigated using two approaches: Linear Stability Theory(LST) and Direct Numerical Simulation(DNS). Initial forcing disturbances are obtained from the LST, and subsequent linear and nonlinear development is simulated using Navier-Stokes equations. We investigate linear and nonlinear growth of Görtler vortices in hypersonic boundary layers. DNS is used to simulate Görtler vortices in hypersonic boundary layers. Two dimensional steady mean flow is computed using a fifth order explicit upwind scheme. Linear growth of disturbances is compared with the LST code to verify the DNS. Nonlinear effects of Görtler vortices are also investigated using DNS. Inflectional profiles develop due to the distortion of the mean flow caused by nonlinear growth of Görtler vortices which induces secondary instability. Secondary instability will be investigated using secondary instability theory and DNS.
NOCTURNAL URBAN BOUNDARY LAYER OVER CINCINNATI, OHIO
JOHN F. CLARKE
1969-01-01
Investigations of the nocturnal temperature and wind structure of the planetary boundary layer over a city were conducted in the Cincinnati, Ohio, metropolitan area. Temperatures near the surface were obtained by means of automobile traverses across the city, the vertical distributions of temperature were measured at several sites with a helicopter, and wind velocities were derived from pilot balloon observations.
Boundary layer control device for duct silencers
NASA Technical Reports Server (NTRS)
Schmitz, Fredric H. (inventor); Soderman, Paul T. (inventor)
1993-01-01
A boundary layer control device includes a porous cover plate, an acoustic absorber disposed under the porous cover plate, and a porous flow resistive membrane interposed between the porous cover plate and the acoustic absorber. The porous flow resistive membrane has a flow resistance low enough to permit sound to enter the acoustic absorber and high enough to damp unsteady flow oscillations.
Particle-laden boundary layers and singularities
NASA Astrophysics Data System (ADS)
Foster, M. R.
2007-11-01
The dusty-gas model for flow in dilute particle suspensions generates a singularity in particle volume fraction in a variety of viscous boundary layer problems. Such a singularity, at say x=xs along the wall, makes it impossible to continue the solution to the equations. Previously, we have found that computation of the Blasius boundary layer, with a modified equation set that permits fluid volume fraction significantly different from 1, still leads to a velocity singularity at a slightly modified location.ootnotetextFoster, Duck & Hewitt, Bull. Amer. Phys. Soc., November, 2006 Contrary to some published work, the Saffman force has not been found to mitigate the singularity for the conventional equation set, and again here, though the Saffman force does become comparable to the Stokes drag near the singularity, it alters the structure only slightly, and does not remove it. If ?o is the particle volume fraction of the fluid in which the boundary layer is embedded, then in certain re-scaled coordinates, the singularity occurs in a region ?ox?o/|?o| about xs, where a reduced set of equations applies. Within this region, there is a downstream-running ray from the origin on which ??1. However, the vertical fluid and particle velocity components are unbounded on that line. On replacing the line with a solid surface of particle material, a narrow boundary layer may be inserted, in which velocity singularities are removed.
SODAR application for estimating boundary layer parameters
Annalisa Capanni; Giovanni Gualtieri
An application of Doppler SODAR technique has been made in order to evaluate the main atmospheric variables affecting the boundary layer structure in a plain terrain. Besides directly monitoring such meteorological variables as wind profiles, the application of a number of methods and algorithms enabled the estimation of features such as atmospheric turbulence, Monin-Obukhov length, friction velocity and PBL depth,
Planetary Boundary Layer from AERI and MPL
Sawyer, Virginia
The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.
Boundary layer transition in hypersonic flows
NASA Technical Reports Server (NTRS)
Malik, M. R.; Zang, T. A.; Bushnell, D. M.
1990-01-01
This paper summarizes some of the recent progress made at NASA Langley Research Center in the understanding, prediction and modeling of high speed boundary-layer transition. Linear and nonlinear theories together with large-eddy and direct numerical simulations have been used to understand various aspects of the transition problem while low disturbance 'quiet' tunnels provide means for validating the theoretical results.
Acoustics of laminar boundary layers breakdown
Meng Wang
1994-01-01
Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable
Interaction between Trapped Waves and Boundary Layers
Qingfang Jiang; James D. Doyle; Ronald B. Smith
2006-01-01
The absorption of trapped lee waves by the atmospheric boundary layer (BL) is investigated based on numerical simulations and theoretical formulations. It is demonstrated that the amplitude of trapped waves decays exponentially with downstream distance due to BL absorption. The decay coefficient, , defined as the inverse of the e-folding decay distance, is found to be sensitive to both surface
Interaction between Trapped Waves and Boundary Layers
Qingfang Jiang; James D. Doyle; Ronald B. Smith
2006-01-01
The absorption of trapped lee waves by the atmospheric boundary layer (BL) is investigated based on numerical simulations and theoretical formulations. It is demonstrated that the amplitude of trapped waves decays exponentially with downstream distance due to BL absorption. The decay coefficient, alpha, defined as the inverse of the e-folding decay distance, is found to be sensitive to both surface
Parameterization of continental boundary layer clouds
Ping Zhu; Wei Zhao
2008-01-01
Large eddy simulations (LESs) of continental boundary layer clouds (BLCs) observed at the southern Great Plains (SGP) are used to study issues associated with the parameterization of sub-grid BLCs in large scale models. It is found that liquid water potential temperature $\\\\theta$l and total specific humidity qt, which are often used as parameterization predictors in statistical cloud schemes, do not
TURBULENCE IN SUPERSONIC AND HYPERSONIC BOUNDARY LAYERS
Martín, Pino
TURBULENCE IN SUPERSONIC AND HYPERSONIC BOUNDARY LAYERS Alexander J. Smits and M. Pino Martin in supersonic and hypersonic flow where the effects of compressibility have a direct influence on the turbulence. Experimental and DNS results are presented and compared. Key words: Turbulence, supersonic, hypersonic, shocks
Boundary Layer Transition on X-43A
NASA Technical Reports Server (NTRS)
Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert
2008-01-01
The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote boundary layer transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the boundary layer trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.
Turbulences in Boundary Layer of Flat Plates
NASA Astrophysics Data System (ADS)
Tesar, Alexander
2014-06-01
The aeroelastic assessment of turbulences appearing in boundary layer of flat plates tested in the wind tunnel is treated in present paper. The approach suggested takes into account multiple functions in the analysis of flat plates subjected to laminar and turbulent wind forcing. Analysis and experimental assessments in the aerodynamic tunnel are presented. Some results obtained are discussed
Rethinking the Boundaries: Response
ERIC Educational Resources Information Center
Oslin, Judy; Collier, Connie
2012-01-01
In his Keynote address, Dr. Kretchmar suggests that children who demonstrate an inability or unwillingness to play may have a "play disability," and thus offers interventions for remediation. In response, Oslin and Collier argue that due to cultural influences, it is more likely that physical educators are play disabled. Oslin and Collier share…
Viscous drag reduction in boundary layers
NASA Astrophysics Data System (ADS)
Bushnell, Dennis M.; Hefner, Jerry N.
The present volume discusses the development status of stability theory for laminar flow control design, applied aspects of laminar-flow technology, transition delays using compliant walls, the application of CFD to skin friction drag-reduction, active-wave control of boundary-layer transitions, and such passive turbulent-drag reduction methods as outer-layer manipulators and complex-curvature concepts. Also treated are such active turbulent drag-reduction technique applications as those pertinent to MHD flow drag reduction, as well as drag reduction in liquid boundary layers by gas injection, drag reduction by means of polymers and surfactants, drag reduction by particle addition, viscous drag reduction via surface mass injection, and interactive wall-turbulence control.
Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers
NASA Technical Reports Server (NTRS)
Popham, Robert; Narayan, Ramesh
1995-01-01
We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.
Boundary layer receptivity phenomena in three-dimensional and high-speed boundary layers
NASA Technical Reports Server (NTRS)
Choudhari, Meelan; Streett, Craig L.
1990-01-01
The process by which the boundary layer internalizes the environmental disturbances in the form of instability waves is known as the boundary-layer receptivity. The paper discusses the importance of receptivity in transition research. The receptivity scenario for three-dimensional and high-speed boundary layers is examined. It is found that, while receptivity mechanisms present in the low-speed case are also operative in these complex flows, certain uniquely 'compressible' receptivity mechanisms may come into play as well. Both numerical, and where convenient, asymptotic procedures are utilized to develop quantitative predictions of the localized generation of a variety of instability types (Tollmien-Schlichting, inflectional, higher modes, crossflow vortices) in boundary layer flows relevant to the National Aero-Space Plane (NASP).
NASA Astrophysics Data System (ADS)
Delle Monache, Luca; Weil, Jeffrey; Simpson, Matthew; Leach, Marty
2009-12-01
A new urban parameterization for a fast-running dispersion prediction modeling system suitable for emergency response situations is introduced. The parameterization represents the urban convective boundary layer in the dispersion prediction system developed by the National Atmospheric Release Advisory Center (NARAC) at Lawrence Livermore National Laboratory. The performance of the modeling system is tested with data collected during the field campaign Joint Urban 2003 (JU03), held in July 2003 in Oklahoma City, Oklahoma. Tests were performed using data from three intense operating periods held during daytime slightly unstable to unstable conditions. The system was run in operational mode using the meteorological data that would be available operationally at NARAC to test its effectiveness in emergency response conditions. The new parameterization considerably improves the performance of the original modeling system, by producing a better degree of pattern of correspondence between predictions and observations (as measured by Taylor diagrams), considerably reducing bias, and better capturing directional effects resulting in plume predictions whose shape and size better resemble the observations (via the measure of effectiveness). Furthermore, the new parameterization shows similar skills to urban modeling systems of similar or greater complexity. The parameterization performs the best at the three JU03 sensor arcs (1, 2, and 4 km downwind the release points), with fractional bias values ranging from 0.13 to 0.4, correlation values from 0.45 to 0.71, and centered root-mean-square error being reduced more than 50% in most cases. The urban parameterization has been tested with grid increments of 125, 250, 500 and 1000 m, performing best at 250 and 500 m. Finally, it has been found that representing the point source by a Gaussian distribution with an initial spread of particles leads to a better representation of the initial spread induced by near-source buildings, resulting in lower bias and improved correlation in downtown Oklahoma City.
Turbulent boundary layers subjected to multiple curvatures and pressure gradients
NASA Technical Reports Server (NTRS)
Bandyopadhyay, Promode R.; Ahmed, Anwar
1993-01-01
The effects of abruptly applied cycles of curvatures and pressure gradients on turbulent boundary layers are examined experimentally. Two two-dimensional curved test surfaces are considered: one has a sequence of concave and convex longitudinal surface curvatures and the other has a sequence of convex and concave curvatures. The choice of the curvature sequences were motivated by a desire to study the asymmetric response of turbulent boundary layers to convex and concave curvatures. The relaxation of a boundary layer from the effects of these two opposite sequences has been compared. The effect of the accompaying sequences of pressure gradient has also been examined but the effect of curvature dominates. The growth of internal layers at the curvature junctions have been studied. Measurements of the Gortler and corner vortex systems have been made. The boundary layer recovering from the sequence of concave to convex curvature has a sustained lower skin friction level than in that recovering from the sequence of convex to concave curvature. The amplification and suppression of turbulence due to the curvature sequences have also been studied.
Two-fluid boundary layer stability
NASA Astrophysics Data System (ADS)
Özgen, S.; Degrez, G.; Sarma, G. S. R.
1998-11-01
The stability of a two-fluid boundary layer is investigated. A boundary layer shears a second fluid that is bounded by the wall and the shearing fluid. The eigenvalue problem governing the linear stability of the configuration is solved using an efficient shooting-search method. Besides the Tollmien-Schlichting mode (hard mode) found in the classical hydrodynamical stability theory an additional Yih-mode (interfacial mode) exists due to the two-fluid interface. Effects of viscosity and density stratifications, thickness of the bounded fluid, gravity, surface tension as well as the non-Newtonian character of the lower fluid on the stability characteristics are determined. The interfacial mode is found to be very sensitive against viscosity stratification. However, with a highly viscous liquid layer, the system approaches a single-layer behavior. The shear-thinning non-Newtonian liquid layer is observed to have a stabilizing effect for both of the modes. Surface tension is stabilizing for short waves for the interfacial mode but a more complex effect was observed for the hard mode. Gravity is stabilizing with a favorable density stratification. Density stratification alone is destabilizing for low and moderate values of this parameter but becomes stabilizing for higher values. When the external boundary layer profile is turbulent, the interfacial mode is more likely to be observed in an experiment. Agreement of the obtained results with experimental, theoretical and numerical results reported in the literature is good. This is encouraging as the study is intended for solving the stability characteristics of de/anti-icing fluid-air systems and comparing the results with the experimental data when they become available.
BOREAS AFM-6 Boundary Layer Height Data
NASA Technical Reports Server (NTRS)
Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)
2000-01-01
The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).
NASA Technical Reports Server (NTRS)
Evans, R. M.
1975-01-01
Accurate predictions of the thrust loss due to boundary layer effects and of the wall heat flux are very important to the design and performance evaluation of rocket nozzles. A method used in analytical procedures for liquid fuel rocket engine performance prediction and evaluation is presented. A computer program is examined that is a fast and accurate procedure for solving the set of boundary layer equation (momentum, energy, and species) for laminar or turbulent, chemically reacting flows with a wide variety of boundary conditions. Results of comparison of the various turbulent models are presented. A summary of the modifications and additions to the program is examined.
The role of nonlinear critical layers in boundary layer transition
NASA Technical Reports Server (NTRS)
Goldstein, M.E.
1995-01-01
Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.
Three dimensional boundary layers in internal flows
NASA Technical Reports Server (NTRS)
Bodonyi, R. J.
1987-01-01
A numerical study of the effects of viscous-inviscid interactions in three-dimensional duct flows is presented. In particular interacting flows for which the oncoming flow is not fully-developed were considered. In this case there is a thin boundary layer still present upstream of the surface distortion, as opposed to the fully-developed pipe flow situation wherein the flow is viscous across the cross section.
Shock-boundary-layer interaction in flight
NASA Technical Reports Server (NTRS)
Bertelrud, Arild
1989-01-01
A brief survey is given on the study of transonic shock/boundary layer effects in flight. Then the possibility of alleviating the adverse shock effects through passive shock control is discussed. A Swedish flight experiment on a swept wing attack aircraft is used to demonstrate how it is possible to reduce the extent of separated flow and increase the drag-rise Mach number significantly using a moderate amount of perforation of the surface.
X-33 HYPERSONIC BOUNDARY LAYER TRANSITION
Scott A. Berry; Thomas J. Horvath; Brian R. Hollis; Richard A. Thompson; H. Harris Hamilton
1999-01-01
Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examinedin the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamlinepatterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations includeangles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; andbody-flap
Seabed Wave Boundary Layer Measurements and Analysis
K. F. Lambrakos
1982-01-01
Velocity measurements made at two elevations off a rough sea floor in 18.3 m of water depth in the Strait of Juan de Fuca suggest the presence of a wave boundary layer. The wave velocities measured at 0.69 m off bottom are, overall, larger in magnitude and also shifted in time relative to the velocities measured at 1.85 m. These
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.
Turbulent Boundary Layers over Filamentous Algae
Michael P. Schultz
1999-01-01
Turbulent boundary layer measurements have been made on surfaces covered with filamentous marine algae. These experiments were conducted in a closed return water tunnel using a two-component, laser Doppler velocimeter (LDV). The axial and wall-normal turbulence intensities and Reynolds shear stress are compared with flows over smooth and conventional k-type rough walls. The results indicate that profiles of these turbulence
The Role of Boundary Layer Processes in Limiting PV Homogenization
Zhang, Yang
A ?-plane multilevel quasigeostrophic channel model with interactive static stability and a simplified parameterization of atmospheric boundary layer physics is used to study the role of different boundary layer processes ...
Shock-wave boundary layer interactions
NASA Technical Reports Server (NTRS)
Delery, J.; Marvin, J. G.; Reshotko, E.
1986-01-01
Presented is a comprehensive, up-to-date review of the shock-wave boundary-layer interaction problem. A detailed physical description of the phenomena for transonic and supersonic speed regimes is given based on experimental observations, correlations, and theoretical concepts. Approaches for solving the problem are then reviewed in depth. Specifically, these include: global methods developed to predict sudden changes in boundary-layer properties; integral or finite-difference methods developed to predict the continuous evolution of a boundary-layer encountering a pressure field induced by a shock wave; coupling methods to predict entire flow fields; analytical methods such as multi-deck techniques; and finite-difference methods for solving the time-dependent Reynolds-averaged Navier-Stokes equations used to predict the development of entire flow fields. Examples are presented to illustrate the status of the various methods and some discussion is devoted to delineating their advantages and shortcomings. Reference citations for the wide variety of subject material are provided for readers interested in further study.
Boundary Layer Structure and Processes in Mid - Ocean Storms.
NASA Astrophysics Data System (ADS)
Bond, Nicholas A.
Measurements taken during the Storm Transfer and Response Experiment (STREX) are used to analyze boundary layer structures and processes in the vicinity of North Pacific storms. Case studies are carried out for the pre -frontal, post-frontal, and frontal sectors of storms. The effects of sub-grid scale processes on the boundary layer and the overlying atmosphere receive special emphasis. The pre-frontal boundary layers are nearly neutrally stratified and the surface heat and moisture fluxes are small. The surface fluxes tend to be downward just ahead of the fronts and are of greater magnitude during stronger storms. Even though the actual entrainment velocities are small, the entrainment fluxes are generally the most important sources of total heat for the pre-frontal boundary layers. Entrainment rates determined from budgets compare well with results calculated from relationships determined in laboratory studies of shear-driven entrainment. Heat and moisture budgets are evaluated in two post-frontal situations. In both cases surface heat and moisture fluxes are the dominant sources of total heating within the boundary layers. The entrainment velocities are larger in post-frontal than pre-frontal regions, but entrainment has only a small and positive net effect on the total heat content of the post-frontal boundary layers. Penetrative convection represents the major sink of boundary layer moisture for the case with a long atmospheric fetch over the ocean. A single strong cold front is analysed. The Sawyer Eliassen secondary circulation equation is used to compare the effects of geostrophic forcing, diabatic heating, and friction on the synoptic-scale ageostrophic flow at the front. Friction is found to be the primary process forcing the low-level updraft at the front. Combined kinematic and thermodynamic analyses show strong relative inflow of warm boundary layer air toward the front from the east and a weaker inflow of cold air from the west. The frontogenetical processes are evaluated and compared with those from previous studies. It is proposed that the intensity of turbulent mixing limits the scale of a front.
Typhoon kinematic and thermodynamic boundary layer structure from dropsonde composites
NASA Astrophysics Data System (ADS)
Ming, Jie; Zhang, Jun A.; Rogers, Robert F.
2015-04-01
The data from 438 Global Positioning System dropsondes in six typhoons are analyzed to investigate the mean atmospheric boundary layer structure in a composite framework. Following a recent study on boundary layer height in Atlantic hurricanes, we aim to quantify characteristics of boundary layer height scales in Western Pacific typhoons including the inflow layer depth (hinflow), height of the maximum tangential wind speed (hvtmax), and thermodynamic mixed layer depth. In addition, the kinematic and thermodynamic boundary layer structures are compared between the dropsonde composites using data in typhoons and hurricanes. Our results show that similar to the hurricane composite, there is a separation between the kinematic and thermodynamic boundary layer heights in typhoons, with the thermodynamic boundary layer depth being much smaller than hinflow and hvtmax in the typhoon boundary layer. All three boundary layer height scales tend to decrease toward the storm center. Our results confirm that the conceptual model of Zhang et al. (2011a) for boundary layer height variation is applicable to typhoon conditions. The kinematic boundary layer structure is generally similar between the typhoon and hurricane composites, but the typhoon composite shows a deeper inflow layer outside the eyewall than the hurricane composite. The thermodynamic structure of the typhoon boundary layer composite is warmer and moister outside the radius of maximum wind speed than the hurricane composite. This difference is attributed to different environmental conditions associated with typhoons compared to the hurricanes studied here.
Shock layers and boundary layers in hypersonic flows
NASA Astrophysics Data System (ADS)
Cousteix, J.; Arnal, D.; Aupoix, B.; Brazier, J. Ph.; Lafon, A.
This paper presents an overview of the physical and numerical aspects of flows encountered around a vehicle in hypersonic flight. These problems are typically related to the reentry phase of a space shuttle into the atmosphere. Nonetheless, it is believed that the material given here is a good background for other applications. Compared with the standard aerodynamic problems on an aircraft in transonic or supersonic flight, hypersonic flows are characterized by a much higher level of energy. The high temperature of the flow can lead to thermochemical non-equilibrium, with chemical reactions and vibrational relaxation. These effects are of prime importance in the evaluation of the heating of the body and they may affect general flow features, including the wall pressure. Basic elements are discussed to understand the physics of these phenomena. Applications are given in the framework of boundary layer calculations and of numerical solutions of the Navier-Stokes equations. In the front of the vehicle, a strong bow shock wave forms and the boundary layer is fed by a rotational flow. A discussion is given concerning how a boundary layer theory can account for these effects. At lower altitudes, the velocity of the flow remains large, the Reynolds number increases and the flow becomes turbulent. In this context, laminar-turbulent transition and turbulence modelling are discussed.
Some features of transonic shock wave turbulent boundary layer interaction
J. Delery
1980-01-01
Physical features of shock wave turbulent boundary layer interaction phenomena in two dimensional steady transonic flows are reviewed. The influence of interaction phenomena on wall pressure distributions in a sonic throat of adjustable cross section is discussed. The effects of a shock wave on the boundary layer, including an increase in boundary layer thickness and rapid variation of the incompressible
Methods for determining the height of the atmospheric boundary layer
J S Nasstrom; G Sugiyama
1999-01-01
The Atmospheric Release Advisory Capability (ARAC) is an operational emergency response program which provides real-time dose assessments of airborne pollutant releases. This report reviews methodologies for determining the height of the atmospheric boundary layer (ABL), which were investigated for use in the next generation of ARAC diagnostic and dispersion models. The ABL height, h_{ABL<\\/sub>, is an essential parameter in atmospheric}
Partially exposed polymer dispersed liquid crystals for boundary layer investigations
NASA Technical Reports Server (NTRS)
Parmar, Devendra S.; Singh, Jag J.
1992-01-01
A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.
Boundary layer elasto-optic switching in ferroelectric liquid crystals
NASA Technical Reports Server (NTRS)
Parmar, D. S.
1992-01-01
The first experimental observation of a change in the director azimuthal angle due to applied shear stress is reported in a sample configuration involving a liquid-crystal-coated top surface exposed directly to gas flow. The electrooptic response caused by the shear stress is large, fast, and reversible. These findings are relevant to the use of liquid crystals in boundary layer investigations on wind tunnel models.
Hypersonic Boundary Layer/Oblique Shockwave Interaction
NASA Astrophysics Data System (ADS)
Lindsay, Haile
2005-11-01
The hypersonic boundary layer/oblique shockwave interaction problem was defined with the use of the full Navier-Stokes (NS) equations and a FORTRAN code was developed to provide numerical solutions to this problem. Further, this problem was studied under two specified sets of boundary conditions: adiabatic wall and constant wall conditions. The MacCormack Technique was used in developing this NS code. To validate the numerical code, the flat plate problem was solved, and the results compared to that published in established journals. In solving these problems, engineering tools such as, FORTRAN, TECPLOT, and EXCEL, were used to generate plots of the primitive variables, such as, the velocity components, u and v, density, and the temperature T. Selected plots were reproduced from various references in validating the work done for the flat plate and hypersonic boundary layer/oblique shockwave interaction problems. All preliminary results indicated that the code was validated and the results obtained agreed with the physical behavior of the flow fields. Now that an aerospace engineering tool was developed, it is recommended that future designers seek to further its development by making the code user-friendly and that they further test accuracy of the code by solving other 2D fluid dynamic problems.
Acoustic radar investigations of boundary layer phenomena
NASA Technical Reports Server (NTRS)
Marks, J. R.
1974-01-01
A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.; Zierke, W. C.
1984-01-01
The characteristics of the flow field about highly loaded turbocompressor blades in a cascade wind tunnel were investigated. Experimental tests were conducted at chord Reynolds number (R sub c) near 500,000. A laser Doppler anemometer was employed in flow velocity measurement. Suction surface mean velocity and turbulence intensity profiles at a single incidence angle are presented. These data contribute to further understanding of two-dimensional boundary layer profiles, points of separation, and transition zones for turbomachine blades, and concomitantly, to compressor cascade predictive models.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.
1981-01-01
The flow field about an airfoil in cascade at a Reynolds number of 5 x 10 to the 5th power is described. Hot wire and laser anemometry are combined with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation, and the transition zone) on a cascade of relatively highly loaded blades. Benchmark data is provided for the evaluation of current and future predictive models, in this way aiding in the compressor design process.
Calculation of boundary layers of oscillating airfoils
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
1984-01-01
A two-point finite difference unsteady laminar and turbulent boundary layer computational method was used to investigate the properties of the flow around an airfoil (NACA 0012) oscillating through angles of attack up to 18 degrees, for reduced frequencies of 0.01 and 0.20. The unsteady potential flow was determined using the unsteady potential flow method of Geissler. The influence of transition location on stal behavior was investigated, using both experimentally determined transition information, and transition located at the pressure peak; the results show the need for viscous-inviscid interaction in future computation of such flows.
Shock/boundary-layer/shock interactions
NASA Astrophysics Data System (ADS)
Smith, Virgil K., III
The shock/shock interference phenomena and shock wave/boundary layer interactions in hypersonic flight are reviewed. The characteristic flow features are described, and the mechanisms for extremely high local heat transfer rates are emphasized. A classical example of interaction heating on the X-15 hypersonic vehicle is reviewed, and the damage caused by the unexpected aerodynamic heating is cited. These results serve as a strong reminder of the importance of shock impingement and interference heating cautions in hypersonic vehicle design, development, test, and evaluation.
Halogen chemistry in the trosopheric boundary layer
NASA Astrophysics Data System (ADS)
Plane, John M. C.; Mahajan, Anoop; Oetjen, Hilke
Iodine and bromine chemistry can affect the lower troposphere in several important ways: (1), change the oxidizing capacity by destroying ozone and affecting the hydroxyl radical concentration; (2), react efficiently with dimethyl sulphide (in the marine boundary layer) and mercury (in the polar regions); and (3), form ultra-fine particles (iodine oxides are highly condensable), which may contribute to cloud condensation nuclei and hence affect climate. This paper will report measurements of IO, BrO, OIO and I2 , made by the technique of differential optical absorption spectroscopy (DOAS), in several contrasting environments: equatorial clean mid-ocean (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar boundary layer (Halley Bay, Antarctica and Hudson Bay, Canada). Both IO and BrO are observed in all these locations at concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. The concentrations of IO in coastal Antarctica, and coastlines rich in certain species of macro-algae, are large enough (> 10 pptv) to promote ultra-fine particle formation. Recently, the first satellite measurements of IO, using the SCIAMACHY instrument on ENVISAT, have been reported by two groups; their results will be compared with the ground-based measurements.
Boundary Layer Transition Flight Experiment Overview
NASA Technical Reports Server (NTRS)
Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.
2011-01-01
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 STS-119, STS-128, STS-131 and STS-133 as well as Space Shuttle Endeavour for STS-134. 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 with emphasis on the STS-131 and STS-133 results. 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 empirically correlated predictions for boundary layer transition onset time closely match the flight data, while predicted surface temperatures were significantly higher than observed flight temperatures. A thermocouple anomaly observed on a number of the missions is discussed as are a number of the mitigation actions that will be taken on the final flight, STS-134, including potential alterations of the flight trajectory and changes to the flight instrumentation.
Near Critical Phenomena in Laminar Boundary Layers
NASA Astrophysics Data System (ADS)
Kluwick, A.; Braun, S.; Cox, E. A.
Recent developments in the construction of airfoils and rotorblades are characterized by an increasing interest in the application of so-called smart structures for active flow control. These are characterized by an interplay of sensors, actuators, real-time controlling data processing systems and the use of new materials e.g. shape alloys with the aim to increase manoeuvrability, reduce drag and radiated sound. The optimal use of such devices obviously requires a detailed insight into the flow phenomena to be controlled and in particular their sensitivity to external disturbances. In this connection locally separated boundary layer flows are of special interest. Asymptotic analysis of boundary layer separation in the limit of large Reynolds number Re? ? has shown that in a number of cases which are of importance from a practical point of view solutions of the resulting interaction equations describing two-dimensional steady flows exist up to a limiting value ? c of the relevant controlling parameter ? only while two branches of solutions exist in a regime ? < ? c . The present study aims at a better understanding of near critical flows ? ? — ? c ? ? 0 and in particular the changes of the flow behaviour associated with the passage of ? through ? c .
NASA Technical Reports Server (NTRS)
Spina, Eric F.
1995-01-01
The primary objective in the two research investigations performed under NASA Langley sponsorship (Turbulence measurements in hypersonic boundary layers using constant temperature anemometry and Reynolds stress measurements in hypersonic boundary layers) has been to increase the understanding of the physics of hypersonic turbulent boundary layers. The study began with an extension of constant-temperature thermal anemometry techniques to a Mach 11 helium flow, including careful examinations of hot-wire construction techniques, system response, and system calibration. This was followed by the application of these techniques to the exploration of a Mach 11 helium turbulent boundary layer (To approximately 290 K). The data that was acquired over the course of more than two years consists of instantaneous streamwise mass flux measurements at a frequency response of about 500 kHz. The data are of exceptional quality in both the time and frequency domain and possess a high degree of repeatability. The data analysis that has been performed to date has added significantly to the body of knowledge on hypersonic turbulence, and the data reduction is continuing. An attempt was then made to extend these thermal anemometry techniques to higher enthalpy flows, starting with a Mach 6 air flow with a stagnation temperature just above that needed to prevent liquefaction (To approximately 475 F). Conventional hot-wire anemometry proved to be inadequate for the selected high-temperature, high dynamic pressure flow, with frequent wire breakage and poor system frequency response. The use of hot-film anemometry has since been investigated for these higher-enthalpy, severe environment flows. The difficulty with using hot-film probes for dynamic (turbulence) measurements is associated with construction limitations and conduction of heat into the film substrate. Work continues under a NASA GSRP grant on the development of a hot film probe that overcomes these shortcomings for hypersonic flows. Each of the research tasks performed during the NASA Langley research grants is discussed separately below.
Leading-edge effects on boundary-layer receptivity
NASA Technical Reports Server (NTRS)
Gatski, Thomas B.; Kerschen, Edward J.
1990-01-01
Numerical calculations are presented for the incompressible flow over a parabolic cylinder. The computational domain extends from a region upstream of the body downstream to the region where the Blasius boundary-layer solution holds. A steady mean flow solution is computed and the results for the scaled surface vorticity, surface pressure and displacement thickness are compared to previous studies. The unsteady problem is then formulated as a perturbation solution starting with and evolving from the mean flow. The response to irrotational time harmonic pulsation of the free-stream is examined. Results for the initial development of the velocity profile and displacement thickness are presented. These calculations will be extended to later times to investigate the initiation of instability waves within the boundary-layer.
Turbulent dispersion in cloud-topped boundary layers
NASA Astrophysics Data System (ADS)
Verzijlbergh, R. A.; Jonker, H. J. J.; Heus, T.; Vilöguerau de Arellano, J.
2009-02-01
Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion - a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.
Turbulent dispersion in cloud-topped boundary layers
NASA Astrophysics Data System (ADS)
Verzijlbergh, R. A.; Jonker, H. J. J.; Heus, T.; Vilöguerau de Arellano, J.
2008-11-01
Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.
Scott R. Nowlin
1993-01-01
This study focuses on the effects of boundary layer pitot pressure fluctuations on fin-induced separation shock unsteadiness. Experiments performed in two phases under adiabatic wall conditions in a Mach 5 wind tunnel used high frequency-response transducers to measure fluctuating pressures in a turbulent boundary layer and a separated flow induced by a hemi-cylindrical unswept fin. Phase 1 results indicate that
Boundary layer roll circulations during FIRE
NASA Technical Reports Server (NTRS)
Shirer, Hampton N.; Haack, Tracy
1990-01-01
The probable mechanism underlying the development of boundary layer roll circulations are studied using wind and temperature profiles measured by the National Center for Atmospheric Research (NCAR) Electra during the stratocumulus phase of the First ISCCP Regional Experiment (FIRE). The expected, or preferred, roll orientations, horizontal wavelengths, and propagation periods are determined by finding the minimum values of the dynamic and thermodynamic forcing parameters, which here are the eddy Reynolds number (Re) and moist Rayleigh number (Ra sub m). These minimum values depend on the height z sub T of the capping temperature inversion and on the values of the Fourier coefficients of the background height-dependent vector wind profile. As input to our nonlinear spectral model, descent and ascent runs by the Electra provide for initial estimates of the inversion height and the wind profiles. In the first phase of the investigation presented here, a mechanism is said to be a probable contributor to the development of roll circulations within the stratocumulus-topped boundary layer if the modeled roll orientation and wavelengths agree with their observed values. Preliminary results using the 14-coefficient model of Haack-Hirschberg (1988) are discussed for the 7 July 1987 Electra Mission 188-A (Flight 5). This mission was flown across a sharp cloud boundary that was within a LANDSAT/SPOT scene. The stratocumulus deck was relatively solid in the eastern part of the scene, while there was a rapid decrease in cloud cover to scattered cumulus clouds aligned in streets to the west. These cloud streets were oriented nearly parallel to the mean wind direction in the layer, which was approximately 340 degrees. The hypothesis that roll circulations occurred in both the relatively clear and the cloudy regions is investigated using as model input a descent profile obtained in the relatively clear air and an ascent profile obtained in the cloudy air. Initial results for the clear air case are that the pure inflection point mode is not possible and the pure thermal mode was oriented 35 degrees to the right of the mean wind direction. The origin of this unacceptably large discrepancy between the observed and modeled results will be investigated further and the conclusions reported at the next FIRE workshop.
Turbulent Boundary Layer in High Rayleigh Number Convection in Air
NASA Astrophysics Data System (ADS)
du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian
2014-03-01
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.
Winds in the Marine Boundary Layer: A Forecaster's Guide
NSDL National Science Digital Library
2014-09-14
This module is intended for experienced forecasters moving from a land-based area to a coastal or Great Lakes region where both over-land and over-water forecast areas exist. This module highlights the differences between marine boundary layer and terrestrial boundary layer winds. The experienced forecaster is relatively familiar with the boundary layer over land and the associated implications for the wind field. Using this as a base, the module compares this known quantity with the lesser-known processes that occur in the marine boundary layer. Three major topics that influence marine boundary layer winds are discussed: stability within the boundary layer, isallobaric influence, and the effects of convection and tropical cyclones.
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.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.; Zierke, W. C.
1984-01-01
The flow field about an airfoil in a cascade at chord Reynolds number (R sub C) near 50,000. The program is experimental and combines laser Doppler anemometry (LDA) with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation and the transition zone) on a cascade of highly-loaded compressor blades. The information provided is to serve as benchmark data for the evaluation of current and future compressor cascade predictive models, in this way aiding in the compressor design process. The completed pressure surface mean velocity profiles, as well as two detailed near wake velocity profiles, all at a single incidence angle are provided.
Modelling of the Evolving Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Sorbjan, Zbigniew
2014-06-01
A single-column model of the evolving stable boundary layer (SBL) is tested for self-similar properties of the flow and effects of ambient forcing. The turbulence closure of the model is diagnostic, based on the K-theory approach, with a semi-empirical form of the mixing length, and empirical stability functions of the Richardson number. The model results, expressed in terms of local similarity scales, are universal functions, satisfied in the entire SBL. Based on similarity expression, a realizability condition is derived for the minimum allowable turbulent heat flux in the SBL. Numerical experiments show that the development of "horse-shoe" shaped, fixed-elevation hodographs in the interior of the SBL around sunrise is controlled by effects imposed by surface thermal forcing.
Boundary-layer and shock-layer solutions to singularly perturbed boundary-value problems
Jeffries, J.S.
1987-01-01
This dissertation concerns the study of certain singularly perturbed boundary value problems. In the first part of this dissertation (Chapters 2 and 3), a singularly perturbed nonlinear system of differential equations are considered over a compact interval, subject to general boundary conditions that allow the coupling of the boundary values at the different endpoints. It is shown, subject to suitable conditions, that there exists solutions of boundary-layer type, i.e., solutions that experience a rapid variation at one or both endpoints. In the second part (Chapter 4), a singularly perturbed second-order scalar differential equation is considered over a compact interval subject to Dirichlet boundary conditions. Subject to suitable conditions, there exist solutions of shock-layer type, i.e., solutions that experience a rapid transition at an interior point. For both the singularly perturbed system and the second-order scalar equation, a proposed approximate solution is constructed using the O'Malley construction, and a Riccati transformation is then used in a direct construction of the Green function for linearization of the problem about the proposed approximate solution.
Halogen chemistry in the marine boundary layer
NASA Astrophysics Data System (ADS)
Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.
2009-04-01
Important atmospheric sources of iodine include the air-sea exchange of biogenic iodocarbons, and the emission of I2 from macro-algae. The major source of bromine is the release of bromide ions from sea-salt aerosol. The subsequent atmospheric chemistry of these halogens (1), changes the oxidizing capacity of the marine boundary layer by destroying ozone and changing the hydroxyl radical concentration; (2), reacts efficiently with dimethyl sulphide and mercury (in the polar regions); and (3), leads to the formation of ultra-fine particles which may contribute to cloud condensation nuclei (CCN) and hence affect climate. This paper will report observations of IO, BrO, OIO and I2 made by the technique of differential optical absorption spectroscopy, in several contrasting marine environments: the equatorial mid-Atlantic (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar marine boundary layer (Hudson Bay, Canada). Both IO and BrO are observed in all these locations at significant concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. To complement the field campaigns we have also carried out wide-ranging laboratory investigation. A new study of OIO photochemistry shows that absorption in the visible bands between 490 and 630 nm leads to I atom production with a quantum yield of unity, which now means that iodine is a particularly powerful ozone-depleting agent. We have also studied the formation and growth kinetics of iodine oxide nano-particles, and their uptake of water, sulphuric acid and di-carboxylic organic acids, in order to model their growth to a size where they can act as CCN. Their ice-nucleating properties will also be reported.
Acoustics of laminar boundary layers breakdown
NASA Technical Reports Server (NTRS)
Wang, Meng
1994-01-01
Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.
Active Boundary Layer Trip for Supersonic Flows
NASA Astrophysics Data System (ADS)
Schloegel, F.; Panigua, G.; Tirtey, S.
2009-01-01
The last decade has been full of excitement and success for the hypersonic community thanks to various Scramjet ground tests and launches. These studies have shown promising potentials but the viability to perform commercial flights at Mach 8 is still to be demonstrated. An ideal Scramjet is one which is capable of self- starting over a wide range of angles of attack and Mach number. The Scramjet designer has to ensure that the boundary layer over the inlet ramp is fully turbulent where shocks impact, hence reducing the risks of chocked flow conditions. Most studies have issued the efficiency of roughness trip to trigger the boundary layer transition. At hypersonic speed, heat transfer and drag dramatically increase resulting in skin friction averaging at 40% of the overall drag. This study investigates the possibility of triggering transition using perpendicular air jets on a flat plate place in a hypersonic cross-flow. Experiments were conducted in the von Karman Institute hypersonic blow down wind tunnel H3. This facility is mounted with a Mach 6 contoured nozzles and provides flows with Reynolds number in the range of 10x106/m to 30x106/m. The model consist of a flat plate manufactured with a built -in settling chamber, equipped with a pressure tap and a thermocouple to monitor the jet conditions. A first flat plate was manufactured with a black-coated Plexiglas top, for surface heat transfer measurement using an infrared camera. On the second model, a Upilex sheet equipped with 32 thin film gages was glued, time dependent heat transfer measurements up to 60kHz. The jet injection conditions have been varied and a Mach number of 5.5 kept constant. The flow topology was investigated using fast schlieren techniques and oil flow, in order to gain a better understanding.
Acoustics of laminar boundary layers breakdown
NASA Astrophysics Data System (ADS)
Wang, Meng
1994-12-01
Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.
Methods and results of boundary layer measurements on a glider
NASA Technical Reports Server (NTRS)
Nes, W. V.
1978-01-01
Boundary layer measurements were carried out on a glider under natural conditions. Two effects are investigated: the effect of inconstancy of the development of static pressure within the boundary layer and the effect of the negative pressure difference in a sublaminar boundary layer. The results obtained by means of an ion probe in parallel connection confirm those results obtained by means of a pressure probe. Additional effects which have occurred during these measurements are briefly dealt with.
Experiment on convex curvature effects in turbulent boundary layers.
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1973-01-01
Turbulent boundary layers along a convex surface of varying curvature were investigated in a specially designed boundary-layer tunnel. A fairly complete set of turbulence measurements was obtained. The effect of curvature is striking. For example, along a convex wall the Reynolds stress is decreased near the wall and vanishes about midway between the wall and the edge of a boundary layer where there exists a velocity profile gradient created upstream of the curved wall.
A Sensitivity Theory for the Equilibrium Boundary Layer Over Land
NASA Astrophysics Data System (ADS)
Cronin, T.
2013-12-01
Due to the intrinsic complexities associated with modeling land-atmosphere interactions, global models typically use elaborate land surface and boundary layer physics parameterizations. Unfortunately, it is difficult to use elaborate models, by themselves, to develop a deeper understanding of how land surface parameters affect the coupled land-atmosphere system. At the same time, it is also increasingly important to gain a deeper understanding of the role of changes in land cover, land use, and ecosystem function as forcings and feedbacks in past and future climate change. Here, we outline the new framework of boundary layer climate sensitivity, which is based on surface energy balance, just as global climate sensitivity is based on top-of-atmosphere energy balance. We develop an analytic theory for the boundary layer climate sensitivity of an idealized model of a diurnally-averaged well-mixed boundary layer over land (Betts, 2000). This analytic sensitivity theory identifies changes in the properties of the land surface - including moisture availability, albedo, and aerodynamic roughness - as forcings, and identifies strong negative feedbacks associated with the surface fluxes of latent and sensible heat. We show that our theory can explain nearly all of the sensitivity of the Betts (2000) full system of equations, and find that nonlinear forcing functions are key to understanding changes in temperature caused by large changes in surface properties; this is directly analogous to the case of climate sensitivity, where nonlinear radiative forcing functions are key to understanding the response of global temperature to large changes in greenhouse gas concentrations. Favorable comparison of the theory and the simulation results from a two-column radiative convective model suggests that the theory may be broadly useful for unifying our understanding of how changes in land use or ecosystem function may affect climate change.
Simulation and optimal control of wind-farm boundary layers
NASA Astrophysics Data System (ADS)
Meyers, Johan; Goit, Jay
2014-05-01
In large wind farms, the effect of turbine wakes, and their interaction leads to a reduction in farm efficiency, with power generated by turbines in a farm being lower than that of a lone-standing turbine by up to 50%. In very large wind farms or `deep arrays', this efficiency loss is related to interaction of the wind farms with the planetary boundary layer, leading to lower wind speeds at turbine level. Moreover, for these cases it has been demonstrated both in simulations and wind-tunnel experiments that the wind-farm energy extraction is dominated by the vertical turbulent transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate the use of optimal control techniques combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large `infinite' wind farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with actuator-disk and actuator-line representations of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind that combines Fourier-spectral discretization in horizontal directions with a fourth-order finite-volume approach in the vertical direction. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in an actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. Optimal model-predictive control (or optimal receding horizon control) is used, where the model simply consists of the full LES equations, and the time horizon is approximately 280 seconds. The optimization is performed using a nonlinear conjugate gradient method, and the gradients are calculated by solving the adjoint LES equations. We find that the extracted farm power increases by approximately 20% when using optimal model-predictive control. However, the increased power output is also responsible for an increase in turbulent dissipation, and a deceleration of the boundary layer. Further investigating the energy balances in the boundary layer, it is observed that this deceleration is mainly occurring in the outer layer as a result of higher turbulent energy fluxes towards the turbines. In a second optimization case, we penalize boundary-layer deceleration, and find an increase of energy extraction of approximately 10%. In this case, increased energy extraction is balanced by a reduction in of turbulent dissipation in the boundary layer. J.M. acknowledges support from the European Research Council (FP7-Ideas, grant no. 306471). Simulations were performed on the computing infrastructure of the VSC Flemish Supercomputer Center, funded by the Hercules Foundation and the Flemish Government.
The effect of an aircraft's boundary layer on propeller noise
NASA Astrophysics Data System (ADS)
Belyaev, I. V.
2012-07-01
This study concerns the influence of the boundary layer at an aircraft's fuselage, simulated by an infinite hard cylinder, on propeller noise in the acoustic far field. Also studied is the effect of the boundary layer on noise as a function of the thickness and profile of the mean velocity of the boundary layer, the Mach number of the incident flow, and the rotation speed of the propeller. It is shown that the boundary layer at the fuselage can substantially modify propeller noise in the far field and should therefore be taken into account in calculating community noise.
Mixing length in low Reynolds number compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Holley, B. B.
1975-01-01
The paper studies the effect of low Reynolds number in high-speed turbulent boundary layers on variations of mixing length. Boundary layers downstream of natural transition on plates, cones and cylinders, and boundary layers on nozzle walls without laminarization-retransition are considered. The problem of whether low Reynolds number amplification of shear stress is a result of transitional flow structure is considered. It is concluded that a knowledge of low Reynolds number boundary layer transition may be relevant to the design of high-speed vehicles.
Improved Boundary Layer Depth Retrievals from MPLNET
NASA Technical Reports Server (NTRS)
Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette
2013-01-01
Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, MD since April 2001. However, because of issues with the operational PBL depth algorithm, the data is not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers, and in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System-version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by 410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they diered the most in the winter.
Acoustic sounding in the planetary boundary layer
NASA Technical Reports Server (NTRS)
Kelly, E. H.
1974-01-01
Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the boundary between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.
Improved boundary layer depth retrievals from MPLNET
NASA Astrophysics Data System (ADS)
Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette
2013-09-01
Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, Maryland, since April 2001. However, because of issues with the operational PBL depth algorithm, the data are not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers and, in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons, which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by ˜410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they differed the most in the winter.
The Application of Optimal Control to Boundary Layer Flow
D. Henningson; A. Hanifi
Modern optimal control theory can be used to calculate the optimal steady suction needed to e.g. relaminarize the flow or to delay transition. This has been used to devise the best possible suction distributions for keeping the flow laminar, and applied for flat plate boundary layers as well as boundary layers on swept wings of airplanes. Optimal control theory can
Boundary layer shear stress in subsonic and supersonic flow
NASA Technical Reports Server (NTRS)
Sandborn, V. A.; Horstman, C. C.
1977-01-01
A wide range of shear stress distributions for turbulent boundary layers is examined. A solution for the shear stress in terms of the mean flow is obtained for the limiting case of large Reynolds numbers. Attention is given to turbulent boundary layer shear stress, zero pressure gradient flow, increasing pressure gradient flow, and decreasing pressure gradient flow.
2-D airfoil tests including side wall boundary layer measurements
W. Bartelheimer; K. H. Horstmann; W. Puffert-Meissner
1994-01-01
The data presented in this contribution were obtained in the DLR Transonic Wind Tunnel Braunschweig. The intent of the experiment was to provide data giving information on the development of the TWB-side wall boundary layer in the presence of a typical transonic airfoil model for further investigation of the influence of the side wall boundary layer on 2-D airfoil measurements.
DNS of Turbulent Boundary Layer Subject Strong Adverse Pressure Gradient
Guillermo Araya; Luciano Castillo
2010-01-01
Direct Numerical Simulations of spatially evolving turbulent boundary layers with prescribed strong adverse pressure gradients are performed. The driven force behind this investigation is to analyze the interaction between the inner and outer layers in adverse pressure gradient with eventual separation. A method for prescribing realistic turbulent velocity inflow boundary conditions is employed. The approach is based on the rescaling-recycling
Helical circulations in the typhoon boundary layer Ryan Ellis1
Businger, Steven
Helical circulations in the typhoon boundary layer Ryan Ellis1 and Steven Businger1 Received 27-level wind data from the WSR-88D in Guam obtained in Typhoon Dale (1996) and Typhoon Keith (1997 circulations in the typhoon boundary layer, J. Geophys. Res., 115, D06205, doi:10.1029/2009JD011819. 1
Sun-Earth connection: Boundary layer waves and auroras
G. S. Lakhina; B. T. Tsurutani; J. K. Arballo; C. Galvan
2000-01-01
Boundary layers are the sites where energy and momentum are exchanged between two distinct plasmas. Boundary layers occurring in space plasmas can support a wide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond. The main characteristics of the broadband plasma waves (with frequencies > 1 Hz) observed in the magnetopause, polar
Turbulence Structure and Wall Signature in Hypersonic Turbulent Boundary Layer
Martín, Pino
Turbulence Structure and Wall Signature in Hypersonic Turbulent Boundary Layer Yin-Chiu Kan , Clara and hypersonic turbulent boundary layer datasets from direct numerical simulation (DNS). Contour plots and Marusic5 and Mathis, Hutchins and Marusic16 ). In contrast to supersonic and hypersonic flow regimes
Mass exchange in the stable boundary layer by coherent structures
Leclerc, Monique Y.
Mass exchange in the stable boundary layer by coherent structures D.I. Cooper a,*, M.Y. Leclerc b December 2004 Abstract Observations of multi-dimensional water vapor structures in the first 75 m of the stable boundary layer (SBL) were made using a high resolution scanning Raman lidar in October 2000 during
Wind Tunnel simulation of diffusion in a convective boundary layer
M. Poreh; J. E. Cermak
1984-01-01
A study of turbulent dispersion of passive tracers in unstable boundary layers, conducted in the Meteorological Wind Tunnel of the Fluid Dynamics and Diffusion Laboratory at Colorado State University, is described. The measured mean and turbulent velocities are found to be similar to those measured in atmospheric convective boundary layers. The diffusion pattern, from ground-level and elevated sources over both
Optimal Disturbances in Compressible Boundary Layers Complete Energy Norm Analysis
Zuccher, Simone
Optimal Disturbances in Compressible Boundary Layers Complete Energy Norm Analysis Simone Zuccher for the sphere, in the range of parameters that are relevant to wind tunnel testing or flight conditions density Subscripts ad adiabatic conditions e edge of the boundary layer in inlet conditions out outlet
The horizontal variability of vertically integrated boundary layer winds
René V. Cormier
1975-01-01
This research provides a study of the horizontal variability of integrated boundary layer winds (IBLW's) for distances of the order of miles (kilometers). This information should be helpful for both theoretical and practical applications, e.g., boundary layer parameterization and air pollution models. The study concerned itself with winds integrated to a height of 1000 ft (300 m) and made use
NASA Astrophysics Data System (ADS)
Lundquist, Julie Kay
2001-08-01
In this study, I use observations and a first-order closure model to study inertial oscillations in the fair- weather atmospheric boundary layer over land. I attempt to determine their origin and confirm the hypothesis developed by Blackadar, that inertial oscillations commence at the evening transition of the boundary due to decoupling of winds aloft from those beneath the surface inversion. I use two months of data from 915 MHz boundary-layer wind profilers associated with the CASES field experiments. Using the data and a new technique for extracting inertial oscillations from boundary-layer winds, I document quantitatively that inertial oscillations are generated at the evening transition as well as at other times in the diurnal cycle. I verify that inertial oscillations are present in the wind speed maximum of the nocturnal low-level jet. I run a one-dimensional first-order closure numerical model to model the dynamics of one night. The model reproduces observed inertial oscillations. The amplitudes of the observed inertial oscillations strongly correlate with the magnitude of the ageostrophic wind at model initiation. Residual mixing aloft causes the amplitudes of the inertial oscillations to deviate slightly from the profile dictated by the initial ageostrophic wind. Using a simple analytical model, I explore the limit in which turbulent stress divergence is small compared to the ageostrophic wind to confirm that whenever the turbulent stress divergence becomes small compared to the ageostrophic term in the momentum equations, inertial oscillations commence with amplitudes equal to the magnitude of the ageostrophic component of the wind at that time.
Large Eddy Simulations of boundary layer flow over fractal trees
Jason Graham; Charles Meneveau
2009-01-01
A large-eddy simulation (LES) of flow over a canopy of fractal trees in the atmospheric boundary layer (ABL) is performed. The fractal trees provide complex boundary- turbulence interactions while maintaining tractable characteristics that can be systematically studied. LES are performed using the immersed boundary method following the implementation of Chester et al. (2007, J. Comp. Phys.). Simulations are performed for
Secondary instabilities in compressible boundary layers
NASA Technical Reports Server (NTRS)
Ng, Lian; Erlebacher, Gordon
1990-01-01
Secondary instabilities are examined in compressible boundary layers at Mach numbers M(sub infinity) = 0, 0.8, 1.6, and 4.5. It is found that there is a broad-band of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M(sub infinity) is less than or equal to 1.6, fundamental resonance dominates at relatively high (2-d) primary disturbance amplitude, while subharmonic resonance is characterized by a low (2-d) primary amplitude. At M(sub infinity) = 4.5, the subharmonic instability which arises from the second mode disturbance is the strongest type of secondary instability. The influence of the inclination, theta, of the primary wave with respect to the mean flow direction on secondary instability is investigated at M(sub infinity) = 1.6 for small to moderate values of theta. It is found that the strongest fundamental instability occurs when the primary wave is inclined at 10 deg to the mean flow direction, although a 2-d primary mode yields the most amplified subharmonic. The subharmonic instability at a high value of theta (namely, theta = 45 deg) is also discussed. Finally, a subset of the secondary instability results are compared against direct numerical simulations.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S.; Spencer, Shelly Anne
1993-01-01
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S. (Principal Investigator); Spencer, Shelly Anne
1993-01-01
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-travelling, sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2(lambda)(sub TS)/pi, of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations and the Stokes wave subtracted) show the generation of 3-D-T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modelling are observed.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.; Zierke, W. C.
1986-01-01
The purpose of NASA Research Grant NSG-3264 is to characterize the flowfield about an airfoil in a cascade at chord Reynolds number(R sub C)near 5 x 10 to the 5th power. The program is experimental and combines laser Doppler velocimeter (LDV) measurements with flow visualization techniques in order to obtain detailed flow data, e.g., boundary layer profiles, points of separation and the transition zone, on a cascade of highly-loaded compressor blades. The information provided by this study is to serve as benchmark data for the evaluation of current and future compressor cascade predictive models, in this way aiding in the compressor design process. Summarized is the research activity for the period 1 December 1985 through 1 June 1986. Progress made from 1 June 1979 through 1 December 1985 is presented. Detailed measurements have been completed at the initial cascade angle of 53 deg. (incidence angle 5 degrees). A three part study, based on that data, has been accepted as part of the 1986 Gas Turbine Conference and will be submitted for subsequent journal publication. Also presented are data for a second cascade angle of 45 deg (an incidence angle of 3 degrees).
A boundary layer model for magnetospheric substorms
NASA Technical Reports Server (NTRS)
Rostoker, Gordon; Eastman, Tim
1987-01-01
An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.
A boundary layer model for magnetospheric substorms
NASA Astrophysics Data System (ADS)
Rostoker, Gordon; Eastman, Tim
1987-11-01
An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.
Destiny of earthward streaming plasma in the plasmasheet boundary layer
NASA Technical Reports Server (NTRS)
Green, J. L.; Horwitz, J. L.
1986-01-01
The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.
On an Asymptotically Consistent Unsteady Interacting Boundary Layer
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2007-01-01
This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.
The wave-induced boundary layer under long internal waves
NASA Astrophysics Data System (ADS)
Lin, Yuncheng; Redekopp, Larry G.
2011-08-01
The boundary layer formed under the footprint of an internal solitary wave is studied by numerical simulation for waves of depression in a two-layer model of the density stratification. The inviscid outer flow, in the perspective of boundary-layer theory, is based on an exact solution for the long wave-phase speed, yielding a family of fully nonlinear solitary wave solutions of the extended Korteweg-de Vries equation. The wave-induced boundary layer corresponding to this outer flow is then studied by means of simulation employing the Reynolds-averaged Navier-Stokes (RANS) formulation coupled with a turbulence closure model validated for wall-bounded flows. Boundary-layer characteristics are computed for an extensive range of environmental conditions and wave amplitudes. Boundary-layer transition, identified by monitoring the eddy viscosity, is correlated in terms of a boundary-layer Reynolds number. The frictional drag is evaluated for laminar, transitional, and turbulent cases, and correlations are presented for the friction coefficient plus relevant measures of the boundary-layer thickness.
Particle image velocimetry measurements of a shock wave\\/turbulent boundary layer interaction
R. A. Humble; F. Scarano; B. W. van Oudheusden
2007-01-01
Particle image velocimetry is used to investigate the interaction between an incident shock wave and a turbulent boundary\\u000a layer at Mach 2.1. A particle response assessment establishes the fidelity of the tracer particles. The undisturbed boundary\\u000a layer is characterized in detail. The mean velocity field of the interaction shows the incident and reflected shock wave pattern,\\u000a as well as the
NASA Technical Reports Server (NTRS)
Deutsch, Steven; Zierke, William C.
1987-01-01
A one-component laser Doppler velocimeter (LDV) has been used to measure the two-dimensional, periodic flow field about a double circular arc, compressor blade in cascade. Eleven boundary layer profiles were taken on both the pressure and suction surfaces of the blade, and two were taken in the near wake. In this part of the study, the LDV system is described and the suction surface flow field is documented. The suction surface profiles appear to separate both at the leading edge and again somewhat beyond midchord; the leading edge separation apparently reattaches by 2.6 percent chord.
Symmetries in Turbulent Boundary Layer Flows
NASA Technical Reports Server (NTRS)
Oberlack, M.
1996-01-01
The objective is the development of a new theory which enables the algorithmic computation of all self-similar mean velocity profiles. The theory is based on Liegroup analysis and unifies a large set of self-similar solutions for the mean velocity of stationary parallel turbulent shear flows. The results include the logarithmic law of the wall, an algebraic law, the viscous sublayer, the linear region in the middle of a Couette flow and in the middle of a rotating channel flow, and a new exponential mean velocity profile not previously reported. Experimental results taken in the outer parts of a high Reynolds number flat-plate boundary layer, strongly support the exponential profile. From experimental as well as from DNS data of a turbulent channel flow the algebraic scaling law could be confirmed in both the center region and in the near wall region. In the case of the logarithmic law of the wall, the scaling with the wall distance arises as a result of the analysis and has not been assumed in the derivation. The crucial part of the derivation of all the different mean velocity profiles is to consider the invariance of the equation for the velocity fluctuations at the same time as the invariance of the equation for the velocity product equations. The latter is the dyad product of the velocity fluctuations with the equation for the velocity fluctuations. It has been proven that all the invariant solutions are also consistent with similarity of all velocity moment equations up to any arbitrary order.
Titan's planetary boundary layer structure at the Huygens landing site
Tetsuya Tokano; Francesca Ferri; Giacomo Colombatti; Teemu Mäkinen; Marcello Fulchignoni
2006-01-01
Huygens Atmospheric Structure Instrument (HASI) for the first time performed an in situ measurement of the thermal structure in Titan's atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer (PBL). The vertical potential temperature profile reveals the presence of a weakly convective PBL, with a surface layer thickness of 10 m and an outer layer with a
Boundary-layer receptivity and laminar-flow airfoil design
NASA Technical Reports Server (NTRS)
Kerschen, Edward J.
1987-01-01
Boundary-layer receptivity examines the way in which external disturbances generate instability waves in boundary layers. Receptivity theory is complementary to stability theory, which studies the evolution of disturbances that are already present in the boundary layer. A transition prediction method which combines receptivity with linear stability theory would directly account for the influence of free-stream disturbances and also consider the characteristics of the boundary layer upstream of the neutral stability point. The current e sup N transition prediction methods require empirical correlations for the influence of environmental disturbances, and totally ignore the boundary layer characteristics upstream of the neutral stability point. The regions where boundary-layer receptivity occurs can be separated into two classes, one near the leading edges and the other at the downstream points where the boundary layer undergoes rapid streamwise adjustments. Analyses were developed for both types of regions, and parametric studies which examine the relative importance of different mechanisms were carried out. The work presented here has focused on the low Mach number case. Extensions to high subsonic and supersonic conditions are presently underway.
On the theory of laminar boundary layers involving separation
NASA Technical Reports Server (NTRS)
Von Karman, TH; Millikan, C
1934-01-01
This paper presents a mathematical discussion of the laminar boundary layer, which was developed with a view of facilitating the investigation of those boundary layers in particular for which the phenomenon of separation occurs. The treatment starts with a slight modification of the form of the boundary layer equation first published by Von Mises. Two approximate solutions of this equation are found, one of which is exact at the outer edge of the boundary layer while the other is exact at the wall. The final solution is obtained by joining these two solutions at the inflection points of the velocity profiles. The final solution is given in terms of a series of universal functions for a fairly broad class of potential velocity distributions outside of the boundary layer. Detailed calculations of the boundary layer characteristics are worked out for the case in which the potential velocity is a linear function of the distance from the upstream stagnation point. Finally, the complete separation point characteristics are determined for the boundary layer associated with a potential velocity distribution made up of two linear functions of the distance from the stagnation point. It appears that extensions of the detailed calculations to more complex potential flows can be fairly easily carried out by using the explicit formulae given in the paper. (author)
Transformation of wing boundary layer in the filament wake
NASA Astrophysics Data System (ADS)
Mikhaelis, M. V.; Zanin, B. Yu.; Katasonov, M. M.
2014-12-01
Results of an experimental study of the air flow past a straight-wing model in a low-turbulence wind tunnel are reported. The influence of a turbulent wake due to a thin filament on the structure of boundary layer on the model surface was examined. Flow visualization in boundary layer, hot-wire measurements of flow velocity, and also measurements of the amplitude and frequency spectra of flow pulsations, were performed. The wake substantially modified the boundary layer flow pattern: the separation bubble disappeared from the flow, and the formation of longitudinal structures was observed.
Interaction of the planetary boundary layer depth with aerosol and boundary-layer clouds
NASA Astrophysics Data System (ADS)
Sawyer, V. R.; Li, Z.
2013-12-01
The depth of the planetary boundary layer (PBL) is driven by surface heating, with strong diurnal and seasonal cycles. Methods to detect the PBL depth from remote sensing instruments such as lidar and infrared spectrometer can take advantage of their high temporal resolution to produce detailed information about PBL development, which in turn has implications for weather, air quality and climate. An algorithm combining two common methods for PBL depth detection (wavelet covariance and iterative curve-fitting) has been evaluated by intercomparison among multiple instruments at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. Radiosonde-derived PBL depths at SGP accounted for over two-thirds the variation in PBL depths from atmospheric emitted radiance interferometer (AERI), and over half the variation in PBL depths from micropulse lidar (MPL). The results are sufficiently robust that the algorithm can be used at other locations that have only one source of atmospheric profiles. The new continuous PBL data set can be used to improve model parameterizations of PBL and our understanding of atmospheric transport of pollutants. Using ground-based MPL profiles from China and the U.S., this study investigates the behavior of the PBL in the presence of aerosol loading, in which the aerosol direct effect would have altitude-dependent consequences, and the interaction of PBL, aerosol and boundary-layer clouds. PBL depths detected by MPL, AERI and radiosonde, overlaid on MPL backscatter during a nine-day period of typical conditions.
Boundary layer structure over areas of heterogeneous heat fluxes
Doran, J.C. [Pacific Northwest Lab., Richland, WA (United States); Barnes, F.J. [Los Alamos National Lab., NM (United States); Coulter, R.L. [Argonne National Lab., IL (United States); Crawford, T.L. [National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.
1993-01-01
In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moreover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations? To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discusses some initial findings from those campaigns.
Boundary layer structure over areas of heterogeneous heat fluxes
Doran, J.C. (Pacific Northwest Lab., Richland, WA (United States)); Barnes, F.J. (Los Alamos National Lab., NM (United States)); Coulter, R.L. (Argonne National Lab., IL (United States)); Crawford, T.L. (National Oceanic and Atmospheric Administration, Oak Ridge, TN (United States). Air Resources Lab. Atmospheric Turbulence and Diffusion Div.)
1993-01-01
In general circulation models (GCMs), some properties of a grid element are necessarily considered homogeneous. That is, for each grid volume there is associated a particular combination of boundary layer depth, vertical profiles of wind and temperature, surface fluxes of sensible and latent heat, etc. In reality, all of these quantities may exhibit significant spatial variations the grid area, and the larger the area the greater the likely variations. In balancing the benefits of higher resolution against increased computational time and expense, it is useful to consider what the consequences of such subgrid-scale variability may be. Moreover, in interpreting the results of a simulation, one must be able to define an appropriate average value over a grid. There are two aspects of this latter problem: (1) in observations, how does one take a set of discrete or volume-averaged measurements and relate these to properties of the entire domain, and (2) in computations, how can subgrid-scale features be accounted for in the model parameterizations To address these and related issues, two field campaigns were carried out near Boardman, Oregon, in June 1991 and 1992. These campaigns were designed to measure the surface fluxes of latent and sensible heat over adjacent areas with strongly contrasting surface types and to measure the response of the boundary layer to those fluxes. This paper discusses some initial findings from those campaigns.
Pressure power spectra beneath a supersonic turbulent boundary layer.
Beresh, Steven Jay; Spillers, Russell Wayne; Henfling, John Francis; Pruett, Brian O. M.
2010-06-01
Wind tunnel experiments up to Mach 3 have provided fluctuating wall-pressure spectra beneath a supersonic turbulent boundary layer to frequencies reaching 400 kHz by combining signals from piezoresistive silicon pressure transducers effective at low- and mid-range frequencies and piezoelectric quartz sensors to detect high frequency events. Data were corrected for spatial attenuation at high frequencies and for wind-tunnel noise and vibration at low frequencies. The resulting power spectra revealed the {omega}{sup -1} dependence for fluctuations within the logarithmic region of the boundary layer, but are essentially flat at low frequency and do not exhibit the theorized {omega}{sup 2} dependence. Variations in the Reynolds number or streamwise measurement location collapse to a single curve for each Mach number when normalized by outer flow variables. Normalization by inner flow variables is successful for the {omega}{sup -1} region but less so for lower frequencies. A comparison of the pressure fluctuation intensities with fifty years of historical data shows their reported magnitude chiefly is a function of the frequency response of the sensors. The present corrected data yield results in excess of the bulk of the historical data, but uncorrected data are consistent with lower magnitudes. These trends suggest that much of the historical compressible database may be biased low, leading to the failure of several semi-empirical predictive models to accurately represent the power spectra acquired during the present experiments.
Planetary boundary layer feedbacks in climate system
NASA Astrophysics Data System (ADS)
Zilitinkevich, S.; Esau, I.
2009-09-01
A remarkable feature of the ongoing global warming is the asymmetry in trends of the daily minima, ?min, and maxima, ?max, of the surface air temperature (SAT): ?min increases faster than ?max, so that the daily temperature range (DTR), ?max-?min, basically decreases. The state of the art general circulation and climate models (GCMs) do not reproduce it and predict approximately the same change rates for ?min and ?max. We propose that the difference in trends of ?min and ?max is caused by the strong stability dependence of the height, h, of the planetary boundary layer (PBL). Indeed, the daytime warming is associated with deep convective (C) PBLs (with the heights hC ~ 103m), in contrast to the nocturnal and/or wintertime cooling associated with shallower mid-latitudinal nocturnal stable (NS) PBLs (with hNS ~ 200m) and even shallower high-latitudinal long-lived stable (LS) PBLs (with hLS ~ 30-50m) developing during longer than night periods of the persistent surface cooling. As a result, one and the same increment, ?Q0, in the surface heat flux leads to only minor increment in ?max in deep C PBLs, but essential increments in ?min in shallow NS and especially NS PBLs. The latter type of the PBL has been discovered only recently and is not yet accounted for in modern GCMs. In the present paper, we derive theoretical estimates of the variations, ??min and ??max, in the SAT minima and maxima associated with the stable and convective PBLs, respectively, and by this means explain the observed asymmetry in the growth rates of ?min and ?max. To characterise the role of PBLs in the climate system, we introduce the concepts of local and general PBL feedbacks. Besides the strengths of feedbacks, we propose to take into account the reaction times of different mechanisms. The proposed concepts could be applied to different climate-change problems from global (as in this paper) to local, in particular, to those caused by the land-use modification.
Brain response to prosodic boundary cues depends on boundary position
Holzgrefe, Julia; Wellmann, Caroline; Petrone, Caterina; Truckenbrodt, Hubert; Höhle, Barbara; Wartenburger, Isabell
2013-01-01
Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)—marking the processing of a prosodic phrase boundary—was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context. PMID:23882234
Brain response to prosodic boundary cues depends on boundary position.
Holzgrefe, Julia; Wellmann, Caroline; Petrone, Caterina; Truckenbrodt, Hubert; Höhle, Barbara; Wartenburger, Isabell
2013-01-01
Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)-marking the processing of a prosodic phrase boundary-was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context. PMID:23882234
The effects of successive distortions on a turbulent boundary layer in a supersonic flow
NASA Astrophysics Data System (ADS)
Smith, Douglas R.; Smits, Alexander J.
1997-11-01
Experiments were conducted to investigate the response of a high-Reynolds-number turbulent boundary layer in a supersonic flow to the perturbation presented by a forward-facing ramp. Two ramps were used: one with sharp corners, the other with rounded corners having radii of curvature equal to 15 initial boundary layer thicknesses. The flow was turned through 20° in each of the compressions and expansions. Hence, there was no net change in the flow direction over the ramps and only a small change in free-stream conditions due to the entropy increase across relatively weak shocks. The two experiments gave similar results. In the middle of the relaxing boundary layer, the streamwise Reynolds stress undershot the undisturbed levels and exhibited a response similar to that observed in subsonic boundary layer flows recovering from an impulse of streamline curvature (Smits, Young & Bradshaw 1979b). The turbulent shear stress vanished throughout most of the boundary layer, and an overall destruction of the turbulence production mechanisms was apparent as the boundary layer exhibited a slow recovery.
Energy efficient engine, low-pressure turbine boundary layer program
NASA Technical Reports Server (NTRS)
Gardner, W. B.
1981-01-01
A study was conducted to investigate development of boundary layers under the influence of velocity distributions simulating the suction side of two state-of-the-art turbine airfoils: a forward loaded airfoil (squared-off design) and an aft loaded airfoil (aft-loaded design). These velocity distributions were simulated in a boundary layer wind tunnel. Detailed measurements of boundary layer mean velocity and turbulence intensity profiles were obtained for an inlet turbulence level of 2.4 percent and an exit Reynolds number of 800,000. Flush-mounted hot film probes identified the boundary layer transition regimes in the adverse pressure gradient regions for both velocity distributions. Wall intermittency data showed good agreement with the correlations of Dhawan and Narasimha for the intermittency factor distribution in transitional flow regimes.
Experimental measurements of unsteady turbulent boundary layers near separation
NASA Technical Reports Server (NTRS)
Simpson, R. L.
1982-01-01
Investigations conducted to document the behavior of turbulent boundary layers on flat surfaces that separate due to adverse pressure gradients are reported. Laser and hot wire anemometers measured turbulence and flow structure of a steady free stream separating turbulent boundary layer produced on the flow of a wind tunnel section. The effects of sinusoidal and unsteadiness of the free stream velocity on this separating turbulent boundary layer at a reduced frequency were determined. A friction gage and a thermal tuft were developed and used to measure the surface skin friction and the near wall fraction of time the flow moves downstream for several cases. Abstracts are provided of several articles which discuss the effects of the periodic free stream unsteadiness on the structure or separating turbulent boundary layers.
Analysis of civil aircraft propulsors with boundary layer ingestion
Hall, David Kenneth
2015-01-01
This thesis describes (i) guidelines for propulsor sizing, and (ii) strategies for fan turbomachinery conceptual design, for a boundary layer ingesting (BLI) propulsion system for advanced civil transport aircraft. For the ...
Performance of a boundary layer ingesting propulsion system
Plas, Angélique (Angélique Pascale)
2006-01-01
This thesis presents an assessment of the aerodynamic performance of an aircraft propulsion system, with embedded engines, in the presence of aircraft fuselage boundary layer ingestion (BLI). The emphasis is on defining ...
Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number
Semper, Michael Thomas
2013-05-15
The purpose of the current study was to answer several questions related to hypersonic, low Reynolds number, turbulent boundary layers, of which available data related to turbulence quantities is scarce. To that end, a unique research facility...
Interacting turbulent boundary layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
The two dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances is considered. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. The interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model. Results are presented for flow over a train of up to six waves for Mach numbers of 10 and 32 million/meter, and wall temperature rations (T sub w/T sub 0) of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given. Detailed results on the influence of small protuberances on surface heating by boundary layers are presented.
Turbulent oceanic western-boundary layers at low latitude
NASA Astrophysics Data System (ADS)
Quam Cyrille Akuetevi, Cataria; Wirth, Achim
2013-04-01
Low latitude oceanic western-boundary layers range within the most turbulent regions in the worlds ocean. The Somali current system with the Great Whirl and the Brazilian current system with its eddy shedding are the most prominent examples. Results from analytical calculations and integration of a one layer reduced-gravity fine resolution shallow water model is used to entangle this turbulent dynamics. Two types of wind-forcing are applied: a remote Trade wind forcing with maximum shear along the equator and a local Monsoon wind forcing with maximum shear in the vicinity of the boundary. For high values of the viscosity (> 1000m2s-1) the stationary solutions compare well to analytical predictions using Munk and inertial layer theory. When lowering the friction parameter time dependence results. The onset of instability is strongly influenced by inertial effects. The unstable boundary current proceeds as a succession of anti-cyclonic coherent eddies performing a chaotic dynamics in a turbulent flow. The dynamics is governed by the turbulent fluxes of mass and momentum. We determine these fluxes by analyzing the (potential) vorticity dynamics. We demonstrate that the boundary-layer can be separated in four sub-layers, which are (starting from the boundary): (1) the viscous sub-layer (2) the turbulent buffer-layer (3) the layer containing the coherent structures and (4) the extended boundary layer. The characteristics of each sub-layer and the corresponding turbulent fluxes are determined, as are the dependence on latitude and the type of forcing. A new pragmatic method of determining the eddy viscosity, based on Munk-layer theory, is proposed. Results are compared to observations and solutions of the multi-level primitive equation model (DRAKKAR).
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.
Wave phenomena in a high Reynolds number compressible boundary layer
NASA Technical Reports Server (NTRS)
Bayliss, A.; Maestrello, L.; Parikh, P.; Turkel, E.
1985-01-01
Growth of unstable disturbances in a high Reynolds number compressible boundary layer is numerically simulated. Localized periodic surface heating and cooling as a means of active control of these disturbances is studied. It is shown that compressibility in itself stabilizes the flow but at a lower Mach number, significant nonlinear distortions are produced. Phase cancellation is shown to be an effective mechanism for active boundary layer control.
Approximation theory for boundary layer suction through individual slits
NASA Technical Reports Server (NTRS)
Walz, A.
1979-01-01
The basic concepts of influencing boundary layers are summarized, especially the prevention of flow detachment and the reduction of frictional resistance. A mathematical analysis of suction through a slit is presented with two parameters, for thickness and for shape of the boundary layer, being introduced to specify the flow's velocity profile behind the slit. An approximation of the shape parameter produces a useful formula, which can be used to determine the most favorable position of the slit. An aerodynamic example is given.
Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer
Michael Manhart
1998-01-01
: Supercritical turbulent boundary layer flow over a hemisphere with a rough surface (Re= 150000) has been simulated using Large Eddy Simulation (LES) and analyzed using the Karhunen--Loève expansion (“Proper Orthogonal\\u000a Decomposition,” POD). The time-dependent inflow condition is provided from a separate LES of a boundary layer developing behind\\u000a a barrier fence and a set of vorticity generators. LES results
Sun-Earth connection: Boundary layer waves and auroras
G S Lakhina; B T Tsurutani; J K Arballo; C Galvan
2000-01-01
Boundary layers are the sites where energy and momentum are exchanged between two distinct plasmas. Boundary layers occurring\\u000a in space plasmas can support a wide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond.\\u000a The main characteristics of the broadband plasma waves (with frequencies >1 Hz) observed in the magnetopause, polar cap,
New algebraic approaches to classical boundary layer problems
Xiao Ping Xu
2011-01-01
Classical non-steady boundary layer equations are fundamental nonlinear partial differential equations in the boundary layer\\u000a theory of fluid dynamics. In this paper, we introduce various schemes with multiple parameter functions to solve these equations\\u000a and obtain many families of new explicit exact solutions with multiple parameter functions. Moreover, symmetry transformations\\u000a are used to simplify our arguments. The technique of moving
Prehistory of Instability in a Hypersonic Boundary Layer
Alexander V. Fedorov; Andrew P. Khokhlov
2001-01-01
. The initial phase of hypersonic boundary-layer transition comprising excitation of boundary-layer modes and their downstream\\u000a evolution from receptivity regions to the unstable region (instability prehistory problem) is considered. The disturbance\\u000a spectrum reveals the following features: (1) the first and second modes are synchronized with acoustic waves near the leading\\u000a edge; (2) further downstream, the first mode is synchronized with
Tropical boundary layer equilibrium in the last ice age
NASA Technical Reports Server (NTRS)
Betts, Alan K.; Ridgway, W.
1992-01-01
A radiative-convective boundary layer model is used to assess the effect of changing sea surface temperature, pressure, wind speed, and the energy export from the tropics on the boundary layer equilibrium equivalent potential temperature. It remains difficult to reconcile the observations that during the last glacial maximum (18,000 yr BP) the snowline on the tropical mountains fell 950 m, while the tropical sea surface temperatures fell only 1-2 K.
Hypersonic boundary layer receptivity to acoustic disturbances over cones
Kursat Kara
2008-01-01
The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity
Generation of Turbulent Inlet Conditions for Thermal Boundary Layer Simulations
Juan G. Araya
2005-01-01
Realistic environments generally imply spatially evolving turbulent boundary layers, being the flat plate the typical example. In this case, periodic boundary conditions cannot be established in the streamwise direction as in fully developed flows in channels. For this reason, it is necessary to generate turbulent fluctuations at the inlet of the computational domain at every time step. Lund et al.
Calculation of rough-wall turbulent boundary layer heat transfer
M. H. Hosni; Hugh W. Coleman; Robert P. Taylor
1991-01-01
Predictions and measurements are presented to investigate the effects of surface roughness on turbulent rough-wall boundary layers. Predictions are compared with Stanton number measurements for the turbulent flow of air over four separate rough surfaces with a variety of thermal boundary conditions. The cases considered are constant wall temperature, constant wall heat flux, step wall temperature, and piecewise linear wall
Entry length requirements for direct simulations of turbulent boundary layers
J. Jimenez; M. P. Simens; S. Hoyas; Y. Mizuno
This report describes the results of a relatively large-scale direct simulation of a tur- bulent boundary layer using a new simulation code, with emphasis on the extent of the contamination of the flowfield due to the inflow boundary conditions. The assumption is that the goal of the simulation is to explore the physics of the flow, about which it is
Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation
Reichenbach, H.; Neuwald, P. [Ernst-Mach-Institut, Freiburg (DE); Kuhl, A.L. [R and D Associates, Los Angeles, CA (United States)
1992-11-01
This technical report describes methods that were applied to investigate turbulent boundary layers generated by inviscid, baroclinic effects. The Cranz-Schardin 24-sparks camera was used to visualize the interactions of a planar shock wave with a Freon R12-layer. The shock propagates more slowly in the Freon layer than in air because of its smaller sound speed. This causes the shock front to be curved and to be reflected between the wall and the layer interface. As a consequence of the reflection process, a series of compression and expansion waves radiate from the layer. Large fluctuations in the streamwise velocity and in pressure develop for about 1 ms. These waves strongly perturb the interface shear layer, which rapidly transitions to a turbulent boundary flow. Pressure measurements showed that the fluctuations in the Freon layer reach a peak pressure 4 times higher than in the turbulent boundary flow. To characterize the preshock Freon boundary layer, concentration measurements were performed with a differential interferometry technique. The refraction index of Freon R12 is so high that Mach-Zehnder interferometry was not successful in these experiments. The evaluation of the concentration profile is described here in detail. Method and results of corresponding LDV measurements under the same conditions are presented in a different report, EMI Report T 9/92. The authors plan to continue the dense gas layer investigations with the gas combination helium/Freon.
A preliminary assessment of the Titan planetary boundary layer
NASA Technical Reports Server (NTRS)
Allison, Michael
1992-01-01
Results of a preliminary assessment of the characteristic features of the Titan planetary boundary are addressed. These were derived from the combined application of a patched Ekman surface layer model and Rossby number similarity theory. Both these models together with Obukhov scaling, surface speed limits and saltation are discussed. A characteristic Akman depth of approximately 0.7 km is anticipated, with an eddy viscosity approximately equal to 1000 sq cm/s, an associated friction velocity approximately 0.01 m/s, and a surface wind typically smaller than 0.6 m/s. Actual values of these parameters probably vary by as much as a factor of two or three, in response to local temporal variations in surface roughness and stability. The saltation threshold for the windblown injection of approximately 50 micrometer particulates into the atmosphere is less than twice the nominal friction velocity, suggesting that dusty breezes might be an occassional feature of the Titan meteorology.
Calculation of boundary layers with sudden transverse strain
NASA Astrophysics Data System (ADS)
Gibson, M. M.; Younis, B. A.
1986-12-01
Modifications to a Reynolds stress closure are proposed in which the weighting of the two components of the pressure-strain correlation is adjusted: the turbulence part is increased to conform with measured rates of return to isotropy and the contribution from the mean-strain part is reduced. Consequential changes are then needed in the other closure assumptions. Their effect is to make the model more generally applicable and to improve predictions of turbulent flows in complex strain fields. The revised model is tested here against the measured response of axisymmetric boundary layers to suddenly imposed rotation. The wall region of this flow is resolved by means of walk functions where it is assumed that the directions of the shear stress and the mean-strain rate are coincident.
Boundary-Layer Receptivity to Freestream Disturbances for A Mach 4.5 Flow over A Flat Plate
Yanbao Ma; Xiaolin Zhong
2001-01-01
In most flight conditions of hypersonic vehicles, the transition from laminar to turbulent flow is a result of nonlinear response of the laminar boundary layers to environmental disturbances. The process of how environment disturbances enter boundary layer and trigger instability waves is termed the receptivity phenomenon. In this paper, the receptivities to three different types of freestream disturbances for a
Analysis and Modeling of Boundary Layer Separation Method (BLSM).
Peth?, Dóra; Horváth, Géza; Liszi, János; Tóth, Imre; Paor, Dávid
2010-09-01
Nowadays rules of environmental protection strictly regulate pollution material emission into environment. To keep the environmental protection laws recycling is one of the useful methods of waste material treatment. We have developed a new method for the treatment of industrial waste water and named it boundary layer separation method (BLSM). We apply the phenomena that ions can be enriched in the boundary layer of the electrically charged electrode surface compared to the bulk liquid phase. The main point of the method is that the boundary layer at correctly chosen movement velocity can be taken out of the waste water without being damaged, and the ion-enriched boundary layer can be recycled. Electrosorption is a surface phenomenon. It can be used with high efficiency in case of large electrochemically active surface of electrodes. During our research work two high surface area nickel electrodes have been prepared. The value of electrochemically active surface area of electrodes has been estimated. The existence of diffusion part of the double layer has been experimentally approved. The electrical double layer capacity has been determined. Ion transport by boundary layer separation has been introduced. Finally we have tried to estimate the relative significance of physical adsorption and electrosorption. PMID:24061827
Application of a Reynolds stress model to separating boundary layers
NASA Technical Reports Server (NTRS)
Ko, Sung HO
1993-01-01
Separating turbulent boundary layers occur in many practical engineering applications. Nonetheless, the physics of separation/reattachment of flows is poorly understood. During the past decade, various turbulence models were proposed and their ability to successfully predict some types of flows was shown. However. prediction of separating/reattaching flows is still a formidable task for model developers. The present study is concerned with the process of separation from a smooth surface. Features of turbulent separating boundary layers that are relevant to modeling include the following: the occurrence of zero wall shear stress, which causes breakdown of the boundary layer approximation; the law of the wall not being satisfied in the mean back flow region; high turbulence levels in the separated region; a significant low-frequency motion in the separation bubble; and the turbulence structure of the separated shear layer being quite different from that of either the mixing layers or the boundary layers. These special characteristics of separating boundary layers make it difficult for simple turbulence models to correctly predict their behavior.
Multiple paths to subharmonic laminar breakdown in a boundary layer
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Hussaini, M. Yousuff
1989-01-01
Numerical simulations demonstrate that laminar breakdown in a boundary layer induced by the secondary instability of two-dimensional Tollmien-Schlichting waves to three-dimensional subharmonic disturbances need not take the conventional lambda vortex/high-shear layer path.
Stabilization of Hypersonic Boundary Layers by Porous Coatings
Alexander V. Fedorov; Norman D. Malmuth; Adam Rasheed; Hans G. Hornung
2001-01-01
A second-mode stability analysis has been performed for a hypersonic boundary layer on a wall covered by a porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplié - cation is found to be due to the disturbance energy absorption by the porous layer. This stabilization effect was demonstrated by experiments recently conducted on a
A study of synthetic large scales in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Duvvuri, Subrahmanyam; Luhar, Mitul; Barnard, Casey; Sheplak, Mark; McKeon, Beverley
2013-11-01
Synthetic spanwise-constant spatio-temporal disturbances are excited in a turbulent boundary layer through a spatially impulsive patch of dynamic wall-roughness. The downstream flow response is studied through hot wire anemometry, pressure measurements at the wall and direct measurements of wall-shear-stress made using a novel micro-machined capacitive floating element sensor. These measurements are phase-locked to the input perturbation to recover the synthetic large-scale motion and characterize its structure and wall signature. The phase relationship between the synthetic large scale and small scale activity provides further insights into the apparent amplitude modulation effect between them, and the dynamics of wall-bounded turbulent flows in general. Results from these experiments will be discussed in the context of the critical-layer behavior revealed by the resolvent analysis of McKeon & Sharma (J Fluid Mech, 2010), and compared with similar earlier work by Jacobi & McKeon (J Fluid Mech, 2011). Model predictions are shown to be in broad agreement with experiments. Synthetic spanwise-constant spatio-temporal disturbances are excited in a turbulent boundary layer through a spatially impulsive patch of dynamic wall-roughness. The downstream flow response is studied through hot wire anemometry, pressure measurements at the wall and direct measurements of wall-shear-stress made using a novel micro-machined capacitive floating element sensor. These measurements are phase-locked to the input perturbation to recover the synthetic large-scale motion and characterize its structure and wall signature. The phase relationship between the synthetic large scale and small scale activity provides further insights into the apparent amplitude modulation effect between them, and the dynamics of wall-bounded turbulent flows in general. Results from these experiments will be discussed in the context of the critical-layer behavior revealed by the resolvent analysis of McKeon & Sharma (J Fluid Mech, 2010), and compared with similar earlier work by Jacobi & McKeon (J Fluid Mech, 2011). Model predictions are shown to be in broad agreement with experiments. The support of AFOSR grant #FA 9550-12-1-0469, Resnick Institute Graduate Research Fellowship (S.D.) and Sandia Graduate Fellowship (C.B.) are gratefully acknowledged.
Effects of mussel filtering activity on boundary layer structure
NASA Astrophysics Data System (ADS)
van Duren, Luca A.; Herman, Peter M. J.; Sandee, Adri J. J.; Heip, Carlo H. R.
2006-01-01
The structure of the benthic boundary layer over a bed of mussels ( Mytilus edulis) was investigated in a large racetrack flume. Flow was observed to be modified both by the physical roughness of the mussel bed and by the momentum input of the exhalent jets of the mussels. Particularly when the mussels were closed, and filtering activity was reduced to a minimum, we observed an internal boundary layer, around 4 cm thick, within the log layer. This internal boundary layer was often masked when the mussels were filtering actively. The presence of an internal boundary layer indicates that the boundary layer is not only structured by friction drag, but that form drag due to roughness elements also plays an important role. Consequently, estimates of bed shear stress based on velocity or Reynolds stress measurements carried out more than a few cm above the bed may be inaccurate. Over inactive mussels the shear velocity in the internal boundary layer (the roughness sub-layer) is smaller and bed shear stress is consequently reduced. Filtration activity of the mussels increased the velocity gradient in the lower layer at low and intermediate velocities, but at higher flow rates velocity profiles were not affected. Clear effects of the exhalent jets on absolute levels of TKE could be measured at all ambient velocities, while the effect on the Reynolds stress was limited. Velocity normalised TKE and Reynolds stress also indicated that the effect of the siphonal currents was limited at high velocities. Our results indicate that mussel filtration activity may have an important effect on exchange processes at the sediment-water interface, but that the extent of the effect is highly dependent on the ambient flow conditions.
Mesoscale Fluctuations in Scalars Generated by Boundary Layer Convection.
NASA Astrophysics Data System (ADS)
Jonker, Harm J. J.; Duynkerke, Peter G.; Cuijpers, Joannes W. M.
1999-03-01
This study has determined energy spectra of turbulent variables in large eddy simulations of the penetrating dry convective boundary layer (microscale convection). The simulated domain has a large aspect ratio, the horizontal size being roughly 16 times the boundary layer depth. It turns out that both the turbulent velocities and the potential temperature exhibit `classic' energy spectra, which means that the dominant contribution to the variance originates from a scale of the order of the boundary layer height.Surprisingly, the authors find that energy spectra of passive scalars in the convective boundary layer can behave completely differently from the velocity and temperature spectra. Depending on the boundary conditions of the scalar, that is, the surface flux and the entrainment flux, the spectrum is either classical in the aforementioned sense or it is dominated by the smallest wavenumbers, implying that the fluctuations are dominated by the largest scales. Loosely speaking the results can be summarized as follows: if the scalar entrainment flux is a negative fraction (about 1/2 ) of the surface flux, the scalar fluctuations are dominated by relatively small scales ( boundary layer depth), whereas in most other cases the scalar fluctuations tend to be dominated by the largest scales resolved ( tenths of kilometers, i.e., mesoscales). The latter result is rather peculiar since neither the velocity components nor the temperature field contains these large-scale fluctuations.
An experimental investigation of turbulent boundary layers along curved surfaces
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1972-01-01
A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.
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.
Nature, theory and modelling of geophysical convective planetary boundary layers
NASA Astrophysics Data System (ADS)
Zilitinkevich, Sergej
2015-04-01
Geophysical convective planetary boundary layers (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer boundaries (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface layer and entrainment layer (at the CPBL inner and outer boundaries) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in horizontal branches of organised structures. This mechanism (Zilitinkevich et al., 2006), was overlooked in conventional local theories, such as the Monin-Obukhov similarity theory, and convective heat/mass transfer law: Nu~Ra1/3, where Nu and Ra are the Nusselt number and Raleigh numbers. References Hellsten A., Zilitinkevich S., 2013: Role of convective structures and background turbulence in the dry convective boundary layer. Boundary-Layer Meteorol. 149, 323-353. Zilitinkevich, S.S., 1973: Shear convection. Boundary-Layer Meteorol. 3, 416-423. Zilitinkevich, S.S., 1991: Turbulent Penetrative Convection, Avebury Technical, Aldershot, 180 pp. Zilitinkevich S.S., 2012: The Height of the Atmospheric Planetary Boundary layer: State of the Art and New Development - Chapter 13 in 'National Security and Human Health Implications of Climate Change', edited by H.J.S. Fernando, Z. Klai?, J.L. McKulley, NATO Science for Peace and Security Series - C: Environmental Security (ISBN 978-94-007-2429-7), Springer, 147-161. Zilitinkevich S.S., 2013: Atmospheric Turbulence and Planetary Boundary Layers. Fizmatlit, Moscow, 248 pp. Zilitinkevich, S.S., Hunt, J.C.R., Grachev, A.A., Esau, I.N., Lalas, D.P., Akylas, E., Tombrou, M., Fairall, C.W., Fernando, H.J.S., Baklanov, and A., Joffre, S.M., 2006: The influence of large convective eddies on the surface layer turbulence. Quart. J. Roy. Met. Soc. 132, 1423-1456. Zilitinkevich S.S., Tyuryakov S.A., Troitskaya Yu. I., Mareev E., 2012: Theoretical models of the height of the atmospheric planetary boundary layer and turbulent entrainment at its upper boundary. Izvestija RAN, FAO, 48, No.1, 150-160 Zilitinkevich, S.S., Elperin, T., Kleeorin, N., Rogachevskii, I., Esau, I.N., 2013: A hierarchy of energy- and flux-budget (EFB) turbulence closure models for stably stratified geophysical flows. Boundary-Layer Meteorol. 146, 341-373.
A Lagrangian Study of Southeast Pacific Boundary Layer Clouds
NASA Astrophysics Data System (ADS)
Painter, Gallia
Low clouds lie at the heart of climate feedback uncertainties. The representation of clouds in global climate models relies on parameterization of many sub-grid scale processes that are crucial to understanding cloud responses to climate; low clouds in particular exist as a result of tightly coupled microphysical, mesoscale, and synoptic mechanisms. The influence of anthropogenic aerosols on cloud properties could have important ramifications for our understanding of how clouds respond to a changing climate. The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS REx) sampled the persistent stratocumulus cloud deck located off the coast of Peru and Chile in the southeastern Pacific ocean. Several cloud features found in the stratocumulus deck during VOCALS exhibit signs of interesting aerosol-cloud interactions, including pockets of open cells (POCs). POCs are regions of open-cellular convection surrounded by closed cell stratocumulus, exhibiting not only a marked transition in mesoscale organization and cloud morphology, but also sharp microphysical gradients (especially in droplet concentration) across the boundary between open-cellular and closed cellular convection. In addition, precipitation is often higher at the POC boundaries, hinting at the importance of precipitation in driving their formation. In order to evaluate the microphysical characteristics of POCs prior cloud breakup, we use Lagrangian trajectories coupled with geostationary satellite imagery and cloud retrievals, as well as observational data from VOCALS REx and model data. In three of our case studies, we found regions of anomalously low droplet concentration 18-24 hours prior to POC formation (coupled with liquid water path similar to or higher than surrounding cloud), supporting a precipitation driven mechanism for POC formation. Another group of features with interesting aerosol-cloud interactions observed during VOCALS were mesoscale hook-like features of high droplet concentration which extend far offshore into regions of normally very clean cloud. We use Lagrangian trajectories to investigate the source of the high droplet concentrations of the mesoscale "hooks", and evaluate whether boundary layer transport of coastal pollutants alone can account for their extent. We find that boundary layer trajectories past 85 W do not pass sufficiently close to the coastline to explain high aerosol concentrations offshore.
NASA Astrophysics Data System (ADS)
Vijayakumar, Ganesh; Lavely, Adam; Jayaraman, Balaji; Craven, Brent; Brasseur, James
2013-11-01
We analyze spatio-temporal changes in blade boundary layer structure on a commercial-scale wind turbine blade interacting with a canonical daytime Atmospheric Boundary Layer (ABL). The time scales of the energy-containing ABL eddies are of order multiple rotations of commercial wind turbines and force large temporal fluctuations in integrated loads and bending moments. We study details of blade boundary layer dynamics underlying space-time variations in surface stress by simulating a single blade of the NREL 5MW turbine in a moderately convective ABL produced using LES from a spectral code at high resolution (147M cells). Inflow ABL boundary conditions are extracted for an OpenFOAM ABL simulation with the rotating blade. The blade boundary layer is well resolved with a new hybrid URANS-LES model that blends a 1-equation SFS stress model in the ABL with the k- ?-SST-SAS model near the blade. We perform Hybrid URANS-LES computations of the flow around the blade and compute spatio-temporal fluctuations in surface stresses in response to ABL turbulence eddies. Of particular interest are sources of integrated load transients, load response time scales, and near wake temporal dynamics of vortex shedding in relationship to passage of energy containing atmospheric eddies. We analyze spatio-temporal changes in blade boundary layer structure on a commercial-scale wind turbine blade interacting with a canonical daytime Atmospheric Boundary Layer (ABL). The time scales of the energy-containing ABL eddies are of order multiple rotations of commercial wind turbines and force large temporal fluctuations in integrated loads and bending moments. We study details of blade boundary layer dynamics underlying space-time variations in surface stress by simulating a single blade of the NREL 5MW turbine in a moderately convective ABL produced using LES from a spectral code at high resolution (147M cells). Inflow ABL boundary conditions are extracted for an OpenFOAM ABL simulation with the rotating blade. The blade boundary layer is well resolved with a new hybrid URANS-LES model that blends a 1-equation SFS stress model in the ABL with the k- ?-SST-SAS model near the blade. We perform Hybrid URANS-LES computations of the flow around the blade and compute spatio-temporal fluctuations in surface stresses in response to ABL turbulence eddies. Of particular interest are sources of integrated load transients, load response time scales, and near wake temporal dynamics of vortex shedding in relationship to passage of energy containing atmospheric eddies. Support: NSF, DOE.
Particle motion in atmospheric boundary layers of Mars and Earth
NASA Technical Reports Server (NTRS)
White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.
1975-01-01
To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.
Linear and nonlinear PSE for compressible boundary layers
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Malik, Mujeeb R.; Erlebacher, Gordon; Hussaini, M. Yousuff
1993-01-01
Compressible stability of growing boundary layers is studied by numerically solving the partial differential equations under a parabolizing approximation. The resulting parabolized stability equations (PSE) account for nonparallel as well as nonlinear effects. Evolution of disturbances in compressible flat-plate boundary layers are studied for freestream Mach numbers ranging from 0 to 4.5. Results indicate that the effect of boundary-layer growth is important for linear disturbances. Nonlinear calculations are performed for various Mach numbers. Two-dimensional nonlinear results using the PSE approach agree well with those from direct numerical simulations using the full Navier-Stokes equations while the required computational time is less by an order of magnitude. Spatial simulation using PSE were carried out for both the fundamental and subharmonic type breakdown for a Mach 1.6 boundary layer. The promising results obtained show that the PSE method is a powerful tool for studying boundary-layer instabilities and for predicting transition over a wide range of Mach numbers.
Anisotropic Mesh Adaptivity for Turbulent Flows with Boundary Layers
NASA Astrophysics Data System (ADS)
Chitale, Kedar C.
Turbulent flows are found everywhere in nature and are studied, analyzed and simulated using various experimental and numerical tools. For computational analysis, a variety of turbulence models are available and the accuracy of these models in capturing the phenomenon depends largely on the mesh spacings, especially near the walls, in the boundary layer region. Special semi-structured meshes called "mesh boundary layers" are widely used in the CFD community in simulations of turbulent flows, because of their graded and orthogonal layered structure. They provide an efficient way to achieve very fine and highly anisotropic mesh spacings without introducing poorly shaped elements. Since usually the required mesh spacings to accurately resolve the flow are not known a priori to the simulations, an adaptive approach based on a posteriori error indicators is used to achieve an appropriate mesh. In this study, we apply the adaptive meshing techniques to turbulent flows with a focus on boundary layers. We construct a framework to calculate the critical wall normal mesh spacings inside the boundary layers based on the flow physics and the knowledge of the turbulence model. This approach is combined with numerical error indicators to adapt the entire flow region. We illustrate the effectiveness of this hybrid approach by applying it to three aerodynamic flows and studying their superior performance in capturing the flow structures in detail. We also demonstrate the capabilities of the current developments in parallel boundary layer mesh adaptation by applying them to two internal flow problems. We also study the application of adaptive boundary layer meshes to complex geometries like multi element wings. We highlight the advantage of using such techniques for superior wake and tip region resolution by showcasing flow results. We also outline the future direction for the adaptive meshing techniques to be useful to the large scale flow computations.
Interferometric data for a shock-wave/boundary-layer interaction
NASA Technical Reports Server (NTRS)
Dunagan, Stephen E.; Brown, James L.; Miles, John B.
1986-01-01
An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.
Thunderstorm influence on boundary layer winds
Schmidt, Jill Marie
1986-01-01
layer and raindrops rapidly evaporate. The latent heat of evaporation cools the mixed air maKing it colder than its environment and thus, negatively buoyant, enhancing the downward movement of a now drier downdraft. Hjelmfelt ( 1984), examining two... the weaker outflows and the other described the stronger outflows. Six significant ambient conditions contributed to the thunderstorm building process, i. e. , I) horizontal moisture convergence below cloud base, B) vertical flux divergence of latent heat...
Semiconductor laser having a boundary-region absorption layer
Mink, J.
1989-09-26
This patent describes a semiconductor laser. It comprises a substrate region of a first conductivity type provided with a connection conductor, a first passive layer of the first conductivity type disposed on the substrate, a resonant cavity, a strip-shaped region located within the resonant cavity and comprising at least one active layer disposed on the first passive layer, a second passive layer of the second opposite conductivity type on the active layer, a pn junction formed by the active layer and the first passive layer by which coherent electromagnetic radiation can be produced by a forward current during operation, and a boundary region provided on both sides of, but not on, the strip-shaped region.
Effects of forebody geometry on subsonic boundary-layer stability
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
1990-01-01
As part of an effort to develop computational techniques for design of natural laminar flow fuselages, a computational study was made of the effect of forebody geometry on laminar boundary layer stability on axisymmetric body shapes. The effects of nose radius on the stability of the incompressible laminar boundary layer was computationally investigated using linear stability theory for body length Reynolds numbers representative of small and medium-sized airplanes. The steepness of the pressure gradient and the value of the minimum pressure (both functions of fineness ratio) govern the stability of laminar flow possible on an axisymmetric body at a given Reynolds number. It was found that to keep the laminar boundary layer stable for extended lengths, it is important to have a small nose radius. However, nose shapes with extremely small nose radii produce large pressure peaks at off-design angles of attack and can produce vortices which would adversely affect transition.
Hypersonic flow separation in shock wave boundary layer interactions
NASA Technical Reports Server (NTRS)
Hamed, A.; Kumar, Ajay
1992-01-01
An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed.
Finite volume solution of the compressible boundary-layer equations
NASA Technical Reports Server (NTRS)
Loyd, B.; Murman, E. M.
1986-01-01
A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicity to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and conceptually simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.
Blow-up and control of marginally separated boundary layers.
Braun, Stefan; Kluwick, Alfred
2005-05-15
Interactive solutions for steady two-dimensional laminar marginally separated boundary layers are known to exist up to a critical value Gamma(c) of the controlling parameter (e.g. the angle of attack of a slender airfoil) Gamma only. Here, we investigate three-dimensional unsteady perturbations of such boundary layers, assuming that the basic flow is almost critical, i.e. in the limit Gamma(c)-Gamma-->0. It is then shown that the interactive equations governing such perturbations simplify significantly, allowing, among others, a systematic study of the blow-up phenomenon observed in earlier investigations and the optimization of devices used in boundary-layer control. PMID:16105768
Defects and boundary layers in non-Euclidean plates
John Gemmer; Shankar Venkataramani
2012-09-07
We investigate the behavior of non-Euclidean plates with constant negative Gaussian curvature using the F\\"oppl-von K\\'arm\\'an reduced theory of elasticity. Motivated by recent experimental results, we focus on annuli with a periodic profile. We prove rigorous upper and lower bounds for the elastic energy that scales like the thickness squared. In particular we show that are only two types of global minimizers -- deformations that remain flat and saddle shaped deformations with isolated regions of stretching near the edge of the annulus. We also show that there exist local minimizers with a periodic profile that have additional boundary layers near their lines of inflection. These additional boundary layers are a new phenomenon in thin elastic sheets and are necessary to regularize jump discontinuities in the azimuthal curvature across lines of inflection. We rigorously derive scaling laws for the width of these boundary layers as a function of the thickness of the sheet.
Boundary layer integral matrix procedure: Verification of models
NASA Technical Reports Server (NTRS)
Bonnett, W. S.; Evans, R. M.
1977-01-01
The three turbulent models currently available in the JANNAF version of the Aerotherm Boundary Layer Integral Matrix Procedure (BLIMP-J) code were studied. The BLIMP-J program is the standard prediction method for boundary layer effects in liquid rocket engine thrust chambers. Experimental data from flow fields with large edge-to-wall temperature ratios are compared to the predictions of the three turbulence models contained in BLIMP-J. In addition, test conditions necessary to generate additional data on a flat plate or in a nozzle are given. It is concluded that the Cebeci-Smith turbulence model be the recommended model for the prediction of boundary layer effects in liquid rocket engines. In addition, the effects of homogeneous chemical reaction kinetics were examined for a hydrogen/oxygen system. Results show that for most flows, kinetics are probably only significant for stoichiometric mixture ratios.
The Turbulent Boundary Layer on a Rough Curvilinear Surface
NASA Technical Reports Server (NTRS)
Droblenkov, V. F.
1958-01-01
A number of semiempirical approximate methods exist for determining the characteristics of the turbulent boundary layer on a curvilinear surface. At present, among these methods, the one proposed by L. G. Loitsianskii is given frequent practical application. This method is sufficiently effective and permits, in the case of wing profiles with technically smooth surfaces, calculating the basic characteristics of the boundary layer and the values of the overall drag with an accuracy which suffices for practical purposes. The idea of making use of the basic integral momentum equation ((d delta(sup xx))/dx) + ((V' delta(sup xx))/V) (2 + H) = (tau(sub 0))/(rho V(exp 2)) proves to be fruitful also for the solution of the problems in the determination of the characteristics of the turbulent boundary layer on a rough surface.
Turbulence in the convective boundary layer observed by microwave interferometry
Shao, X.M.; Carlos, R.C.; Kirkland, M.W.
1997-12-01
A 9-antenna, 400 meter microwave interferometer was utilized in SALSA MEX on the San Pedro River area in July and August, 1997, to measure the turbulence in the Convective Boundary Layer. Water vapor has an appreciable index of refraction at radio frequencies around 10 GHz, and acts as a passive tracer of the magnitude and motion of turbulence. The relative phase changes of a signal from a satellite were tracked by an array of 9 antennas, and the phase differences between antennas were then used to derive the turbulence properties of the boundary layer. Preliminary analysis shows clearly different characteristics for the convection activity of the boundary layer between day and night. From the structure function analysis they can see that the turbulence structure starts to decorrelate at scale sizes of 200 meters for a temporal passband around 100 seconds. Derivation of average wind fields is currently in process.
Numerical Simulations of Wake/Boundary Layer Interactions
NASA Technical Reports Server (NTRS)
Piomelli, Ugo; Choudhari, Meelan M.; Ovchinnikov, Victor; Balaras, Elias
2003-01-01
Direct and large-eddy simulations of the interaction between the wake of a circular cylinder and a flat-plate boundary layer are conducted. Two Reynolds numbers are examined. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re(sub theta) achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established.
Slow Growth Formulation for DNS of Temporally Evolving Boundary Layers
NASA Astrophysics Data System (ADS)
Topalian, Victor; Sahni, Onkar; Oliver, Todd; Moser, Robert
2011-11-01
A formulation for DNS of temporally evolving boundary layers is developed and demonstrated. The formulation relies on a multiscale approach to account separately for the slow time evolution of statistical averages, and the fast time evolution of turbulent fluctuations. The source terms that arise from the multiscale analysis are modeled assuming a self-similar evolution of the averages. The performance of the formulation is evaluated using DNS of spatially evolving compressible boundary layers. This formulation was developed to provide data for the calibration of turbulence model parameters and enable the quantification of uncertainty due to the models. The extension of this formulation to homogenize spatially evolving boundary layers will also be discussed. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615]. Current Affiliation: Rensselaer Polytechnic Institute.
Wind Tunnel Simulation of the Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Hohman, Tristen; Smits, Alexander; Martinelli, Luigi
2012-11-01
To simulate the interaction of large Vertical Axis Wind Turbines (VAWT) with the Atmospheric Boundary Layer (ABL) in the laboratory, we implement a variant of Counihan's technique in which a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements is used to create an artificial ABL profile in a standard closed loop wind tunnel. We report hotwire measurements in a plane normal to the flow direction at various downstream positions and free stream velocities to examine the development and formation of the artificial ABL. It was found possible to generate a boundary layer at Re? ~106 , with a mean velocity that followed the 1/7 power law of a neutral ABL over rural terrain and longitudinal turbulence intensities and power spectra that compare well with the data obtained by Hultmark in 2010 for high Reynolds number flat plate turbulent boundary layers. Supported by Hopewell Wind Power Ltd., and the Princeton Grand Challenges Program.
Influence of wall permeability on turbulent boundary-layer properties
NASA Technical Reports Server (NTRS)
Wilkinson, S. P.
1983-01-01
Experimental boundary-layer studies of a series of low pressure drop, permeable surfaces have been conducted to characterize their surface interaction with a turbulent boundary layer. The models were flat and tested at nominally zero pressure gradient in low speed air. The surfaces were thin metal sheets with discrete perforations. Direct drag balance measurements of skin friction indicate that the general effect of surface permeability is to increase drag above that of a smooth plate reference level. Heuristic arguments are presented to show that this type of behavior is to be expected. Other boundary-layer data are also presented including mean velocity profiles and conditionally sampled streamwise velocity fluctuations (hot wire) for selected models.
Supersonic separated turbulent boundary - layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
A prediction method is developed for calculating distributions of surface heating rates, pressure and skin friction over a wavy wall in a two-dimensional supersonic flow. Of particular interest is the flow of thick turbulent boundary layers. The surface geometry and the flow conditions considered are such that there exists a strong interaction between the viscous and inviscid flow. First, using the interacting turbulent boundary layer equations, the problem is formulated in physical coordinates and then a reformulation of the governing equations in terms of Levy-Lees variables is given. Next, a numerical scheme for solving interacting boundary layer equations is adapted. A number of modifications which led to the improvement of the numerical algorithm are discussed. Finally, results are presented for flow over a train of up to six waves at various flow conditions.
Interacting turbulent boundary layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
This paper is concerned with the two-dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. Here the interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model of Cebeci and Smith. Results are presented for flow over a train of up to six waves for Mach numbers of 2.5 and 3.5, Reynolds numbers of 10,000,000/m and 32,000,000/m, and wall temperature ratios of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given.
Effect of Blowing on Boundary Layer of Scarf Inlet
NASA Technical Reports Server (NTRS)
Gerhold, Carl H.; Clark, Lorenzo R.
2004-01-01
When aircraft operate in stationary or low speed conditions, airflow into the engine accelerates around the inlet lip and pockets of turbulence that cause noise and vibration can be ingested. This problem has been encountered with engines equipped with the scarf inlet, both in full scale and in model tests, where the noise produced during the static test makes it difficult to assess the noise reduction performance of the scarf inlet. NASA Langley researchers have implemented boundary layer control in an attempt to reduce the influence of the flow nonuniformity in a 12-in. diameter model of a high bypass fan engine mounted in an anechoic chamber. Static pressures and boundary layer profiles were measured in the inlet and far field acoustic measurements were made to assess the effectiveness of the blowing treatment. The blowing system was found to lack the authority to overcome the inlet distortions. Methods to improve the implementation of boundary layer control to reduce inlet distortion are discussed.
Acoustic measurements of boundary layer flow and sediment flux.
Thorne, P D; Taylor, J
2000-10-01
Results are reported on an assessment of the application of coherent Doppler and cross-correlation techniques to measure nearbed boundary layer flow. The approaches use acoustic backscattering from sediments entrained into the water column from the bed, to obtain high-resolution profiles of the nearbed hydrodynamics. Measurements are presented from a wave tunnel experiment in which sediment was entrained by unidirectional, oscillatory, and combined flows. The data collected have been used to evaluate the capability of the two flow techniques to measure boundary layer mean, turbulent, and intrawave velocity profiles. Further, the backscattered signal has been used to measure suspended sediment concentration profiles, which have been combined with the velocity profiles to obtain high-resolution measurements of boundary layer sediment flux. PMID:11051485
Asymptotic analysis: Working note {number_sign}3, boundary layers
Garbey, M. [Universite Claude Bernard Lyon 1, Villeurbanne (France). Laboratoire d`Analyse Numerique; Kaper, H.G. [Argonne National Lab., IL (United States)
1993-09-01
In this chapter the authors discuss the asymptotic approximation of functions that display boundary-layer behavior. The purpose here is to introduce the basic concepts underlying the phenomenon, to illustrate its importance, and to describe some of the fundamental tools available for its analysis. To achieve their purpose in the clearest way possible, the authors will work with functions that are assumed to be given explicitly -- that is, functions f : (0,{epsilon}{sub 0}) {yields} X whose expressions are known, at least in principle. Only in the following chapter will they begin the study of functions that are given implicitly as solutions of boundary value problems -- the real stuff of which singular perturbation theory is made. Boundary-layer behavior is associated with asymptotic expansions that are regular {open_quotes}almost everywhere{close_quotes} -- that is, expansions that are regular on every compact subset of the domain of definition, but not near the boundary. These regular asymptotic expansions can be continued in a certain sense all the way up to the boundary, but a separate analysis is still necessary in the boundary layer. The boundary-layer analysis is purely local and aims at constructing local approximations in the neighborhood of each point of the singular part of the boundary. The problem of finding an asymptotic approximation is thus reduced to matching the various local approximations to the existing regular expansion valid in the interior of the domain. The authors are thinking, for example, of fluid flow (viscosity), combustion (Lewis number), and superconductivity (Ginzburg-Landau parameter) problems. Their solution may remain smooth over a wide range of parameter values, but as the parameters approach critical values, complicated patterns may emerge.
Three dimensional shock wave/boundary layer interactions
NASA Astrophysics Data System (ADS)
Mowatt, S.; Skews, B.
2011-09-01
An investigation into a three-dimensional, curved shock wave interacting with a three-dimensional, curved boundary layer on a slender body is presented. Three different nose profiles mounted on a cylindrical body were tested in a supersonic wind tunnel and numerically simulated by solving the Navier-Stokes equations. The conical and hemispherical nose profiles tested were found to generate shock waves of sufficient strength to separate the boundary layer on the cylinder, while the shock wave generated by the ogival profile did not separate the boundary layer. For the separated flow, separation was found to occur predominantly on the windward side of the cylinder with the lee-side remaining shielded from the direct impact of the incident shock wave. A thickening of the boundary layer on the lee-side of all the profiles was observed, and in the conical and hemispherical cases this leads to the re-formation of the incident shock wave some distance away from the surface of the cylinder. A complex reflection pattern off the shock wave/boundary layer interaction (SWBLI) was also identified for the separated flow cases. For comparative purposes, an inviscid simulation was performed using the hemispherical profile. Significant differences between the viscous and inviscid results were noted including the absence of a boundary layer leading to a simplified shock wave reflection pattern forming. The behaviour of the incident shock wave on the lee-side of the cylinder was also affected with the shock wave amalgamating on the surface of the cylinder instead of away from the surface as per the viscous case. Test data from the wind tunnel identified two separation lines present on the cylindrical surface of the hemispherical SWBLI generator. The pair of lines were not explicitly evident in the original CFD simulations run, but were later identified in a high-resolution simulation.
Wind Tunnel Simulation of the Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Hohman, Tristen; Smits, Alexander; Martinelli, Luigi
2013-11-01
To simulate the interaction of large Vertical Axis Wind Turbines (VAWT) with the Atmospheric Boundary Layer (ABL) in the laboratory, we implement a variant of Counihan's technique [Counihan 1969] in which a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements is used to create an artificial ABL profile in a standard closed loop wind tunnel. To examine the development and formation of the artificial ABL hotwire and SPIV measurements were taken at various downstream locations with changes in wall roughness, wall type, and vortex generator arrangements. It was found possible to generate a boundary layer at Re? ~106 , with a mean velocity that followed the 1/7 power law of a neutral ABL over rural terrain and longitudinal turbulence intensities and power spectra that compare well with the data obtained for high Reynolds number flat plate turbulent boundary layers [Hultmark et al. 2010]. To simulate the interaction of large Vertical Axis Wind Turbines (VAWT) with the Atmospheric Boundary Layer (ABL) in the laboratory, we implement a variant of Counihan's technique [Counihan 1969] in which a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements is used to create an artificial ABL profile in a standard closed loop wind tunnel. To examine the development and formation of the artificial ABL hotwire and SPIV measurements were taken at various downstream locations with changes in wall roughness, wall type, and vortex generator arrangements. It was found possible to generate a boundary layer at Re? ~106 , with a mean velocity that followed the 1/7 power law of a neutral ABL over rural terrain and longitudinal turbulence intensities and power spectra that compare well with the data obtained for high Reynolds number flat plate turbulent boundary layers [Hultmark et al. 2010]. Supported by Hopewell Wind Power Ltd., and the Princeton Grand Challenges Program.
NASA Technical Reports Server (NTRS)
Parmar, D. S.; Singh, J. J.
1993-01-01
Polymer dispersed liquid crystal thin films have been deposited on a glass substrate, utilizing the processes of polymerization and solvent evaporation induced phase separation. Liquid crystal microdroplets trapped on the upper surface of the thin film respond to the shear stress due to air or gas flow on the surface layer. Response to an applied step shear stress input on the surface layer has been measured by measuring the time response of the transmitted light intensity. Initial results on the measurements of the light transmission as a function of the air flow differential pressure indicate that these systems offer features suitable for boundary layer and gas flow sensors.
Receptivity of Hypersonic Boundary Layers over Straight and Flared Cones
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam; Kegerise, Michael A.
2010-01-01
The effects of adverse pressure gradients on the receptivity and stability of hypersonic boundary layers were numerically investigated. Simulations were performed for boundary layer flows over a straight cone and two flared cones. The steady and the unsteady flow fields were obtained by solving the two-dimensional Navier-Stokes equations in axi-symmetric coordinates using the 5th order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The mean boundary layer profiles were analyzed using local stability and non-local parabolized stability equations (PSE) methods. After the most amplified disturbances were identified, two-dimensional plane acoustic waves were introduced at the outer boundary of the computational domain and time accurate simulations were performed. The adverse pressure gradient was found to affect the boundary layer stability in two important ways. Firstly, the frequency of the most amplified second-mode disturbance was increased relative to the zero pressure gradient case. Secondly, the amplification of first- and second-mode disturbances was increased. Although an adverse pressure gradient enhances instability wave growth rates, small nose-tip bluntness was found to delay transition due to the low receptivity coefficient and the resulting weak initial amplitude of the instability waves. The computed and measured amplitude-frequency spectrums in all three cases agree very well in terms of frequency and the shape except for the amplitude.
Laminar Boundary Layer Behind a Strong Shock Moving into Air
NASA Technical Reports Server (NTRS)
Mirels, Harold
1961-01-01
The laminar wall boundary layer behind a strong shock advancing into stationary air has been determined. Numerical results have been obtained for shock Mach numbers up to 14 using real gas values for density and viscosity and assuming Prandtl and Lewis numbers of 0.72 and 1, respectively. The numerical results for shear and heat transfer agree, within 4 percent, with a previously presented approximate analytical expression for these quantities. A slight modification of this expression results in agreement with the numerical data to within 2.5 percent. Analytical expressions for boundary-layer thickness and displacement thickness, correct to within 4 percent for the present data, have also been obtained.
Interactive boundary-layer calculations of a transonic wing flow
NASA Technical Reports Server (NTRS)
Kaups, Kalle; Cebeci, Tuncer; Mehta, Unmeel
1989-01-01
Results obtained from iterative solutions of inviscid and boundary-layer equations are presented and compared with experimental values. The calculated results were obtained with an Euler code and a transonic potential code in order to furnish solutions for the inviscid flow; they were interacted with solutions of two-dimensional boundary-layer equations having a strip-theory approximation. Euler code results are found to be in better agreement with the experimental data than with the full potential code, especially in the presence of shock waves, (with the sole exception of the near-tip region).
An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake
NASA Technical Reports Server (NTRS)
Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.
2001-01-01
An innovative flow-measuring device, a thermocouple boundary layer rake, was developed. The sensor detects the flow by using a thin-film thermocouple (TC) array to measure the temperature difference across a heater strip. The heater and TC arrays are microfabricated on a constant-thickness quartz strut with low heat conductivity. The device can measure the velocity profile well into the boundary layer, about 65 gm from the surface, which is almost four times closer to the surface than has been possible with the previously used total pressure tube.
Experimental demonstration of the Rayleigh acoustic viscous boundary layer theory
NASA Astrophysics Data System (ADS)
Castrejón-Pita, J. R.; Castrejón-Pita, A. A.; Huelsz, G.; Tovar, R.
2006-03-01
Amplitude and phase velocity measurements on the laminar oscillatory viscous boundary layer produced by acoustic waves are presented. The measurements were carried out in acoustic standing waves in air with frequencies of 68.5 and 114.5Hz using laser Doppler anemometry and particle image velocimetry. The results obtained by these two techniques are in good agreement with the predictions made by the Rayleigh viscous boundary layer theory and confirm the existence of a local maximum of the velocity amplitude and its expected location.
Simulation of glancing shock wave and boundary layer interaction
NASA Technical Reports Server (NTRS)
Hung, Ching-Mao
1989-01-01
Shock waves generated by sharp fins, glancing across a laminar boundary layer growing over a flat plate, are simulated numerically. Several basic issues concerning the resultant three-dimensional flow separation are studied. Using the same number of grid points, different grid spacings are employed to investigate the effects of grid resolution on the origin of the line of separation. Various shock strengths (generated by different fin angles) are used to study the so-called separated and unseparated boundary layer and to establish the existence or absence of the secondary separation. The usual interpretations of the flow field from previous studies and new interpretations arising from the present simulation are discussed.
Data Assimilation Strategies in the Planetary Boundary Layer
Brian P. Reen; David R. Stauffer
2010-01-01
We investigate the effect of the assimilation of surface and boundary-layer mass-field observations on the planetary boundary\\u000a layer (PBL) within a one-dimensional (1D) version of the non-hydrostatic Fifth-Generation Pennsylvania State University\\/National\\u000a Center for Atmospheric Research Mesoscale Model (MM5). We focus on the vertical extent and effects of mass-field nudging within\\u000a the PBL based on surface observations, and the added value
Boundary layer study on nozzle wall at hypersonic velocities
NASA Technical Reports Server (NTRS)
Jones, Kenneth M.; Dejarnette, Fred R.; Griffith, Wayland C.; Yanta, William J.
1992-01-01
The boundary layer on the wall of the Hypervelocity Tunnel 9 was investigated with pitot pressure and total temperature measurements. Experimental results are presented for standard and supercooled Mach 14 runs. The boundary layer data at supercooled conditions are compared to numerical predictions made with a Navier-Stokes algorithm including vibrational nonequilibrium and intermolecular force effects. For standard tunnel conditions, the numerical solutions agree well with experimental data. For the supercooled cases, the numerical code predicts the total temperature but overpredicts the pitot pressure.
The Saharan atmospheric boundary layer: Turbulence, stratification and mixing
NASA Astrophysics Data System (ADS)
Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.
2013-04-01
High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (?1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer concentrations, demonstrating the potential for variability in, for example, dust concentrations independent of external forcings. The residual layer, where long-range transport can take place, is analyzed in particular detail. Various processes which can lead to transport into and mixing within the residual layer are explored, including shear-driven turbulence at the residual layer top and the potential for detrainment from the convective boundary layer top due to the combination of a weak lid and a neutral layer above.
Design of an Instrumentation System for a Boundary Layer Transition Wing Glove Experiment
Williams, Thomas 1987-
2012-08-23
for differential measurements to be made with an uncertainty of +/- 0.03 degrees. Static pressure ports and high frequency response Kulite transducers will also be employed. Hotfilm sensors will be used to verify the state of the boundary layer on the glove...
Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer
Roy, Subrata
spatial frequency in x Complex spatial frequency in z Complex temporal frequency 99% Boundary layer Reynolds number Velocity ratio F Dimensionless frequency, F = R/Re Subscript i direction I Imaginary R. It can be flush mounted on a surface. The response of the device is on electrical (not fluidic) time
Scaling of heat transfer augmentation due to mechanical distortions in hypervelocity boundary layers
NASA Astrophysics Data System (ADS)
Flaherty, W.; Austin, J. M.
2013-10-01
We examine the response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature. Surface heat transfer and visual boundary layer thickness data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. This scaling may be explained by the application of Lees similarity. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortices to an adverse pressure gradient is investigated. Surface streak evolution is visualized over the different surface geometries using fast response pressure sensitive paint. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures.
Modeling the planetary boundary layer — Extension to the stable case
J. C. Wyngaard; Hanscom AFB
1975-01-01
A higher-order-closure model, which contains equations for turbulence covariances as well as the mean field, was developed and used to investigate the structure of the stably-stratified planetary boundary layer. The calculated surface-layer profiles of wind shear, temperature gradient, and dissipation rate agree well with the 1968 Kansas data. A simulation of the evolution of the nocturnal PBL reproduces fairly accurately
Atmospheric dispersion modeling based upon boundary-layer parameterization
Silvertsen, B.; Gryning, S.E.; Holtslag, A.A.M.; Irwin, J.S.
1985-10-01
Characteristic scaling parameters in the planetary boundary layer have been applied to estimate the dispersion of nonbuoyant gaseous pollutants. Vertical and lateral spread are treated separately, and the choice of parameters for the dispersion models depends upon the actual state of the planetary boundary layer. The lateral concentration distribution at the surface was usually found to be a Gaussian distribution. The vertical concentration distribution was more often other than Gaussian. For the different scaling regions of the atmosphere, methods are proposed for estimating the crosswind integrated concentrations, as functions of distance from the source, and are compared using results from tracer experiments. The proposed methods estimate the transport and dispersion directly from the turbulent state of the atmosphere. In all the scaling regions, the various methods adequately estimated the observed concentrations. The turbulence, and thus the dispersion, is better explained and modeled in the surface layer of the atmosphere (stable and unstable), than within the layers above the surface layer. Some success was demonstrated for releases in the stable local scaling (z-less) layer, and in the mixed layer and the near-neutral layer.
Effects of Hybrid Flow Control on a Normal Shock Boundary-Layer Interaction
NASA Technical Reports Server (NTRS)
Hirt, Stefanie M.; Vyas, Manan A.
2013-01-01
Hybrid flow control, a combination of micro-ramps and steady micro-jets, was experimentally investigated in the 15x15 cm Supersonic Wind Tunnel at the NASA Glenn Research Center. A central composite design of experiments method, was used to develop response surfaces for boundary-layer thickness and reversed-flow thickness, with factor variables of inter-ramp spacing, ramp height and chord length, and flow injection ratio. Boundary-layer measurements and wall static pressure data were used to understand flow separation characteristics. A limited number of profiles were measured in the corners of the tunnel to aid in understanding the three-dimensional characteristics of the flowfield.
Turbulence in rough-wall boundary layers: universality issues
NASA Astrophysics Data System (ADS)
Amir, Mohammad; Castro, Ian P.
2011-08-01
Wind tunnel measurements of turbulent boundary layers over three-dimensional rough surfaces have been carried out to determine the critical roughness height beyond which the roughness affects the turbulence characteristics of the entire boundary layer. Experiments were performed on three types of surfaces, consisting of an urban type surface with square random height elements, a diamond-pattern wire mesh and a sand-paper type grit. The measurements were carried out over a momentum thickness Reynolds number ( Re ?) range of 1,300-28,000 using two-component Laser Doppler anemometry (LDA) and hot-wire anemometry (HWA). A wide range of the ratio of roughness element height h to boundary layer thickness ? was covered (0.04 ? h/? ? 0.40). The results confirm that the mean profiles for all the surfaces collapse well in velocity defect form up to surprisingly large values of h/?, perhaps as large as 0.2, but with a somewhat larger outer layer wake strength than for smooth-wall flows, as previously found. At lower h/?, at least up to 0.15, the Reynolds stresses for all surfaces show good agreement throughout the boundary layer, collapsing with smooth-wall results outside the near-wall region. With increasing h/?, however, the turbulence above the near-wall region is gradually modified until the entire flow is affected. Quadrant analysis confirms that changes in the rough-wall boundary layers certainly exist but are confined to the near-wall region at low h/?; for h/? beyond about 0.2 the quadrant events show that the structural changes extend throughout much of the boundary layer. Taken together, the data suggest that above h/? ? 0.15, the details of the roughness have a weak effect on how quickly (with rising h/?) the turbulence structure in the outer flow ceases to conform to the classical boundary layer behaviour. The present results provide support for Townsend's wall similarity hypothesis at low h/? and also suggest that a single critical roughness height beyond which it fails does not exist. For fully rough flows, the data also confirm that mean flow and turbulence quantities are essentially independent of Re ?; all the Reynolds stresses match those of smooth-wall flows at very high Re ?. Nonetheless, there is a noticeable increase in stress contributions from strong sweep events in the near-wall region, even at quite low h/?.
Simulating Dispersion in the Evening-Transition Boundary Layer
NASA Astrophysics Data System (ADS)
Taylor, Alexander C.; Beare, Robert J.; Thomson, David J.
2014-12-01
We investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows `lofting' of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent `trapping' of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer.
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.
The layering phenomenon and boundary formation in radiographs.
Nilson, A E
1986-01-01
In a radiographic examination using a water-soluble contrast medium this may form a layer beneath a body fluid. Between the two liquids a zone consisting of a mixture of the two liquids then forms through diffusion. This diffusion layer produces some characteristic features in the radiographic image, an analysis of which was the purpose of the model experiments performed in this investigation. In this analysis of the layering phenomenon the radiographed objects were cylindrical tubes of methyl methacrylate partly filled with water. In some cases a rod was placed concentrically in the tube. Contrast medium was layered below the water. Radiographs were produced with the tube either vertical or inclined, and with either a horizontal or a vertical projection. In the image the layer of contrast medium was visualized as a light field, and the water layer as an overlying relatively dark field. The diffusion layer was visualized as a transitional zone--the diffusion field. Distinct boundaries and Mach lines observed in the bottom field were produced by the interface between the contrast medium and the solid wall where it was touched by the roentgen rays. These boundaries continued into the diffusion field where they gradually became less visible and eventually disappeared. The upper and lower boundaries of the diffusion field were diffuse and associated with dark and light Mach bands, respectively. The upper boundary appeared to be convex upwards. In the case of the inclined model and a vertical beam the diffusion field was elliptical, with a still more diffuse transition to the fields above and below than in the case of the vertical model and a horizontal beam.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3716870
CFD simulation of the atmospheric boundary layer: wall function problems
Bert Blocken; Ted Stathopoulos; Jan Carmeliet
Accurate Computational Fluid Dynamics (CFD) simulations of atmospheric boundary layer (ABL) flow are essential for a wide variety of atmospheric studies including pollutant dispersion and deposition. The accuracy of such simulations can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type
ATMOSPHERIC DISPERSION IN THE ARCTIC: WINTERTIME BOUNDARY-LAYER MEASUREMENTS
The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...
Flow phenomena peculiar to calculation of compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
1977-01-01
Calculation procedures for compressible turbulent boundary layers were based upon techniques, modeling constants, etc., developed originally for the low speed case. Significant differences and new or altered physics which occur in the compressible case were considered, as compared with the low speed situation. Possible pitfalls and sources of inaccuracy in the calculations were indicated.
Retinal layer segmentation of macular OCT images using boundary classification
Lang, Andrew; Carass, Aaron; Hauser, Matthew; Sotirchos, Elias S.; Calabresi, Peter A.; Ying, Howard S.; Prince, Jerry L.
2013-01-01
Optical coherence tomography (OCT) has proven to be an essential imaging modality for ophthalmology and is proving to be very important in neurology. OCT enables high resolution imaging of the retina, both at the optic nerve head and the macula. Macular retinal layer thicknesses provide useful diagnostic information and have been shown to correlate well with measures of disease severity in several diseases. Since manual segmentation of these layers is time consuming and prone to bias, automatic segmentation methods are critical for full utilization of this technology. In this work, we build a random forest classifier to segment eight retinal layers in macular cube images acquired by OCT. The random forest classifier learns the boundary pixels between layers, producing an accurate probability map for each boundary, which is then processed to finalize the boundaries. Using this algorithm, we can accurately segment the entire retina contained in the macular cube to an accuracy of at least 4.3 microns for any of the nine boundaries. Experiments were carried out on both healthy and multiple sclerosis subjects, with no difference in the accuracy of our algorithm found between the groups. PMID:23847738
FLUID MODELING OF ATMOSPHERIC DISPERSION IN THE CONVECTIVE BOUNDARY LAYER
Study of convective boundary layer (CBL) processes has depended largely upon laboratory analogs for many years. The pioneering work of Willis and Deardorff (1974) and some 35 subsequent papers by the same authors showed that much useful research could be accomplished with a re...
DNS of a Turbulent Boundary Layer with Surface Roughness
Yi Chen; James Cardillo; Guillermo Araya; Luciano Castillo; Kenneth Jansen
2010-01-01
A Direct numerical simulation (DNS) of a high Reynolds number, zero pressure gradient, turbulent boundary layer (Retheta= 2400) subjected to sandpaper surface roughness is performed. The surface roughness is modeled with a roughness parameter k^+ ˜ 25 to match the experiments at similar Reynolds number and roughness distribution. The employed computational method involves a synergy of the multi-scale dynamic approach
Turbulent dispersion in the Atmospheric Convective Boundary Layer
A. Dosio
2005-01-01
The dispersion of a plume in the Atmospheric Boundary Layer is a very complex phenomenon that includes the transport, the mixing and the chemical transformations of the plume material. When a plume is dispersed in the ABL, its shape, evolution, and internal structure are determined by the interaction between the plume and the turbulent eddies that characterize the atmospheric motion.
Iodine monoxide in the Western Pacific marine boundary layer
NASA Astrophysics Data System (ADS)
Großmann, K.; Frieß, U.; Peters, E.; Wittrock, F.; Lampel, J.; Yilmaz, S.; Tschritter, J.; Sommariva, R.; von Glasow, R.; Quack, B.; Krüger, K.; Pfeilsticker, K.; Platt, U.
2012-10-01
A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved, if an additional sea-air flux of inorganic iodine (e.g. I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.
Iodine monoxide in the Western Pacific marine boundary layer
NASA Astrophysics Data System (ADS)
Großmann, K.; Frieß, U.; Peters, E.; Wittrock, F.; Lampel, J.; Yilmaz, S.; Tschritter, J.; Sommariva, R.; von Glasow, R.; Quack, B.; Krüger, K.; Pfeilsticker, K.; Platt, U.
2013-03-01
A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved if an additional sea-air flux of inorganic iodine (e.g., I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.
The influence of freestream turbulence spectrum on boundary layer transition
Jorge Costa; Tony Arts
1991-01-01
The flow in turbomachines is characterized by a high turbulent activity. Its spectrum frequently reveals energy peaks at privileged frequencies. They generally have an influence upon the boundary layer transition onset. This type of forced transition was studied at the von Karman Institute in a low speed wind tunnel along a flat test surface. Discrete frequency energy peaks were generated
Receptivity of Supersonic Boundary Layers to Acoustic Disturbances
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Balakumar, P.
2005-01-01
Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results 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 (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The effect of leading-edge thickness is also studied and bluntness is found to stabilize the boundary layer. The relative significance of fast acoustic waves is enhanced in the presence of bluntness.
Stability of Supersonic Boundary Layers Over Blunt Wedges
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam
2006-01-01
Receptivity and stability of supersonic boundary layers over blunt flat plates and wedges are numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 10(exp 6)/inch. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. Computations are performed for a flat plate with leading edge thicknesses of 0.0001, 0.001, 0.005 and 0.01 inches that give Reynolds numbers based on the leading edge thickness ranging from 1000 to 10000. Calculations are also performed for a wedge of 10 degrees half angle with different leading edge radii 0.001 and 0.01 inches. The linear stability results showed that the bluntness has a strong stabilizing effect on the stability of two-dimensional boundary layers. The transition Reynolds number for a flat plate with a leading edge thickness of 0.01 inches is about 3.5 times larger than it is for the Blasius boundary layer. It was also revealed that boundary layers on blunt wedges are far more stable than on blunt flat plates.
The oscillating turbulent boundary layer in a conical diffuser
M. E. Tomsho
1978-01-01
The turbulent boundary layer in a conical diffuser, with the inlet airflow oscillating sinusoidally, was studied experimentally and theoretically. The diffuser inlet diameter is 100 mm and the flow is characterized by an entrance Reynolds number on the order of 120000. The 3-degree (half-angle) diffuser flow is in the turbulent regime throughout the test section, and no separation occurs. Oscillation
The bottom boundary layer of the deep ocean
Laurence Armi; Robert C. Millard
1976-01-01
Some aspects of the bottom boundary layer of the deep ocean are exhibited in profiles of salinity and temperature made with a Woods Hole Oceanographic Institution\\/Brown CTD microprofiler. Profiles from the center of the Hatteras Abyssal Plain have a signature that is characteristic of mixing up a uniformly stratified region. Over rough or sloping topography, to the east and west
ANALYTICAL PARAMETERIZATIONS OF DIFFUSION: THE CONVECTIVE BOUNDARY LAYER
A brief review is made of data bases which have been used for developing diffusion parameterizations for the convective boundary layer (CBL). A variety of parameterizations for lateral and vertical dispersion, (sigma sub) and (sigma sub z), are surveyed; some of these include mec...
MOTIONS IN A BOSE CONDENSATE BOUNDARY LAYER SEPARATION
Soatto, Stefano
MOTIONS IN A BOSE CONDENSATE VII. BOUNDARY LAYER SEPARATION Natalia G. Berlo#11;, Paul H. Roberts This is the seventh in a series of papers devoted to the Bose condensate as applied to super uid helium and especially by an impurity such as a positive ion 4 He + 2 moving in super uid helium at low temperature has been studied
Boundary layer measurements using hot-film sensors
NASA Technical Reports Server (NTRS)
Holmes, Harlan K.; Carraway, Debra L.
1986-01-01
Measurements in the aerodynamic boundary layer using heat transfer, hot-film sensors are receiving a significant amount of effort at the Langley Research Center. A description of the basic sensor, the signal conditioning employed, and several manifestations of the sensor are given. Results of a flow reversal sensor development are presented, and future work areas are outlined.
Nonequilibrium boundary layer of potassium-seeded combustion products
M. S. Benilov; P. A. Pozdeev; B. V. Rogov; V. A. Sinelshchikov
1994-01-01
Results are reported from numerical modeling and experimental study of a chemically reacting boundary layer, formed on a body inserted into a stream of potassium-seeded combustion products of gaseous hydrocarbon fuels. The numerical model developed in previous work is modified to incorporate current data on potassium chemical kinetics. The temperature and potassium atom number density profiles are measured across the
Determination of Stability and Translation in a Boundary Layer
NASA Technical Reports Server (NTRS)
Crepeau, John; Tobak, Murray
1996-01-01
Reducing the infinite degrees of freedom inherent in fluid motion into a manageable number of modes to analyze fluid motion is presented. The concepts behind the center manifold technique are used. Study of the Blasius boundary layer and a precise description of stability within the flow field are discussed.
Thickness and concentration profile of the boundary layer in electrodialysis
M. Law; T. Wen; G. S. Solt
1997-01-01
Back electrical motive force (emf) measurements with spiral electrodialysis (SpED) modules showed that obtaining the profile of the back emf transient curves during depolarization is difficult from the Nernst model, and the assumption of a linear concentration profile in a stirred polarized boundary layer is oversimplified. A non-linear concentration distribution model derived from the error function is introduced.
Turbulence in the convective boundary layer observed by microwave interferometry
X. M. Shao; R. C. Carlos; M. W. Kirkland
1997-01-01
A 9-antenna, 400 meter microwave interferometer was utilized in SALSA MEX on the San Pedro River area in July and August, 1997, to measure the turbulence in the Convective Boundary Layer. Water vapor has an appreciable index of refraction at radio frequencies around 10 GHz, and acts as a passive tracer of the magnitude and motion of turbulence. The relative
Simple viscous flows: From boundary layers to the renormalization group
John Veysey II; Nigel Goldenfeld
2007-01-01
The seemingly simple problem of determining the drag on a body moving through a very viscous fluid has, for over 150 years, been a source of theoretical confusion, mathematical paradoxes, and experimental artifacts, primarily arising from the complex boundary layer structure of the flow near the body and at infinity. The extensive experimental and theoretical literature on this problem is
Boundary-layer model of pattern formation in solidification
E. Ben-Jacob; N. Goldenfeld; J. S. Langer; G. Schon
1984-01-01
A model of pattern formation in crystal growth is proposed, and its analytic properties are investigated. The principal dynamical variables in this model are the curvature of the solidification front and the thickness (or heat content) of a thermal boundary layer, both taken to be functions of position along the interface. This model is mathematically much more tractable than the
A sensitivity theory for the equilibrium boundary layer over land
NASA Astrophysics Data System (ADS)
Cronin, Timothy W.
2013-12-01
Due to the intrinsic complexities associated with modeling land-atmosphere interactions, global models typically use elaborate land surface and boundary layer physics parameterizations. Unfortunately, it is difficult to use elaborate models, by themselves, to develop a deeper understanding of how land surface parameters affect the coupled land-atmosphere system. At the same time, it is also increasingly important to gain a deeper understanding of the role of changes in land cover, land use, and ecosystem function as forcings and feedbacks in past and future climate change. To improve the foundation of our understanding, we outline a framework for boundary layer climate sensitivity based on surface energy balance; just as global climate sensitivity is based on top-of-atmosphere energy balance. We develop an analytic theory for the boundary layer climate sensitivity of an idealized model of a diurnally averaged well-mixed boundary layer over land. This analytic sensitivity theory identifies changes in the properties of the land surface—including moisture availability, albedo, and aerodynamic roughness—as forcings, and identifies strong negative feedbacks associated with the surface fluxes of latent and sensible heat. We show that our theory can explain nearly all of the sensitivity of the Betts (2000) full system of equations. Favorable comparison of the theory and the simulation results from a two-column radiative convective model suggests that the theory may be broadly useful for unifying our understanding of how changes in land use or ecosystem function may affect climate change.
Effects of mussel filtering activity on boundary layer structure
Luca A. van Duren; Peter M. J. Herman; Adri J. J. Sandee; Carlo H. R. Heip
2006-01-01
The structure of the benthic boundary layer over a bed of mussels (Mytilus edulis) was investigated in a large racetrack flume. Flow was observed to be modified both by the physical roughness of the mussel bed and by the momentum input of the exhalent jets of the mussels. Particularly when the mussels were closed, and filtering activity was reduced to
Measurements Of Turbulence In Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Driver, David M.
1993-01-01
Report describes experimental study of turbulence in two boundary-layer flows with adverse gradients of pressure. Flows produced about cylinder oriented with axis along that of low-speed wind tunnel of rectangular cross section. Fluctuations of velocities analyzed with respect to various mathematical models of turbulence.
Air flow in the boundary layer near a plate
NASA Technical Reports Server (NTRS)
Dryden, Hugh L
1937-01-01
The published data on the distribution of speed near a thin flat plate with sharp leading edge placed parallel to the flow (skin friction plate) are reviewed and the results of some additional measurements are described. The purpose of the experiments was to study the basic phenomena of boundary-layer flow under simple conditions.
Large-Scale Streamwise Turbulent Structures in Hypersonic Boundary Layers
English, Benjamin L.
2013-04-22
Velocimetry in a M = 4.9 blow-down wind tunnel accompanied by a series of data analysis in order to identify the existence of streamwise-elongated large-scale turbulence structures in a hypersonic boundary layer. Furthermore, this study identified physical...
Large-eddy and direct simulations of accelerating boundary layers
Junlin Yuan; Valerio Grazioso; Ugo Piomelli
2010-01-01
Turbulent boundary layers subject to a favorable pressure gradient (which induces freestream acceleration) are found in many engineering applications, such as airfoils or curved ducts. If the acceleration is sufficiently large, turbulence production decreases, and the flow reverts to a laminar or quasi-laminar state. Once the cause of relaminarization is removed, the flow re-transitions to turbulence in a process that
Turbulence Structure and Wall Signature in Hypersonic Boundary Layer
Martín, Pino
Turbulence Structure and Wall Signature in Hypersonic Boundary Layer Yin-Chiu Kan , Beekman Izaak and low- speed features, found in subsonic experiments, are present in our supersonic and hypersonic and hypersonic regimes due to the lack of detailed flow field data, and the studies have been mostly restricted
Structure and dynamics of the oceanic bottom boundary layer
Georges L. Weatherly; Paul J. Martin
1978-01-01
The Mellor and Yamada (1974) Level II turbulence closure scheme is used to study the oceanic bottom boundary layer (BBL). The model is tested against observations of the BBL obtained on the western Florida Shelf reported in Weatherly and Van Leer (1977) and in turn conclusions about the BBL made in that paper are tested against the model. The agreement
Measurement of Boundary-Layer Transition by Towing Wind Tunnel
S. Yoshioka; Y. Kohama; T. Kato; F. Ohta; M. Tokuyama; S. Kikuchi
2005-01-01
In this paper a newly constructed Towing wind tunnel facility is introduced. This Towing wind tunnel system can create highly complex flow and zero free stream turbulence condition. The performance of this facility is first explained. The results of our first experiment on the boundary layer transition on a flat plate are then given. We concluded that this facility has
Spatially developing turbulent boundary layer on a flat plate
Lee, J H; Hutchins, N; Monty, J P
2012-01-01
This fluid dynamics video submitted to the Gallery of Fluid motion shows a turbulent boundary layer developing under a 5 metre-long flat plate towed through water. A stationary imaging system provides a unique view of the developing boundary layer as it would form over the hull of a ship or fuselage of an aircraft. The towed plate permits visualisation of the zero-pressure-gradient turbulent boundary layer as it develops from the trip to a high Reynolds number state ($Re_\\tau \\approx 3000$). An evolving large-scale coherent structure will appear almost stationary in this frame of reference. The visualisations provide an unique view of the evolution of fundamental processes in the boundary layer (such as interfacial bulging, entrainment, vortical motions, etc.). In the more traditional laboratory frame of reference, in which fluid passes over a stationary body, it is difficult to observe the full evolution and lifetime of turbulent coherent structures. An equivalent experiment in a wind/water-tunnel would requ...
Boundary layer transition: Prediction and wind tunnel simulation
D. Arnal
1993-01-01
This paper gives a survey of theoretical and experimental results related to the problem of boundary layer transition; emphasis is given on applications of practical prediction methods. In the first part of the paper, it is shown that the linear stability theory can provide a good estimate of the transition location if the free stream disturbance level is low enough;
Detection of boundary-layer transitions in wind tunnels
NASA Technical Reports Server (NTRS)
Wood, W. R.; Somers, D. M.
1978-01-01
Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent boundary-layer transitions on wind-tunnel models. Technique allows measurements above or below atmospheric pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.
Atmospheric Boundary Layer Wind Tunnel Applications in Wind Turbine Siting
W. D. Lubitz; B. R. White
Atmospheric boundary layer wind tunnels (ABLWTs) have been used for 40 years to simulate the interaction of the wind and earth in the lowest few hundred meters of the atmosphere. ABLWTs are well-suited for investigating flow in complex terrain and have different strengths and weaknesses than numerical modeling. There are a wide variety of applications, including performing wind resource assessments
ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS
Pessah, Martin E. [Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen O (Denmark); Chan, Chi-kwan, E-mail: mpessah@nbi.dk, E-mail: ckch@nordita.org [NORDITA, Roslagstullsbacken 23, 106 91 Stockholm (Sweden)
2012-05-20
Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.
Thermal boundary layer in liquid metals with variable thermal conductivity
M. Arunachalam; N. R. Rajappa
1978-01-01
This paper deals with the analysis of the steady state laminar thermal boundary layer in liquid metals with variable thermal conductivity. For a general class of inviscid flows specified by the power law distribution, explicit closed form analytical solutions are given for temperature distributions using regular perturbation technique and they are compared with the available exact numerical solutions and found
An Asymptotic Description of the Attached, Turbulent, Oscillatory Boundary Layer
M. J. Butler; P. W. Duck; P. K. Stansby
1998-01-01
The attached, temporally-oscillating turbulent boundary layer is investigated by use of asymptotic matching techniques, valid for the limit of large Reynolds numbers. Much of the analysis is applicable to generally accepted turbulence models (which satisfy a few basic assumptions as detailed in the paper), and this is then applied in particular to two well established turbulence models, namely the k
Large-Scale Streamwise Turbulent Structures in Hypersonic Boundary Layers
English, Benjamin L.
2013-04-22
Prior research in the field of boundary layer turbulence has identified streamwise-elongated large-scale turbulence structures in both low speed compressible and high speed (M=2.0) flow. No experimental work has been done in any flow of M> or =3...
On the Effects of Surface Roughness on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack
2009-01-01
Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.
On the growth of turbulent regions in laminar boundary layers
NASA Technical Reports Server (NTRS)
Gad-El-hak, M.; Riley, J. J.; Blackwelder, R. F.
1981-01-01
Turbulent spots evolving in a laminar boundary layer on a nominally zero pressure gradient flat plate are investigated. The plate is towed through an 18 m water channel, using a carriage that rides on a continuously replenished oil film giving a vibrationless tow. Turbulent spots are initiated using a solenoid valve that ejects a small amount of fluid through a minute hole on the working surface. A novel visualization technique that utilizes fluorescent dye excited by a sheet of laser light is employed. Some new aspects of the growth and entrainment of turbulent spots, especially with regard to lateral growth, are inferred from the present experiments. To supplement the information on lateral spreading, a turbulent wedge created by placing a roughness element in the laminar boundary layer is also studied both visually and with probe measurements. The present results show that, in addition to entrainment, another mechanism is needed to explain the lateral growth characteristics of a turbulent region in a laminar boundary layer. This mechanism, termed growth by destabilization, appears to be a result of the turbulence destabilizing the unstable laminar boundary layer in its vicinity. To further understand the growth mechanisms, the turbulence in the spot is modulated using drag-reducing additives and salinity stratification.
Completed double layer boundary element method for periodic suspensions
Xi-Jun Fan; Nhan Phan-Thien; Rong Zheng
1998-01-01
In this paper, a traction-based boundary element method is formulated and implemented for periodic suspensions. Hydrodynamic interaction of particles at infinity is handled by O'Brien's method (1979), which is suitably modified for the adjoint double layer using the mean field values of the traction and the background flow. After a deflation of the extreme eigenvalue -1 of the adjoint double
Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects
NASA Technical Reports Server (NTRS)
Lachowicz, Jason T.; Chokani, Ndaona
1996-01-01
Hypersonic boundary layer measurements over a flared cone were conducted in a Mach 6 quiet wind tunnel at a freestream unit Reynolds number of 2.82 million/ft. This Reynolds number provided laminar-to-transitional flow over the cone model in a low-disturbance environment. Four interchangeable nose-tips, including a sharp-tip, were tested. Point measurements with a single hot-wire using a novel constant voltage anemometer were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the transitional state of the boundary layer and to identify instability modes. Results suggest that second mode disturbances were the most unstable and scaled with the boundary layer thickness. The second mode integrated growth rates compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode subharmonic. The subharmonic disturbance wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that nonlinear disturbances are not associated with 'high' free stream disturbance levels. Nose-tip radii greater than 2.7% of the base radius completely stabilized the second mode.
Hypersonic Boundary Layer Stability over a Flared Cone in a Quiet Tunnel
NASA Technical Reports Server (NTRS)
Lachowicz, Jason T.; Chokani, Ndaona; Wilkinson, Stephen P.
1996-01-01
Hypersonic boundary layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82x106/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the model in a low-disturbance environment. Point measurements with a single hot wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode disturbances were the most unstable and scaled with the boundary layer thickness. The integrated growth rates of the second mode compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with high free stream disturbance levels.
Large-eddy simulation of an infinitely large wind farm in a stable atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Lu, Hao; Porté-Agel, Fernando
2010-05-01
When deployed as large arrays, wind turbines interact among themselves and with atmospheric boundary layer. To optimize their geometric arrangements, accurate knowledge of wind-turbine array boundary layer is of great importance. In this study, we integrated large eddy simulation with an actuator line technique, and used it to study the characteristics of wind-turbine wake in an idealized wind farm inside a stable atmospheric boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were placed in a well-known SBL turbulent case that has a boundary layer height of approximately 180m. The super-geostrophic nocturnal jet near the top of the boundary layer was highly reduced due to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric behavior of wake structure was observed in response to the non-uniform incoming turbulence, the Coriolis effects, and the rotational effects induced by blade motions. The turbulence intensity was persistent and reached its saturation value, and the Coriolis force caused an inclined spatial structure and drove certain amount of turbulent energy away from the center of the wake. The height of SBL was increased, while the magnitudes of the surface momentum flux and the surface buoyancy flux were reduced by approximately 30%. Evaluation of the vertical transport of momentum and heat shows enhanced mixing, especially at the top-tip level.
Anomalous plasma diffusion and the magnetopause boundary layer
NASA Technical Reports Server (NTRS)
Treumann, Rudolf A.; Labelle, James; Haerendel, Gerhard; Pottelette, Raymond
1992-01-01
An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.
Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Grosch, C. E.; Gatski, T. B. (Technical Monitor)
2002-01-01
The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.
Provenance of the K/T boundary layers
NASA Technical Reports Server (NTRS)
Hildebrand, A. R.; Boynton, W. V.
1988-01-01
An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.
A Novel Method to Induce Hydrodynamic Instability in Boundary Layer Flows
NASA Astrophysics Data System (ADS)
Gharib, Morteza; Jeon, David; Pereira, Francisco; McKeon, Beverley
2013-11-01
We have developed a method to induce passive hydrodynamic displacement of boundary layer type flows by implementing spatially patterned hydrophobic patches in the form of bands and spots on the surface of a boundary layer plate. These patterns can be designed as parallel bands of a certain width, spacing and direction, or spots with a random or regular distribution of a certain shape, size and spatial density. We will present results from a series of experiments where the response of boundary layers in low to medium Reynolds number ranges to these spatial forcing will be demonstrated. Also, we will discuss potential use of this novel technique for drag reduction and separation delay applications where our technique could be used to replace riblets, trip wires and vortex generators. We have developed a method to induce passive hydrodynamic displacement of boundary layer type flows by implementing spatially patterned hydrophobic patches in the form of bands and spots on the surface of a boundary layer plate. These patterns can be designed as parallel bands of a certain width, spacing and direction, or spots with a random or regular distribution of a certain shape, size and spatial density. We will present results from a series of experiments where the response of boundary layers in low to medium Reynolds number ranges to these spatial forcing will be demonstrated. Also, we will discuss potential use of this novel technique for drag reduction and separation delay applications where our technique could be used to replace riblets, trip wires and vortex generators. This work is supported by ONR- N00014-11-1-0031.
Boundary Layer Dynamical Structure During Secondary Eyewall Formation
NASA Astrophysics Data System (ADS)
Abarca, S. F.; Montgomery, M. T.; McWilliams, J. C.
2014-12-01
Secondary eyewall formation (SEF) is widely recognized as an important research problem in the dynamics of mature tropical cyclones. It has been shown that the development of the wind maxima in SEF occurs within the boundary layer and that it follows a chain of events initiated by a substantial radial expansion of the tangential wind field. In this context, there is not yet a consensus on the phenomenon's essential physics. It has been proposed that the boundary-layer dynamics of a maturing hurricane vortex is an important controlling element in SEF. However, recent literature also argues that hurricane boundary layers and the related coupling with the interior flow can be described through an Ekman-like balance and that shock-like structures are relevant in the swirling boundary layer of the inner core of mature storms. We analyze the radial and vertical structure of the specific forces and accelerations in in the boundary layer in a mature hurricane that includes a canonical eyewall replacement cycle. The case occurred in a mesoscale, convection-permitting numerical simulation of a tropical cyclone, integrated from an initial weak mesoscale vortex in an idealized quiescent environment. The simulation has been studied extensively in the literature. We find that momentum advection is almost everywhere important (some of it is associated with asymmetric eddies). We discuss the implication of our findings on the proposed importance of Ekman-like balance dynamics during SEF. Finally, our analysis does not support the recently proposed idea that the radial advection of radial momentum, and shock-like structures, are closely related to the supergradient wind phenomena observed during SEF.
Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Hess, Robert V.
1959-01-01
An appraisal is made of existing solutions of magnetohydrodynamic boundary-layer equations for stagnation flow and flat-plate flow, and some new solutions are given. Since an exact solution of the equations of magnetohydrodynamics requires complicated simultaneous treatment of the equations of fluid flow and of electromagnetism, certain simplifying assumptions are generally introduced. The full implications of these assumptions have not been brought out properly in several recent papers. It is shown in the present report that for the particular law of deformation which the magnetic lines are assumed to follow in these papers a magnet situated inside the missile nose would not be able to take up any drag forces; to do so it would have to be placed in the flow away from the nose. It is also shown that for the assumption that potential flow is maintained outside the boundary layer, the deformation of the magnetic lines is restricted to small values. The literature contains serious disagreements with regard to reductions in heat-transfer rates due to magnetic action at the nose of a missile, and these disagreements are shown to be mainly due to different interpretations of reentry conditions rather than more complicated effects. In the present paper the magnetohydrodynamic boundary-layer equation is also expressed in a simple form that is especially convenient for physical interpretation. This is done by adapting methods to magnetic forces which in the past have been used for forces due to gravitational or centrifugal action. The simplified approach is used to develop some new solutions of boundary-layer flow and to reinterpret certain solutions existing in the literature. An asymptotic boundary-layer solution representing a fixed velocity profile and shear is found. Special emphasis is put on estimating skin friction and heat-transfer rates.
NASA Technical Reports Server (NTRS)
Frank, L. A.; Decoster, R. J.; Ackerson, K. L.
1977-01-01
Hones 1977 points out the marked disagreement between the plasma flow measurements reported by Frank et al. 1976 and those obtained with the LASL plasma analyzer. He suggests (1) that solar ultraviolet background rates may have been incorrectly accounted for in the computation of proton bulk flows in the magnetotail as reported by Frank et al. 1976 and (2) that bulk flows with substantial speeds, i.e., those speeds greater than 50 km per sec, are seldom encountered in the plasma sheet at geocentric radial distances approx. equal to 35 R sub E. It is demonstrated that such ultraviolet responses were carefully considered by Frank et al. 1976 and thus the conclusion is maintained that bulk flows greater than 50 km per sec frequently occur in the plasma sheet at these radial distances. Further, a direct comparison of the capabilities of the LASL plasma analyzer employed by Hones and of the LEPEDEA Frank et al., 1976 indicates that there are rather severe restrictions on which plasmas in the plasma sheet can be properly measured to gain proton temperatures, number densities and flow velocities with the LASL plasma analyzer.
Surface pressure fluctuations in hypersonic turbulent boundary layers
NASA Technical Reports Server (NTRS)
Raman, K. R.
1974-01-01
The surface pressure fluctuations on a flat plate model at hypersonic Mach numbers of 5.2, 7.4 and 10.4 with an attached turbulent boundary layer were measured using flush mounted small piezoelectric sensors. A high frequency resolution of the pressure field was achieved using specially designed small piezoelectric sensors that had a good frequency response well above 300 KHz. The RMS pressures and non-dimensional energy spectra for all above Mach numbers are presented. The convective velocities, obtained from space time correlation considerations are equal to 0.7 U sub infinity. The results indicate the RMS pressures vary from 5 to 25 percent of the mean static pressures. The ratios of RMS pressure to dynamic pressure are less than the universally accepted subsonic value of 6 x 10/3. The ratio decreases in value as the Mach number or the dynamic pressure is increased. The ratio of RMS pressure to wall shear for Mach number 7.4 satisfies one smaller than or equal to p/tau sub w smaller than or equal to three.
Nocturnal boundary layer turbulence over a tree canopy
NASA Astrophysics Data System (ADS)
Stoughton, Thomas Ellsworth
This dissertation is a compilation of studies that probe into many facets of nocturnal boundary layer (NBL) turbulence over tree canopies. Primarily, these studies focused on investigations into scales of NBL motions, stability classification, vertical dispersion and kinematic flux calculations. The chapters present: (1)a NBL wind component signal analysis where fast response data were used to determine the resolution of NBL turbulence, (2)a NBL vertical dispersion study where a lidar system was used to measure plume growth over a deciduous forest in the NBL, and (3)a new method for rotating NBL three-dimensional wind data measurements. The main work was prompted by questions raised by earlier studies that are included in the appendices. The main conclusions of this research were: (1)a sampling rate of 50 Hz is required to capture an unbiased NBL turbulence signal, (2)a gradient based stability parameter offers a more precise description of stability in the NBL due to the low levels of turbulence present, (3)the ergodic condition, which assumes that time and space averages are equal, was found to be met in the NBL above a tree canopy as demonstrated by a consistent prediction of vertical dispersion to actual dispersion as measured with a lidar system, and (4)a frequency-weighted technique was developed to reduce flow intermittency effects that skew NBL calculations using the traditional rotation techniques.
Reactive chlorine chemistry in the boundary layer of coastal Antarctica
NASA Astrophysics Data System (ADS)
Zielcke, Johannes; Poehler, Denis; Friess, Udo; Hay, Tim; Eger, Philipp; Kreher, Karin; Platt, Ulrich
2015-04-01
A unique feature of the polar troposphere is the strong impact of halogen photochemistry, in which reactive halogen species are responsible for ozone depletion as well as the oxidation of elemental mercury and dimethyl sulphide. The source, however, as well as release and recycling mechanisms of these halogen species - for some species even abundances - are far from being completely known, especially of chlorine and iodine compounds. Here we present active long-path differential optical absorption spectroscopy (LP-DOAS) measurements conducted during austral spring 2012 at Ross Island, Antarctica, observing several species (BrO, O3, NO2, IO, ClO, OBrO, OClO, OIO, I2, CHOCHO, HCHO, HONO). For the first time, ClO was detected and quantified in the marine boundary layer of coastal Antarctica, with typical mixing ratios around 20 pptv and maxima around 50 pptv. Meteorological controls on the mixing ratio of ClO as well as the interplay with other halogen compounds will be discussed, such as the lack of observed OClO (< 1 pptv). The results seem to reflect previously in chamber studies observed dependences on ozone levels and solar irradiance.
Impact Wind Farms on the Marine Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Volker, P.; Capps, S. B.; Huang, H. J.; Sun, F.; Badger, J.; Hahmann, A.
2012-12-01
We introduce a new, validated wind farm parametrization (Explicit Wake Parametrization, EWP) which is based on the assumption that the downstream propagation of a single turbine wake can be described by a turbulent diffusion process. Thus, the downstream velocity deficit distribution can be described explicitly. Additionally, it allows us to take into account turbine interactions, making it possible to determine the unresolved turbine hub height velocities. Both the EWP wind farm parametrization and the wind farm scheme available in the Weather Research & Forecasting Model (WRF) have been validated against in situ measurements from Horns Rev I (A large offshore wind farm consisting of 80 2MW turbines situated near the west coast of Denmark). The main quantities of interest are the thrust applied to the flow, a consequence of the energy extracted by the wind turbines which determines mainly the wind farm wake extension (around 50 km for Horns Rev I) and the vertical velocity deficit distribution. Results show that the thrust in the WRF-WF scheme is overestimated inside the wind farm. We noticed that the velocity deficit propagates from the first turbine-containing-grid-cell up to the boundary layer top, which is in contrast to the theoretical expected expansion (confirmed by turbulence resolving models and wind tunnel results). The vertical expansion of the velocity deficit is a consequence of the additional turbulence source term in the WRF-WF scheme. The EWP scheme estimates the total amount of thrust correctly and is also able to follow the reduced thrust downstream since it considers the turbine interaction. From the good agreement with the far wake measurement, we can conclude that the formulation of the sub grid scale vertical extension of the velocity deficit must be correct. We will present results from WRF simulations in which we analyze the atmospheric response within the wake of wind farms resulting from the energy extraction of wind turbines. We place hypotetical wind farms in offshore areas with good wind resources near California. The wind farm sizes are choosen to be comparable to present ones errected in the European North Sea. Of particular interest is the influence of wind farms on the persistent stratocumulus clouds of the California coastal region, the thermal stratification of the boundary layer and wind stress changes due to reduced wind speeds near the surface. Although no wind farms are presently constructed along the Californian coast, fast and steady wind speeds makes it an attractive region for future offshore wind farms, especially if the first floating turbines near the coast of Norway are proven to be a success.
Dynamical Simulation of Cloudy Boundary Layer Flow during Cold Air Outbreaks
Chiu-Wai Yuen
1983-01-01
A two-dimensional primitive equation planetary boundary layer model has been constructed and applied to simulate downwind evolution of coupled dynamical, thermodynamical and cloud properties in the planetary boundary layer (PBL) developed during cold air outbreaks over warm ocean. A layered parametric approach is adopted to model the inversion -capped convective boundary layer filled with shallow cumuli, or topped by stratocumulus
The influence of a chemical boundary layer on the fixity, spacing and lifetime of mantle plumes
A. Mark Jellinek; Michael Manga
2002-01-01
Seismological observations provide evidence that the lowermost mantle contains superposed thermal and compositional boundary layers that are laterally heterogeneous. Whereas the thermal boundary layer forms as a consequence of the heat flux from the Earth's outer core, the origin of an (intrinsically dense) chemical boundary layer remains uncertain. Observed zones of `ultra-low' seismic velocity suggest that this dense layer may
BLSTA: A boundary layer code for stability analysis
NASA Technical Reports Server (NTRS)
Wie, Yong-Sun
1992-01-01
A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.
Investigation Of Boundary Layers Fine Structure In Arid Regions
NASA Astrophysics Data System (ADS)
Golitsyn, G. S.; Granberg, I. G.; Andronova, A. V.; Zilitinkevich, S. S.; Smirnov, V. V.; Ponomarev, V. M.
In connection with insufficiency of the quantitative items of information about the structure of surface and boundary layers structure of the atmosphere in the periods previous dusty ejection, and also absence of the description of an arid atmospheres micrometeorological mode, when the dry spreading surface thermally is non-uniform, that is characteristic for midday hours, the forwarding researches of fine structure of boundary layers in deserted regions of Kalmykia (1995-1997) and on dried bottom of the Aral sea (1991-1992 and in 1998) were carried out. Is was established that in dry hot weather above sandy "saucers" at heights of 1-2 meters there are micro- inversions of temperature and humidity. On our supervisions, this process occurs at temperatures of air above 25 deg.C and relative humidity less than 40%. Thus the gra- dient of temperature in bottom (5 cm) layer in absence of an external wind reaches 200-500 , i.e., arises strongly unstable subsurface boundary layer. Thus during dehydration of aggregate particles consisting, as has shown the soil anal- ysis, from particles of size 80-150 microns, the organic-mineral compositions (OMC) are allocated, and the thin-dispersion aerosol is formed. These thin-dispersion par- ticles (0.01-0.1 microns) first accumulate in this layer, and then at the expense of strong temperature (vertical and horizontal) gradient pass through viscous sub-layer and rise above, as whirlwinds - standing motionless thermics, or dust-devils, or as sim- ple convective of flows. During investigations, is was established, that in a hot season in absence of dusty storms convective processes lift into air from sandy landscapes of Kalmykia and Sub-Aral regions, consisting from aggregate particles, significant amounts of long-living aerosol of size less than 5 microns (including thin-dispersion (0.01-0.1 microns) aerosol), which renders essential influence on formation of aerosol pollution of an atmosphere and, thus, on a climate. Is was established, that the in- termediate condition between unstable and homogeneous atmosphere is characteristic for a structure of a boundary layer during dusty ejection. The analysis of the basic characteristics of boundary layers fine structure in deserted regions was carried out.
Steady and unsteady 3D interactive boundary layers
NASA Astrophysics Data System (ADS)
Smith, F. T.
The paper describes theoretical and computational research on 3D steady and unsteady flows at medium-to-high Reynolds numbers (Re), aimed at increasing understanding of 3D separation and boundary-layer transition. Concerning steady 3D flows first, an interactive-boundary-layer (IBL) formulation for 3D laminar flow of an incompressible fluid over a surface-mounted obstacle is addressed computationally and compared with other methods at various Re. The computational approach is designed deliberately to capture the extra ellipicity present due to the three-dimensionality, making use of skewed shears in linear quasi-planar sweeps of the boundary layer and local updating in the 3D interaction law. Results including separation are presented for a range of Re and obstacle heights, together with grid-effect studies, and comparisons are made, first with triple-deck predictions for high Re and, second, with an alternative IBL approach presented in a companion work. The latter and the current work together yield a broad agreement on predictions for the 3D flow, stretching from the triple-deck through the IBL to thin-layer Navier-Stokes predictions, over a wide range of Re. Second, the computational approach is extended to unsteady 3D flows, for the triple-deck limit including linear and nonlinear Tollmien-Schlichting waves. Results for small and nonsmall disturbances and comparisons are presented, showing fairly encouraging agreement between theory, computations and experiments.
Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Gatski, T. B.; Erlebacher, G.
2002-01-01
The results from direct numerical simulations of a spatially evolving, supersonic, flat-plate turbulent boundary-layer flow, with free-stream Mach number of 2.25 are presented. The simulated flow field extends from a transition region, initiated by wall suction and blowing near the inflow boundary, into the fully turbulent regime. Distributions of mean and turbulent flow quantities are obtained and an analysis of these quantities is performed at a downstream station corresponding to Re(sub x)= 5.548 x10(exp 6) based on distance from the leading edge.
Edge Plasma Boundary Layer Generated By Kink Modes in Tokamaks
L.E. Zakharov
2010-11-22
This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the ?-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Acoustic Radiation from High-Speed Turbulent Boundary Layers
NASA Astrophysics Data System (ADS)
Duan, Lian; Choudhari, Meelan
2013-11-01
Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a high-speed turbulent boundary layer with nominal freestream Mach number of 6 and Karman number of Re? ~ 464 . The emphasis is on comparing the primarily vortical pressure signal at the wall with the acoustic freestream signal under higher Mach number conditions. Moreover, the Mach-number dependence of pressure signals is investigated by comparing the current results with those of a supersonic boundary layer at Mach 2.5 and Re? ~ 510 . It is found that the freestream pressure intensity exhibits a strong Mach number dependence, irrespective of whether it is normalized by the mean wall shear stress or by the mean pressure. Spectral analysis shows that both the wall and freestream pressure fluctuations of the Mach 6 boundary layer have enhanced energy content at high frequencies. The computed Mach-number dependence of the acoustic field, including radiation intensity, directionality, and convection speed, is consistent with trends in measurements. The numerical database is used to understand the acoustic source mechanisms for both adiabatic and cold wall configurations. Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a high-speed turbulent boundary layer with nominal freestream Mach number of 6 and Karman number of Re? ~ 464 . The emphasis is on comparing the primarily vortical pressure signal at the wall with the acoustic freestream signal under higher Mach number conditions. Moreover, the Mach-number dependence of pressure signals is investigated by comparing the current results with those of a supersonic boundary layer at Mach 2.5 and Re? ~ 510 . It is found that the freestream pressure intensity exhibits a strong Mach number dependence, irrespective of whether it is normalized by the mean wall shear stress or by the mean pressure. Spectral analysis shows that both the wall and freestream pressure fluctuations of the Mach 6 boundary layer have enhanced energy content at high frequencies. The computed Mach-number dependence of the acoustic field, including radiation intensity, directionality, and convection speed, is consistent with trends in measurements. The numerical database is used to understand the acoustic source mechanisms for both adiabatic and cold wall configurations. Supported by NASA.
Air Flow in a Separating Laminar Boundary Layer
NASA Technical Reports Server (NTRS)
Schubauer, G B
1936-01-01
The speed distribution in a laminar boundary layer on the surface of an elliptic cylinder, of major and minor axes 11.78 and 3.98 inches, respectively, has been determined by means of a hot-wire anemometer. The direction of the impinging air stream was parallel to the major axis. Special attention was given to the region of separation and to the exact location of the point of separation. An approximate method, developed by K. Pohlhausen for computing the speed distribution, the thickness of the layer, and the point of separation, is described in detail; and speed-distribution curves calculated by this method are presented for comparison with experiment.
Atmospheric tides on Venus. III - The planetary boundary layer
NASA Astrophysics Data System (ADS)
Dobrovolskis, A. R.
1983-10-01
Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.
Correlation of boundary layer stability analysis with flight transition data
NASA Technical Reports Server (NTRS)
Collier, F. S., Jr.; Bartlett, D. W.; Wagner, R. D.; Tat, V. V.; Anderson, B. T.
1990-01-01
Recently, NASA completed a boundary-layer transition flight test on an F-14 aircraft which has variable-sweep capability. Transition data were acquired for a wide variety of sweep angles, pressure distributions, Mach numbers, and Reynolds numbers. In this paper, the F-14 flight test is briefly described and N-factor correlations with measured transition locations are presented for one of two gloves flown on the F-14 wing in the flight program; a thin foam and fiberglass glove which provided a smooth sailplane finish on the basic F-14, modified NACA 6-series airfoil. For these correlations, an improved linear boundary-layer stability theory was utilized that accounts for compressibility and surface and streamline curvature effects for the flow past swept wings.
Atmospheric surface and boundary layers of the Amazon Basin
NASA Technical Reports Server (NTRS)
Garstang, Michael
1987-01-01
Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.
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.
Logarithmic Boundary Layers in Strong Taylor-Couette Turbulence
NASA Astrophysics Data System (ADS)
Lohse, Detlef; Huisman, Sander; Ostilla, Rodolfo; Scharnowski, Sven; Cierpka, Christian; Kähler, Christian; Verzicco, Roberto; Sun, Chao; Grossmann, Siegfried
2013-11-01
We provide direct measurements of boundary layer profiles in highly turbulent Taylor-Couette flow up to Re = 2 ×106 using high-resolution particle image velocimetry and particle tracking velocimetry, complemented by DNS data on the same system up to Re =105 . We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von Kármán log law, but with corrections due to the curvature of the cylinder, which we theoretically account for, based on the Navier-Stokes equation and a closure assumption for the turbulent diffusivity. In particular, we study how these corrections depend on the cylinder radius ratio and show that they are different for the boundary layers at the inner and at the outer cylinder.
Boundary-layer turbulence as a kangaroo process
NASA Astrophysics Data System (ADS)
Dekker, H.; de Leeuw, G.; Maassen van den Brink, A.
1995-09-01
A nonlocal mixing-length theory of turbulence transport by finite size eddies is developed by means of a novel evaluation of the Reynolds stress. The analysis involves the contruct of a sample path space and a stochastic closure hypothesis. The simplifying property of exhange (strong eddies) is satisfied by an analytical sampling rate model. A nonlinear scaling relation maps the path space onto the semi-infinite boundary layer. The underlying near-wall behavior of fluctuating velocities perfectly agrees with recent direct numerical simulations. The resulting integro-differential equation for the mixing of scalar densities represents fully developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type of stochastic process. The model involves a scaling exponent ? (with ?-->? in the diffusion limit). For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields ?~=0.58.
Possibilities for drag reduction by boundary layer control
NASA Technical Reports Server (NTRS)
Naiman, I.
1946-01-01
The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.
Boundary layer receptivity due to three-dimensional convected gusts
NASA Technical Reports Server (NTRS)
Choudhari, Meelan; Kerschen, Edward J.
1990-01-01
Compressible fully three-dimensional interactions involving convected free-stream disturbances are analyzed by utilizing a rapid distortion theory in conjunction with triple-deck concepts. Only one class of regions where the boundary layer is receptive is considered; these regions are downstream from the leading edge, where a local feature, such as a wall hump, forces the boundary layer to make a short-scale adjustment. The results obtained are applicable to a variety of situations such as receptivity due to shallow three-dimensional roughness elements or three-dimensional wall-suction distributions. The influence of the gust orientation, frequency, and the type of mean flow disturbance on the amplitudes of the generated instability waves is demonstrated. It is found that a three-dimensional instability wave can be generated by the interaction of an oblique gust with a two-dimensional mean flow disturbance.
Aerosol Observations by Lidar in the Nocturnal Boundary Layer
NASA Astrophysics Data System (ADS)
di Girolamo, Paolo; Ambrico, Paolo Francesco; Amodeo, Aldo; Boselli, Antonella; Pappalardo, Gelsomina; Spinelli, Nicola
1999-07-01
Aerosol observations by lidar in the nocturnal boundary layer (NBL) were performed in Potenza, Southern Italy, from 20 January to 20 February 1997. Measurements during nine winter nights were considered, covering a variety of boundary-layer conditions. The vertical profiles of the aerosol backscattering coefficient at 355 and 723.37 nm were determined through a Klett-modified iterative procedure, assuming the extinction-to-backscattering ratio within the NBL has a constant value. Aerosol average size characteristics were retrieved from almost simultaneous profiles of the aerosol backscattering coefficient at 355 and 723.37 nm, the measurements being consistent with an accumulation mode radius not exceeding 0.4 m. Similar results in terms of aerosol sizes were obtained from measurements of the extinction-to-backscattering ratio profile at 355 nm performed on six nights during the measurement campaign. Backscattering profiles at 723.37 nm were also converted into profiles of aerosol liquid water content.
Turbulent boundary layers with large streamline curvature effects
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1978-01-01
It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.
Boundary layer integral matrix procedure code modifications and verifications
NASA Technical Reports Server (NTRS)
Evans, R. M.; Morse, H. L.
1974-01-01
A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented.
Turbulent boundary layer investigation at large Re with micron resolution
NASA Astrophysics Data System (ADS)
Kaehler, Christian J.; Cierpka, Christian; Scharnowski, Sven
2012-11-01
The reliable measurement of statistical quantities in turbulent boundary layer flows down to the wall is a challenging problem for many decades. However, due to the progress in laser based experimental techniques in the last years, it is now non-intrusively possible to measure statistical quantities, such as the mean velocity profile, wall-shear stress, Reynolds stresses or the probability density functions of the turbulent fluctuations, with micron resolution (Kähler et al. Exp. Fluids, 2012). The high spatial resolution allows for accurate measurements as typical bias errors, caused by spatial averaging effects of the probe size, can be avoided. Using advanced optical techniques, we have investigated a turbulent boundary layer flow along a 22 m long flat plate, installed in a wind-tunnel with a 2m by 2m cross-section, at different Reynolds numbers. The statistical results of the investigation will be discussed in the contribution.
A review of unsteady turbulent boundary-layer experiments
NASA Technical Reports Server (NTRS)
Carr, L. W.
1981-01-01
The essential results of a comprehensive review of existing unsteady turbulent boundary-layer experiments are presented. Different types of unsteady flow facilities are described, and the related unsteady turbulent boundary-layer experiments are cataloged and discussed. The measurements that were obtained in the various experiments are described, and a complete list of experimental results is presented. All the experiments that measured instantaneous values of velocity, turbulence intensity, or turbulent shear stress are identified, and the availability of digital data is indicated. The results of the experiments are analyzed, and several significant trends are identified. An assessment of the available data is presented, delineating gaps in the existing data, and indicating where new or extended information is needed. Guidelines for future experiments are included.
Numerical solution of the resistive magnetohydrodynamic boundary-layer equations
Glasser, A.H.; Jardin, S.C.; Tesauro, G.
1983-10-01
Three different techniques are presented for numerical solution of the equations governing the boundary layer of resistive magnetohydrodynamic tearing and interchange instabilities in toroidal geometry. Excellent agreement among these methods and with analytical results provides confidence in the correctness of the results. Solutions obtained in regimes where analytical medthods fail indicate a new scaling for the tearing mode as well as the existence of a new regime of stability.
Vortex/boundary-layer interactions: Data report, volume 2
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Bradshaw, P.
1987-01-01
This report summarizes the work done under NASA grant NAGw-581, Vortex/Boundary-Layer Interactions, to date. The experimental methods are discussed in detail and the results presented as a large number of figures, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in preparation.
Prediction of boundary-layer characteristics of an oscillating airfoil
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
1981-01-01
The evolution of unsteady boundary layers on oscillating airfoils is investigated by solving the governing equations by the Characteristic Box scheme. The difficulties associated with computing the first profile on a given time line, and the velocity profiles with partial flow reversal are solved. A sample calculation is performed for an external velocity distribution typical of those found near the leading edge of thin airfoils. The viability of the calculation procedure is demonstrated.
Spectral features of wall pressure fluctuations beneath turbulent boundary layers
Theodore M. Farabee; Mario J. Casarella
1991-01-01
Experimental measurements of the frequency spectra and frequency cross-spectra of the wall pressure fluctuations beneath a turbulent boundary layer were made in a low-noise flow facility. The data, taken over a range of flow speeds, clearly display a dimensionless frequency (??\\/u?=50) at which the spectra achieve a maximum and a low-frequency range with an approximately ?2 rolloff. The scaling laws
Acoustic receptivity of laminar boundary layers over wavy walls
M. Wiegel; R. W. Wlezien
1993-01-01
Acoustic receptivity of laminar boundary layers over surfaces with nonlocalized low-amplitude periodic waviness is experimentally investigated. An array of 2D strips is used to simulate continuous wall waviness. Particular attention to measurement techniques is required to minimize facility-dependent flow and acoustic field anomalies. Balanced arrays of acoustic sources upstream and downstream of the test section are used to generate a
Simulation of aerosol substance transfer in the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Lezhenin, A. A.; Raputa, V. F.; Shlychkov, V. Ð. ?.
2014-11-01
A model for the reconstruction of the surface concentration of a heavy non-homogeneous substance transfered in the atmosphere is proposed. The model is used to simulate the snow surface contamination by benzo(a)pyren in the vicinity of Power Station-3 in the city of Barnaul. The effects of wind rotation in the atmospheric boundary layer on the field of long-term aerosol substance are assessed.
Kubo-Anderson Mixing in the Turbulent Boundary Layer
NASA Astrophysics Data System (ADS)
Dekker, H.; de Leeuw, G.; Brink, A. Maassen Van Den
A novel ab initio analysis of the Reynolds stress is presented in order to model non-local turbulence transport. The theory involves a sample path space and a stochastic hypothesis. A scaling relation maps the path space onto the boundary layer. Analytical sampling rates are shown to model mixing by exchange. Nonlocal mixing involves a scaling exponent ??0.58 (??? in the diffusion limit). The resulting transport equation represents a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process.
Water vapour flux profiles in the convective boundary layer
H. Linné; B. Hennemuth; J. Bösenberg; K. Ertel
2007-01-01
Summary Water vapour flux profiles in the atmospheric boundary layer have been derived from measurements of water vapour density fluctuations\\u000a by a ground-based Differential Absorption Lidar (DIAL) and of vertical wind fluctuations by a ground-based Doppler lidar.\\u000a The data were collected during the field experiment LITFASS-2003 in May\\/June 2003 in the area of Lindenberg, Germany. The\\u000a eddy-correlation method was applied, and
Nonlinear stability and saturation in 3-D boundary layers
William Saric
1997-01-01
The important recent progress in three-dimensional boundary-layer transition is reviewed. We focus on the crossflow instability that leads to nonlinear saturation and transition on swept wings with pressure gradients. Following a brief overview of swept-wing instability mechanisms and the crossflow problem, a summary of the important findings of the 1990s is given. The discussion is presented from the experimental viewpoint
Nonlinear Stability and Transition in 3-D Boundary Layers
WILLIAM S. SARIC; RUBEN B. CARRILLO; MARK S. REIBERT
1998-01-01
The important recent progress in three-dimensional boundary-layer transition research is reviewed with emphasis on the crossflow instability that leads to transition on swept wings with a favorable pressure gradient. Following a brief overview of swept-wing instability mechanisms and the crossflow problem, a summary of the important findings of the 1990s is given. The discussion is presented from the experimental viewpoint,
Spatially developing secondary instabilities in compressible swept airfoil boundary layers
Fei Li; Meelan M. Choudhari
2011-01-01
Two-dimensional eigenvalue analysis is used on a massive scale to study the spatial instabilities of compressible shear flows\\u000a with two inhomogeneous directions. The main focus of the study is crossflow dominated swept-wing boundary layers although\\u000a the methodology can also be applied to study other types of flows, such as the attachment-line flow. Certain unique aspects\\u000a of formulating a spatial, two-dimensional
Instabilities in compressible attachment-line boundary layers
Anne Le Duc; Jörn Sesterhenn; Rainer Friedrich
2006-01-01
The hydrodynamic stability of the weakly compressible attachment-line boundary layer, with a sweep Mach number ranging from 0.1 to 1.3, is studied using a temporal compressible direct numerical simulation. A flow impinging non-normally onto an infinitely extended flat plate was computed. This complements the study of Hall et al. [Proc. R. Soc. London, Ser. A 395, 229 (1984)] who investigated
Effect of compliant wall motion on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Hefner, J. N.; Ash, R. L.
1977-01-01
A critical analysis of available wall data which indicated drag reduction under turbulent boundary layers. Detailed structural dynamic calculations suggest the surfaces responded in a resonant, rather than compliant, manner. Alternate explanations are given for drag reductions observed in two classes of experiments: flexible pipe flown, and waterbacked membranes in air. Analysis indicates the wall motion for the remaining data is typified by short wave lengths in agreement with the requirement of a possible compliant wall drag reduction mechanism recently suggested by Langley.
Parametric study of pulsed thermal bumps in supersonic boundary layer
H. Yan; D. Gaitonde
2011-01-01
A three-dimensional numerical study is performed to explore the effect of pulsed spanwise-periodic surface thermal perturbation\\u000a (also denoted as thermal bump) in a Mach 1.5 flat plate laminar boundary layer. A high-resolution upwind-biased Roe method\\u000a is used with the compressive Van Leer harmonic limiter on a suitably refined mesh. The dependence of flow stability characteristics\\u000a on the variation of thermal
A kappa-epsilon calculation of transitional boundary layers
NASA Technical Reports Server (NTRS)
Yang, Z.; Shih, T. H.
1992-01-01
A recently proposed kappa-epsilon model for low Reynolds number turbulent flows was modified by introducing a new damping function f(sub mu). The modified model is used to calculate the transitional boundary layer over a flat plate with different freestream turbulence levels. It is found that the model could mimic the transitional flow. However, the predicted transition is found to be sensitive to the initial conditions.
Boundary-layer receptivity for a parabolic leading edge
P. W. Hammerton; E. J. Kerschen
1996-01-01
The eect of the nose radius of a body on boundary-layer receptivity is analyzed for the case of a symmetric mean flow past a body with a parabolic leading edge. Asymptotic methods based on large Reynolds number are used, supplemented by numerical results. The Mach number is assumed small, and acoustic free-stream disturbances are consid- ered. The case of free-stream
NASA Technical Reports Server (NTRS)
Maestrello, L.; Grosveld, F. W.
1991-01-01
The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.
An Examination of Configurations for Using Infrared to Measure Boundary Layer Transition
Freels, Justin Reed
2012-10-19
Infrared transition location estimates can be fast and useful measurements in wind tunnel and flight tests. Because turbulent boundary layers have a much higher rate of convective heat transfer than laminar boundary layers, a difference in surface...
Surface-cooling effects on compressible boundary-layer instability
NASA Technical Reports Server (NTRS)
Seddougui, Sharon O.; Bowles, R. I.; Smith, F. T.
1990-01-01
The influence of surface cooling on compressible boundary layer instability is discussed theoretically for both viscous and inviscid modes, at high Reynolds numbers. The cooling enhances the surface heat transfer and shear stress, creating a high heat transfer sublayer. This has the effect of distorting and accentuating the viscous Tollmien-Schlichting modes to such an extent that their spatial growth rates become comparable with, and can even exceed, the growth rates of inviscid modes, including those found previously. This is for moderate cooling, and it applies at any Mach number. In addition, the moderate cooling destabilizes otherwise stable viscous or inviscid modes, in particular triggering outward-traveling waves at the edge of the boundary layer in the supersonic regime. Severe cooling is also discussed as it brings compressible dynamics directly into play within the viscous sublayer. All the new cooled modes found involve the heat transfer sublayer quite actively, and they are often multi-structured in form and may be distinct from those observed in previous computational and experimental investigations. The corresponding nonlinear processes are also pointed out with regard to transition in the cooled compressible boundary layer. Finally, comparisons with Lysenko and Maslov's (1984) experiments on surface cooling are presented.
Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances
NASA Technical Reports Server (NTRS)
Balakamar, P.; Kegerise, Michael A.
2011-01-01
Boundary layer receptivity to two-dimensional acoustic disturbances at different incidence angles and to vortical disturbances is investigated by solving the Navier-Stokes equations for Mach 6 flow over a 7deg half-angle sharp-tipped wedge and a cone. Higher order spatial and temporal schemes are employed to obtain the solution. The results 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 as compared to the fast waves. It is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases when the incidence angle is increased from 0 to 30 degrees. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The maximum receptivity is obtained when the wave incident angle is about 20 degrees. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that for the acoustic waves. Vortical disturbances first generate the fast acoustic modes and they switch to the slow mode near the continuous spectrum.
New insights into adverse pressure gradient boundary layers
NASA Astrophysics Data System (ADS)
George, William K.; Stanislas, Michel; Laval, Jean-Philippe
2010-11-01
In a recent paper Shah et al. 2010 (Proc. of the WALLTURB Meeting, 2009), Lille, FR, Springer, in press) documented a number of adverse pressure gradient flows (APG's), with and without wall curvature, where the turbulence intensity peak moved quite sharply away from the wall with increasing distance. They further suggested that this peak was triggered by the adverse pressure gradient and had its origin in an instability hidden in the turbulent boundary layer, developing soon after the change of sign of the pressure gradient. They then offered that this may explain the difficulties encountered up to now in finding a universal scaling for turbulent boundary layers. We build on these observations, and show that in fact there is clear evidence in the literature (in most experiments, both old and new) for such a development downstream of the imposition of an adverse pressure gradient. The exact nature of the evolution and the distance over which it occurs depends on the upstream boundary layer and the manner in which the APG is imposed. But far enough downstream the mean velocity profile in all cases becomes an inflectional point profile with the location of the inflection point corresponding quite closely to the observed peak in the streamwise turbulence intensity. This does not seem to have been previously noticed.
Advanced boundary layer transition measurement methods for flight applications
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.
1986-01-01
In modern laminar flow flight research, it is important to understand the specific cause(s) of laminar to turbulent boundary-layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The transition modes of interest in current flight investigations include the viscous Tollmien-Schlichting instability, the inflectional instability at laminar separation, and the crossflow inflectional instability, as well as others. This paper presents the results to date of research on advanced devices and methods used for the study of laminar boundary-layer transition phenomena in the flight environment. Recent advancements in the development of arrayed hot-film devices and of a new flow visualization method are discussed. Arrayed hot-film devices have been designed to detect the presence of laminar separation, and of crossflow vorticity. The advanced flow visualization method utilizes color changes in liquid-crystal coatings to detect boundary-layer transition at high altitude flight conditions. Flight and wind tunnel data are presented to illustrate the design and operation of these advanced methods. These new research tools provide information on disturbance growth and transition mode which is essential to furthering our understanding of practical design limits for applications of laminar flow technology.
Discrete modes and continuous spectra in supersonic boundary layers
NASA Technical Reports Server (NTRS)
Balakumar, P.; Malik, M. R.
1992-01-01
The disturbance field induced due to a harmonic point source consists of discrete eigenmodes and a continuous spectrum; these are studied by using generalized Fourier transform techniques. For a supersonic boundary layer, there exist seven branches of the continuous spectrum in the complex wavenumber space, four of which (two acoustic waves, one vorticity wave and one entropy wave) contribute to the flowfield downstream of the source. The discrete eigenmodes spring off from these branches at some critical Reynolds numbers. The results for Mach 2 and 4.5 boundary layers show that the receptivity coefficients for the stable discrete modes are much larger than that for the unstable mode. Therefore, the flow very near the source is dominated by the continuous spectrum and the stable discrete modes. However, the unstable mode takes over sufficiently far away from the source. It is shown that it is only necessary to consider the first few discrete modes to construct the solution. Calculations also show that, in a supersonic boundary layer, upstream influence from a localized disturbance is minimal.
Coupling of magnetopause-boundary layer to the polar ionosphere
Wei, C.Q.; Lee, L.C. (Univ. of Alaska, Fairbanks (United States))
1993-04-01
The authors develop a model which seeks to explain ultraviolet auroral images from the Viking satellite which show periodic bright regions which resemble [open quotes]beads[close quotes] or [open quotes]pearls[close quotes] aligned along the postnoon auroral oval. ULF geomagnetic pulsations observed in the cusp region are also addressed by this model. The model addresses plasma dynamics in the low-latitude boundary layer and interactions with the polar ionosphere by means of field-aligned current. The Kelvin-Helmholtz instability can develop in the presence of driven plasma flow, which can lead to the formation and growth of plasma vortices in the boundary layer. The finite conductivity of the earth ionosphere causes these vortices to decay. However regions of enhanced field-aligned power density in the postnoon auroral oval can be associated with field-aligned current filaments and boundary layer vortices. These structures may explain the observed bright spots. The authors also discuss the frequency spectrum and the polarization state of the pulsations.
The singularity in particle-laden boundary layers
NASA Astrophysics Data System (ADS)
Foster, M. R.; Duck, P. W.; Hewitt, R. E.
2006-11-01
The classical ``dusty gas'' equations have been used recently in a number of investigations by the authors to model boundary-layer flows of dilute suspensions of heavy particles. Though none of the difficulties of well-posedness that so often occur in more complicated particle-laden flow models seems to arise for this equation set, what does nearly always appear, and is now well documented in a variety of boundary layers, is a wall singularity that occurs at a finite distance from the leading edge, where the volume fraction is unbounded. The dusty-gas approximation replaces the quantity ``1-?'' everywhere in the particle-laden equations by ``1''. One is forced to seek a more complicated model in order to remove the unphysical singularity, and there are plenty of candidates--including particle pressure, added mass, particle-particle interactions. From the point of view of modifying the theory in the simplest possible way, we restore ``1-?'' where it had been replaced by ``1,'' and do nothing more. Such a procedure removes the singularity in boundary-layer flows, and we present computational and analytical results under such a change See, most recently, Foster, Duck & Hewitt (2006) Proc. Roy. Soc A 462, 1145
Minnowbrook II 1997 Workshop on Boundary Layer Transition in Turbomachines
NASA Technical Reports Server (NTRS)
LaGraff John E. (Editor); Ashpis, David E. (Editor)
1998-01-01
The volume contains materials presented at the Minnowbrook II - 1997 Workshop on Boundary Layer Transition in Turbomachines, held at Syracuse University Minnowbrook Conference Center, New York, on September 7-10, 1997. The workshop followed the informal format at the 1993 Minnowbrook I workshop, focusing on improving the understanding of late stage (final breakdown) boundary layer transition, with the engineering application of improving design codes for turbomachinery in mind. Among the physical mechanisms discussed were hydrodynamic instabilities, laminar to turbulent transition, bypass transition, turbulent spots, wake interaction with boundary layers, calmed regions, and separation, all in the context of flow in turbomachinery, particularly in compressors and high and low pressure turbines. Results from experiments, DNS, computation, modeling and theoretical analysis were presented. Abstracts and copies of viewgraphs, a specifically commissioned summation paper prepared after the workshop, and a transcript of the extensive working group reports and discussions are included in this volume. They provide recommendations for future research and clearly highlight the need for continued vigorous research in the technologically important area of transition in turbomachines.
Nonequilibrium boundary layer of potassium-seeded combustion products
Benilov, M.S.; Pozdeev, P.A.; Rogov, B.V.; Sinel'shchikov, V.A. (Russian Academy of Sciences, Moscow (Russian Federation). Inst. for High Temperatures)
1994-09-01
Results are reported from numerical modeling and experimental study of a chemically reacting boundary layer, formed on a body inserted into a stream of potassium-seeded combustion products of gaseous hydrocarbon fuels. The numerical model developed in previous work is modified to incorporate current data on potassium chemical kinetics. The temperature and potassium atom number density profiles are measured across the boundary layer formed on a cylindrical specimen of Al[sub 2]O[sub 3] dense ceramics by flow of combustion products of a propane-air mixture. The numerical results are compared with present experimental data as well as those available from the literature. The comparison is carried out for a broad range of experimental conditions including the postflame burned-gas region, and the boundary layers on a cylinder and on a flat plate. It provides verification of the proposed model, revision of the rate constants of some reactions of potassium-containing species, and supports the value of potassium superoxide dissociation energy of 247 kJ/mol.
Concentration boundary layers in osmotic membrane transport processes
NASA Astrophysics Data System (ADS)
Jensen, Kaare; Bohr, Tomas; Bruus, Henrik
2009-11-01
It has long been recognized, that the osmotic transport characteristics of membranes may be strongly influenced by the presence of unstirred concentration boundary layers adjacent to the membrane [1,2]. Previous experimental as well as theoretical works have focused on the case where the solution on both sides of the membrane remain well-mixed due to an external stirring mechanism. We present a theoretical investigation the effects of concentration boundary layers on the efficiency of osmotic pumping processes in the absence of external stirring i.e. when the stirring is provided by the osmotically generated flow itself. For such systems, we show that no well defined boundary layer thickness exist and that the reduction in concentration can be estimated by a surprisingly simple mathematical relation valid across a wide range of geometries and P'eclet numbers. [4pt] [1] T.J.Pedley, Q. Rev. Biophys., 1983, 16, 115[0pt] [2] K.H.Jensen et al., Lab Chip, 2009, 9, 2093
The nonlinear development of Gortler vortices in growing boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip
1986-01-01
The development of Gortler vortices in boundary layers over curved walls in the nonlinear regime is investigated. The growth of the boundary layer makes a parallel flow analysis impossible except in the high wavenumber regime so in general the instability equations must be integrated numerically. Here the spanwise dependence of the basic flow is described using Fourier series expansion whilst the normal and streamwise variations are taken into account using finite differences. The calculations suggest that a given disturbance imposed at some position along the wall will eventually reach a local equilibrium state essentially independent of the initial conditions. In fact, the equilibrium state reached is qualitatively similar to the large amplitude high wave-number solution described asymptotically by Hall (1982). In general, it is found that the nonlinear interactions are dominated by a mean field type of interaction between the mean flow and the fundamental. Thus, even though higher harmonics of the fundamental are necessarily generated, most of the disturbance energy is confined to the mean flow correction and the fundamental. A major result of the calculations is finding that the downstream velocity field develops a strongly inflection character as the flow moves downstream. The latter result suggests that the major effect of Gortler vortices on boundary layers of practical importance might be to make them highly receptive to rapidly growing Rayleigh modes of instability.
Thermocapillary Bubble Migration: Thermal Boundary Layers for Large Marangoni Numbers
NASA Technical Reports Server (NTRS)
Balasubramaniam, R.; Subramanian, R. S.
1996-01-01
The migration of an isolated gas bubble in an immiscible liquid possessing a temperature gradient is analyzed in the absence of gravity. The driving force for the bubble motion is the shear stress at the interface which is a consequence of the temperature dependence of the surface tension. The analysis is performed under conditions for which the Marangoni number is large, i.e. energy is transferred predominantly by convection. Velocity fields in the limit of both small and large Reynolds numbers are used. The thermal problem is treated by standard boundary layer theory. The outer temperature field is obtained in the vicinity of the bubble. A similarity solution is obtained for the inner temperature field. For both small and large Reynolds numbers, the asymptotic values of the scaled migration velocity of the bubble in the limit of large Marangoni numbers are calculated. The results show that the migration velocity has the same scaling for both low and large Reynolds numbers, but with a different coefficient. Higher order thermal boundary layers are analyzed for the large Reynolds number flow field and the higher order corrections to the migration velocity are obtained. Results are also presented for the momentum boundary layer and the thermal wake behind the bubble, for large Reynolds number conditions.
RANS Modeling of Benchmark Shockwave / Boundary Layer Interaction Experiments
NASA Technical Reports Server (NTRS)
Georgiadis, Nick; Vyas, Manan; Yoder, Dennis
2010-01-01
This presentation summarizes the computations of a set of shock wave / turbulent boundary layer interaction (SWTBLI) test cases using the Wind-US code, as part of the 2010 American Institute of Aeronautics and Astronautics (AIAA) shock / boundary layer interaction workshop. The experiments involve supersonic flows in wind tunnels with a shock generator that directs an oblique shock wave toward the boundary layer along one of the walls of the wind tunnel. The Wind-US calculations utilized structured grid computations performed in Reynolds-averaged Navier-Stokes mode. Three turbulence models were investigated: the Spalart-Allmaras one-equation model, the Menter Shear Stress Transport wavenumber-angular frequency two-equation model, and an explicit algebraic stress wavenumber-angular frequency formulation. Effects of grid resolution and upwinding scheme were also considered. The results from the CFD calculations are compared to particle image velocimetry (PIV) data from the experiments. As expected, turbulence model effects dominated the accuracy of the solutions with upwinding scheme selection indicating minimal effects.!
Turbulent thermal boundary layers subjected to severe acceleration
NASA Astrophysics Data System (ADS)
Araya, Guillermo; Castillo, Luciano
2013-11-01
Favorable turbulent boundary layers are flows of great importance in industry. Particularly, understanding the mechanisms of quasi-laminarization by means of a very strong favorable streamwise pressure gradient is indeed crucial in drag reduction and energy management applications. Furthermore, due to the low Reynolds numbers involved in the quasi-laminarization process, abundant experimental investigation can be found in the literature for the past few decades. However, several grey zones still remain unsolved, principally associated with the difficulties that experiments encounter as the boundary layer becomes smaller. In addition, little attention has been paid to the heat transfer in a quasi-laminarization process. In this investigation, DNS of spatially-developing turbulent thermal boundary layers with prescribed very strong favorable pressure gradients (K = 4 × 10-6) are performed. Realistic inflow conditions are prescribed based on the Dynamic Multi-scale Approach (DMA) [Araya et al. JFM, Vol. 670, pp. 581-605, 2011]. In this sense the flow carries the footprint of turbulence, particularly in the streamwise component of the Reynolds stresses.
Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.
Pérez-De-Tejada
1999-11-01
A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvénic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics. PMID:10511515
Study of Bubbly Flows in Turbulent Boundary Layers
NASA Astrophysics Data System (ADS)
Torres-Nieves, Sheilla; Lebron-Bosques, Jose; Moraga, Francisco; Castillo, Luciano
2006-11-01
Microbubble injection into a liquid turbulent boundary layer has been proven to effectively reduce frictional drag. Most of the experiments done to date have been conducted on flat plate geometries were bubbles are injected into a nominally zero-pressure-gradient turbulent boundary layer. Numerical simulations, although limited, have been performed to support these experiments. In fact, none of the published bubbly flow simulations deal with the case of non-zero pressure gradients. In this work, Reynolds Averaged Navier Stokes (RANS) simulations are performed to study different boundary layers, containing bubbles, on a horizontal flat plate. The behavior and distribution of these bubbles, and their effect on the mean velocity, Reynolds stresses and turbulent kinetic energy will be considered in this investigation. CFDShipM, a code developed at Rensselaer, will be modified in order to account for both a favorable and an adverse pressure gradient. Simulations will cover a range of void fractions, and bubble sizes. Furthermore, the results will be compared against the LDA data from Cal et al (2006), Brzek et al. (2006) and others.
Multi-dimensional Longwave Forcing of Boundary Layer Cloud Systems
Mechem, David B.; Kogan, Y. L.; Ovtchinnikov, Mikhail; Davis, Anthony B; Evans, K. F.; Ellingson, Robert G.
2008-12-20
The importance of multi-dimensional (MD) longwave radiative effects on cloud dynamics is evaluated in a large eddy simulation (LES) framework employing multi-dimensional radiative transfer (Spherical Harmonics Discrete Ordinate Method —SHDOM). Simulations are performed for a case of unbroken, marine boundary layer stratocumulus and a broken field of trade cumulus. “Snapshot” calculations of MD and IPA (independent pixel approximation —1D) radiative transfer applied to LES cloud fields show that the total radiative forcing changes only slightly, although the MD effects significantly modify the spatial structure of the radiative forcing. Simulations of each cloud type employing MD and IPA radiative transfer, however, differ little. For the solid cloud case, relative to using IPA, the MD simulation exhibits a slight reduction in entrainment rate and boundary layer TKE relative to the IPA simulation. This reduction is consistent with both the slight decrease in net radiative forcing and a negative correlation between local vertical velocity and radiative forcing, which implies a damping of boundary layer eddies. Snapshot calculations of the broken cloud case suggest a slight increase in radiative cooling, though few systematic differences are noted in the interactive simulations. We attribute this result to the fact that radiative cooling is a relatively minor contribution to the total energetics. For the cloud systems in this study, the use of IPA longwave radiative transfer is sufficiently accurate to capture the dynamical behavior of BL clouds. Further investigations are required in order to generalize this conclusion for other cloud types and longer time integrations. 1
A study of zero pressure-gradient and separating boundary layers using DPIV
Alfonso Gracia-Portilla; Tim Nickels
2003-01-01
Measurements are made of a turbulent boundary layer developing in a large water tunnel using DPIV. The thick boundary layer (delta = 10cm) improves the resolution of the detection of structures in turbulent boundary layers. Several ZPG turbulent boundary layers within the range 1700< Re_theta < 11,000 were observed, specifically in their streamwise-versus-wall-normal planes. Mean velocity and turbulent intensity profiles
Xiaolin Zhong
1998-01-01
Direct numerical simulation (DNS) has become a powerful tool in studying fundamental phenomena of laminar-turbulent transition of high-speed boundary layers. Previous DNS studies of supersonic and hypersonic boundary layer transition have been limited to perfect-gas flow over flat-plate boundary layers without shock waves. For hypersonic boundary layers over realistic blunt bodies, DNS studies of transition need to consider the effects
Adaptive nonlinear polynomial neural networks for control of boundary layer/structural interaction
NASA Technical Reports Server (NTRS)
Parker, B. Eugene, Jr.; Cellucci, Richard L.; Abbott, Dean W.; Barron, Roger L.; Jordan, Paul R., III; Poor, H. Vincent
1993-01-01
The acoustic pressures developed in a boundary layer can interact with an aircraft panel to induce significant vibration in the panel. Such vibration is undesirable due to the aerodynamic drag and structure-borne cabin noises that result. The overall objective of this work is to develop effective and practical feedback control strategies for actively reducing this flow-induced structural vibration. This report describes the results of initial evaluations using polynomial, neural network-based, feedback control to reduce flow induced vibration in aircraft panels due to turbulent boundary layer/structural interaction. Computer simulations are used to develop and analyze feedback control strategies to reduce vibration in a beam as a first step. The key differences between this work and that going on elsewhere are as follows: that turbulent and transitional boundary layers represent broadband excitation and thus present a more complex stochastic control scenario than that of narrow band (e.g., laminar boundary layer) excitation; and secondly, that the proposed controller structures are adaptive nonlinear infinite impulse response (IIR) polynomial neural network, as opposed to the traditional adaptive linear finite impulse response (FIR) filters used in most studies to date. The controllers implemented in this study achieved vibration attenuation of 27 to 60 dB depending on the type of boundary layer established by laminar, turbulent, and intermittent laminar-to-turbulent transitional flows. Application of multi-input, multi-output, adaptive, nonlinear feedback control of vibration in aircraft panels based on polynomial neural networks appears to be feasible today. Plans are outlined for Phase 2 of this study, which will include extending the theoretical investigation conducted in Phase 2 and verifying the results in a series of laboratory experiments involving both bum and plate models.
NASA Technical Reports Server (NTRS)
Deutsch, Steven; Zierke, William C.
1987-01-01
A one-component laser Doppler velocimeter (LDV) has been used to measure the two-dimensional periodic flow field about a double circular arc, compressor blade in cascade. Eleven boundary layer profiles were taken on both the pressure and suction surfaces of the blade, and two profiles were taken in the near wake. In this part of the study, the detailed LDV studies are described. The measurements indicate that the onset of transition occurs near 60 percent chord. The lack of a logarithmic region in the data measured at 97.9 percent chord indicates that transition is not complete. The thin laminar boundary layers near the leading edge led to some measurement problems, characterized by large turbulence intensities, in using the LDV.
NASA Astrophysics Data System (ADS)
Dekker, H.; de Leeuw, G.; van den Brink, A. Maassen
A nonlocal turbulence transport theory is presented by means of a novel analysis of the Reynolds stress, inter alia involving the construct of a sample path space and a stochastic hypothesis. An analytical sampling rate model (satisfying exchange) and a nonlinear scaling relation (mapping the path space onto the boundary layer) lead to an integro-differential equation for the mixing of scalar densities, which represents fully-developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process. The underlying near-wall behavior (i.e. for y +?0) of fluctuating velocities fully agrees with recent direct numerical simulations. The model involves a scaling exponent ?, with ??? in the diffusion limit. For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields ??0.58. The significance of ? as a turbulence Cantor set dimension (in the logarithmic profile region, i.e. for y +??) is discussed.
Local boundary-layer receptivity to a convected free-stream disturbance
A. J. Dietz
1999-01-01
An investigation of the local receptivity of a Blasius boundary layer to a harmonic vortical disturbance is presented as a step towards understanding boundary-layer receptivity to free-stream turbulence. Although there has been solid experimental verification of the linear theory describing acoustic receptivity of boundary layers, this was the first experimental verification of the mechanism behind local receptivity to a convected
Sliding mode control with varying boundary layers for an electro-hydraulic position servo system
Hong-Ming Chen; Jyh-Chyang Renn; Juhng-Perng Su
2005-01-01
In this study, a new sliding mode control with varying boundary layers is proposed to improve the tracking performance of a nonlinear electro-hydraulic position servo system, which can be found in many manufacturing devices. The key feature of the proposed control scheme is the use of varying boundary layers instead of fixed boundary layers, which are usually employed in conventional
Diverging solutions of the boundary-layer equations near a plane of symmetry
Hans Thomann
1994-01-01
Experiments with converging and diverging turbulent boundary layers near a plane of symmetry are described by Pompeo et al. The test section used to generate the boundary layers on the plane y = 0 is shown. The experiments were compared with computations based on a finite-difference boundary-layer code by Bettelini. The prediction of the diverging flow agreed fairly well with
Evolution of a storm-driven cloudy boundary layer in the Arctic
J Inoue; B Kosovic; J A Curry
2003-01-01
The cloudy boundary layer under stormy conditions during the summertime Arctic has been studied using observation from the SHEBA experiment and large-eddy simulations (LES). On 29 July 1998, a stable Arctic cloudy boundary layer event was observed after passage of a synoptic low. The local dynamic and thermodynamic structure of the boundary layer was determined from aircraft measurement including analysis
A COMPARISON OF MODELS FOR THE WAVENUMBER–FREQUENCY SPECTRUM OF TURBULENT BOUNDARY LAYER PRESSURES
W. R. Graham
1997-01-01
Aircraft cabin noise due to the fuselage boundary layer is determined by, among other factors, the wavenumber–frequency spectrum of the fluctuating boundary layer pressures, a quantity for which a number of models have been proposed. In this work predictions for the sound radiated by a boundary layer driven plate are investigated, with a view to determining which model is most
Turbulence measurements in the boundary layer of a low-speed wind tunnel using laser velocimetry
E. T. Schairer
1980-01-01
Laser velocimeter measurements in an incompressible, turbulent boundary layer along the wall of a low-speed wind tunnel are presented. The laser data are compared with existing hot-wire anemometer measurements of a flat plate, incompressible, turbulent, boundary layer with zero pressure gradient. An argument is presented to explain why previous laser velocimeter measurements in zero pressure gradient, turbulent boundary layers have
Atmospheric boundary layer simulation in a wind tunnel, using air injection
T. J. Sluman; H. R. E. van Maanen; G. Ooms
1980-01-01
The inner part of a neutral atmospheric boundary layer has been simulated in a wind tunnel, using air injection through the wind tunnel floor to thicken the boundary layer. The flow over both a rural area and an urban area has been simulated by adapting the roughness of the wind tunnel floor. Due to the thickening of the boundary layer
Marusic, Ivan
Reynolds Number Boundary Layer Wind Tunnel (HRNBLWT) is an open-return blower wind-tunnel with working BOUNDARY LAYERS Nick Hutchins, Jason Monty, Min Chong & Ivan Marusic Walter Bassett Aerodynamics Laboratory flow and in zero-pressure-gradient flat-plate turbulent boundary layers. The unique facilities
Experimental review of devices to artificially thicken wind tunnel boundary layers
J. E. Sargison; G. J. Walker
Three devices that artificially increase the thickness of the boundary layer in a wind tunnel working section have been tested. These included a serrated fence to disturb the flow, and the use of various secondary jet arrays injected into the boundary layer through the bounding surface. Momentum and turbulence profiles in the boundary layer downstream from the thickening devices were
ANALYSIS OF VORTEX PACKETS AND REYNOLDS STRESS IN A TURBULENT BOUNDARY LAYER
Marusic, Ivan
AND METHODS The experiments were performed in a suction type boundary layer wind tunnel. MeaANALYSIS OF VORTEX PACKETS AND REYNOLDS STRESS IN A TURBULENT BOUNDARY LAYER E K Longmire, B boundary layer with Re = 1060. Two-point spatial correlations obtained from fields in the logarithmic
Interaction of aerodynamic noise with laminar boundary layers in supersonic wind tunnels
M. R. Schopper
1984-01-01
The interaction between incoming aerodynamic noise and the supersonic laminar boundary layer is studied. The noise field is modeled as a Mach wave radiation field consisting of discrete waves emanating from coherent turbulent entities moving downstream within the supersonic turbulent boundary layer. The individual disturbances are likened to miniature sonic booms and the laminar boundary layer is staffed by the
A proposal for a new atmospheric boundary layer wind tunnel in the Netherlands
Peter Builtjes; Bert Holtslag; Harm Jonker
In this paper a short description is given of the plans to establish a new atmospheric boundary layer wind tunnel in the Netherlands. The main feature is that next to the normal neutral boundary layer, also stable and convective boundary layers will be simulated. The concept is to develop a multi- purpose\\/modular wind tunnel, also suited to investigate for example
Large-eddy simulation of a very large wind farm in a stable atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Lu, Hao; Porté-Agel, Fernando
2011-06-01
When deployed as large arrays, wind turbines significantly interact among themselves and with the atmospheric boundary layer. In this study, we integrate a three-dimensional large-eddy simulation with an actuator line technique to examine the characteristics of wind-turbine wakes in an idealized wind farm inside a stable boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were "immersed" in a well-known SBL case that bears a boundary layer height of approximately 175m. Two typical spacing setups were adopted in this investigation. The super-geostrophic low-level jet near the top of the boundary layer was eliminated owing to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric wind-turbine wakes were observed in response to the non-uniform incoming turbulence, the Coriolis effect, and the rotational effects induced by blade motion. The Coriolis force caused a skewed spatial structure and drove a part of the turbulence energy away from the center of the wake. The SBL height was increased, while the magnitude of the surface momentum flux was reduced by more than 30%, and the magnitude of the surface buoyancy flux was reduced by more than 15%. The wind farm was also found to have a strong effect on vertical turbulent fluxes of momentum and heat, an outcome that highlights the potential impact of wind farms on local meteorology.
NASA Astrophysics Data System (ADS)
Wei, Ping
In this thesis three sets of experiments of turbulent Rayleigh-B e nard convection with modified boundary conditions are presented. The first set of measurements were made in cylindrical cells with aspect ratio one and with various combinations of smooth and rough plates in the form of regularly-arrayed pyramids. The experimental results suggest that the Nu -- Ra relationship can be represented by the combination of two power laws, corresponding to the bulk dominant regime (exponent=1/2) and boundary layer dominant one (exponent=1/4) of the Grossmann-Lohse model. The behaviors of the coefficients of the two power laws suggest that the roughness of the plate can enhance the contribution of bulk and push the system to change from the boundary dominant state to bulk dominant state. A further examination of the individual plates reveal that the heat transport properties of smooth plates are insensitive to the surface and boundary conditions of the other plate of the same cell, whether smooth or rough, or whether under constant flux or constant temperature. The heat transport properties of the rough plates, on the other hand, appear to depend on surface and boundary conditions of the other plate of the same cell. In the second set of experiments we study the effect of polymer additives in two Rayleigh-Be nard convection cells, one with smooth top and bottom plates and the other with rough top and bottom plates. For the cell with smooth plates, a reduction of the measured Nusselt number (Nu) was observed. Furthermore, the amount of Nu reduction increases with increasing polymer concentration (c), reaching ~ 12% for c = 120 ppm and an apparent level-off thereafter. For the cell with rough plates, however, an enhancement (~ 4%) of Nu was observed when the polymer concentration is greater than 120 ppm. The third set of experiments investigates the properties of the velocity boundary layer in turbulent Rayleigh-Bénard convection in a cylindrical cell when it is tilted with respect to gravity. It is found that at small tilt angles (theta ? 1°), the measured viscous boundary layer thickness delta v scales with the Reynolds number Re with an exponent close to that for a Prandtl-Blasius laminar boundary layer. For larger tilt angles, the scaling exponent of deltav with Re decreases with theta. The normalized mean horizontal velocity profiles measured at the same tilt angle but with different Ra are found to have an invariant shape. But for different tilt angles, the shape of the normalized profiles is different.
Dynamic Immersed Boundary Method for Modeling of Turbulent Boundary Layers over Bio-Fouled Surfaces
NASA Astrophysics Data System (ADS)
Yang, Xiang; Sadique, Jasim; Mittal, Rajat; Meneveau, Charles
2013-11-01
The growth of large organisms on ship surfaces, i.e. macrobiofouling, is a major contributor to drag, and consequently, fuel consumption. The problem of turbulence over biofouled surfaces may be reduced to that of a developing turbulent boundary layer over a surface with a wide range of roughness length scales. Due to the presence of these scales, direct numerical simulation (DNS) or even wall-resolved large-eddy-simulation (LES) is prohibitively expensive. We address this challenge by developing a dynamic immersed boundary method that does not require the flow field nor the roughness to be fully resolved. The effect of unresolved small eddies are included via an LES sub-grid model. The large-scale roughness elements are resolved by a sharp-interface immersed boundary method and the effect of small (unresolved) roughness elements is incorporated through the use of a wall model that assumes a log-law at the grid point closest to the wall. This computationally efficient method is validated against experiments of developing turbulent boundary layer with multiple-scale roughness elements. We present results from this study and provide a discussion of our findings. The growth of large organisms on ship surfaces, i.e. macrobiofouling, is a major contributor to drag, and consequently, fuel consumption. The problem of turbulence over biofouled surfaces may be reduced to that of a developing turbulent boundary layer over a surface with a wide range of roughness length scales. Due to the presence of these scales, direct numerical simulation (DNS) or even wall-resolved large-eddy-simulation (LES) is prohibitively expensive. We address this challenge by developing a dynamic immersed boundary method that does not require the flow field nor the roughness to be fully resolved. The effect of unresolved small eddies are included via an LES sub-grid model. The large-scale roughness elements are resolved by a sharp-interface immersed boundary method and the effect of small (unresolved) roughness elements is incorporated through the use of a wall model that assumes a log-law at the grid point closest to the wall. This computationally efficient method is validated against experiments of developing turbulent boundary layer with multiple-scale roughness elements. We present results from this study and provide a discussion of our findings. This work is funded by the Office of Naval Research (ONR) grant N00014-12-1-0582. Fruitful interactions with M. Schultz (USNA), B. Ganapathisubramani and M. Placidi (Southhampton) are also gratefully acknowledged.
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.
Spatial three-dimensional secondary instability compressible boundary-layer flows
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1989-01-01
Three-dimensional linear secondary instability theory is extended for compressible and high Mach number boundary layer flows. The small but finite amplitude compressible Tollmien-Schlichting wave effect on the growth of 3-D perturbations is investigated. The focus is on principal parametric resonance responsible for the strong growth of subharmonic in low disturbance environment. The effect of increasing Mach number on the onset, growth, the shape of eigenfunctions of the subharmonic is assessed, and the resulting vortical structure is examined.
Secondary subharmonic instability of boundary layers with pressure gradient and suction
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1988-01-01
Three-dimensional linear secondary instability is investigated for boundary layers with pressure gradient and suction in the presence of a finite amplitude TS wave. The focus is on principal parametric resonance responsible for a strong growth of subharmonics in a low disturbance environment. Calculations are presented for the effect of pressure gradients and suction on controlling the onset and amplification of the secondary instability.
Surface-mounted optical fiber sensors for measurement of hypersonic boundary layer instability modes
Tran, T.A.; Greene, J.A. [Fiber and Sensor Technologies, Inc., Blacksburg, VA (United States); Claus, R.O.; Murphy, K.A.; Jones, M.; Burford, M. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)
1994-12-31
This paper describes a combination of analytical models and experimental investigations to demonstrate the feasibility of characterizing hypersonic boundary layer instability modes using fiber optic sensor-instrumented materials. The combination of such sensor performance with the response of internal actuator elements and the performance of a supervisory control algorithm could allow aerodynamic and hydrodynamic vortex control via an intelligent material system. Such control could allow improved flight control of aircraft and reduced noise signature for hydrospace vehicles.
Coupling the dynamics of boundary layers and evolutionary dunes.
Ortiz, Pablo; Smolarkiewicz, Piotr K
2009-04-01
A theoretical formulation and corresponding numerical solutions are presented for fluid flow and sediment transport past evolutionary sand dunes. Time-dependent curvilinear coordinates are employed to fully couple flow aloft with the developing landform. The differential conservation law that defines shape of the lower boundary depends on details of local surface stress, thereby favoring the large eddy simulation of the boundary layer. To shrink the gap between the time scales characteristic of planetary boundary layer flows O(10(3)) s and sand dune evolution O(10(6)) s, a hypothetical "severe-wind scenario" is adopted with the saltation flux amplified up to 3 orders of magnitude. While the results are largely insensitive to the rescaling, the efficacy of computations is greatly improved. The flux-form partial differential equation for the interface profile--via saltation and sand avalanches--is formulated as an advection-diffusion equation, to facilitate discrete integrations. Numerical experiments verify the adopted theoretical framework by reproducing scaling results reported in the literature. The versatility of the approach is illustrated with evolution of a sandhole--an example of application likely never addressed in the literature, yet realizable in nature. PMID:19518224
Discrete Roughness Effects on High-Speed Boundary Layers
NASA Astrophysics Data System (ADS)
Iyer, Prahladh Satyanarayanan
This dissertation studies the effects of a discrete roughness element on a high-speed boundary layer using Direct Numerical Simulations (DNS) on unstructured grids. Flow past a cylindrical roughness element placed perpendicular to the flow and a hemispherical bump is studied. A compressible linear stability theory (LST) solver for parallel flows is developed based on the algorithm by Malik and validated for a range of Mach numbers ranging from incompressible to Mach 10. The evolution of the perturbations from DNS is validated with the linear stability solver making the DNS algorithm suitable to study transition problems. Flow past a cylindrical roughness element at Mach 8.12 is simulated using DNS and the velocity profiles in the symmetry and wall---parallel planes are compared to the experiments of Bathel et al.. The flow remains steady and laminar, and does not transition. Overall, good agreement is observed between DNS and experiments, thus validating our algorithm to study effect of roughness on high-speed flows. However, differences are observed in the separation region upstream and recirculation region downstream of the roughness. The DNS results are used to quantify possible uncertainties in the measurement technique as suggested by Danehy [20]. The effect of upstream injection (5% of the free-stream velocity) is also simulated to quantify its effects on the velocity profiles to mimic the injection of NO into air in the experiment. While the boundary layer thickness of the flow increases downstream of the injection location, its effect on the velocity profiles is small when the profiles are scaled with the boundary layer thickness. Flow past a hemispherical bump at Mach 3.37, 5.26 and 8.23 are simulated using DNS with the flow conditions matching the experiments of Danehy et al. to understand the different flow features associated with the flow and the physical mechanism that causes the flow to transition to turbulence. It is observed that the Mach 3.37 and 5.26 flows transition to turbulence while the Mach 8.23 flow remains laminar downstream of the roughness element. The roughness element used in this study is large since the boundary layer thickness of the laminar boundary layer at the location of the roughness is smaller than the roughness height.The Mach 3.37 flow undergoes transition closer to the bump when compared to Mach 5.26, in agreement with experimental observations. Transition is accompanied by an increase in Cf and Ch (Stanton number). Even for the case that did not undergo transition (Mach 8.23), streamwise vortices induced by the roughness cause a significant rise in Cf until 20D downstream. Mean Van-Driest transformed velocity and Reynolds stress for Mach 3.37 and 5.26 shows good agreement with available data. The transition process involves the following key elements---Upon interaction with the roughness element, the boundary layer separates to form a series of spanwise vortices upstream of the roughness, and a separation shear layer. The system of spanwise vortices wrap around the roughness element in the form of horseshoe/necklace vortices to yield a system of counter-rotating streamwise vortices downstream of the element. These vortices are located beneath the separation shear layer and perturb it, which results in the formation of trains of hairpin-shaped vortices further downstream of the roughness for the cases that undergo transition. These hairpins spread in the span with increasing downstream distance and the flow increasingly resembles a fully developed turbulent boundary layer. A local Reynolds number based on the wall properties is seen to correlate the onset of transition for the cases considered. To assess the effect of roughness height on transition, a Mach 3.37 flow past a hemispherical bump is studied by varying the boundary layer thickness (k/delta = 2.54, 1.0, 0.25 & 0.125) where k is the roughness height and delta is the laminar boundary layer thickness at the location of the roughness. Transition occurs in all cases, and the essential mechanism of transition appears to b
Boundary-layer oxygen depletion in blood gas analysis.
Venkatesh, S; Cumming, G
1981-07-01
When O2 is withdrawn from blood by diffusion through a membrane and an O2-depleted boundary layer is formed, it is suggested that the depletion can cause significant dissociation of oxyhemoglobin (HbO2) in this layer. The resulting nonlinear relation between net diffusive flux of O2 through the membrane and the blood PO2 should be observable with membrane systems having a sufficiently high permeability to O2. Evidence for this suggestion is presented from in vitro experiments using a mass spectrometer to analyze the O2 flux through membrane systems. A theoretical model of HbO2 dissociation in the depleted boundary layer of blood that explains these results qualitatively is developed to yield quantitative predictions found to be in reasonable agreement with the experimental observations. The effect was seen to be of significance for membrane systems with O2-sampling rates of about 2 X 10(-9) ml. s-1. Torr-1 and over; so if such systems are to be used for the analysis of blood PO2, the phenomenon must be taken into account. PMID:7263420
Thermographic analysis of turbulent non-isothermal water boundary layer
Znamenskaya, Irina A
2015-01-01
The paper is devoted to the investigation of the turbulent water boundary layer in the jet mixing flows using high-speed infrared (IR) thermography. Two turbulent mixing processes were studied: a submerged water jet impinging on a flat surface and two intersecting jets in a round disc-shaped vessel. An infrared camera (FLIR Systems SC7700) was focused on the window transparent for IR radiation; it provided high-speed recordings of heat fluxes from a thin water layer close to the window. Temperature versus time curves at different points of water boundary layer near the wall surface were acquired using the IR camera with the recording frequency of 100 Hz. The time of recording varied from 3 till 20 min. The power spectra for the temperature fluctuations at different points on the hot-cold water mixing zone were calculated using the Fast Fourier Transform algorithm. The obtained spectral behavior was compared to the Kolmogorov "-5/3 spectrum" (a direct energy cascade) and the dual-cascade scenario predicted for...
Cloud-Scale Numerical Modeling of the Arctic Boundary Layer
NASA Technical Reports Server (NTRS)
Kruegen, Steven K.; Delnore, Victor E. (Technical Monitor)
2002-01-01
The research objective of this NASA grant-funded project was to determine in detail how large-scale processes. in combination with cloud-scale radiative, microphysical, and dynamical processes, govern the formation and multi-layered structure of Arctic stratus clouds. This information will be useful for developing and improving 1D (one dimensional) boundary layer models for the Arctic. Also, to quantitatively determine the effects of leads on the large-scale budgets of sensible heat, water vapor, and condensate in a variety of Arctic winter conditions. This information will be used to identify the most important lead-flux processes that require parameterization in climate models. Our approach was to use a high-resolution numerical model, the 2D (two dimensional) University of Utah Cloud Resolving Model (UU CRM), and its 1D version, the University of Utah Turbulence Closure Model (UU TCM), a boundary layer model based on third-moment turbulence closure, as well as a large-eddy simulation (LES) model originally developed by C.H. Moeng.
Interaction between strain and vorticity in compressible turbulent boundary layer
NASA Astrophysics Data System (ADS)
Chu, YouBiao; Wang, Li; Lu, XiYun
2014-12-01
The interaction of strain and vorticity in compressible turbulent boundary layers at Mach number 2.0 and 4.9 is studied by direct numerical simulation (DNS) of the compressible Navier-Stokes equations. Some fundamental characteristics have been studied for both the enstrophy producing and destroying regions. It is found that large enstrophy production is associated with high dissipation and high enstrophy, while large enstrophy destruction with moderate ones. The enstrophy production and destruction are also correlated with the dissipation production and destruction. Moreover, the enstrophy producing region has a distinct tendency to be `sheet-like' structures and the enstrophy destroying region tends to be `tube-like' in the inner layer. Correspondingly, the tendency to be `sheet-like' or `tube-like' structures is no longer obvious in the outer layer. Further, the alignment between the vorticity vector and the strain-rate eigenvector is analyzed in the flow topologies. It is noticed that the enstrophy production rate depends mainly on the alignment between the vorticity vector and the intermediate eigenvector in the inner layer, and the enstrophy production (destruction) mainly on the alignment between the vorticity vector and the extensive (compressive) eigenvector in the outer layer.
Free-stream disturbances, continuous eigenfunctions, boundary-layer instability and transition
NASA Technical Reports Server (NTRS)
Salwen, H.
1980-01-01
A rational foundation is provided for the application of the linear stability theory of parallel shear flows to transition prediction. An explicit method is given for carrying out the necessary calculations. The expansions are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbance 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 Tollmein-Schlichting waves are an extremely small fraction of the amplitude of the disturbance.
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.
Chandra, A S; Kollias, P; Giangrande, S E; Klein, S A
2009-08-20
A long-term study of the turbulent structure of the convective boundary layer (CBL) at the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Climate Research Facility is presented. Doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the CBL. The observations cover four summer periods (2004-08) and are classified into cloudy and clear boundary layer conditions. Profiles of vertical velocity variance, skewness, and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions. A conditional sampling method is applied to the original Doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport. Overall, the derived turbulent statistics are consistent with previous aircraft and lidar observations. The observations provide unique insight into the daytime evolution of the convective boundary layer and the role of increased cloudiness in the turbulent budget of the subcloud layer. Coherent structures (plumes-thermals) are found to be responsible for more than 80% of the total turbulent transport resolved by the cloud radar system. The extended dataset is suitable for evaluating boundary layer parameterizations and testing large-eddy simulations (LESs) for a variety of surface and cloud conditions.
LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW
NASA Technical Reports Server (NTRS)
Albers, J. A.
1994-01-01
This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.
Calculation of rough-wall turbulent boundary layer heat transfer
NASA Astrophysics Data System (ADS)
Hosni, M. H.; Coleman, Hugh W.; Taylor, Robert P.
1991-01-01
Predictions and measurements are presented to investigate the effects of surface roughness on turbulent rough-wall boundary layers. Predictions are compared with Stanton number measurements for the turbulent flow of air over four separate rough surfaces with a variety of thermal boundary conditions. The cases considered are constant wall temperature, constant wall heat flux, step wall temperature, and piecewise linear wall temperature distributions. Furthermore, predictions are presented and compared with experimental heat transfer data for accelerated flow cases. A modified roughness energy transport model for the discrete element prediction method is presented and used for rough-wall calculations. The predictions are shown to be in excellent agreement with the available data. Particularly encouraging was the ability to predict the heat transfer for all rough-wall flow regimes - aerodynamically smooth, transitionally rough, and fully rough - with a single model and without prior knowledge of the regime.
Tollmien-Schlichting/vortex interactions in compressible boundary layer flows
NASA Technical Reports Server (NTRS)
Blackaby, Nicholas D.
1993-01-01
The weakly nonlinear interaction of oblique Tollmien-Schlichting waves and longitudinal vortices in compressible, high Reynolds number, boundary-layer flow over a flat plate is considered for all ranges of the Mach number. The interaction equations comprise of equations for the vortex which is indirectly forced by the waves via a boundary condition, whereas a vortex term appears in the amplitude equation for the wave pressure. The downstream solution properties of interaction equations are found to depend on the sign of an interaction coefficient. Compressibility is found to have a significant effect on the interaction properties; principally through its impact on the waves and their governing mechanism, the triple-deck structure. It is found that, in general, the flow quantities will grow slowly with increasing downstream co-ordinate; i.e. in general, solutions do not terminate in abrupt, finite-distance 'break-ups'.
Thermal and wind structure of the monsoon trough boundary layer
NASA Astrophysics Data System (ADS)
Rajkumar, G.; Narasimha, R.; Singal, S. P.; Gera, B. S.
1996-09-01
Radiosonde data from Jodhpur, taken at 0530, 1730 and around 1100 hr IST during MONTBLEX 1990, reveal that the distribution of virtual potential temperature 0 v below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus led to introduce a characterization of the observed thermal structure through a sequence of the symbols N, S and U, standing respectively for neutral, stable or unstable conditions in the different layers, beginning with the one closest to the ground. It is found that, of the 29 combinations possible, only the seven classes, S, SS', SNS', NS, NSS', USS' and UNS are observed, where S' stands for a stable layer with a different gradient of 0 r. than in the layer S. It is also found that, in 90% of the launches at 0530 hr, 48% of the launches at 1730 hr and 69% of the launches around 1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11 % of the data set analysed, and, if present on other occasions, must have been less than 250 m in height, the first level at which radiosonde data are available. Supplementing the above data, sodar echograms, available during 82% of the time between June and August 1990, suggest a stable layer up to a few tens of metres 48% of the time. A comparative study of the radiosonde data at Ranchi shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights generally ranging from 400 to 900 m with wind speeds of 6 to 15 m/s. Based on these results, it is conjectured that the lowest layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such a stable layer during daytime.
Interaction of a Boundary Layer with a Turbulent Wake
NASA Technical Reports Server (NTRS)
Piomelli, Ugo
2004-01-01
The objective of this grant was to study the transition mechanisms on a flat-plate boundary layer interacting with the wake of a bluff body. This is a simplified configuration presented and designed to exemplify the phenomena that occur in multi-element airfoils, in which the wake of an upstream element impinges on a downstream one. Some experimental data is available for this configuration at various Reynolds numbers. The first task carried out was the implementation and validation of the immersed-boundary method. This was achieved by performing calculations of the flow over a cylinder at low and moderate Reynolds numbers. The low-Reynolds number results are discussed, which is enclosed as Appendix A. The high-Reynolds number results are presented in a paper in preparation for the Journal of Fluid Mechanics. We performed calculations of the wake-boundary-layer interaction at two Reynolds numbers, Re approximately equal to 385 and 1155. The first case is discussed and a comparison of the two calculations is reported. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. This is shown: long streaky structures appear in the boundary layer in correspondence of the three-dimensionalities in the rollers. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established. A third simulation was subsequently carried out at a higher Reynolds number, Re=3900. This calculation gave results similar to those of the Re=l155 case. Turbulence was established at fairly low Reynolds number, as a consequence of the high level of the free-stream perturbation. An instantaneous flow visualization for that case is shown. A detailed examination of flow statistics in the transitional and turbulent regions, including the evolution of the turbulent kinetic energy (TKE) budget and frequency spectra showed the formation and evolution of turbulent spots characteristic of the bypass transition mechanism. It was also observed that the turbulent eddies achieved an equilibrium, fully developed turbulent states first, as evidenced by the early agreement achieved by the terms in the TKE budget with those observed in turbulent flows. Once a turbulent Reynolds stress profile had been established, the velocity profile began to resemble a turbulent one, first in the inner region and later in the outer region of the wall layer. An extensive comparison of the three cases, including budgets, mean velocity and Reynolds stress profiles and flow visualization, is included. The results obtained are also presented.
Boundary layer conductance, leaf temperature and transpiration of Abies amabilis branches.
Martin, Timothy A.; Hinckley, Thomas M.; Meinzer, Frederick C.; Sprugel, Douglas G.
1999-06-01
We used three methods to measure boundary layer conductance to heat transfer (g(bH)) and water vapor transfer (g(bV)) in foliated branches of Abies amabilis Dougl. ex J. Forbes, a subalpine forest tree that produces clumped shoot morphology on sun-formed branches. Boundary layer conductances estimated in the field from energy balance measurements increased linearly from approximately 10 mm s(-1) at low wind speeds (< 0.1 m s(-1)) to over 150 mm s(-1) at wind speeds of 2.0 m s(-1). Boundary layer conductances measured on shoot models in a wind tunnel were consistently higher than field measurements. The difference between wind tunnel values and field measurements was attributable to variation in path length between the two experimental environments. Boundary layer conductance estimated by subtracting stomatal resistance (r(sV)) measured with a porometer from the total branch vapor phase resistance were unusually small. Sensitivity analysis demonstrated that this method is not suitable for coniferous foliage or when stomatal conductance (g(sV)) is small compared with g(bV). Analysis of the relative magnitudes of g(sV) and g(bV) revealed that, under most conditions, A. amabilis branches are well coupled (i.e., g(sV) is the dominant controller of transpiration). The boundary layer conductance to heat transfer is small enough that leaf temperature can become substantially higher than air temperature when radiation is high and wind speed is low. Over a two-month period, the maximum difference between leaf and air temperatures exceeded 6 degrees C. Leaf temperature exceeded air temperature by more than 2 degrees C on 10% of the daylight hours during this period. Consideration of both the photosynthetic temperature response of A. amabilis foliage as well as the summer air temperature conditions in its habitat suggests that these elevated leaf temperatures do not have a significant impact on carbon gain during the growing season. PMID:12651549
Large-eddy simulation of an infinitely large wind farm in a stable atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Lu, H.; Porté-Agel, F.
2010-09-01
When deployed as large arrays, wind turbines interact among themselves and with atmospheric boundary layer. To optimize their geometric arrangements, accurate knowledge of wind-turbine array boundary layer is of great importance. In this study, we integrated large eddy simulation with an actuator line technique, and used it to study the characteristics of wind-turbine wake in an idealized wind farm inside a stably stratified atmospheric boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were placed in a well-known SBL turbulent case that has a boundary layer height of approximately 180m. The super-geostrophic nocturnal jet near the top of the boundary layer was eliminated due to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric behavior of wake structure was observed in response to the non-uniform incoming turbulence, the Coriolis effects, and the rotational effects induced by blade motions. The turbulence intensity in the simulated turbine wakes was found to reach a maximum at the top-tip level and a downwind distance of approximately 3-5 rotor diameters from the turbines. The Coriolis effects caused a skewed spatial structure and drove certain amount of turbulent energy away from the center of the wake. The SBL height was increased, while the magnitudes of the surface momentum flux and the surface buoyancy flux were reduced by approximately 30%. The wind farm was also found to have a strong effect on area-averaged vertical turbulent fluxes of momentum and heat, which highlights the potential impact of wind farms on local meteorology.
Characteristics of Submeso Winds in the Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Mahrt, Larry
2009-01-01
The characteristics of submeso motions in the stable boundary layer are examined using observations from networks of sonic anemometers with network sizes ranging from a few hundred metres to 100 km. This study examines variations on time scales between 1 min and 1 h. The analysis focuses on the behaviour of the spectra of the horizontal kinetic energy, the ratios of the three velocity variances, their kurtosis, the dependence of horizontal variability on time scale, and the inter-relationship between vertical vorticity, horizontal divergence and deformation. Motions on larger time and space scales in the stable boundary layer are found to be nearly two-dimensional horizontal modes although the ratio of the vorticity to the divergence is generally on the order of one and independent of scale. One exception is a small network where stronger horizontal divergence is forced by a decrease in surface roughness. The horizontal variability, averaged over 1 h, appears to be strongly influenced by surface heterogeneity and increases with wind speed. In contrast, the time dependence of the horizontal structure on time scales less than one hour tends to be independent of wind speed for the present datasets. The spectra of the horizontal kinetic energy and the ratio of the crosswind velocity variance to the along-wind variance vary substantially between networks. This study was unable to isolate the cause of such differences. As a result, the basic behaviour of the submeso motions in the stable boundary layer cannot be generalized into a universal theory, at least not from existing data.
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.
Marine Boundary Layer Aerosol Profiling with a Camera Lidar
NASA Astrophysics Data System (ADS)
Barnes, J. E.; Parikh Sharma, N. C.; Kaplan, T.; Clarke, A. D.
2010-12-01
Aerosol measurements at a coastal site on the Big Island of Hawaii were made to assess the usefulness of a new aerosol profiling technique called CLidar (camera lidar). A scientific-grade digital camera was used with a wide-angle lens (>100 deg) to image a vertically-pointed laser beam which was 122 meters away. The image was then analyzed for aerosol scatter much in the same way a monostatic lidar signal is analyzed except that the altitude information is determined by the geometry. The technique has sub-meter altitude resolution near the ground and can be directly compared with in-situ instruments. Aerosol profiles can be acquired through the boundary-layer with lower altitude resolution. CLidar aerosol measurements were made on two evenings where coastal breaking waves from about 400 meters away were added to the background marine boundary layer. A NASA/AERONET aerosol phase function, as well as a previously directly-measured phase function, were used to convert the single-angle CLidar scatter into extinction. A large gradient in aerosols with altitude was found for the first 35 meters with a lower gradient up to 200 meters. This was probably the region affected by the breaking waves. This is a useful result in characterizing the sampling environment. Nephelometers with intakes at 7 and 25 meters were directly compared with the CLidar results. Agreement was better with the directly-measured phase function on the evening with higher wind, possibly indicating the breaking-wave aerosol was changing during the longer transit time of the other evening. Aerosol optical depths (AOD) were calculated with the CLidar data by integrating though the boundary layer. The first evening was clear and agreed, within error bars, with the NASA/MODIS overpass. The CLidar AOD on the second evening, which was partly cloudy, was significantly lower than the MODIS value possibly because of an over estimate of the MODIS instrument near clouds.
Effects of Initial Conditions on FPG Turbulent Boundary Layers
NASA Astrophysics Data System (ADS)
Bayoan Cal, Raul; Johansson, Gunnar; Castillo, Luciano
2004-11-01
A new set of measurements has been obtained using Laser Doppler Anemometry (LDA) for favorable pressure gradient (FPG) turbulent boundary layer flows. In the light of the complexity of the FPG flow, a question of whether the nitial conditions affect the downstream development is one that has yet to be answered. Initial conditions such as wind-tunnel speed, U_o, position of the tripping device, x_o, size of the tripping device, d_o, and angle of the smooth plate, ?, have been altered in order to observe the effects of these parameters on the downstream flow. The controversial parameter ? defined as the pressure parameter, ? =frac? ? U_? ^2d?/dxfracdP_? dx, by Castillo and George (2001) has been explored. It will be shown that the velocity deficit profiles collapse to a single curve regardless of its initial conditions for the FPG flow when scaled with the free-stream velocity, U_?, or with the scaling proposed by Zagarola/Smits (1998), U_??/?_*. Furthermore, the higher order quantities such as the Reynolds stresses are susceptible to the initial conditions, which were carefully kept constant for each case. More importantly, it is found that the turbulence quantities in an FPG flow are higher for the slower velocity case (i.e. 5m/s upstream speed) than for the higher velocity of 10m/s given the change of the upstream velocity initial condition. Furthermore, it was found that the boundary layer parameters are directly affected by its initial conditions. In addition, the pressure parameter, ?, changes as the development of the boundary layer increases.
User's manual for the Langley boundary layer noise propagation program (MRS-BLP)
NASA Technical Reports Server (NTRS)
Spence, Peter L.
1991-01-01
A computer program, McAninch-Rawls-Spence Boundary Layer Propagation (MRS-BLP), is described. This program models the refractive and scattering effects on acoustic pressure waves propagating through a boundary layer encompassing an aircraft's fuselage. The noise source is assumed known and generated by a propeller. The fuselage is represented by an infinitely long cylinder embedded in a longitudinal flow. By matching a numerical solution inside the boundary layer with an analytical solution outside the boundary layer, the program calculates the acoustic pressure at the surface of the cylinder given the incident field at the top of the boundary layer. The boundary layer flow velocity and sound speed profiles, as well as the boundary layer thickness may be specified by the user. A detailed description of the input parameters and how to execute the program is given. Example executions of MRS-BLP showing results are also included.
User's manual for the Langley boundary layer noise propagation program (MRS-BLP)
NASA Astrophysics Data System (ADS)
Spence, Peter L.
1991-08-01
A computer program, McAninch-Rawls-Spence Boundary Layer Propagation (MRS-BLP), is described. This program models the refractive and scattering effects on acoustic pressure waves propagating through a boundary layer encompassing an aircraft's fuselage. The noise source is assumed known and generated by a propeller. The fuselage is represented by an infinitely long cylinder embedded in a longitudinal flow. By matching a numerical solution inside the boundary layer with an analytical solution outside the boundary layer, the program calculates the acoustic pressure at the surface of the cylinder given the incident field at the top of the boundary layer. The boundary layer flow velocity and sound speed profiles, as well as the boundary layer thickness may be specified by the user. A detailed description of the input parameters and how to execute the program is given. Example executions of MRS-BLP showing results are also included.
Prandtl boundary layers for the Phan-Thien Tanner and Giesekus fluid
NASA Astrophysics Data System (ADS)
Renardy, Michael
2015-06-01
The Prandtl equations, arising naturally in the description of high Reynolds number boundary layers, have turned out to be quite difficult from the point of view of mathematical analysis. Recent work by the author has shown that the analogous problem for the upper-convected Maxwell fluid is actually better behaved, and the well-posedness of the boundary layer equations has been established. In this paper, boundary layers for the Phan-Thien-Tanner and Giesekus fluid are considered. It turns out that there are two fundamentally different types of boundary layers, which we shall call elastic and viscometric boundary layers. The elastic boundary layers will be analyzed in an analogous fashion as those for the upper-convected Maxwell fluid. On the other hand, for viscometric boundary layers, which occur only for the PTT fluid, the equations are equivalent to those for a power law fluid.
Supersonic and hypersonic shock/boundary-layer interaction database
NASA Technical Reports Server (NTRS)
Settles, Gary S.; Dodson, Lori J.
1994-01-01
An assessment is given of existing shock wave/tubulent boundary-layer interaction experiments having sufficient quality to guide turbulence modeling and code validation efforts. Although the focus of this work is hypersonic, experiments at Mach numbers as low as 3 were considered. The principal means of identifying candidate studies was a computerized search of the AIAA Aerospace Database. Several hundred candidate studies were examined and over 100 of these were subjected to a rigorous set of acceptance criteria for inclusion in the data-base. Nineteen experiments were found to meet these criteria, of which only seven were in the hypersonic regime (M is greater than 5).
Wave phenomena in a high Reynolds number compressible boundary layer
NASA Technical Reports Server (NTRS)
Bayliss, A.; Maestrello, L.; Parikh, P.; Turkel, E.
1987-01-01
The behavior of spatially unstable waves in a high Reynolds number compressible laminar boundary layer is investigated by solution of the laminar two-dimensional compressible Navier-Stokes equations (solved to fourth-order accuracy) over a flat plate with a fluctuating disturbance generated at the inflow. A significant nonlinear distortion is produced, in qualitative agreement with experimental data. It is shown that increasing compressibility can significantly stabilize the flow over a flat plate, and that the mechanism of phase cancellation is a viable mechanism for the control of growing disturbances.
Turbulence modeling in shock wave/turbulent boundary layer interactions
NASA Technical Reports Server (NTRS)
Smits, A. J.
1992-01-01
The research performed was an experimental program to help develop turbulence models for shock wave boundary layer interactions. The measurements were taken in a Mach 3, 16 deg compression corner interaction, at a unit Reynolds number of 63 x 10(exp 6)/m. The data consisted of heat transfer data taken upstream and downstream of the interaction, hot wire measurements of the instantaneous temperature and velocity fluctuations to verify the Strong Reynolds Analogy, and single- and double-pulsed Rayleigh scattering images to study the development of the instantaneous shock/turbulence interaction.
Gust structure in the neutral surface boundary layer
Doran, J.C.; Powell, D.C.
1982-01-01
Measured characteristics of gust amplitudes and times in the neutral surface boundary layer are presented. The probability of gust amplitudes exceeding a prescribed level is shown to decrease exponentially with amplitude, provided the amplitude is scaled with the root-mean-square turbulent speed. The 25 and 75 percentile conditional probabilities of gust duration obey power laws in the scaled amplitudes if the durations are normalized by N/sub 0/, the frequency of occurance of all gusts. These relationships are nearly independent of mean wind speed and measurement height. The effects of digital filtering of the data also are discussed.
Numerical analysis of Weyl's method for integrating boundary layer equations
NASA Technical Reports Server (NTRS)
Najfeld, I.
1982-01-01
A fast method for accurate numerical integration of Blasius equation is proposed. It is based on the limit interchange in Weyl's fixed point method formulated as an iterated limit process. Each inner limit represents convergence to a discrete solution. It is shown that the error in a discrete solution admits asymptotic expansion in even powers of step size. An extrapolation process is set up to operate on a sequence of discrete solutions to reach the outer limit. Finally, this method is extended to related boundary layer equations.
Effect of roughness on the stability of boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.; Ragab, Saad A.; Al-Maaitah, Ayman
1987-01-01
An analysis is conducted on the effect of imperfections consisting of humps and dips on the stability of incompressible flows over flat plates. The mean flow is calculated using interacting boundary layers. Linear quasiparallel spatial stability is used to calculate the growth rates and mode shapes of two-dimensional disturbances. Then, the amplification factor is computed. A search for the most dangerous frequency is conducted based on an amplification factor of 9 in the shortest distance. Correlations are made with the transition experiment of Walker and Greening using the e sup 9 method.
Aerodynamic heating for gaps in laminar and transitional boundary layers
NASA Technical Reports Server (NTRS)
Bertin, J. J.; Goodrich, W. D.
1980-01-01
The presence of gaps, slots, and/or steps in a surface may significantly perturb a supersonic boundary layer. The paper discusses heat-transfer distributions for a variety of gap configurations which were obtained by placing instrumented inserts in a flat-plate structural carrier. The data were obtained in a 3.50 foot hypersonic wind tunnel at a freestream Mach number of 5.10 over a range of Reynolds number from 2,570,000 to 8,110,000. The variables of the test program included the freestream Reynolds number and the gap configuration, e.g., width, depth, step height, number, and orientation.
Coherence and chaos in a model of turbulent boundary layer
NASA Astrophysics Data System (ADS)
Zhou, Xiang; Sirovich, L.
1992-12-01
The paper considers the dynamics of coherent structures in the wall region of a turbulent channel flow. The Karhunen-Loeve eigenfunctions and Galerkin procedure are employed to derive the dynamical description. A well-posed Hermitian theory is developed and convergence questions do not arise. No exterior pressure is required by this theory. It is shown that the behavior of the resulting model equations include intermittency, quasi-periodic, and chaotic solutions. Three-dimensional effects are introduced into the dynamics in order to produce a physically more realistic dynamical theory. It is argued that the bursting and ejection events in turbulent boundary layers are explained more satisfactorily within this framework.
Effect of compliant wall motion on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Hefner, J. N.; Ash, R. L.
1977-01-01
A critical analysis of available compliant wall data which indicated drag reduction under turbulent boundary layers is presented. Detailed structural dynamic calculations suggest that the surfaces responded in a resonant, rather than a compliant, manner. Alternate explanations are given for drag reductions observed in two classes of experiments: (1) flexible pipe flows and (2) water-backed membranes in air. Analysis indicates that the wall motion for the remaining data is typified by short wavelengths in agreement with the requirements of a possible compliant wall drag reduction mechanism recently suggested by Langley.
Numerical simulation of convective boundary layer above polynyas and leads.
NASA Astrophysics Data System (ADS)
Debolskiy, Andrey; Stepanenko, Victor
2013-04-01
Arctic region is very important as one of drivers for global atmosphere circulation. Meanwhile, results of modern global atmospheric models, both climatic and weather forecasting differs significantly from each other and observations in this region. One of the reasons for these uncertainties can be inaccurate simulation of ice and snow cover distribution, which accuracy depends in turn on variety of factors. Among others, appropriate parameterizations of atmospheric boundary layer over inhomogeneous surface, not explicitly resolved at the atmospheric model grid, can decrease these inaccuracies. The main objective of these parameterizations is to calculate surface heat and water vapor fluxes, averaged over the whole model cell. However, due to great differences in structure of boundary layers formed over cold ice and relatively warm open water, which cause nonlinear dependencies,the parameterizations suggested to the moment can hardly be regarded as applicable for "complete" set of synoptic scenarios . The present paper attempts to improve standard mosaic method of flux aggregation, which is still common in climate models [1]. The main idea is to derive heat fluxes using data from numerical experiments, explicitly reproducing most of sub grid (for global models) turbulence motions spectra, and compare with fluxes calculated using mosaic method implying the part of model domain to be a global model cell. The study is based on idealized high resolution (~10 m) experiments with typically observed surface parameters (temperature and roughness), ice-open water distribution, initial temperature and wind profiles distribution included in Large Eddy Simulation model of Insitute of Numerical Mathematics RAS [2],[3]. Analysis of other boundary layer characteristics such as its height, eddy diffusivity profiles, kinetic energy is presented. The modeling results are compared with field experiments' data gathered at White Sea. References: 1. V.M. Stepanenko, P.M. Miranda, V.N. Lykosov. Numerical simulation of mesoscale iteration of atmosphere and hydrological inhomogeneous surface (in Russian). Computational technologies,2006, vol. 11 No.7: p.118-127 2. A.V. Glazunov, V.N. Lykossov. Large eddy simulation of interaction of ocean and atmospheric boundary layers. Russian Journal of Numerical Analysis and Mathematical Modeling. 2003 Vol.18, No. 4: p.279-295 3. Glazunov A.V. Modeling of neutral-stratified turbulent flow over horizontal rough surface(in Russian) Izvestiya. Atmospheric and Oceanic Physics vol.42, No3: p.307-325
Boundary layer effects above a Himalayan valley near Mount Everest
NASA Astrophysics Data System (ADS)
Sun, Fanglin; Ma, Yaoming; Li, Maoshan; Ma, Weiqiang; Tian, Hui; Metzger, Stefan
2007-04-01
Periodical Wind Profiler and Radio Acoustic Sounding System observations have been commenced at the Himalayas' northern slope nearby Mount Everest in September 2005. Primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions. Substantial findings include the detection of two wind shears and the phenomenon of glacier wind at a distance of 25 km from the glaciers. The latter lead to a reversed compensatory flow in a vertical scale of up to 2000 m above ground level, pointing at supra regional impact.
NASA Astrophysics Data System (ADS)
Sen, Sudeshna; Moreno, J.; Jarrell, M.; Vidhyadhiraja, N. S.
2015-04-01
We investigate the effect of disorder on the dynamical spectrum of layered f -electron systems. With random dilution of f sites in a single Kondo insulating layer, we explore the range and extent to which Kondo hole incoherence can penetrate into adjacent layers. We consider three cases of neighboring layers: band insulator, Kondo insulator, and simple metal. The disorder-induced spectral weight transfer, used here for quantification of the proximity effect, decays algebraically with distance from the boundary layer. Further, we show that the spectral weight transfer is highly dependent on the frequency range considered as well as the presence of interactions in the clean adjacent layers. The changes in the low-frequency spectrum are very similar when the adjacent layers are either metallic or Kondo insulating, and hence are independent of interactions. In stark contrast, a distinct picture emerges for the spectral weight transfers across large energy scales. The spectral weight transfer over all energy scales is much higher when the adjacent layers are noninteracting as compared to when they are strongly interacting Kondo insulators. Thus, over all scales, interactions screen the disorder effects significantly. We discuss the possibility of a crossover from non-Fermi-liquid to Fermi-liquid behavior upon increasing the ratio of clean to disordered layers in particle-hole asymmetric systems.
On the helicity estimation in the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Victorovna Vazaeva, Natalia; Feodosevich Kramar, Valeriy; Dmitrievich Kouznetsov, Rostislav; Sergeevich Lyulyukin, Vasily; Guramovich Chkhetiani, Otto
2015-04-01
Large-scale motions in the atmospheric boundary layer (ABL) are sustained by the cooperative effect of friction and Earth rotation. This flows have a non-zero helicity [1,2]. Consequently, turbulence in the ABL is also characterize by the non-zero helicity [3]. This property has been observed in the atmospheric experiments [4] and the DNS modeling [5]. The role of helicity in the atmospheric and ocean large-scale dynamics and its possible prognostics sense attracts permanent interest. The purpose of the present investigation is to determine the helicity in terms of experimental data and to check the possibility of the ABL helicity estimation. The integral helicity in the Ekman layer is given by 0 ? ? H = UG2 + VG2 [1], PIC
Effect of bulges on the stability of boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.; Ragab, Saad A.; Al-Maaitah, Ayman A.
1988-01-01
The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear-layer instabilities. Separation is found to increase significantly the amplification factor.
Aerodynamic Models for Hurricanes III. Modeling hurricane boundary layer
Leonov, Arkady I
2008-01-01
The third paper of the series (see previous ones in Refs.[1-2]) discusses basic physicalprocesses in the (quasi-) steady hurricane boundary layer (HBL), develops an approximate airflow model, establishes the HBL structure, and presents integral balance relations for dynamic and thermodynamic variables in HBL. Models of evaporation and condensation are developed, where the condensation is treated similarly to the slow combustion theory. A turbulent approximation for the lower sub-layer of HBL is applied to the sea-air interaction to establish the observed increase in angular momentum in the outer region of HBL.A closed set of balance relations has been obtained. Simple analytical solution of the set yields expressions for the basic dynamic variables - maximal tangential and radial velocities in hurricane, maximal vertical speed in eye wall, the affinity speed of hurricane travel, and the maximal temperature increase after condensation. Estimated values of the variables seem to be realistic. An attempt is also ...
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.
Onset of new particle formation in boundary layer
NASA Astrophysics Data System (ADS)
Manninen, Hanna E.; Lampilahti, Janne; Mirme, Sander; Nieminen, Tuomo; Ehn, Mikael; Pullinen, Iida
2014-05-01
At this moment, the mechanisms of atmospheric new particle formation (NPF), and the vapors participating in this process are not truly understood. Especially, in which part of the atmosphere the NPF takes place, is still an open question. To detect directly the very first steps of NPF in the atmosphere, we measured these chemical and physical processes within the Planetary Boundary Layer (PBL). We used airborne Zeppelin and Cessna measurements, and ground based in-situ measurements. Using Zeppelin, we focused on the time of the development of the PBL (altitudes up to 1 km) from sunrise until noon to measure vertical profiles of aerosol particles and chemical compounds. This is also the time when NPF typically occurs at ground level. On summer 2012, Zeppelin was measuring nucleation occurring in the polluted Po Valley area, Northern Italy, especially over the San Pietro Capofiume field site. A year later, Zeppelin had a spring campaign in boreal forest area, close to Hyytiälä field site in Southern Finland. During both campaigns, we aimed on measuring the vertical and the horizontal extension for NPF events using an instrumented Zeppelin. The vertical profile measurements represent the particle and gas concentrations in the lower parts of the atmosphere: the residual layer, the nocturnal boundary layer, and the PBL. At the same time, the ground based measurements records present conditions in the surface layer. The key instruments to measure the onset of NPF were an Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF), a Particle Size Magnifier (PSM), and a Neutral cluster and Air Ion Spectrometer (NAIS). These instruments are able to measure particles at the size range ~1-2 nm where atmospheric nucleation and cluster activation takes place. The onset of NPF was usually observed onboard Zeppelin when it was measuring inside the rising mixed layer which is connected to the surface layer by effective vertical mixing. The newly formed, subsequently growing, particles were observed to be homogeneously distributed inside the mixed layer. These measurements are part of the PEGASOS project which aims to quantify the magnitude of regional to global feedbacks between the atmospheric chemistry and physics, and thus quantify the changing climate.
Large Eddy Simulation of a boundary layer flow over urban-like roughness
Kojiro Nozawa; Tetsuro Tamura
2005-01-01
In this study, Large Eddy Simulation (LES) of a boundary layer flow over large-scale roughness was performed targeting the experiments conducted by Cheng and Castro [Boundary-Layer Meteorology 104, 229-259 (2002)]. In order to duplicate the experimental conditions, the pseudo periodic boundary method for rough-wall boundary flows [Nozawa and Tamura (2000)] was applied to the inlet boundary conditions and the computational
An active control system for the turbulent boundary layer
NASA Astrophysics Data System (ADS)
Lew, James
This thesis presents the development process and the experimental results of a system constructed to apply real-time control to the structures of the turbulent boundary layer region in order to reduce surface shear stress. The system is composed of three main components: an array of MEMS surface shear stress, tauw sensors; a MEMS flap actuator; and a control logic which integrates the hardware components together into a closed system. The objective of this system is to reduce the stress contained in streak-like regions of high tauw. The sensor array, used to image the tauw distribution, is an extension of the thermal based tauw sensor developed by Jiang. Numerous studies have been performed using this device, the results of which have validated its performance. For this study, a new temperature compensation methodology, based on the surface temperature of the sensor chip, was employed in order to account for possible temperature variations at the wall surface. The actuator, a pneumatically driven flap, is developed as part of the present research. The device is, in essence, a 3 mm x 1 mm cantilever beam that sits on top of an inflatable diaphragm and is capable of actuation frequencies of over 200 Hz and amplitudes of over .11 mm. When it is oscillated in the open loop mode, the effect over one cycle of motion is an average reduction by as much as 2.5% in tauw in the region immediately downstream. A neural network is employed to identify the streak-like regions of interest. Results have shown that this network is successful in identifying the streak-like regions of interest. The control logic employs this network in a predictive, feed-forward scheme to determine the appropriate actuator response. Offline studies have shown that under optimal conditions, the signature of the streak-like regions can be eliminated. Online results conform well to the offline predictions. While unable to achieve the optimal conditions, online experiments show that the system is capable of responding to the streak-like regions in real-time. More significantly, the results show that the signatures of the streak-like regions are significantly altered by the control actions.
Importance of boundary layer entrainment for surface fluxes over land
NASA Astrophysics Data System (ADS)
McGrath-Spangler, Erica L.
An idealized experiment examined the impacts of entrainment in a coupled ecosystem-atmosphere model by implementing an enhanced entrainment parameterization based on the assumption that the heat flux at the top of the PBL is negatively proportional to the heat flux at the surface. This experiment found that entrainment produced a warmer, drier, and deeper PBL and that the surface fluxes of heat and moisture were modified by the vegetative response to the altered atmospheric conditions. A realistic simulation for the summer of 1999 found that enhanced entrainment produced stronger early morning growth of the PBL and a deeper midday depth. This better captured the monthly mean diurnal cycle of PBL depth from observations by a radar sounding system in northern Wisconsin. Additionally, the complex land-atmosphere interactions produced a time-mean spatial CO 2 gradient of 7 ppm over 1000 km. A sensitivity analysis performed for June 2007 to the strength of the PBL-top entrainment flux found subtle spatial variations in the time mean. The addition of entrainment from overshooting thermals weakened the Bermuda high circulation and weakened the spatial gradients between the warm, dry semiarid southwestern United States and cooler, moister locations in eastern North America. These subtle variations produced a 3.5 ppm CO2 change in the time mean across 280 km. One possible explanation for these more subtle results is that additional changes to the coupled model resulted in persistent cloud cover that produced relatively cold and dark conditions. In order to evaluate and improve model simulations, PBL depth has been estimated using the backscatter from the LIDAR onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Using an automated method, millions of estimates have been derived to which model results can be compared. This method evaluates the maximum vertical variance of the backscatter in order to identify backscatter features associated with the top of the PBL and helps to identify the vertical extent of turbulent mixing. This analysis sheds some light on the spatial heterogeneity of boundary layer processes. The derived depths are shallower over water than over land and show a local minimum along the Mississippi River valley. Deeper features are found over the desert Southwest and deeper than expected values are retrieved over the Boreal forests.
Numerical simulation of roll vortices in the convective boundary layer
NASA Astrophysics Data System (ADS)
Liu, Huizhi; Sang, Jianguo
2011-05-01
Roll vortices, which often appear when cold air outbreaks over warm ocean surfaces, are an important system for energy and substance exchange between the land surface and atmosphere. Numerical simulations were carried out in the study to simulate roll vortices in the convective boundary layer (CBL). The results indicate, that with proper atmospheric conditions, such as thermal instability in the CBL, stable stratification in the overlying layer and suitable wind shear, and a temperature jump between the two layers in a two-layer atmosphere, convective bands appear after adding initial pulses in the atmosphere. The simulated flow and temperature fields presented convective bands in the horizontal and roll vortices in the crosswind section. The structure of the roll vortices were similar to those observed in the cloud streets, as well as those from analytical solutions. Simulations also showed the influence of depth and instability strength of the CBL, as well as the stratification above the top of the CBL, on the orientation spacing and strength of the roll vortices. The fluxes caused by the convective rolls were also investigated, and should perhaps be taken into account when explaining the surface energy closure gap in the CBL.
Why does the Tibetan Plateau support the highest planetary boundary layer?
NASA Astrophysics Data System (ADS)
Chen, Xuelong; Škerlak, Bojan; Rotach, Mathias; Añel, Juan; Su, Zhongbo; Ma, Yaoming; Li, Maoshan
2015-04-01
The planetary boundary layer over the Tibetan Plateau reaches an unprecedented height of 9.4 km above sea level (i.e., about 5 km above ground), therefore nearly reaching the stratosphere. This proximity facilitates exchange between the stratosphere and the boundary layer, which has important impacts for atmospheric chemistry and the transport of pollution. Both, observations from radio soundings and numerical model simulations have demonstrated that the mixed layer of the plateau planetary boundary layer (PBL) can grow to heights near the tropopause, but the underlying mechanisms responsible for this deep PBL remained uncertain. Here we explore these mechanisms using measurements of the PBL, the associated surface fluxes and regional numerical simulations. Our results indicate that the dry conditions of both ground soil and atmosphere in late winter cannot explain the development of extraordinarily deep PBLs even if wetter conditions (in summer) naturally depress PBL growth. COSMO simulations exhibit very good correspondence to the observed mean PBL structure and show realistic turbulent kinetic energy distribution throughout the full PBL depth. Modeling results demonstrate the key influence of the stability of the free atmosphere for the growth of extremely deep PBLs over the Tibetan Plateau. Weak atmospheric stability and hence deep PBLs, is found to be associated to a more southerly jet position and higher upper-level baroclinicity. This work completes a picture of the complex interplay between PBL, surface heating, stability and upper-level dynamics.
NASA Astrophysics Data System (ADS)
Casadio, S.; di Sarra, A.; Fiocco, G.; Fuà, D.; Lena, F.; Rao, M. P.
1996-06-01
Convective plume patterns, characteristic of clear sky and light wind daytime boundary layers over land, were observed for two nights with a tri-axial Doppler sodar operated in the central area of Rome during the summer of 1994. An urban heat island effect, combined with a continuation of a breeze from the sea late into night during both days, is believed to be responsible for the observed nocturnal convection. Estimates of the surface heat flux and the vertical velocity scaling parameter are obtained from profiles of vertical velocity variance, and the Raman lidar water vapor measurements are used to obtain the humidity scaling parameter. Convective scaling results for vertical wind and humidity fairly agree with the results of other experiments and models. On the basis of available measurements, it appears that mixed-layer similarity formulations used to characterize the daytime convective boundary layer over horizontally homogeneous surfaces can also be applied to the nocturnal urban boundary layer during periods of reasonable convective activity.
Optimizing EDMF parameterization for stratocumulus-topped boundary layer
NASA Astrophysics Data System (ADS)
Jones, C. R.; Bretherton, C. S.; Witek, M. L.; Suselj, K.
2014-12-01
We present progress in the development of an Eddy Diffusion / Mass Flux (EDMF) turbulence parameterization, with the goal of improving the representation of the cloudy boundary layer in NCEP's Global Forecast System (GFS), as part of a multi-institution Climate Process Team (CPT). Current GFS versions substantially under-predict cloud amount and cloud radiative impact over much of the globe, leading to large biases in the surface and top of atmosphere energy budgets. As part of the effort to correct these biases, the CPT is developing a new EDMF turbulence scheme for GFS, in which local turbulent mixing is represented by an eddy diffusion term while nonlocal shallow convection is represented by a mass flux term. The sum of both contributions provides the total turbulent flux. Our goal is for this scheme to more skillfully simulate cloud radiative properties without negatively impacting other measures of weather forecast skill. One particular challenge faced by an EDMF parameterization is to be able to handle stratocumulus regimes as well as shallow cumulus regimes. In order to isolate the behavior of the proposed EDMF parameterization and aid in its further development, we have implemented the scheme in a portable MATLAB single column model (SCM). We use this SCM framework to optimize the simulation of stratocumulus cloud top entrainment and boundary layer decoupling.
Experimental investigation of boundary-layer flashback in swirl flames
NASA Astrophysics Data System (ADS)
Ebi, Dominik; Clemens, Noel
2013-11-01
Swirling flows are widely employed for flame stabilization purposes in gas turbine combustors. However, flames in swirling flows are more prone to flashback, a potentially catastrophic phenomenon leading to thermal damage of the burner. The physical mechanism driving flashback in a swirling flow is not yet fully understood. The mechanism is particularly complex if the upstream flame propagation interacts with a boundary layer. In a previous study we showed that the flame/boundary-layer interaction is important for burners, which include an axial swirler and a central body attached to the swirler hub. We are investigating the mechanism of flashback in atmospheric pressure lean-premixed methane/hydrogen-air flames inside the mixing tube of our confined model swirl combustor. Flashback occurs at an equivalence ratio of approximately 0.7. The effect of hydrogen is investigated by testing different methane-to-hydrogen ratios. The duration of a single flashback event is on the order of 100 ms, requiring high-speed diagnostic techniques. We are applying simultaneous stereoscopic PIV, flame front detection based on Mie scattering, and chemiluminescence imaging to investigate the flame/flow interaction during flashback events.
Flow coefficient behavior for boundary layer bleed holes and slots
NASA Astrophysics Data System (ADS)
Willis, B. P.; Davis, D. O.; Hingst, W. R.
1995-01-01
An experimental investigation into the flow coefficient behavior for nine boundary layer bleed orifice configurations is reported. This test was conducted for the purposes of exploring boundary layer control through mass flow removal and does not address issues of stability bleed. Parametric data consist of bleed region flow coefficient as a function of Mach number, bleed plenum pressure, and bleed orifice geometry. Seven multiple hole configurations and two single slot configurations were tested over a supersonic Mach number range of 1.3 to 2.5 (nominal). Advantages gained by using multiple holes in a bleed region instead of a single spanwise slot are discussed and the issue of modeling an entire array of bleed orifices based on the performance of a single orifice is addressed. Preconditioning the flow approaching a 90 degree inclined (normal) hole configuration resulted in a significant improvement in the performance of the configuration. The same preconditioning caused only subtle changes in performance for a 20 degree inclined (slanted) configuration.
Generation of 'artificial' bursts in a turbulent boundary layer
NASA Technical Reports Server (NTRS)
Gad-El-hak, M.; Hussain, A. K. M. F.
1986-01-01
In an effort to better understand the physics and structure of coherent events in a turbulent boundary layer, an attempt is made to produce 'artificial' bursts. These are generated in a unique turbulent boundary layer, developed on a flat plate towed in an 18-m water channel, and thus with negligible freestream turbulence. The burst-like events are produced by either withdrawing near-water fluid from two minute holes separated in the spanwise direction, or by pitching a miniature delta wing that is flush-mounted to the wall. Either of these two actions generates a hairpin-like vortex and low-speed streak that resemble naturally occurring structures. The resulting sequence of events that occur at a given location can be controlled at will, thus allowing detailed examination via phase-locked measurements and flow visualization. In this paper, the artificial bursts are compared with natural, random bursts, using flow visualization and hot-film signals. Detailed quantitative data on topographical details and dynamical significance of the bursting structure will be addressed in a forthcoming article.
A Boundary-Layer Scaling for Turbulent Katabatic Flow
NASA Astrophysics Data System (ADS)
Shapiro, Alan; Fedorovich, Evgeni
2014-10-01
Scaling relationships are proposed for the turbulent katabatic flow of a stably stratified fluid down a homogeneously cooled planar slope—the turbulent analogue of a Prandtl-type slope flow. The Theorem predicts that such flows are controlled by three non-dimensional parameters: the slope angle, the Prandtl number, and a Reynolds number defined in terms of the surface thermal forcing (surface buoyancy or surface buoyancy flux), Brunt-Väisälä frequency, slope angle, and molecular viscosity and diffusivity coefficients. However, by exploiting the structure of the governing differential equations in a boundary-layer form, scaled equations are deduced that involve only two non-dimensional parameters: the Prandtl number and a modified Reynolds number. In the proposed scaling framework, the slope angle does not appear as an independent governing parameter, but merely acts as a stretching factor in the scales for the dependent and independent variables, and appears in the Reynolds number. Based on the boundary-layer analysis, we hypothesize that the full katabatic-flow problem is largely controlled by two rather than three parameters. Preliminary tests of the scaling hypothesis using data from direct numerical simulations provide encouraging results.
Scaling of normal Reynolds stresses in ZPG turbulent boundary layers
NASA Astrophysics Data System (ADS)
Nagib, Hassan M.; Chauhan, Kapil A.; Monkewitz, Peter A.
2007-11-01
An extensive set of experimental data for zero pressure gradient (ZPG) boundary layers over a wide range of Reynolds number is re-evaluated in another attempt to reveal appropriate scaling of the turbulence normal stresses. In view of the lack of well developed theoretical foundations for even the second- order statistics, the task is complex, and rigorous theoretical arguments cannot be made in favor of any of the commonly used non-dimensionalizatios; namely, inner, outer or mixed velocity scales. While the correlation of the data reveals some interesting and sometime contradicting trends, the limitations on measurement accuracy and spatial resolution, particularly in the near wall region, prevent us from reaching definitive conclusions. However, examining the role of the normal Reynolds stress difference (NSD) term in the K'arm'an integral equation using recent results from asymptotic theory suggests that the outer velocity scaling is likely not correct, in spite of the better collapse of the available data it produces in the outer part of the boundary layer. While the NSD must be included in any large Reynolds number asymptotics, we conclude that, for any practically relevant Reynolds number, the NSD integral in the K'arm'an equation represents a small correction which can be neglected as it has been done up to now.
Flowfield Measurements Inside a Boundary-Layer Bleed Slot
NASA Technical Reports Server (NTRS)
Davis, D. O.; Willis, B. P.; Hingst, W. R.
1996-01-01
An experimental investigation was conducted to determine the flowfield inside a bleed slot used to control an oblique shock-wave and turbulent boundary-layer interaction. The slot was oriented normal to the primary flow direction and had a width of 1.0 cm (primary flow direction) and a length of 2.54 cm and spanned 16.5 cm. The approach boundary layer upstream of the interaction was nominally 3.0 cm thick. Two operating conditions were studied: M = 1.98 with a shock generator deflection angle of 6 deg and M = 2.46 with a shock generator deflection angle of 8 deg. Measurements include surface and flowfield static pressure, pitot pressure, and total mass flow through the slot. The results show that despite an initially two-dimensional interaction for the zero-bleed-flow case, the slot does not remove mass uniformly in the spanwise direction. Inside the slot, the flow is characterized bv two separation regions, which significantly reduce the effective flow area. The upper separation region acts as an aerodynamic throat, resulting in supersonic flow through much of the slot.
Analytical Studies of Boundary Layer Generated Aircraft Interior Noise
NASA Technical Reports Server (NTRS)
Howe, M. S.; Shah, P. L.
1997-01-01
An analysis is made of the "interior noise" produced by high, subsonic turbulent flow over a thin elastic plate partitioned into "panels" by straight edges transverse to the mean flow direction. This configuration models a section of an aircraft fuselage that may be regarded as locally flat. The analytical problem can be solved in closed form to represent the acoustic radiation in terms of prescribed turbulent boundary layer pressure fluctuations. Two cases are considered: (i) the production of sound at an isolated panel edge (i.e., in the approximation in which the correlation between sound and vibrations generated at neighboring edges is neglected), and (ii) the sound generated by a periodic arrangement of identical panels. The latter problem is amenable to exact analytical treatment provided the panel edge conditions are the same for all panels. Detailed predictions of the interior noise depend on a knowledge of the turbulent boundary layer wall pressure spectrum, and are given here in terms of an empirical spectrum proposed by Laganelli and Wolfe. It is expected that these analytical representations of the sound generated by simplified models of fluid-structure interactions can used to validate more general numerical schemes.
Packet Structure of Surface Eddies in the Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Hommema, Scott E.; Adrian, Ronald J.
A smoke visualization experiment has beenperformed in the first 3,m ofneutral and unstable atmospheric boundary layersat very large Reynolds number(Re > 106). Under neutral atmosphericconditions mean wind profiles agreewell with those in the canonical flatplate zero-pressure-gradient turbulentboundary layer. The experiment was designedto minimize the temperaturedifference between the passive marker (smoke)and the air to ensure that anyobserved structures were due to vortical, ratherthan buoyant, motions. Imagesacquired in the streamwise-wall-normal planeusing a planar laser light-sheetare strikingly similar to those observed inlaboratory experiments at low to moderate Reynolds numbers. They reveal large-scaleramp-like structures withdownstream inclination of 3°-35°.This inclination isinterpreted as the hairpin packet growthangle following the hairpin vortexpacket model ofAdrian, Meinhart, and Tomkins.The distribution of this characteristicangle agrees with the results of experiments at far lower Reynolds numbers,suggesting a similarity in structures among low, moderate, and high Reynoldsnumber boundary layers at vastly different scales. These results indicate thatthe hairpin vortex packet model extends over a large range of scales. Theeffect of vertical heat transport in an unstable atmosphere on wall structuresis investigated in terms of the hairpin vortex packet model.
A study of the factors affecting boundary layer two-dimensionality in wind tunnels
NASA Technical Reports Server (NTRS)
Mehta, R. D.; Hoffmann, P. H.
1986-01-01
The effect of screens, honeycombs, and centrifugal blowers on the two-dimensionality of a boundary layer on the test section floors of low-speed blower tunnels is studied. Surveys of the spanwise variation in surface shear stress in three blower tunnels revealed that the main component responsible for altering the spanwise properties of the test section boundary layer was the last screen, thus confirming previous findings. It was further confirmed that a screen with varying open-area ratio, produced an unstable flow. However, contrary to popular belief, it was also found that for given incoming conditions and a screen free of imperfections, its open-area ratio alone was not enough to describe its performance. The effect of other geometric parameters such as the type of screen, honeycomb, and blower were investigated. In addition, the effect of the order of components in the settling chamber, and of wire Reynolds number were also studied.
NASA Technical Reports Server (NTRS)
Randall, D. A.; Abeles, J. A.; Corsetti, T. G.
1985-01-01
The formulation of the planetary boundary layer (PBL) and stratocumulus parametrizations in the UCLA general circulation model (GCM) are briefly summarized, and extensive new results are presented illustrating some aspects of the simulated seasonal changes of the global distributions of PBL depth, stratocumulus cloudiness, cloud-top entrainment instability, the cumulus mass flux, and related fields. Results from three experiments designed to reveal the sensitivity of the GCM results to aspects of the PBL and stratocumulus parametrizations are presented. The GCM results show that the layer cloud instability appears to limit the extent of the marine subtropical stratocumulus regimes, and that instability frequently occurs in association with cumulus convection over land. Cumulus convection acts as a very significant sink of PBL mass throughout the tropics and over the midlatitude continents in winter.
A general approach for the prediction of localized instability generation in boundary layer flows
NASA Technical Reports Server (NTRS)
Choudhari, Meelan; Ng, Lian; Streett, Craig L.
1991-01-01
The present approach to the prediction of instability generation that is due to the interaction of freestream disturbances with regions of subscale variations in surface boundary conditions can account for the finite Reynolds number effects, while furnishing a framework for the study of receptivity in compressible flow and in 3D boundary layers. The approach is illustrated for the case of Tollmien-Schlichting wave generation in a Blasius boundary layer, due to the interaction of a freestream acoustic wave with a localized wall inhomogeneity. Results are presented for the generation of viscous and inviscid instabilities in adverse pressure-gradient boundary layers, supersonic boundary layer instabilities, and cross-flow vortex instabilities.
OPTIMIZING GREEN'S FUNCTIONS IN GROUNDED LAYERED MEDIA WITH ARTIFICIAL BOUNDARY CONDITIONS
L. F. Knockaert
2006-01-01
Artificial boundary conditions, which can be identified as Robin boundary conditions positioned at a complex space coordinate, are introduced in order to obtain pertinent approximations for the Green's functions in grounded layered media. These artificial boundary conditions include perfectly matched layers backed by perfectly electric or magnetic conductors. As a first result, we obtain analytical expressions for the differences of
Thickness of the Atmospheric Boundary Layer Above Dome A, Antarctica, during 2009
Ashley, Michael C. B.
Thickness of the Atmospheric Boundary Layer Above Dome A, Antarctica, during 2009 C. S. BONNER,1 M s at Dome A, Antarctica between 2009 February 4 and 2009 August 18. The median thickness of the boundary increase. Winds within the boundary layer over Antarctica are usually katabatic in na- ture. This suggests
Theoretical and experimental investigation of the turbulent boundary layer behind a piston in a tube
NASA Astrophysics Data System (ADS)
Seiler, F.
1985-12-01
The compressible, turbulent boundary layer in a gun barrel was calculated and experimentally verified. The exterior flow behind the projectile for a given projectile position is constant; the instantaneous flow conditions at the projectile base are taken into account in the calculation; the turbulent velocity profile in the boundary layer obeys an exponential law; the whole boundary layer consists of an unsteady piston boundary layer and a stationary plate boundary layer. The connection between the two layers was made where they have equal thickness. The solutions provide expressions for the boundary layer thickness, the heat flux density, and the transversal velocity. The computation results were verified using an experimental gun working with air under realistic flow conditions.
Seasonal Characteristics of Planetary Boundary Layer in Qatar.
NASA Astrophysics Data System (ADS)
Ackermann, Luis; Ayoub, Mohammed A.; Astudillo, Daniel P.; Bachour, Dunia A.
2015-04-01
Understanding the mechanisms driving the Planetary Boundary Layer (PBL) development as well as its seasonal characteristics is essential for predicting meteorological and air quality phenomena. Using data from the vertical backscatter profile of the atmosphere above Qatar from a ceilometer, coupled with a novel Layer Identification Algorithm (LIA) developed by QEERI, a continuous time series of the PBL has been attained. This data has been carefully validated against in-situ measurements via coinciding radiosonde launches. These launches were performed weekly at 13:00 local time during 2014; with occasional launches at 07:00. The detected PBL depth from the sondes show good correlation with LIA. This algorithm uses image recognition methods to identify boundary layers not only by their vertical characteristics; but also by their temporal and spatial signatures. This algorithm was written in Python and is designed to process the ceilometer's output data in real time or as a post-process. The behavior of the PBL depth diurnal variation in Qatar was observed to vary in correlation with the change in seasons. During the winter months the mean PBL depth was higher compared to the summer months; in addition, the diurnal amplitude was higher during winter. Apart from seasonal variations in the PBL depth behavior, short term fluctuations in the daily signature of the PBL structure were observed; with some days exhibiting a well-developed PBL followed by a day with no significant PBL variation. This behavior of the summer PBL (lower daily mean depth and lower diurnal amplitude relative to winter) was explained after looking at diurnal humidity and temperature variations. During these months, the intense temperature and humidity enhances the energy flux towards latent heat, actually diminishing the effect of the high insolation towards the development of the PBL. Lower mean PBL depths during the months of higher photochemical activity affect surface concentrations of secondary pollutants and particle matter.
Large eddy simultations of the atmospheric boundary layer east of the Colorado Rockies
Costigan, K.R.; Cotton, W.R.
1992-10-22
Large eddy simulation, LES, has often been carried out for the idealized situation of a simple convective boundary layer. Studies of dual Doppler radar and aircraft data from the Phoenix II experiment indicate that the boundary layer of the Colorado High Plains is not a purely convective boundary layer and it is influenced by the mountains to the west. The purpose of this study is to investigate the atmospheric boundary layer on one particular day on the Colorado High Plains. This research applies a LES nested within larger grids, which contain realistic topography and can simulate the larger-scale circulations initiated by the presence of the mountain barrier. How and to what extent the atmospheric boundary layer of the Colorado High Plains is influenced by larger scale circulations and other phenomena associated with the mountain barrier to the west is investigated. The nested grid LES reproduces the characteristics of the atmosphere for the case study day reasonably well. The mountains influence the atmospheric boundary layer over the plains to the east in several ways. The mountains contribute to the vertical shear of the horizontal winds through the thermally-induced mountain-plains circulation. As a consequence of the wind shear, the boundary layer that develops over the mountains is advected eastward over the top of the plains boundary layer, which is developing separately. This layer is marked by a mixture of gravity waves and turbulence and is atypical of a purely convective boundary layer. Just below this layer, the capping inversion of the plains boundary layer is weak and poorly defined compared to the inversions capping purely convective boundary layers. Gravity waves, triggered by the obstacle of the Rocky Mountains and by convection in the mountain boundary layer, also influence the atmosphere above the Colorado High Plains. These influences are found to have significant effects on the turbulence statistics and the energy spectra.
A revised conceptual model of the tropical marine boundary layer
NASA Astrophysics Data System (ADS)
Davison, Jennifer L.
This work consists of the development and validation of a new radar product based on Bragg scattering retrievals from clear air S-band radar returns, a re-conceptualization of the tropical marine boundary layer based on this new radar product, and supplemental analysis of other data from this environment. The running theme throughout is moisture variability---its presence, how it can be better detected, and how it should be portrayed in the tropical marine environment. Data examined include National Center for Atmospheric Research's (NCAR's) S-band Dual Polarization (S-Pol) radar data, rawinsondes, dropsondes, and portable automated mesonet surface station (PAMS) data from the Rain in Cumulus over the Ocean (RICO) field campaign, along with satellite data which was partially coincident with these other data sets. Dropsondes, released in 34 sets of ˜6 per set, with each sonde released 5 min (30 km) apart around a 60 km diameter circle, demonstrated both the high moisture variability in the tropical marine boundary layer (TMBL) and the inadequacy of an individual sounding for characterizing its moisture field. Same altitude relative humidity (RH) measurements varied by as much as 70% (7-8 g kg-1) and the TMBL top altitude could vary by 2+ km across a single set. Clear-air Bragg scattering layers (BSLs) were common during RICO. An algorithm was developed to determine the location of BSL base and top altitudes, which were used to generate time-height diagrams. These revealed long-lived coherent structure. A statistical comparison of BSL altitudes and RH profiles from the rawinsondes supported the hypothesis that BSL tops are found near altitudes associated with RH minima and BSL bases near altitudes of RH maxima. Mechanisms for BSL formation/maintenance were discussed. On average 4-5 BSLs were detected (including the transition layer), and each BSL as well as the "clear" layers separating them had median depths of 350 m. Both BSLs and clear layers tended to be deeper on days with higher rain rates, and more (fewer) layers tended to be present when surface winds were more southerly (northerly). BSL statistics serve as the basis for a revised conceptual model of the TMBL, which contains 2-3 more layers of enhanced static stability, layered structure to the moisture variability and extends more than a km higher than the previous conceptual model. When compared, the distribution curves as functions of altitude for 1) BSL tops and 2) satellite derived cloud top heights had a correlation coefficient of 0.92, lending satellite support to the radar portrayal of the TMBL. Frequency by altitude diagrams (FADs) of rawinsonde data showed that the TMBL was sufficiently turbulent to support the Bragg scattering. RH gradients across 350 m intervals ranged from changes of greater than 95% to less than -60%, and all values of RH had a nearly equal probability of occurrence between 2 and 4 km. There were no preferred heights for temperature inversions, with inversions found across both 50 m and 350 m intervals for all altitudes above 1.2 km. The FAD of equivalent potential temperature indicated that the air modified by the ocean typically extended up to 4 km. Disturbed days (e.g., those with rain rates > 2 mm day-1) tended to be moister---with the moisture extending higher, than undisturbed days. The disturbed days also tended to be cooler between 2 and 4.5 km and have less northerly winds in the lowest 4 km.
Embedded function methods for supersonic turbulent boundary layers
NASA Technical Reports Server (NTRS)
He, J.; Kazakia, J. Y.; Walker, J. D. A.
1990-01-01
The development of embedded functions to represent the mean velocity and total enthalpy distributions in the wall layer of a supersonic turbulent boundary layer is considered. The asymptotic scaling laws (in the limit of large Reynolds number) for high speed compressible flows are obtained to facilitate eventual implementation of the embedded functions in a general prediction method. A self-consistent asymptotic structure is derived, as well as a compressible law of the wall in which the velocity and total enthalpy are logarithmic within the overlap zone, but in the Howarth-Dorodnitsyn variable. Simple outer region turbulence models are proposed (some of which are modifications of existing incompressible models) to reflect the effects of compressibility. As a test of the methodology and the new turbulence models, a set of self-similar outer region profiles is obtained for constant pressure flow; these are then coupled with embedded functions in the wall layer. The composite profiles thus obtained are compared directly with experimental data and good agreement is obtained for flows with Mach numbers up to 10.
The receptivity of boundary layers on blunt bodies to oscillations in the free stream
NASA Technical Reports Server (NTRS)
Grosch, C. E.
1982-01-01
One aspect of the boundary layer receptivity problem is examined, that of the flow induced in the bounday layer on the forward portion of a blunt body by unsteadiness in the mean flow. An approximate solution for the disturbances generated in the boundary layer by a long wavelength sound wave impinging normally on the front of a body in steady motion is also provided.
Redeveloping turbulent boundary layer in the backward-facing step flow
Jung Y. Yoo; Se J. Baik
1992-01-01
An experimental study has been performed to investigate the redeveloping turbulent boundary layer beyond separation-reattachment for a transitional separated flow. By considering the distribution of the intermittency, it has been confirmed that the turbulent structure changes gradually from a mixing layer to a turbulent boundary layer downstream of reattachment. The balances of the respective terms in the turbulent kinetic energy
Structure and formation of the highly stable marine boundary layer over the Gulf of Maine
Wayne M. Angevine; J. E. Hare; C. W. Fairall; Daniel E. Wolfe; R. J. Hill; W. A. Brewer; Allen B. White
2006-01-01
A shallow, stable boundary layer is ubiquitous over the cool waters of the Gulf of Maine in summer. This layer affects pollutant transport throughout the region by isolating overlying flow from the surface. In this paper, we explore how the stable boundary layer is formed and describe its characteristics. The temperature profile of the lowest 1–2 km of the atmosphere
Unattended automatic monitoring of boundary layer structures with cost effective lidar ceilometers
Christoph Münkel; Reijo Roininen
2010-01-01
The vertical temperature and moisture distribution affect the layering of the atmospheric boundary layer and the existence of inversions within this layer or on the top of it. These layers have a strong influence on the development of episodes of high concentrations of air pollutants which might be harmful to people and ecosystems. The height of the mixing layer is
Effect of boundary layers on solid walls in three-dimensional subsonic wind tunnels
NASA Technical Reports Server (NTRS)
Adcock, J. B.; Barnwell, R. W.
1984-01-01
A solution for the tunnel wall boundary layer effects for three-dimensional subsonic tunnels is presented. The model potentials are represented with simple singularities placed on the centerline of the tunnel and Laplace's equation in cylindrical coordinates is solved for either the conventional homogeneous slotted-wall boundary condition, the solid-wall viscous boundary condition, or a combination of them. The most pronounced wall boundary layer effect is on solid blockage for completely closed wind tunnels. Boundary layers on the wall reduce the blockage from the solid-wall, no-boundary-layer case in a manner similar to opening slots in a solid wall. Additionally, for solid-wall tunnel configurations, the streamline curvature interference factor is reduced by a significant amount, whereas the lift interference factor at the model station does not depend on the boundary layer parameter. For combination wall configurations, the slot effect of the horizontal walls dominates the viscous effect of the solid sidewalls.
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.
Integration of satellite and surface data using a radiative-convective oceanic boundary-layer model
NASA Technical Reports Server (NTRS)
Betts, Alan K.; Minnis, Patrick; Ridgway, W.; Young, David F.
1992-01-01
A mixing-line boundary-layer model is used to retrieve cloud-top height from satellite-derived cloud-top temperatures, using 700-hPa National Meteorological Center (NMC) analyses and the Comprehensive Ocean and Atmosphere Data Set (COADS) surface data as supporting datasets. Results are compared with the fixed-lapse-rate method of retrieving boundary-layer depth from sea surface temperatures (SST) and cloud-top temperatures. A radiative-convective equilibrium boundary-layer model is used to retrieve boundary-layer structure given SST and surface wind, satellite cloud-top temperatures and cloud fraction, and the 700-hPa NMC thermodynamic analyses. Good agreement is found between the COADS data and the model solutions for low-level temperature and moisture. This suggests that equilibrium boundary-layer models may be of use over remote oceans in the retrieval of boundary-layer structure.
A theoretical analysis of simulated transonic boundary layers in cryogenic-nitrogen wind tunnels
NASA Technical Reports Server (NTRS)
Adcock, J. B.; Johnson, C. B.
1980-01-01
A theoretical analysis was made to determine the real gas effects on simulation of transonic boundary layers in wind tunnels with cryogenic nitrogen as the test gas. The analysis included laminar and turbulent flat plate boundary layers and turbulent boundary layers on a two dimensional airfoil. The results indicate that boundary layers in such wind tunnels should not be substantially different from ideal gas boundary layers at standard conditions. At a pressure of 9.0 atm, two separate effects produce deviations of real gas values from ideal gas values which are in the opposite direction from deviations at 1.0 atm and are of the same insignificant order of magnitude. Results also show that nonadiabatic boundary layers should be adequately simulated if the enthalpy ratio is the correlating parameter rather than the temperature ratio.
Comparison of several methods for predicting separation in a compressible turbulent boundary layer
NASA Technical Reports Server (NTRS)
Gerhart, P. M.; Bober, L. J.
1974-01-01
Several methods for predicting the separation point for a compressible turbulent boundary layer were applied to the flow over a bump on a wind-tunnel wall. Measured pressure distributions were used as input. Two integral boundary-layer methods, three finite-difference boundary-layer methods, and three simple methods were applied at five free-stream Mach numbers ranging from 0.354 to 0.7325. Each of the boundary-layer methods failed to explicitly predict separation. However, by relaxing the theoretical separation criteria, several boundary-layer methods were made to yield reasonable separation predictions, but none of the methods accurately predicted the important boundary-layer parameters at separation. Only one of the simple methods consistently predicted separation with reasonable accuracy in a manner consistent with the theory. The other methods either indicated several possible separation locations or only sometimes predicted separation.
Polar cap boundary layer waves: An auroral zone phenomenon
NASA Astrophysics Data System (ADS)
Tsurutani, Bruce T.; Arballo, John K.; Galvan, Carlos; Zhang, Liwei Dennis; Zhou, Xiao-Yan; Lakhina, Gurbax S.; Hada, Tohru; Pickett, Jolene S.; Gurnett, Donald A.
2001-09-01
Polar cap boundary layer waves are ELF/VLF electric and magnetic waves detected on field lines just adjacent to the polar cap. Intense waves are present at this location essentially all (96%) of the time. The wave latitude-local time distribution is shown to be the same as that of the Feldstein auroral oval, a distribution centered at ~75° at local noon and ~65° at local midnight. The most intense waves are detected coincident with the strongest magnetic field gradients (field-aligned currents). Statistically, the wave intensities are greatest near local noon (10-13mV2m-1 at 3 kHz) and midnight and are least near dawn and dusk (~5×10-15mV2m-1 at 3 kHz). The noon and midnight wave intensities increase slightly when the interplanetary magnetic field is directed southward. The dawn and dusk waves appear to be controlled by the solar wind speed. Using high-resolution data, specific frequency bands of electromagnetic whistler-mode waves are identified: ~200 Hz and 1-2 and ~5 kHz. These may correspond to previously identified ``magnetic noise bursts'' and ``auroral hiss'', respectively. Assuming cyclotron resonant interactions, the 1- to 5-kHz auroral hiss is shown to be resonant with ~50-eV to ~1.0-keV electrons. Several mechanisms, both resonant (nonlocal) and nonresonant (local), are suggested for the generation of the ~200-Hz electromagnetic waves. Three types of intense electric signals are present: solitary bipolar pulses (electron holes), waves at ~4×102 to 6×103Hz (lower hybrid waves), and narrowband waves at ~10 kHz (electrostatic waves near the upper hybrid resonance frequency). Solitary bipolar pulse onset events have been detected for the first time. The bipolar pulses reached 2 mV m-1 peak-to-peak amplitudes within 3 ms. An exponential growth rate of 0.72 ms, or 0.25 fcc, was determined. The previously reported ``broadband nature'' of the polar cap boundary layer (and low-latitude boundary layer) waves is now postulated to be caused by a fast switching between the various electromagnetic and electrostatic modes described above. The polar cap boundary layer waves are most likely a consequence of instabilities associated with auroral zone field-aligned currents carried by 50-eV to 1.0-keV electrons and protons. The currents in turn have been ascribed to be driven by the solar wind-magnetosphere global interaction. One consequence of the presence of the waves at high altitudes is diffusion of magnetosheath plasma into the magnetosphere and magnetospheric plasma out into the magnetosheath (cross-field diffusion, due to parasitic wave-particle interactions). It is speculated that field-aligned currents and similar wave modes will be detected at all planetary magnetospheres.
Unsteady Phenomena in Shock Wave/Boundary Layer Interaction
NASA Technical Reports Server (NTRS)
Dolling, D. S.
1993-01-01
A brief review is given of the unsteadiness of shock wave/turbulent boundary layer interaction. The focus is on interactions generated by swept and unswept compression ramps, by flares, steps and incident shock waves, by cylinders and blunt fins, and by glancing shock waves. The effects of Mach number, Reynolds number, and separated flow scale are discussed as are the physical causes of the unsteadiness. The implications that the unsteadiness has for interpreting time-average surface and flowfield data, and for comparisons of such experimental data with computation, is also briefly discussed. Finally, some suggestions for future work are given. It is clear that there are large gaps in the data base and that many aspects of such phenomena are poorly understood. Much work remains to be done.
Equidistributed error mesh for problems with exponential boundary layers
NASA Astrophysics Data System (ADS)
Solín, Pavel; Ávila, José
2008-08-01
In this paper we present a new piecewise-linear finite element mesh suitable for the discretization of the one-dimensional convection-diffusion equation -[epsilon]u''-bu'=0, u(0)=0, u(1)=1. The solution to this equation exhibits an exponential boundary layer which occurs also in more complicated convection-diffusion problems of the form -[epsilon][Delta]u-b[not partial differential]u/[not partial differential]x+cu=f. The new mesh is based on the equidistribution of the interpolation error and it takes into account finite computer arithmetic. It is demonstrated numerically that for the above problem, the new mesh has remarkably better convergence properties than the well-known Shishkin and Bakhvalov meshes.
Wall pressure fluctuations beneath supersonic turbulent boundary layers
NASA Astrophysics Data System (ADS)
Bernardini, Matteo; Pirozzoli, Sergio
2011-08-01
The structure of the wall pressure field beneath supersonic adiabatic turbulent boundary layers is analyzed by means of direct numerical simulations at free-stream Mach number M? = 2, 3, 4, spanning a relatively large range of Reynolds numbers. The data reported in the paper, which include wall pressure fluctuations intensities, frequency spectra, space-time correlations, and convection velocities, show that when pressure is scaled by the wall shear stress, most statistics well conform to low-speed findings, contradicting the conclusions of previous experimental studies. Genuine compressibility effects are found to provide a small contribution to the magnitude of the wall pressure fluctuations, their influence being limited to the high-frequency end of the spectra, where a systematic increase with the Mach number is observed.
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.
Boundary layers in rotating weakly turbulent Rayleigh-Bénard convection
NASA Astrophysics Data System (ADS)
Stevens, Richard J. A. M.; Clercx, Herman J. H.; Lohse, Detlef
2010-08-01
The effect of rotation on the boundary layers (BLs) in a Rayleigh-Bénard system at a relatively low Rayleigh number, i.e., Ra=4×107, is studied for different Pr by direct numerical simulations and the results are compared with laminar BL theory. In this regime, we find a smooth onset of the heat transfer enhancement as function of increasing rotation rate. We study this regime in detail and introduce a model based on the Grossmann-Lohse theory to describe the heat transfer enhancement as function of the rotation rate for this relatively low Ra number regime and weak background rotation Ro?1. The smooth onset of heat transfer enhancement observed here is in contrast to the sharp onset observed at larger Ra?108 by Stevens et al. [Phys. Rev. Lett. 103, 024503 (2009)], although only a small shift in the Ra-Ro-Pr phase space is involved.
Hypersonic Boundary-Layer Trip Development for Hyper-X
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Auslender, Aaron H.; Dilley, Authur D.; Calleja, John F.
2000-01-01
Boundary layer trip devices for the Hper-X forebody have been experimentally examined in several wind tunnels. Five different trip configurations were compared in three hypersonic facilities, the LaRC 20-Inch Mach 6 Air Tunnel, the LaRC 31 -Inch Mach 10 Air Tunnel, and in the HYPULSE Reflected Shock Tunnel at GASL. Heat transfer distributions, utilizing the phosphor thermography and thin-film techniques, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. Parametric variations include angles-of-attack of 0-deg, 2-deg, and 4-deg; Reynolds numbers based on model length of 1.2 to 15.4 million: and inlet cowl door simulated in both open and closed positions. Comparisons of transition due to discrete roughness elements have led to the selection of a trip configuration for the Hyper-X Mach 7 flight vehicle.
Numerical Simulations of the Boundary Layer Transition Flight Experiment
NASA Technical Reports Server (NTRS)
Tang, Chun Y.; Trumble, Kerry A.; Campbell, Charles H.; Lessard, Victor R.; Wood, William A.
2010-01-01
Computational Fluid Dynamics (CFD) simulations were used to study the possible effects that the Boundary Layer Transition (BLT) Flight Experiments may have on the heating environment of the Space Shuttle during its entry to Earth. To investigate this issue, hypersonic calculations using the Data-Parallel Line Relaxation (DPLR) and Langley Aerothermodynamic Upwind Relaxation (LAURA) CFD codes were computed for a 0.75 tall protuberance at flight conditions of Mach 15 and 18. These initial results showed high surface heating on the BLT trip and the areas surrounding the protuberance. Since the predicted peak heating rates would exceed the thermal limits of the materials selected to construct the BLT trip, many changes to the geometry were attempted in order to reduce the surface heat flux. The following paper describes the various geometry revisions and the resulting heating environments predicted by the CFD codes.
Wave-turbulence dynamics in the stably stratified boundary layer
NASA Technical Reports Server (NTRS)
Einaudi, F.; Finnigan, J. J.
1993-01-01
New data obtained at the Boulder Atmospheric Observatory are analyzed to obtain separation of wave, turbulence, and mean field necessary for a complete treatment of wave-turbulence interaction. The data were compared with a linear stability analysis of the background atmospheric state, showing good agreement between measured wave parameters (such as wavelength, period, and vector phase velocity) and the eigenvalues of the linear solution. The analysis of the budgets of wave heat flux and temperature variance revealed the essential role of wave-turbulence interaction in maintaining a large amplitude temperature wave and countergradient heat flux. A mechanism for the maintenance of turbulence by waves in strongly stratified boundary layers is described, which emphasizes that the time-mean Richardson number is an irrelevant parameter at such times.
Small particle transport across turbulent nonisothermal boundary layers
NASA Technical Reports Server (NTRS)
Rosner, D. E.; Fernandez De La Mora, J.
1982-01-01
The interaction between turbulent diffusion, Brownian diffusion, and particle thermophoresis in the limit of vanishing particle inertial effects is quantitatively modeled for applications in gas turbines. The model is initiated with consideration of the particle phase mass conservation equation for a two-dimensional boundary layer, including the thermophoretic flux term directed toward the cold wall. A formalism of a turbulent flow near a flat plate in a heat transfer problem is adopted, and variable property effects are neglected. Attention is given to the limit of very large Schmidt numbers and the particle concentration depletion outside of the Brownian sublayer. It is concluded that, in the parameter range of interest, thermophoresis augments the high Schmidt number mass-transfer coefficient by a factor equal to the product of the outer sink and the thermophoretic suction.
Precipitation from convective boundary layers in arctic air masses
NASA Astrophysics Data System (ADS)
Ólafsson, Haraldur; Økland, Hans
1994-01-01
Cold air mass formed over the ice-covered polar area during the winter season often moves southward over the Norwegian Sea. The heat flux from the water produces a CBL (convective boundary layer) with increasing thickness and temperature in the downstream direction. Usually, snow showers are observed over the sea and at the coast of Norway. The object of this investigation is to examine the amount of precipitation measured at the coast in relation to the temperature and thickness of the CBL. A sample consisting of 37 cases is collected and a positive correlation is established between the precipitation measured by 5 coastal stations and the CBL thickness, while the temperature seems to be of minor importance. Some of the data indicates a two-regime precipitation pattern, divided by a threshold value in the thickness of the CBL. This is discussed in relation to microphysical precipitation processes. Peculiar differences in the records from the observing stations indicate interesting orographic shadow effects.
Laminar boundary-layer flow of non-Newtonian fluid
NASA Technical Reports Server (NTRS)
Lin, F. N.; Chern, S. Y.
1979-01-01
A solution for the two-dimensional and axisymmetric laminar boundary-layer momentum equation of power-law non-Newtonian fluid is presented. The analysis makes use of the Merk-Chao series solution method originally devised for the flow of Newtonian fluid. The universal functions for the leading term in the series are tabulated for n from 0.2 to 2. Equations governing the universal functions associated with the second and the third terms are provided. The solution together with either Lighthill's formula or Chao's formula constitutes a simple yet general procedure for the calculation of wall shear and surface heat transfer rate. The theory was applied to flows over a circular cylinder and a sphere and the results compared with published data.
Simple Viscous Flows: from Boundary Layers to the Renormalization Group
John Veysey; Nigel Goldenfeld
2007-01-23
The seemingly simple problem of determining the drag on a body moving through a very viscous fluid has, for over 150 years, been a source of theoretical confusion, mathematical paradoxes, and experimental artifacts, primarily arising from the complex boundary layer structure of the flow near the body and at infinity. We review the extensive experimental and theoretical literature on this problem, with special emphasis on the logical relationship between different approaches. The survey begins with the developments of matched asymptotic expansions, and concludes with a discussion of perturbative renormalization group techniques, adapted from quantum field theory to differential equations. The renormalization group calculations lead to a new prediction for the drag coefficient, one which can both reproduce and surpass the results of matched asymptotics.
Convex curvature effects on the heated turbulent boundary layer
NASA Technical Reports Server (NTRS)
Simon, T. W.; Moffat, R. J.
1982-01-01
A convexly curved and isothermally heated wall with a 45-cm radius of curvature is subjected to turbulent boundary layer flow measurements in order to determine wall heat transfer rates and mean velocity and temperature profiles. Significant curvature effects are noted, with Stanton number and skin friction coefficient reductions of 35-40 percent by comparison with flat plate values for the same momentum or enthalpy thickness Reynolds numbers. Profiles of mean velocity and temperature show a more rapid growth of the wake regions, and a shortening of the log-linear region, as a result of curvature. Turbulent Prandtl numbers deduced from the mean temperature profiles under the assumption of a wall thermal law were found to be increased by 40-50 percent by this strong convex curvature.
Direct numerical simulation of shockwave and turbulent boundary layer interactions
NASA Astrophysics Data System (ADS)
Wu, Minwei
Direct numerical simulations (DNS) of a shockwave/turbulent boundary layer interaction (STBLI) at Mach number 3 and Reynolds number based on the momentum thickness of 2300 are performed. A 4th-order accurate, bandwidth-optimized weighted-essentially-non-oscillatory (WENO) scheme is used and the method is found to be too dissipative for the STBLI simulation due to the over-adaptation properties of this original WENO scheme. In turn, a relative limiter is introduced to mitigate the problem. Tests on the Shu-Osher problem show that the modified WENO scheme decreases the numerical dissipation significantly. By utilizing a combination of the relative limiter and the absolute limiter described by Jiang & Shu [32], the DNS results are improved further. The DNS data agree well with the reference experiments of Bookey et al. [10] in the size of the separation bubble, the separation and reattachment point, the mean wall-pressure distribution, and the velocity profiles both upstream and downstream of the interaction region. The DNS data show that velocity profiles change dramatically along the streamwise direction. Downstream of the interaction, the velocity profiles show a characteristic "dip" in the logarithmic region, as shown by the experiments of Smits & Muck [66] at much higher Reynolds number. In the separation region, the velocity profiles are found to resemble those of a laminar flow, yet the flow does not fully relaminarize. The mass-flux turbulence intensity is amplified by a factor of about 5 throughout the interaction, which is consistent with that found in higher Reynolds experiments of Selig et al. [52]. All Reynolds stress components are greatly amplified by the interaction. Assuming that the ow is still two dimensional downstream of the interaction, the components rhou'u', rhov'v', rho w'w', and rho u'w' are amplified by factors of 6, 6, 12, and 24, respectively, where u is the streamwise and w is the wall-normal velocity. However, analyses of the turbulence structure show that the ow is not uniform in the spanwise direction downstream of the interaction. A pair of counter-rotating vortices is observed in streamwise-wall-normal planes in the mean ow downstream of the ramp corner. Taking the three-dimensionality into account, the amplification factors of the Reynolds stresses are greatly decreased. The component rhou'w' is amplified by a factor of about 10, which is comparable to that found in the experiments of Smits & Muck [66]. Strong Reynolds analogy (SRA) relations are also studied using the DNS data. The SRA is found to hold in the incoming boundary layer of the DNS. However, inside and downstream of the interaction region, the SRA relations are not satisfied. From the DNS analyses, the shock motion is characterized by a low frequency component (of order 0.01Uinfinity/delta). In addition, the motion of the shock is found to have two aspects: a spanwise wrinkling motion and a streamwise oscillatory motion. The spanwise wrinkling is observed to be a local feature with high frequencies (of order Uinfinity /delta). Two-point correlations reveal that the spanwise wrinkling is closely related to the low momentum motions in the incoming boundary layer as they convect through the shock. The low frequency shock motion is found to be a streamwise oscillation motion. Conditional statistics show that there is no significant difference in the mean properties of the incoming boundary layer when the shock is at an upstream or downstream location. However, analyses of the unsteadiness of the separation bubble reveal that the low frequency shock motion is driven by the downstream flow.
Control of Unstable Waves in Three Dimensional Boundary Layers
NASA Technical Reports Server (NTRS)
Saric, William S.
1996-01-01
Stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg. swept airfoil. The pressure gradient is designed to provide purely crossflow-dominated transition; that is, the boundary layer is subcritical to Tollmien- Schlichting (T-S) disturbances. The airfoil surface is hand polished to a 0.25 micron rms finish. Under these conditions, stationary crossflow disturbances grow to nonuniform amplitude due to submicron surface irregularities near the leading edge. Spectral de-compositions isolate single-mode growth rates for the fundamental and harmonic disturbances. The measurements show early nonlinear growth causing amplitude saturation well before transition. Comparisons with nonlinear PSE calculations show excellent agreement in both the amplitude saturation and the disturbance mode shape.
Analysis of the photodiode boundary layer transition indicator
Kuntz, D.W.; Wilken, A.C.; Payne, J.L.
1994-01-01
The photodiode transition indicator is a device which has been successfully used to determine the onset of boundary layer transition on numerous hypersonic flight vehicles. The exact source of the electromagnetic radiation detected by the photodiode at transition was not understood. In some cases early saturation of the device occurred, and the device failed to detect transition. Analyses have been performed to determine the source of the radiation producing the photodiode signal. The results of these analyses indicate that the most likely source of the radiation is blackbody emission from the heatshield material bordering the quartz window of the device. Good agreement between flight data and calculations based on this radiation source has been obtained. Analyses also indicate that the most probable source of the radiation causing early saturation is blackbody radiation from carbon particles which break away from the nosetip during the ablation process.
Effect of crossflow on Goertler instability in incompressible boundary layers
NASA Technical Reports Server (NTRS)
Zurigat, Y. H.; Malik, M. R.
1994-01-01
Linear stability theory is used to study the effect of crossflow on Goertler instability in incompressible boundary layers. The results cover a wide range of sweep angle, pressure gradient, and wall curvature parameters. It is shown that the crossflow stabilizes Goertler disturbances by reducing the maximum growth rate and shrinking the unstable band of spanwise wave numbers. On the other hand, the effect of concave wall curvature on crossflow instability is destabilizing. Calculations show that the changeover from Goertler to crossflow instabilities is a function of Goertler number, pressure gradient, and sweep angle. The results demonstrate that Goertler instability may still be relevant in the transition process on swept wings even at large angles of sweep if the pressure gradient is sufficiently small. The influence of pressure gradient and sweep can be combined by defining a crossflow Reynolds number. Thus, the changeover from Goertler to crossflow instability takes place at some critical crossflow Reynolds number whose value increases with Goertler number.
A low-density boundary-layer wind tunnel facility
NASA Technical Reports Server (NTRS)
White, B. R.
1987-01-01
This abstract describes a low-density wind-tunnel facility that was established at NASA Ames in order to aid interpretation and understanding of data received from the Mariner and Viking spacecraft through earth-based simulation. The wind tunnel is a boundary-layer type which is capable of operating over a range of air densities ranging from 0.01 to 1.24 kg/cu m, with the lower values being equivalent to the near-surface density of the planet Mars. Although the facility was developed for space and extraterrestrial simulation, it also can serve as a relatively large-scale, low-density aerodynamic test facility. A description of this unique test facility and some Pitot-tube and hot-wire anemometry data acquired in the facility are presented.
Radiative transfer in a polluted urban planetary boundary layer
NASA Technical Reports Server (NTRS)
Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.
1977-01-01
Radiative transfer in a polluted urban atmosphere is studied using a dynamic model. The diurnal nature of radiative transfer for summer conditions is simulated for an urban area 40 km in extent and the effects of various parameters arising in the problem are investigated. The results of numerical computations show that air pollution has the potential of playing a major role in the radiative regime of the urban area. Absorption of solar energy by aerosols in realistic models of urban atmosphere are of the same order of magnitude as that due to water vapor. The predicted effect of the air pollution aerosol in the city is to warm the earth-atmosphere system, and the net effect of gaseous pollutant is to warm the surface and cool the planetary boundary layer, particularly near the top.
Displacement interaction and surface curvature effects on hypersonic boundary layers.
NASA Technical Reports Server (NTRS)
Wornom, S. F.; Werle, M. J.
1972-01-01
The title problem was studied employing implicit finite-difference methods to obtain numerical solutions to a composite set of boundary-layer equations valid to second order. Results are given for flow up a two-dimensional cubic compression ramp for free-stream Mach numbers of 6, 8, and 12.25 and for free-stream Re/inch equal to 85,800 and 25,800 at a wall-to-stagnation temperature ratio of 0.223. Comparisons with independent theories and experimental results are given. Nonsingular separation was produced at a free-stream Mach number of 12.25. For all cases considered, displacement and curvature effects canceled one another when a consistent treatment of inviscid and viscous curvature corrections was employed - the second-order theory virtually reproducing the first-order results.
An algebraic model for dissipation in supersonic boundary layers
NASA Technical Reports Server (NTRS)
He, J.; Kazakia, J. Y.; Ruban, A. I.; Walker, J. D. A.
1992-01-01
With increasing mainstream Mach number, viscous dissipation becomes a progressively important influence in high-speed compressible turbulent boundary layers. An asymptotic analysis is carried out for high Reynolds numbers and Mach numbers of order 1, and it is shown that viscous dissipation gives rise to important terms in the solution of the total enthalpy equation. For simplicity, the case of supersonic flow over an adiabatic wall is considered. An expression for the adiabatic wall temperature is derived. It is shown that the asymptotic analysis constrains the types of turbulence models that can be used to represent the effects of viscous dissipation. A simple algebraic turbulence model is proposed and comparisons with measured total enthalpy profile data show good agreement.
Combined core/boundary layer transport simulations in tokamaks
Prinja, A.K.; Schafer, R.F. Jr.; Conn, R.W.; Howe, H.C.
1986-04-01
Significant new numerical results are presented from self-consistent core and boundary or scrape-off layer plasma simulations with 3-D neutral transport calculations. For a symmetric belt limiter it is shown that, for plasma conditions considered here, the pump limiter collection efficiency increases from 11% to 18% of the core efflux as a result of local reionization of blade deflected neutrals. This hitherto unobserved effect causes a significant amplification of upstream ion flux entering the pump limiter. Results from coupling of an earlier developed two-zone edge plasma model ODESSA to the PROCTR core plasma simulation code indicates that intense recycling divertor operation may not be possible because of stagnation of upstream flow velocity. This results in a self-consistent reduction of density gradient in an intermediate region between the central plasma and separatrix, and a concomitant reduction of core-efflux. There is also evidence of increased recycling at the first wall.