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1

Development of instrumentation for boundary layer transition detection

A steady state heat transfer technique is developed and evaluated for detecting boundary layer transition on a flat plate in incompressible flow. The method involves adhering encapsulated temperature sensitive liquid crystals to a constant heat flux surface. A heater composed of unidirectional carbon fibers is developed and tested with the aim of in-flight boundary layer transition detection on a natural

Steven B. Harrison

1991-01-01

2

Development of Instrumentation for Boundary Layer Transition Detection.

National Technical Information Service (NTIS)

A steady state heat transfer technique is developed and evaluated for detecting boundary layer transition on a flat plate in incompressible flow. The method involves adhering encapsulated temperature sensitive liquid crystals to a constant heat flux surfa...

S. B. Harrison

1991-01-01

3

Interaction between soil hydrology and boundary-layer development

A two-layer model of soil hydrology and thermodynamics is combined with a one-dimensional model of the planetary boundary layer to study various interactions between evolution of the boundary layer and soil moisture transport. Boundary-layer moistening through surface evaporation reduces the potential and actual surface evaporation as well as the boundary-layer growth. With more advanced stages of soil drying, the restricted

H.-L. Pan; L. Mahrt

1987-01-01

4

Numerical simulations of spatially developing, accelerating boundary layers

NASA Astrophysics Data System (ADS)

We present the results of direct and large-eddy simulations of spatially developing boundary layers subjected to favorable pressure gradient, strong enough to cause reversion of the flow towards a quasi-laminar state. The numerical results compare well with experimental data. Visualization of the flow structures shows the well-known stabilization of the streaks, the re-orientation of outer layer vortices in the streamwise direction, and the appearance of turbulent spots in the re-transition region. Both instantaneous visualizations and turbulent statistics highlight the significant damping of wall-normal and spanwise fluctuations. The fast component of the pressure fluctuations appears to be the main driver of this process, contributing to reduce pressure fluctuations and, as a consequence, the energy redistribution term in the Reynolds stress budgets. The streamwise stresses, in whose budget a separate production term plays a role, do not decay but remain frozen at their upstream value. The decrease of wall-normal and spanwise fluctuations appears to be the main cause of the inner-layer stabilization, by disrupting the generation and subsequent growth of streaks, consistent with various models of the turbulence-generation cycle proposed in the literature. The outer layer seems to play a passive role in this process. The stretching and reorientation of the outer-layer vortices results in a more orderly and organized structure; since fewer ejections occur, the inner layer does not break this re-organization, which is maintained until re-transition begins.

Piomelli, Ugo; Yuan, Junlin

2013-10-01

5

LASE measurements of convective boundary layer development during SGP97

NASA Technical Reports Server (NTRS)

The Southern Great Plains 1997 (SGP97) field experiment was conducted in Oklahoma during June-July 1997 to validate the models used for computing remote soil moisture using measurements by microwave radiometers. One of the objectives of SGP97 was to examine the effect of soil moisture on the evolution of the Atmospheric Boundary Layer (ABL) and clouds over the Southern Great Plains (SGP) during the warm season. The LASE (Lidar Atmospheric Sensing Experiment) airborne DIAL (Differential Absorption Lidar) system, which was flown autonomously on the NASA ER-2 aircraft during previous missions, was reconfigured to fly on the NASA P3 research aircraft. During SGP97 LASE was used to study the morning evolution of the ABL, particularly as manifested in the development of the convective boundary layer, and to study the influence of soil moisture variations on the development of ABL. The ABL development is strongly influenced by the surface energy budget, which is in turn influenced by soil moisture, mesoscale meteorology, clouds, and solar insolation. LASE data acquired during this mission are being used to study the ABL water vapor budget, the development of the ABL, spatial and temporal variabilities in the ABL, and the meteorological factors that influence the ABL development. This field experiment also permitted comparisons of LASE water vapor measurements with water vapor profiles acquired by radiosondes launched at the DOE (Department of Energy) Atmospheric Radiation Measurement (ARM) Southern Great Plain (SGP) site and at NASA/Wallops Flight Facility, as well as with measurements from other SGP97 aircraft.

Ismail, Syed; Browell, Edward V.; Ferrare, Richard A.; Senff, Christoph; Davis, Kenneth J.a; Lenschow, Donald H.; Kooi, Susan; Brackett, Vince; Clayton, Marian

1998-01-01

6

Development of Turbulent Boundary Layers Along the Curved Walls of an Annular Diffusing Passage.

National Technical Information Service (NTIS)

Turbulent boundary layer development along the curved walls of an axisymmetric diffusing annulus was determined experimentally and compared with results calculated using a form of the von Karman momentum integral boundary layer equation and several sets o...

S. Fujii T. H. Okiisi

1972-01-01

7

Development of boundary layer rolls from dynamic instabilities

NASA Technical Reports Server (NTRS)

Using three three-dimensional spectral models of flow in a neutral atmosphere, the development of atmospheric boundary layer rolls from the inflection point and parallel instabilities is examined. Using the Ekman profile, the ability of the various models to reproduce the modes arising from the parallel and inflection point instability mechanisms was tested by comparing the results from the spectral models with the results from larger models used by other investigators. It was found that the truncated spectral models used in this investigation yielded preferred values of orientation angle and aspect ratio that agreed with those produced by the larger models, as well as with the observations data taken on September 1981 during the West-German KonTur experiment.

Stensrud, David J.; Shirer, Hampton N.

1988-01-01

8

Surface energy balance and boundary layer development during snowmelt

NASA Astrophysics Data System (ADS)

Improved prediction of snowmelt requires comprehensive data collection, including surface, subsurface, and atmospheric processes, during the snowmelt period. We report results of field research in which all components of the surface energy balance were measured during two different snowmelt periods, along with boundary layer soundings. The two periods were quite different, the first being overcast and the second occurring under clear skies. However, snowmelt was estimated relatively well from the cumulative residual of the energy balance in both cases. Downward infrared radiation and sensible heat flux were important contributors to the melt during overcast conditions, with net radiation providing about two thirds of the energy for melt and sensible heat providing the remainder. The sunny melt was dominated by direct solar heating of the surface. In both cases, estimation of melt as a residual of the energy balance agreed well with visual and gravimetric observations. The boundary layer soundings revealed the importance of advection, which was generally consistent with synoptic patterns during the period of the study. The data also showed a transition from advection-dominated to turbulence-dominated boundary layer budgets as the snowpack disappeared. The potential for convective cloud formation was also examined. Surface heating and entrainment outweighed adiabatic cooling and evaporation, resulting in the boundary layer top relative humidity decreasing as the snow melted and turbulent mixing increased.

Baker, J. M.; Davis, K. J.; Liknes, G. C.

1999-08-01

9

NASA Astrophysics Data System (ADS)

Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted aircraft systems and two manned aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the models runs are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase of the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed, and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Finally, we also investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.

Blay-Carreras, E.; Pino, D.; Vilà-Guerau de Arellano, J.; van de Boer, A.; De Coster, O.; Darbieu, C.; Hartogensis, O.; Lohou, F.; Lothon, M.; Pietersen, H.

2014-05-01

10

NASA Astrophysics Data System (ADS)

Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted airplane systems and two aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the numerical simulations are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable to model the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. The simulation shows a large increase of the entrainment buoyancy heat flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Additionally, we investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.

Blay-Carreras, E.; Pino, D.; Van de Boer, A.; De Coster, O.; Darbieu, C.; Hartogensis, O.; Lohou, F.; Lothon, M.; Pietersen, H.; Vilà-Guerau de Arellano, J.

2013-12-01

11

Visualization of Boundary-Layer Development on Turbomachine Blades with Liquid Crystals.

National Technical Information Service (NTIS)

This report documents a study of the use of liquid crystals to visualize boundary layer development on a turbomachine blade. A turbine blade model in a linear cascade of blades was used for the tests involved. Details of the boundary layer development on ...

D. E. Vanzante T. H. Okiishi

1991-01-01

12

Hypersonic Boundary-Layer Trip Development for Hyper-X

NASA Technical Reports Server (NTRS)

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.

Berry, Scott A.; Auslender, Aaron H.; Dilley, Authur D.; Calleja, John F.

2000-01-01

13

Spatially developing secondary instabilities in compressible swept airfoil boundary layers

NASA Astrophysics Data System (ADS)

Two-dimensional eigenvalue analysis is used on a massive scale to study the spatial instabilities of compressible shear flows with two inhomogeneous directions. The main focus of the study is crossflow dominated swept-wing boundary layers although the methodology can also be applied to study other types of flows, such as the attachment-line flow. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed, namely, fixing the spatial growth direction unambiguously through a non-orthogonal formulation of the linearized disturbance equations. A primary test case used for parameter study corresponds to Numerical results are presented for the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. In particular, the control mode itself, if initiated with too large an amplitude, may lead to an earlier transition.

Li, Fei; Choudhari, Meelan M.

2011-06-01

14

Boundary layer development in axial compressors and turbines. Part 4 of 4: Computations and analyses

This is Part Four of a four-part paper. It begins with Section 16.0 and concludes the description of the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this paper, the computational predictions made using several modern boundary layer codes are presented. Both steady codes and an unsteady code were evaluated. The results are compared with time-averaged and unsteady integral parameters measured for the boundary layers. Assessments are made to provide guidance in using the predictive codes to locate transition and predict loss. Conclusions from the computational analyses are then presented.

Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)

1997-01-01

15

Boundary layer development in axial compressors and turbines. Part 1 of 4: Composite picture

Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components.Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of the experimental findings by using sketches to show how boundary layers develop on compressor and turbine blading. Parts 2 and 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and discusses comparisons with experimental data. Readers not interested in experimental detail can go directly from Part 1 to Part 4.

Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)

1997-01-01

16

Development of a Boundary Layer Property Interpolation Tool in Support of Orbiter Return To Flight

NASA Technical Reports Server (NTRS)

A new tool was developed to predict the boundary layer quantities required by several physics-based predictive/analytic methods that assess damaged Orbiter tile. This new tool, the Boundary Layer Property Prediction (BLPROP) tool, supplies boundary layer values used in correlations that determine boundary layer transition onset and surface heating-rate augmentation/attenuation factors inside tile gouges (i.e. cavities). BLPROP interpolates through a database of computed solutions and provides boundary layer and wall data (delta, theta, Re(sub theta)/M(sub e), Re(sub theta)/M(sub e), Re(sub theta), P(sub w), and q(sub w)) based on user input surface location and free stream conditions. Surface locations are limited to the Orbiter s windward surface. Constructed using predictions from an inviscid w/boundary-layer method and benchmark viscous CFD, the computed database covers the hypersonic continuum flight regime based on two reference flight trajectories. First-order one-dimensional Lagrange interpolation accounts for Mach number and angle-of-attack variations, whereas non-dimensional normalization accounts for differences between the reference and input Reynolds number. Employing the same computational methods used to construct the database, solutions at other trajectory points taken from previous STS flights were computed: these results validate the BLPROP algorithm. Percentage differences between interpolated and computed values are presented and are used to establish the level of uncertainty of the new tool.

Greene, Francis A.; Hamilton, H. Harris

2006-01-01

17

Boundary layer development and energy exchange over a patchy mountain snow cover

NASA Astrophysics Data System (ADS)

Once the snow cover gets patchy in spring, small-scale thermal internal boundary layers develop, involving strong vertical and horizontal flux divergences. Furthermore, the advection of warm air from bare ground towards snow-covered areas can promote strong atmospheric stabilities and boundary layer decoupling above snow, that suppress the net turbulent heat flux close to the snow surface, thus, changing the heat budget there. We experimentally and numerically investigated the small-scale boundary layer dynamics over snow patches and their effect on the energy balance at the snow surface. Local eddy flux measurements at an alpine test site revealed that wind velocity, wind fetch distance and topographical curvature control the boundary layer growth, boundary layer decoupling and the efficiency of advective heat transport to contribute to snow ablation. These results were verified in a wind tunnel experiment on the boundary layer development over a single snow patch. The experiments showed that heat advection was very efficient at short fetch distances and high wind velocities forming strong thermal gradients close to the snow surface. The heat potentially available from the advective heat transport was, however, not efficiently transferred towards the snow surface. The turbulent heat exchange was strongly suppressed at the lowest centimetres above the snow surface, where the Richardson number exceeded the critical value. Thus, boundary layer decoupling caused by very shallow layers of increased thermal stability could be shown to be very efficient, even for higher wind velocities. In addition to experiments, we numerically analysed the effect of heat advection, boundary layer decoupling and changing patterns of secondary flows on the energy balance of patchy snow cover characterized by different snow-cover fractions. The atmospheric boundary layer flows over patchy snow-covers were calculated with an atmospheric model (Advanced Regional Prediction System) on a very high resolution of 5 m. The numerical results revealed that the relative importance of boundary layer processes and the development of local flow patterns depend on the snow patch size distribution and the synoptic wind forcing. Calculations for quiescent wind situations demonstrated that well-developed katabatic winds exerted a major control on the energy balance at the patchy snow cover leading to a maximum in the mean downward heat flux over snow for high snow-cover fractions. Although, katabatic wind systems result in a decoupling of the local atmosphere from its warmer surrounding, the strong suppression of turbulence close to the snow cover was not captured. In contrast, strong synoptic winds promote the effect of heat advection and mitigate the impact of boundary layer decoupling on the catchments melt behaviour. The strong heat advection resulted in a maximum in the heat flux directed towards the snow cover for low snow-cover fractions if the flow field was forced by a synoptic wind. A sensitivity analysis to grid resolution suggests that the grid resolution is a critical factor for energy balance calculations over patchy snow covers. The comparison of simulations results from coarse (50 m) and fine (5 m) grid resolutions show a difference in the mean turbulent heat flux of 40% for high snow-cover fractions and of 70% for low snow-cover fractions. The lower mean values of the turbulent heat flux over snow for coarser grid resolutions can be explained by the inadequate representation of thermal internal boundary layers and the mitigation of local advection of sensible heat. A resolution smaller than 5 m would be, however, necessary to calculate the very shallow stable layers close to the surface, where efficient boundary layer decoupling occurs.

Mott, Rebecca; Daniels, Megan; Horender, Stefan; Crivelli, Philip; Lehning, Michael

2014-05-01

18

The Atmospheric Boundary Layer

ERIC Educational Resources Information Center

Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

Tennekes, Hendrik

1974-01-01

19

The fully nonlinear development of Goertler vortices in growing boundary layers

NASA Technical Reports Server (NTRS)

The fully nonlinear development of small wavelength Goertler vortices in a growing boundary layer is investigated using a combination of asymptotic and numerical methods. The starting point for the analysis is the weakly nonlinear theory of Hall (1982b) who discussed the initial development of small amplitude vortices in a neighborhood of the location where they first become linearly unstable. That development is unusual in the context of nonlinear stability theory in that it is not described by the Stuart-Watson approach. In fact the development is governed by a pair of coupled nonlinear partial differential evolution equations for the vortex flow and the mean flow correction. Here the further development of this interaction is considered for vortices so large that the mean flow correction driven by them is as large as the basic state. Surprisingly it is found that such a nonlinear interaction can still be described by asymptotic means. It is shown that the vortices spread out across the boundary layer and effectively drive the boundary layer. In fact the system obtained by writing down the equations for the fundamental component of the vortex generate a differential equation for the basic state. Thus the mean flow adjusts so as to make these large amplitude vortices locally neutral. Moreover in the region where the vortices exist the mean flow has a square-root profile and the vortex velocity field can be written down in closed form. The upper and lower boundaries of the region of vortex activity are determined by a free-boundary problem involving the boundary layer equations. In general it is found that this region ultimately includes almost all of the original boundary layer and much of the free-stream. In this situation the mean flow has essentially no relationship to the flow which exists in the absence of the vortices.

Hall, Philip; Lakin, William D.

1987-01-01

20

Studies of hypersonic boundary layer behavior

Here, we present the final technical report on AFOSR Grant F49620-93-0064, Studies Of Hypersonic Boundary Layer Behavior. The grant covered three interrelated research efforts: a study of the structure of hypersonic turbulent boundary layers and shock wave boundary layer interactions, a study of boundary layer transition at supersonic and hypersonic speeds, and the development and application of new optical techniques

A. J. Smits; R. B. Miles; G. L. Brown

1995-01-01

21

The Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

A comprehensive and lucid account of the physics and dynamics of the lowest one to two kilometers of the Earth's atmosphere in direct contact with the Earth's surface, known as the atmospheric boundary layer (ABL). Dr. Garratt emphasizes the application of the ABL problems to numerical modeling of the climate, which makes this book unique among recent texts on the subject. He begins with a brief introduction to the ABL before leading to the development of mean and turbulence equations and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modeling of the ABL is crucially dependent for its realism on the surface boundary conditions, so chapters four and five deal with aerodynamic and energy considerations, with attention given to both dry and wet land surfaces and the sea. The author next treats the structure of the clear-sky, thermally stratified ABL, including the convective and stable cases over homogeneous land, the marine ABL, and the internal boundary layer at the coastline. Chapter seven then extends this discussion to the cloudy ABL. This is particularly relevant to current research because the extensive stratocumulus regions over the subtropical oceans and stratus regions over the Arctic have been identified as key players in the climate system. In the final chapters, Dr. Garratt summarizes the book's material by discussing appropriate ABL and surface parameterization schemes in general circulation models of the atmosphere that are being used for climate stimulation.

Garratt, J. R.

1994-05-01

22

Development of an Acoustic Vorticity Meter to Measure Shear in Ocean-Boundary Layers.

National Technical Information Service (NTIS)

This thesis describes the analysis and development of an acoustic vorticity meter to measure shear in ocean boundary layers over smaller measurement volumes than previously possible. The instrument measures three axis vorticity at 0.83 and 2.45 meters bel...

F. T. Thwaites

1995-01-01

23

Separated laminar boundary layers

NASA Technical Reports Server (NTRS)

Classical boundary layer theory is inadequate to deal with the problem of flow separation owing to its underlying assumption that the boundary layer has an insignificant effect on the external stream. This difficulty is resolved by a theory which includes interaction with the external flow. This theory is described from the viewpoint of the asymptotic triple deck structure. Several triple deck studies are reviewed with emphasis on results of interest in aeronautical applications.

Burggraf, O. R.

1976-01-01

24

During the last decade there has been a surge in efforts to understand the processes at work in the inhomogeneous atmospheric boundary layer. Much of the interest in the problem has been driven by increasingly urgent needs to develop accurate assessments of man`s Contribution to climate change. It has been argued that subgrid-scale secondary circulations in the boundary layer can cause significant errors in parameterized turbulent surface fluxes. Such circulations -- variously termed ``inland breezes``, ``lake breezes``, ``snow breezes``, or ``nonclassical mesoscale circulations`` are becoming widely discussed and modeled. Because surface fluxes are part of the lower boundary condition for global climate models, it is important to understand when these circulations occur and what their effects are on overall turbulent transfer. What are not yet clear are the combinations of the ambient wind and the horizontal scale and intensity of surface flux variability under which we may expect boundary layer secondary circulations to occur. Several authors have modeled the development of these circulations for ad hoc situations of alternating surface characteristics, and SA have developed one parameterization relating the scale of surface heat flux variability and the ambient wind to the evolution of NCMCs. In this paper we present observations, collected in a region of inhomogeneous surface fluxes, that suggest the development of a ``farm breeze``, and we develop an alternative scaling argument to that of SA that better represents our measurement conditions.

Shaw, W.J.; Doran, J.C.

1994-03-01

25

Boundary layer transition studies

NASA Technical Reports Server (NTRS)

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.

Watmuff, Jonathan H.

1995-01-01

26

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

NASA Technical Reports Server (NTRS)

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

Vanzante, Dale E.; Okiishi, Theodore H.

1991-01-01

27

NASA Astrophysics Data System (ADS)

The Boundary Layer Radiometer is a small, low mass (<1kg) radiometer with only a single moving part - a scan/calibration mirror. The instrument consists of a three mirror telescope system incorporating an intermediate focus for use with miniature infrared and visible filters. It also has an integrated low power blackbody calibration target to provide long-term calibration stability The instrument may be used as an upward looking boundary layer radiometer for both the terrestrial and Martian atmospheres with appropriate filters for the mid-infrared carbon dioxide band, as well as a visible channel for the detection of aerosol components such as dust. The scan mirror may be used to step through different positions from the local horizon to the zenith, allowing the vertical temperature profile of the atmosphere to be retrieved. The radiometer uses miniature infrared filter assemblies developed for previous space-based instruments by Oxford, Cardiff and Reading Universities. The intermediate focus allows for the use of upstream blocking filters and baffles, which not only simplifies the design of the filters and focal plane assembly, but also reduces the risk of problems due to stray light. Combined with the calibration target this means it has significant advantages over previous generations of small radiometers.

Irshad, Ranah; Bowles, N. E.; Calcutt, S. B.; Hurley, J.

2010-10-01

28

NASA Astrophysics Data System (ADS)

Well-resolved measurements of the streamwise velocity in zero pressure gradient turbulent boundary layers are presented for friction Reynolds numbers up to 19,670. Distinct from most studies, the present boundary layers undergo nearly a decade increase in Reynolds number solely owing to streamwise development. The profiles of the mean and variance of the streamwise velocity exhibit logarithmic behavior in accord with other recently reported findings at high Reynolds number. The inner and mid-layer peaks of the variance profile are evidenced to increase at different rates with increasing Reynolds number. A number of statistical features are shown to correlate with the position where the viscous force in the mean momentum equation loses leading order importance, or similarly, where the mean effect of turbulent inertia changes sign from positive to negative. The near-wall peak region in the 2-D spectrogram of the fluctuations is captured down to wall-normal positions near the edge of the viscous sublayer at all Reynolds numbers. The spatial extent of this near-wall peak region is approximately invariant under inner normalization, while its large wavelength portion is seen to increase in scale in accord with the position of the mid-layer peak, which resides at a streamwise wavelength that scales with the boundary layer thickness.

Vincenti, P.; Klewicki, J.; Morrill-Winter, C.; White, C. M.; Wosnik, M.

2013-12-01

29

Boundary layer simulator improvement

NASA Technical Reports Server (NTRS)

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

1989-01-01

30

Development of Concentration Boundary Layer in Viscous Sublayer of Turbulent Flows at Sc>>1

NASA Astrophysics Data System (ADS)

An analysis is presented on the evolution of diffusion-sublayer thickness for micro-chemical probes flushed with a solid wall adjacent to a fully-developed turbulent boundary layer. Using the Von-Karman approximate technique, we derive a unique differential equation for the diffusion-layer thickness development on the entire probe length. Solutions to this approximate equation can be found in two limits: one in the leading edge of the probe where streamwise diffusion and convection are of the same order, and the second where the transverse turbulent eddy-diffusion plays a role in the mass-transfer process. Simple analytical expressions are derived in these limits. According to this analysis, in the close vicinity of the leading edge, the diffusion layer develops according to x^1 law, with x being the stearmwise distance from the leading edge. In the region in which both stearmwise diffusion and turbulent eddy-diffusion are unimportant, the classical similarity solution of x^1/3 is recovered. As the concentration boundary layer becomes thicker, it approaches exponentially to its fully-developed value. The analysis matches well the mass-transfer data of Son and Hanratty. But, interestingly, this approximate analysis indicates that the similarity zone encompasses only a small section of the diffusion-sublayer development.

Abedian, Behrouz; Bates, Steven

1996-11-01

31

Nonequilibrium Chemistry Boundary Layer Integral Matrix Procedure.

National Technical Information Service (NTIS)

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 ch...

A. C. Buckingham H. Tong H. L. Morse

1973-01-01

32

Study of Boundary Layer Development in a Two-Stage Low-Pressure Turbine

NASA Technical Reports Server (NTRS)

Experimental data from jet-engine tests have indicated that unsteady blade row interactions and separation can have a significant impact on the efficiency of low-pressure turbine stages. Measured turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Several recent studies have revealed that Reynolds number effects may contribute to the lower efficiencies at cruise conditions. In the current study numerical simulations have been performed to study the boundary layer development in a two-stage low-pressure turbine, and to evaluate the transition models available for low Reynolds number flows in turbomachinery. The results of the simulations have been compared with experimental data, including airfoil loadings and integral boundary layer quantities. The predicted unsteady results display similar trends to the experimental data, but significantly overestimate the amplitude of the unsteadiness. The time-averaged results show close agreement with the experimental data.

Dorney, Daniel J.; Ashpis, David E.; Halstead, David E.; Wisler, David C.

1999-01-01

33

Boundary layer development in axial compressors and turbines. Part 2 of 4: Compressors

This is Part Two of a four-part paper. It begins with Section 6.0 and continues to describe the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this part, the authors present the experimental evidence used to construct the composite picture for compressors given in the discussion in Section 5.0 of Part 1. They show the data from the surface hot-film gages and the boundary layer surveys, give a thorough interpretation for the baseline operating condition, and then show how this picture changes with variations in Reynolds number, airfoil loading, frequency of occurrence of wakes and wake turbulence intensity. Detailed flow features are described using raw time traces. The use of rods to simulate airfoil wakes is also evaluated.

Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)

1997-07-01

34

... BBL - defined here as the portion of the water column and surface sediments impacted by the presence ... to comprise the bottom boundary layer of the water column and surface sediment layer. The dynamic ...

35

NASA Astrophysics Data System (ADS)

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.

Costigliola, V.

2010-09-01

36

Upper thermal boundary layer of planetary atmosphere: an experience of developing a general theory

Any planetary atmosphere has an upper layer where molecular heat conduction contributes significantly to the energy balance. In that layer the heat from absorbed solar radiation is transferred down to the lower atmosphere where it is removed away by the longwave radiation of atmosphere. We call that layer an upper thermal boundary layer and propose a general model for it

A. Semenov; G. Shved

2005-01-01

37

The Effects of Blade Count on Boundary Layer Development in a Low-Pressure Turbine

NASA Technical Reports Server (NTRS)

Experimental data from jet-engine tests have indicated that turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Recent studies have shown that Reynolds number effects contribute to the lower efficiencies at cruise conditions. In the current study numerical simulations have been performed to study the boundary layer development in a two-stage low-pressure turbine, and to evaluate the models available for low Reynolds number flows in turbomachinery. In a previous study using the same geometry the predicted time-averaged boundary layer quantities showed excellent agreement with the experimental data, but the predicted unsteady results showed only fair agreement with the experimental data. It was surmised that the blade count approximation used in the numerical simulations generated more unsteadiness than was observed in the experiments. In this study a more accurate blade approximation has been used to model the turbine, and the method of post-processing the boundary layer information has been modified to more closely resemble the process used in the experiments. The predicted results show improved agreement with the unsteady experimental data.

Dorney, Daniel J.; Flitan, Horia C.; Ashpis, David E.; Solomon, William J.

2000-01-01

38

Boundary layer simulator improvement

NASA Technical Reports Server (NTRS)

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.

Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

1984-01-01

39

Nonequilibrium chemistry boundary layer integral matrix procedure

NASA Technical Reports Server (NTRS)

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.

Tong, H.; Buckingham, A. C.; Morse, H. L.

1973-01-01

40

Development and structure of a film-cooling jet in a turbulent boundary layer with heat transfer

NASA Astrophysics Data System (ADS)

The development of a film-coolng jet in a turbulent boundary layer is investigated by measuring the mean velocity, turbulence structure, and heat transfer downstream of a jet issuing from a single film-cooling hole inclined at 30 deg with respect to the wall beneath a turbulent boundary layer. Particular attention is given to the downstream development of the turbulence structure due to the interaction of the injectant and the boundary layer when the blowing ratio is about 1.5. Stanton number distributions are also given for blowing ratios of 0.49, 0.99, and 1.48, as measured on a constant heat flux surface.

Subramanian, C. S.; Ligrani, P. M.; Green, J. G.; Doner, W.; Kaisuwan, P.

41

Dynamical Model Simulation of the Morning Boundary Layer Development in Deep Mountain Valleys.

NASA Astrophysics Data System (ADS)

A dry, two-dimensional version of the Colorado State University Multi-dimensional Cloud/Mesoscale Model was used to study the cross-valley evolution of the wind and temperature structures in an idealized east-west oriented mountain valley. Two simulations were performed, one in which the valley was heated symmetrically and a second in which a mid-latitude heating distribution was imposed. Both runs were initiated identically with a stable layer filling the valley to ridgetop and a neutral layer above the ridge. A specified sinusoidal surface potential temperature flux function approximating the diurnal cycle forced the model at the lower boundary.The results of the two simulations were remarkably similar. The model realistically reproduced the gross features found in actual valleys in both structure and timing. The simulated inversions were destroyed three and one-half hours after sunrise as a result of a neutral layer growing up from the surface meeting a descending inversion top. Slope winds with speeds of 3-5 m s1 developed over both sidewalls two and one-half hours after sunrise. Both cases revealed the development of strongly stable pockets of air over the sidewalls which form when cold air advected upslope loses its buoyancy at higher elevations. These stable pockets temporarily block the slope flow and force transient cross-valley circulations to form which act to destabilize the valley boundary layer. Cross-valley mixing and gravity waves rapidly redistribute heat across the valley to prevent large potential temperature gradients from forming. As a result, oven large differences in heating rates between opposing sidewalls do not result in significant cross-valley potential temperature differences. Organized cross-valley circulations and eddy motions enhance lateral mixing in the stable layer as well.

Bader, David C.; McKee, Thomas B.

1983-03-01

42

HUD - PREDICTION OF BOUNDARY-LAYER DEVELOPMENT ON TWO-DIMENSIONAL OR AXISYMETRIC BODIES

NASA Technical Reports Server (NTRS)

HUD is an integral code based on the Spaulding-Chi method for predicting boundary-layer development in laminar, transitional, and turbulent flow regions on two-dimensional or axisymetric bodies. This program was developed using integral-momentum, moment-of-momentum, and energy equations and has the capability of approximating non-equilibrium velocity profiles as well as the local surface friction in the presence of a pressure gradient. An approach was also developed for predicting heat transfer in a turbulent boundary layer in the presence of a high axial pressure gradient. Provisions are included for pressure gradients normal and lateral to the surface. The program is designed with particular emphasis on its applicability to supersonic combustion, thus, real gas flow effects were included. The resulting method permits estimation of cooling requirements for scramjet engines. Because of this capability, the HUD program has been incorporated into several scramjet cycle performance analysis codes including SCRAM (ARC-12338) and SRGULL (LEW-15093). HUD is written in machine independent FORTRAN 77 and should be portable to any computer with a valid FORTRAN compiler. On an IBM PC compatible under MS-DOS, HUD requires 145K RAM. The program is available on a 5.25 inch 360K MS-DOS diskette. HUD was developed in 1970 and last updated in 1991. IBM PC is a registered trademark of International Business Machines Corporation. MS-DOS is a registered trademark of Microsoft Corporation.

Pinckney, S. Z.

1994-01-01

43

Field Evaluation of Nortek Vectrino II Profiling Velocimeter in a Developing Tidal Boundary Layer

NASA Astrophysics Data System (ADS)

The Nortek Vectrino II is a newly developed acoustic Doppler profiling velocimeter. The three dimensional velocity profiles over a 3 cm range can resolve flow fields at a sampling rate of 100 Hz with a bin resolution of 1 mm. During June 2011, the Vectrino II was deployed in the Great Bay Estuary of New Hampshire, a tidal estuary in a long straight channel, where its capabilities were compared to a single point Nortek Vector ADV. In the first phase of the experiment, the Vectrino II was placed 13 cm from the flat muddy sand bed where it measured a relatively uniform velocity profile over the 3 cm range. Velocity magnitudes compared reasonably well to those of the Vector at 75 cm from the bed when fitting a boundary layer profile to the point measurements. Comparisons between the energy spectrum of the Vectrino II and Vector showed that the Vectrino II had a lower noise out to 5 Hz and reached the noise floor at roughly 8 Hz when the velocity of flow was 0.4 m/s or less. The vertical profiles allowed for estimates of the shear stress that are compared against estimates using Reynold stress and empirical drag law formulations. In the second phase of the experiment, the Vectrino II was moved such that the sampling region was within the water-bed boundary. Here, the Vectrino II read zero velocity measurements in the bed, and was able to resolve a velocity profile consistent with a developing boundary layer over the incoming half of a tidal cycle. Within 0.5 cm from the boundary, the Vectrino II can show intermittent evidence of beam interference by the bed. Within this very near bed region, histograms of the velocity, correlations, and amplitude allow for improved velocity estimates and suggest the presence of a viscous sublayer.

Foster, D.; Wengrove, M.

2011-12-01

44

Unsteady turbulent boundary layer analysis

NASA Technical Reports Server (NTRS)

The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent boundary layers. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent boundary layer.

Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.

1973-01-01

45

Boundary layer stability calculations

NASA Technical Reports Server (NTRS)

In this paper numerical calculation of the spatial stability of disturbances in the parallel and nonparallel Blasius boundary layers is considered. Chebyshev polynomials are used for discretization. The problem with the boundary condition at infinity is overcome, and the resulting nonlinear matrix eigenvalue problem is attacked directly. The secondary eigenvalue problem for three-dimensional disturbances is shown to be uniformly stable, and particular solutions of this problem generated by the Orr-Sommerfeld equation are shown. A numerical solution of the nonparallel problem is considered using Chebyshev polynomials. The matrix equations are analyzed directly and the problem of uniqueness of the nonparallel correction is settled by careful application of the Fredholm alternative. Nonparallel corrections to the streamwise eigenfunction are shown.

Bridges, Thomas J.; Morris, Philip J.

1987-01-01

46

NASA Technical Reports Server (NTRS)

This paper reports on progress towards developing a spatial stability code for compressible shear flows with two inhomogeneous directions, such as crossflow dominated swept-wing boundary layers and attachment line flows. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined. Finally, extension of the spatial stability analysis to supersonic attachment line flows is also considered.

Li, Fei; Choudhari, Meelan M.

2008-01-01

47

NASA Technical Reports Server (NTRS)

The end-wall boundary layer development in a compressor stage, including the inlet guide vane (IGV) passage and the rotor passage, was measured. The measurement upstream of the rotor and inside the IGV passage were carried out with a five-hole probe. The data (blade-to-blade) inside the IGV passage were carried out with a five-hole probe. The data (blade-to-blade) inside the rotor passage were measured using a three-sensor rotating hot-wire below the tip clearance region and "V' configuration probe inside the clearance region. The rotor exit measurements (blade-to-blade) were acquired with a laser Doppler velocimeter. The velocity profiles and the integral properties are presented and interpreted. The boundary layer is comparatively well behaved up to the leading edge of the rotor, beyond which complex interactions result in very unconventional profiles. The momentum thicknesses decrease in the leakage flow region of the rotor. The momentum thicknesses and the limiting streamline angles predicted from a momentum integral technique agree well with the data up to the leading edge of the rotor.

Lakshminarayana, B.; Murthy, K. N. S.; Pouagare, M.; Govindan, T. R.

1983-01-01

48

Suction on a turbulent boundary layer is applied through a narrow strip in order to understand the effects suction can have\\u000a on the boundary layer development and turbulent structures in the flow. Detailed two-component laser Doppler velocimetry (LDV)\\u000a and laser-induced fluorescence (LIF) based measurements have been undertaken in regions close to the suction strip and further\\u000a downstream. The region close

Amit Agrawal; Lyazid Djenidi; R. A. Antonia

2010-01-01

49

NASA Technical Reports Server (NTRS)

The goal of this project was to compare observations of marine and arctic boundary layers with: (1) parameterization systems used in climate and weather forecast models; and (2) two and three dimensional eddy resolving (LES) models for turbulent fluid flow. Based on this comparison, we hoped to better understand, predict, and parameterize the boundary layer structure and cloud amount, type, and thickness as functions of large scale conditions that are predicted by global climate models. The principal achievements of the project were as follows: (1) Development of a novel boundary layer parameterization for large-scale models that better represents the physical processes in marine boundary layer clouds; and (2) Comparison of column output from the ECMWF global forecast model with observations from the SHEBA experiment. Overall the forecast model did predict most of the major precipitation events and synoptic variability observed over the year of observation of the SHEBA ice camp.

Bretherton, Christopher S.

2002-01-01

50

Study of Boundary Layer Development in a Two-Stage Low-Pressure Turbine

NASA Technical Reports Server (NTRS)

Experimental data from jet-engine tests have indicated that unsteady blade row (wake) interactions and separation can have a significant impact on the efficiency of turbine stages. The effects of these interactions can be intensified in low-pressure turbine stages because of the low Reynolds number operating environment. Measured turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Thus, during the last decade a significant amount of effort has been put into determining the effects of transition and turbulence on the performance of low pressure turbine stages. Experimental investigations have been performed, for example, by Hodson et al. and Halstead et al. These investigations have helped identify/clarify the roles that factors such as the Reynolds number, free stream turbulence intensity, pressure gradient and curvature have in the generation of losses. In parallel to the experimental investigations, there have been significant analytical efforts to improve the modeling of transition. Examples of such efforts include the works of Mayle and Gostelow et al. These newer models show promise of providing accurate transition predictions over a wide range of flow conditions, although they have yet to be implemented into the numerical flow analyses used by the turbine design community. Some recent computational investigations of interest include the works of Chernobrovkin and Lakshminarayana and Eulitz and Engel. The focus of the current effort has been to -use a viscous, unsteady quasi-three-dimensional Navier-Stokes analysis to study boundary layer development in a two-stage low-pressure turbine. A two-layer algebraic turbulence model, along with a natural transition model and a bubble transition model, have been used, The geometry used in the simulations has been the subject of extensive experiments. The predicted results have been compared with experimental data, including airfoil loadings and time-averaged/unsteady integral boundary layer quantities.

Dorney, Daniel J.; Ashpis, David E.; Halstead, David E.; Wisler, David C.

1998-01-01

51

Streamwise development of the wind turbine boundary layer over a model wind turbine array

NASA Astrophysics Data System (ADS)

The streamwise development of turbulence statistics and mean kinetic energy in a model wind farm consisting of 3 × 5 wind turbines is studied experimentally in a wind tunnel. The analysis uses planar Particle Image Velocimetry data obtained at the centerline plane of the wind farm, covering the inflow as well as four planes in between five downstream wind turbines. The data analysis is organized by dividing these measurement planes into three regions: the above-rotor, rotor-swept, and below-rotor regions. For each field, flow development is quantified using a properly defined relative difference norm based on an integration over each of the regions. Using this norm, it is found that the mean streamwise velocity approaches a fully developed state most rapidly, whereas the flow development is more gradual for the second-order statistics. The vertical entrainment flux of the mean kinetic energy by the Reynolds shear stress, __, is observed to develop at a rate similar to that of the Reynolds shear stress rather than the mean streamwise velocity component. Its development is slowest in the layer nearest to the ground. Analysis of various terms in the mean kinetic energy equation shows that the wind turbine boundary layer has not yet reached fully developed conditions by the fifth turbine but that it is approaching such conditions. By comparing the vertical entrainment flux with the horizontal flux due to the mean flow, it is found that the former increases, whereas the latter decreases, as function of downstream distance, but that the former is already an important contributor in the developing region.__

Newman, Jensen; Lebron, Jose; Meneveau, Charles; Castillo, Luciano

2013-08-01

52

Development of a Multi-Planet Planetary Boundary Layer (PBL) Model

NASA Astrophysics Data System (ADS)

The planetary boundary layer (PBL) is critical to the atmospheric behavior of any terrestrial planet---as such, there is a plethora of numerical models designed to capture the dynamics of this region. However, many of these models are highly parameterized, relying on data measurements of the planet's atmosphere, typically Earth; such models cannot be reliably applied to other planets without recalibrating for the new environment. This is a challenging task where atmospheric PBL data is rare or non-existent, such as on Venus, Titan, and Triton. In order to reduce the dependence of the PBL model on in situ data, our approach is to draw on recent advances in engineering turbulence research by employing the detached-eddy simulation (DES) concept [Spalart, et. al., 1997]. Our attraction to DES is threefold: it is able to reproduce a variety of benchmark and practical engineering turbulent flows with a high degree of success, it readily fits into eddy viscosity models for turbulence closure, and it transits smoothly from a Reynolds-Averaged Navier-Stokes (RANS) model in the PBL to a Large Eddy Simulation (LES) model aloft, thus providing turbulence closure for the entire atmosphere. We are developing a multi-planet, DES-based PBL model using the EPIC atmospheric model as the platform. The EPIC model is designed to be applicable to all the planetary atmospheres, and therefore requires an accurate, universal boundary layer formulation. We will describe the formulation of a DES-based PBL model within EPIC and present first results obtained for benchmark flows resembling geophysical topography. This work is sponsored by the NASA EPSCoR and Planetary Atmospheres Programs Spalart, P.R., W-H Jou, M. Strelets, and S.R. Allmaras, 1997. ``Comments on the Feasibility of LES for Wings, and on a Hybrid RANS/LES approach'', 1st AFOSR Int. Conference on DNS/LES, in Advances in DNS/LES, C. Liu and Z. Liu (eds), Greyden Press, Columbus, OH.

Parimi, V. K.; LeBeau, R. P.; Dowling, T. E.

2003-05-01

53

Coupled groundwater-atmosphere modeling: effects on atmospheric boundary layer development

NASA Astrophysics Data System (ADS)

Newly-developed coupled land-atmosphere models which incorporate both subsurface and atmospheric moisture dynamics have the potential to change our understanding of the hydrologic cycle. This presentation describes the effects of coupled groundwater-atmosphere modeling on simulations of the atmospheric boundary layer. Both field observations and simulations indicate strong sensitivity of atmospheric dynamics to land-surface conditions, in particular surface soil moisture. Simulations of atmospheric flow in Owens Valley (California) and in the Riviera Valley (Switzerland) show strong sensitivity to land-surface conditions, thus motivating the need for more accurate representations of soil moisture. In addition to influences from weather and seasonal changes, soil moisture dynamics respond to diurnal heat fluxes on the land surface. Using our new fully-coupled groundwater-atmosphere model, we have demonstrated correlations of soil moisture and land-surface heat fluxes with groundwater fluctuations on short, diurnal time scales. By explicitly calculating groundwater dynamics for our domain of interest, we are able to produce realistic time- and space-varying soil moisture distributions that naturally correspond to variations in topography and surface evaporation. Simulations in idealized and real watersheds are shown to illustrate these effects. The observed variations in surface moisture distribution have large impacts on the moisture and temperature structure in the atmosphere, leading to changes in boundary layer depth and convective motions as compared to standard soil moisture representations. Our coupled model framework will allow detailed investigation of the complex cycle of land-atmosphere processes affecting moisture distributions in the subsurface and the atmosphere.

Chow, F. K.; Maxwell, R. M.; Kollet, S. J.; Daniels, M. H.; Rihani, J. F.

2007-12-01

54

NEW DEVELOPMENT IN DISPERSION EXPERIMENTS AND MODELS FOR THE CONVECTIVE BOUNDARY LAYER

We present recent experiments and modeling studies of dispersion in the convective boundary layer (CBL) with focus on highly-buoyant plumes that "loft" near the CBL top and resist downward mixing. Such plumes have been a significant problem in earlier dispersion models; they a...

55

NASA Technical Reports Server (NTRS)

A study of the effect of free-stream thermal-energy release from shock-induced exothermic reactions on boundary-layer development and transition is presented. The flow model is that of a boundary layer developing behind a moving shock wave in two-dimensional unsteady flow over a shock-tube wall. Matched sets of combustible hydrogen-oxygen-nitrogen mixtures and inert hydrogen-nitrogen mixtures were used to obtain transition data over a range of transition Reynolds numbers from 1,100,000 to 21,300,000. The heat-energy is shown to significantly stabilize the boundary layer without changing its development character. A method for application of this data to flat-plate steady flows is included.

Hall, J. L.

1974-01-01

56

Large Eddy Simulation study of fully developed thermal wind-turbine array boundary layers

NASA Astrophysics Data System (ADS)

It is well known that when wind turbines are deployed in large arrays, their efficiency decreases due to complex interactions among themselves and with the atmospheric boundary layer (ABL). For wind farms whose length exceeds the height of the ABL by over an order of magnitude, a “fully developed” flow regime can be established. In this asymptotic regime, changes in the stream-wise direction can be neglected and the relevant exchanges occur in the vertical direction. Such a fully developed wind-turbine array boundary layer (WTABL) has recently been studied1 using Large Eddy Simulations (LES) under neutral stability conditions. The simulations showed the existence of two log-laws, one above and one below the wind turbine region. This enabled the development of more accurate parameterizations of the effective roughness scale for a wind farm. Now, a suite of Large Eddy Simulations, in which wind turbines are also modeled using the classical “drag disk” concept are performed but for non-neutral conditions. The aim is to study the effects of different thermal ABL stratifications, and thus to study the efficiency and characteristics of large wind farms and the associated land-atmosphere interactions for realistic atmospheric flow regimes. Such studies help to unravel the physics involved in extensive aggregations of wind turbines, allowing us to design better wind farm arrangements. By considering various turbine loading factors, surface roughness values and different atmospheric stratifications, it is possible to analyze the influence of these into the induced surface roughness, and the sensible heat roughness length. These last two can be used to model wind turbine arrays in simulations of atmospheric dynamics at larger (regional and global) scales2, where the coarse meshes used do not allow to account for the specifics of each wind turbine. Results from different sets of simulations under stable and unstable conditions will be presented, for which also the corresponding effective roughness length-scales will be determined. Simulations use imposed heat flux at the bottom or an imposed temperature. The simulation results will be analyzed to determine how stratification affects momentum and scalar transport processes in the wind turbine wakes.

Calaf, M.; Meneveau, C. V.; Parlange, M. B.

2010-12-01

57

Large Eddy Simulation study of fully developed thermal wind-turbine array boundary layers

NASA Astrophysics Data System (ADS)

It is well known that when wind turbines are deployed in large arrays, their efficiency decreases due to complex interactions among themselves and with the atmospheric boundary layer (ABL). For wind farms whose length exceeds the height of the ABL by over an order of magnitude, a "fully developed" flow regime can be established. In this asymptotic regime, changes in the stream-wise direction can be neglected and the relevant exchanges occur in the vertical direction. Such a fully developed wind-turbine array boundary layer (WTABL) has recently been studied using Large Eddy Simulations (LES) under neutral stability conditions (Calaf et al. Physics of Fluids 22, 2010). Related wind-tunnel experiments on the WTABL are reported in Cal et al., J. Renewable and Sustainable Energy 2, 2010). The simulations showed the existence of two log-laws, one above and one below the wind turbine region. These results confirm basic assumptions made in prior work by Frandsen (J. Wind Eng. Ind. Aerodyn. 39, 1992) and Frandsen et al. (Wind Energy 9, 2006), and have enabled the development of more accurate parameterizations of the effective roughness scale for a wind farm. Now, a suite of Large Eddy Simulations, in which wind turbines are also modeled using the classical "drag disk" concept are performed but for non-neutral conditions. The aim is to study the effects of different thermal ABL stratifications, and thus to better understand the efficiency and characteristics of large wind farms and the associated land-atmosphere interactions for realistic atmospheric flow regimes. Such studies help to unravel the physics involved in extensive aggregations of wind turbines, allowing us to design better wind farm arrangements. By considering various turbine loading factors, surface roughness values and different atmospheric stratifications, it is possible to analyze the influence of these on the induced surface roughness, and the sensible heat roughness length. These last two can be used to model wind turbine arrays in simulations of atmospheric dynamics at larger (regional and global) scales, where the coarse meshes used do not allow to account for the specifics of each wind turbine. Results from different sets of large-eddy simulations under stable and unstable conditions will be presented, for which also the corresponding effective roughness length-scales are determined. Supported by the Swiss National Science Foundation (project 200021-107910/1) and US National Science Foundation (Project No. CBET 0730922).

Meneveau, Charles; Calaf, Marc; Parlange, Marc B.

2010-05-01

58

Study of the development of natural instabilities in a laminar boundary layer in incompressible flow

NASA Technical Reports Server (NTRS)

Natural instabilities which are created in a laminar boundary layer and which consist of intermittent wave trains were studied. The spectral analysis of these fluctuations makes it possible to localize them in terms of frequency and to isolate their spectrum of amplitude modulation. The variation in terms of abscissa value and ordinate value of these instabilities is compared with the results derived from the solution of the Orr-Sommerfeld equation.

Burnel, S.; Gougat, P.

1981-01-01

59

National Technical Information Service (NTIS)

The feasibility of a new experimental technique for studying the effect of unsteady flows on boundary layers is under development. The method studied uses a stationary NACA 0012 airfoil in a steady subsonic wind tunnel. Unsteadiness in the flow over the a...

E. E. Covert A. R. Kanevsky

1978-01-01

60

A detailed experimental study of turbulent boundary layers developing over rough surfaces subjected to both zero and adverse pressure gradients was undertaken. Two rough surfaces constituted by distributed random elements have been chosen. The experiments were conducted in the range of the Reynolds number R? based upon the momentum thickness varying from 2200 to 5800 and 3200 to 3800, respectively,

G. Pailhas; Y. Touvet; B. Aupoix

2008-01-01

61

Vortex boundary-layer interactions

NASA Technical Reports Server (NTRS)

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.

Bradshaw, P.

1985-01-01

62

Transient response of a turbulent boundary layer

NASA Technical Reports Server (NTRS)

A unique feature of the present ensemble-averaged measurements of a turbulent boundary layer's transient response to a spontaneous change in the free stream velocity distribution, is that the test boundary layer is a standard, steady, flat plate turbulent boundary layer at the entrance to the unsteady region, and is then subjected to sudden changes in free stream velocity distribution in the test section. These water tunnel tests were controlled by minicomputer. It is noted that the boundary layer development was relatively slow, with a characteristic time that was greater than the free stream time-of-flight by a factor of as much as 3. Response varied dramatically across the boundary layer, and the evolution of the turbulent stress field occurred on the same time scale as that of the ensemble-averaged velocity field.

Parikh, P. G.; Jayaraman, R.; Reynolds, W. C.; Carr, L. W.

1983-01-01

63

Upper thermal boundary layer of planetary atmosphere: An attempt of developing a general model

In any planetary atmosphere there is an uppermost layer in which the molecular thermal conduction is a significant mechanism of forming the thermal structure of the atmosphere. In this paper, the similarity approach is first used to develop the 1-D general model of aforementioned layer. The main concepts of the model are (i) the radiative equilibrium condition at the lower

A. O. Semenov; G. M. Shved

2008-01-01

64

NASA Astrophysics Data System (ADS)

Multielement surface hot-film sensors for ascertaining the laminar-to-turbulent transition region, and characterizing the frequencies of the most highly amplified disturbances in turbulent boundary layers, have been extended through the discovery of phase-reversal signatures that can accurately determine the spatial locations of stagnation, separation, and reattachment points. To this has been added the breakthrough in thermal anemometry represented by a high-sensitivity/broad bandwidth anemometer that is uniquely suited for wind tunnel and flight-test applications.

Mangalam, S. M.; Kuppa, S.

65

The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted in the test facility CW-22 at NASA Lewis Research Center. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter-rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. The crossplane structure of embedded vortices is observed to be very similar to that exhibited by the two dimensional Oseen vortex with matching descriptors. Quantitative comparisons are established. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen vortex. Vortex trajectories are successfully modelled by including the convective effects of neighbors, and images to represent the wall. The streamwise decay of circulation is successfully modelled for the single vortex, and for large initial spacings, by accounting for the effects of wall friction. An additional mechanism associated with the turbulent stress field in the near vicinity of the vortex cores is postulated to explain the large losses in the circulation obtained for the smaller initial spacings. The streamwise decay of vortex circulation at the smaller spacings is successfully modelled by summing wall friction losses and 'proximity' losses. These proximity losses are found to be proportional to the gradient in streamwise vorticity occurring between an embedded vortex and its adjacent counter-rotating neighbors.

Wendt, Bruce James

1991-07-01

66

Boundary-layer linear stability theory

NASA Technical Reports Server (NTRS)

Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer reached a stage of development which permit the direct solution of the primary differential equations, numerical results were obtained from the linear theory during the next 10 years for many different boundary layer flows: three dimensional boundary layers; free convention boundary layers; compressible boundary layers; boundary layers on compliant walls; a recomputation of Falkner-Skan flows; unsteady boundary layers; and heated wall boundary layers.

Mack, L. M.

1984-01-01

67

Linear optimal control applied to instabilities in spatially developing boundary layers

NASA Astrophysics Data System (ADS)

The work presented extends previous research on linear controllers in temporal channel flow to spatially evolving boundary layer flow. The flows studied are those on an infinite swept wedge described by the Falkner Skan Cooke (FSC) velocity profiles, including the special case of the flow over a flat plate. These velocity profiles are used as the base flow in the Orr Sommerfeld Squire equations to compute the optimal feedback control through blowing and suction at the wall utilizing linear optimal control theory. The control is applied to a parallel FSC flow with unstable perturbations. Through an eigenvalue analysis and direct numerical simulations (DNS), it is shown that instabilities are stabilized by the controller in the parallel case. The localization of the convolution kernels for control is also shown for the FSC profiles.

Högberg, Markus; Henningson, Dan S.

2002-11-01

68

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

69

Physics of magnetospheric boundary layers

NASA Technical Reports Server (NTRS)

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.

Cairns, Iver H.

1995-01-01

70

NASA Astrophysics Data System (ADS)

Gravitationally unstable, transient, diffusive boundary layers play an important role in carbon dioxide sequestration. Though the linear stability of these layers has been studied extensively, there is wide disagreement in the results, and it is not clear which methodology best reflects the physics of the instability. We demonstrate that this disagreement stems from an inherent sensitivity of the problem to how perturbation growth is measured. During an initial transient period, the concentration and velocity fields exhibit different growth rates and these rates depend on the norm used to measure perturbation amplitude. This sensitivity decreases at late times as perturbations converge to dominant quasi-steady eigenmodes. Therefore, we characterize the linear regime by measuring the duration of the initial transient period, and we interpret the convergence process by examining the growth rates and non-orthogonality of the quasi-steady eigenmodes. To judge the relevance of various methodologies and perturbation structures to physical systems, we demonstrate that every perturbation has a maximum allowable initial amplitude above which the sum of the base-state and perturbation produces unphysical negative concentrations. We then perform direct numerical simulations to demonstrate that optimal perturbations considered in previous studies cannot support finite initial amplitudes. Consequently, convection in physical systems is more likely triggered by ``sub-optimal'' perturbations that support finite initial amplitudes.

Tilton, Nils; Daniel, Don; Riaz, Amir

2013-09-01

71

Internal Layers in The Turbulent Boundary Layer*

NASA Astrophysics Data System (ADS)

Coherent structures in zero-pressure gradient turbulent boundary layers are investigated using particle image velocimetry (PIV). Instantaneous streamwise and normal velocity components were measured in a two-dimensional plane at Req = 1000 and 7000. The images have a wide field of view to capture over three d in the streamwise direction. Recent evidence1 suggests that growing, internal boundary layers exist close to the wall, and may be modulated by the large-scale bulges of the outer region. The investigation focuses on the existance and nature of these layer, the properties of outer region turbulent bulges, and the possible interaction of these two structures. 1 C. D. Meinhart and R. J. Adrian, Phys., Fluids 7 1995. * Work supported by ONR Grant No. N00014-93-1-0552

Tomkins, C. D.; Adrian, Ronald J.

1996-11-01

72

NASA Astrophysics Data System (ADS)

During the last 5 years, the Small Unmanned Meteorological Observer SUMO has been developed as a flexible tool for atmospheric boundary layer (ABL) research to be operated as sounding system for the lowest 4 km of the atmosphere. Recently two main technical improvements have been accomplished. The integration of an inertial measurement unit (IMU) into the Paparazzi autopilot system has expanded the environmental conditions for SUMO operation. The implementation of a 5-hole probe for determining the 3D flow vector with 100 Hz resolution and a faster temperature sensor has enhanced the measurement capabilities. Results from two recent field campaigns are presented. During the first one, in Denmark, the potential of the system to study the effects of wind turbines on ABL turbulence was shown. During the second one, the BLLAST field campaign at the foothills of the Pyrenees, SUMO data proved to be highly valuable for studying the processes of the afternoon transition of the convective boundary layer.

Reuder, Joachim; Jonassen, Marius O.; Ólafsson, Haraldur

2012-10-01

73

``Broadband'' plasma waves in the boundary layers

Boundary layers are commonly encountered in space and astrophysical plasmas. For example, interaction of solar wind plasma with the planets and comets produces magnetopause and cometopause boundary layers, respectively. Generally, the boundary layers are formed when plasmas with different characteristics interact with each other. The plasma sheet boundary layer in the Earth's magnetotail is formed owing to the interaction of

G. S. Lakhina; B. T. Tsurutani; H. Kojima; H. Matsumoto

2000-01-01

74

This is a collaborative project with Dr. Ping Zhu at Florida International University. It was designed to address key issues regarding the treatment of boundary layer cloud processes in climate models with UM’s research focusing on the analyses of ARM cloud radar observations from MMCR and WACR and FIU’s research focusing on numerical simulations of boundary layer clouds. This project capitalized on recent advancements in the ARM Millimeter Cloud Radar (MMCR) processing and the development of the WACR (at the SGP) to provide high temporal and spatial resolution Doppler cloud radar measurements for characterizing in-cloud turbulence, large-eddy circulations, and high resolution cloud structures of direct relevance to high resolution numerical modeling studies. The principal focus of the observational component of this collaborative study during this funding period was on stratocumulus clouds over the SGP site and fair-weather cumuli over the Nauru site. The statistical descriptions of the vertical velocity structures in continental stratocumulus clouds and in the Nauru shallow cumuli that are part of this study represents the most comprehensive observations of the vertical velocities in boundary layer clouds to date and were done in collaboration with Drs. Virendra Ghate and Pavlos Kollias.

Albrecht, Bruce,

2013-07-12

75

NASA Astrophysics Data System (ADS)

During the last 5 years, the Small Unmanned Meteorological Observer SUMO has been developed as a new and flexible tool for atmospheric boundary layer (ABL) research to be operated as controllable and recoverable atmospheric sounding system for the lowest 4 km above the Earth's surface. In the year 2011 two main technical improvements of the system have been accomplished. The integration of an inertial measurement unit (IMU) into the Paparazzi autopilot system has expanded the environmental conditions for SUMO operation to now even allowing incloud flights. In the field of sensor technology the implementation of a 5-hole probe for the determination of the 3 dimensional flow vector impinging the aircraft with a 100 Hz resolution and of a faster Pt1000 based temperature sensor have distinctly enhanced the meteorological measurement capabilities. The extended SUMO version has recently been operated during two field campaigns. The first one in a wind farm close to Vindeby on Lolland, Denmark, was dedicated to the investigation of the effects of wind turbines on boundary layer turbulence. In spite of a few pitfalls related to configuration and synchronisation of the corresponding data logging systems, this campaign provided promising results indicating the capability and future potential of small UAS for turbulence characterization in and around wind farms. The second one, the international BLLAST (Boundary Layer Late Afternoon and Sunset Transition) field campaign at the foothills of the Pyrenees in Lannemezan, France was focussing on processes related to the afternoon transition of the convective boundary layer. On a calm sunny day during this experiment, the SUMO soundings revealed an unexpected 2°C cooling in the ABL during morning hours. By a comparison with model simulations this cooling can be associated with thermally-driven upslope winds and the subsequent advection of relatively cool air from the lowlands north of the Pyrenees.

Reuder, J.; Jonassen, M. O.; Ólafsson, H.

2012-04-01

76

Investigation of Mesoscale Variability in Convective Boundary Layer Development Using LASE

NASA Technical Reports Server (NTRS)

Throughout this research effort we have analyzed data collected from the Southern Great Plains 1997 (SGP) experiment to evaluate terms in the budget of water vapor in the atmospheric boundary layer (ABL). The analysis is centered on using data obtained from the Lidar Atmospheric Sensing Experiment (LASE) downward-looking differential absorption lidar (DIAL) that was flown on the NASA-P3 aircraft. The DIAL is able to measure vertical profiles of water vapor, as well as aerosol backscatter, throughout the ABL. Initial work on using the DIAL is summarized in the attached meeting preprint, which discusses results from a segment of the 12 July 1997 flight. Additional analysis has been carried out using both the DIAL data and in situ measurements to obtain more complete and detailed estimates of terms in the ABL water vapor budget. This includes data from the Canadian National Research Council Twin Otter aircraft, as well as from a spectrum of surface-based instruments. This work is expected to lead to a refereed article planned for submission to the Journal.

Lenschow, Donald H.

2000-01-01

77

Entrainment Parameterization in Convective Boundary Layers.

NASA Astrophysics Data System (ADS)

Various runs were performed with a large eddy simulation (LES) model to evaluate different types of entrainment parametrizations. For this evaluation, three types of boundary layers were simulated: a clear convective boundary layer (CBL), a boundary layer containing a smoke concentration, and a cloud-topped boundary layer. It is shown that the assumption that the entrainment flux equals the product of the entrainment rate and the jump over a discontinuous inversion is not valid in CBLs simulated by an LES model. A finite inversion thickness (i.e., a first-order jump model) is needed to define an entrainment flux for which this approximation of the flux is valid. This entrainment flux includes not only the buoyancy flux at the inversion, but also the surface heat flux. The parameterization of the buoyancy flux at the inversion is evaluated for different closures, as suggested in the literature (i.e., Eulerian partitioning, process partitioning, and a closure developed by Deardorff), and where needed is extended for use in a first-order jump model. The closure based on process partitioning is found to yield consistent results in all types of convective boundary layers and shows the best agreement with the limit found in LES results if the longwave radiative flux divergence takes place in a much shallower layer than the mixed layer.

Vanzanten, Margreet C.; Duynkerke, Peter G.; Cuijpers, Joannes W. M.

1999-03-01

78

NASA Astrophysics Data System (ADS)

Wind-turbines deployed in a large array experience a decrease in individual efficiency due to interactions among themselves and the atmospheric boundary layer (ABL). A fully developed flow regime can be established when this wind-turbine array is an order of magnitude longer than the height of the ABL. Under this condition, vertical entrainment of kinetic energy is essential for power extraction. In order to characterize this entrainment process, a Large Eddy Simulation of the fully developed wind-turbine atmospheric boundary layer (WTABL) is performed using a pseudo-spectral method with periodic boundary conditions in the horizontal directions. The wind-turbines are modeled as drag disks with a force proportional to the local disk-averaged velocity (Calaf et al. 2010, Phys. Fluids 22, 015110). Conditional averaging of the WTABL velocity field based on thresholds set on the instantaneous power extraction is performed to determine conditional coherent flow structures associated with large values of power extraction. Properties of the conditional structures are examined and their dependencies on WT loading factors are studied.

Verhulst, Claire; Meneveau, Charles

2010-11-01

79

Boundary Layer Cloudiness Parameterizations Using ARM Observations

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.

Bruce Albrecht

2004-09-15

80

The intent of the present contribution is to explain theoretically the experimentally measured surface heat transfer rates on a slightly concave surface with a thin boundary layer in an otherwise laminar flow. As the flow develops downstream, the measured heat transfer rate deviates from the local laminar value and eventually exceeds the local turbulent value in a non-trivial manner even in the absence of turbulence. While the theory for steady strong nonlinear development of streamwise vortices can bridge the heat transfer from laminar to the local turbulent value, further intensification is attributable to the transport effects of instability of the basic steady streamwise vortex system. The problem of heat transport by steady and fluctuating nonlinear secondary instability is formulated. An extended Reynolds analogy for Prandtl number unity, Pr=1, is developed, showing the similarity between streamwise velocity and the temperature. The role played by the fluctuation-induced heat flux is similar to momentum flux by the Reynolds shear stress. Inferences from the momentum problem indicate that the intensified heat flux developing well beyond the local turbulent value is attributed to the transport effects of the nonlinear secondary instability, which leads to the formation of 'coherent structures' of the flow. The basic underlying pinions of the non-linear hydrodynamic stability problem are the analyses of J. T. Stuart, which uncovered physical mechanisms of nonlinearities that are crucial to the present developing boundary layers supporting streamwise vortices and their efficient scalar transporting mechanisms. PMID:18495623

Liu, J T C

2008-08-13

81

NASA Astrophysics Data System (ADS)

Field observations of sediment suspension within a developing tidal boundary layer were collected with a newly developed Nortek Vectrino II Profiling Velocimeter acoustic backscatter probe; while nutrient release and sediment chemistry were sampled with pore water samples from sediment core sections. The velocimeter is capable of measuring a three dimensional velocity profile at 1 mm increments over a range of 3 cm. The observations were obtained in the Great Bay tidal Estuary of New Hampshire. The monitored area was a long straight channel with maximum depth of 20 m MLLW, tidal range of 3 m and depth of 1.5 m MLLW at the sampling location. During the incoming half tidal cycle, the tidal forcing produces a fairly unidirectional flow over the flat sandy mud sediment bed. Three methods for estimating the bed stress were evaluated and compared against laboratory observations with a sediment core erosion chamber. When wind conditions are low to moderate and there are low hydrologic influences, the roughly 30 cm/s near the bed flows resulted in peak shields parameters near the threshold for motion of 0.07 to 0.16 for a dimensionless grain size of 1.96. During periods of larger wind and/or higher hydrologic conditions, the threshold is exceeded and there is evidence to suggest a local response in the sediment chemistry. During the developing phase of the tidal boundary layer, the observations provide evidence for a viscous sublayer in the lowest 0.5 cm of the water column before moving into turbulent boundary layer flow. Observations of the stress placed upon the bed in relation to the nutrient chemistry of the sediment column provide an image of the types of loads and stresses the Great Bay Estuary receives during various hydraulic and weather related forcing conditions.

Wengrove, M.; Foster, D.; Kalnejais, L. H.; Percuoco, V.

2011-12-01

82

Stability of compressible boundary layers

NASA Technical Reports Server (NTRS)

The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

Nayfeh, Ali H.

1989-01-01

83

Boundary layer energy transport in plasma devices

NASA Astrophysics Data System (ADS)

The purpose of this research was to develop a model of boundary-layer energy transport in electric launchers, and perform a numerical simulation to investigate the influence of turbulence, thermal radiation and ablation on energy flux to the surface. The model developed combines boundary-layer conservation equations with a k-o turbulence model and multi-group radiation transport, and uses plasma models for fluid properties such as viscosity, thermal conductivity and specific heat capacity. The resulting TURBFIRE computer code is the first code to model turbulence and radiation transport in a self-consistent manner for electric launchers. Although approximations have been made to simplify the physics enough to permit a numerical solution, this is the most comprehensive boundary-layer simulation of turbulence and radiation transport to date.

Orton, Nigel Paul

2000-11-01

84

The Martian Surface Boundary Layer

NASA Technical Reports Server (NTRS)

The acquisition of meteorological data from the surface of Mars by the two Viking Landers and Mars Pathfinder make it possible to estimate atmospheric boundary layer parameters and surface properties at three different locations on the planet. Because the Martian atmosphere is so thin the majority of the solar radiance is converted to heat at the surface. The difference between surface and atmospheric temperature can also constraint surface albedo, thermal inertia, and infrared emissivity. The Mars Pathfinder Atmospheric Structure Instrument/Meteorological package (ASI/MET) was the most capable weather monitoring system ever sent to the surface of another planet to date. One of the prime objectives of the ASI/MET package is to characterize the surface boundary layer parameters, particularly the heat and momentum fluxes, scaling temperature and friction velocity, and estimate surface roughness. Other important boundary layer parameters, such as Richardson Number, Monin-Obukhov length, analysis of turbulence characteristics of wind and temperature, and atmospheric stability class can also be determined from these measurements.

Wilson, G. R.; Joshi, M.

1999-01-01

85

Boundary layers in dilute particle suspensions

NASA Astrophysics Data System (ADS)

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).

Foster, M. R.; Duck, P. W.; Hewitt, R. E.

2005-11-01

86

NASA Astrophysics Data System (ADS)

Measurements of the turbulent fluxes of momentum, heat, and salinity in the oceanic boundary layer are difficult to obtain, as both a stable platform and high-resolution instrumentation are required. The overall objective of the present investigation was to develop a boundary layer instrumentation system capable of measuring turbulent fluxes in the marginal ice zone environment. This investigation focuses on a feasibility study toward development of a diode laser Doppler velocimeter (DLDV) to be used as the velocity sensor for a high-resolution velocity/temperature/conductivity cluster, with a spatial resolution of 1 to 2 cm. Phase 1 findings show very promising results for the DLDV in laboratory environments. Measurements in a pipe flow facility demonstrated very distinctive Doppler burst signals, with more than adequate signal-to-noise ratio, even in clean tap water passed through a 10 micrometer filter. Excellent burst density was observed when a small quantity of Puget Sound water was added to the tap water. For all practical purposes, the performance of the DLDV is at least as good as that of a well-established LDV system using a helium-neon laser as the light source.

Schedvin, J. C.; Liu, H. T.

1984-05-01

87

Boundary layer blockage in expansion tube nozzles

NASA Technical Reports Server (NTRS)

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.

Sudnitsin, Olga; Morgan, Richard G.

1995-01-01

88

Turbulent Boundary Layer Inner-Outer Interactions.

National Technical Information Service (NTIS)

A summary of work performed to study the interactions between the inner and outer regions of a turbulent boundary layer is presented. The interactions were studied by observing the response of the boundary layer to different perturbations. The inner regio...

D. G. Bogard C. Lim A. Kohli

1993-01-01

89

NASA Astrophysics Data System (ADS)

A new APG boundary layer flow has been generated to examine the nature of the flow development based on the Cp distribution and the effects of the upstream conditions on the downstream flow. X-wire measurements of the longitudinal and lateral velocity components are recorded at 20 streamwise locations. It is shown that when flows experience changing pressure gradients from ZPG/FPG to APG, a similar flow development exists, regardless of the nature of the APG. Although the equilibrium pressure parameter of Castillo/George (2001) yields a better understanding of flow development than the Cp distribution, this type of flow development prevents most traditional scalings from exhibiting a universal behavior. A new scaling is shown which provides a way to scale such developing flows. It is applied to the new flow and the APG boundary layer flows of Anderson, Bradshaw, Clauser and Newman.

Brzek, Brian; Anderson, Catherine; Castillo, Luciano; Turan, Ozden

2004-11-01

90

Boundary-layer theory for blast waves

NASA Technical Reports Server (NTRS)

It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.

Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.

1975-01-01

91

DYNAMIC BOUNDARY CONTROL OF BEAMS USING ACTIVE CONSTRAINED LAYER DAMPING

A globally stable boundary control strategy is developed to damp the vibration of beams fully treated with active constrained layer damping (ACLD) treatments. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced generates a control force and moment acting at the boundary of the treated beam. The development of the boundary

A. Baz

1997-01-01

92

Performance and boundary-layer evaluation of a sonic inlet

NASA Technical Reports Server (NTRS)

Tests were conducted to determine the boundary layer characteristics and aerodynamic performance of a radial vane sonic inlet with a length/diameter ratio of 1 for several vane configurations. The sonic inlet was designed with a slight wavy wall type of diffuser geometry, which permits operation at high inlet Mach numbers (sufficiently high for good noise suppression) without boundary layer flow separation and with good total pressure recovery. A new method for evaluating the turbulent boundary layer was developed to separate the boundary layer from the inviscid core flow, which is characterized by a total pressure variation from hub to tip, and to determine the experimental boundary layer parameters.

Schmidt, J. F.; Ruggeri, R. S.

1976-01-01

93

Bursting frequency prediction in turbulent boundary layers

The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.

LIOU,WILLIAM W.; FANG,YICHUNG

2000-02-01

94

NASA Astrophysics Data System (ADS)

Plane metal layers loading by an oblique shock wave during explosive welding and various shields' effects on a contact boundary state after the loading were experimentally investigated. The stabilizing effect of thin metal coating on the explosive welding and disturbance evolution at a contact boundary was experimentally found. For example for copper -- copper contact boundary disturbance amplitude is a 350 ?m. For contact boundary for the same pair, but under the loading through a zinc layer ? 22 ?m thick, the disturbance amplitude decreased up to a 15 ?m. Thermophysical properties of a coating material affect the stabilization. The phenomenon of perturbation attenuation can be explained by the character of occurred hydrodynamic flow and complicated stress -- strain state of substance.

Drennov, Oleg

2005-07-01

95

NASA Astrophysics Data System (ADS)

A MHz rate Shack-Hartmann sensor has been developed which allows the measurement of wavefront phase distortion due to the density fluctuations in high speed flows. It is capable of obtaining 30 frame movies at up to 500 kHz or 1 MHz with a 2 is pause at every fifth frame. The sensor was used to obtain the distortion due to flow over a wedge at Mach 2.4 at a 7.8 kHz framing rate. It was also used at 500 kHz to measure the optical path difference due to a nitrogen free jet and due to a hypersonic boundary layer at Mach 8.

Wyckham, Chris; Zaidi, Sohail; Miles, Dick; Smits, Lex

2003-11-01

96

Flow unsteadiness effects on boundary layers

NASA Technical Reports Server (NTRS)

The development of boundary layers at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on boundary layer growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire boundary layer for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.

Murthy, Sreedhara V.

1989-01-01

97

NASA Astrophysics Data System (ADS)

A dynamic procedure is developed to compute the model coefficients in the recently introduced modulated gradient models for both momentum and scalar fluxes. The magnitudes of the subgrid-scale (SGS) stress and the SGS flux are estimated using the local equilibrium hypothesis, and their structures (relative magnitude of each of the components) are given by the normalized gradient terms, which are derived from the Taylor expansion of the exact SGS stress/flux. Previously, the two model coefficients have been specified on the basis of theoretical arguments. Here, we develop a dynamic SGS procedure, wherein the model coefficients are computed dynamically according to the statistics of the resolved turbulence, rather than provided a priori or ad hoc. Results show that the two dynamically calculated coefficients have median values that are approximately constant throughout the turbulent atmospheric boundary layer (ABL), and their fluctuations follow a near log-normal distribution. These findings are consistent with the fact that, unlike eddy-viscosity/diffusivity models, modulated gradient models have been found to yield satisfactory results even with constant model coefficients. Results from large-eddy simulations of a neutral ABL and a stable ABL using the new closure show good agreement with reference results, including well-established theoretical predictions. For instance, the closure delivers the expected surface-layer similarity profiles and power-law scaling of the power spectra of velocity and scalar fluctuations. Further, the Lagrangian version of the model is tested in the neutral ABL case, and gives satisfactory results.

Lu, Hao; Porté-Agel, Fernando

2014-06-01

98

NASA Astrophysics Data System (ADS)

A dynamic procedure is developed to compute the model coefficients in the recently introduced modulated gradient models for both momentum and scalar fluxes. The magnitudes of the subgrid-scale (SGS) stress and the SGS flux are estimated using the local equilibrium hypothesis, and their structures (relative magnitude of each of the components) are given by the normalized gradient terms, which are derived from the Taylor expansion of the exact SGS stress/flux. Previously, the two model coefficients have been specified on the basis of theoretical arguments. Here, we develop a dynamic SGS procedure, wherein the model coefficients are computed dynamically according to the statistics of the resolved turbulence, rather than provided a priori or ad hoc. Results show that the two dynamically calculated coefficients have median values that are approximately constant throughout the turbulent atmospheric boundary layer (ABL), and their fluctuations follow a near log-normal distribution. These findings are consistent with the fact that, unlike eddy-viscosity/diffusivity models, modulated gradient models have been found to yield satisfactory results even with constant model coefficients. Results from large-eddy simulations of a neutral ABL and a stable ABL using the new closure show good agreement with reference results, including well-established theoretical predictions. For instance, the closure delivers the expected surface-layer similarity profiles and power-law scaling of the power spectra of velocity and scalar fluctuations. Further, the Lagrangian version of the model is tested in the neutral ABL case, and gives satisfactory results.

Lu, Hao; Porté-Agel, Fernando

2014-05-01

99

The Effect of Nonlinear Critical Layers on Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear and spatially growing instability waves evolve downstream in nominally two-dimensional and spanwise periodic 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 an appropriate superposition of linear instability waves. The amplitudes of these waves are determined by either a single integro-differential equation or by a pair of integro-differential equations with quadratic to quartic-type nonlinearities.

Goldstein, Marvin E.

1995-01-01

100

NASA Technical Reports Server (NTRS)

A program is developed to investigate the linear stability of three-dimensional compressible boundary layer flows over bodies of revolutions. The problem is formulated as a two dimensional (2D) eigenvalue problem incorporating the meanflow variations in the normal and azimuthal directions. Normal mode solutions are sought in the whole plane rather than in a line normal to the wall as is done in the classical one dimensional (1D) stability theory. The stability characteristics of a supersonic boundary layer over a sharp cone with 50 half-angle at 2 degrees angle of attack is investigated. The 1D eigenvalue computations showed that the most amplified disturbances occur around x(sub 2) = 90 degrees and the azimuthal mode number for the most amplified disturbances range between m = -30 to -40. The frequencies of the most amplified waves are smaller in the middle region where the crossflow dominates the instability than the most amplified frequencies near the windward and leeward planes. The 2D eigenvalue computations showed that due to the variations in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the most amplified disturbances are shifted to 120 degrees compared to 90 degrees for the parallel theory. It is also observed that the nonparallel amplification rates are smaller than that is obtained from the parallel theory.

Balakumar, P.; Jeyasingham, Samarasingham

1999-01-01

101

Vortex boundary-layer interactions

NASA Technical Reports Server (NTRS)

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.

Bradshaw, P.

1986-01-01

102

Boundary layer theory and subduction

NASA Astrophysics Data System (ADS)

Numerical models of thermally activated convective flow in Earth's mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the 'rigid lid' style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth's mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.

Fowler, A. C.

1993-12-01

103

Boundary layer theory and subduction

Numerical models of thermally activated convective flow in Earth`s mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the `rigid lid` style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth`s mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.

Fowler, A.C. [Oxford Univ., Oxford (United Kingdom)

1993-12-01

104

Experimental evidence during the past three decades indicates that injection of gaseous microbubbles into a liquid turbulent boundary layer over a flat plate or over axisymmetrical bodies can reduce the skin-friction by as much as 80% from its value without bubble injection. However, the basic physical mechanisms responsible for that reduction are not yet fully understood. The present study is

Antonino Ferrante

2004-01-01

105

NASA Astrophysics Data System (ADS)

A novel method for generating realistic turbulent velocity and thermal inlet boundary conditions is presented for simulations of evolving turbulent boundary layers. The approach is based on the rescaling-recycling method proposed by Lund et al. (1998). The standard rescaling process requires prior knowledge about how the appropriate velocity and length scales are related between the inlet and recycle stations (e.g. classic scaling laws). Here a dynamic approach is proposed in which such information is deduced dynamically by involving an additional plane, the ``test plane'', which is located between the inlet and recycle stations. This improvement, as well as the use of multiple velocity scales, permits the simulations of turbulent boundary layers subjected to arbitrary pressure gradients. DNS for zero (ZPG), adverse (APG) and favorable (FPG) pressure gradient flows are discussed. The agreement obtained by comparing present results with experimental and numerical data demonstrates the suitability of the present method as a turbulent inflow generator.

Araya, Guillermo; Castillo, Luciano; Jansen, Kenneth; Meneveau, Charles

2008-11-01

106

Dynamical modeling of marine boundary layer convection

The interaction between dynamics and infrared radiation is investigated, as well as the problem of entrainment instability in the cloud-topped marine boundary layer. A two-dimensional Boussinesq moist model with a numerical technique (Fourier-Chebysheve tau method) and resolution sufficient to simulate cloud top processes was developed. Previous measurements suggest that the cloud-top radiative cooling is likely to undergo significant horizontal and

Hung-Chi Kuo

1987-01-01

107

Dynamical Modeling of Marine Boundary Layer Convection

This dissertation investigates the interaction between dynamics and infrared radiation as well as the problem of entrainment instability in the cloud-topped marine boundary layer. A two-dimensional Boussinesq moist model with a numerical technique (Fourier-Chebysheve tau method) and resolution sufficient to simulate cloud top processes has been developed. Previous measurements suggest that the cloud-top radiative cooling is likely to undergo significant

Hung-Chi Kuo

1987-01-01

108

Three-dimensional boundary layers approaching separation

NASA Technical Reports Server (NTRS)

The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer.

Williams, J. C., III

1976-01-01

109

This work presents the development of a laser-induced fluorescence technique to measure atmospheric formaldehyde. In conjunction with the technique, the design of a compact, narrow linewidth, etalon-tuned titanium: sapphire laser cavity which is pumped by the second harmonic of a kilohertz Nd:YAG laser is also presented. The fundamental tunable range is from 690-1100 nm depending on mirror reflectivities and optics

Anne Theresa Case Hanks

2008-01-01

110

Shock-wave boundary layer interactions

NASA Technical Reports Server (NTRS)

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.

Delery, J.; Marvin, J. G.; Reshotko, E.

1986-01-01

111

Technology developments for laminar boundary layer control on subsonic transport aircraft

NASA Technical Reports Server (NTRS)

The development of laminar flow technology for commercial transport aircraft is discussed and illustrated in a review of studies undertaken in the NASA Aircraft Energy Efficiency (ACEE) program since 1976. The early history of laminar flow control (LFC) techniques and natural laminar flow (NLF) airfoil designs is traced, and the aims of ACEE are outlined. The application of slotted structures, composites, and electron beam perforated metals in supercritical LFC airfoils, wing panels, and leading edge systems is examined; wind tunnel and flight test results are summarized; studies of high altitude ice effects are described; and hybrid (LFC/NLF designs are characterized. Drawings and photographs are provided.

Wagner, R. D.; Maddalon, D. V.; Fischer, M. C.

1984-01-01

112

Structure of the low latitude boundary layer

NASA Technical Reports Server (NTRS)

Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.

Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

1980-01-01

113

NASA Technical Reports Server (NTRS)

Analysis is presented on the possible similarity solutions of the three-dimensional, laminar, incompressible, boundary-layer equations referred to orthogonal, curvilinear coordinate systems. Requirements of the existence of similarity solutions are obtained for the following: flow over developable surface and flow over non-developable surfaces with proportional mainstream velocity components.

Hansen, Arthur G.

1958-01-01

114

NASA Astrophysics Data System (ADS)

An experimental study was conducted in Lehigh University's low-speed water channel to examine the effects of a zero, adverse, and favorable pressure gradients on the development of single hairpin vortices. Single hairpin vortices were generated in an initially laminar environment using controlled fluid injection through a streamwise slot at a Re(delta)* = 380, 440, and 570. Behavior of hairpin structures was determined by the use of dye and hydrogen bubble flow visualization techniques. Visualization results indicate that as a single hairpin vortex convects downstream a complicated growth process due to viscous-inviscid interactions and Biot-Savart deformation results in the generation of secondary and subsidiary vortices, eventually yielding a turbulent spot-like structure. The hairpin vortex structures are observed to be strongly affected by the presence of a pressure gradient, undergoing significant spatial growth changes, as well as experiencing significant flow structure modifications. As the hairpin initiation location is moved further into an adverse pressure gradient, the hairpin vortex lifts and rotates farther away from the surface relative to the behavior in a zero pressure gradient. Regions of low and high-velocity fluid near the surface are accentuated within an adverse pressure gradient, which amplifies the low-speed streak formation and breakdown process, accelerating the formation of vortical substructures and ejection of fluid from the surface.

Taylor, Blaine Keith

115

Modeling cathode boundary layer discharges

NASA Astrophysics Data System (ADS)

A Cathode Boundary Layer Discharge or CBL (Schoenbach, et al Plasma Sources Sci. Technol. 13, 177,2004) is an electrode/dielectric/electrode sandwich with a central hole pierced through the dielectric and one of the electrodes (the anode). Thus, the cathode surface area available to the discharge is limited by the annular dielectric, and the discharge operates in an abnormal glow mode with a positive V-I characteristic at higher current. Using a two-dimensional fluid model, we have studied the electrical properties of CBLs in argon at 100 and 400 torr pressure. The spatial profiles of charged particle and metastable densities, potential, and gas temperature, as well as calculated V-I characteristics will be shown for a range of conditions for a 800 micron hole diameter. One interesting result (anticipated in the work of Belostotskiy, et al, Plasma Sources Sci. Technol 17, 045018, 2008) is that there is a sharp increase in the slope of the V-I characteristic when gas heating is taken into account. This current limiting effect is not observed when the discharge is able to expand on the outer surface of the cathode as in the case of the MicroHollow Cathode Discharge (MHCD) configuration, for example.

Munoz-Serrano, E.; Boeuf, J. P.; Pitchford, L. C.

2009-10-01

116

NASA Astrophysics Data System (ADS)

We studied the role of the planetary boundary layer (PBL) in intensity and inner core structure of extremely intense tropical cyclones (TC) using a 2 km mesh nonhydrostatic atmospheric model (NHM2) developed for operational use by the Japan Meteorological Agency. To investigate the effects of the PBL on simulated TCs, we used four PBL schemes: level 2.5 and level 3 Mellor-Yamada-Nakanishi-Niino closure schemes, a nonlocal scheme, and the Deardorff-Blackadar scheme. The numerical results indicated that the subgrid-scale mixing length determined by the PBL scheme plays a critical role in the determination of maximum TC intensity and inner core structure, even when the same expressions are provided for surface roughness lengths and the air-sea momentum and heat transfer coefficients. Different vertical eddy-diffusivity coefficient values derived from the PBL schemes cause differences in the TC intensity, inner core structure, and the relationship between maximum wind speed (MWS) and central pressure (CP). In particular, large vertical eddy diffusivities in lower layers (height <300 m) lead to large heat and water vapor transfers, resulting in extremely intense TCs accompanied by an upright, contracted eyewall structure. We also conducted numerical experiments using a 5 km mesh nonhydrostatic atmospheric model (NHM5) and the same PBL schemes to investigate the effect of horizontal resolution on simulated TCs. The NHM5 was insufficient to accurately represent the MWS or CP of an extremely intense TC, suggesting that NHM2 is required to simulate an extremely intense TC characterized by an upright, contracted eyewall structure.

Kanada, Sachie; Wada, Akiyoshi; Nakano, Masuo; Kato, Teruyuki

2012-02-01

117

DNS of Decelerating Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

We conduct Direct Numerical Simulation (DNS) of turbulent plane-channel flow subjected to bulk deceleration and to a uniform strain field consisting of streamwise compression (partial U/partial x < 0) and wall-normal stretching (partial V/partial y > 0). This creates a time-developing flow containing most of the essential physics of spatially developing APG boundary layers, particularly in the outer layer. The logistics are much more favorable than those of a true spatial case, both for the DNS and for the testing of turbulence models. The computations are performed at two Reynolds numbers, with initial Re_? = 180 and 395, and advanced past the point when the deceleration causes the mean skin friction to change sign. This parallel-flow analog of ``separation'' isolates outer-layer features of separated boundary layers that are due to mean strain and vanishing surface stress from those caused by streamline curvature. Files are available to allow comparisons at the level of skin friction, velocity and stress profiles, and Reynolds-stress budgets. Changes in the velocity--pressure-gradient term ?_ij are found to dominate the initial evolution of the flow.

Coleman, G. N.; Kim, J.; Spalart, P. R.

1998-11-01

118

The role of nonlinear critical layers in boundary layer transition

NASA Technical Reports Server (NTRS)

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.

Goldstein, M.E.

1995-01-01

119

Cyclone separator having boundary layer turbulence control

A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.

Krishna, Coimbatore R. (Mt. Sinai, NY); Milau, Julius S. (Port Jefferson, NY)

1985-01-01

120

Elevated Residual Layers and Their Influence on Surface Boundary-Layer Evolution

Elevated mixed layers (EMLs) are an important factor in the development of springtime thunderstorms over the United States. EMLs can be considered a subset of a larger class, called residual layers, since the mean state variables are the same, at least initially, as those of the boundary layers in which EMLs a formed. It is possible, however, for boundary or

David J. Stensrud

1993-01-01

121

NASA Astrophysics Data System (ADS)

This work is devoted to computer modeling of aerodynamic flows into the boundary layers [1] with usage of nonlinear dynamics methods including the matrix decomposition method in the state-space [2] and the fractal- topological methods [3]. The computer simulation of air flows is carried out by means of program package STAR-CD [4].The computer modeling based on STAR-CD includes the realization of the procedures for import of CAD 3D-geometry of the treated surfaces into the instrumental tool of Pro*am STAR-CD, the treatment of the imported surfaces and generation of new surface, variable subsurface thickness and volume meshes with the usage of the tool of Pro*am STAR-CD, the computing aerodynamic flows into the boundary layers based on STAR-CD [4]. The obtained vector field of velocities as well as the scalar field of mass density and the distribution of pressure into the boundary layers are analysed then as depending on initial and boundary conditions. According to the first approach, the obtained time series of the component velocity, mass density and pressure are proceed into the pseudo-phase space.The reconstructed attractors are investigated by means of estimations of their fractal-topological characterictics (the minimal attractor embedding dimension, Lyapunov exponents, etc.). According to the second approach, the system of partial differential equations of Prandtl and Karman (describing aerodynamic processes in the boundary layers) is reduced to the system of ordinary differential equations based on the Galerkin's method.Then the fractal-topological characterictics of attractor of this system are investigated.The obtained results of analysis in accord with the first and the second approaches are compared with each other. References: [1] H. Schlichting, Grenzschicht-Theorie. Verlag G Braun, Karlsruhe, 1970. [2] A.M. Krot, "Matrix decompositions of vector functions and shift operators on the trajectories of a nonlinear dynamical system", Nonlinear Phenomena in Complex Systems, vol. 4, N2, 2001, pp. 106-115. [3] A.M. Krot and H.B. Minervina "Minimal attractor embedding estimation based on matrix decomposition for analysis of dynamical systems", Nonlinear Phenomena in Complex Systems, vol.5, N2, 2002, pp.161-172. [4] Methodology for STAR-CD: Version 3.15A ((c)2002 Computational Dynamics Limited).

Minervina, H.; Krot, A.; Tkachova, P.

122

Longitudinal vortices imbedded in turbulent boundary layers

NASA Astrophysics Data System (ADS)

The attenuation of skew-induced longitudinal vortices by turbulent or viscous stresses is studied for the case of pure, artificially-generated longitudinal vortices entrained into initially two-dimensional boundary layers in nominally zero pressure gradients. Three types of vortex-boundary interactions are studied in detail: (1) an isolated vortex in a two-dimensional boundary layer; (2) a vortex pair in a turbulent boundary layer with the common flow between the vortices moving away from the surface; (3) a vortex pair in a boundary layer with the common flow moving towards the surface. Detailed mean flow and turbulence measurements are made, showing that the eddy viscosities defined for the different shear-stress components behave in different and complicated ways. Terms in the Reynolds stress transport equations, notably the triple products that effect turbulent diffusion of Reynolds stress, also fail to obey simple rules.

Mehta, R. D.; Shabaka, I. M. M.; Shibl, A.; Bradshaw, P.

1983-01-01

123

Planetary Boundary Layer Simulation Using TASS

NASA Technical Reports Server (NTRS)

Boundary conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the atmospheric boundary layer. Several options are now available, including the use of a surface energy balance. In addition, we compare convective boundary layer simulations with the Wangara and Minnesota field experiments as well as with other model results. We find excellent agreement of modelled mean profiles of wind and temperature with observations and good agreement for velocity variances. Neutral boundary simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.

Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael

1996-01-01

124

Modelling the low-latitude boundary layer with reconnection entry

NASA Technical Reports Server (NTRS)

We develop a one-dimensional Low Latitude Boundary Layer (LLBL) model for northward interplanetary magnetic field (IMF). The boundary layer in this model is uniform in the direction normal to the magnetopause, a 'plateau-type' boundary layer. The boundary layer motion is decoupled from the magnetosheath motion and driven by the plasma pressure associated with the incoming solar wind plasma near local noon, which has become entrained on closed field lines as a result of reconnection in the cusp region. Dissipation in the ionosphere at the feet of the boundary layer field lines opposes this motion. There are two physical solutions for the model. In one, the boundary layer reaches a terminal velocity in the tail as the boundary layer plasma effectively joins the solar wind flow. In the other solution, the flow is nearly stopped in the far tail. In combination with other mechanisms, this latter solution may correspond to the case in which the boundary layer plasma participates in magnetospheric convection and returns sunward. The density, velocity, and thickness as functions of distance from local noon are studied, assuming that the magnetopause hasa elliptical shape and the magnetospheric field is dipolar.

Song, P.; Holzer, T. E.; Russell, C. T.; Wang, Z.

1994-01-01

125

Boundary layer flow visualization for flight testing

NASA Technical Reports Server (NTRS)

Flow visualization is used extensively in flight testing to determine aerodynamic characteristics such as surface flow direction and boundary layer state. Several visualization techniques are available to the aerodynamicist. Two of the most popular are oil flows and sublimating chemicals. Oil is used to visualize boundary layer transition, shock wave location, regions of separated flow, and surface flow direction. Boundary layer transition can also be visualized with sublimating chemicals. A summary of these two techniques is discussed, and the use of sublimating chemicals is examined in some detail. The different modes of boundary layer transition are characterized by different patterns in the sublimating chemical coating. The discussion includes interpretation of these chemical patterns and the temperature and velocity operating limitations of the chemical substances. Information for selection of appropriate chemicals for a desired set of flight conditions is provided.

Obara, Clifford J.

1986-01-01

126

Sound from Turbulent Boundary Layer Excited Panels.

National Technical Information Service (NTIS)

The acoustic power radiated by thin flexible panels excited by turbulent boundary layer pressure fluctuations is estimated using a modal analysis, light fluid loading effects being included. Previous estimates of the modal radiation coefficients are impro...

H. G. Davies

1969-01-01

127

Boundary layer control on magnetohydrodynamic numerical simulations

NASA Astrophysics Data System (ADS)

In the context of planetary interiors the geometry and magnitude of magnetic fields has been found to be controlled by the heat flux through the outer boundary (e.g., Olson & Christensen 2006). However, there is indication, based on experimental work, that the balance between thermal, viscous, and Coriolis effects defines the flow behaviour in non-magnetic fluids by means of boundary layer control (King et al. 2009). Using numerical models of magnetohydrodynamic fluids in spherical shells, we find that the force balances at the top boundary may be determining the overall behaviour of the flow. Similar to flow control by boundary layers in non-magnetic convective systems, we find that boundary layers associated with temperature, viscosity, Coriolis forces, and magnetic fields play an important role in determining the large scale flow. Boundary layer relative thicknesses are found to correlate with the internal force balances. For planetary dynamos, this implies that the boundary conditions at the top of the dynamo region - not only the heat flux through the boundary - control the mode of convection as well as magnetic field magnitude, geometry and secular variation.

Gomez Perez, N.; Heimpel, M. H.

2012-12-01

128

BUBBLE – an Urban Boundary Layer Meteorology Project

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

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

129

Varicose instabilities in turbulent boundary layers

NASA Astrophysics Data System (ADS)

An investigation of a model of turbulence generation in the wall region of a turbulent boundary layer is made through direct numerical simulations. The model is based on the varicose instability of a streak. First, a laminar boundary layer disturbed by a continuous blowing through a slot is simulated in order to reproduce and further investigate the results reported from the experiments of Acarlar and Smith [J. Fluid Mech. 175, 43 (1987)]. An isolated streak with an inflectional profile is generated that becomes unstable, resulting in a train of horseshoe vortices. The frequency of the vortex generation is equal to the experimental results. Comparison of the instability characteristics to those predicted through an Orr-Sommerfeld analysis are in good agreement. Second, a direct numerical simulation of a turbulent boundary layer is performed to point out the similarities between the horseshoe vortices in a turbulent and a laminar boundary layer. The characteristics of streaks and the vortical structures surrounding them in a turbulent boundary layer compare well with the model streak. The results of the present study show that one mechanism for the generation of horseshoe vortices in turbulent boundary layers is related to a normal inflectional instability of the streaks.

Skote, M.; Haritonidis, J. H.; Henningson, D. S.

2002-07-01

130

Analytical Parameterizations of Diffusion: The Convective Boundary Layer.

National Technical Information Service (NTIS)

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; ...

G. A. Briggs

1985-01-01

131

Microphone System for the Measurement of Boundary Layer Pressure Fluctuations.

National Technical Information Service (NTIS)

This report presents a description of a condenser microphone system developed for use in the measurement of boundary layer pressure fluctuations. Prime consideration in the design of the transducer of the system was the requirement for operation in abnorm...

J. C. Ortega

1967-01-01

132

Assessment of inflow boundary conditions for compressible turbulent boundary layers

NASA Astrophysics Data System (ADS)

A description of different inflow methodologies for turbulent boundary layers, including validity and limitations, is presented. We show that the use of genuine periodic boundary conditions, in which no alteration of the governing equations is made, results in growing mean flow and decaying turbulence. Premises under which the usage is valid are presented and explained, and comparisons with the extended temporal approach [T. Maeder, N. A. Adams, and L. Kleiser, ``Direct simulation of turbulent supersonic boundary layers by an extended temporal approach,'' J. Fluid Mech. 429, 187 (2001)] are used to assess the validity. Extending the work by Lund et al. [J. Comput. Phys. 140, 233 (1998)], we propose an inflow generation method for spatial simulations of compressible turbulent boundary layers. The method generates inflow by reintroducing a rescaled downstream flow field to the inlet of a computational domain. The rescaling is based on Morkovin's hypothesis [P. Bradshaw, ``Compressible turbulent shear layers,'' Annu. Rev. Fluid Mech. 9, 33 (1977)] and generalized temperature-velocity relationships. This method is different from other existing rescaling techniques [S. Stolz and N. A. Adams, ``Large-eddy simulation of high-Reynolds-number supersonic boundary layers using the approximate deconvolution model and a rescaling and recycling technique,'' Phys. Fluids 15, 2398 (2003); G. Urbin and D. Knight, ``Large-eddy simulation of a supersonic boundary layer using an unstructured grid,'' AIAA J. 39, 1288 (2001)], in that a more consistent rescaling is employed for the mean and fluctuating thermodynamic variables. The results are compared against the well established van Driest II theory and indicate that the method is efficient and accurate.

Xu, Sheng; Martin, M. Pino

2004-07-01

133

BUBBLE an Urban Boundary Layer Meteorology Project

NASA Astrophysics Data System (ADS)

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 and a Lidar near the city center were profiling the entire lower troposphere. During an intensive observation period (IOP) of one month duration, several sub-studies on street canyon energetics and satellite ground truth, as well as on urban turbulence and profiling (sodar, RASS, tethered balloon) were performed. Also tracer experiments with near-roof-level release and sampling were performed. In parallel to the experimental activities within BUBBLE, a meso-scale numerical atmospheric model, which contains a surface exchange parameterization, especially designed for urban areas was evaluated and further developed. Finally, the area of the full-scale tracer experiment which also contains several sites of other special projects during the IOP (street canyon energetics, satellite ground truth) is modeled using a very detailed physical scale-model in a wind tunnel. In the present paper details of all these activities are presented together with first results.

Rotach, M. W.; Vogt, R.; Bernhofer, C.; Batchvarova, E.; Christen, A.; Clappier, A.; Feddersen, B.; Gryning, S.-E.; Martucci, G.; Mayer, H.; Mitev, V.; Oke, T. R.; Parlow, E.; Richner, H.; Roth, M.; Roulet, Y.-A.; Ruffieux, D.; Salmond, J. A.; Schatzmann, M.; Voogt, J. A.

2005-07-01

134

Vortex filament stability and boundary layer dynamics

Coherent structures in fluid boundary layers at high Reynolds numbers are a prominent feature of these flows. The structures appear as concentrations of vorticity into hairpin'' and other shapes. We explore the inviscid interaction and stability of vortex filaments initially situated spanwise to the mean flow in a model of a boundary layer. Both for a single vortex filament and its image through the boundary and for an infinite line of such filaments with their images we find a linear instability associated with deformations of the filament along its length with maximum instability having a wavelength on the order of the height of the filament above the boundary. The linear unstable manifold for this instability points at approximately 45[degree] from the plane of the boundary in accord with experimental observations and numerical modeling of these coherent structures. This provides a dynamical origin to the observations of the orientation of these coherent structures.

Abarbanel, H.D.I. (Department of Physics, Institute for Nonlinear Science and Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, Mail Code 0402, La Jolla, California 92093-0402 (United States)); Lisi, A.G. (Department of Physics and Institute for Nonlinear Science, University of California, San Diego, Mail Code 0402, La Jolla, California 92093-0402 (United States)); Rouhi, A.; Wright, J.A. (Institute for Nonlinear Science, University of California, San Diego, Mail Code 0402, La Jolla, California 92093-0402 (United States))

1994-08-01

135

Ground observations of magnetospheric boundary layer phenomena

NASA Technical Reports Server (NTRS)

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.

Mchenry, Mark A.; Clauer, C. Robert; Friis-Christensen, Eigil; Newell, Patrick T.; Kelly, J. D.

1990-01-01

136

Experiments in Boundary-Layer Turbulence

NASA Technical Reports Server (NTRS)

Motion in layer highly three-dimensional. Report describes experimental studies of disturbances induced by weak free-stream turbulence in pre-transitional Blasius boundary layer. Asks and partially answers some fundamental questions concerning large-amplitude, low-frequency disturbances.

Kendall, James M., Jr.

1987-01-01

137

During the last few years the development of a second-generation regional climate modeling system (RegCM2) has been completed at the National Center for Atmospheric Research (NCAR). Based upon the National Center for Atmospheric Research-Pennsylvania State University Mesoscale Model (MM4), RegCM2 includes improved formulations of boundary layer, radiative transfer, surface physics, cumulus convection, and time integration technique, which make it more

Filippo Giorgi; Maria Rosaria Marinucci; Gary T. Bates

1993-01-01

138

On the theory of laminar boundary layers involving separation

NASA Technical Reports Server (NTRS)

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)

Von Karman, TH; Millikan, C

1934-01-01

139

Lear jet boundary layer/shear layer laser propagation experiments

NASA Technical Reports Server (NTRS)

Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

Gilbert, K.

1980-01-01

140

Bypass transition in compressible boundary layers

NASA Technical Reports Server (NTRS)

Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar transitional state. The effects of large free stream turbulence in compressible boundary layers at Mach numbers are examined both in the subsonic and transonic regime using direct numerical simulations. The flow is computed over a flat plate and curved surface. while many applications operate in the transonic regime. Due the nature of their numerical scheme, a non-conservation formulation of the Navier-Stokes equations, it is a non-trivial extension to compute flow fields in the transonic regime. This project aims at better understanding the effects of large free-stream turbulence in compressible boundary layers at mach number both in the subsonic and transonic regime using direct numerical simulations. The present project aims at computing the flow over a flat plate and curved surface. This research will provide data which can be used to clarify mechanisms leading to transition in an environment with high free stream turbulence. This information is useful for the development of turbulence models, which are of great importance for CFD applications, and are currently unreliable for more complex flows, such as transitional flows.

Vandervegt, J. J.

1992-01-01

141

High enthalpy hypersonic boundary layer flow

NASA Technical Reports Server (NTRS)

A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

Yanow, G.

1972-01-01

142

Pressure Gradient Boundary Layers With Eventual Separation

NASA Astrophysics Data System (ADS)

Using the similarity analysis for turbulent boundary layer with pressure gradient by Castillo and George(Castillo, L. and George, W.K.,``Similarity Analysis for Turbulent Boundary Layer with Pressure Gradient: out flow,'' AIAA Journal, Vol.39,2001) it will be shown that the outer part of adverse pressure gradient turbulent boundary layers tends to remain in equilibrium similarity, even near (and sometimes past) separation. Thus such boundary layers are characterized by a single pressure parameter, ?_? =frac? ? U_? ^2d? /dxfracdP_? dx, and its value appears to be the same for all adverse pressure gradient flows; i.e., ?_? ? 0.22. Using this pressure parameter and the momentum integral boundary layer equation, it is possible to show that the shape factor at separation must have a single value, H_sep ? 2.5. Both the conditions for equilibrium similarity and the value of H_sep are shown to be in reasonable agreement with a variety of experimental estimates.

Wang, Xia; Castillo, Luciano; George, William K.

2001-11-01

143

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

144

Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer

: 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

Michael Manhart

1998-01-01

145

Modelling of the Evolving Stable Boundary Layer

NASA Astrophysics Data System (ADS)

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.

Sorbjan, Zbigniew

2014-06-01

146

Chemistry of a polluted cloudy boundary layer

NASA Astrophysics Data System (ADS)

A one-dimensional photochemical model for cloud-topped boundary layers has been developed to include descriptions of gas- and aqueous-phase chemistry and the radiation field in and below the cloud. The model is applied to the accumulation of pollutants during a wintertime episode with low stratus over Bakersfield, CA. The mechanisms of sulfate production and the balance between the concentrations of acids and bases are examined. It is shown that most of the sulfate production may be explained by the Fe(III)-catalyzed autoxidation of S(IV). Another source of sulfate is the oxidation of SO2 by OH in both the gas and the aqueous phase. It is shown that the sulfate production in the model is controlled by the availability of NH3. It is suggested that this explains the balance observed between total concentration of acids and bases.

Jacob, Daniel J.; Gottlieb, Elaine W.; Prather, Michael J.

1989-09-01

147

Boundary layer receptivity to freestream turbulence

NASA Technical Reports Server (NTRS)

Freestream turbulence of weak but adjustable intensity incident upon a flat plate test model induced Tollmien-Schichting (TS) waves and wave packets. These were studied using a newly-developed sensor by which the packets could be followed from a station nearly as far forward as the minimum critical Reynolds number to the onset of transition. Conclusions reached from these studies were: (1) weak freestream turbulence induced TS wave packets in a Blasius boundary-layer, (2) packets gained strength during propagation through expansion of lateral and longitudinal scales, and through an increase in peak amplitude, (3) the average wave strength at stations of observation was not related to the freestream velocity fluctuation in a linear manner, and (4) packets typically evolved into turbulent spots.

Kendall, James M.

1990-01-01

148

NASA Technical Reports Server (NTRS)

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.

Mack, L. M.

1967-01-01

149

Stability of separating subsonic boundary layers

NASA Technical Reports Server (NTRS)

The primary and subharmonic instabilities of separating compressible subsonic two-dimensional boundary layers in the presence of a two-dimensional roughness element on a flat plate are investigated. The roughness elements considered are humps and forward- and backward-facing steps. The use of cooling and suction to control these instabilities is studied. The similarities and differences between the instability characteristics of separating boundary layers and those of the boundary layer over a flat plate with a zero pressure gradient are pointed out and discussed. The theoretical results agree qualitatively and quantitatively with the experimental data of Dovgal and Kozlov. Cooling and suction decrease the growth rates of primary and subharmonic waves in the attached-flow regions but increase them in the separated-flow regions.

Masad, Jamal A.; Nayfeh, Ali H.

1994-01-01

150

Diffusion processes in the magnetopause boundary layer

NASA Technical Reports Server (NTRS)

A quantitative estimate is calculated for the effect of wave-particle scattering on the structure of the magnetopause boundary layer. It is assumed that large cross-B electric fields are absent in the observed penetration of magnetosheath plasma into the magnetopause boundary layer, thus allowing for cross-field transport comparable to 10% of the Bohm diffusion. It is shown that magnetosheath ions, resonant with low frequency electrostatic waves, can account for the typical boundary layer thickness when transported at 10% of the diffusion rate 1000 sq km/sec. The conditions are required to occur at all local times and under all interplanetary conditions. Significant mass and momentum transfer are then possible across the magnetopause when field merging is not occurring.

Tsurutani, B. T.; Thorne, R. M.

1982-01-01

151

Power Law for Rough Favorable Pressure Gradient Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

Current studies on rough favorable pressure gradient (FPG) boundary layers are very challenging particularly since it is difficult to obtain values of skin friction as a function of roughness, pressure gradient strength and Re?. This study presents a new modified form of the power law from George and Castillo (1997) developed for smooth zero pressure gradient boundary layers. The new form accounts for mild pressure gradients, and aids in the account for rough surface boundary layers. Emphasis will be given to its application to rough FPG flows. The values of the skin friction for smooth FPG boundary layers are obtained within 3%. Moreover, the composite profile for the mean velocity accurately describes both FPG and APG flows. The modified power law solution has the advantage of being a continuous solution for smooth and rough profiles subject to external pressure gradients. In addition, by using the Navier Stokes equation the Reynolds shear stress is accurately calculated from the composite description of the mean velocity.

Newhall, Katherine; Castillo, Luciano

2006-11-01

152

Coherent Motions of the Turbulent Boundary Layer (Invited)

NASA Astrophysics Data System (ADS)

Over the last decade a model has been developed in which the structure of the turbulent boundary consists of quasi-streamwise vortices near the wall, a hierarchy of hairpin vortex packets that extends through the logarithmic layer, large-scale motions having streamwise extent of the order of the thickness of the boundary layer, and very-large-scale motions that are much longer than the boundary layer thickness. Figure 1 shows a cartoon sketch of the hairpin packet hierarchy. The evidence indicates that the large and very-large-scale motions become increasingly important as the Reynolds number increases, implying that geophysical boundary layer have considerably different character than low Reynolds number laboratory experiments and simulations. Work is in progress to discern the form of the large motions and incorporate them into a more complete model. Fig. 1. Hierarchy of hairpin packets begins at the surface.

Adrian, R. J.

2009-12-01

153

New evolution equations for turbulent boundary layers

NASA Astrophysics Data System (ADS)

Perry, Marusic & Li (1994) (Phys. Fluids, vol. 6(2) part 2) initially developed a mathematical framework for computing the evolution of boundary layers using classical similarity laws such as Prandtl's law of the wall and Coles' law of the wake together with the momentum integral and differential equations. It was found that these equations show that there are 4 parameters which control the streamwise evolution of the layer and the Reynolds shear stress distribution and these are S, ?, ? and ?. S = U_1/U_?, ? is Coles wake factor, ? is the Clauser pressure gradient parameter and ?=S?_cd?/dx. In this early work the evolution equations were incomplete and the only problems which could be solved were the so called quasi-equilibrium flow cases where it could be assumed that ? was sufficiently small to neglect its effect. Here we present the full set of evolution equations for finite ? so that the more general problem of non-equilibrium layers can be tackled. In this initial study here, closure is obtained assuming that \\calF[S, ?, ?, ?] = 0 and this function is mapped out semi-empirically. The formulation is consistent with the recently extended attached eddy hypothesis of Perry & Marusic (1995) (JFM vol. 298) from which once the mean flow evolution has been calculated, the broadband turbulence intensities and spectra can be calculated. The use of topology as a diagnostic tool to interpret DNS data tends to support this recently developed hypothesis (Chong et al. 1998) (JFM vol. 357) and preliminary modeling is carried out in conjunction with these evolution equations so as to obtain closure based on physical arguments. Some nonequilibrium flow data is compared with computations using these new evolution equations.

Perry, A. E.

1998-11-01

154

Influence of Bowen Ratio on Boundary-Layer Cloud Structure.

NASA Astrophysics Data System (ADS)

An investigation of the influence of the ratio of surface sensible heat flux to latent heat flux, the Bowen ratio. on the structure of boundary-layer clouds is carried out utilizing numerical large eddy simulations (LES). The role of cloud-top radiational cooling, cloud-top temperature and moisture jump conditions, and wind shear are included in a secondary way. Although no detailed comparisons have been made, the LES results appear to be qualitatively consistent with the Atlantic Stratocumulus Transition Experiment, the recent field study on marine boundary-layer cloud structure. Some conclusions that follow from an examination of these LES results are the following: First, there is a highly bimodal character to the cloud ceiling frequency within a very low Bowen ratio boundary layer. The updrafts tend to produce a lower cloud ceiling than the surrounding environment with its weak downdrafts. Second, a very low Bowen ratio with the aid of some boundary-layer shear makes the development of persistent microcell cloud circulations possible within the boundary layer. Third, when the surface latent heat flux is the dominant factor in the dynamics of the boundary layer, the approach to a conditionally stable lapse rate results in the potential for subsequent decoupling. Last, the maximum partial cloud fraction is very well represented by the relation suggested by Sommeria and Deardorff for a Gaussian probability distribution for the range of conditions studied.

Lewellen, D. C.; Lewellen, W. S.; Yoh, S.

1996-01-01

155

Particle-laden boundary layers and singularities

NASA Astrophysics Data System (ADS)

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.

Foster, M. R.

2007-11-01

156

Turbulent Boundary Layer Flow over Superhydrophobic Surfaces.

National Technical Information Service (NTIS)

The objective of this project was to determine whether drag caused by turbulence in boundary layer flow can be reduced through the use of modified surfaces. This study encompassed the testing of four different surfaces: 1) Teflon SLIP, 2) Aluminum SLIP, 3...

A. J. Rydalch

2013-01-01

157

Convection in the atmospheric boundary layer

Recent advances in the study of clear and partly cloudy convective boundary layers are reviewed. The techniques and results of observational studies of the structure and dynamics of convective elements are discussed. These findings have important consequences for pollution dispersion. They also form the basis for a test of LES dispersion models which is more discriminating than those based on

George S. Young

1988-01-01

158

Boundary layer control device for duct silencers

NASA Technical Reports Server (NTRS)

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.

Schmitz, Fredric H. (inventor); Soderman, Paul T. (inventor)

1993-01-01

159

Note on the calculation of boundary layers

NASA Technical Reports Server (NTRS)

The properties of the solutions of the hydrodynamic equations of viscous fluid by "boundary-layer omission" are discussed. A method is indicated for the numerical determination of the solution for a known initial profile u(x(sub o),y) and pressure distribution p(x) within the region.

Prandtl, L

1940-01-01

160

Turbulences in Boundary Layer of Flat Plates

NASA Astrophysics Data System (ADS)

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

Tesar, Alexander

2014-06-01

161

Soot and radiation in combusting boundary layers

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

1982-01-01

162

Soot and radiation in combusting boundary layers

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

1981-01-01

163

Boundary Layer Transition on X-43A

NASA Technical Reports Server (NTRS)

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.

Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert

2008-01-01

164

Turbulence in a separated boundary layer

NASA Astrophysics Data System (ADS)

Results are reported from an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separation region. The gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer with its axis in the spanwise direction. Data on the structure of the turbulent flow within the separation region are presented in extensive graphs, and many features are shown to be similar to those that occur in separated regions produced in a very dissimilar manner. Similarities with boundary layers separating under the action of much weaker pressure gradients are found as well. These similarities and also some noticeable differences are discussed, and several inferences concerning the application of turbulence models to separated flows are presented.

Dianat, M.; Castro, Ian P.

1991-05-01

165

Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation

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.

Reichenbach, H.; Neuwald, P. [Ernst-Mach-Institut, Freiburg (DE); Kuhl, A.L. [R and D Associates, Los Angeles, CA (United States)

1992-11-01

166

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...

167

Turbulent boundary layer to single-stream shear layer: the transition region

NASA Astrophysics Data System (ADS)

This communication presents the results and conclusions of an experimental study of the near-separation region of a single-stream shear layer. The momentum thickness at separation (x {=} 0) was theta_0 {=} 9.6 mm, with Reynolds number shape Re_theta {=} 4650. Boundary layer separation was caused by a sharp 90(°) edge. Detailed single- and multi-point measurements of the velocity field were acquired at the streamwise locations 0 {<} x/theta_0 {<} 100. This represents the transition region between two of the canonical turbulent shear flows: the zero-pressure-gradient turbulent boundary layer and the single-stream shear layer. From the viewpoint of a separating boundary layer, the results describe how the turbulent flow reacts to a sudden change in wall boundary conditions. From the viewpoint of the developed shear layer, the results describe the transition to the self-similar region. The data acquired suggest that the initial shear layer instability occurs in the region very near separation (x {?} theta_0), and that it involves only the vorticity filaments which originate in the near-wall region of the upstream boundary layer. This ‘near-wall region’ roughly defines the origin of a narrow wedge-shaped domain that was identified from the velocity statistics. This domain is termed the ‘sub-shear layer’. The statistics of the velocity field in the region bounded by the sub-shear layer and the free-stream flow were found to represent the normative continuation of the upstream boundary layer. The sub-shear layer has been found to exhibit many of the standard features observed in fully developed shear layers. For example, velocity measurements on the entrainment side of the shear layer indicate that large-scale motions with spanwise coherence were observed. The streamwise dependence of the dominant frequency, convection velocity, and spanwise velocity correlation have been documented in order to characterize the sub-shear layer phenomenon.

Morris, Scott C.; Foss, John F.

2003-11-01

168

Feasibility study of optical boundary layer transition detection method

NASA Technical Reports Server (NTRS)

A high sensitivity differential interferometer was developed to locate the region where the boundary layer flow undergoes transition from laminar to turbulent. Two laboratory experimental configurations were used to evaluate the performance of the interferometer: open shear layer, and low speed wind tunnel turbulent spot configuration. In each experiment, small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements were compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 0.001 the laser wavelength. An attempt to detect boundary layer transition over a flat plate at NASA-Langley Unitary Supersonic Wind Tunnel using the interferometer system was performed. The phase variations during boundary layer transition in the supersonic wind tunnel were beyond the minimum signal-to-noise level of the instrument.

Azzazy, M.; Modarress, D.; Trolinger, J. D.

1986-01-01

169

Particulate plumes in boundary layers with obstacles

NASA Astrophysics Data System (ADS)

This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary boundaries. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex boundary. In viscous atmosphere with as small as one likes coefficient of molecular viscosity, the non-slip boundary condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring layers energy dissipation of atmosphere flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in atmosphere movement characterizing by a high Reynolds number the boundary layer is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external boundary of the layer that are quite close to ones in ideal atmosphere flow. In that layer fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid boundary caused not only by non-slip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of big wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations.We deal with describing big field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena.

Petrosyan, Arakel; Karelsky, Kirill

2013-04-01

170

Hairpin vortices in turbulent boundary layers

NASA Astrophysics Data System (ADS)

The present work addresses the question whether hairpin vortices are a dominant feature of near-wall turbulence and which role they play during transition. First, the parent-offspring mechanism is investigated in temporal simulations of a single hairpin vortex introduced in a mean shear flow corresponding to turbulent channels and boundary layers up to Re? = 590. Using an eddy viscosity computed from resolved simulations, the effect of a turbulent background is also considered. Tracking the vortical structure downstream, it is found that secondary hairpins are created shortly after initialization. Thereafter, all rotational structures decay, whereas this effect is enforced in the presence of an eddy viscosity. In a second approach, a laminar boundary layer is tripped to transition by insertion of a regular pattern of hairpins by means of defined volumetric forces representing an ejection event. The idea is to create a synthetic turbulent boundary layer dominated by hairpin-like vortices. The flow for Re? < 250 is analysed with respect to the lifetime of individual hairpin-like vortices. Both the temporal and spatial simulations demonstrate that the regeneration process is rather short-lived and may not sustain once a turbulent background has formed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former DNS studies is an outer layer phenomenon not being connected to the onset of near-wall turbulence.

Eitel-Amor, G.; Flores, O.; Schlatter, P.

2014-04-01

171

Particle motion in atmospheric boundary layers of Mars and Earth

NASA Technical Reports Server (NTRS)

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.

White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

1975-01-01

172

Control of the Transitional Boundary Layer

NASA Astrophysics Data System (ADS)

This work makes advances in the delay of boundary layer transition from laminar to turbulent flow via feedback control. The applications include the reduction of drag over streamline bodies (e.g., airplane wings) and the decrease of mixing and heat transfer (e.g., over turbine blades in jet engines). A difficulty in many fields is designing feedback controllers for high-dimensional systems, be they experiments or high-fidelity simulations, because the required time and resources are too large. A cheaper alternative is to approximate the high-dimensional system with a reduced-order model and design a controller for the model. We implement several model reduction algorithms in "modred", an open source and publicly available library that is applicable to a wide range of problems. We use this library to study the role of sensors and actuators in feedback control of transition in the 2D boundary layer. Previous work uses a feedforward configuration in which the sensor is upstream of the actuator, but we show that the actuator-sensor pair is unsuitable for feedback control due to an inability to sense the exponentially-growing Tollmien-Schlichting waves. A new actuator-sensor pair is chosen that more directly affects and measures the TS waves, and as a result it is effective in a feedback configuration. Lastly, the feedback controller is shown to outperform feedforward controllers in the presence of unmodeled disturbances. Next, we focus on a specific type of actuator, the single dielectric barrier discharge (SDBD) plasma actuator. An array of these plasma actuators is oriented to produce stream-wise vorticity and thus directly cancel the structures with the largest transient growth (so-called stream-wise streaks). We design a feedback controller using only experimental data by first developing an empirical input-output quasi-steady model. Then, we design feedback controllers for the model such that the controllers perform well when applied to the experiment. Lastly, we also simulate the plasma actuators and determine a suitable numerical model for the forces they create by comparing with experimental results. This physical force model is essential to future numerical studies on delaying bypass transition via feedback control and plasma actuation.

Belson, Brandt A.

173

Boundary layer transition detection by luminescence imaging

NASA Astrophysics Data System (ADS)

In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.

McLachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.

1993-01-01

174

BOREAS AFM-6 Boundary Layer Height Data

NASA Technical Reports Server (NTRS)

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).

Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

175

Boundary Layer Theory. Part 1; Laminar Flows

NASA Technical Reports Server (NTRS)

The purpose of this presentation is to give you a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.

Schlichting, H.

1949-01-01

176

Lidar probing the urban nocturnal boundary layer

Lidar observations to study the nocturnal boundary layer in the atmosphere were made on selected evenings during December 1997 - March 1998 at the City University of Hong Kong (lat. 20 degree(s)20'6', long. 114 degree(s)10'18', at 57 m AMSL), Hong Kong. The ground-based Nd:YAG lidar has been operated to detect the vertical distribution of aerosols in the NBL at a

T. M. Mok; Kang M. Leung; A. H. Ho; J. C. Chan; C. N. Ng

1998-01-01

177

Turbulent boundary layer studies using polynomial interpolation

For laminar flows, higher-order differential methods derived from polynomial spline interpolation and Hermitian collocation have significantly reduced the numbers of mesh points required to achieve accuracy equal to that of conventional second-order finite-difference methods. This study is intended to evaluate the applicability of two of these techniques for simulating the thicker, higher-shear turbulent boundary layer on a flat plate, with

S. G. Rubin; P. K. Khosla; S. Rivera

1977-01-01

178

Boundary Layer Control for Hypersonic Airbreathing Vehicles

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

179

Longitudinal vortices in boundary layer transition

NASA Astrophysics Data System (ADS)

It is recognized that longitudinal vortices in boundary layer can attain significant amplitudes under the influence of moderate to high freestream turbulence owing to transient growth. The present theoretical-numerical study is carried out in order to understand the origin and effect of longitudinal vortices in boundary layer transition. The origin of longitudinal vortices is connected to freestream turbulence through the continuum modes of the Orr-Sommerfeld and Squire equations. With the inclusion of transverse flow velocity, the theoretical results match several inherent characteristics of longitudinal vortices observed experimentally. The linear instability of the flow with longitudinal vortices superimposed upon an otherwise unperturbed boundary layer is examined using the Floquet theory. Under mild modulations, the three-dimensional unstable modes have the same spanwise wavelength as longitudinal vortices and maintain the characteristics of two-dimensional Tollmien-Schlichting (TS) waves. If the spanwise modulation is sufficiently strong, a new type of instability, very different from TS waves, appears. The unstable modes of the new instability intensify as a result of subharmonic resonance at rates and frequencies much higher than TS waves. The subharmonic modes have a modal shape different from that of TS waves and they propagate faster than the TS waves. Longitudinal vortices with narrower spanwise length scales will cause subharmonic secondary modes to grow at higher frequencies. It is likely that the fast amplification of the secondary modes, not longitudinal vortices themselves, will lead to imminent transition.

Su, Yi-Chung

1999-11-01

180

Interaction of the planetary boundary layer depth with aerosol and boundary-layer clouds

NASA Astrophysics Data System (ADS)

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.

Sawyer, V. R.; Li, Z.

2013-12-01

181

Kahuku kite wind study. I. Kahuka beach boundary layer

In the coastal plain of Kahuku, Oahu, during August 1980 and February to April 1981, the boundary layer and the mechanism that creates it were investigated. Four sets of two automatically-recording tethered aerodynamically lifting anemometer (TALA) kites flying continuously at 100 and 300 ft, and conventional 30 ft instruments were used concurrently at four sites along a transect parallel to the prevailing trade winds. Hand-held short-term kite measurements were used to verify the data from the prototype automatic kites during the first survey. Because of surface heating and vertical mixing, a rapidly expanding boundary develops soon after sunrise. Other forces that modify the daytime air flow in the lower layers are: surface friction, local scale thermal wind, a sea breeze and mechanical forcing. The nighttime boundary is established through heat conduction from the surface air to the ground. This layer grows slowly and reaches only a few hundred feet in depth. Other mechanisms that modify the winds in and around the nighttime boundary layer include: confluence into the boundary layer, local scale thermal wind, land breeze-drainage winds, and friction. In the second survey, the boundary layer was neither as high nor as well-developed as in the first because the ground was saturated after the winter rains. The consequent latent heat exchange prevented extreme surface temperature fluctuation. The commonly-used wind profile law exponent was found to depend on speed in the lower 100 ft of the atmosphere above which the exponent is constant. Estimates of long-term speeds at some sites differed by up to four mph between the two surveys. This underlines the importance of surveying not only all major wind regimes but also under different surface conditions. Long term speed estimates for the sties are high enough to make the area probably profitable for wind power development.

Daniels, P.A.; Oshiro, N.E.

1982-09-01

182

The Atmospheric Boundary Layer Growth In An Urban Area

NASA Astrophysics Data System (ADS)

The development and maintenance of the atmospheric boundary layer (ABL) plays a key role on the distribution of atmospheric constituents, specially in a polluted urban area. In particular, the atmospheric boundary layer has a direct impact on the con- centration and transformation of pollutants. It is therefore very important to obtain an accurate estimation of the boundary layer growth. The ABL growth is driven primarily by the surface fluxes (sensible and latent) and entrainment of warmer air from the free troposphere. It can also be influenced by the presence of mesoscale phenomena such as the sea-breeze or the mountain valley circulation. In order to analyse the different mechanisms which control the boundary layer growth, we have simulated by means of the non-hydrostatic model MM5 several boundary layer observed in the city of Barcelona (Spain). Sensitivity analysis of the modelled ABL are carried out by using various descriptions of the planetary boundary layer. Direct and continuous measure- ments of the boundary layer height taken by a LIDAR are used to evaluate the results obtained by the model. Depending on the LIDAR data availability, we have repeated our study under different meteorological situations. The intercomparison shows that the modelled boundary layer strongly depends on the selected parameterisation. In our presentation, we will show that in general the obser- vations provide the highest value of the maximum of ABL height. Moreover, the more simple parameterisation (Medium Range Forecast) simulates an ABL with values of the inversion height similar to those found with the LIDAR. On the contrary, the pa- rameterisation that solves the TKE prognostic equation (ETA) yields lowest values of the ABL height and does not fit with the observations. One possible source of differ- ences may be the heat and specific humidity surface fluxes calculated by the model. It is therefore advisable to measure surface fluxes in combination with LIDAR obser- vations to fully understand the boundary layer growth in an urban area. In addition, it would be also interesting to make this campaign at different places in the Barcelona area, in order to study the possible breeze effects and the influence of soil conditions in the ABL growth.

Pino, D.; Vilà-Guerau de Arellano, J.; Comerón, A.; Rocadenbosch, F.

183

Boundary Layer Experiment 1996 (BLX96).

NASA Astrophysics Data System (ADS)

The University of Wyoming King Air aircraft was the primary instrument platform for turbulence measurements in the bottom half of the convective boundary layer during 15 July-13 August 1996. A total of 12 successful research flights were made, each of about 4.5-h duration. Crosswind (east-west) flight patterns were flown in Oklahoma and Kansas over three sites of different land use: forest, pasture, and crops.Measurements of mean values, turbulent deviations, and turbulent fluxes of temperature, moisture, and momentum were made to test theories of convective transport, the radix layer, and cumulus potential. Additional portions of each flight included slant soundings and near-surface horizontal flights in order to determine mixed layer (ML) scaling variables such as ML depth zi, Deardorff velocity w and buoyancy velocity wB. While the ML was shallower and the ground wetter than anticipated based on climatology, a high-quality dataset was obtained.

Stull, Roland; Santoso, Edi; Berg, Larry; Hacker, Joshua

1997-06-01

184

Bubbly turbulent drag reduction is a boundary layer effect.

In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to 4 x 10(5), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in the rough-wall case no smooth boundary layers can develop, the results demonstrate that bubbly drag reduction is a pure boundary layer effect. PMID:17359101

van den Berg, Thomas H; van Gils, Dennis P M; Lathrop, Daniel P; Lohse, Detlef

2007-02-23

185

Effects of variable properties in film cooled turbulent boundary layers

NASA Astrophysics Data System (ADS)

The effects of variable properties on heat transfer in a film-cooled turbulent boundary layer were investigated. A new procedure was developed to deduce adiabatic effectiveness from heat transfer coefficients based on the wall to freestream temperature difference, where both are representative of variable property flow conditions. The new technique was shown to be valid using data from the literature for injection into a turbulent boundary layer from one and two rows of injection holes. From these results, the variation of the coolant to mainstream density ratio was shown to have a significantly greater effect on heat transfer than variations of viscosity and thermal conductivity.

Walz, A. F., Jr.

1986-03-01

186

An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

187

Calculation of Turbulent Boundary Layer Wall Pressure Spectra.

National Technical Information Service (NTIS)

This study is an investigation into the suitability of various wavevector-frequency models of turbulent boundary layer wall pressure fluctuations for the prediction of experimental measurements of turbulent boundary layer wall pressure spectra. Three sepa...

D. E. Capone G. C. Lauchle

1993-01-01

188

Boundary layer transition and separation on a compressor rotor airfoil

This paper presents boundary layer calculations based on these potential flow results and comparison with surface flow visualization results indicating the locations of boundary layer transition and separation. 4 refs.

Dring, R.P.

1982-01-01

189

Wall shear stress in Görtler vortex boundary layer flow

NASA Astrophysics Data System (ADS)

The development of wall shear stress in concave surface boundary layer flows in the presence of Görtler vortices was experimentally studied by means of hot-wire measurements. The wavelengths of the vortices were preset by thin vertical perturbation wires so to produce the most amplified wavelengths. Three different vortex wavelengths of 12, 15, and 20 mm were considered, and near-wall velocity measurements were carried out to obtain the ``linear'' layers of velocity profiles in the boundary layers. The wall shear stress coefficient Cf was estimated from the velocity gradient of the ``linear'' layer. The streamwise developments of boundary layer displacement and momentum thickness at both upwash and downwash initially follow the Blasius (laminar boundary layer) curve up to a certain streamwise location. Further downstream, they depart from the Blasius curve such that they increase at upwash and decrease at downwash before finally converge to the same value due to the increased mixing as a consequence of transition to turbulence. The spanwise-averaged wall shear stress coefficient Cf, which initially follows the Blasius curve, increases well above the local turbulent boundary layer value further downstream due to the nonlinear effect of Görtler instability and the secondary instability modes. Three different regions are identified based on the streamwise development of Cf, namely linear, nonlinear, and transition to turbulence regions. The onset of nonlinear region is defined as the streamwise location where the Cf begins to depart from the Blasius curve. In the nonlinear region, the spanwise distribution of Cf at the downwash becomes narrower, and there is no inflection point found further downstream.

Tandiono; Winoto, S. H.; Shah, D. A.

2009-08-01

190

NASA Astrophysics Data System (ADS)

The increasingly adverse pressure gradient boundary layer flow of Samuel and Joubert (1974) is compared with a similar flow from the Victoria University wind tunnel. The flow development in these two flows is described with the Zagarola/Smits (1998) scaling. Moreover, the equilibrium pressure parameter of Castillo/George (2001) is used to further quantify the transition from FPG/ZPG to APG flow behavior, as exhibited by the variation of the pressure coefficient, Cp. Although Cp is insufficient to predict outer flow scaling characteristics, it is important in understanding the nature of the flow development. Reynolds stress data from the Victoria University wind tunnel experiment is also presented to show that an equilibrium behavior in the sense of Townsend, is not demonstrated either with the classical or Castillo/George (2001) scaling.

Anderson, Catherine; Brzek, Brian; Castillo, Luciano; Turan, Ozden

2004-11-01

191

Modeling the planetary boundary layer — Extension to the stable case

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

J. C. Wyngaard; Hanscom AFB

1975-01-01

192

Leaky waves in boundary layer flow

NASA Astrophysics Data System (ADS)

Linear stability analysis of boundary layer flow is traditionally performed by solving the Orr-Sommerfeld equation (OSE), either in a temporal or a spatial framework. The mode structure of the OSE is in both cases composed of a finite number of discrete modes which decay at infinity in the wall- normal direction y, and a continuous spectrum of propagating modes behaving as (±ik y) when y->?, with real k. A peculiarity of this structure is that the number of discrete modes changes with the Reynolds number, Re. They indeed seem to disappear behind the continuous spectrum at certain Re. This phenomenon is here investigated by studying the response of the Blasius boundary layer forced instantaneously in space and time. Since the solution of the forced and homogeneous Laplace-transformed problem both depend on the free-stream boundary conditions, it is shown here that a suitable change of variables can remove the branch cut in the Laplace plane. As a result, integration of the inverse Laplace transform along the two sides of the branch cut, which gives rise to the continuous spectrum, can be replaced by a sum of residues corresponding to an additional set of discrete eigenvalues. These new modes grow at infinity in the y direction, and are analogous to the leaky waves found in the theory of optical waveguides, i.e. optical fibers, which are attenuated in the direction of the waveguide but grow unbounded in the direction perpendicular to it.

Pralits, Jan

2005-11-01

193

Microscale heat transfer enhancement using thermal boundary layer redeveloping concept

We demonstrated a new silicon microchannel heat sink, composing of parallel longitudinal microchannels and several transverse microchannels, which separate the whole flow length into several independent zones, in which the thermal boundary layer is in developing. The redeveloping flow is repeated for all of the independent zones thus the overall heat transfer is greatly enhanced. Meanwhile, the pressure drops are

J. L. Xu; Y. H. Gan; D. C. Zhang; X. H. Li

2005-01-01

194

Low Reynold's Number Boundary Layers in a Disturbed Environment.

National Technical Information Service (NTIS)

Studies of flat plate boundary layer development were made in a low speed wind tunnel at turbulence levels from 2%to 7%. Only transitional and turbulent flows were observed in the range 280 Re sub theta 700. The mean turbulent velocity profiles display la...

D. K. Paik E. Reshotko

1986-01-01

195

Aircraft measurements within the planetary boundary layer over water

The basic overall objective of the program has been to develop a relatively inexpensive airborne sensing system for study of the marine boundary layer in support of the NAVAIR Marine Fog Investigation. This extends into the third dimension measurement of most of the significant parameters which have been studied from ships and land stations. The operational flexibility of the aircraft

R. Markson

1977-01-01

196

Lagrangian model for dispersion in the atmospheric boundary layer.

National Technical Information Service (NTIS)

A Random Walk Model for simulating dispersion in the daytime boundary layer has been developed. The model is a one-dimensional model, in which the horizontal dispersion is considered negligible. The model can simulate dispersion for a continuous range of ...

C. Tassone

1995-01-01

197

Diffusion of Drag Reducing Polymers in a Turbulent Boundary Layer.

National Technical Information Service (NTIS)

The diffusion of diluted drag reducing polymers and the effect of the diffusing polymers on the development of the boundary layer are analyzed. The analysis suggests that the diffusion rate is reduced together with the drag. However, in most practical sit...

M. Poreh K. S. Hsu

1971-01-01

198

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

199

Spatial Linear Instability of Confluent Wake/Boundary Layers.

National Technical Information Service (NTIS)

The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a...

W. W. Liou F. J. Liu

2001-01-01

200

THE EFFECTS OF PERIODIC WAKE STRUCTURES ON TURBULENT BOUNDARY LAYERS

Compressor and turbine blade boundary layers in axial-flow turbomachines are subject to periodically disturbed flow. This study modelled these conditions in a wind tunnel with circular cylinders traversing in front of a flat plate. Turbulent boundary layer velocity profiles on the flat plate were measured with a hot-wire anemometer. The turbulence intensity in the boundary layer was found to be

R. M. Holland; R. L. Evans

1996-01-01

201

Acoustic radar investigations of boundary layer phenomena

NASA Technical Reports Server (NTRS)

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.

Marks, J. R.

1974-01-01

202

Numerical Modeling of the Evolving Stable Boundary Layer

NASA Astrophysics Data System (ADS)

A single-column model of the evolving stable boundary layer is tested for the consistency of turbulence parameterization, self-similar properties of the flow, and effects of ambient forcing. The turbulence closure of the model is based on the K-theory approach, with stability functions based on empirical data, and a semi-empirical form of the mixing length. The model has one internal, governing stability parameter, the Richardson number Ri, which dynamically adjusts to the boundary conditions and to external forcing. Model results, expressed in terms of local similarity scales, are universal functions of the Richardson number, i.e. they are satisfied in the entire stable boundary layer, for all instants of time, and all kinds of external forcing. Based on similarity expression, a realizability condition is derived for the minimum turbulent heat flux in the stable boundary layer. Numerical experiments show that the development of 'horse-shoe' shaped, 'fixed-elevation' wind hodographs in the interior of the stable boundary layer are solely caused by effects imposed by surface thermal forcing, and are not related to the inertial oscillation mechanism.

Sorbjan, Z.

2013-12-01

203

Additive thermochemical effects in turbulent erosive boundary layers

Previously obtained interior ballistics and wall boundary layer modeling results indicate that significant reduction in erosive heating can be expected when finely divided particles are dispersed through the propellant combustion flow field. Attention was first placed on the particle size influences, together with particle dispersal dynamics in both turbulent combustion core flow and the erosive wall boundary layer region. Submicron thermochemically inert particles were predicted to disperse readily to the near wall region where they were then entrained in the boundary layer. This was estimated to substantially reduce the predicted erosive heat and mass transfer and experimentally confirmed. Examination of the time-averaged turbulent boundary layer macrostructure changes indicated that inertial influences were primarily responsible for this reduction in erosive heating to gun barrel walls. The boundary layers were thickened by the additives and erosive diffusion gradients were correspondingly reduced. The isolated inertial mechanisms are now understood but are difficult to apply in general dimensional analysis scaling or in analytical heat transfer correlation predictions. Three major factors which contribute to these difficulties are: time dependence of both developing mean flow and particle field; turbulence-particle interactions; and thermochemical heat release and exchange between reactive gas components and particles, particles and wall surface, and reactive gas and wall surface. To help illustrate the influence of thes mechanisms and provide a basis for prediction, the influence of submicron additives in unsteady turbulent boundary layer growth and interaction regions adjacent to a model of a chemically active metallic (steel) surface are examined. Equilibrium chemistry is assumed for all phases.

Buckingham, A.C.; Levatin, J.L.

1983-01-18

204

Flow Quality and Boundary Layer Transition

NASA Technical Reports Server (NTRS)

The widely held view is that transition to turbulence in the Blasius boundary layer occurs via amplification and eventual nonlinear breakdown of initially small amplitude instabilities i.e. Tollmien-Schlichting (TS) waves. However this scenario is only observed for low amplitude free-stream turbulence levels, i.e. u/U < 0.1%. Bypass of linear TS instability mechanism occurs for higher EST levels, yet considerable differences exist between the few experiments carefully designed to assess the effect of EST on transition. The consensus is that EST leads to longitudinal streaks that form near the leading edge in the boundary layer . These streaks appeal to be regions of concentrated streamwise vorticity and they are often referred to as Klebanoff modes. The importance of mean flow free-stream nonuniformity (FSN) is not as widely appreciated as EST for characterizing wind tunnel flow quality. Here it is shown that, although the v like generated by a d=50micron wire located upstream of the contraction (Re(sub d)=6.6, x/d=45,000) is immeasurably small by the time it interacts with the leading edge in the test section, it is responsible for generation of a pair of weak streamwise vortices in the boundary layer downstream. The characteristics of these wake-induced vortices and their effect on TS waves are demonstrated. Small remnant FSN variations are also shown to exist downstream of a turbulence grid. The question arises Are the adverse effects introduced by the turbulence grid caused by FST or by small remnant FSN variations?

Watmuff, Jonathan H; Tobak, M.; Davis, Sanford S. (Technical Monitor)

1997-01-01

205

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

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

2006-01-01

206

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

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

2006-01-01

207

SAID: A turbulent plasmaspheric boundary layer (Invited)

NASA Astrophysics Data System (ADS)

The new features of subauroral ion drifts (SAID) observed from the Cluster, DMSP, and Polar satellites are reviewed, including the discovery of SAID-related plasma waves. These observations confirm and expand on the Mishin and Puhl-Quinn [GRL, 34, L24101, 2007] concept of the SAID channel being a turbulent boundary layer, formed via a short circuit of the substorm-injected plasmoid by the plasmasphere. These observations show that SAID formation is related to enhanced lower hybrid/fast magnetosonic waves. Their excitation leads to anomalous circuit resistivity and magnetic diffusion, similar to the well-documented plasmoid-magnetic barrier problem, including impulsive penetration at the magnetopause.

Mishin, E. V.

2010-12-01

208

SAID: A turbulent plasmaspheric boundary layer

NASA Astrophysics Data System (ADS)

This paper presents novel features of subauroral ion drifts (SAID) observed from a unique conjunction of the Cluster, DMSP, and Polar satellites, including the discovery of SAID-related plasma waves. These observations confirm and expand on our proposed concept of the SAID channel being a turbulent boundary layer, formed via a short circuit of the substorm-injected plasmoid by the plasmasphere. We show that SAID formation is related to enhanced lower hybrid/fast magnetosonic waves. Their excitation leads to anomalous circuit resistivity and magnetic diffusion, similar to the well-documented plasmoid-magnetic barrier problem, including impulsive penetration at the magnetopause.

Mishin, E. V.; Puhl-Quinn, P. A.; Santolik, O.

2010-04-01

209

The minisodar and planetary boundary layer studies

The minisodar, in addition to being smaller than conventional sodar, operates at higher frequencies, obtains usable signal returns closer to the surface, and can use smaller range gates. Because the max range is generally limited to the lower 200 m above the surface, the minisodar is not able to interrogate the entire daytime atmospheric Planetary Boundary Layer (PBL); however it can be a very useful tool for understanding the PBL. In concert with other instruments, the minisodar can add significant new insights to our understanding of the PBL. This paper gives examples of past and potential uses of minisodars in such situations.

Coulter, R.L.

1996-06-01

210

Boundary-layer Transition at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.

Low, George M

1956-01-01

211

Convective Surface Layers: Influence of the Boundary Layer Depth

NASA Astrophysics Data System (ADS)

Two methods, one semi-empirical and the other theoretical, are employed to develop a new theory for predicting the behavior of turbulence characteristics in convective surface layers. This theory is based on three length scales; the height above the ground, the Monin-Obukhov length, and the boundary layer depth (h). The chief advantages are its relative simplicity, its ability to predict the height dependence of the mean gradients and second moments in a manner consistent with their observed behavior in the atmosphere and in large-eddy simulations, and it is consistent with the theoretical requirements of free convection similarity. The semi-empirical method is based on nonlinear least squares fits to a generalized Businger-Dyer formulation with up to four unknown parameters. Using data obtained primarily from the Kansas and Minnesota field experiments, this method is applied to the universal functions for the wind and temperature gradients, the standard deviation of the horizontal wind velocity (v(,*)), the variances of vertical velocity and temperature, the streamwise heat flux, and the turbulence dissipation. Analyses of the Kansas data are performed using both drag-plate and eddy -correlation measurements of u(,*). To indirectly include the influence of h and also obtain the best statisti- cal results, the dimensionless shear, (xi) and Ri are modified by the ratio (kappa)v(,*)/u(,*). Unfortunately, this procedure often results in solutions which do not satisfy the requirements of free convection theory. An apparent reason for this is found when the differences between the drag-plate and eddy-correlation values of n(,*) are analyzed. Using the flow distortion equations developed by Wyngaard (1982), results in close agreement with Wieringa (1980) are obtained. Despite this, it is found that the ratio (kappa)v(,*)/u(,*) is apparently equal to unity in neutral conditions and that the height dependence of some quantities may not be the same as is currently accepted. A theoretical approach which imposes free convection require- ments is developed. Vector-like quantities are found to be propor- tional to the shear stress and all quantities are found to depend on both w(,*) and w(theta)(' )in an identical manner. New flux-gradient relationships are proposed.

Loveland, Kurt Tyler

212

Dynamic Boundary Control of Beams Using Active Constrained Layer Damping

NASA Astrophysics Data System (ADS)

A globally stable boundary control strategy is developed to damp the vibration of beams fully treated with active constrained layer damping (ACLD) treatments. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced generates a control force and moment acting at the boundary of the treated beam. The development of the boundary control strategy is based on a distributed-parameter model of the beam/ACLD system in order to avoid the classical spillover problems resulting from using 'truncated' finite element models. Such an approach makes the boundary controller capable of controlling all the modes of vibration of the ACLD-treated beams and guarantees that the total energy norm of the system is decreasing continuously with time. The control strategy is provided also with a dynamic compensator to shape the vibration damping characteristics of the ACLD in the frequency domain. The effectiveness of the ACLD in damping out the vibration of cantilevered beams is determined for different control gains and compared with the performance of conventional passive constrained layer damping (PCLD). The results obtained demonstrate the high damping characteristics of the boundary controller particularly over broad frequency bands.

Baz, A.

1997-11-01

213

A sensitivity theory for the equilibrium boundary layer over land

NASA Astrophysics Data System (ADS)

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.

Cronin, Timothy W.

2013-12-01

214

Soot profiles in boundary-layer flames

Carbon particulate volume fractions and approximate particle size distributions are measured in a free laminar combusting boundary layer for liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, toluene) and polymethylmethacrylate (PMMA). A multiwavelength laser transmission technique determines a most probable radius and the total particle concentration, which are two parameters in an assumed form for the size distribution. In the combusting boundary layer, a sooting region exists between the pyrolyzing fuel surface and the flame zone. 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 -5/ for toluene, an aromatic. The PMMA volume fractions, f/sub v/ approx. 5 X 10/sup -7/, are approximately the same as the values previously reported for pool fires. The soot volume fractions increase with height; convection of carbon particles downstream widens the soot region with height. For all fuels tested, the most probable radius is between 20 nm and 50 nm, and it changes only slightly with height and distance from the fuel surface.

Beier, R.A.; Pagni, P.J.

1981-12-01

215

Boundary Layer Transition Flight Experiment Overview

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

216

For the theoretical consideration of a system for reducing skin friction, a mathematical model was derived to represent, in a two-phase field, the effect on skin friction of the injection of micro air bubbles into the turbulent boundary layer of a liquid stream. Based on the Lagrangian method, the equation of motion governing a single bubble was derived. The random

Yuki Yoshida; Yoshiaki Takahashi; Hiroharu Kato; Akira Masuko; Osamu Watanabe

1997-01-01

217

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

218

Secondary eyewall formation as a progressive boundary layer response

NASA Astrophysics Data System (ADS)

The robust observational (satellite based) evidence that secondary eyewalls are common features in major hurricanes contrasts with the scarce in situ observations of the phenomena and its life cycle. This lack of observations has resulted in an incomplete understanding of the dynamics of secondary eyewall formation (SEF). A wide variety of physical processes have been invoked to explain SEF, but only the recently proposed theory of a progressive boundary layer control in SEF has been supported by a variety of full physics mesoscale numerical integrations. The RAINEX field project provided unique observations of the secondary eyewall of Hurricane Rita (2005) both before and during the time Rita exhibited a clear secondary eyewall structure. These observations have contributed to the advancement of the understanding of the secondary eyewall phenomenon. However, in the RAINEX experiment, there was limited data sampling during the development of the secondary wind maxima, thereby precluding a complete observational investigation of the dynamics of SEF. In this presentation we adopt an azimuthally-averaged perspective of the flow dynamics and we test the newly proposed theory of a progressive boundary layer control on SEF. Specifically, we use both RAINEX data as well as data from high resolution, full physics mesoscale numerical simulations to initialize and force an axisymmetric slab boundary layer model with radial diffusion included. The objective is to investigate whether such a reduced boundary layer model can generate secondary wind maxima as a response to environments like those that result in SEF in nature and in full physics simulations.

Abarca, S. F.; Montgomery, M. T.; Bell, M. M.

2012-12-01

219

The role of acoustic feedback in boundary-layer instability

NASA Astrophysics Data System (ADS)

In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which acoustic feedback loop plays an essential role. The first concerns a boundary layer over a flat plate, on which two well separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave, which propagates upstream and impinges on the upstream roughness to regenerate the T-S wave thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that at high Reynolds numbers and for moderate roughness heights the long-range acoustic coupling may lead to global instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns supersonic 'twin boundary layers', which develop along the two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the usual unconfined boundary layer.

Wu, Xuesong

2013-10-01

220

On the Effects of Surface Roughness on Boundary Layer Transition

NASA Technical Reports Server (NTRS)

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.

Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack

2009-01-01

221

Hair receptor sensitivity to changes in laminar boundary layer shape.

Biologists have shown that bat wings contain distributed arrays of flow-sensitive hair receptors. The hair receptors are hypothesized to feedback information on airflows over the bat wing for enhanced stability or maneuverability during flight. Here, we study the geometric specialization of hair-like structures for the detection of changes in boundary layer velocity profiles (shapes). A quasi-steady model that relates the flow velocity profile incident on the longitudinal axis of a hair to the resultant moment and shear force at the hair base is developed. The hair length relative to the boundary layer momentum thickness that maximizes the resultant moment and shear-force sensitivity to changes in boundary layer shape is determined. The sensitivity of the resultant moment and shear force is shown to be highly dependent on hair length. Hairs that linearly taper to a point are shown to provide greater output sensitivity than hairs of uniform cross-section. On an order of magnitude basis, the computed optimal hair lengths are in agreement with the range of hair receptor lengths measured on individual bat species. These results support the hypothesis that bats use hair receptors for detecting changes in boundary layer shape and provide geometric guidelines for artificial hair sensor design and application. PMID:20157224

Dickinson, B T

2010-03-01

222

Measurements using stereo particle image velocimetry are presented for a developing turbulent boundary layer in a wind tunnel\\u000a with a Mach 2.75 free stream. As the boundary layer exits from the tunnel nozzle and moves through the wave-free test section,\\u000a small initial departures from equilibrium turbulence relax, and the boundary layer develops toward the equilibrium zero-pressure-gradient\\u000a form. This relaxation process

Andrew P. LapsaWerner; Werner J. A. Dahm

2011-01-01

223

Lidar probing the urban nocturnal boundary layer

NASA Astrophysics Data System (ADS)

Lidar observations to study the nocturnal boundary layer in the atmosphere were made on selected evenings during December 1997 - March 1998 at the City University of Hong Kong (lat. 20 degree(s)20'6', long. 114 degree(s)10'18', at 57 m AMSL), Hong Kong. The ground-based Nd:YAG lidar has been operated to detect the vertical distribution of aerosols in the NBL at a subtropical urban site. It is shown that the vertical relative signal profiles can be employed to determine the heights of the single or multiple nocturnal inversions. In a clear sky and light wind evening transition period, the strong radiative cooling caused the air near the ground becomes stably stratified. The nocturnal inversion starts to emerge soon before sunset and grows vertically as the night progresses. The study also showed that the temporal evolution of the nocturnal inversion depth was rapidly increased soon after sunset and a slower rate in the midnight hours. The results of the study indicate that the vertical aerosol distribution in the multiple-layer is more complicated than that in the single-layer, of NBL. The early morning transition of the NBL is also discussed. A comparison of the lidar aerosol signals and radiosonde measurements was performed to evaluate the consistency of observations between the different systems.

Mok, T. M.; Leung, Kang M.; Ho, A. H.; Chan, J. C.; Ng, C. N.

1998-08-01

224

Chemistry of a polluted cloudy boundary layer

A one-dimensional photochemical model for cloud-topped boundary layers is developed which includes detailed descriptions of gas-phase and aqueous-phase chemistry, and of the radiation field in and below cloud. The model is used to interpret the accumulation of pollutants observed over Bakersfield, California, during a wintertime stagnation episode with low stratus. The main features of the observations are well simulated; in particular, sulfate accumulates progressively over the course of the episode due to sustained aqueous-phase oxidation of SO{sub 2} in the stratus cloud. The major source of sulfate is the reaction S(IV)+Fe(III), provided that this reaction proceeds by a non radical mechanism in which Fe(III) is not reduced. A radical mechanism with SO{sup {minus}}{sub 3} and Fe(II) as immediate products would quench sulfate production because of depletion of Fe(III). The model results suggest that the non radical mechanism is more consistent with observations, although this result follows from the absence of a rapid Fe(II) oxidation pathway in the model. Even with the non-radical mechanis most of the soluble iron is present as FE(II) because Fe(III) is rapidly reduced by O{sup {minus}}{sub 2}. The S(IV)+Fe(III) reacton provides the principal source of H{sub 2}O{sub 2} in the model; photochemical production of H{sub 2}O{sub 2} from HO{sub 2} or O{sub 2}({minus}I) is slow because HO{sub 2} is depleted by high levels of NO{sub {ital x}}. The aqueous-phase reaction S(IV)+OH initiates a radical-assisted S(IV) oxidation chain but we find that the chain is not propagated due to efficient termination by SO{sup {minus}}{sub 4}+Cl{sup {minus}} followed by Cl+H{sub 2}O. A major uncertainty attached to that result is that the reactivities of S(IV)-carbonyl adducts with radical oxidants are unknown.

Jacob, D.J.; Gottlieb, E.W. (Department of Earth and Planetary Sciences and Division of Applied Sciences, Harvard University, Cambridge, Massachusetts (US)); Prather, M.J. (NASA Goddard Institute of Space Studies, New York, New York)

1989-09-20

225

Boundary Layer Resolving Pseudospectral Methods For Singular Perturbation Problems

. Pseudospectral methods are investigated for singularly perturbed boundary valueproblems for ordinary differential equations which possess boundary layers. It is well known that ifthe boundary layer is very small then a very large number of spectral collocation points is requiredto obtain accurate solutions. We introduce here a new effective procedure, based on coordinatestretching and the Chebyshev pseudospectral method to resolve

Tao Tang Manfred R. Trummer

1993-01-01

226

National Technical Information Service (NTIS)

A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux a...

C. D. Whiteman J. M. Alzheimer G. A. Anderson W. J. Shaw

1993-01-01

227

Water channel simulation of the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

As part of a programme of work designed to assess the feasibility of modelling the dispersion of heavy plumes in a water channel it has been necessary to develop artificially structured shear layers which attempt to simulate atmospheric conditions. For a variety of reasons the choice of simulation is similar to that developed by Counihan (1969) and consists of a rough surface preceded by a castellated barrier and a number of profiled vorticity generators. Mean velocity and turbulence distributions, together with turbulent spectra and integral length scales, compared favourably with boundary layers modelled in wind tunnels and with full scale experiments in rural surroundings.

Cheah, S. C.; Cleaver, J. W.; Millward, A.

228

Streamwise vortices in heated boundary layers

NASA Technical Reports Server (NTRS)

The nonlinear instability of the boundary layer on a heated flat plate placed in an oncoming flow is investigated. Such flows are unstable to stationary vortex instabilities and inviscid traveling wave disturbances governed by the Taylor-Goldstein equation. For small temperature differences the Taylor-Goldstein equation reduces to Rayleigh's equation. When the temperature difference between the wall and free stream is small the preferred mode of instability is a streamwise vortex. It is shown in this case that the vortex, assumed to be of small wavelength, restructures the underlying mean flow to produce a profile which can be massively unstable to inviscid traveling waves. The mean state is shown to be destabilized or stabilized to inviscid waves depending on whether the Prandtl number is less or greater than unity.

Hall, Philip

1992-01-01

229

Some measurements in synthetic turbulent boundary layers

NASA Astrophysics Data System (ADS)

Synthetic turbulent boundary layers are examined which were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1,700,000. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft which displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e., the probability of observing turbulent flow at a particular point in space and time. The results are reported in x-t diagrams showing the evolution of various synthetic flows along the plate. The dimensionless celerity or phase velocity of the large eddies is found to be 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows which contained appreciable laminar regions. The large eddies shifted in formation to new positions, intermediate to their original ones, while preserving their hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, are used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study. The values recommended are: spanwise scale/thickness = 2.5, streamwise scale/thickness = 8.

Savas, O.

1980-01-01

230

Halogen chemistry in the marine boundary layer

NASA Astrophysics Data System (ADS)

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.

Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.

2009-04-01

231

Acoustics of laminar boundary layers breakdown

NASA Astrophysics Data System (ADS)

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.

Wang, Meng

1994-12-01

232

Acoustics of laminar boundary layers breakdown

NASA Technical Reports Server (NTRS)

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.

Wang, Meng

1994-01-01

233

Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows

NASA Technical Reports Server (NTRS)

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.

Hess, Robert V.

1959-01-01

234

Li metal was electrodeposited galvanostatically on aLi metal substrate in propylene carbonate (PC) containing 0.5 M lithium perchlorate (LiClO4). The concentration profile of Li+ ion developed with electrodeposition was measured in situ by holographic interferometry. The interference fringe shift at a higher current density indicates that the mass transfer rate of Li+ ion along a vertical cathode is primarily governed

M Ota; S Izuo; K Nishikawa; Y Fukunaka; E Kusaka; R Ishii; J. R Selman

2003-01-01

235

Boundary-layer and shock-layer solutions to singularly perturbed boundary-value problems

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.

Jeffries, J.S.

1987-01-01

236

NASA Technical Reports Server (NTRS)

An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization of vortex structure. Vortex structure was characterized by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen Vortex. Vortex trajectories are modelled by including the convective effects of neighbors.

Wendt, Bruce J.; Greber, Isaac; Hingst, Warren R.

1991-01-01

237

Study of boundary-layer transition using transonic-cone preston tube data

NASA Technical Reports Server (NTRS)

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.

Reed, T. D.; Moretti, P. M.

1980-01-01

238

National Technical Information Service (NTIS)

A planetary boundary layer (PBL) parameterization based on the generalized similarity theory (GST) was developed for tropical cyclone models. This parameterization, with only one layer, is necessary in modeling tropical cyclones for computational speed. T...

S. W. Chang R. V. Madala

1980-01-01

239

A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform's operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.

Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.

1993-03-01

240

A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform`s operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.

Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.

1993-03-01

241

Acoustic sounding in the planetary boundary layer

NASA Technical Reports Server (NTRS)

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.

Kelly, E. H.

1974-01-01

242

Boundary-layer turbulence as a kangaroo process

NASA Astrophysics Data System (ADS)

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.

Dekker, H.; de Leeuw, G.; Maassen van den Brink, A.

1995-09-01

243

Boundary layer energization by means of optimized vortex generators

NASA Technical Reports Server (NTRS)

A three-dimensional, multi-block, multi-zone, Euler analysis has been developed and applied to analyze the flow processes induced by a lateral array of low profile vortex generators (VG). These vortex generators have been shown to alleviate boundary layer separation through the generation of streamwise vorticity. The analysis has been applied to help develop improved VG configurations in an efficient manner. Special attention has been paid to determining the accuracy requirements of the solver for calculations in which vortical mechanisms are dominant. The analysis has been used to assess the effectiveness or boundary layer energization capacity of different VG's, including the effect of scale and shape variation. Finally, the analysis has been validated through comparisons with experimental data obtained in a large-scale low-speed wind tunnel.

Barber, T. J.; Mounts, J. S.; Mccormick, D. C.

1993-01-01

244

BLSTA: A boundary layer code for stability analysis

NASA Technical Reports Server (NTRS)

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.

Wie, Yong-Sun

1992-01-01

245

Winds in the Marine Boundary Layer: A Forecaster's Guide

NSDL National Science Digital Library

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.

Spangler, Tim

2006-12-01

246

Turbulent Boundary Layer in High Rayleigh Number Convection in Air

NASA Astrophysics Data System (ADS)

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.

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-01

247

Boundary Layer Transition Experiments in Support of the Hypersonics Program

NASA Technical Reports Server (NTRS)

Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.

Berry, Scott A.; Chen, Fang-Jenq; Wilder, Michael C.; Reda, Daniel C.

2007-01-01

248

Large Eddy Simulation of the ventilated wave boundary layer

A Large Eddy Simulation (LES) of (1) a fully developed turbulent wave boundary layer and (2) case 1 subject to ventilation (i.e., suction and injection varying alternately in phase) has been performed, using the Smagorinsky subgrid-scale model to express the subgrid viscosity. The model was found to reproduce experimental results well. However, in case 1, the near-bed ensemble averaged velocity

I. P. Lohmann; J. Fredsøe; B. M. Sumer; E. D. Christensen

2006-01-01

249

Vortex/boundary-layer interactions: Data report, volume 1

NASA Technical Reports Server (NTRS)

This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, 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 course of preparation.

Cutler, A. D.; Bradshaw, P.

1987-01-01

250

Direct numerical simulation of supersonic turbulent boundary layers

NASA Astrophysics Data System (ADS)

The objectives of this research were to develop a method by which the spatially developing compressible turbulent boundary layer could be simulated using a temporally developing numerical simulation and to study the physics of the compressible turbulent boundary layer. We take advantage of the technique developed by Spalart (1987, 1988) for the incompressible case. In this technique, it is recognized that the boundary layer exhibits slow growth in the streamwise direction, so the turbulence can be treated as approximately homogeneous in this direction. The slow growth is accounted for with a coordinate transformation and a multiple scale analysis. The result is a modified system of equations (Navier-Stokes plus some extra terms, which we call "slow growth terms") that are homogeneous in both the streamwise and spanwise directions and represent the state of the boundary layer at a given streamwise location (or, equivalently, a given thickness). The compressible Navier-Stokes equations are solved using a mixed Fourier and B-spline "spectral" method. The dependent variables are expanded in terms of a Fourier representation in the horizontal directions and a B-spline representation in the wall-normal direction. In the wall-normal direction non-reflecting boundary conditions are used at the freestream boundary, and zero-heat-flux no-slip boundary conditions are used at the wall. This combination of splines and Fourier methods produces a very accurate numerical method. Mixed implicit/explicit time discretization is used. Results are presented for a case with a Mach number of 2.5, and a Reynolds number, based on momentum integral thickness and wall viscosity, of Rsb{thetasp'} = 840. The results show that the van Driest transformed velocity satisfies the incompressible scalings and a narrow logarithmic region is obtained. The results for the turbulence intensities compare well with the incompressible simulations of Spalart. Pressure fluctuations are found to be higher than in incompressible flow. Morkovin's strong Reynolds analogy does not agree with the results of the simulation, however, an analogy is found between the rate of turbulent heat transfer and the rate of turbulent momentum transfer. Reynolds stress and turbulent kinetic energy budgets are computed and compared with the budgets from Spalart's incompressible simulations.

Guarini, Stephen

251

Boundary-layer wind structure in a landfalling tropical cyclone

In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a\\u000a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical\\u000a cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of

Xiaodong Tang; Zhemin Tan

2006-01-01

252

Nonparallel stability of boundary layers with pressure gradients and suction

NASA Technical Reports Server (NTRS)

An analysis is presented for the linear nonparallel stability of boundary layer flows with pressure gradients and suction. The effect of the boundary layer growth is included by using the method of multiple scales. The present analysis is compared with those of Bouthier and Gaster and the roles of the different definitions of the amplification rates are discussed. The results of these theories are compared with experimental data for the Blasius boundary layer. Calculations are presented for stability characteristics of boundary layers with pressure gradients and nonsimilar suction distributions.

Saric, W. S.; Nayfeh, A. H.

1977-01-01

253

Effect of the noise on boundary layer transition

NASA Astrophysics Data System (ADS)

In this paper, an experimental study of stream noise affecting the boundary layer transition in the test section of a wind tunnel is conducted. The effect of sortie input on the boundary layer transition is examined and stream noise in test section is measured. The results show that there are sensitive regions of sonic frequency and pressure affecting the boundary layer transition. The frequency band of the stream noise in the test section is wide and the low frequency is dominant and important in its effect on the boundary layer transition. Stream noise increases with the wind velocity and turbulence rises with added grid in the settling chamber.

Zheng, Guofeng

1993-04-01

254

Evolution and structure of sink-flow turbulent boundary layers

NASA Astrophysics Data System (ADS)

An experimental and theoretical investigation of turbulent boundary layers developing in a sink-flow pressure gradient was undertaken. Three flow cases were studied, corresponding to different acceleration strengths. Mean-flow measurements were taken for all three cases, while Reynolds stresses and spectra measurements were made for two of the flow cases. In this study attention was focused on the evolution of the layers to an equilibrium turbulent state. All the layers were found to attain a state very close to precise equilibrium. This gave equilibrium sink flow data at higher Reynolds numbers than in previous experiments. The mean velocity profiles were found to collapse onto the conventional logarithmic law of the wall. However, for profiles measured with the Pitot tube, a slight ‘kick-up’ from the logarithmic law was observed near the buffer region, whereas the mean velocity profiles measured with a normal hot wire did not exhibit this deviation from the logarithmic law. As the layers approached equilibrium, the mean velocity profiles were found to approach the pure wall profile and for the highest level of acceleration [Pi] was very close to zero, where [Pi] is the Coles wake factor. This supports the proposition of Coles (1957), that the equilibrium sink flow corresponds to pure wall flow. Particular interest was also given to the evolutionary stages of the boundary layers, in order to test and further develop the closure hypothesis of Perry, Marusic & Li (1994). Improved quantitative agreement with the experimental results was found after slight modification of their original closure equation.

Jones, M. B.; Marusic, Ivan; Perry, A. E.

2001-02-01

255

NASA Astrophysics Data System (ADS)

Observations of the Saharan boundary layer, made during the GERBILS field campaign, show that mesoscale land surface temperature variations (which were related to albedo variations) induced mesoscale circulations, and that mesoscale and boundary-layer circulations affected dust uplift and transport. These processes are unrepresented in many climate models, but may have significant impacts on the vertical transport and uplift of desert dust. Mesoscale effects in particular tend to be difficult to parameterise. With weak winds along the aircraft track, land surface temperature anomalies with scales of greater than 10 km are shown to significantly affect boundary-layer temperatures and winds. Such anomalies are expected to affect the vertical mixing of the dusty and weakly stratified Saharan Air Layer (SAL). Mesoscale variations in winds are also shown to affect dust loadings in the boundary-layer. In a region of local uplift, with strong along-track winds, boundary-layer rolls are shown to lead to warm moist dusty updraughts in the boundary layer. Large eddy model (LEM) simulations suggest that these rolls increased uplift by approximately 30%. The modelled effects of boundary-layer convection on uplift is shown to be larger when the boundary-layer wind is decreased, and most significant when the mean wind is below the threshold for dust uplift and the boundary-layer convection leads to uplift which would not otherwise occur.

Marsham, J. H.; Parker, D. J.; Grams, C. M.; Grey, W. M. F.; Johnson, B. T.

2008-05-01

256

Boundary layer features observed during NAME 2004

NASA Astrophysics Data System (ADS)

S-Pol radar data from the North American Monsoon Experiment (NAME) are examined to investigate the characteristics of sea breezes that occurred during the North American Monsoon in the late summer of 2004, as well as their role in modulating monsoon convection. Zero degree plan position indicated (PPI) scans were examined to determine the presence of a sea breeze fine line in the S-Pol radar data. Sea breeze fine lines were typically observed over land very near the coast of the Gulf of California (GoC), and usually moved onshore around 1700--1800 UTC (11:00 AM--12:00 PM local time), and then continued to move slowly inland on the coastal plain. The sea breezes typically moved on land and dissipated before any significant interactions with Sierra Madre Occidental (SMO) convection could occur. Fine lines varied in reflectivity strength, but were typically around 10 to 20 dBZ. Surface winds from the Estacion Obispo (ETO) supersite were analyzed to confirm the presence of a shift in wind direction on days in which a fine line had been identified. Typically winds changed from light and variable to consistently out of the west or southwest. Vertical plots of S-Pol reflectivity were created to examine sea breeze structure in the vertical, but these were not found to be useful as the sea breeze signature was nearly impossible to distinguish from other boundary layer features. Horizontal structure was further investigated using wind profiler relative reflectivity, vertical velocity, and horizontal winds from the profiler located at ETO. Relative reflectivity and vertical velocity fields revealed a complex boundary layer structure on some days of repeating updrafts and downdrafts. Further examination of S-Pol PPI data revealed that these vertical motions are likely due to the presence of horizontal convective rolls. Profiler horizontal winds revealed that the depth and vertical structure of the sea breezes varied significantly from day to day, but that the height of the sea breeze is around 1 km above the ground. Sea breezes observed during NAME almost never initiated convection on their own. It is hypothesized that a weak thermal contrast between the GoC and the land leads to comparatively weak sea breezes, which don't have enough lift to trigger convection.

Stuckmeyer, Elizabeth A.

257

Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

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 Decomposition,'' POD). The time-dependent inflow condition is provided from a separate LES of a boundary layer developing behind a barrier fence and a set of vorticity generators. LES results using significantly different grid resolutions are compared with a corresponding wind tunnel experiment to demonstrate the reliability of the simulation. The separation processes are analyzed by inspecting second-order moments, time spectra, and instantaneous velocity distributions. Applying POD, a detailed study of the spatiotemporal structure of the separation processes has been carried out. From this analysis it can be concluded that the major event in the separated flow behind the obstacle is the shedding of ``von Kármán''-type vortices, which can be represented by the first three energetically dominant modes.

Manhart, Michael

258

Turbulent transition mechanism in general three-dimensional boundary layers

NASA Astrophysics Data System (ADS)

Boundary layers developing over either a spinning body, curved body, or yawed body experience body force such as centrifugal force. The turbulent transition is proceeded by stream wise vortices. In order to clarify the general transition mechanism, we did investigations on several different test models. As a result, we found that the Secondary high frequency instability is the key disturbance. There is no chance in the case of a swept wing boundary layer that the transition is driven by absolute instability. If the transition exists due to absolute instability, then it will be only on spinning cones with a large angle close to a disk. Consistent transition process is apparent when the stationary stream wise vortices start to appear as a primary instability. Then this instability generates an unstable local condition for the inflectional instability. At each top of the stream wise vortices, the frequency of the turbulence is increased, and is spread into the whole flow region.

Kohama, Yasuaki; Watanabe, Hideo; Kikuchi, Satoshi; Egami, Yasuhiro

2001-11-01

259

Forward marching procedure for separated boundary-layer flows

NASA Technical Reports Server (NTRS)

A forward-marching procedure for separated boundary-layer flows which permits the rapid and accurate solution of flows of limited extent is presented. The streamwise convection of vorticity in the reversed flow region is neglected, and this approximation is incorporated into a previously developed (Carter, 1974) inverse boundary-layer procedure. The equations are solved by the Crank-Nicolson finite-difference scheme in which column iteration is carried out at each streamwise station. Instabilities encountered in the column iterations are removed by introducing timelike terms in the finite-difference equations. This provides both unconditional diagonal dominance and a column iterative scheme, found to be stable using the von Neumann stability analysis.

Carter, J. E.; Wornom, S. F.

1975-01-01

260

NASA Astrophysics Data System (ADS)

Stagnant meteorological conditions and high anthropogenic emissions make the Po Valley in Northern Italy one of Europe's most polluted regions. Understanding the processes controlling ozone production in this environment is essential for developing effective mitigation strategies. As both a source of HO2 radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. During the Pan-European Gas-AeroSOls Climate Interaction Study (PEGASOS), HCHO measurements were acquired via a Fiber Laser-Induced Fluorescence (FiLIF) instrument onboard a Zeppelin airship. This mission represents the first successful airborne deployment of the FiLIF instrument. With low flight speeds and vertical profiling capabilities, these Zeppelin-based observations in conjunction with other measurements may offer new insights into the spatial and temporal variability of atmospheric composition within the Po Valley region. Preliminary comparisons of modeled and measured HCHO concentrations at various altitudes and VOC/NOx regimes will be presented. Analysis will focus on 1) the transition from nocturnal to daytime boundary layers, and 2) the potential role of "non-classical" radical chemistry in ozone production.

Kaiser, J.; Wolfe, G. M.; Keutsch, F. N.

2012-12-01

261

New insights into adverse pressure gradient boundary layers

NASA Astrophysics Data System (ADS)

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.

George, William K.; Stanislas, Michel; Laval, Jean-Philippe

2010-11-01

262

Improving subtropical boundary layer cloudiness in the 2011 NCEP GFS

NASA Astrophysics Data System (ADS)

The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of shortwave cloud radiative forcing, and affect predicted sea-surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parametrisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.

Fletcher, J. K.; Bretherton, C. S.; Xiao, H.; Sun, R.; Han, J.

2014-04-01

263

Coupling of magnetopause-boundary layer to the polar ionosphere

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.

Wei, C.Q.; Lee, L.C. (Univ. of Alaska, Fairbanks (United States))

1993-04-01

264

A Sensitivity Theory for the Equilibrium Boundary Layer Over Land

NASA Astrophysics Data System (ADS)

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.

Cronin, T.

2013-12-01

265

DNS of Hypersonic Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

We present a direct numerical simulation database of supersonic and hypersonic turbulent boundary layers. The systematic procedure for initializing the turbulent flow fields at controlled Mach number and Reynolds number conditions is described. It is shown that simulation transients are less than 10% of the time required for gathering statistical data of the turbulent flows. The experimental conditions of Debiève ( Debieve, Gouin, and Gaviglio, Proceedings ICHMT/IUTAM Symposium on the Structure of Turbulence and Heat and Mass Transfer, Dubrovnik, 1981. ) ( Debieve, Thèse Université d'Aix Marseille II, 1983, Marseille, France. ) and Elena ( Eléna, Lacharme, and Gaviglio, In: Dybb, A. & Pfund, P.A. (eds), International Symposium on Laser Anemometry. ASME, 1985.) ( Eléna and Lacharme, ) are simulated and the simulation and experimental data are in excellent agreement. Using the direct numerical simulation database we perform parametric studies varying freestream Mach number in the range of 3 to 8 and wall-temperature condition for wall-to-freestream-temperature ratio of 2 to 5.5.

Pino Martin, M.

2004-11-01

266

Non-equilibrium Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

Clauser (1954) in his now classical paper on pressure gradients concluded that equilibrium flows are very special flows difficult to achieve experimentally and that few flows were in equilibrium. However, using a similarity analysis of the Navier-Stokes equations Castillo and George(Castillo, L. and George, W.K.,``Similarity Analysis for Turbulent Boundary Layer with Pressure Gradient: out flow,'' AIAA Journal, Vol.39,2001) concluded that an equilibrium flow is one where the pressure parameter, ? =frac? ? U_? ^2d? /dxfracdP_? dx, is a constant. They further concluded that most flows are in equilibrium and the exception are non-equilibrium flows; those where the ? neq constant. Using the equations of motion and similarity analysis, it will be shown that even non-equilibrium flows-mainly those over airfoils or with sudden changes on external pressure gradient, and separated flows-are in an equilibrium state but locally. Moreover, in the case of airfoils where the external pressure gradient changes from favorable to zero pressure gradient and to adverse pressure gradient, three distinctive regions are identified each given by a constant value of ?. The most interesting result is that there seems to be a universal value for the pressure parameter, ? ~= 0.22, for all adverse pressure gradients including relaxed flows and separated flows.

Castillo, Luciano; Wang, Xia

2001-11-01

267

Effect of sound on boundary layer stability

NASA Technical Reports Server (NTRS)

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.

Saric, William S.; Spencer, Shelly Anne

1993-01-01

268

Effect of sound on boundary layer stability

NASA Technical Reports Server (NTRS)

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.

Saric, William S. (Principal Investigator); Spencer, Shelly Anne

1993-01-01

269

Numerical experiments on dense water descending with bottom boundary layer model in high latitude

NASA Astrophysics Data System (ADS)

Importance of dense water formation in the Arctic shelf and slope has been suggested from observations in the Arctic coastal region, and several numerical experiments also showed dense water formation in the Arctic coast. The dense water is believed as one of the source of cold halocline, and is thought to transported from coastal region toward basin through mainly bottom boundary layer. Bottom boundary plays an important role in ocean circulation. Bottom boundary layer transports dense water to one's neutral depth on formation process of intermediate and deep water. Fine grid interval is needed to simulate bottom boundary layer, but now computational resources are not sufficient to simulate bottom boundary layer exactly, especially in global ocean circulation experiment with coarse grid. Several bottom boundary layer models therefore have been developed. But transport by bottom boundary layer is not simulated well as observed, and tends to underestimate the transport. It is important to improve bottom boundary layer model with coarse grid. So we carry out sensitivity experiments with bottom boundary layer model on its parameterization, especially on bottom friction and height of bottom boundary layer. We carry out numerical experiments of descending of dense water with and without bottom boundary layer. The primitive equation model with z-coordinate (MOM) is used for rectangular idealized model ocean. The model ocean assumes the shelf region in the Arctic Ocean, with zonal lateral boundary condition being cyclic. Bottom is inclined meridionally as southern boundary has 100 meters depth, and northern boundary depth has 470 meters depth. As forcing, surface salt flux is added from southern boundary to y=30 km. The forcing assumes brine rejection in coastal polynya in the Arctic. The flux gradually decreases from y =30 km, and becomes zero at 50 km, and is homogeneous zonally. Only salt flux is used, and surface wind and heat flux are not used. Bottom boundary layer following Gnanadesikan's model is used. The layer depth is constant. Numerical experiments with coarse grid are carried out to simulate descending of the dense water. The surface salt flux makes surface water denser at southern boundary. The water descends to bottom, and starts to flow along bottom slope. In case of experiments without bottom boundary layer model, dense water flows almost along coast. On the other hand, in case of experiments with bottom boundary layer model, dense water start to descends toward ocean basin. Even in case of experiments with coarse grid, dense water descending is reproduced. These transport are compared with results of fine grid experiments.

Takahashi, J.; Wang, J.; Ikeda, M.

2002-12-01

270

NASA Astrophysics Data System (ADS)

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.

Dekker, H.; de Leeuw, G.; van den Brink, A. Maassen

271

Advanced boundary layer transition measurement methods for flight applications

NASA Technical Reports Server (NTRS)

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.

Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.

1986-01-01

272

Boundary Layer Transition in the NTF: HSR Experience and Plans

NASA Technical Reports Server (NTRS)

Efforts towards understanding boundary layer transition characteristics on a High Speed Civil Transport (HSCT)-class configuration in the National Transonic Facility (NTF) are ongoing. The majority of the High Speed Research (HSR) data base in the NTF has free transition on the wing, even at low Reynolds numbers (Rn) attainable in conventional facilities. Limited data has been obtained and is described herein showing the effects of a conventional, Braslow method based wing boundary-layer trip on drag. Comparisons are made using force data polars and surface flow visualization at selected angles-of-attack and Mach number. Minimum drag data obtained in this study suggest that boundary layer transition occurred very near the wing leading edge by a chord Rn of 30 million. Sublimating chemicals were used in the air mode of operation only at low Rn and low angles-of-attack with no flap deflections; sublimation results suggest that the forebody and outboard wing panel are the only regions with significant laminar flow. The process and issues related to the sublimating chemical technique as applied in the NTF are discussed. Beyond the existing experience, status of efforts to develop a production transition detection system applicable to both air and cryogenic nitrogen environments is presented.

Owens, Lewis R., Jr.; Wahls, Richard A.; Hamner, Marvine P.

1999-01-01

273

Study of the morning transition of the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

In this work it will be analyzed the main physical processes related to the transition of the Atmospheric Boundary Layer (ABL) that takes place from the last hours of the night until the first hours of the morning. In order to achieve that, it will be used data from field campaigns which took place in the Research Centre for the Lower Atmosphere (CIBA), especially those gathered in the campaign carried out in June, 2008 where information was obtained from a 10m height mast provided with temperature, wind speed and direction, and moisture sensors at several levels. Also a sonic anemometer (20 Hz sampling rate) at 10m was available. The database is complemented by a triangle of microbarometers installed next to the surface, and another two microbarometers placed in a 100m meteorological tower at 50 and 100m respectively. A GRIMM particle monitor (MODEL 365), which can be used to continuously measure each six seconds simultaneously the PM10, PM2.5 and PM1 values, was also available to evaluate the degree of mixing taking place near the surface. The thermodynamic characteristics of the first hundreds of meters remain registered from information obtained with a tethered balloon and with a RASS-SODAR. The main turbulent and stability parameters, as well as coherent structures present in the Nocturnal Boundary Layer are studied in connection to their influence in the developing of the next Convective Boundary Layer.

Sastre, M.; Yagüe, C.; Maqueda, G.; Viana, S.

2009-04-01

274

Boundary layer control by means of wall parallel Lorentz forces

NASA Astrophysics Data System (ADS)

Lorentz forces can be used to control the near wall flow of low conducting liquids like sea-water. To achieve force densities strong enough to modify the flow, both magnetic and electric fields have to be applied to the fluid. Here, wall parallel Lorentz forces in the streamwise direction were used to influence the velocity profile of a flat plate boundary layer as well as the flow around a symmetric hydrofoil. Velocity measurements inside the boundary layer and direct force measurements are given for the flat plate. At moderate force strength, the mean velocity profile is characterized by a momentum thickness smaller than in the unforced case, whereas at high enough Hartmann numbers a wall jet develops. Additionally, a turbulent, but approximately non-growing boundary layer has been observed. The effect of a suction-side, streamwise Lorentz force on a NACA-0017-like hydrofoil is quantified by means of force balance measurements. Depending on the angle of attack, two different effects are observed. (1) At small angles of incidence, a moderate increase in lift due to additional circulation is observed. Simultaneously, a decrease in drag of the hydrofoil is caused by the momentum added. (2) At higher angles of attack, where the unforced hydrofoil would normally stall, a more pronounced lift increase and a corresponding drag reduction are observed due to separation prevention. Figs 8, Refs 15.

Weier, T.; Fey, U.; Gerbeth, G.; Mutschke, G.; Lielausis, O.; Platacis, E.

2001-06-01

275

Boundary-layer equations in generalized curvilinear coordinates

NASA Technical Reports Server (NTRS)

A set of higher-order boundary-layer equations is derived valid for three-dimensional compressible flows. The equations are written in a generalized curvilinear coordinate system, in which the surface coordinates are nonorthogonal; the third axis is restricted to be normal to the surface. Also, higher-order viscous terms which are retained depend on the surface curvature of the body. Thus, the equations are suitable for the calculation of the boundary layer about arbitrary vehicles. As a starting point, the Navier-Stokes equations are derived in a tensorian notation. Then by means of an order-of-magnitude analysis, the boundary-layer equations are developed. To provide an interface between the analytical partial differentiation notation and the compact tensor notation, a brief review of the most essential theorems of the tensor analysis related to the equations of the fluid dynamics is given. Many useful quantities, such as the contravariant and the covariant metrics and the physical velocity components, are written in both notations.

Panaras, Argyris G.

1987-01-01

276

Improved Inlet Noise Attenuation by Alteration of Boundary Layer Profiles

NASA Technical Reports Server (NTRS)

Acoustic liners are an essential component of technology used to reduce aircraft engine noise. Flow affects attenuation due to the liner in several ways, one of which is that boundary layers adjacent to the liner refract the sound. In the case of inlet noise, the boundary layer causes sound to be refracted away from the liner, thus degrading attenuation. A concept to improve attenuation by the liner by alteration of inlet boundary layer profiles is presented. The alteration of profiles is achieved by inlet blowing. Computational fluid dynamics and duct mode propagation theory for ducts carrying a parallel sheared flow have been used to design experiments to explore such a possibility in the NASA Langley Research Center Grazing Incidence Tube using an inlet blowing scheme developed at General Electric Global Research. The effects of inlet blowing on two liner configurations were evaluated. Calculated results will be shown for blowing ratios (injected flow/duct flow) of approximately 12% and frequencies up to 3 kHz. These results emphasize changes of attenuation achieved by blowing for the two liners. Experimental results of measured flow profiles (with and without blowing) in the Grazing Incidence Tube, and of corresponding changes in attenuation by the liner due to blowing will be presented.

Mani, Ramani; Luedke, Jon; Jones, Michael G.; Nark, Douglas M.

2004-01-01

277

Growth behavior of the marine submicron boundary layer aerosol

NASA Astrophysics Data System (ADS)

A box model for investigating the chemistry and growth of submicron particles in the marine boundary layer was developed. Processes simulated by the model were gas phase chemistry, in-cloud sulfate production, gas-to-particle transfer of condensable vapors, coagulation, dry deposition of particles and gases, and entrainment between the boundary layer and the free troposphere. According to model simulations, the most influential factor for the growth of nuclei and Aitken mode particles is the production rate of methane sulfonic acid (MSA) and other low-volatility compounds in the gas phase. Processes controlling SO2 concentrations dictate the amount of non-sea-salt sulfate produced in the boundary layer but are less important for particle growth. The ratio of MSA to non-sea-salt sulfate in the particulate phase may vary largely, even when a constant MSA yield from dimethylsulfide (DMS) oxidation is assumed. Clouds decrease nuclei lifetime but do not affect their growth significantly, unless the time between two cloud passages is very short. Sources other than DMS may produce condensable vapors that assist particle growth to some extent. With our current knowledge of the concentrations of condensible matter in the marine boundary layer, however, it seems unlikely that small nuclei are able to grow into cloud condensation nuclei size over their lifetime. More information is needed on heterogeneous surface reactions that may occur between submicron particles and vapors such as SO2, as well as on potential transport limitations between condensable vapors and particles caused by thermodynamics or organic surfactants.

Kerminen, Veli-Matti; Wexler, Anthony S.

1997-08-01

278

Acoustic emissions from unsteady transitional boundary layer flow structures

NASA Astrophysics Data System (ADS)

The acoustic radiation contribution of boundary layer flow structures has long been the subject of debate. The research described critically examines the popular approaches to modeling the radiation mechanisms and attempts to bring some degree of closure to the physical and practical significance of noise and pseudo-noise originating in the laminar-to-turbulent transition zone within a natural boundary layer. This includes improving models to include recent computational and experimental statistics, evaluation of model sensitivities to input parameters, and applicability to situations of engineering relevance. Prior efforts to model wall pressure fluctuation statistics resulting from boundary layer transition zone flow structures allow further development of direct radiation prediction codes. Several refinements were made to theoretical models for directly radiated noise based upon the Liepmann analogy for fluctuating displacement thickness including the incorporation of a semi- empirically derived space-time correlation function for the intermittency indicator. A similar two-fluids model uses a Lighthill acoustic analogy. Radiation by vortex structures and direct numerical simulation methods are reviewed to help define their useful role in predicting sound radiation from transition. The role of pressure gradient in axisymmetric body flows, flat plate flows, and over hydrofoils is investigated. A quiet airflow facility was developed to measure the direct acoustic radiation from a naturally transitioning boundary layer. Real-time acoustic intensity measurement instrumentation was developed if measurements of isolated spots in otherwise laminar flow had been necessary. This technique uses a hot film signal from the transition structure to obtain the coherent output intensity (COI). Model predictions are compared to the measured acoustic radiation from a naturally transitioning boundary layer. Radiated noise measurements isolating the direct transition zone radiation demonstrated similar dependence with axial location within the transition zone as previous wall pressure measurements. The measurements suggest that radiation from transition flow structures is multipolar and has low radiation efficiency. Transition noise per unit area is greater than TBL noise per unit area. Thus, the contribution to overall directly radiated flow noise from the transition zone in typical engineering applications is negligible compared to the radiation from the much larger area of fully turbulent flow.

Marboe, Richard Chostner

279

Some characteristics of turbulent boundary layers in rapidly accelerated flows

NASA Technical Reports Server (NTRS)

An analysis of time-mean-turbulent boundary layer velocity profiles measured in a rapidly accelerating flow suggests that the outer region of the velocity profiles consists of essentially inviscid, rotational flow. The extent of this inviscid outer region was observed in some cases to exceed 90 percent of what is ordinarily thought of as the turbulent boundary layer thickness. On the other hand, the inner frictional region of these velocity profiles appears to have turbulent characteristics similar to those of more conventional turbulent boundary layers. Hence, the outer edge boundary condition for this inner region is more properly the external rotational flow region than the free stream.

Brinich, P. F.; Neumann, H. E.

1971-01-01

280

Vertical Transport of Water in the Martian Boundary Layer.

National Technical Information Service (NTIS)

We are continuing our examination of the transport of H2O through the martian boundary layer, and we have written a one-dimensional numerical model of the exchange of H2O between the atmosphere and subsurface of Mars through the planetary boundary layer (...

A. P. Zent R. M. Haberle H. C. Houben

1993-01-01

281

Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration

The influence of concentration polarization on the permeate flux in the ultrafiltration of aqueous Dextran T70 solutions can be described by (i) the osmotic pressure model and (ii) the boundary layer resistance model. In the latter model the hydrodynamic resistance of the non-gelled boundary layer is computed using permeability data of the Dextran molecules obtained by sedimentation experiments. It is

J. G. Wijmans; S. Nakao; Berg van den J. W. A; F. R. Troelstra; C. A. Smolders

1985-01-01

282

Boundary Layer Integral Matrix Procedure: Verification of Models.

National Technical Information Service (NTIS)

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 e...

W. S. Bonnett R. M. Evans

1977-01-01

283

Numerical simulation of shock wave-turbulent boundary layer interaction

Numerical solutions of the Navier-Stokes equations are presented for the interactions of a shock wave and a turbulent boundary layer. The turbulent closure is provided by a relaxation eddy viscosity model which approximates the response of turbulence to a severe pressure gradient. The eddy viscosity model is verified by investigating shock impingement on a turbulent boundary layer. Computations were performed

J. S. Shang; W. L. Hankey Jr.; C. H. Law

1976-01-01

284

The Application of Optimal Control to Boundary Layer Flow

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

D. Henningson; A. Hanifi

285

Microbubble Drag Reduction in Liquid Turbulent Boundary Layers

The interactions between a dense cloud of small bubbles and a liquid turbulent boundary layer are reviewed on the basis of available experimental observations to understand and quantify their capability for reducing skin friction. Gas bubbles are generally introduced into the boundary layer by injection through a porous surface or by electrolysis. After injection, the bubbles stay near the wall

Charles L. Merkle; Steven Deutsch

1992-01-01

286

MHD boundary-layer flow of an upper-convected Maxwell fluid in a porous channel

Two-dimensional magnetohydrodynamic (MHD) boundary layer flow of an upper-convected Maxwell fluid is investigated in a channel. The walls of the channel are taken as porous. Using the similarity transformations and boundary layer approximations, the nonlinear partial differential equations are reduced to an ordinary differential equation. The developed nonlinear equation is solved analytically using the homotopy analysis method. An expression for

Z. Abbas; M. Sajid; T. Hayat

2006-01-01

287

DNS of a shock wave turbulent boundary layer interaction at M=2.25

The flow field associated to the impingment of an oblique shock wave on a supersonic turbulent boundary layer developing on a flat plate at Mach 2.25 is analyzed by means of a full direct numerical simulation. For the selected test conditions significant separation of the turbulent boundary layer occurs, and the flow exhibits large scale unsteadiness. The numerical procedure used

Sergio Pirozzoli; Francesco Grasso; Thomas B. Gatski

2004-01-01

288

A class of unsteady, three-dimensional flow structures in turbulent boundary layers

NASA Technical Reports Server (NTRS)

A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary layer.

Ash, R. L.

1981-01-01

289

NASA Technical Reports Server (NTRS)

The focus was on developing means of controlling and reducing unsteady pressure loads in separated shock wave turbulent boundary layer interactions. Section 1 describes how vortex generators can be used to effectively reduce loads in compression ramp interaction, while Section 2 focuses on the effects of 'boundary-layer separators' on the same interaction.

Dolling, David S.; Barter, John W.

1995-01-01

290

On optical imaging through aircraft turbulent boundary layers

NASA Technical Reports Server (NTRS)

Optical resolution quality as affected by aircraft turbulent boundary layers is analyzed. Wind-tunnel data was analyzed to obtained the variation of boundary layer turbulence scale length and mass density rms fluctuations with Mach number. The data gave good agreement with a mass density fluctuation turbulence spectrum that is either isotropic of orthogonally anisotropic. The data did not match an isotropic turbulence velocity spectrum which causes an anisotropic non-orthogonal mass density fluctuation spectrum. The results indicate that the average mass density rms fluctuation is about 10% of the maximum mass density across the boundary layer and that the transverse turbulence scale size is about 10% of the boundary layer thickness. The results indicate that the effect of the turbulent boundary layer is large angle scattering which decreases contrast but not resolution. Using extinction as a criteria the range of acceptable aircraft operating conditions are given.

Sutton, G. W.

1980-01-01

291

Dusty boundary layer in a surface-burst explosion

Dusty boundary layers are an inherent feature of explosions over ground surfaces. Detailed knowledge of dusty boundary layer characteristics is needed in explosion safety analysis (e.g., to calculate the drag loads on structures). Also, to predicct the amount of dust in the rising fireball of an explsion, one must know the dusty boundary layer swept up during the positive and negative phases of the blast wave and how much of this boundary layer dust is entrained into the stem of the dust cloud. This paper describes the results of numerical simulations of the dusty boundary layer created by a surface burst explosion. The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws.

Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States); Ferguson, R.E.; Chien, K.Y.; Collins, J.P. [Naval Surface Warfare Center, Silver Spring, MD (United States)

1993-08-01

292

On optical imaging through aircraft turbulent boundary layers

NASA Astrophysics Data System (ADS)

Optical resolution quality as affected by aircraft turbulent boundary layers is analyzed. Wind-tunnel data was analyzed to obtained the variation of boundary layer turbulence scale length and mass density rms fluctuations with Mach number. The data gave good agreement with a mass density fluctuation turbulence spectrum that is either isotropic of orthogonally anisotropic. The data did not match an isotropic turbulence velocity spectrum which causes an anisotropic non-orthogonal mass density fluctuation spectrum. The results indicate that the average mass density rms fluctuation is about 10% of the maximum mass density across the boundary layer and that the transverse turbulence scale size is about 10% of the boundary layer thickness. The results indicate that the effect of the turbulent boundary layer is large angle scattering which decreases contrast but not resolution. Using extinction as a criteria the range of acceptable aircraft operating conditions are given.

Sutton, G. W.

1980-04-01

293

Dynamic behavior of an unsteady trubulent boundary layer

NASA Technical Reports Server (NTRS)

Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.

Parikh, P. G.; Reynolds, W. C.; Jayaramen, R.; Carr, L. W.

1981-01-01

294

Perturbing Spanwise Modes in Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

The objective of the current study was to manipulate the coherent vortex packets in a turbulent boundary layer at Re ?=2480 by inserting a small scale cylinder array and to improve the understanding of the downstream flow stability issues. The height of the cylinders was H/?=0.2 (H+=500) with aspect ratio (AR=cylinder height/base diameter) of 4, and three cases were studied using single array of 0.2?, 0.4? and 0.6? spaced cylinders. Both fixed location data and flying data were acquired at z+=296 using PIV, and the spanwise scales of the packets and the wake-packet interactions downstream of the cylinder array were also discussed. The non-perturbed flow was studied first and the dominant spanwise scale of the vortex packets was found to be ˜0.6?. From the flying data, the organization of vortex packets was found to persist over a streamwise distance of ˜8?. The averaged results of the perturbed cases showed a spanwise variation of the streamwise velocity downstream of the cylinder array, and the spanwise scales of the low speed regions were most stable for the 0.6? spacing case. Also, distinct downwash behavior was observed directly behind each cylinder. The flying data showed frequent spanwise interactions of cylinder wakes in the 0.2? case and the downstream structures were affected greatly by the incoming flow condition. The 0.4? and 0.6? cases were discussed based on the relative spanwise location of the upstream vortex packets and the cylinders and it was concluded that the organization of flow structures was most stable when the perturbation scale was the same as the dominant spanwise mode of the non-perturbed flow.

Zheng, Shaokai

295

Boundary Layer Control of Rotating Convection Systems

NASA Astrophysics Data System (ADS)

Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6? E ? ?; and Prandtl number, 1? Pr ? 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

2008-12-01

296

End-wall boundary layer prediction for axial compressors

NASA Technical Reports Server (NTRS)

An integral boundary layer procedure was developed for the computation of viscous and secondary flows along the annulus walls of an axial compressor. The procedure is an outgrowth and extension of the pitch-averaged methods of Mellor and Horlock. In the present work secondary flow theory is used to develop approximations for the velocity profiles inside a rotating blade row and for the blade force deficit terms in the momentum integral equations. The computer code based on this procedure was iteratively coupled to a quasi-one-dimensional model for the external inviscid flow. Computed results are compared with measurements in a compressor cascade.

Sockol, P. M.

1978-01-01

297

Mixing dynamics within a turbid bottom boundary layer

NASA Astrophysics Data System (ADS)

Mixing dynamics within a turbid bottom boundary layer in a littoral zone of the Mediterranean Sea is analyzed. Data were taken in June 2004 with a free falling microstructure profiler. Mesoscale dynamics in the region was influenced by the outflow of the Ebre River and by the southwestern Catalan Current originating in the Gulf of Genoa. The magnitude of the near bottom current was 5-8 cm/s and the flow was affected by inertial oscillations. During the entire field campaign, the wind of ~ 6 m/s was from the northeast. The mean depth of the upper mixed layer was about 15 m, the thermocline occupied the depth range between 15 and 30 m, and the thickness of the turbid bottom boundary layer varied from 8 to 12 m. Different stations ranged from 15 to 60 m depth. Thorpe displacement, Th, was used to determine the turbulent patches and, in general, Thmax within the patches and the Thorpe scale, LTh, were found to be highly correlated and linearly dependent: Tmax= 2.6LTh. If Thmax and LTh were calculated at equidistant segments of the profiles, then Thmax ~ LTh0.85. Within the bottom layer turbulent patches were found to affect 35% of the total depth of the layer. The median size of the patches was 41 cm and their median buoyancy Reynolds number was 252. State of the turbulence within the bottom layer is discussed based on the turbulent Reynolds and the turbulent Froude numbers. According to the hydrodynamic diagram and the vertical profiles of the turbulent kinetic energy dissipation rate, different zones are identified, including an upper interface where Kelvin-Helmholtz instability develop. The different station-dependent structure of the turbidity profiles is related to the different mixing dynamics. Mean turbulent diffusivity of the turbid layer was obtained following the Osborn approach and found to be 2 x 10-5 m2/s.

Bastida, I.; Planella, J.; Roget, E.

2009-04-01

298

NASA Technical Reports Server (NTRS)

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.

Spina, Eric F.

1995-01-01

299

NASA Astrophysics Data System (ADS)

We have developed instrumentation packages for unmanned aerial vehicles (UAVs) to measure ocean surface processes along with momentum fluxes and latent, sensible, and radiative heat fluxes in the marine atmospheric boundary layer (MABL). The packages have been flown over land on BAE Manta C1s and over water on Boeing-Insitu ScanEagles. The low altitude required for accurate surface flux measurements (< 30 m) is below the typical safety limit of manned research aircraft; however, with advances in laser altimeters, small-aircraft flight control, and real-time kinematic differential GPS, low-altitude flight is now within the capability of small UAV platforms. Fast-response turbulence, hygrometer, and temperature probes permit turbulent flux measurements, and short- and long-wave radiometers allow the determination of net radiation, surface temperature, and albedo. Onboard laser altimetry and high-resolution visible and infrared video permit observations of surface waves and fine-scale (O(10) cm) ocean surface temperature structure. Flight tests of payloads aboard ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center Dahlgren Division (Dahlgren, VA), where measurements of water vapor, heat, and momentum fluxes were made from low-altitude (31-m) UAV flights over water (Potomac River). ScanEagles are capable of ship-based launch and recovery, which can extend the reach of research vessels and enable scientific measurements out to ranges of O(10-100) km and altitudes up to 5 km. UAV-based atmospheric and surface observations can complement observations of surface and subsurface phenomena made from a research vessel and avoid the well-known problems of vessel interference in MABL measurements. We present a description of the instrumentation, summarize results from flight tests, and discuss potential applications of these UAVs for ship-based MABL studies.

Reineman, B. D.; Lenain, L.; Statom, N.; Melville, W. K.

2012-12-01

300

Mean velocity and turbulence measurements in a 90 deg curved duct with thin inlet boundary layer

NASA Technical Reports Server (NTRS)

The experimental database established by this investigation of the flow in a large rectangular turning duct is of benchmark quality. The experimental Reynolds numbers, Deans numbers and boundary layer characteristics are significantly different from previous benchmark curved-duct experimental parameters. This investigation extends the experimental database to higher Reynolds number and thinner entrance boundary layers. The 5% to 10% thick boundary layers, based on duct half-width, results in a large region of near-potential flow in the duct core surrounded by developing boundary layers with large crossflows. The turbulent entrance boundary layer case at R sub ed = 328,000 provides an incompressible flowfield which approaches real turbine blade cascade characteristics. The results of this investigation provide a challenging benchmark database for computational fluid dynamics code development.

Crawford, R. A.; Peters, C. E.; Steinhoff, J.; Hornkohl, J. O.; Nourinejad, J.; Ramachandran, K.

1985-01-01

301

On the stability of the decelerating laminar boundary layer

NASA Technical Reports Server (NTRS)

The stability of a decelerating boundary-layer flow is investigated experimentally and numerically. Experimentally, a flat plate having a Blasius boundary layer is decelerated in an 18 m towing tank. The boundary layer becomes unstable to two-dimensional waves, which break down into three-dimensional patterns, hairpin vortices, and finally turbulent bursts when the vortices lift off the wall. The unsteady boundary-layer equations are solved numerically to generate instantaneous velocity profiles for a range of boundary and initial conditions. A quasi-steady approximation is invoked and the stability of local velocity profiles is determined by solving the Orr-Sommerfeld equation using Chebyshev matrix methods. Comparisons are made between the numerical predictions and the experimentally observed instabilities.

Gad-El-hak, M.; Mcmurray, J. T.; Davis, S. H.; Orszag, S. A.

1984-01-01

302

Cloud-Scale Numerical Modeling of the Arctic Boundary Layer

NASA Technical Reports Server (NTRS)

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.

Kruegen, Steven K.; Delnore, Victor E. (Technical Monitor)

2002-01-01

303

Hypersonic boundary layer receptivity to acoustic disturbances over cones

NASA Astrophysics Data System (ADS)

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 to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8x106/ft. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations in two-dimensional and axisymmetric coordinates. Computations are performed in three steps. After the steady mean flow field is computed, linear stability analysis is performed to find the most amplified frequency and the unstable disturbance modes in different flow regions. Then time accurate computations are performed using slow and fast mode acoustic disturbances, and the initial generation, interaction and evolution of instability waves inside the boundary layers are studied. Receptivity computations showed that the acoustic disturbance waves propagated uniformly to downstream, interact with the bow shock, enter the boundary layer, and then generate the initial amplitude of the instability waves in the leading edge region. Effects of the entropy layer due to nose bluntness to the receptivity process are studied. It is found that transition location moves downstream and is delayed by increasing bluntness, and the role of the entropy layer in this process is revealed. Also, the effects of wall cooling to the receptivity process using slow and fast mode acoustic disturbances are studied. The effects of cooling on the first and second mode regions are investigated. It is found that the first mode is stabilized and the second mode is destabilized by wall cooling when the flow is forced by acoustic waves in the slow mode.

Kara, Kursat

304

Spatial Linear Instability of Confluent Wake/Boundary Layers

NASA Technical Reports Server (NTRS)

The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the confluent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identified. The boundary layer mode is found amplified as the wake approaches the wall. On the other hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.

Liou, William W.; Liu, Feng-Jun; Rumsey, C. L. (Technical Monitor)

2001-01-01

305

A Boundary Layer Interacting with a Point Vortex

NASA Astrophysics Data System (ADS)

A model of the interaction of a boundary layer with a point vortex is presented. By varying the vortex strength and distance from the wall, a wide range of phenomena--localized disturbances, wave trains, entrainment of irrotational fluid, ejection of vortical fluid--is seen, which mimic the diversity of behavior found in actual boundary layers. The model equations, which are two-dimensional and inviscid, are expected to be valid at large Reynolds number. Both the evolution of the boundary layer and the trajectory of the vortex, which may be above or within the boundary layer, are determined. Analytical results are obtained where possible; otherwise, contour dynamics is used. It is found that when the vortex is within the boundary layer, a resonance condition yields a lengthening interval of growing waves. For a vortex extremely close to the wall, the disturbance amplitude is independent of the vortex strength. When the vortex is above the boundary layer, it may produce a second vortex-like structure within the boundary layer undercut by a narrow crevice of entrained irrotational fluid. Under other conditions, a spire of irrotational fluid is ejected.

Lichter, Seth

1997-11-01

306

Titan's planetary boundary layer structure at the Huygens landing site

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

Tetsuya Tokano; Francesca Ferri; Giacomo Colombatti; Teemu Mäkinen; Marcello Fulchignoni

2006-01-01

307

Integral method for the calculation of three-dimensional, laminar and turbulent boundary layers

NASA Technical Reports Server (NTRS)

The method for turbulent flows is a further development of an existing method; profile families with two parameters and a lag entrainment method replace the simple entrainment method and power profiles with one parameter. The method for laminar flows is a new development. Moment of momentum equations were used for the solution of the problem, the profile families were derived from similar solutions of boundary layer equations. Laminar and turbulent flows at the wings were calculated. The influence of wing tapering on the boundary layer development was shown. The turbulent boundary layer for a revolution ellipsoid is calculated for 0 deg and 10 deg incidence angles.

Stock, H. W.

1978-01-01

308

Boundary Layer Control by Means of Plasma Actuators

The development of controlled transition in a flat-plate boundary layer is investigated using Large Eddy Simulations (LES) with the dynamic Smagorinsky model. The analysis of flow control with the objective to optimize the effects of Tollmien-Schlichting waves on a flat plate by means of plasma actuators was studied. The plasma effect is modeled as a body force in the momentum equations. These equations are solved in a uniform grid using a 2nd-order finite difference scheme in time and space. The response of plasma actuators operating in different time-dependent conditions, produced by transient or periodic inputs at different frequencies, is also analyzed.

Quadros, R. [UFRGS/PPGMAp-TUD-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany); Bortoli, A. L. de [UFRGS/DMPA-Departamento de Matematica Pura e Aplicada, Bento Goncalves 9500, Agronomia-P.O. Box 15080, Porto Alegre-RS (Brazil); Tropea, C. [TUD/SLA-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany)

2007-09-06

309

Effects of Boundary Layer on Supersonic Panel Flutter

NASA Astrophysics Data System (ADS)

A fluid-structure coupled computation code has been developed and applied to a panel flutter problem. The flutter velocities and the amplitudes of limit cycle oscillations obtained using the present method agree well with those of Dowell. It is found that the boundary layer over the panel can suppress flutter particularly in the Mach number region between 1.2 and 1.35, the effect of which increases with viscosity. In a 3D problem, good agreement was obtained between computation and experiment.

Hashimoto, Atsushi; Yagi, Naoto; Nakamura, Yoshiaki

310

Drag on intruders in granular beds: A boundary layer approach

NASA Astrophysics Data System (ADS)

We performed a parametric study of the drag on vertical intruders with uniform cross sections of different sizes and shapes, from which we developed a semiempirical model. Baffling techniques were used to isolate the contributions of the intruder's different subsurfaces, and we observed size effects and force focusing on edges. We propose a boundary layer approach, whereby the drag is the surface integral of an effective stress over a monolayer of particles contacting the intruder. The stress has a simple lithostatic dependence and is a function of the orientation relative to the intruder's direction of motion. This approach is experimentally verified and is consistent with the semiempirical model.

Goldsmith, Jonathan; Guo, Hong; Hunt, Shelby N.; Tao, Mingjiang; Koehler, Stephan

2013-09-01

311

NASA Technical Reports Server (NTRS)

The method presented is designed to improve the accuracy and computational efficiency of existing numerical methods for the solution of flows with compressible turbulent boundary layers. A compressible defect stream function formulation of the governing equations assuming an arbitrary turbulence model is derived. This formulation is advantageous because it has a constrained zero-order approximation with respect to the wall shear stress and the tangential momentum equation has a first integral. Previous problems with this type of formulation near the wall are eliminated by using empirically based analytic expressions to define the flow near the wall. The van Driest law of the wall for velocity and the modified Crocco temperature-velocity relationship are used. The associated compressible law of the wake is determined and it extends the valid range of the analytical expressions beyond the logarithmic region of the boundary layer. The need for an inner-region eddy viscosity model is completely avoided. The near-wall analytic expressions are patched to numerically computed outer region solutions at a point determined during the computation. A new boundary condition on the normal derivative of the tangential velocity at the surface is presented; this condition replaces the no-slip condition and enables numerical integration to the surface with a relatively coarse grid using only an outer region turbulence model. The method was evaluated for incompressible and compressible equilibrium flows and was implemented into an existing Navier-Stokes code using the assumption of local equilibrium flow with respect to the patching. The method has proven to be accurate and efficient.

Wahls, Richard A.

1990-01-01

312

A numerical investigation of supersonic nozzle boundary layer transition

NASA Technical Reports Server (NTRS)

The boundary layer stability within the high-area-ratio nozzle at NASA Lewis was tested at five chamber pressure conditions. For all nozzle conditions examined, Taylor-Goertler vortices grew more rapidly than Tollmien-Schlichting waves. The experimental heat flux was accurately predicted by a laminar boundary layer computation, thereby confirming the laminar nature of the nozzle boundary layer flow. When the chamber pressure was increased in a series of cases, the transition point occurred farther upstream. The number of vortices contained in the dominant instability increased with chamber pressure.

Pauley, Laura L.; Dagher, Samir N.

1991-01-01

313

Velocity profiles for turbulent boundary layers under freestream turbulence

NASA Astrophysics Data System (ADS)

Correlations for changes of skin friction coefficients and wake parameters, relative to the low freestream turbulence condition, are presented for the case of turbulent boundary layers under freestream turbulence with zero and adverse pressure gradients. The turbulent boundary layers were evaluated on a plate in a wind tunnel using a monoplane rod set turbulence generator; comparisons were also made using the data of several other investigators. The results, which define the velocity profiles within the boundary layers, were found to collapse for a large range of the pressure gradient parameter.

Hoffmann, J. A.; Mohammadi, K.

1991-09-01

314

Formation of pre-sheath boundary layers in electronegative plasmas

In electronegative plasmas Coulomb scattering between positive and negative ions can lead to the formation of a pre-sheath boundary layer containing the bulk of the negative ions. The negative ion boundary layer forms when momentum transfer from positive to negative ions dominates the negative ion acceleration from the electric field. This condition is met in Inductively Coupled Plasma reactors that operate at low pressure and high plasma density. Simulations of the GEC reactor for Chlorine and Oxygen chemistries using the INDUCT95 2D model are presented showing the pre-sheath boundary layer structure as a function of applied power and neutral pressure.

Vitello, P., LLNL

1998-05-01

315

Experimental investigation of streamwise vortices in turbulent boundary layer separation control

NASA Astrophysics Data System (ADS)

A separating Adverse Pressure Gradient (APG) turbulent boundary layer was effectively controlled by introducing streamwise vortices by means of Vortex Generators (VGs) in a wind-tunnel experiment. Velocity measurements were made using PIV in the region which was previously separated. VGs were employed at different streamwise positions, i.e. at different local boundary layer thicknesses and pressure gradients, upstream of the separation line. It is first concluded that the streamwise vortices are confined to the boundary layer and grow as the boundary layer develops downstream. Secondly, with a VG height on the order of the local boundary layer thickness, the mean velocity and turbulence profiles in the controlled region show very similar features independent on the VG streamwise position (as long as they are positioned sufficiently far upstream of the separation). Furthermore, these results hold also for a reduction of the VG height by 40vortices become smaller.

Angele, Kristian

2002-11-01

316

The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification of three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.

Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M., E-mail: rrr@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)

2013-06-10

317

Infrared Imaging of Boundary Layer Transition Flight Experiments

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

318

Large eddy simulation and study of the urban boundary layer

NASA Astrophysics Data System (ADS)

Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind velocity near the canopy is decreased, turbulence is intensified, TKE, variance, and momentum flux are increased, the momentum and heat flux at the top of the PBL are increased, and the development of the PBL is quickened; (3) the height of the roughness sublayer (RS) of the actual city buildings is the maximum building height (1.5 3 times the mean building height), and a constant flux layer (CFL) exists in the lower part of the UBL.

Miao, Shiguang; Jiang, Weimei

2004-08-01

319

Non-uniqueness in wakes and boundary layers

NASA Astrophysics Data System (ADS)

In streamlined flow past a flat plate aligned with a uniform stream, it is shown that (a) the Goldstein near-wake and (b) the Blasius boundary layer are nonunique solutions locally for the classical boundary layer equations, whereas (c) the Rott-Hakkinen (1965) very-near-wake appears to be unique. In each of (a) and (b) an alternative solution exists, which has reversed flow and which apparently cannot be discounted on immediate grounds. So, depending mainly on how the alternatives for (a), (b) develop downstream, the symmetric flow at high Reynolds numbers could have two, four or more steady forms. Concerning nonstreamlined flow, for example past a bluff obstacle, new similarity forms are described for the pressure-free viscous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include nonuniqueness, singularities and algebraic behavior, consistent with nonentraining shear layers with algebraic decay. Nonuniqueness also seems possible in reattachment onto a solid surface and for nonsymmetric or pressure-controlled flows including the wake of a symmetric cascade.

Smith, F. T.

1984-01-01

320

NASA Astrophysics Data System (ADS)

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

2014-05-01

321

Nonlinear spatial evolution of inviscid instabilities on hypersonic boundary layers

NASA Technical Reports Server (NTRS)

The spatial development of an initially linear vorticity-mode instability on a compressible flat-plate boundary layer is considered. The analysis is done in the framework of the hypersonic limit where the free-stream Mach number M approaches infinity. Nonlinearity is shown to become important locally, in a thin critical layer, when sigma, the deviation of the phase speed from unity, becomes o(M(exp -8/7)) and the magnitude of the pressure fluctuations becomes 0(sigma(exp 5/2)M(exp 2)). The unsteady flow outside the critical layer takes the form of a linear instability wave but with its amplitude completely determined by the nonlinear flow within the critical layer. The coupled set of equations which govern the critical-layer dynamics reflect a balance between spatial-evolution, (linear and nonlinear) convection and nonlinear vorticity-generation terms. The numerical solution to these equations shows that nonlinear effects produce a dramatic reduction in the instability-wave amplitude.

Wundrow, David W.

1996-01-01

322

An investigation of planetary convection: The role of boundary layers

NASA Astrophysics Data System (ADS)

Thermal and gravitational energy sources drive turbulent convection in Earth's vast liquid metal outer core. These fluid motions generate the electric currents that are believed to power Earth's magnetic field through a process known as dynamo action. Core flow is subject to the influence of Earth's rotation via the Coriolis force, which has an organizational effect on otherwise chaotic motions. Furthermore the magnetic field generated by convection acts back on the flow via Lorentz forces. Fluid motions in Earth's core, and the magnetic field generating regions of other planets and stars, are then governed by three main ingredients: convection, rotation, and magnetic fields. The goal of my Ph.D. research is to further our understanding of the systematic fluid dynamics occurring in dynamo systems. To accomplish this, I have developed a unique experimental device that allows me to produce fluid conditions approaching those expected in Earth's core and other planetary and stellar environments. The results presented here stem from a broad parameter survey of non-magnetic, rotating convection. In this study, I examine the interplay between rotation and convection by broadly varying the strength of each and measuring the efficiency of convective heat transfer. This parameter survey allows me to argue that the importance of rotation in convection dynamics is determined by boundary layer physics, where the Ekman (rotating) and thermal (non-rotating) boundary layers compete for control of convection dynamics. I develop a simple predictive scaling of this convective regime transition using theoretical boundary layer thickness scalings. This transition scaling permits a unified description of heat transfer in rotating convection, which reconciles contrasting results from previous studies. I also extend this experimental result to a broad array of numerical dynamo models, arguing that the boundary layer control of convective regimes is also evident in the dynamo models. A notable implication of this regime transition scaling is that it is much easier than previously thought for non-rotating style dynamics to occur in convection experiments and simulations, and perhaps also in planets and stars.

King, Eric M.

323

Boundary Layers in Strain-Gradient Theory of Linear Elasticity.

National Technical Information Service (NTIS)

In a previous investigation based on couple-stress theory the presence of an elastic boundary layer of minute thickness was established in which the states of stress and displacement differ essentially and significantly from classical elasticity solutions...

M. A. Sadowsky S. L. Pu

1970-01-01

324

Boundary Layer Integral Matrix Procedure Code Modifications and Verifications.

National Technical Information Service (NTIS)

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 applicati...

R. M. Evans H. L. Morse

1974-01-01

325

On Strong Slot Injection Into a Subsonic Laminar Boundary Layer.

National Technical Information Service (NTIS)

This paper is concerned with the problem of strong slot injection into a subsonic laminar boundary layer at asymptotically high Reynolds number. The problem is formulated and the governing equations are presented within the context of triple deck theory. ...

M. Napolitano R. E. Messick

1978-01-01

326

Asymptotic analysis: Working note (number sign)3, boundary layers.

National Technical Information Service (NTIS)

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 fu...

M. Garbey H. G. Kaper

1993-01-01

327

Boundary-layer transition effects on airplane stability and control

NASA Technical Reports Server (NTRS)

Surface contamination of laminar-flow airfoils can significantly modify the location of transition from laminar-to-turbulent boundary-layer flow. The contamination can be the result of insect debris, environmental effects such as ice crystals and moisture due to mist or rain, surface damage, or other contamination adhering to the surface. Location and mode of transition have a dominant effect on the lift-and-drag characteristics of a lifting surface. The influences of laminar boundary-layer flow behavior on airplane stability and control are examined through theoretical results and experimental (wind-tunnel and free-flight) data. For certain airfoils with a relatively steep pressure recovery it is shown that loss of laminar flow near the leading edge can result in premature separation of the turbulent boundary layer and, consequently, in loss of lift and control effectiveness. Aerodynamic modifications which minimize boundary-layer transition effects on airplane stability and control are also discussed.

Van Dam, C. P.; Holmes, B. J.

1986-01-01

328

Theoretical and Modeling Studies of the Marine Planetary Boundary Layer.

National Technical Information Service (NTIS)

We do not currently understand what determines the fractional cloudiness in partly cloudy boundary layers, how it is influenced by cloud-top entrainment instability, or what controls the transition from stratocumulus to cumulus conditions. These questions...

D. A. Randall

1991-01-01

329

On stability of free laminar boundary layer between parallel streams

NASA Technical Reports Server (NTRS)

An analysis and calculations on the stability of the free laminar boundary layer between parallel streams were made for an incompressible fluid using the Tollmien-Schlichting theory of small disturbances. Because the boundary conditions are at infinity, two solutions of the Orr-Sommerfeld stability equations need not be considered, and the remaining two solutions are exponential in character at the infinite boundaries. The calculations show that the flow is unstable except for very low Reynolds numbers.

Lessen, Martin

1950-01-01

330

Swirling Flow Problem in Boundary Layer Theory.

National Technical Information Service (NTIS)

The paper deals with the boundary value problem on t > or = 0 given by f triple primed + f(f double primed) + beta(g sup 2 - omega sup 2 - f primed sup 2) = 0, g double primed + f(g primed) - 2b(f primed)g = 0, f(0), f primed(0), g(0) given and f primed (...

P. Hartman

1971-01-01

331

Chebyshev solution of laminar boundary layer flow

An expansion procedure using the Chebyshev polynomials is proposed by using El-Gendi method [1], which yields more accurate results than those computed by P. M. Beckett [2] and A. R. Wadia and F. R. Payne [6] as indicated from solving the Falkner-Skan equation, which uses a boundary value technique. This method is accomplished by starting with Chebyshev approximation for the

H. Nasr; I. A. Hassanien; H. M. El-Hawary

1990-01-01

332

A Distributional Approach to the Boundary Layer Theory

We present a distributional approach for solving problems in the boundary layer and singular perturbation theories. We discuss the asymptotic expansions in the inner and outer regions and their matching in the overlapping domain by our theory. This technique is illustrated with various examples from the initial value and boundary value problems. From this discussion we find that the distributional

R. Estrada; R. P. Kanwal

1995-01-01

333

Calculation of turbulent boundary layer wall pressure spectra

This study is an investigation into the suitability of various wavevector-frequency models of turbulent boundary layer wall pressure fluctuations for the prediction of experimental measurements of turbulent boundary layer wall pressure spectra. Three separate models of the wavevector-frequency spectrum proposed by D. M. Chase in 1980 and 1987 are evaluated. The wavevector-frequency spectral models are integrated numerically using a formulation

D. E. Capone; G. C. Lauchle

1993-01-01

334

Tropical boundary layer equilibrium in the last ice age

NASA Technical Reports Server (NTRS)

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.

Betts, Alan K.; Ridgway, W.

1992-01-01

335

Approximation theory for boundary layer suction through individual slits

NASA Technical Reports Server (NTRS)

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.

Walz, A.

1979-01-01

336

Boundary Layers in Self-Gravitating, Collisional Rings

Recently, it has been proposed that boundary layers on the edges of planetary rings may play a key role in the behavior of the ring as a whole. In particular, Chiang and Goldreich (2002) proposed that that narrow eccentric rings have high-velocity-dispersion boundary layers that work against apse alignment. Self-gravity should be a key player in the formation of these

J. W. Weiss; G. R. Stewart

2003-01-01

337

A multidisciplinary optimization method for designing boundary layer ingesting inlets

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over-wing engines. Two types of engine installations have been considered for this aircraft. One installation is quite conventional with podded engines mounted on pylons. The other installation has partially buried engines with boundary layer ingesting inlets. Although ingesting the low-momentum flow in a boundary layer can improve propulsive efficiency, poor inlet

David Leonard Rodriguez

2001-01-01

338

Flow visualization of shock-boundary layer interaction

NASA Technical Reports Server (NTRS)

Two and three-dimensional shock-boundary layer interaction data were obtained from supersonic wind tunnel tests. These interactions are studied both with and without boundary layer bleed. The data verify computational fluid dynamic codes. Surface static pressure, pitot pressure, flow angularity, and bleed rates, are studied by flow visualization techniques. Surface oil flow using fluorescent dye and laser sheet using water droplets as the scattering material are used for flow visualization.

Hingst, W. R.; Jurkovich, M.

1982-01-01

339

Separating and turbulent boundary layer calculations using polynomial interpretation

NASA Technical Reports Server (NTRS)

Higher order numerical methods derived from polynomial spline interpolation or Hermitian differencing are applied to a separating laminar boundary layer, i.e., the Howarth problem, and the turbulent flat plate boundary layer flow. Preliminary results are presented. It is found that accuracy equal to that of conventional second order accurate finite difference methods is achieved with many fewer mesh points and with reduced computer storage and time requirements.

Rubin, S. G.; Rivera, S.

1977-01-01

340

Nonlinear disturbances in a hypersonic laminar boundary layer

NASA Technical Reports Server (NTRS)

Three separate but similar experiments on the growth of naturally-occurring instability waves in the laminar boundary-layers on sharp cones at hypersonic Mach numbers have been conducted. Each provided clear evidence that the theoretically-predicted second mode of instability was responsible for high-amplitude wave trains observed to prevail upstream of boundary-layer transition to turbulence. However, each also seemed to reveal the presence of an additional instability not accounted for by the linear theory. Here, examination is made of the tape-recorded hot-wire anemometer signals of one experiment on a sharp cone at Mach 8 for evidence of nonlinearity, the finding of which would explain the presence of the additional mode as a consequence of harmonic generation. Several approaches for identification of the residual effects of nonlinearity are described and utilized. Also, a simplified model describing certain fluctuation characteristics has been developed. Altogether, the evidence of nonlinear wave development is found to be strong. Quantitative comparisons of linear theory to experiments must be made with caution when nonlinearity is present in the experiment.

Kimmel, Roger L.; Kendall, James M.

1991-01-01

341

Unsteady separation in vortex-induced boundary layers.

This paper provides a brief review of the analytical and numerical developments related to unsteady boundary-layer separation, in particular as it relates to vortex-induced flows, leading up to our present understanding of this important feature in high-Reynolds-number, surface-bounded flows in the presence of an adverse pressure gradient. In large part, vortex-induced separation has been the catalyst for pulling together the theory, numerics and applications of unsteady separation. Particular attention is given to the role that Prof. Frank T. Smith, FRS, has played in these developments over the course of the past 35 years. The following points will be emphasized: (i) unsteady separation plays a pivotal role in a wide variety of high-Reynolds-number flows, (ii) asymptotic methods have been instrumental in elucidating the physics of both steady and unsteady separation, (iii) Frank T. Smith has served as a catalyst in the application of asymptotic methods to high-Reynolds-number flows, and (iv) there is still much work to do in articulating a complete theoretical understanding of unsteady boundary-layer separation. PMID:24936011

Cassel, K W; Conlisk, A T

2014-07-28

342

Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 µm when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness.

Ekberg, Peter; Su, Rong; Chang, Ernest W.; Yun, Seok Hyun; Mattsson, Lars

2014-01-01

343

Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 ?m when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness. PMID:24562018

Ekberg, Peter; Su, Rong; Chang, Ernest W; Yun, Seok Hyun; Mattsson, Lars

2014-02-01

344

Turbulent boundary layer in high rayleigh number convection in air.

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. PMID:24724653

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

345

Interaction of a Boundary Layer with a Turbulent Wake

NASA Technical Reports Server (NTRS)

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.

Piomelli, Ugo

2004-01-01

346

The perfectly matched layer (PML) boundary condition for the beam propagation method

The perfectly matched layer (PML) boundary condition for the Helmoltz equation is developed and applied to the finite-difference beam propagation method. Its effectiveness is verified by way of examples.

W. P. Huang; C. L. Xu; W. Lui; K. Yokoyama

1996-01-01

347

Flowfield Analysis for Successive Oblique Shock Wave Interactions with a Turbulent Boundary Layer.

National Technical Information Service (NTIS)

A computation procedure is described for predicting flow fields which develop when successive interactions between oblique shock waves and a turbulent boundary layer occur. Computations were carried out for axisymmetric internal flows at free stream Mach ...

C. Sun M. E. Childs

1973-01-01

348

Formulation of Subgrid Variability and Boundary-Layer Cloud Cover in Large-Scale Models.

National Technical Information Service (NTIS)

This report describes work on the Oregon State University (OSU) atmospheric boundary-layer (ABL) model. This model was developed to provide ABL and land-surface parameterization schemes for large-scale numerical weather prediction models. We address five ...

M. Ek L. Mahrt S. Chang G. Levy A. A. Holtslag

1999-01-01

349

Stability and Transition of Wall Boundary Layers Induced by Moving Waves.

National Technical Information Service (NTIS)

The present study concerns a theoretical investigation of stability and an experimental investigation of transition for wall boundary layers developed within unsteady plane expansion waves and behind shock waves traveling into a gas at rest. The theoretic...

J. G. Hall Y. M. Amr

1979-01-01

350

Stability Limits and Transition Times of Wave-Induced Wall Boundary Layers.

National Technical Information Service (NTIS)

The study concerns theoretical analysis of stability and experimental investigation of transition for laminar wall boundary layers developed within the plane expansion waves and behind shock waves traveling into gas at rest. The stability analyses involve...

Y. M. Amr J. G. Hall

1981-01-01

351

The Role of S-Shaped Crossflow Profiles in Three-Dimensional Boundary Layer Theory.

National Technical Information Service (NTIS)

A method is developed which allows the calculation of characteristic parameters (scale factor delta, main flow parameter m, crossflow parameter B) of three-dimensional turbulent boundary layers under the assumption of a third-degree polynomial for the tem...

E. A. Eichlbrenner J. L. Peube

1966-01-01

352

National Technical Information Service (NTIS)

An approximate analytical theory is developed for predicting nonsimilar laminar boundary layer flows with separation, reversed flow and reattachment including subsonic viscous-inviscid interation, with application to a separation bubble problem. The analy...

B. Dutt G. R. Inger

1973-01-01

353

Hypersonic Turbulent Wall Boundary Layer Computations.

National Technical Information Service (NTIS)

The Baldwin-Lomax algebraic turbulence model was modified for hypersonic flow conditions. Two coefficients in the outer layer eddy viscosity model were determined as functions of Mach number and temperature ratio. By matching the solutions from the Baldwi...

S. C. Kim G. J. Harloff

1988-01-01

354

Influences on the Height of the Stable Boundary Layer as Seen in LES.

National Technical Information Service (NTIS)

Climate models, numerical weather prediction (NWP) models, and atmospheric dispersion models often rely on parameterizations of planetary boundary layer height. In the case of a stable boundary layer, errors in boundary layer height estimation can result ...

B. Kosovic J. K. Lundquist

2004-01-01

355

Magnetic domination of recollimation boundary layers in relativistic jets

NASA Astrophysics Data System (ADS)

We study the collimation of relativistic magnetohydrodynamic jets by the pressure of an ambient medium, in the limit where the jet interior loses causal contact with its surroundings. This follows up a hydrodynamic study in a previous paper, adding the effects of a toroidal magnetic field threading the jet. As the ultrarelativistic jet encounters an ambient medium with a pressure profile with a radial scaling of p ? r-? where 2 < ? < 4, it loses causal contact with its surroundings and forms a boundary layer with a large pressure gradient. By constructing self-similar solutions to the fluid equations within this boundary layer, we examine the structure of this layer as a function of the external pressure profile. We show that the boundary layer always becomes magnetically dominated far from the source, and that in the magnetic limit, physical self-similar solutions are admitted in which the total pressure within the layer decreases linearly with distance from the contact discontinuity inwards. These solutions suggest a 'hollow-cone' behaviour of the jet, with the boundary-layer thickness prescribed by the value of ?. In contrast to the hydrodynamical case, however, the boundary layer contains an asymptotically vanishing fraction of the jet energy flux.

Kohler, Susanna; Begelman, Mitchell C.

2012-10-01

356

Characteristics of natural wind simulations in the TUM boundary layer wind tunnel

The boundary layer wind tunnel at the Technische Universität München was tested for atmospheric boundary layer (ABL) simulations.\\u000a The ABLs developing above rural, suburban, and urban terrains were reproduced using the Counihan method, i.e., castellated\\u000a barrier wall, vortex generators, and a fetch of surface roughness elements. A series of flow-characteristic evaluations was\\u000a performed to investigate the flow development and uniformity.

Hrvoje Kozmar

357

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

358

Modelling Unsteady Wall Pressures Beneath Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

As a structural entity of turbulence, hairpin vortices are believed to play a major role in developing and sustaining the turbulence process in the near wall region of turbulent boundary layers and may be regarded as the simplest conceptual model that can account for the essential features of the wall pressure fluctuations. In this work we focus on fully developed typical hairpin vortices and estimate the associated surface pressure distributions and their corresponding spectra. On the basis of the attached eddy model, we develop a representation of the overall surface pressure spectra in terms of the eddy size distribution. Instantaneous wavenumber spectra and spatial correlations are readily derivable from this representation. The model is validated by comparison of predicted wavenumber spectra and cross-correlations with existing emperical models and experimental data.

Ahn, B-K.; Graham, W. R.; Rizzi, S. A.

2004-01-01

359

The separated turbulent boundary layer over a wavy wall

NASA Technical Reports Server (NTRS)

A study and application of the fourth order spline collocation procedure, numerical solution of boundary layer like differential equations, is presented. A simple inversion algorithm for the simultaneous solution of the resulting difference equations is given. Particular attention is focused on the boundary condition representation for the spline second derivative approximations. Solutions using the spline procedure, as well as the three point finite difference method, are presented for several model problems in order to assess and improve the spline numerical scheme. Application of the resulting algorithm to the incompressible laminar self similar boundary layer equations is presented.

Polak, A.; Werle, M. J.

1977-01-01

360

Wintertime Boundary Layer Structure in the Grand Canyon.

NASA Astrophysics Data System (ADS)

Wintertime temperature profiles in the Grand Canyon exhibit a neutral to isothermal stratification during both daytime and nighttime, with only rare instances of actual temperature inversions. The canyon warms during daytime and cools during nighttime more or less uniformly through the canyon's entire depth. This weak stability and temperature structure evolution differ from other Rocky Mountain valleys, which develop strong nocturnal inversions and exhibit convective and stable boundary layers that grow upward from the valley floor. Mechanisms that may be responsible for the different behavior of the Grand Canyon are discussed, including the possibility that the canyon atmosphere is frequently mixed to near-neutral stratification when cold air drains into the top of the canyon from the nearby snow-covered Kaibab Plateau. Another feature of canyon temperature profiles is the sharp inversions that often form near the canyon rims. These are generally produced when warm air is advected over the canyon in advance of passing synoptic-scale ridges.Wintertime winds in the main canyon are not classical diurnal along-valley wind systems. Rather, they are driven along the canyon axis by the horizontal synoptic-scale pressure gradient that is superimposed along the canyon's axis by passing synoptic-scale weather disturbances. They may thus bring winds into the canyon from either end at any time of day.The implications of the observed canyon boundary layer structure for air pollution dispersion are discussed.

Whiteman, C. David; Zhong, Shiyuan; Bian, Xindi

1999-08-01

361

Generation of 'artificial' bursts in a turbulent boundary layer

NASA Technical Reports Server (NTRS)

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.

Gad-El-hak, M.; Hussain, A. K. M. F.

1986-01-01

362

Hypersonic boundary-layer transition on a flared cone

NASA Astrophysics Data System (ADS)

Transition on a flared cone with zero angle of attack was studied in our newly established Mach 6 quiet wind tunnel (M6QT) via wall pressure measurement and flow visualization. High-frequency pressure transducers were used to measure the second-mode waves' amplitudes and frequencies. Using pulsed schlieren diagnostic and Rayleigh scattering technique, we got a clear evolution of the second-mode disturbances. The second-mode waves exist for a long distance, which means that the second-mode waves grow linearly in a large region. Strong Mach waves are radiated from the edge of the boundary layer. With further development, the second-mode waves reach their maximum magnitude and harmonics of the second-mode instability appear. Then the disturbances grow nonlinearly. The second modes become weak and merge with each other. Finally, the nonlinear interaction of disturbance leads to a relatively quiet zone, which further breaks down, resulting in the transition of the boundary layer. Our results show that transition is determined by the second mode. The quiet zone before the final breakdown is observed in flow visualization for the first time. Eventual transition requires the presence of a quiet zone generated by nonlinear interactions.

Zhang, Chuan-Hong; Tang, Qing; Lee, Cun-Biao

2013-02-01

363

Shock/boundary-layer interaction model for three-dimensional transonic flow calculations

NASA Astrophysics Data System (ADS)

A new computational model for three-dimensional shock-boundary layer interaction has been developed for use in viscous transonic flow calculations. In general, the new model has been found to be an improvement over the old method in which the boundary-layer equations are simply integrated through the shock. The basic empirical content of the method was tested against detailed boundary-layer measurements in two-dimensional transonic airfoil flows, and the new model was found, in general, to give better agreement with experiment. The new model has also been tested in coupled viscous-inviscid interaction calculations for wings and for nacelles.

McLean, J. D.; Matoi, T. K.

1984-08-01

364

Boundary Layer Clouds and Vegetation–Atmosphere Feedbacks

An analysis of boundary layer cumulus clouds and their impact on land surface-atmosphere exchange is presented. Seasonal trends indicate that in response to increasing insolation and sensible heat flux, both the mixed-layer height (zi) and the lifting condensation level (LCL) peak (;1250 and 1700 m) just before the growing season commences. With the commencement of transpiration, the Bowen ratio falls

Jeffrey M. Freedman; David R. Fitzjarrald; Kathleen E. Moore; Ricardo K. Sakai

2001-01-01

365

ILLIAC 4 and lifting surface theory with boundary layer

NASA Technical Reports Server (NTRS)

Aerodynamic flutter and a re-written computer program for its study are discussed. Data cover: (1) lifting surface theory with boundary layer, (2) incompressible, two dimensional, unsteady flow with control surfaces, (3) improved unsteady theory, (4) combined transonic airfoil thickness and shear layer thickness effects, and (5) bending-torsion flutter calculations.

Dowell, E. H.

1976-01-01

366

BULK MODELS OF THE ATMOSPHERIC CONVECTIVE BOUNDARY LAYER

The paper presents an overview of modeling the atmospheric convective boundary layer (CBL) using bulk parameterizations for the vertical structure of the layer. Such parameterizations are constructed based on empirical knowledge about vertical distributions of meteorological variables in the CBL. Two main types of CBL bulk models are presented and discussed. The first model considered is the so-called zero-order jump

E. FEDOROVICH

1998-01-01

367

ON AERODYNAMIC AND BOUNDARY LAYER RESISTANCES WITHIN DRY DEPOSITION MODELS

There have been many empirical parameterizations for the aerodynamic and boundary layer resistances proposed in the literature, e.g. those of the Meyers Multi-Layer Deposition Model (MLM) used with the nation-wide dry deposition network. Many include arbitrary constants or par...

368

Unsteady gun-barrel boundary-layer calculations

The paper describes current progress in the calculation of nonsteady boundary layers involved in internal flow situations to determine the dominant mechanisms of erosion. A time-dependent description of the viscous (laminar and turbulent) layer is formulated, and numerical solutions are obtained by application of a factored ADI scheme. The conservation equations in the alternate-sweep form are then solved under prescribed

S. W. Kang; J. L. Levatin

1980-01-01

369

Stability of a Time Dependent Boundary Layer.

National Technical Information Service (NTIS)

The aim of this article is to determine the stability characteristics of a Rayleigh layer, which is known to occur when the fluid above a flat plate has a velocity imparted to it (parallel to the plate). This situation is intrinsically unsteady, however, ...

S. R. Otto

1993-01-01

370

Lidar-based remote sensing of atmospheric boundary layer height over land and ocean

NASA Astrophysics Data System (ADS)

Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and ABL vertical structure over ocean (TWP_C2 cite) and land (SGP_C1) are analyzed. The new methods are also applied to satellite lidar measurements. The derived global marine boundary layer structure database shows good agreement with marine ABL stratiform cloud top height.

Luo, T.; Yuan, R.; Wang, Z.

2013-09-01

371

Lidar-based remote sensing of atmospheric boundary layer height over land and ocean

NASA Astrophysics Data System (ADS)

Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of the ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and the ABL vertical structure over ocean and land are analyzed. The new methods are then applied to satellite lidar measurements. The aerosol-derived global marine boundary layer heights are evaluated with marine ABL stratiform cloud top heights and results show a good agreement between them.

Luo, T.; Yuan, R.; Wang, Z.

2014-01-01

372

An experimental investigation of turbulent boundary layers along curved surfaces

NASA Technical Reports Server (NTRS)

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.

So, R. M. C.; Mellor, G. L.

1972-01-01

373

Sheared boundary layers in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Thermal boundary layers in turbulent Rayleigh-Benard convection are studied experimentally using a novel system in which the convecting fluid is sheared from below with a flowing layer of mercury. Oscillatory shear substantially alters the spatial structure and frequency of the eruptions, with minimal effect on the heat flux (less than 5 percent). The temperature probability distribution function (PDF) just above the lower boundary layer changes from Gaussian to exponential without significant changes in the interior PDF. Implications for theories of 'hard' turbulence are discussed.

Solomon, T. H.; Gollub, J. P.

1990-05-01

374

Numerical Studies of Boundary-Layer Receptivity

NASA Technical Reports Server (NTRS)

Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.

Reed, Helen L.

1995-01-01

375

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

NASA Technical Reports Server (NTRS)

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Hoffert, M. I.; Sud, Y. C.

1976-01-01

376

A class of unsteady, three-dimensional flow structures in turbulent boundary layers

A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary

R. L. Ash

1981-01-01

377

UNSTEADY SHOCK WAVE - TURBULENT BOUNDARY LAYER INTERACTION IN THE LAVAL NOZZLE

The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wave-boundary layer interaction. Oscillations may be induced by natural separation unsteadiness or forced by boundary conditions. Significant improvements of CFD tools, increased computer resources and the development of experimental methods have again drawn the attention of researchers to this topic. Forced oscillations of a transonic

PIOTR DOERFFER; OSKAR SZULC; FRANCO MAGAGNATO

378

Manipulation of the structure of a turbulent boundary layer

NASA Astrophysics Data System (ADS)

The manipulation of a turbulent boundary layer for the purpose of net drag reduction is an attractive topic for research, because even modest success will result in large energy savings. The focus is on passive manipulation, one of the simplest manipulation techniques. The most promising manipulator is the so-called BLADE device, consisting of two thin ribbons or foils suspended in the outer portion of the boundary layer. When the research was begun, there was significant controversy over the magnitude of the net drag reduction possible (20 percent) and the maximum skin friction reduction obtainable (50 percent). Accurate local skin-friction measurements were made using sublayer fences in a perturbed boundary layer. By comparing the direct measurements with those obtained by indirect methods, it was determined that the degree of drag reduction obtained depends on the method used to calculate the combined device drag and skin friction drag. Using auto and two-point correlation measurements as well as space-time correlations, the effects of BLADE were investigated on the turbulent structures in the boundary layer, comparing them with wire devices, which are not known to produce a net reduction in drag. The space-time correlation revealed that the most significant effect of the BLADE device was on the large structures (the dominant structures in the outer region of the boundary layer). The inner layer devices consisting of sublayer wires were also investigated. The results from both the inner and outer layer manipulations suggest that the effective alteration of a turbulent boundary layer depends on the scaling of the device.

Lynn, Theodore Brooks

379

The Boundary Layer Late Afternoon and Sunset Turbulence Project

NASA Astrophysics Data System (ADS)

The BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) project aims at better understanding the turbulence processes which occur during the transition from a well-mixed convective boundary layer to a residual layer overlying a stabilized nocturnal layer. This phase of the diurnal cycle is challenging from both modeling and observational perspectives: it is transitory, most of the forcings are small or null during the transition and the turbulence regime changes from the fully convective regime of turbulence, close to homogeneous and isotropic, toward more heterogeneous and intermittent turbulence during its decay. Those issues motivated a field campaign that was conducted from 14 June to 8 July 2011 in southern France in complex terrain and consisted of a range of integrated instrument platforms including: full-size aircraft, Remotely Piloted Airplane Systems (RPAS), remote sensing instruments, radiosoundings, tethered balloons, surface flux stations, and various meteorological towers deployed over different surface covers. The boundary layer, from the earth's surface to free troposphere was densely probed during the entire day, with a focus and intense observations from midday until sunset. The field dataset now forms the base of a set of studies utilizing the observations and several types of models including: Large Eddy Simulation, Mesoscale models, forecast models. The presentation will expose an overview of this experiment and of the current observational and modeling studies, with the focus on: the turbulence decay process within the entire boundary layer from surface to the top, the mesoscale forcings of importance during BLLAST, the ability of the forecast models to represent the diurnal cycle, the relevance of the Monin Obukhov similarity theory, and shallow drainage flows. Reference: Lothon M. et al., 2012. The Boundary-Layer Late Afternoon and Sunset Turbulence field experiment, Proc. of the 20th Symposium on Boundary-Layers and Turbulence, 7-13 July, Boston, MA, USA.

Lothon, Marie; Lohou, Fabienne; Darbieu, Clara; Couvreux, Fleur; Pino, David; Blay, Estel; Vila-Guerau de Arellano, Jordi; Pietersen, Henk; Hartogensis, Oscar; Pardyjak, Eric; Alexander, Daniel; Reuder, Joachim; Baaserud, Line; Nilsson, Erik; Jimenez, Maria Antonia; Faloona, Ian; Sastre-Marugan, Mariano; Angevine, Wayne M.; Canut, Guylaine; Bazile, Eric

2014-05-01

380

Three-dimensional visualization of large structures in the turbulent boundary layer

NASA Astrophysics Data System (ADS)

A new method of visualizing the coherent structures in the boundary layer is used to develop insight into how these structures form and to provide information on the relative frequency of typical shapes noticed in the near-wall flow. These results were achieved in a water channel using a recently developed tracer which remains as a moving dye streak while conforming to the convoluted motions in the boundary layer. The tracer is formulated from a surfactant-polymer-emulsion mixture which retains its capabilities as a marker of evolving flow motions in the boundary layer for a meter or more before eventually dispersing. Three-dimensional, continuous visualization of the structures can be obtained as they move along a flat plate. Photos and video frames demonstrate the evolution and properties of the most widely discussed boundary-layer structure, the Theodorsen (horseshoe) vortex.

Hoyt, J. W.; Sellin, R. H. J.

381

Surface modes in sheared boundary layers over impedance linings

NASA Astrophysics Data System (ADS)

Surface modes, being duct modes localized close to the duct wall, are analysed within a lined cylindrical duct with uniform flow apart from a thin boundary layer. As well as full numerical solutions of the Pridmore-Brown equation, simplified mathematical models are given where the duct lining and boundary layer are lumped together and modelled using a single boundary condition (a modification of the Myers boundary condition previously proposed by the author), from which a surface mode dispersion relation is derived. For a given frequency, up to six surface modes are shown to exist, rather than the maximum of four for uniform slipping flow. Not only is the different number and behaviour of surface modes important for frequency-domain mode-matching techniques, which depend on having found all relevant modes during matching, but the thin boundary layer is also shown to lead to different convective and absolute stability than for uniform slipping flow. Numerical examples are given comparing the predictions of the surface mode dispersion relation to full solutions of the Pridmore-Brown equation, and the accuracy with which surface modes are predicted is shown to be significantly increased compared with the uniform slipping flow assumption. The importance of not only the boundary layer thickness but also its profile (tanh or linear) is demonstrated. A Briggs–Bers stability analysis is also performed under the assumption of a mass–spring–damper or Helmholtz resonator impedance model.

Brambley, E. J.

2013-08-01

382

Numerical studies on evolution of secondary streamwise vortices in transitional boundary layers

Formation and evolution of secondary streamwise vortices in the compressible transitional boundary layers over a flat plate\\u000a are studied using a direct numerical simulation method with high-order accuracy and highly effective non-reflecting characteristic\\u000a boundary conditions. Generation and development processes of the secondary streamwise vortices in the complicated transitional\\u000a boundary flow are clearly analyzed based on the of numerical results, and

Lin Chen; Deng-bin Tang; Chao-qun Liu

2011-01-01

383

Dynamic behavior of an unsteady turbulent boundary layer

NASA Technical Reports Server (NTRS)

Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70 percent greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle. Previously announced in STAR as N81-28392

Parikh, P. G.; Reynolds, W. C.; Jayaraman, R.; Carr, L. W.

1981-01-01

384

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

385

Stability and separation of freely interacting boundary layers

NASA Astrophysics Data System (ADS)

The triple-deck theory to describe boundary-layer free interaction and separation is carefully investigated from the viewpoint of how it predicts stability properties of a viscous flow. The linearized version of this theory gives the same results as the linear stability theory based on the Orr-Sommerfeld equation if the flow is incompressible and the wave number of small disturbances goes to zero. Hence, a rather general criterion results to fix limits for a subsonic boundary layer to be stable. On the contrary, the linear approximation to the triple-deck theory leads to discouraging conclusions when the velocity of the oncoming stream exceeds the speed of sound, since it fails to reveal the boundary-layer instability. The Prandtl equations with a self-induced pressure gradient included are used to formulate a nonlinear approach for elucidating stability properties of freely inter acting boundary layers both for subsonic and supersonic cases. The shock-wave boundary-layer interaction and separation on a moving wall is numerically studied, the formation of two recirculation bubbles being the most striking feature. With the shock strength increasing, both bubbles tend to divide into smaller vortex cells whence the nonsteady process of velocity field "breathing" stems.

Ryzhov, Oleg S.; Zhuk, Vladimir I.

386

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

A study of the attenuation of bending boundary layers in balanced and unbalanced, symmetrically and unsymmetrically laminated cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize the effects of laminate orthotropy and anisotropy on the bending boundary-layer decay length in a very general manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all laminates considered, the results show that the differences between results obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that, in some cases, neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and, in other cases, results in an overestimation.

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

387

Three-dimensional Large Eddy Simulation of wave bottom boundary layer

NASA Astrophysics Data System (ADS)

Bottom boundary layer developed under surface waves has been widely studied in the past few decades because of the crucial role it plays in hydrodynamic dissipation and sediment transport. However, most of the previous numerical research simplified the wave field above the bottom boundary layer as fully-developed oscillatory flow. Many processes, such as boundary layer streaming, are neglected. With the aim of better understanding bottom boundary layer processes under real waves and to further investigate the interaction between the surface generated turbulence (e.g., breaking waves; wave-current interaction) and bottom boundary layer turbulence, a numerical study of three-dimensional Large Eddy Simulation (LES) is carried out. OpenFOAM, an open-source C++ toolbox which provides a solver of 3D Navier-Stokes equations and free-surface tracking, is utilized with a dynamic Smagorinsky closure. An idealized domain that contains a single wave is established with periodic boundary conditions in the streamwise and spanwise directions. The width of the channel is sufficiently large to contain the largest turbulent eddies. Firstly, laboratory data of bottom boundary layer under non-breaking waves is used to validate the numerical model and a good agreement is obtained. A more detailed investigation of the three-dimensional bottom boundary layer of non-breaking waves, e.g., the distribution of shear stress, turbulence structure and boundary layer streaming are investigated. Model results are compared with those in an oscillatory channel flow to contrast the effect of the inhomogeneous wave field. During the conference, we will also present preliminary results for wave-current interaction and wave breaking processes.

Zhou, Z.; Hsu, T.

2012-12-01

388

NASA Technical Reports Server (NTRS)

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

Vanness, W.

1978-01-01

389

Formation of ordered vortex structures from unstable oscillations in a boundary layer

NASA Astrophysics Data System (ADS)

The propagation of perturbations with a relatively large amplitude in a boundary layer is investigated using an asymptotic approach. The properties of the nonlinear process are described using the Benjamin-Ono equation, and the behavior of a periodic solution to this equation is investigated as a function of arbitrary constants. It is shown that the development of Tollmien-Schlichting waves with a rising amplitude in the boundary layer leads to the formation of soliton-type ordered vortex structures.

Ryzhov, O. S.

1990-12-01

390

Shipboard measurements of the cloud-capped marine boundary layer during FIRE/ASTEX

Results are reported on measurements of the cloud-capped marine boundary layer during FIRE/ASTEX. A method was developed from the ASTEX dataset for measuring profiles of liquid water content, droplet size and concentration from cloud radar/microwave radiometer data in marine boundary layer clouds. Profiles were also determined from the first three moments of the Doppler spectrum measured in drizzle with the ETL cloud radar during ASTEX.

NONE

1997-09-01

391

Location of acoustic sources placed under a boundary layer - Effect of the pressure field

NASA Astrophysics Data System (ADS)

Experimental results on the superconvection of sound waves in transitional and turbulent boundary layers have been obtained, and a propagation model to account for pressure fluctuations is developed. The results reveal a downstream shift of the source position which is strongly correlated with pressure fluctuations of the transitional-turbulent boundary layer. The results do not provide evidence for reciprocal coupling between the acoustic wave and the flow. Good agreement is found between theoretical and experimental results.

Dufourcq, Ph.; Guyomar, D.

1988-06-01

392

Can new particle formation occur in the clean marine boundary layer?

An analysis of new particle formation probability in the marine boundary layer (MBL) is conducted using a detailed aerosol dynamics and gas-phase chemistry model, thermodynamically correct classical binary (H2O-H2SO4) nucleation theory, and recently developed ternary (H2O-H2SO4-NH3) nucleation theory. Additionally, the effect of boundary-layer meteorology (i.e., adiabatic cooling, small scale fluctuations, and entrainment) in enhancing nucleation is also examined. The results

Liisa Pirjola; Colin D. O'Dowd; Ian M. Brooks; Markku Kulmala

2000-01-01

393

The effects of expansion on the turbulence structure of compressible boundary layers

A fully developed Mach 3 turbulent boundary layer subjected to four expansion regions (centred and gradual expansions of 7° and 14°) was investigated with laser Doppler velocimetry. Measurements were acquired in the incoming flat-plate boundary layer and to s\\/[delta][simeq R: similar, equals]20 downstream of the expansions. While mean velocity profiles exhibit significant progress towards recovery by the most downstream measurements,

Stephen A. Arnette; Mo Samimy; Gregory S. Elliott

1998-01-01

394

Interferometric data for a shock-wave/boundary-layer interaction

NASA Technical Reports Server (NTRS)

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.

Dunagan, Stephen E.; Brown, James L.; Miles, John B.

1986-01-01

395

Hypersonic turbulent wall boundary layer computations

NASA Technical Reports Server (NTRS)

The Baldwin-Lomax (1978) algebraic turbulence model was modified for hypersonic flow conditions. Two coefficients in the outer-layer eddy-viscosity model were determined as functions of Mach number and temperature ratio. By matching the solutions from the Baldwin-Lomax model to those from the Cebeci-Smith (1974) model for a flat plate at hypersonic speed, the new values of the coefficients were obtained. The results show that the values of C(cp) and C(kleb) are functions of both Mach number and wall temperature ratio. The C(cp) and C(kleb) variations with Mach number and wall temperature were used for the calculations of both a 4-deg wedge flow at Mach 18 and an axisymmetric Mach 20 nozzle flow. The Navier-Stokes equations with thin-layer approximation were solved for the above hypersonic flow conditions and the results were compared with existing experimental data. The agreement between the numerical solutions and the existing experimental data were good. The modified Baldwin-Lomax model thus is useful in the computations of hypersonic flows.

Kim, S. C.; Harloff, G. J.

1988-01-01

396

Hypersonic turbulent wall boundary layer computations

NASA Technical Reports Server (NTRS)

The Baldwin-Lomax algebraic turbulence model was modified for hypersonic flow conditions. Two coefficients in the outer layer eddy viscosity model were determined as functions of Mach number and temperature ratio. By matching the solutions from the Baldwin-Lomax model to those from the Cebeci-Smith model for a flat plate at hypersonic speed, the new values of the coefficient were obtained. The results show that the values of C sub cp and C sub kleb are functions of both Mach number and wall temperature ratio. The C sub cp and C sub kleb variations with Mach number and wall temperature were used for the calculations of both a 4 deg wedge flow at Mach 18 and an axisymmetric Mach 20 nozzle flow. The Navier-Stokes equations with thin layer approximation were solved for the above hypersonic flow conditions and the results were compared with existing experimental data. The agreement between the numerical solutions and the existing experimental data were good. The modified Baldwin-Lomax model thus is useful in the computations of hypersonic flows.

Kim, S. C.; Harloff, G. J.

1988-01-01

397

Non-linear processes in the Earth atmosphere boundary layer

NASA Astrophysics Data System (ADS)

The work is connected with studying electromagnetic fields in the resonator Earth-Ionosphere. There is studied the interconnection of tide processes of geophysical and astrophysical origin with the Earth electromagnetic fields. On account of non-linear property of the resonator Earth-Ionosphere the tides (moon and astrophysical tides) in the electromagnetic Earth fields are kinds of polyharmonic nature. It is impossible to detect such non-linear processes with the help of the classical spectral analysis. Therefore to extract tide processes in the electromagnetic fields, the method of covariance matrix eigen vectors is used. Experimental investigations of electromagnetic fields in the atmosphere boundary layer are done at the distance spaced stations, situated on Vladimir State University test ground, at Main Geophysical Observatory (St. Petersburg), on Kamchatka pen., on Lake Baikal. In 2012 there was continued to operate the multichannel synchronic monitoring system of electrical and geomagnetic fields at the spaced apart stations: VSU physical experimental proving ground; the station of the Institute of Solar and Terrestrial Physics of Russian Academy of Science (RAS) at Lake Baikal; the station of the Institute of volcanology and seismology of RAS in Paratunka; the station in Obninsk on the base of the scientific and production society "Typhoon". Such investigations turned out to be possible after developing the method of scanning experimental signal of electromagnetic field into non- correlated components. There was used a method of the analysis of the eigen vectors ofthe time series covariance matrix for exposing influence of the moon tides on Ez. The method allows to distribute an experimental signal into non-correlated periodicities. The present method is effective just in the situation when energetical deposit because of possible influence of moon tides upon the electromagnetic fields is little. There have been developed and realized in program components in the form of PAS instruments of processes of geophysical and man-triggered nature; to predict the presence of the features of geophysical nature in the electromagnetic field of the atmosphere boundary surface layer; to study dynamics the analyzed signals coming from the geophysical and man-triggered sources in the electrical and magnetic fields of the atmosphere boundary surface layer; to expose changes of the investigated time series in the periods preceding the appearance of the predicted phenomena; to form clusters of the time series being the features of the predicted events. On the base of the exposed clusters of the time series there have been built the predicting rules allowing to coordinate the probability of appearing the groups of the occurred events. The work is carried out with supporting of Program FPP #14.B37.210668, FPP #5.2071.2011, RFBR #11-05-97518.

Grunskaya, Lubov; Valery, Isakevich; Dmitry, Rubay

2013-04-01

398

Boundary-layer-ingesting inlet flow control system

NASA Technical Reports Server (NTRS)

A system for reducing distortion at the aerodynamic interface plane of a boundary-layer-ingesting inlet using a combination of active and passive flow control devices is disclosed. Active flow control jets and vortex generating vanes are used in combination to reduce distortion across a range of inlet operating conditions. Together, the vortex generating vanes can reduce most of the inlet distortion and the active flow control jets can be used at a significantly reduced control jet mass flow rate to make sure the inlet distortion stays low as the inlet mass flow rate varies. Overall inlet distortion, measured and described as average SAE circumferential distortion descriptor, was maintained at a value of 0.02 or less. Advantageous arrangements and orientations of the active flow control jets and the vortex generating vanes were developed using computational fluid dynamics simulations and wind tunnel experimentations.

Owens, Lewis R. (Inventor); Allan, Brian G. (Inventor)

2010-01-01

399

The transport of enstrophy in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

A miniature, nine-sensor, hot-wire probe has been developed for simultaneous measurements of the three components of the velocity vector and all nine components of the velocity gradient fields. The kinematics and dynamics of Reynolds stress generation in a turbulent boundary layer have been examined with this probe. Measurements of the values of the terms in the time averaged transport equations are described for instantaneous, mean, and fluctuating enstrophy. The results obtained show that conditionally averaged entrophy is about 40 percent greater than the unconditioned data for y+ less than 20. For mean enstrophy, the viscous diffusion and direct dissipitation are shown to be the dominant processes for y+ less than 25. For fluctuating enstrophy, the rotation and stretching term and the viscous dissipation term are shown to dominate. For the instantaneous transport of enstrophy, the averaged transport equation reveals more of the physics of the vorticity dynamics than when the equation is decomposed into mean and fluctuating parts.

Balint, J.-L.; Vukoslavcevic, P.; Wallace, J. M.

400

Secondary instability in boundary-layer flows

NASA Technical Reports Server (NTRS)

The stability of a secondary Tollmien-Schlichting wave, whose wavenumber and frequency are nearly one half those of a fundamental Tollmien-Schlichting instability wave is analyzed using the method of multiple scales. Under these conditions, the fundamental wave acts as a parametric exciter for the secondary wave. The results show that the amplitude of the fundamental wave must exceed a critical value to trigger this parametric instability. This value is proportional to a detuning parameter which is the real part of k - 2K, where k and K are the wavenumbers of the fundamental and its subharmonic, respectively. For Blasius flow, the critical amplitude is approximately 29% of the mean flow, and hence many other secondary instabilities take place before this parametric instability becomes significant. For other flows where the detuning parameter is small, such as free-shear layer flows, the critical amplitude can be small, thus the parametric instability might play a greater role.

Nayfeh, A. H.; Bozatli, A. N.

1979-01-01

401

The effects of forcing on a single stream shear layer and its parent boundary layer

NASA Technical Reports Server (NTRS)

Forcing and its effect on fluid flows has become an accepted tool in the study and control of flow systems. It has been used both as a diagnostic tool, to explore the development and interaction of coherent structures, and as a method of controlling the behavior of the flow. A number of forcing methods have been used in order to provide a perturbation to the flow; among these are the use of an oscillating trailing edge, acoustically driven slots, external acoustic forcing, and mechanical piston methods. The effect of a planar mechanical piston forcing on a single stream shear layer is presented; it can be noted that this is one of the lesser studied free shear layers. The single stream shear layer can be characterized by its primary flow velocity scale and the thickness of the separating boundary layer. The velocity scale is constant over the length of the flow field; theta (x) can be used as a width scale to characterize the unforced shear layer. In the case of the forced shear layer the velocity field is a function of phase time and definition of a width measure becomes somewhat problematic.

Haw, Richard C.; Foss, John F.

1990-01-01

402

A revised conceptual model of the tropical marine boundary layer

NASA Astrophysics Data System (ADS)

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 a