Note: This page contains sample records for the topic boundary layer response from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

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

2

Response of the Tropical Boundary Layer to Weak Surface Forcing  

NASA Technical Reports Server (NTRS)

During the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), a series of airborne thermal infrared observations and in situ atmospheric measurements were made near the sea surface through heights exceeding 4 km. Air movements associated with the sea surface temperature and the marine atmospheric boundary layer were studied.

Hagan, D.; Rogers, D.

1995-01-01

3

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

4

Total Solar Eclipses and Atmospheric Boundary Layer Response  

NASA Astrophysics Data System (ADS)

The effect of three total solar eclipses on meteorological parameters is discussed in the paper. Measurements were conducted at the village of Ravnets,General Toshevo municipality, Bulgaria, 1999,in Manavgat, near Antalya, Turkey, 2006 and in Tian Huang Ping, China, 2009. The observed decrease of the sky illumination (incoming solar radiation) during the eclipses was proportional to the percentage of solar coverage. The after eclipse sky illumination level is due to the effect of the natural change of the solar elevation angle. For the 1999 TSE it did not regain its pre eclipse value, it has exactly the same value for the 2006 TSE, and, It is three times larger than the pre eclipse value for the 2009 TSE. This fact can be easily explained by the Local Time of the maximum of the eclipses: LT 13:12, LT 12:58, and LT 09:34, respectively. Measurements showed significant changes in the surface air temperature. The minimum of the air temperature during the 2009 TSE (Tmin=4.5°C) was measured 6 min after the end of the total phase. This minimal temperature drop and larger time lag can be explained with the huge artificial lake near the place of observation, which minimizes the temperature response due to its larger heat capacity. During the 1999 TSE, minimal temperature (Tmin=6.4°C) is measured 7 min 30 s after the total phase, and for the 2006 TSE (Tmin=5°C) - 5 min. It is in accordance with the fact that the temperature minima at residential/commercial stations occurred in general, before the minima at stations in agricultural terrains. In 2006 we were at the yard of the hotel, and in 1999 in the countryside. The wind velocity drops during the total phase as a result of the cooling and stabilization of the atmospheric boundary layer. The wind direction during the total phase changes and the wind begins to blow in the same direction as the direction of motion of the lunar shadow on the earth. Cirrus and cirrostratus clouds were observed during the 2006 total solar eclipse. Cloud structures in the form of narrow concentric arcs, equally detached from one another were observed for 20 minutes, after the beginning of the maximum phase of the 1999 TSE.

Stoev, A.; Stoeva, P.; Kuzin, S.

2012-11-01

5

Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.  

PubMed

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

6

Fuselage Structure Response to Boundary Layer, Tonal Sound, and Jet Noise  

NASA Technical Reports Server (NTRS)

Experiments have been conducted to study the response of curved aluminum and graphite-epoxy fuselage structures to flow and sound loads from turbulent boundary layer, tonal sound, and jet noise. Both structures were the same size. The aluminum structure was reinforced with tear stoppers, while the graphite-epoxy structure was not. The graphite-epoxy structure weighed half as much as the aluminum structure. Spatiotemporal intermittence and chaotic behavior of the structural response was observed, as jet noise and tonal sound interacted with the turbulent boundary layer. The fundamental tone distributed energy to other components via wave interaction with the turbulent boundary layer. The added broadband sound from the jet, with or without a shock, influenced the responses over a wider range of frequencies. Instantaneous spatial correlation indicates small localized spatiotemporal regions of convected waves, while uncorrelated patterns dominate the larger portion of the space. By modifying the geometry of the tear stoppers between panels and frame, the transmitted and reflected waves of the aluminum panels were significantly reduced. The response level of the graphite-epoxy structure was higher, but the noise transmitted was nearly equal to that of the aluminum structure. The fundamental shock mode is between 80 deg and 150 deg and the first harmonic is between 20 deg and 80 deg for the underexpanded supersonic jet impinging on the turbulent boundary layer influencing the structural response. The response of the graphite-epoxy structure due to the fundamental mode of the shock impingement was stabilized by an externally fixed oscillator.

Maestrello, L.

2004-01-01

7

Satellite evidence of wintertime atmospheric boundary layer responses to multiple SST fronts in the Japan Sea  

Microsoft Academic Search

We present satellite evidence of wintertime atmospheric boundary layer responses to multiple sea surface temperature (SST) fronts in the Japan Sea under cold-air outbreak during 22-28 December 2005. It is found that the lower atmosphere adheres to the stepwise SST variations, focusing on a wind trajectory from the Eurasian continent to the northern Japan, which goes through the meandering Polar

Teruhisa Shimada; Hiroshi Kawamura

2008-01-01

8

Satellite evidence of wintertime atmospheric boundary layer responses to multiple SST fronts in the Japan Sea  

Microsoft Academic Search

We present satellite evidence of wintertime atmospheric boundary layer responses to multiple sea surface temperature (SST) fronts in the Japan Sea under cold-air outbreak during 22–28 December 2005. It is found that the lower atmosphere adheres to the stepwise SST variations, focusing on a wind trajectory from the Eurasian continent to the northern Japan, which goes through the meandering Polar

Teruhisa Shimada; Hiroshi Kawamura

2008-01-01

9

Effect of Pressure Gradients on Plate Response and Radiation in a Supersonic Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

Using the model developed by the author for zero-pressure gradient turbulent boundary layers, results are obtained for adverse and favorable pressure gradients. It is shown that when a flexible plate is located in an adverse pressure gradient area, it vibrates more than if it were in a favorable pressure gradient one. Therefore the noise generated by the plate in an adverse pressure gradient is much greater than that due to the plate in a favorable pressure gradient. The effects of Reynolds number and boundary layer thickness are also analyzed and found to have the same effect in both adverse and favorable pressure gradient cases. Increasing the Reynolds number is found to increase the loading on the plate and therefore acoustic radiation. An increase in boundary layer thickness is found to decrease the level of the high frequencies and therefore the response and radiation at these frequencies. The results are in good qualitative agreement with experimental measurements.

Frendi, Abdelkader

1997-01-01

10

Effects of Boundary Conditions on Thermal Response of a Cellulose Acetate Layer Using Hottel's Zonal Method  

NASA Astrophysics Data System (ADS)

Energy can transfer internally by radiation in addition to conduction in translucent polymers. Since radiant propagation is very rapid, it can provide energy within the layer more quickly than diffusion by heat conduction. Thus, the transient thermal response of a layer for combined radiative and conduction may be extremely different from that of conduction alone. In this paper, the behavior of a heat conducting, absorbing, and emitting layer of Cellulose Acetate layer is investigated during the transient interval when both conductive and radiative heat transfer are considered. Specifically, the effects of boundary conditions on the response of the layer are considered here. These boundary conditions include both conductive boundary conditions, such as convection coefficient and convective fluid temperature, and radiation boundary conditions, like radiation surrounding temperature and specular reflectivity. To this end, the governing differential equations including the equation of radiative heat transfer within the material coupled to the transient energy equation with radiative terms are presented. The solution procedure is based on nodal analysis and Hottel's zonal method extended by the ray tracing method. The transient energy equation including the radiative internal energy source is solved using a time marching finite difference procedure with variable space and time increments.

Safavisohi, Babak; Sharbati, Ehsan; Aghanajafi, Cyrus; Firoozabadi, Seyed Reza Khatami

2006-12-01

11

Satellite evidence of wintertime atmospheric boundary layer responses to multiple SST fronts in the Japan Sea  

NASA Astrophysics Data System (ADS)

We present satellite evidence of wintertime atmospheric boundary layer responses to multiple sea surface temperature (SST) fronts in the Japan Sea under cold-air outbreak during 22-28 December 2005. It is found that the lower atmosphere adheres to the stepwise SST variations, focusing on a wind trajectory from the Eurasian continent to the northern Japan, which goes through the meandering Polar Front and the Tsushima Warm Current. Wind speed anomaly and wind divergence are linearly related to the SST anomaly and downwind SST gradient, respectively. Vertically uniform layers of potential temperature are accomplished when reaching the Polar Front and Tsushima Warm Current. Variations of water vapor mixing ratio and the resulting surface turbulent heat fluxes show also stepwise increases. Little wind vertical shear on the Japanese coast suggests that well-mixed boundary layer is eventually formed.

Shimada, Teruhisa; Kawamura, Hiroshi

2008-12-01

12

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

13

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

14

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

15

Investigating Response from Turbulent Boundary Layer Excitations on a Real Launch Vehicle using SEA  

NASA Technical Reports Server (NTRS)

Statistical Energy Analysis (SEA) response has been fairly well anchored to test observations for Diffuse Acoustic Field (DAF) loading by others. Meanwhile, not many examples can be found in the literature anchoring the SEA vehicle panel response results to Turbulent Boundary Layer (TBL) fluctuating pressure excitations. This deficiency is especially true for supersonic trajectories such as those required by this nation s launch vehicles. Space Shuttle response and excitation data recorded from vehicle flight measurements during the development flights were used in a trial to assess the capability of the SEA tool to predict similar responses. Various known/measured inputs were used. These were supplemented with a range of assumed values in order to cover unknown parameters of the flight. This comparison is presented as "Part A" of the study. A secondary, but perhaps more important, objective is to provide more clarity concerning the accuracy and conservatism that can be expected from response estimates of TBL-excited vehicle models in SEA (Part B). What range of parameters must be included in such an analysis in order to land on the conservative side in response predictions? What is the sensitivity of changes in these input parameters on the results? The TBL fluid structure loading model used for this study is provided by the SEA module of the commercial code VA One.

Harrison, Phillip; LaVerde,Bruce; Teague, David

2009-01-01

16

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

17

A synthesis approach for reproducing the response of aircraft panels to a turbulent boundary layer excitation.  

PubMed

Random wall-pressure fluctuations due to the turbulent boundary layer (TBL) are a feature of the air flow over an aircraft fuselage under cruise conditions, creating undesirable effects such as cabin noise annoyance. In order to test potential solutions to reduce the TBL-induced noise, a cost-efficient alternative to in-flight or wind-tunnel measurements involves the laboratory simulation of the response of aircraft sidewalls to high-speed subsonic TBL excitation. Previously published work has shown that TBL simulation using a near-field array of loudspeakers is only feasible in the low frequency range due to the rapid decay of the spanwise correlation length with frequency. This paper demonstrates through theoretical criteria how the wavenumber filtering capabilities of the radiating panel reduces the number of sources required, thus dramatically enlarging the frequency range over which the response of the TBL-excited panel is accurately reproduced. Experimental synthesis of the panel response to high-speed TBL excitation is found to be feasible over the hydrodynamic coincidence frequency range using a reduced set of near-field loudspeakers driven by optimal signals. Effective methodologies are proposed for an accurate reproduction of the TBL-induced sound power radiated by the panel into a free-field and when coupled to a cavity. PMID:21302997

Bravo, Teresa; Maury, Cédric

2011-01-01

18

Dynamical response of the Arctic atmospheric boundary layer to sea ice in Polar WRF model  

NASA Astrophysics Data System (ADS)

Impact of sea ice concentration (SIC) on the Arctic atmospheric boundary layer (ABL) is investigated using a Polar-optimized version of the Weather Research and Forecasting (Polar WRF) model. A detailed comparison of the simulations forced with various SIC datasets to historical ship and ice station based data are presented demonstrating the reasonable representation of the observed ABL evolution by the Polar WRF. Further, two dynamically distinctive effects of sea ice on the surface wind were found, which act on different spatial scales. Reduced SIC lowers ABL stability, thereby increasing surface wind (W10) speeds. The spatial scale of this response is comparable to the basin-scale of the SIC difference. In contrast, near-surface geostrophic wind (Wg) shows a strong response in the MIZ, where, a good spatial correspondence exists among the Laplacian of the sea level pressure (SLP), the surface wind convergence, and the vertical motion within the ABL. This indicates that SIC affects Wg through variation in SLP but on a much narrower scale. Larger-amplitude and broader-scale response in W10 implies that surface wind stress derived from Wg to drive ice-ocean models may not fully reflect the effect of SIC changes.

Seo, Hyodae; Yang, Jiayan

2014-05-01

19

Time-dependent boundary-layer response in a propeller slipstream  

NASA Technical Reports Server (NTRS)

The time-dependent behavior of a wing boundary layer immersed in a propeller slipstream has been studied experimentally in wind-tunnel tests and in flight. Hot-wire anemometer measurements were made through the boundary layer for time-dependent, ensemble-average velocity and turbulence-intensity profiles at various chord locations. The boundary layer has a coherent, time-dependent cycle of transitional behavior, varying from a laminar to a turbulent-transitional state. Local drag coefficients determined from the velocity profiles for the freewheeling propeller case in flight show that the time-dependent drag in the propeller slipstream varies from the undisturbed laminar value to a value less than that predicted for fully turbulent flow. Local drag coefficients determined from the thrusting propeller case in the wind tunnel indicate that the effects of the slipstream are to enhance the stability of the boundary layer and to reduce the drag coefficient in the laminar portion of the cycle below its undisturbed laminar value.

Howard, Richard M.; Miley, Stan J.

1989-01-01

20

Dynamical response of the Arctic atmospheric boundary layer process to uncertainties in sea-ice concentration  

NASA Astrophysics Data System (ADS)

Impact of sea-ice concentration (SIC) on the Arctic atmospheric boundary layer (ABL) is investigated using a polar-optimized version of the Weather Research and Forecasting (Polar WRF) model forced with SIC conditions during three different years. We present a detailed comparison of the simulations with historical ship and ice station based data focusing on September. Our analysis shows that Polar WRF provides a reasonable representation of the observed ABL evolution provided that SIC uncertainties are small. Lower skill is obtained, however, with elevated SIC uncertainties associated with incorrect seasonal evolution of sea ice and misrepresentation of ice thickness near the marginal ice zone (MIZ). The result underscores the importance of accurate representation of ice conditions for skillful simulation of the Arctic ABL. Further, two dynamically distinctive effects of sea ice on the surface wind were found, which act on different spatial scales. Reduced SIC lowers ABL stability, thereby increasing surface-wind (W10) speeds. The spatial scale of this response is comparable to the basin scale of the SIC difference. In contrast, near-surface geostrophic wind (Wg) shows a strong response in the MIZ, where a good spatial correspondence exists among the Laplacian of the sea level pressure (SLP), the surface-wind convergence, and the vertical motion within the ABL. This indicates that SIC affects Wg through variation in SLP but on a much narrower scale. Larger-amplitude and broader-scale response in W10 implies that surface-wind stress derived from Wg to drive ice-ocean models may not fully reflect the effect of SIC changes.

Seo, Hyodae; Yang, Jiayan

2013-11-01

21

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

22

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

23

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

24

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

25

Response Timescales and Multiple Equilibria in Boundary-Layer Cloud-Aerosol Interaction  

NASA Astrophysics Data System (ADS)

Large-eddy simulations (LES) of subtropical stratocumulus-topped boundary layers coupled to an interactive aerosol model are run for multiday periods to examine their coupled equilibria and adjustment timescales. The LES includes two-moment Morrison microphysics, interactive radiation, and Razzak-Ghan cloud droplet activation from a single log-normal size distribution of hygroscopic aerosol with prognosed total aerosol mass and number. The aerosol evolves due to surface and entrainment sources, dry coalescence, precipitation sinks coupled to the Morrison microphysics due to autoconversion and accretion of cloud droplets (and a source due to raindrop evaporation), and cloud and rain scavenging of interstitial aerosol. Simulations are initialized with an idealized southeast Pacific stratocumulus sounding based on observations during VOCALS REx and forced with specified SST, mean subsidence, geostrophic wind, and free-tropospheric aerosol concentration. The surface aerosol source is based on the Clarke parameterization for the dependence of sea-salt number concentration on wind speed. Both surface and free-tropospheric aerosol are assumed to quickly grow to a specified size due to a surface DMS source. The goal is to explore the adjustment timescales and long-term equilibria produced by this model, to compare with studies such as Wood et al. (2012) that postulate that remote marine boundary layer aerosol concentrations are controlled as much by the precipitation sink as the surface and entrainment sources. We show that the coupled cloud-aerosol model supports rapid transitions from a solid, high aerosol, stratocumulus-capped state to a cumulus-like state reminisniscent of pockets of open cells as the liquid water path rises above a threshold supporting sufficient precipitation. The system can support multiple long-term equilibria for the same boundary forcing, or slow oscillations between a collapsed POC-like state and a deepening, thickening stratocumulus-capped boundary layer for other plausible choices of forcing. The behavior of the system is analyzed in terms of a two-dimensional 'slow manifold' characterized by the boundary-layer mean depth and aerosol number concentration.

Bretherton, C. S.; Berner, A.; Wood, R.

2012-12-01

26

The Boundary Layer Radiometer  

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

27

Boundary-Layer & health  

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

28

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

29

Response of the atmospheric boundary layer to a mesoscale oceanic eddy in the northeast Atlantic  

NASA Astrophysics Data System (ADS)

Fields of air-sea turbulent fluxes and bulk variables were derived from satellite sensor data from February to April 2001, over a region of the northeast Atlantic where a field experiment, Programme Océan Multidisciplinaire Meso Echelle (POMME), was conducted. The satellite products are in good agreement with in situ data in terms of heat fluxes, sea surface temperature, and wind speed. The central part of the experimental domain presented a cyclonic eddy in the ocean, which corresponded to a cold sea surface temperature (SST) anomaly. Winds were weaker within the eddy than outside of it, with lower latent and sensible heat loss. In order to analyze the relationship between the SST and wind anomalies, three numerical experiments were conducted with a regional atmospheric model. Three 3-month runs of the model were performed, using a realistic SST field, a smoothed SST field in which the cold SST was not present (reference run), and an SST field where the cold anomaly was increased by two degrees, successively. The fields simulated with the realistic SST were consistent with satellite sensor derived observations. In particular, the weak wind area over the cold SST anomaly was successfully rendered, whereas it was not present in the forcing fields. Taken individually, the three runs did not reveal the presence of secondary circulations. However, anomalous secondary circulations were clearly identified with respect to the reference run. The origin of the latter circulations was investigated with the Giordani and Planton generalization of the Sawyer-Eliassen equations. According to our results, differential heating induced by the cold SST anomaly mostly altered the vertical wind through the effect of friction and only marginally through pressure gradient forces. In the upper part of the boundary layer, the wind speed increased (decreased) over (downstream) the cold SST. We found that stability was the main factor that induced the simulated patterns of the friction term in the diagnostic equations. Therefore our results show that mesoscale wind patterns were significantly affected by SST gradients through the effect of stability, in a region of low oceanic eddy activity.

Bourras, Denis; Reverdin, Gilles; Giordani, Hervé; Caniaux, Guy

2004-09-01

30

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

31

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

32

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

33

Experimental Measurement of Transonic Fan Wake Response to Uniform and Simulated Boundary Layer Ingesting Inlet Flows  

NASA Technical Reports Server (NTRS)

BWB Aircraft with embedded engines and BLI inlets offer attractive advantages in terms of reduced noise from engines and increased range and fuel economy. The BLI inlet produces inlet distortion patterns that can reduce fan performance and stall margin, and can produce undesirable forced responses. Knowledge of the dynamic response of fan flow when subjected to flow distortions of the type produced by BLI inlets is important for the design of distortion tolerant fans. This project is investigating fan response to flow distortion by measuring the response of the fan of a JT15D engine to a flow pattern following the results of the NASA Inlet A BLI wind tunnel tests.

O'Brien, Walter F.; Ferrar, Anthony M.; Arend, David

2011-01-01

34

``Broadband'' plasma waves in the boundary layers  

Microsoft Academic Search

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

35

Studies of hypersonic boundary layer behavior  

Microsoft Academic Search

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

36

The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion  

NASA Astrophysics Data System (ADS)

A direct numerical simulation study is presented, which examines the response of a spatially developing boundary layer to oscillatory spanwise wall motion imposed over a limited streamwise stretch. At the heart of the study is the dependence of the streamwise variations in skin friction and turbulence properties on the period of the oscillatory motion, with particular emphasis placed on the behaviour downstream of the start of the actuation. The friction Reynolds number just upstream of the actuation is Re? = 520, and the wall-scaled actuation period, T+ = Tu?2/?, covers the range 80-200. In contrast to channel flow, the present configuration allows the processes during the transition stretch from the unactuated state to the low-drag state and the recovery from the low-drag state to be studied. Attention focuses primarily on the former. Results are included for the time-averaged turbulent stresses, their budgets and probability-density functions, as well as a range of phase-averaged properties. The study brings out, for low-drag conditions, a number of features and processes that are common with those in actuated channel flow, but suggests that the maximum drag-reduction margins are lower than those in equivalent channel flow, and that the optimum actuation period is significantly shorter. The transition to the low-drag state occurs over about 5 boundary-layer thicknesses, and is characterised by substantial oscillations in all phase-averaged properties. These oscillations, provoked at the start of the spanwise motion, propagate convectively as waves and decay as the low-drag state is approached. The interactions contributing to the oscillations are discussed as part of the analysis of phase-averaged quantities.

Lardeau, Sylvain; Leschziner, Michael A.

2013-07-01

37

Soot and radiation in combusting boundary layers  

Microsoft Academic Search

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

38

Soot and radiation in combusting boundary layers  

Microsoft Academic Search

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

39

Boundary Layer Cloudiness Parameterizations Using ARM Observations  

SciTech Connect

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

40

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

41

Response of the topography and gravity field on Venus to mantle upwelling beneath a chemical boundary layer  

NASA Technical Reports Server (NTRS)

The long wavelength correlation of the gravity and topography and the large apparent depths of compensation (approximately 150-300 km) for large highland regions on Venus require significant differences between the interior structure of Earth and Venus. The morphology, geologic history, and large apparent depths of compensation for many highlands have been interpreted to indicate areas of mantle upwelling. A large apparent depth of compensation at a mantle upwelling is generally interpreted to indicate the base of the thermal boundary layer of convection. A boundary layer thickness of 150-300 km implies that the interior of Venus is presently much colder than Earth and thus tectonically less active. The recent Magellan mission has provided contradictory evidence regarding the present level of tectonic activity on Venus, prompting considerable debate. In this study, we investigate the possibility that a chemical boundary layer acts together with a thermal boundary layer to produce large apparent depths of compensation, or equivalently, large geoid-to-topography-ratios (GTR's). The crust of a planet forms through partial melting of mantle materials. Both the melt and the residuum are lower in density than unmelted (or undepleted) mantle. In the absence of vigorous plate tectonics, a thick layer of buoyant residuum, or depleted mantle, may collect beneath the lithosphere. In this scenario, the thermal lithosphere does not need to be thick and cold to match the GTR's. Cooling of the depleted layer may lead to overturn of the upper mantle and episodic resurfacing with time scales on the order of 300-500 MY, consistent with the resurfacing age of Venus.

Smrekar, Suzanne E.; Parmentier, E. Marc

1993-01-01

42

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

43

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

44

Effects of Boundary Conditions on Thermal Response of a Cellulose Acetate Layer Using Hottel’s Zonal Method  

Microsoft Academic Search

Energy can transfer internally by radiation in addition to conduction in translucent polymers. Since radiant propagation is very rapid, it can provide energy within the layer more quickly than diffusion by heat conduction. Thus, the transient thermal response of a layer for combined radiative and conduction may be extremely different from that of conduction alone. In this paper, the behavior

Babak Safavisohi; Ehsan Sharbati; Cyrus Aghanajafi; Seyed Reza Khatami Firoozabadi

2006-01-01

45

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

46

Numerical simulation of shock wave-turbulent boundary layer interaction  

Microsoft Academic Search

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

47

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

48

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

49

Boundary layer theory and subduction  

SciTech Connect

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

50

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

51

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

52

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

53

Cyclone separator having boundary layer turbulence control  

DOEpatents

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

54

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

55

Observed response of the marine atmospheric boundary layer to the Southern Ocean fronts during the IPY BGH 2008 cruise  

NASA Astrophysics Data System (ADS)

A set of meteorological instruments was added to an oceanographic cruise crossing the Southern Ocean from Cape Town to 57°33' S on board the R/V Marion Dufresne during the summer 2008. The Cape Cauldron, the subtropical, subantarctic, polar and southern Antarctic circumpolar current fronts were successively crossed. The recorded data permitted to derive the exchange of momentum, heat and water vapour at the ocean-atmosphere interface. A set of 38 radiosonde releases complemented the dataset. The marine atmospheric boundary layer characteristics and air-sea interaction when ship crossed the fronts and eddies are discussed. The specific role of the atmospheric synoptic systems advection on the air-sea interaction is highlighted over these regions. The dynamic associated with these systems drive the vertical mixing of the MABL by wind shear effect and/or the vertical thermal mixing. The MABL is stabilized (destabilized) and mixing is inhibited (enhanced) over the warm front sides if meridional wind component is northerly (southerly).

Messager, C.; Speich, S.; Key, E.

2012-03-01

56

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

57

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

58

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

59

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

60

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

61

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

62

SH Wave Number Green's Function for a Layered, Elastic Half-Space. Part I: Theory and Dynamic Canyon Response by the Discrete Wave Number Boundary Element Method  

NASA Astrophysics Data System (ADS)

We present a closed-form frequency-wave number (? - k) Green's function for a layered, elastic half-space under SH wave propagation. It is shown that for every (? - k) pair, the fundamental solution exhibits two distinctive features: (1) the original layered system can be reduced to a system composed by the uppermost superficial layer over an equivalent half-space; (2) the fundamental solution can be partitioned into three different fundamental solutions, each one carrying out a different physical interpretation, i.e., an equivalent half-space, source image impact, and dispersive wave effect, respectively. Such an interpretation allows the proper use of analytical and numerical integration schemes, and ensures the correct assessment of Cauchy principal value integrals. Our method is based upon a stiffness-matrix scheme, and as a first approach we assume that observation points and the impulsive SH line-source are spatially located within the uppermost superficial layer. We use a discrete wave number boundary element strategy to test the benefits of our fundamental solution. We benchmark our results against reported solutions for an infinitely long circular canyon subjected to oblique incident SH waves within a homogeneous half-space. Our results show an almost exact agreement with previous studies. We further shed light on the impact of horizontal strata by examining the dynamic response of the circular canyon to oblique incident SH waves under different layered half-space configurations and incident angles. Our results show that modifications in the layering structure manifest by larger peak ground responses, and stronger spatial variability due to interactions of the canyon geometry with trapped Love waves in combination with impedance contrast effects.

Restrepo, Doriam; Gómez, Juan David; Jaramillo, Juan Diego

2014-02-01

63

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

64

BUBBLE – an Urban Boundary Layer Meteorology Project  

Microsoft Academic Search

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

65

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

66

Boundary Layer Clouds and Vegetation–Atmosphere Feedbacks  

Microsoft Academic Search

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

67

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

68

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

69

Vortex filament stability and boundary layer dynamics  

SciTech Connect

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

70

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

71

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

72

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

73

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

74

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

75

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

76

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

77

Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow  

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

78

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

79

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

80

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

81

A novel technique for response function determination of shear sensitive cholesteric liquid crystals for boundary layer investigations  

Microsoft Academic Search

A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength

D. S. Parmar

1991-01-01

82

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

83

Rethinking the Boundaries: Response  

ERIC Educational Resources Information Center

In his Keynote address, Dr. Kretchmar suggests that children who demonstrate an inability or unwillingness to play may have a "play disability," and thus offers interventions for remediation. In response, Oslin and Collier argue that due to cultural influences, it is more likely that physical educators are play disabled. Oslin and Collier share…

Oslin, Judy; Collier, Connie

2012-01-01

84

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

85

A novel technique for response function determination of shear sensitive cholesteric liquid crystals for boundary layer investigations  

NASA Technical Reports Server (NTRS)

A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength of the incident light. Application of a step input shear stress results in a liquid crystal time response that can be described as consisting of an initial delay, a shear induced helix deformation, and a relaxation to the initial state through diffusion processes. The method has been used for quantitative calibration of a shear sensitive liquid crystal by observing the peak in reflected light intensity, at a given wavelength, as a function of the shear stress.

Parmar, D. S.

1991-01-01

86

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

87

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

88

Convection in the atmospheric boundary layer  

Microsoft Academic Search

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

89

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

90

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

91

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

92

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

93

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

94

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

95

INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT  

EPA Science Inventory

Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

96

Secondary three-dimensional instability in compressible boundary layers  

NASA Technical Reports Server (NTRS)

Three dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting waves. The focus is on principal parametric resonance responsible for strong growth of subharmonics in low disturbance environment.

El-Hady, Nabil M.

1989-01-01

97

Oscillations of the Boundary Layer and High-frequency QPOs  

NASA Astrophysics Data System (ADS)

We observed persistent high-frequency oscillations of the boundary layer near an accreting, weakly-magnetized star in global 3D MHD simulations. The tilted dipole magnetic field is not strong enough to open a gap between the star and the disk. Instead, it forms a highly-wrapped azimuthal field near the surface of the star which slows down rotation of the disk matter, while a small tilt of the field excites oscillations of the boundary layer with a frequency below the Keplerian frequency. This mechanism may be responsible for the high-frequency oscillations in accreting neutron stars, white dwarfs and classical T Tauri stars.

Blinova, A. A.; Bachetti, M.; Romanova, M. M.

2014-01-01

98

Bursting frequency prediction in turbulent boundary layers  

SciTech Connect

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

99

Method for laminar boundary layer transition visualization in flight  

NASA Technical Reports Server (NTRS)

Disclosed is a method of visualizing laminar to turbulent boundary layer transition, shock location, and laminar separation bubbles around a test surface. A liquid crystal coating is formulated using an unencapsulated liquid crystal operable in a temperature bandwidth compatible with the temperature environment around the test surface. The liquid crystal coating is applied to the test surface, which is preferably pretreated by painting with a flat, black paint to achieve a deep matte coating, after which the surface is subjected to a liquid or gas flow. Color change in the liquid crystal coating is produced in response to differences in relative shear stress within the boundary layer around the test surface. The novelty of this invention resides in the use of liquid crystals which are sensitive to shear stress to show aerodynamic phenomena such as a boundary layer transition, shock location, and laminar separation bubbles around a test surface.

Holmes, Bruce J. (inventor); Gall, Peter D. (inventor)

1988-01-01

100

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

101

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

102

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

103

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

104

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

105

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

106

Interaction between soil hydrology and boundary-layer development  

Microsoft Academic Search

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

107

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

108

Dynamical modeling of marine boundary layer convection  

Microsoft Academic Search

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

109

Dynamical Modeling of Marine Boundary Layer Convection  

Microsoft Academic Search

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

110

Lidar probing the urban nocturnal boundary layer  

Microsoft Academic Search

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

111

Turbulent boundary layer studies using polynomial interpolation  

Microsoft Academic Search

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

112

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

113

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

114

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

115

A new urban boundary layer and dispersion parameterization for an emergency response modeling system: Tests with the Joint Urban 2003 data set  

NASA Astrophysics Data System (ADS)

A new urban parameterization for a fast-running dispersion prediction modeling system suitable for emergency response situations is introduced. The parameterization represents the urban convective boundary layer in the dispersion prediction system developed by the National Atmospheric Release Advisory Center (NARAC) at Lawrence Livermore National Laboratory. The performance of the modeling system is tested with data collected during the field campaign Joint Urban 2003 (JU03), held in July 2003 in Oklahoma City, Oklahoma. Tests were performed using data from three intense operating periods held during daytime slightly unstable to unstable conditions. The system was run in operational mode using the meteorological data that would be available operationally at NARAC to test its effectiveness in emergency response conditions. The new parameterization considerably improves the performance of the original modeling system, by producing a better degree of pattern of correspondence between predictions and observations (as measured by Taylor diagrams), considerably reducing bias, and better capturing directional effects resulting in plume predictions whose shape and size better resemble the observations (via the measure of effectiveness). Furthermore, the new parameterization shows similar skills to urban modeling systems of similar or greater complexity. The parameterization performs the best at the three JU03 sensor arcs (1, 2, and 4 km downwind the release points), with fractional bias values ranging from 0.13 to 0.4, correlation values from 0.45 to 0.71, and centered root-mean-square error being reduced more than 50% in most cases. The urban parameterization has been tested with grid increments of 125, 250, 500 and 1000 m, performing best at 250 and 500 m. Finally, it has been found that representing the point source by a Gaussian distribution with an initial spread of particles leads to a better representation of the initial spread induced by near-source buildings, resulting in lower bias and improved correlation in downtown Oklahoma City.

Delle Monache, Luca; Weil, Jeffrey; Simpson, Matthew; Leach, Marty

2009-12-01

116

Additive thermochemical effects in turbulent erosive boundary layers  

SciTech Connect

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

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

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

120

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

121

Boundary layer transition and separation on a compressor rotor airfoil  

SciTech Connect

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

122

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

123

THE EFFECTS OF PERIODIC WAKE STRUCTURES ON TURBULENT BOUNDARY LAYERS  

Microsoft Academic Search

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

124

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

125

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

126

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

127

Laminarization of Turbulent Boundary Layer on Flexible and Rigid Surfaces  

NASA Technical Reports Server (NTRS)

An investigation of the control of turbulent boundary layer flow over flexible and rigid surfaces downstream of a concave-convex geometry has been made. The concave-convex curvature induces centrifugal forces and a pressure gradient on the growth of the turbulent boundary layer. The favorable gradient is not sufficient to overcome the unfavorable; thus, the net effect is a destabilizing, of the flow into Gortler instabilities. This study shows that control of the turbulent boundary layer and structural loading can be successfully achieved by using localized surface heating because the subsequent cooling and geometrical shaping downstream over a favorable pressure gradient is effective in laminarization of the turbulence. Wires embedded in a thermally insulated substrate provide surface heating. The laminarized velocity profile adjusts to a lower Reynolds number, and the structure responds to a lower loading. In the laminarization, the turbulent energy is dissipated by molecular transport by both viscous and conductivity mechanisms. Laminarization reduces spanwise vorticity because of the longitudinal cooling gradient of the sublayer profile. The results demonstrate that the curvature-induced mean pressure gradient enhances the receptivity of the flow to localized surface heating, a potentially viable mechanism to laminarize turbulent boundary layer flow; thus, the flow reduces the response of the flexible structure and the resultant sound radiation.

Maestrello, Lucio

2001-01-01

128

Boundary Layer Relaminarization and High-Lift Aerodynamics  

NASA Astrophysics Data System (ADS)

Modern high-lift devices are complicated systems that exhibit a variety of complex flow physics phenomena. Thomas( Thomas, F.O., Liu, X., & Nelson, R.C., 1997, ``Experimental Investigation of the Confluent Boundary Layer of a High-Lift System,'' AIAA Paper 97-1934.) outlines several critical flow phenomena, dubbed ``high-lift building block flows'', that can be found in a typical multi-element high-lift system. One such high-lift building block flow is turbulent boundary layer relaminarization, which may be responsible for such phenomena as ``inverse Reynolds number effects.'' Flight test experiments on leading edge transition and relaminarization conducted by Yip, et al(Yip, et al), ``The NASA B737-100 High-Lift Flight Research Program--Measurements and Computations,'' Aeronautical Journal, Paper No. 2125, Nov. 1995. using the NASA Transport Systems Research Vehicle, a Boeing 737-100, have provided tantalizing evidence but not proof of the existence of relaminarization in high-lift systems. To investigate the possibility of boundary layer relaminarization occuring on a high-lift system, a joint wind tunnel/flight test program is in progress with the NASA Dryden Flight Research Center to determine the role, if any, that turbulent boundary layer relaminarization plays in high-lift aerodynamics. Sponsored under NASA grant No. NAG4-123

Bourassa, Corey; Thomas, Flint O.; Nelson, Robert C.

1998-11-01

129

An Experimental Investigation Of A Highly Accelerated Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

An investigation of a highly accelerated turbulent boundary layer (Re_? = 5000) is in progress at the Hessert Center for Aerospace Research at the University of Notre Dame. Unique to this experiment is the ability to expose the boundary layer to a range of favorable pressure gradients in which the acceleration parameter K = frac?u^2 fracdudx is maintained constant over an appreciable streamwise distance. Values of 0.5 x 10-6 < K < 4.5 x 10-6 have been investigated. The objective of the research is to elucidate the fundamental mechanisms responsible for turbulent boundary layer relaminarization, or reverse transition, by examining the underlying flow structure of the turbulent boundary layer and exploring how these structures change during rapid flow acceleration. Results to be discussed include profiles of the mean velocity, fluctuating streamwise and wall normal velocity, and the Reynolds stress. In addition, skin friction values measured using oil film interferometry, flow visualization results, and preliminary 2D PIV velocity contours will be presented.

Bourassa, Corey; Thomas, Flint; Nelson, Robert

2001-11-01

130

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

131

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

132

The minisodar and planetary boundary layer studies  

SciTech Connect

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

133

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

134

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

135

Partially exposed polymer dispersed liquid crystals for boundary layer investigations  

NASA Technical Reports Server (NTRS)

A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.

Parmar, Devendra S.; Singh, Jag J.

1992-01-01

136

Boundary layer elasto-optic switching in ferroelectric liquid crystals  

NASA Technical Reports Server (NTRS)

The first experimental observation of a change in the director azimuthal angle due to applied shear stress is reported in a sample configuration involving a liquid-crystal-coated top surface exposed directly to gas flow. The electrooptic response caused by the shear stress is large, fast, and reversible. These findings are relevant to the use of liquid crystals in boundary layer investigations on wind tunnel models.

Parmar, D. S.

1992-01-01

137

Soot profiles in boundary-layer flames  

SciTech Connect

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

138

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

139

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

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

Simple Lagrangian formulation of bubbly flow in a turbulent boundary layer (bubbly boundary layer flow)  

Microsoft Academic Search

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

142

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

143

Boundary Layer Resolving Pseudospectral Methods For Singular Perturbation Problems  

Microsoft Academic Search

. 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

144

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

145

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

146

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

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

Turbulence measurements in hypersonic boundary layers using constant-temperature anemometry and Reynolds stress measurements in hypersonic boundary layers  

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

149

DYNAMIC BOUNDARY CONTROL OF BEAMS USING ACTIVE CONSTRAINED LAYER DAMPING  

Microsoft Academic Search

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

150

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

151

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

152

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

153

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

154

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

SciTech Connect

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

155

The Interaction between a Compliant Material and an Unstable Boundary Layer Flow  

NASA Astrophysics Data System (ADS)

The response of a compliant coating to pressure fluctuations due to an unsteady boundary layer flow and the effect of the response on the stability of the flow field are examined. A pseudospectral solution of the Navier-Stokes equations is coupled to a finite element calculation of the behavior of the compliant material. In particular, the effect of material response on the growth rate of a Tollmien-Schlichting type instability in an unstable boundary layer is examined. Results are presented for three materials; a soft polyvinylchloride (PVC), a stiffer PVC, and a two-layer material consisting of a thick layer of soft PVC covered by a thin layer of neoprene.

Hall, M. S.

1988-05-01

156

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

157

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

158

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

159

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

160

Boundary-layer wind structure in a landfalling tropical cyclone  

Microsoft Academic Search

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

161

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

162

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

163

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

164

Simulation and optimal control of wind-farm boundary layers  

NASA Astrophysics Data System (ADS)

In large wind farms, the effect of turbine wakes, and their interaction leads to a reduction in farm efficiency, with power generated by turbines in a farm being lower than that of a lone-standing turbine by up to 50%. In very large wind farms or `deep arrays', this efficiency loss is related to interaction of the wind farms with the planetary boundary layer, leading to lower wind speeds at turbine level. Moreover, for these cases it has been demonstrated both in simulations and wind-tunnel experiments that the wind-farm energy extraction is dominated by the vertical turbulent transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate the use of optimal control techniques combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large `infinite' wind farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with actuator-disk and actuator-line representations of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind that combines Fourier-spectral discretization in horizontal directions with a fourth-order finite-volume approach in the vertical direction. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in an actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. Optimal model-predictive control (or optimal receding horizon control) is used, where the model simply consists of the full LES equations, and the time horizon is approximately 280 seconds. The optimization is performed using a nonlinear conjugate gradient method, and the gradients are calculated by solving the adjoint LES equations. We find that the extracted farm power increases by approximately 20% when using optimal model-predictive control. However, the increased power output is also responsible for an increase in turbulent dissipation, and a deceleration of the boundary layer. Further investigating the energy balances in the boundary layer, it is observed that this deceleration is mainly occurring in the outer layer as a result of higher turbulent energy fluxes towards the turbines. In a second optimization case, we penalize boundary-layer deceleration, and find an increase of energy extraction of approximately 10%. In this case, increased energy extraction is balanced by a reduction in of turbulent dissipation in the boundary layer. J.M. acknowledges support from the European Research Council (FP7-Ideas, grant no. 306471). Simulations were performed on the computing infrastructure of the VSC Flemish Supercomputer Center, funded by the Hercules Foundation and the Flemish Government.

Meyers, Johan; Goit, Jay

2014-05-01

165

Observations of mesoscale and boundary-layer circulations affecting dust uplift and transport in the Saharan boundary layer  

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

166

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.

167

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.

168

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

169

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

170

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

171

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

172

Boundary Layer Control by Means of Plasma Actuators  

SciTech Connect

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

173

Aeromechanics Analysis of a Boundary Layer Ingesting Fan  

NASA Technical Reports Server (NTRS)

Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn but these systems must overcome the challe nges related to aeromechanics-fan flutter stability and forced response dynamic stresses. High-fidelity computational analysis of the fan a eromechanics is integral to the ongoing effort to design a boundary layer ingesting inlet and fan for fabrication and wind-tunnel test. A t hree-dimensional, time-accurate, Reynolds-averaged Navier Stokes computational fluid dynamics code is used to study aerothermodynamic and a eromechanical behavior of the fan in response to both clean and distorted inflows. The computational aeromechanics analyses performed in th is study show an intermediate design iteration of the fan to be flutter-free at the design conditions analyzed with both clean and distorte d in-flows. Dynamic stresses from forced response have been calculated for the design rotational speed. Additional work is ongoing to expan d the analyses to off-design conditions, and for on-resonance conditions.

Bakhle, Milind A.; Reddy, T. S. R.; Herrick, Gregory P.; Shabbir, Aamir; Florea, Razvan V.

2013-01-01

174

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

175

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

176

Development of instrumentation for boundary layer transition detection  

Microsoft Academic Search

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

177

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

178

Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration  

Microsoft Academic Search

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

179

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

180

The Application of Optimal Control to Boundary Layer Flow  

Microsoft Academic Search

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

181

Microbubble Drag Reduction in Liquid Turbulent Boundary Layers  

Microsoft Academic Search

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

182

Hypersonic boundary-layer stability across a compression corner  

NASA Astrophysics Data System (ADS)

Stability of a hypersonic boundary-layer over a compression corner was investigated numerically. The three-dimensional compressible Navier-Stokes equations were solved using a fifth-order weighted essentially non-oscillating (ArENO) shock capturing scheme to study the shock wave and boundary-layer interactions. The boundary-layer stability was studied in three distinct regions: upstream of the separation region, inside the separation region and downstream of the separation region. After the mean flow field was computed, linear stability theory was employed to predict the unstable disturbance modes in different flow regions and also to find the most amplified disturbance frequency across the compression corner. Gortler instability computations were performed to study the influence of the streamline curvatures on boundary-layer stability, and PSE(parabolized stability equation) method was employed to obtain the initial disturbances for direct numerical simulation. To study the boundary-layer stability by direct numerical simulation, two- or three-dimensional initial disturbances were introduced at the initial streamwise location of the computational domain. Two-dimensional disturbance evolution simulation shows that two-dimensional high frequency linear disturbances grow exponentially upstream and downstream of the separation region and remain neutral in the separation region, but two-dimensional low frequency linear disturbances only grow in a narrow area inside the separation region and remain neutral upstream and downstream of the separation region. Two-dimensional nonlinear disturbances will saturate downstream of the separation region when their amplitudes reach quit large amplitude. The three-dimensional disturbance evolution simulations show that three-dimensional linear mono-frequency disturbances are less amplified than its two-dimensional counterpart across the compression corner. The three-dimensional nonlinear mono-frequency disturbance evolution indicates that mode (0,2) is responsible for the oblique breakdown. Three-dimensional disturbances are much more amplified with the presence of two-dimensional primary disturbance due to the secondary instability. Finally, the simulations of three-dimensional random frequency disturbance evolution with the presence of a two-dimensional primary disturbance show that the secondary instability first occurs downstream of the separation region and a fundamental or K-type breakdown will be triggered by this secondary instability.

Zhao, Hongwu

183

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

184

Dusty boundary layer in a surface-burst explosion  

SciTech Connect

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

185

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

186

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

187

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

188

Brain response to prosodic boundary cues depends on boundary position.  

PubMed

Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)-marking the processing of a prosodic phrase boundary-was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context. PMID:23882234

Holzgrefe, Julia; Wellmann, Caroline; Petrone, Caterina; Truckenbrodt, Hubert; Höhle, Barbara; Wartenburger, Isabell

2013-01-01

189

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

190

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

191

Chemistry of a polluted cloudy boundary layer  

SciTech Connect

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

192

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

193

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

194

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

195

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

196

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

Microsoft Academic Search

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

197

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

Microsoft Academic Search

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

198

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

199

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

200

Formation of pre-sheath boundary layers in electronegative plasmas  

SciTech Connect

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

201

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

202

Stable boundary layer intermittent turbulence in Cases99  

NASA Astrophysics Data System (ADS)

Examination of turbulence in very stable boundary layers is complicated because the turbulence is not continuous, is intermittent or sporadic and the origin of this intermittence is not very well understood. There are several physical phenomena that can be related to it, as Kelvin-Helmholtz instabilities, gravity waves or elevated shears associated with low level jets. In this study we have focused our analysis in this latter phenomena when turbulence is predominantly generated at levels above the surface and transports downwards atmospheric quantities which have a very important role in controlling turbulent fluxes between the level of the jet and the surface. In addition, these turbulent fluxes modify some small scale phenomena as thin drainage flows generated in small scales slopes. To characterize this phenomenon, time series of wind components and temperature recorded at different levels have been analysed using wavelet methods. Data were collected during the CASES-99 experiment by fast-response instruments set up on a 60 m tower and a 10 m tower, this last located on a shallow gully. Wavelet-based analysis methods allow detection and characterisation of different turbulent structures. In addition, they provide an image of their time evolution and motion across different levels of the stable boundary layer.

Soler, M. R.; Ferreres, E.; Terradellas, E.; Cuxart, J.; Bravo, M.

2003-04-01

203

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

204

Turbulent boundary layer pressure field-induced vibrations in a thin flexible plate under water  

Microsoft Academic Search

Two point turbulent boundary layer pressure spectra at the wall were determined empirically in a low noise water tunnel. The measured pressure spectra were used in a linear theory to predict the response of a thin stainless steel rectangular plate attached to the water tunnel. The predicted responses were found to agree well with the measured responses of the plate.

Nilabh Narayan

1989-01-01

205

Turbulent Boundary Layer Pressure Field-Induced Vibrations in a Thin Flexible Plate Under Water  

Microsoft Academic Search

Two point Turbulent Boundary Layer pressure spectra at the wall were determined empirically in a low noise water tunnel. The measured pressure spectra were used in a linear theory to predict the response of a thin stainless steel rectangular plate attached to the water tunnel. The predicted responses were found to agree well with the measured responses of the plate.

Nilabh Narayan

1989-01-01

206

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

207

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

208

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

209

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

210

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

211

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

212

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

213

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

214

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

215

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

216

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

217

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

218

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

219

Chebyshev solution of laminar boundary layer flow  

Microsoft Academic Search

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

220

A Distributional Approach to the Boundary Layer Theory  

Microsoft Academic Search

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

221

Calculation of turbulent boundary layer wall pressure spectra  

Microsoft Academic Search

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

222

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

223

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

224

Boundary Layers in Self-Gravitating, Collisional Rings  

Microsoft Academic Search

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

225

Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer  

Microsoft Academic Search

:   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

226

A multidisciplinary optimization method for designing boundary layer ingesting inlets  

Microsoft Academic Search

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

227

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

228

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

229

Turbulent boundary layer in high rayleigh number convection in air.  

PubMed

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

230

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

231

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

232

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

SciTech Connect

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

233

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

234

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

235

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

236

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

237

BULK MODELS OF THE ATMOSPHERIC CONVECTIVE BOUNDARY LAYER  

Microsoft Academic Search

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

238

ON AERODYNAMIC AND BOUNDARY LAYER RESISTANCES WITHIN DRY DEPOSITION MODELS  

EPA Science Inventory

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...

239

Unsteady gun-barrel boundary-layer calculations  

Microsoft Academic Search

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

240

Optimal Control of Shock Wave Turbulent Boundary Layer Interactions Using Micro-Array Actuation  

NASA Technical Reports Server (NTRS)

The intent of this study on micro-array flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to determine optimal designs of micro-array actuation for controlling the shock wave turbulent boundary layer interactions within supersonic inlets and compare these concepts to conventional bleed performance. The term micro-array refers to micro-actuator arrays which have heights of 25 to 40 percent of the undisturbed supersonic boundary layer thickness. This study covers optimal control of shock wave turbulent boundary layer interactions using standard micro-vane, tapered micro-vane, and standard micro-ramp arrays at a free stream Mach number of 2.0. The effectiveness of the three micro-array devices was tested using a shock pressure rise induced by the 10 shock generator, which was sufficiently strong as to separate the turbulent supersonic boundary layer. The overall design purpose of the micro-arrays was to alter the properties of the supersonic boundary layer by introducing a cascade of counter-rotating micro-vortices in the near wall region. In this manner, the impact of the shock wave boundary layer (SWBL) interaction on the main flow field was minimized without boundary bleed.

Anderson, Bernhard H.; Tinapple, Jon; Surber, Lewis

2006-01-01

241

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

242

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

243

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

244

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

245

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

246

Interaction between a compliant material and an unstable boundary layer flow  

SciTech Connect

The response of a compliant coating to pressure fluctuations due to an unsteady boundary layer flow and the effect of the response on the stability of the flow field are examined. A pseudospectral solution of the Navier--Stokes equations is coupled to a finite element calculation of the behavior of the compliant material. In particular, the effect of material response on the growth rate of a Tollmien--Schlichting type instability in an unstable boundary layer is examined. Results are presented for three materials; a soft polyvinylchloride (PVC), a stiffer PVC, and a two-layer material consisting of a thick layer of soft PVC covered by a thin layer of neoprene. copyright 1988 Academic Press, Inc.

Hall, M.S.

1988-05-01

247

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

248

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

249

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

250

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.

251

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

252

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

253

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

254

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.

255

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

256

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

NASA Technical Reports Server (NTRS)

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

257

Active Flow Control on a Boundary-Layer-Ingesting Inlet  

NASA Technical Reports Server (NTRS)

Boundary layer ingestion (BLI) is explored as means to improve overall system performance for Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides framework within which to assess the benefits of an integrated BLI inlet and lays the groundwork for higher-fidelity systems studies. The results of the system study show that BLI provides a significant improvement in vehicle performance if the inlet distortion can be controlled, thus encouraging the pursuit of active flow control (AFC) as a BLI enabling technology. The effectiveness of active flow control in reducing engine inlet distortion was assessed using a 6% scale model of a 30% BLI offset, diffusing inlet. The experiment was conducted in the NASA Langley Basic Aerodynamics Research Tunnel with a model inlet designed specifically for this type of testing. High mass flow pulsing actuators provided the active flow control. 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 was determined by 120 total pressure measurements located at the aerodynamic interface plane. The test matrix was limited to a maximum freestream Mach number of 0.15 with scaled mass flows through the inlet for that condition. The data show that the pulsed actuation can reduce distortion from 29% to 4.6% as measured by the circumferential distortion descriptor DC60 using less than 1% of inlet mass flow. Closed loop control of the actuation was also demonstrated using a sidewall surface static pressure as the response sensor.

Gorton, Susan Althoff; Owens, Lewis R.; Jenkins, Luther N.; Allan, Brian G.; Schuster, Ernest P.

2004-01-01

258

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

259

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

260

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

261

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

262

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

263

Asymptotic analysis: Working note {number_sign}3, boundary layers  

SciTech Connect

In this chapter the authors discuss the asymptotic approximation of functions that display boundary-layer behavior. The purpose here is to introduce the basic concepts underlying the phenomenon, to illustrate its importance, and to describe some of the fundamental tools available for its analysis. To achieve their purpose in the clearest way possible, the authors will work with functions that are assumed to be given explicitly -- that is, functions f : (0,{epsilon}{sub 0}) {yields} X whose expressions are known, at least in principle. Only in the following chapter will they begin the study of functions that are given implicitly as solutions of boundary value problems -- the real stuff of which singular perturbation theory is made. Boundary-layer behavior is associated with asymptotic expansions that are regular {open_quotes}almost everywhere{close_quotes} -- that is, expansions that are regular on every compact subset of the domain of definition, but not near the boundary. These regular asymptotic expansions can be continued in a certain sense all the way up to the boundary, but a separate analysis is still necessary in the boundary layer. The boundary-layer analysis is purely local and aims at constructing local approximations in the neighborhood of each point of the singular part of the boundary. The problem of finding an asymptotic approximation is thus reduced to matching the various local approximations to the existing regular expansion valid in the interior of the domain. The authors are thinking, for example, of fluid flow (viscosity), combustion (Lewis number), and superconductivity (Ginzburg-Landau parameter) problems. Their solution may remain smooth over a wide range of parameter values, but as the parameters approach critical values, complicated patterns may emerge.

Garbey, M. [Universite Claude Bernard Lyon 1, Villeurbanne (France). Laboratoire d`Analyse Numerique; Kaper, H.G. [Argonne National Lab., IL (United States)

1993-09-01

264

Hypersonic flow separation in shock wave boundary layer interactions  

NASA Technical Reports Server (NTRS)

An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed.

Hamed, A.; Kumar, Ajay

1992-01-01

265

Effect of Blowing on Boundary Layer of Scarf Inlet  

NASA Technical Reports Server (NTRS)

When aircraft operate in stationary or low speed conditions, airflow into the engine accelerates around the inlet lip and pockets of turbulence that cause noise and vibration can be ingested. This problem has been encountered with engines equipped with the scarf inlet, both in full scale and in model tests, where the noise produced during the static test makes it difficult to assess the noise reduction performance of the scarf inlet. NASA Langley researchers have implemented boundary layer control in an attempt to reduce the influence of the flow nonuniformity in a 12-in. diameter model of a high bypass fan engine mounted in an anechoic chamber. Static pressures and boundary layer profiles were measured in the inlet and far field acoustic measurements were made to assess the effectiveness of the blowing treatment. The blowing system was found to lack the authority to overcome the inlet distortions. Methods to improve the implementation of boundary layer control to reduce inlet distortion are discussed.

Gerhold, Carl H.; Clark, Lorenzo R.

2004-01-01

266

Turbulence in the convective boundary layer observed by microwave interferometry  

SciTech Connect

A 9-antenna, 400 meter microwave interferometer was utilized in SALSA MEX on the San Pedro River area in July and August, 1997, to measure the turbulence in the Convective Boundary Layer. Water vapor has an appreciable index of refraction at radio frequencies around 10 GHz, and acts as a passive tracer of the magnitude and motion of turbulence. The relative phase changes of a signal from a satellite were tracked by an array of 9 antennas, and the phase differences between antennas were then used to derive the turbulence properties of the boundary layer. Preliminary analysis shows clearly different characteristics for the convection activity of the boundary layer between day and night. From the structure function analysis they can see that the turbulence structure starts to decorrelate at scale sizes of 200 meters for a temporal passband around 100 seconds. Derivation of average wind fields is currently in process.

Shao, X.M.; Carlos, R.C.; Kirkland, M.W.

1997-12-01

267

The Turbulent Boundary Layer on a Rough Curvilinear Surface  

NASA Technical Reports Server (NTRS)

A number of semiempirical approximate methods exist for determining the characteristics of the turbulent boundary layer on a curvilinear surface. At present, among these methods, the one proposed by L. G. Loitsianskii is given frequent practical application. This method is sufficiently effective and permits, in the case of wing profiles with technically smooth surfaces, calculating the basic characteristics of the boundary layer and the values of the overall drag with an accuracy which suffices for practical purposes. The idea of making use of the basic integral momentum equation ((d delta(sup xx))/dx) + ((V' delta(sup xx))/V) (2 + H) = (tau(sub 0))/(rho V(exp 2)) proves to be fruitful also for the solution of the problems in the determination of the characteristics of the turbulent boundary layer on a rough surface.

Droblenkov, V. F.

1958-01-01

268

The phase-dependence of a swirling, turbulent boundary layer  

NASA Astrophysics Data System (ADS)

Measurements have been made in a swirling turbulent boundary layer affected by the angular momentum instability. The flow field seen by a rotating observer was obtained from a fixed hot-wire probe using the technique of phase-locked averaging. The instability is localized to the wall region of the boundary layer and there is some evidence that it has produced 'streamwise' vortices analogous to the Taylor-Goertler vortices in a boundary layer on a concave wall. The mean velocities and Reynolds stresses show a significant phase dependence which appears to originate in the swirl generator. The conventional Reynolds stresses are not equally affected by the phase dependence and this has implications for the turbulence modeling of swirling flows.

Koh, S. G.; Clausen, P. D.; Wood, D. H.

269

Boundary layer effects on particle impaction and capture  

NASA Technical Reports Server (NTRS)

The inertial impaction and deposition of small particles on larger bodies with viscous boundary layers are considered theoretically, in a detailed comment on a paper by Menguturk et al. (1983). Topics addressed include cushion effects, the dimensionless groups corresponding to the diameter range (3-6 microns) examined by Menguturk et al. in a numerical example, analogous effects of particle-gas energy and mass exchange in boundary layers, and the combined effects of particle inertia and diffusion. It is argued that the inertial effects can be characterized in terms of a body, boundary-layer, or sublayer Stokes number. In a reply by Menguturk et al., the focus is on the application of the theoretical model to the erosion of blade surfaces in large gas turbines; the Stokes number is found to be of limited practical value in these cases, because the particle motion is not primarily normal to the blade surfaces.

Rosner, D. E.; Fernandez De La Mora, J.

1984-01-01

270

Numerical Simulations of Wake/Boundary Layer Interactions  

NASA Technical Reports Server (NTRS)

Direct and large-eddy simulations of the interaction between the wake of a circular cylinder and a flat-plate boundary layer are conducted. Two Reynolds numbers are examined. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re(sub theta) achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established.

Piomelli, Ugo; Choudhari, Meelan M.; Ovchinnikov, Victor; Balaras, Elias

2003-01-01

271

DNS of Turbulent Boundary Layers under Highenthalpy Conditions  

NASA Astrophysics Data System (ADS)

To study real-gas effects and turbulence-chemistry interaction, direct numerical simulations (DNS) of hypersonic boundary layers are conducted under typical hypersonic conditions. We consider the boundary layer on a lifting-body consisting of a flat plate at an angle of attack, which flies at altitude 30km with a Mach number 21. Two different inclined angles, 35^o and 8^o, are considered,representing blunt and slender bodies. Both noncatalytic and supercatalytic wall conditions are considered. The DNS data are studied to assess the validity of Morkovin's hypothesis, the strong Reynolds analogy, as well as the behaviors of turbulence structures under high-enthalpy conditions.Relative to low-enthalpy conditions [1], significant differences in typical scalings are observed. [4pt] [1] L. Duan and I. Beekman and M. P. Mart'in, Direct numerical simulation of hypersonic turbulent boundary layers. Part 2: Effect of temperature, J. Fluid Mech. 655 (2010), 419-445.

Duan, Lian; Martín, Pino

2010-11-01

272

Blow-up and control of marginally separated boundary layers.  

PubMed

Interactive solutions for steady two-dimensional laminar marginally separated boundary layers are known to exist up to a critical value Gamma(c) of the controlling parameter (e.g. the angle of attack of a slender airfoil) Gamma only. Here, we investigate three-dimensional unsteady perturbations of such boundary layers, assuming that the basic flow is almost critical, i.e. in the limit Gamma(c)-Gamma-->0. It is then shown that the interactive equations governing such perturbations simplify significantly, allowing, among others, a systematic study of the blow-up phenomenon observed in earlier investigations and the optimization of devices used in boundary-layer control. PMID:16105768

Braun, Stefan; Kluwick, Alfred

2005-05-15

273

Simple turbulence models and their application to boundary layer separation  

NASA Technical Reports Server (NTRS)

Measurements in the boundary layer and wake of a stalled airfoil are presented in two coordinate systems, one aligned with the airfoil chord, the other being conventional boundary layer coordinates. The NACA 4412 airfoil is studied at a single angle of attack corresponding to maximum lift, the Reynolds number based on chord being 1.5 x 10 to the 6th power. Turbulent boundary layer separation occurred at the 85 percent chord position. The two-dimensionality of the flow was documented and the momentum integral equation studied to illustrate the importance of turbulence contributions as separation is approached. The assumptions of simple eddy-viscosity and mixing-length turbulence models are checked directly against experiment. Curvature effects are found to be important as separation is approached.

Wadcock, A. J.

1980-01-01

274

A modeling study of boundary layer processes associated with ozone layers observed during the 1993 North Atlantic Regional Experiment  

NASA Astrophysics Data System (ADS)

Boundary layer processes associated with three pollution events during the North Atlantic Regional Experiment (NARE) 1993 field campaign are examined using airborne measurements and a Lagrangian particle dispersion model in conjunction with a mesoscale model employing four-dimensional data assimilation. This nonphotochemical modeling system was able to qualitatively reproduce many of the observed features during a 15-day period of the NARE field campaign. Simulated particle releases from urban regions within the daytime convective boundary layer were transported to heights up to 2 km above ground level. Particles located in the upper part of the residual layer in the early evening hours were quickly advected by higher wind speeds aloft to the sampling domain; however, particles released within the nocturnal stable boundary layer or the marine boundary layer remained within 200 m of the surface and often exhibited complex circulation patterns. As a consequence of the diurnal boundary layer characteristics, emissions released within a relatively close time interval were often found to have significantly different trajectories. Mixing of particles from various source regions results in a plume that does not have a unique age but is better characterized by a distribution of ages which vary with altitude. It is shown that much of the layering over Yarmouth is well established by convective boundary layer processes and vertical wind shears prior to the air masses leaving land. As expected, sea surface temperatures were found to play an important role in defining the vertical gradient of potential temperature and hence the amount of vertical mixing over the Gulf of Maine. Peak particle concentrations within 1 km of the ocean were often associated with a low-level jet over the Gulf of Maine. A common feature during the analysis period is synoptic-scale lifting in advance of low-pressure systems which appears to be partially responsible for lifting particles to the heights observed over Yarmouth.

Fast, Jerome D.; Berkowitz, Carl M.

1996-12-01

275

Kahuku kite wind study. I. Kahuka beach boundary layer  

SciTech Connect

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

276

Receptivity of Hypersonic Boundary Layers over Straight and Flared Cones  

NASA Technical Reports Server (NTRS)

The effects of adverse pressure gradients on the receptivity and stability of hypersonic boundary layers were numerically investigated. Simulations were performed for boundary layer flows over a straight cone and two flared cones. The steady and the unsteady flow fields were obtained by solving the two-dimensional Navier-Stokes equations in axi-symmetric coordinates using the 5th order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The mean boundary layer profiles were analyzed using local stability and non-local parabolized stability equations (PSE) methods. After the most amplified disturbances were identified, two-dimensional plane acoustic waves were introduced at the outer boundary of the computational domain and time accurate simulations were performed. The adverse pressure gradient was found to affect the boundary layer stability in two important ways. Firstly, the frequency of the most amplified second-mode disturbance was increased relative to the zero pressure gradient case. Secondly, the amplification of first- and second-mode disturbances was increased. Although an adverse pressure gradient enhances instability wave growth rates, small nose-tip bluntness was found to delay transition due to the low receptivity coefficient and the resulting weak initial amplitude of the instability waves. The computed and measured amplitude-frequency spectrums in all three cases agree very well in terms of frequency and the shape except for the amplitude.

Balakumar, Ponnampalam; Kegerise, Michael A.

2010-01-01

277

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

278

On the Contribution of Turbulent Boundary Layers to the Noise Inside a Fuselage  

NASA Technical Reports Server (NTRS)

The following report deals in preliminary fashion with the transmission through a fuselage of random noise generated on the fuselage skin by a turbulent boundary layer. The concept of attenuation is abandoned and instead the problem is formulated as a sequence of two linear couplings: the turbulent boundary layer fluctuations excite the fuselage skin in lateral vibrations and the skin vibrations induce sound inside the fuselage. The techniques used are those required to determine the response of linear systems to random forcing functions of several variables. A certain degree of idealization has been resorted to. Thus the boundary layer is assumed locally homogeneous, the fuselage skin is assumed flat, unlined and free from axial loads and the 'cabin' air is bounded only by the vibrating plate so that only outgoing waves are considered. Some of the details of the statistical description have been simplified in order to reveal the basic features of the problem. The results, strictly applicable only to the limiting case of thin boundary layers, show that the sound pressure intensity is proportional to the square of the free stream density, the square of cabin air density and inversely proportional to the first power of the damping constant and to the second power of the plate density. The dependence on free stream velocity and boundary layer thickness cannot be given in general without a detailed knowledge of the characteristics of the pressure fluctuations in the boundary layer (in particular the frequency spectrum). For a flat spectrum the noise intensity depends on the fifth power of the velocity and the first power of the boundary layer thickness. This suggests that boundary layer removal is probably not an economical means for decreasing cabin noise. In general, the analysis presented here only reduces the determination of cabin noise intensity to the measurement of the effect of any one of our variables (free stream velocity, boundary layer thickness, plate thickness or the characteristic velocity of propagation in the plate). The plate generates noise by vibrating in resonance over a wide range of frequencies and increasing the damping constant is consequently an effective method of decreasing noise generation. One of the main features of the results is that the relevant quantities upon which noise intensity depends are non-dimensional numbers in which boundary layer and plate properties enter as ratios. This is taken as an indication that in testing models of structures for boundary layer noise it is not sufficient to duplicate in the model the structural characteristics of the fuselage. One must match properly the characteristics of the exicitng pressure fluctuations to that of the structure.

Corcos, G. M.; Liepmann, H. W.

1956-01-01

279

Existence results for nano boundary layer flows with nonlinear Navier boundary condition  

NASA Astrophysics Data System (ADS)

The standard no slip boundary condition of classical fluid mechanics is no longer valid at the micro- and nano-scale and should be replaced by a boundary condition that allows some degree of tangential slip. In the present work, the classical laminar boundary layer equation of the flow away from the origin past a wedge with the no-slip boundary condition replaced by a nonlinear Navier boundary condition is revisited. This boundary condition includes an arbitrary index parameter, denoted by n>0, which appears in the coefficients of the differential equation to be solved. It is proved corresponding to the value n=1/3, there are exactly three situations for the problem: (i) there is no solution; (ii) there exist two solutions; (iii) there exist four solutions. Furthermore, the exact analytical solution of the problem is given in terms of parabolic cylinder functions for further physical interpretations.

Shivanian, Elyas

2013-12-01

280

Bubbly turbulent drag reduction is a boundary layer effect.  

PubMed

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

281

A New Scaling for Adverse Pressure Gradient Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

A new scaling for strong adverse pressure gradient (APG) turbulent boundary layers (TBL) is presented. The new scaling is applied to data from the author's APG TBL experiment as well as several previous experimental studies. Both steady and unsteady flows are considered. The new scaling is shown to provide an excellent collapse of not only the mean velocity but also the turbulent stress profiles. The physical motivation for the scaling is presented in terms of underlying stability mechanisms as evidenced by a series of conditional boundary layer measurements. The implications of the scaling on the physics of strong APG TBL flows is also discussed.

Thomas, Flint; Schatzman, David

2011-11-01

282

Effects of shock on hypersonic boundary layer stability  

NASA Astrophysics Data System (ADS)

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

Pinna, F.; Rambaud, P.

2013-06-01

283

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

284

Boundary Layer Dynamics as seen from MER Mini-TES  

NASA Astrophysics Data System (ADS)

We will present results from the high temporal frequency observations of the martian atmospheric boundary layer from MER Mini-TES. This work will address not only the detailed retrievals from these observations, but also their diurnal trends, seasonal differences and differences between the rovers. We will also discuss analysis of the information content of the Mini-TES retrievals. The extent of convection, the strength of turbulent overturnings and the dominant frequencies for each of these processes will be reported. Inferences about the convective or shear instability of the atmospheric boundary layer will be drawn from the results.

Banfield, D.; Smith, M.; Wolff, M.; Christensen, P.

2005-12-01

285

Laminar Boundary Layer Behind a Strong Shock Moving into Air  

NASA Technical Reports Server (NTRS)

The laminar wall boundary layer behind a strong shock advancing into stationary air has been determined. Numerical results have been obtained for shock Mach numbers up to 14 using real gas values for density and viscosity and assuming Prandtl and Lewis numbers of 0.72 and 1, respectively. The numerical results for shear and heat transfer agree, within 4 percent, with a previously presented approximate analytical expression for these quantities. A slight modification of this expression results in agreement with the numerical data to within 2.5 percent. Analytical expressions for boundary-layer thickness and displacement thickness, correct to within 4 percent for the present data, have also been obtained.

Mirels, Harold

1961-01-01

286

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

287

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

288

Flow characteristics around a circular cylinder with a slit. II Effect of boundary layer suction  

Microsoft Academic Search

The effects of boundary layer suction are investigated for a circular cylinder with a two-dimensional slit placed along a diameter. Flow characteristics around the cylinder are examined for cases of intermittent boundary layer suction (Pattern I), alternate boundary layer suction and blowing (Pattern II), and the transition regions. Among other results, it is found that the boundary layer suction is

T. Igarashi

1982-01-01

289

The Saharan atmospheric boundary layer: Turbulence, stratification and mixing  

NASA Astrophysics Data System (ADS)

High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (?1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer concentrations, demonstrating the potential for variability in, for example, dust concentrations independent of external forcings. The residual layer, where long-range transport can take place, is analyzed in particular detail. Various processes which can lead to transport into and mixing within the residual layer are explored, including shear-driven turbulence at the residual layer top and the potential for detrainment from the convective boundary layer top due to the combination of a weak lid and a neutral layer above.

Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.

2013-04-01

290

A new absorbing layer boundary condition for the wave equation  

SciTech Connect

A new absorbing boundary condition using an absorbing layer is presented for application to finite-difference time-domain (FDTD) calculation of the wave equation. This algorithm is by construction a hybrid between the Berenger perfectly matched layer (PML) algorithm and the one-way Sommerfeld algorithm. The new prescription contains both of these earlier ones as particular cases, and retains benefits from both. Numerical results indicate that the new algorithm provides absorbing rates superior to those of the PML algorithm.

Vay, J.L.

2000-09-11

291

Application of Vortex Generators to Bubbly Boundary Layers  

Microsoft Academic Search

The use of micro-bubbles for skin friction drag reduction has been known at least since the 1970's. However, a limitation on the effectiveness of micro-bubbles has been bubble migration, whereby bubbles move to the outer parts of the boundary layer. Since these bubbles need to be fairly close to the wall to be useful (typically in the buffer layer or

David Jeon; Mory Gharib

2004-01-01

292

Modeling the planetary boundary layer — Extension to the stable case  

Microsoft Academic Search

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

293

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

294

An Adaptive Finite Difference Solver for Nonlinear Two-Point Boundary Problems with Mild Boundary Layers  

Microsoft Academic Search

A variable-order finite difference solver for first-order nonlinear system subject to two-point boundary conditions is described. The method uses deferred corrections, and adaptive meshes are automatically produced in order to detect and resolve mild boundary layers and other sharp-gradient situations. A set of numerical examples solved with an implementation of the algorithm is presented, together with comparisons with several other

M. Lentini; V. Pereyra

1977-01-01

295

Transportation of particulate plumes in boundary layer 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 nonslip 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 high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles. 1

Petrosyan, A.; Karelsky, K.; Smirnov, I.

2010-05-01

296

Modeling of particulate plumes transportation 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 nonslip 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 high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles.

Karelsky, K. V.; Petrosyan, A. S.

2012-04-01

297

Transportation of particulate plumes in boundary layer 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 nonslip 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 high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles. 1

Karelsky, K.; Petrosyan, A.; Smirnov, I.

2009-09-01

298

Modeling of particulate plumes transportation 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 nonslip 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 high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles.

Karelsky, K.; Petrosyan, A.; Smirnov, I.

2010-09-01

299

Transport of Particulates in Boundary Layer 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 nonslip 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 high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles.

Karelsky, Kirill; Petrosyan, Arakel

2014-05-01

300

Radon daughter disequilibria in the lower marine boundary layer  

Microsoft Academic Search

Radon daughters are produced as free ions, but they become attached to aerosol particles at a rate depending on the particle concentration. In the lower marine boundary layer, most of those which do not become attached plate out on the ocean surface. In this paper a simple model is used to examine the influence of several parameters on radon\\/radon daughter

S. Whittlestone; Private MailBag

1990-01-01

301

Stability of hypersonic boundary-layer flows with chemistry  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

302

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

303

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

304

Boundary-Layer Receptivity and Integrated Transition Prediction  

NASA Technical Reports Server (NTRS)

The adjoint parabold stability equations (PSE) formulation is used to calculate the boundary layer receptivity to localized surface roughness and suction for compressible boundary layers. Receptivity efficiency functions predicted by the adjoint PSE approach agree well with results based on other nonparallel methods including linearized Navier-Stokes equations for both Tollmien-Schlichting waves and crossflow instability in swept wing boundary layers. The receptivity efficiency function can be regarded as the Green's function to the disturbance amplitude evolution in a nonparallel (growing) boundary layer. Given the Fourier transformed geometry factor distribution along the chordwise direction, the linear disturbance amplitude evolution for a finite size, distributed nonuniformity can be computed by evaluating the integral effects of both disturbance generation and linear amplification. The synergistic approach via the linear adjoint PSE for receptivity and nonlinear PSE for disturbance evolution downstream of the leading edge forms the basis for an integrated transition prediction tool. Eventually, such physics-based, high fidelity prediction methods could simulate the transition process from the disturbance generation through the nonlinear breakdown in a holistic manner.

Chang, Chau-Lyan; Choudhari, Meelan

2005-01-01

305

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

306

ATMOSPHERIC DISPERSION IN THE ARCTIC: WINTERTIME BOUNDARY-LAYER MEASUREMENTS  

EPA Science Inventory

The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...

307

A wave equation for the SGEMP boundary layer  

NASA Astrophysics Data System (ADS)

Time-independent solutions of the fluid equations pertaining to the SGEMP boundary layer are found and oscillations about these static solutions are considered. Unstable waves are found by linearizing the fluid equations. An explanation is proposed for the absence of significant oscillations when electrons are emitted with a realistic energy spectrum. Numerical simulations are used to substantiate the validity of the analytic solutions.

Perez, J. D.

1984-12-01

308

Adiabatic Oscillations of the One-Dimensional SGEMP Boundary Layer  

Microsoft Academic Search

Adiabatic oscillations of the one-dimensional SGEMP boundary layer about equilibrium are described in a fluid approximation. The solution for monoenergetic emission normal to the surface is found and compared with a computer solution. Solutions for photoelectron emission with a cosine distribution for a monoenergetic and a linear times exponential energy distribution are also found. It appears that these latter solutions

Roger Stettner

1977-01-01

309

Scaling Behavior of the Time-Dependent SGEMP Boundary Layer  

Microsoft Academic Search

The analysis and results given here show that boundary layer dynamics obeys very useful scaling laws which permit one solution of the basic equations to hold for many cases. In particular, during the time that the X-ray pulse is linearly rising, or when the pulse time history changes slowly after a rapid rise, (or when the pulse behaves as any

N. J. CarronandC; C. L. Longmire

1978-01-01

310

A wave equation for the SGEMP boundary layer  

SciTech Connect

A static solution and a linear dispersion relationship are obtained from fluid equations to address the frequency content of the radiation from the SGEMP boundary layer. Numerical simulations confirm the results and indicate nonlinear behavior. No new SGEMP threat to satellites is predicted.

Perez, J.D.

1984-12-01

311

Microscale heat transfer enhancement using thermal boundary layer redeveloping concept  

Microsoft Academic Search

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

312

The core-mantle boundary layer and deep Earth dynamics  

Microsoft Academic Search

Recent seismological work has revealed new structures in the boundary layer between the Earth's core and mantle that are altering and expanding perspectives of the role this region plays in both core and mantle dynamics. Clear challenges for future research in seismological, experimental, theoretical and computational geophysics have emerged, holding the key to understanding both this dynamic system and geological

Thorne Lay; Quentin Williams; Edward J. Garnero

1998-01-01

313

Measurements Of Turbulence In Boundary-Layer Flows  

NASA Technical Reports Server (NTRS)

Report describes experimental study of turbulence in two boundary-layer flows with adverse gradients of pressure. Flows produced about cylinder oriented with axis along that of low-speed wind tunnel of rectangular cross section. Fluctuations of velocities analyzed with respect to various mathematical models of turbulence.

Driver, David M.

1993-01-01

314

Higher eigenmodes in the Blasius boundary-layer stability problem  

NASA Technical Reports Server (NTRS)

The higher spatial-stability eigenmodes for the Blasius boundary layer are examined by using asymptotic theory, and an infinite number of modes are found. The asymptotic results are shown to be in close agreement with results from a direct numerical solution of the Orr-Sommerfeld problem. The asymptotic theory would therefore provide an efficient tool in exploratory searches for the eigenvalues.

Hultgren, Lennart S.

1987-01-01

315

Hair receptor sensitivity to changes in laminar boundary layer shape.  

PubMed

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

316

Flow physics of discrete boundary layer suction measurements and predictions  

Microsoft Academic Search

The primary objective of this work is to determine the detailed characteristics of the flow features induced in a boundary layer by suction through laminar flow control (LFC) perforations. An additional goal is to validate a predictive method for generic LFC suction surfaces and to apply this technique to typical flight condition configurations. Fundamental insights into the flow physics of

D. G. MacManus; J. A. Eaton

2000-01-01

317

Signatures of transient boundary layer processes observed with Viking  

Microsoft Academic Search

Observations of magnetosheath plasma intrusion made by Viking in the dayside magnetosphere at auroral latitudes are presented. The intrusion is not connected with the well-known quasi-steady state entry of magnetosheath plasma in the cusp regions; rather, it is of a temporal, transient type. Since these intrusion events are observed on flux tubes which are populated by background boundary layer plasma

J. Woch; R. Lundin

1992-01-01

318

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

319

Atmospheric boundary layer studies in FIFE - Challenges and advances  

NASA Technical Reports Server (NTRS)

A review is presented of a number of other articles concerning the atmospheric boundary layer (ABL) that focus on challenges and progress in experimental design and analysis represented by those studies. The articles address problems posed by the experimental site itself (inhomogeneity of terrain, size, and vegetation) and examine relationships between the ABL and remote sensing measurements.

Kelly, Robert D.

1992-01-01

320

The Efiect of Vortex Persistence on Boundary Layer Behavior  

Microsoft Academic Search

Flow visualization experiments in a water tunnel at moderate Reynolds number reveal that the addition of a stationary vortex to an otherwise turbulent boundary layer results in laminar ?ow. This result is consis- tent with earlier heat transfer experiments of Touel (1) and Balle (2), who found laminar wall heat ?uxes under stationary vortices. Cotel's theory of persistent vortices (3)

Olivia R. Dawson; Robert E. Breidenthal

321

Receptivity of Supersonic Boundary Layers to Acoustic Disturbances  

NASA Technical Reports Server (NTRS)

Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The effect of leading-edge thickness is also studied and bluntness is found to stabilize the boundary layer. The relative significance of fast acoustic waves is enhanced in the presence of bluntness.

Malik, Mujeeb R.; Balakumar, P.

2005-01-01

322

ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS  

SciTech Connect

Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

Pessah, Martin E. [Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen O (Denmark); Chan, Chi-kwan, E-mail: mpessah@nbi.dk, E-mail: ckch@nordita.org [NORDITA, Roslagstullsbacken 23, 106 91 Stockholm (Sweden)

2012-05-20

323

Unsteady magnetic boundary layer flow of power-law fluids  

Microsoft Academic Search

The Galerkin approximation technique is used to solve the flow problem of an infinite plate immersed in a non-Newtonian power law fluid in the presence of a constant transverse magnetic field. The velocity outside the boundary layer depends exponentially on time.

Djordje S. Djukic

1974-01-01

324

CFD simulation of the atmospheric boundary layer: wall function problems  

Microsoft Academic Search

Accurate Computational Fluid Dynamics (CFD) simulations of atmospheric boundary layer (ABL) flow are essential for a wide variety of atmospheric studies including pollutant dispersion and deposition. The accuracy of such simulations can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type

Bert Blocken; Ted Stathopoulos; Jan Carmeliet

2007-01-01

325

Aircraft measurements within the planetary boundary layer over water  

Microsoft Academic Search

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

326

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

327

SUPPRESSION DYNAMICS OF A BOUNDARY-LAYER DIFFUSION FLAME  

Microsoft Academic Search

Flame stability, suppression, and extinction phenomena are intrinsically time dependent. Solutions are obtained for unsteady, full Navier-Stokes equations using Barely Implicit Correction to Flux Corrected Transport (BIC- FCT) algorithms for a boundary-layer diffusion flame formed over a flat porous plate, through which a fuel gas is injected uniformly. The solutions include calculation of surface temperature and composition as functions of

Ramagopal Ananth; Chuka C. Ndubizu; P. A. Tatem; Gopal Patnaik; K. Kailasanath

2001-01-01

328

FLUID MODELING OF ATMOSPHERIC DISPERSION IN THE CONVECTIVE BOUNDARY LAYER  

EPA Science Inventory

Study of convective boundary layer (CBL) processes has depended largely upon laboratory analogs for many years. The pioneering work of Willis and Deardorff (1974) and some 35 subsequent papers by the same authors showed that much useful research could be accomplished with a re...

329

Microphone Detects Waves In Laminar Boundary-Layer Flow  

NASA Technical Reports Server (NTRS)

Simple noninvasive acoustical technique effective in measurement of instability waves, which precede onset of turbulence in laminar boundary layer flows. Microphone mounted below surface detects pressure waves indicative of instabilities in laminar flow. Relatively insensitive to long-wavelength background noise. Such measurements important in research on aerodynamic flows and potential applications in control of turbulence (with consequent reduction of drag) on aircraft.

Kendall, James M.

1990-01-01

330

Stability of Supersonic Boundary Layers Over Blunt Wedges  

NASA Technical Reports Server (NTRS)

Receptivity and stability of supersonic boundary layers over blunt flat plates and wedges are numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 10(exp 6)/inch. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. Computations are performed for a flat plate with leading edge thicknesses of 0.0001, 0.001, 0.005 and 0.01 inches that give Reynolds numbers based on the leading edge thickness ranging from 1000 to 10000. Calculations are also performed for a wedge of 10 degrees half angle with different leading edge radii 0.001 and 0.01 inches. The linear stability results showed that the bluntness has a strong stabilizing effect on the stability of two-dimensional boundary layers. The transition Reynolds number for a flat plate with a leading edge thickness of 0.01 inches is about 3.5 times larger than it is for the Blasius boundary layer. It was also revealed that boundary layers on blunt wedges are far more stable than on blunt flat plates.

Balakumar, Ponnampalam

2006-01-01

331

Numerical calculations of shock-wave/boundary-layer flow interactions  

NASA Technical Reports Server (NTRS)

The paper presents results of calculations for 2-D supersonic turbulent compression corner flows. The results seem to indicate that the newer, improved kappa-epsilon models offer limited advantages over the standard kappa-epsilon model in predicting the shock-wave/boundary-layer flows in the 2-D compression corner over a wide range of corner angles and flow conditions.

Huang, P. G.; Liou, W. W.

1994-01-01

332

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

333

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

334

Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers  

NASA Technical Reports Server (NTRS)

The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.

Grosch, C. E.; Gatski, T. B. (Technical Monitor)

2002-01-01

335

Anomalous plasma diffusion and the magnetopause boundary layer  

NASA Technical Reports Server (NTRS)

An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.

Treumann, Rudolf A.; Labelle, James; Haerendel, Gerhard; Pottelette, Raymond

1992-01-01

336

New, quasi-simultaneous method to calculate interacting boundary layers  

NASA Astrophysics Data System (ADS)

A quasi-simultaneous method is described to calculate laminar, incompressible boundary layers interacting with an inviscid outer flow. The essential feature of this method is an interactive boundary condition prescribing a linear combination of pressure and displacement thickness which models the behavior of the outer flow. This way the quasi-simultaneous method avoids difficulties incurred when either direct or inverse methods are used, resulting in fast convergence of the iterative procedure involved. The method is consistent with the asymptotic triple-deck theory. Results will be presented for two problems which exhibit strong interaction between the viscous and inviscid regions: a boundary layer with a separation bubble, and the flow near the trailing edge of a flat plate.

Veldman, A. E. P.

1981-01-01

337

On Supersonic-Inlet Boundary-Layer Bleed Flow  

NASA Technical Reports Server (NTRS)

Boundary-layer bleed in supersonic inlets is typically used to avoid separation from adverse shock-wave/boundary-layer interactions and subsequent total pressure losses in the subsonic diffuser and to improve normal shock stability. Methodologies used to determine bleed requirements are reviewed. Empirical sonic flow coefficients are currently used to determine the bleed hole pattern. These coefficients depend on local Mach number, pressure ratio, hole geometry, etc. A new analytical bleed method is presented to compute sonic flow coefficients for holes and narrow slots and predictions are compared with published data to illustrate the accuracy of the model. The model can be used by inlet designers and as a bleed boundary condition for computational fluid dynamic studies.

Harloff, Gary J.; Smith, Gregory E.

1995-01-01

338

Particle image velocimetry measurements of a shock wave/turbulent boundary layer interaction  

NASA Astrophysics Data System (ADS)

Particle image velocimetry is used to investigate the interaction between an incident shock wave and a turbulent boundary layer at Mach 2.1. A particle response assessment establishes the fidelity of the tracer particles. The undisturbed boundary layer is characterized in detail. The mean velocity field of the interaction shows the incident and reflected shock wave pattern, as well as the boundary layer distortion. Significant reversed flow is measured instantaneously, although, on average no reversed flow is observed. The interaction instantaneously exhibits a multi-layered structure, namely, a high-velocity outer region and a low-velocity inner region. Flow turbulence shows the highest intensity in the region beneath the impingement of the incident shock wave. The turbulent fluctuations are found to be highly anisotropic, with the streamwise component dominating. A distinct streamwise-oriented region of relatively large kinematic Reynolds shear stress magnitude appears within the lower half of the redeveloping boundary layer. Boundary layer recovery towards initial equilibrium conditions appears to be a gradual process.

Kolling, S.; Bois, P. A. Du; Benson, D. J.; Feng, W. W.

2007-08-01

339

Vortex-induced boundary-layer separation. I - The unsteady limit problem Re approaching infinity. II - Unsteady interacting boundary-layer theory  

NASA Astrophysics Data System (ADS)

The viscous response induced in a flow near a solid wall by the motion of a vortex above the surface when the flow is at Reynolds numbers approaching infinity was investigated using a specially developed upwind-downwind ADI method. It is shown that the boundary-layer solution ultimately evolves toward a sharply focused eruption and to a terminal state virtually identical to that described by Elliot et al. (1983). Interacting boundary-layer solutions are then obtained over a range of Re numbers between 10 exp 5 and 10 exp 8, using a Lagrangian algorithm for the boundary layer, making it possible to carry out numerical integrations all the way through the formation of a singularity. It is shown that the effect of interaction is to promote boundary-layer breakdown at an earlier time (confirming the scalings obtained by Elliott et al.) for the first interactive state, and that a second singularity quickly occurs. The results confirm quantitatively that this second singularity is identical to that described by Smith (1988).

Peridier, Vallorie J.; Smith, F. T.; Waker, J. D. A.

1991-11-01

340

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

341

Overcoming the Boundary Layer Turbulence at Dome C: Ground-Layer Adaptive Optics versus Tower  

NASA Astrophysics Data System (ADS)

The unique atmospheric conditions present at sites such as Dome C on the Antarctic plateau are very favorable for high spatial resolution astronomy. At Dome C, the majority of the optical turbulence is confined to a 30 to 40 m thick stable boundary layer that results from the strong temperature inversion created by the heat exchange between the air and the ice-covered ground. To fully realize the potential of the exceptionally calm free atmosphere, this boundary layer must be overcome. In this article we compare the performance of two methods proposed to beat the boundary layer: mounting a telescope on a tower that physically puts it above the turbulent layer, and installing a telescope at ground level with a ground-layer adaptive optics system. A case is also made to combine these two methods to further improve the image quality.

Travouillon, T.; Jolissaint, L.; Ashley, M. C. B.; Lawrence, J. S.; Storey, J. W. V.

2009-06-01

342

Turbulent boundary layer on a convex, curved surface  

NASA Technical Reports Server (NTRS)

The effects of strong convex curvature on boundary layer turbulence were investigated. The data gathered on the behavior of Reynolds stress suggested the formulation of a simple turbulence model. Three sets of data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning, and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero - thus avoiding any effects of streamwise acceleration on the wall layers. Results show that after a sudden introduction of curvature, the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. In contrast, when the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions.

Gillis, J. C.; Johnston, J. P.; Kays, W. M.; Moffat, R. J.

1980-01-01

343

Stability of the boundary layer on a compliant rotating disc  

NASA Astrophysics Data System (ADS)

Transition to turbulence of the three-dimensional boundary layer on a rotating disc can be preceded by the emergence of crossflow vortices that are stationary with respect to the disc. These result from an inviscid instability mechanism associated with an inflexion point in the boundary layer velocity profile or a mechanism induced by the balance between viscous and Coriolis forces. Past studies for other flows have shown that compliance can substantially postpone the onset of transition. We use numerical and asymptotic methods to investigate the effect of compliance on this instability by considering the flow over a rotating finite depth viscoelastic layer. Growth rates are calculated and neutral solutions produced for both inviscid and viscous modes. The results obtained are compared to recent experiments.

Stephen, Sharon; John, Jo-Anne

2007-11-01

344

Measurements on the Effect of Transducer Size on the Resolution of Boundary-Layer Pressure Fluctuations.  

National Technical Information Service (NTIS)

The response of a flush-mounted transducer to the pressure field in a turbulent boundary layer is known to depend on the spatial and temporal characteristics of the transducer. This paper presents an experimental study of this dependence. The reduced data...

F. E. Geib

1970-01-01

345

Application of temperature sensitive paint for detection of boundary layer transition  

Microsoft Academic Search

Temperature sensitive paint systems exploit the variation in convective heat transfer associated with changes from laminar to turbulent flow for detection of boundary layer transition. For this detection technique, it is important for wind tunnel models to have slow thermal response relative to convection heat transfer. Wind tunnels that can produce rapid changes in freestream temperature can create a model

Thomas G. Popernack; L. R. Owens; Marvine P. Hamner; M. J. Morris

1997-01-01

346

Secondary instability of compressible boundary layer to subharmonic three-dimensional disturbances  

NASA Technical Reports Server (NTRS)

Three-dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting (T-S) waves. The focus is on principal parametric resonance responsible for the strong growth of harmonics in a low disturbance environment.

El Hady, Nabil M.

1989-01-01

347

Secondary instability of compressible boundary layer to subharmonic three-dimensional disturbances  

NASA Technical Reports Server (NTRS)

Three-dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting (T-S) waves. The focus is on principal parametric resonance responsible for the strong growth of harmonics in a low disturbance environment.

El-Hady, Nabil M.

1988-01-01

348

Shear-induced surface alignment of polymer dispersed liquid crystal microdroplets on the boundary layer  

NASA Technical Reports Server (NTRS)

Polymer dispersed liquid crystal thin films have been deposited on a glass substrate, utilizing the processes of polymerization and solvent evaporation induced phase separation. Liquid crystal microdroplets trapped on the upper surface of the thin film respond to the shear stress due to air or gas flow on the surface layer. Response to an applied step shear stress input on the surface layer has been measured by measuring the time response of the transmitted light intensity. Initial results on the measurements of the light transmission as a function of the air flow differential pressure indicate that these systems offer features suitable for boundary layer and gas flow sensors.

Parmar, D. S.; Singh, J. J.

1993-01-01

349

Impact Wind Farms on the Marine Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

We introduce a new, validated wind farm parametrization (Explicit Wake Parametrization, EWP) which is based on the assumption that the downstream propagation of a single turbine wake can be described by a turbulent diffusion process. Thus, the downstream velocity deficit distribution can be described explicitly. Additionally, it allows us to take into account turbine interactions, making it possible to determine the unresolved turbine hub height velocities. Both the EWP wind farm parametrization and the wind farm scheme available in the Weather Research & Forecasting Model (WRF) have been validated against in situ measurements from Horns Rev I (A large offshore wind farm consisting of 80 2MW turbines situated near the west coast of Denmark). The main quantities of interest are the thrust applied to the flow, a consequence of the energy extracted by the wind turbines which determines mainly the wind farm wake extension (around 50 km for Horns Rev I) and the vertical velocity deficit distribution. Results show that the thrust in the WRF-WF scheme is overestimated inside the wind farm. We noticed that the velocity deficit propagates from the first turbine-containing-grid-cell up to the boundary layer top, which is in contrast to the theoretical expected expansion (confirmed by turbulence resolving models and wind tunnel results). The vertical expansion of the velocity deficit is a consequence of the additional turbulence source term in the WRF-WF scheme. The EWP scheme estimates the total amount of thrust correctly and is also able to follow the reduced thrust downstream since it considers the turbine interaction. From the good agreement with the far wake measurement, we can conclude that the formulation of the sub grid scale vertical extension of the velocity deficit must be correct. We will present results from WRF simulations in which we analyze the atmospheric response within the wake of wind farms resulting from the energy extraction of wind turbines. We place hypotetical wind farms in offshore areas with good wind resources near California. The wind farm sizes are choosen to be comparable to present ones errected in the European North Sea. Of particular interest is the influence of wind farms on the persistent stratocumulus clouds of the California coastal region, the thermal stratification of the boundary layer and wind stress changes due to reduced wind speeds near the surface. Although no wind farms are presently constructed along the Californian coast, fast and steady wind speeds makes it an attractive region for future offshore wind farms, especially if the first floating turbines near the coast of Norway are proven to be a success.

Volker, P.; Capps, S. B.; Huang, H. J.; Sun, F.; Badger, J.; Hahmann, A.

2012-12-01

350

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

351

Model simulations of the Arctic atmospheric boundary-layer from the SHEBA year.  

PubMed

We present Arctic atmospheric boundary-layer modeling with a regional model COAMPS, for the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Model results are compared to soundings, near-surface measurements and forecasts from the ECMWF model. The near-surface temperature is often too high in winter, except in shorter periods when the boundary layer was cloud-capped and well-mixed due to cloud-top cooling. Temperatures are slightly too high also during the summer melt season. Effects are too high boundary-layer moisture and formation of too dense stratocumulus, generating a too deep well-mixed boundary layer with a cold bias at the simulated boundary-layer top. Errors in temperature and therefore moisture are responsible for large errors in heat flux, in particular in solar radiation, by forming these clouds. We conclude that the main problems lie in the surface energy balance and the treatment of the heat conduction through the ice and snow and in how low-level clouds are treated. PMID:15264600

Tjernström, Michael; Zagar, Mark; Svensson, Gunilla

2004-06-01

352

Hypersonic Boundary Layer Stability over a Flared Cone in a Quiet Tunnel  

NASA Technical Reports Server (NTRS)

Hypersonic boundary layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82x106/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the model in a low-disturbance environment. Point measurements with a single hot wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode disturbances were the most unstable and scaled with the boundary layer thickness. The integrated growth rates of the second mode compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with high free stream disturbance levels.

Lachowicz, Jason T.; Chokani, Ndaona; Wilkinson, Stephen P.

1996-01-01

353

Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects  

NASA Technical Reports Server (NTRS)

Hypersonic boundary layer measurements over a flared cone were conducted in a Mach 6 quiet wind tunnel at a freestream unit Reynolds number of 2.82 million/ft. This Reynolds number provided laminar-to-transitional flow over the cone model in a low-disturbance environment. Four interchangeable nose-tips, including a sharp-tip, were tested. Point measurements with a single hot-wire using a novel constant voltage anemometer were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the transitional state of the boundary layer and to identify instability modes. Results suggest that second mode disturbances were the most unstable and scaled with the boundary layer thickness. The second mode integrated growth rates compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode subharmonic. The subharmonic disturbance wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that nonlinear disturbances are not associated with 'high' free stream disturbance levels. Nose-tip radii greater than 2.7% of the base radius completely stabilized the second mode.

Lachowicz, Jason T.; Chokani, Ndaona

1996-01-01

354

Measurements near Bluff Bodies in Turbulent Boundary Layers Intended to Simulate Atmospheric Surface Layers.  

National Technical Information Service (NTIS)

A relatively new counter-jet technique is shown to be suitable for producing thick turbulent boundary layers which may be used to simulate neutral atmospheric surface layers in wind tunnels of moderate length. The increased thickness is achieved by provid...

J. Tan-Atichat H. M. Nagib

1974-01-01

355

Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

The results from direct numerical simulations of a spatially evolving, supersonic, flat-plate turbulent boundary-layer flow, with free-stream Mach number of 2.25 are presented. The simulated flow field extends from a transition region, initiated by wall suction and blowing near the inflow boundary, into the fully turbulent regime. Distributions of mean and turbulent flow quantities are obtained and an analysis of these quantities is performed at a downstream station corresponding to Re(sub x)= 5.548 x10(exp 6) based on distance from the leading edge.

Gatski, T. B.; Erlebacher, G.

2002-01-01

356

Edge Plasma Boundary Layer Generated By Kink Modes in Tokamaks  

SciTech Connect

This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the ?-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.

L.E. Zakharov

2010-11-22

357

Mean-Velocity Profile of Turbulent Boundary Layers Approaching Separation  

NASA Astrophysics Data System (ADS)

Turbulent boundary layers approaching separation are a common flow situation in many technical applications. Numerous theoretical, experimental and numerical attempts have been made to find the proper scaling for the mean-velocity profile of this type of wall-bounded flow. However, none of these approaches seems to be completely satisfactory, and controversy still persists regarding the behavior of the mean velocity profile of turbulent boundary layers approaching separation. In this talk, we present new water-tunnel experiments of adverse-pressure-gradient turbulent boundary layers that clearly show the breakdown of the logarithmic law. Using these data and experimental results from several independent research groups, we analyze the classical scaling for ZPG TBL and the scaling by George & Castillo and Zagarola & Smits for APG TBL. Only the latter can be applied successfully for the outer region of the mean-velocity profile close to separation. It is shown that Zagarola & Smits' scaling is consistent with the classical two-layer approach, and can be applied to collapse the different data. Analyzing the Reynolds shear stress, the George & Castillo's scaling shows a reasonably good collapse of the data in the outer region.

Indinger, Thomas; Buschmann, Matthias H.; Gad-El-Hak, Mohamed

2005-11-01

358

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

359

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

360

Effects of surface wave breaking on the oceanic boundary layer  

NASA Astrophysics Data System (ADS)

Existing laboratory studies suggest that surface wave breaking may exert a significant impact on the formation and evolution of oceanic surface boundary layer, which plays an important role in the ocean-atmosphere coupled system. However, present climate models either neglect the effects of wave breaking or treat them implicitly through some crude parameterization. Here we use a one-dimensional ocean model (General Ocean Turbulence Model, GOTM) to investigate the effects of wave breaking on the oceanic boundary layer on diurnal to seasonal time scales. First a set of idealized experiments are carried out to demonstrate the basic physics and the necessity to include wave breaking. Then the model is applied to simulating observations at the northern North Sea and the Ocean Weather Station Papa, which shows that properly accounting for wave breaking effects can improve model performance and help it to successfully capture the observed upper ocean variability.

He, Hailun; Chen, Dake

2011-04-01

361

Correlation of boundary layer stability analysis with flight transition data  

NASA Technical Reports Server (NTRS)

Recently, NASA completed a boundary-layer transition flight test on an F-14 aircraft which has variable-sweep capability. Transition data were acquired for a wide variety of sweep angles, pressure distributions, Mach numbers, and Reynolds numbers. In this paper, the F-14 flight test is briefly described and N-factor correlations with measured transition locations are presented for one of two gloves flown on the F-14 wing in the flight program; a thin foam and fiberglass glove which provided a smooth sailplane finish on the basic F-14, modified NACA 6-series airfoil. For these correlations, an improved linear boundary-layer stability theory was utilized that accounts for compressibility and surface and streamline curvature effects for the flow past swept wings.

Collier, F. S., Jr.; Bartlett, D. W.; Wagner, R. D.; Tat, V. V.; Anderson, B. T.

1990-01-01

362

Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

363

A review of unsteady turbulent boundary-layer experiments  

NASA Technical Reports Server (NTRS)

The essential results of a comprehensive review of existing unsteady turbulent boundary-layer experiments are presented. Different types of unsteady flow facilities are described, and the related unsteady turbulent boundary-layer experiments are cataloged and discussed. The measurements that were obtained in the various experiments are described, and a complete list of experimental results is presented. All the experiments that measured instantaneous values of velocity, turbulence intensity, or turbulent shear stress are identified, and the availability of digital data is indicated. The results of the experiments are analyzed, and several significant trends are identified. An assessment of the available data is presented, delineating gaps in the existing data, and indicating where new or extended information is needed. Guidelines for future experiments are included.

Carr, L. W.

1981-01-01

364

Finite-element numerical modeling of atmospheric turbulent boundary layer  

NASA Technical Reports Server (NTRS)

A dynamic turbulent boundary-layer model in the neutral atmosphere is constructed, using a dynamic turbulent equation of the eddy viscosity coefficient for momentum derived from the relationship among the turbulent dissipation rate, the turbulent kinetic energy and the eddy viscosity coefficient, with aid of the turbulent second-order closure scheme. A finite-element technique was used for the numerical integration. In preliminary results, the behavior of the neutral planetary boundary layer agrees well with the available data and with the existing elaborate turbulent models, using a finite-difference scheme. The proposed dynamic formulation of the eddy viscosity coefficient for momentum is particularly attractive and can provide a viable alternative approach to study atmospheric turbulence, diffusion and air pollution.

Lee, H. N.; Kao, S. K.

1979-01-01

365

Slender-Body Hypervelocity Boundary-Layer Instability  

NASA Astrophysics Data System (ADS)

With novel application of optical techniques, the slender-body hypervelocity boundary-layer instability is characterized in the previously unexplored regime where thermo-chemical effects are important. Narrowband disturbances (500-3000 kHz) are measured in boundary layers with edge velocities of up to 5~km/s at two points along the generator of a 5 degree half angle cone. Experimental amplification factor spectra are presented. Linear stability and PSE analysis is performed, with fair prediction of the frequency content of the disturbances; however, the analysis over-predicts the amplification of disturbances. The results of this work have two key implications: 1) the acoustic instability is present and may be studied in a large-scale hypervelocity reflected-shock tunnel, and 2) the new data set provides a new basis on which the instability can be studied.

Parziale, Nick

366

Atmospheric surface and boundary layers of the Amazon Basin  

NASA Technical Reports Server (NTRS)

Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.

Garstang, Michael

1987-01-01

367

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

368

Calculation of turbulent shear stress in supersonic boundary layer flows  

NASA Technical Reports Server (NTRS)

An analysis of turbulent boundary layer flow characteristics and the computational procedure used are discussed. The integrated mass and momentum flux profiles and differentials of the integral quantities are used in the computations so that local evaluation of the streamwise velocity gradient is not necessary. The computed results are compared with measured shear stress data obtained by using hot wire anemometer and laser velocimeter techniques. The flow measurements were made upstream and downstream of an adiabatic unseparated interaction of an oblique shock wave with the turbulent boundary layer on the flat wall of a two dimensional wind tunnel. A comparison of the numerical analysis and actual measurements is made and the effects of small differences in mean flow profiles on the computed shear stress distributions are discussed.

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

1974-01-01

369

Additive erosion reduction influences in the turbulent boundary layer  

SciTech Connect

Results of a sequence of flow, heat and mass transfer calculations are presented which theoretically characterize the erosive environment at the wall surface of refractory metal coated and uncoated gun barrels. The theoretical results include analysis of the wall surface temperature, heat flux, and shear stress time histories on thin (10 mil. or 0.254 mm) Cr, Mo, Nb, and Ta plated steel barrel walls as uncoated steel walls. The calculations combine effects of a number of separate processes which have been previously (and purposely) studied individually. These include solid particle additive concentrations, gas-wall thermo-chemical influences, and transient turbulent wall boundary layer flow with multi-component molecular diffusion and reactions from interaction of propellant combustion and the eroding surface. The boundary layer model includes particulate additive concentrations as well as propellant combustion products, considered for the present to be in the local thermochemical equilibrium.

Buckingham, A.C.

1981-05-06

370

A drag reduction method for turbulent boundary layers  

NASA Technical Reports Server (NTRS)

A novel method to reduce skin friction drag in a turbulent boundary layer is presented. The technique combines the beneficial effects of a longitudinally ribbed surface and suction. The streamwise grooves act as a nucleation site causing a focusing of low-speed streaks over the peaks. Suction is then applied intermittently through longitudinal slots located at selected locations along those peaks to obliterate the low-speed regions and to prevent bursting. During the first phase of the present research, selective suction from a single streamwise slot was used to eliminate either a single burst-like event or a periodic train of artificially generated bursts in laminar and turbulent boundary layers. The experiments were conducted using a flat plate towed in an 18-m water channel. Flow visualization and hot-film probe measurements were used together with pattern recognition algorithms to demonstrate the feasibility of the drag-reducing method.

Gad-El-hak, Mohamed; Blackwelder, Ron F.

1987-01-01

371

Nonparallel instability of supersonic and hypersonic boundary layers  

NASA Technical Reports Server (NTRS)

Multiple scaling technique is used to examine the nonparallel instability of supersonic and hypersonic boundary-layer flows to three dimensional (first mode) and two dimensional (second mode) disturbances. The method is applied to the flat plate boundary layer for a range of Mach numbers from 0 to 10. Growth rates of disturbances are calculated based on three different criteria: following the maximum of the mass-flow disturbance, using an integral of the disturbance kinetic energy, and using the integral of the square of the mass-flow amplitude. By following the maximum of the mass-flow disturbance, the calculated nonparallel growth rates are in good quantitative agreement with the experimental results at Mach number 4.5.

El-Hady, Nabil M.

1991-01-01

372

Crossing shock wave-turbulent boundary layer interactions  

NASA Technical Reports Server (NTRS)

Three-dimensional interactions between crossing shock waves generated by symmetric sharp fins and a turbulent boundary layer on a flat plate are investigated experimentally and theoretically at Mach number 2.95 and freestream unit Reynolds number 1.96 x 10 to the 7th/ft. The incoming boundary layer has a thickness of 4 mm at the location of the fin leading edges. A comparison of experimental and computational results for two sets of fin angles (11 x 11 and 9 x 9 deg) shows general agreement with regard to surface pressure measurements and surface streamline patterns. The principal feature of the streamline structure is a collision of counterrotating vortical structures emanating from near the fin leading edges and meeting at the geometric centerline of the interaction.

Narayanswami, N.; Knight, D. D.; Bogdonoff, S. M.; Horstman, C. C.

1991-01-01

373

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

374

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

375

Boundary layer integral matrix procedure code modifications and verifications  

NASA Technical Reports Server (NTRS)

A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented.

Evans, R. M.; Morse, H. L.

1974-01-01

376

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

377

The Boundary Layer Flows of a Rivlin-Ericksen Fluid  

NASA Astrophysics Data System (ADS)

The present work deals with the two-dimensional incompressible, laminar, steady-state boundary layer equations. First, we determine a family of velocity distributions outside the boundary layer such that these problems may have similarity solutions. We study the Falkner-Skan flow of a viscoelastic fluid governed by second order model, as the Reynolds number Re? ?. We obtain an ordinary forth order differential equation to obtain the stream function, velocity profile and the stress. The stream function is then governed by a generalized Falkner-Skan equation. In comparison with Newtonian Falkner-Skan equation that has two coefficients this new one has four coefficients that two of them represent elastic properties of the fluid. The effects of the elastic parameter on the velocity filed have been discussed. As it is shown in the figure there is a good agreement between numerical results and previous special cases confirm the validity of the presented algorithm.

Sadeghy, K.; Khabazi, N.; Taghavi, S. M.

378

Possibilities for drag reduction by boundary layer control  

NASA Technical Reports Server (NTRS)

The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.

Naiman, I.

1946-01-01

379

Numerical study of the laminar shock-boundary layer interaction  

NASA Astrophysics Data System (ADS)

The interaction of an oblique shock wave with a laminar boundary layer on an adiabatic flat plane was analyzed numerically with solutions of the two dimensional Navier-Stokes equations using McCormack's explicit finite volume method. The agreement between numerical calculations and experimental results is good. Local and global properties of the interaction region are discussed regarding shock strength, separation bubble length using a similarity law, and separation environment. The assymmetrical structure inside the separation bubble produces an assymmetrical shape of the wall shear stress distribution. The calculation speed was increased by algorithm vectorization on a CRAY 1S supercomputer. Further investigations for determination of a similarity law in interaction with turbulent boundary layer, of the physical mechanisms of the laminar interaction, and for study of the wall temperature transfer are recommended.

Katzer, E.

1986-04-01

380

Numerical study of the laminar shock boundary layer interaction  

NASA Astrophysics Data System (ADS)

The interaction of an oblique shock wave with a laminar boundary layer on an adiabatic flat plate was analyzed numerically with solutions of the two dimensional Navier-Stokes equations using McCormack's explicit finite volume method. The agreement between numerical calculations and experimental results is good. Local and global properties of the interaction region are discussed regarding shock strength, separation bubble length using a similarity law, and separation environment. The asymetrical structure inside the separation bubble produces an asymetrical shape of the wall shear stress distribution. The calculation speed was increased by algorithm vectorization on a CRAY 1S supercomputer. Further investigations for determination of a similarity law in interaction with turbulent boundary layer, of the physical mechanisms of the laminar interaction, and for study of the wall temperature transfer are recommended.

Katzer, E.

1985-02-01

381

Nonlinear Interaction of Frequency-Detuned Modes in Boundary Layers  

NASA Technical Reports Server (NTRS)

The present critical-layer asymptotic analysis for the nonlinear interaction of frequency-detuned modes in boundary-layer transition indicates that the interaction between a plane mode at the fundamental frequency and a pair of symmetrical oblique waves at the near-subharmonic frequency amplifies another pair of symmetrical oblique waves at the 'mirror frequency'. This type of interaction is stronger in the frequency-detuned case than the resonant triad case, and leads to a sharp drop in the oblique waves' peak with small detuning.

Mankbadi, Reda R.

1993-01-01

382

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.

383

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

384

Atmospheric dispersion in the arctic: Wintertime boundary-layer measurements  

Microsoft Academic Search

The winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF6 tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to

Alex Guenther; Brian Lamb

1989-01-01

385

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

386

Large Eddy Simulation of the ventilated wave boundary layer  

Microsoft Academic Search

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

387

Kubo-Anderson Mixing in the Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

A novel ab initio analysis of the Reynolds stress is presented in order to model non-local turbulence transport. The theory involves a sample path space and a stochastic hypothesis. A scaling relation maps the path space onto the boundary layer. Analytical sampling rates are shown to model mixing by exchange. Nonlocal mixing involves a scaling exponent ??0.58 (??? in the diffusion limit). The resulting transport equation represents a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process.

Dekker, H.; de Leeuw, G.; Brink, A. Maassen Van Den

388

Compressible boundary layer calculation by finite element mixed approach  

NASA Astrophysics Data System (ADS)

A method for the compressible laminar boundary layer calculations is presented, based on the use of finite element of Hermitian type for the determination of the velocity profile, coupled with a space marching procedure in the streamwise direction. The theoretical and numerical aspects of the method are discussed. The method was applied to simple calculations, of which the exact solutions exist in the literature, with good agreement between the obtained and the exact solutions, demonstrating the correctness and reliability of the presented approach.

Martelli, F.; Bidini, G.

389

Streamline-curvature effect in three-dimensional boundary layers  

NASA Technical Reports Server (NTRS)

The effect of including wall and streamline curvature terms in swept-wing boundary-layer stability calculations is studied. The linear disturbance equations are cast on a fixed, body-intrinsic, curvilinear coordinate system. Those nonparallel terms which contribute mainly to the streamline-curvature effect are retained in this formulation and approximated by their local finite-difference values. Convex-wall curvature has a stabilizing effect, while streamline curvature is destabilizing if the curvature exceeds a critical value.

Reed, Helen L.; Lin, Ray-Sing; Petraglia, Media M.

1992-01-01

390

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

391

Spectral Stability of Noncharacteristic Isentropic Navier–Stokes Boundary Layers  

Microsoft Academic Search

Building on the work of Barker, Humpherys, Lafitte, Rudd, and Zumbrun in the shock wave case, we study stability of compressive,\\u000a or shock-like, boundary layers of the isentropic compressible Navier–Stokes equations with ?-law pressure by a combination of asymptotic ODE estimates and numerical Evans function computations. Our analytical results\\u000a include convergence of the Evans function in the shock and large-amplitude

Nicola Costanzino; Jeffrey Humpherys; Toan Nguyen; Kevin Zumbrun

2009-01-01

392

Control of Boundary-Layer Separation for Lifting Surfaces  

Microsoft Academic Search

The lack of understanding of most of the relevant physical mechanisms when applying flow control limits the prospects of successfully transitioning flow-control technologies into real flight vehicles. Successful control of boundary-layer separation for lifting surfaces promises major performance gains especially when large laminar runs are desired in order to minimize the skin-friction drag. We systematically explore the fundamental mechanisms of

W. Balzer; A. Gross; H. F. Fasel

2009-01-01

393

Numerical investigation of the turbulent boundary layer over a bump  

Microsoft Academic Search

Large-eddy simulation (LES) has been used to calculate the flow of a statistically two-dimensional turbulent boundary layer over a bump. Subgrid-scale stresses in the ltered Navier{Stokes equations were closed using the dynamic eddy viscosity model. LES predictions for a range of grid resolutions were compared to the experimental measurements of Webster et al. (1996). Predictions of the mean flow and

KYLE D. S QUIRES

394

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

395

Similarity solutions of boundary layer equations for second order fluids  

NASA Astrophysics Data System (ADS)

An isovector derived via exterior calculus for the boundary layers of second-order fluids is presently used to ascertain the ordinary differential equations that lead to the similarity solutions. Taking the problem as an initial-value problem, an effort is made to find the arbitrary condition by resort to the shooting method. The shear stress of the similarity solution is calculated, together with the profile corresponding to the solution.

Pakdemirli, M.; Suhubi, E. S.

1992-05-01

396

LASTRAC.3d: Transition Prediction in 3D Boundary Layers  

NASA Technical Reports Server (NTRS)

Langley Stability and Transition Analysis Code (LASTRAC) is a general-purpose, physics-based transition prediction code released by NASA for laminar flow control studies and transition research. This paper describes the LASTRAC extension to general three-dimensional (3D) boundary layers such as finite swept wings, cones, or bodies at an angle of attack. The stability problem is formulated by using a body-fitted nonorthogonal curvilinear coordinate system constructed on the body surface. The nonorthogonal coordinate system offers a variety of marching paths and spanwise waveforms. In the extreme case of an infinite swept wing boundary layer, marching with a nonorthogonal coordinate produces identical solutions to those obtained with an orthogonal coordinate system using the earlier release of LASTRAC. Several methods to formulate the 3D parabolized stability equations (PSE) are discussed. A surface-marching procedure akin to that for 3D boundary layer equations may be used to solve the 3D parabolized disturbance equations. On the other hand, the local line-marching PSE method, formulated as an easy extension from its 2D counterpart and capable of handling the spanwise mean flow and disturbance variation, offers an alternative. A linear stability theory or parabolized stability equations based N-factor analysis carried out along the streamline direction with a fixed wavelength and downstream-varying spanwise direction constitutes an efficient engineering approach to study instability wave evolution in a 3D boundary layer. The surface-marching PSE method enables a consistent treatment of the disturbance evolution along both streamwise and spanwise directions but requires more stringent initial conditions. Both PSE methods and the traditional LST approach are implemented in the LASTRAC.3d code. Several test cases for tapered or finite swept wings and cones at an angle of attack are discussed.

Chang, Chau-Lyan

2004-01-01

397

Sheet flow and suspension of sand in oscillatory boundary layers  

Microsoft Academic Search

after revisionTime-dependent measurements of flow velocities and sediment concentrations were conducted in a large oscillating water tunnel. The measurements were aimed at the flow and sediment dynamics in and above an oscillatory boundary layer in plane bed and sheet-flow conditions. Two asymmetric waves and one sinusoidal wave were imposed using quartz sand with D50 = 0.21 mm. A new electro-resistance

Jan S. Ribberink; Abdullah A. Al-Salem

1995-01-01

398

Recent advances in active control of turbulent boundary layers  

NASA Astrophysics Data System (ADS)

In this article, we review the recent progress in active control of a turbulent boundary layer for skin-friction drag reduction. Near-wall coherent structures, which are closely associated with large skin-friction drag and are thus often the target to be manipulated, are discussed briefly, providing a rationale of various control strategies. Open- and closed-loop controls are extensively reviewed, largely focusing on techniques and drag-reduction mechanisms. Finally, some concluding remarks are given.

Zhou, Yu; Bai, HongLei

2011-07-01

399

Turbulence and skin friction evolutions in an oscillating boundary layer  

Microsoft Academic Search

The paper presents and analyzes experimental results on an oscillating flat plate turbulent boundary layer. Emphasis is placed on quantities, which characterize the evolution of turbulence and of the skin friction. These results have been obtained in a rather large range of reduced frequencies with (omega nu)\\/(U-tau\\/bar\\/)-squared in the interval from 0.0035 to 0.013 and (omega XO)\\/(U-e\\/bar\\/) in the interval

J. Cousteix; R. Houdeville

1985-01-01

400

Interaction of Pulsed Vortex Generator Jets with Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

Vortex Generator Jets (VGJ) have been proposed as a means for active control of turbulent boundary layer separation by Johnston footnote AIAA J. 28, 989 (1990). It has been shown that a vortex generator jet can create weak longitudinal vorticity of a single sign when the surface-mounted jets are pitched and skewed with respect to the solid surface. The primary advantages of VGJs when compared to solid vortex generators are their lack of parasitic drag when the jets are off and the ability to rapidly activate and deactivate the jets for dynamic control. Pulsing of the jets is proposed as a way of increasing the turbulent mixing and therefore, improving the performance of vortex generator jets. Initial experiments with jets pitched at 45 deg and skewed at 90 deg degrees in air have indicated that large-scale turbulent structures are formed by the pulsed VGJs. Subsequent flow visualization experiments in a water tunnel suggest that fully-modulated jets embedded in a flat plate boundary layer result in a series of puffs which penetrate through the boundary layer. The influence of jet velocity, diameter, pulsing frequency and duty-cycle will be discussed. * Supported by NSF and PSI.

McManus, K. R.; Johari, H.

1996-11-01

401

The singularity in particle-laden boundary layers  

NASA Astrophysics Data System (ADS)

The classical ``dusty gas'' equations have been used recently in a number of investigations by the authors to model boundary-layer flows of dilute suspensions of heavy particles. Though none of the difficulties of well-posedness that so often occur in more complicated particle-laden flow models seems to arise for this equation set, what does nearly always appear, and is now well documented in a variety of boundary layers, is a wall singularity that occurs at a finite distance from the leading edge, where the volume fraction is unbounded. The dusty-gas approximation replaces the quantity ``1-?'' everywhere in the particle-laden equations by ``1''. One is forced to seek a more complicated model in order to remove the unphysical singularity, and there are plenty of candidates--including particle pressure, added mass, particle-particle interactions. From the point of view of modifying the theory in the simplest possible way, we restore ``1-?'' where it had been replaced by ``1,'' and do nothing more. Such a procedure removes the singularity in boundary-layer flows, and we present computational and analytical results under such a change See, most recently, Foster, Duck & Hewitt (2006) Proc. Roy. Soc A 462, 1145

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

2006-11-01

402

Effect of thermally induced perturbation in supersonic boundary layers  

NASA Astrophysics Data System (ADS)

This paper investigates the mechanism of steady and unsteady thermal perturbation (also denoted as thermal bump) in a Mach 1.5 flat plate boundary layer. A high-fidelity upwind-biased third-order Roe scheme is used with the compressive van Leer harmonic limiter on a suitably refined mesh. The study consists of two parts. In the first part, the effects of the steady and pulsed thermal bumps are explored. It is shown that the finite-span thermal bumps generate streamwise vortices. With steady heating, the disturbance decays downstream. However, when the thermal bump is pulsed, vortex shedding is observed and the streamwise vortical disturbance grows with downstream distance, consistent with linear stability analysis. The integrated disturbance energy indicates that streamwise kinetic disturbance energy growth dominates over those associated with other two velocity and thermodynamic components. The second part of this paper explores the physical consequences of the nonlinear dynamics between the vortices produced by the pulsed bump and the compressible boundary layer. The resulting three-dimensional flow distortion generates hairpin structures which are aligned in the streamwise direction, suggesting that the transition process bears some similarity to K-type breakdown. The arrangement of these vortices is connected to the low-speed streaks observed in the evolving boundary layer. The shape factor, velocity, and Reynolds stress profiles suggest that the perturbed flow shows initiation of transition to turbulence, but remains transitional at the end of the plate.

Yan, Hong; Gaitonde, Datta

2010-06-01

403

Cloud-Scale Numerical Modeling of the Arctic Boundary Layer  

NASA Technical Reports Server (NTRS)

The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate models (GCMs) result in large differences between the Arctic, and global, climates simulated by different models. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary layer clouds must be accurately represented in climate models to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary layer clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary layer clouds in GCMs.

Krueger, Steven K.

1998-01-01

404

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

405

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

406

Thermocapillary Bubble Migration: Thermal Boundary Layers for Large Marangoni Numbers  

NASA Technical Reports Server (NTRS)

The migration of an isolated gas bubble in an immiscible liquid possessing a temperature gradient is analyzed in the absence of gravity. The driving force for the bubble motion is the shear stress at the interface which is a consequence of the temperature dependence of the surface tension. The analysis is performed under conditions for which the Marangoni number is large, i.e. energy is transferred predominantly by convection. Velocity fields in the limit of both small and large Reynolds numbers are used. The thermal problem is treated by standard boundary layer theory. The outer temperature field is obtained in the vicinity of the bubble. A similarity solution is obtained for the inner temperature field. For both small and large Reynolds numbers, the asymptotic values of the scaled migration velocity of the bubble in the limit of large Marangoni numbers are calculated. The results show that the migration velocity has the same scaling for both low and large Reynolds numbers, but with a different coefficient. Higher order thermal boundary layers are analyzed for the large Reynolds number flow field and the higher order corrections to the migration velocity are obtained. Results are also presented for the momentum boundary layer and the thermal wake behind the bubble, for large Reynolds number conditions.

Balasubramaniam, R.; Subramanian, R. S.

1996-01-01

407

Numerical Investigation of a Fuselage Boundary Layer Ingestion Propulsion Concept  

NASA Technical Reports Server (NTRS)

In the present study, a numerical assessment of the performance of fuselage boundary layer ingestion (BLI) propulsion techniques was conducted. This study is an initial investigation into coupling the aerodynamics of the fuselage with a BLI propulsion system to determine if there is sufficient potential to warrant further investigation of this concept. Numerical simulations of flow around baseline, Boundary Layer Controlled (BLC), and propelled boundary layer controlled airships were performed. Computed results showed good agreement with wind tunnel data and previous numerical studies. Numerical simulations and sensitivity analysis were then conducted on four BLI configurations. The two design variables selected for the parametric study of the new configurations were the inlet area and the inlet to exit area ratio. Current results show that BLI propulsors may offer power savings of up to 85% over the baseline configuration. These interim results include the simplifying assumption that inlet ram drag is negligible and therefore likely overstate the reduction in power. It has been found that inlet ram drag is not negligible and should be included in future analysis.

Elmiligui, Alaa A.; Fredericks, William J.; Guynn, Mark D.; Campbell, Richard L.

2013-01-01

408

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

409

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

410

Longitudinal vortices imbedded in turbulent boundary layers. I - Single vortex  

NASA Astrophysics Data System (ADS)

Detailed mean-flow and turbulence measurements have been made in a low-speed turbulent boundary layer in zero pressure gradient with an isolated, artificially generated vortex imbedded in it. The vortex was generated by a half-delta wing on the floor of the wind-tunnel settling chamber, so that the vortex entering the working section had the circulation as that originally generated, while axial-component velocity variations were very much reduced, relative to the local mean velocity, from values just behind the generator. The measurements show that the circulation around the vortex imbedded in the boundary layer is almost conserved, being reduced only by the spanwise-component surface shear stress. Therefore the region of flow affected by the vortex continues to grow downstream, its cross-sectional dimensions being roughly proportional to the local boundary-layer thickness. The behavior of the various components of eddy viscosity, deduced from measured Reynolds stresses, and of the various triple products, suggests that the simple empirical correlations for these quantities used in present-day turbulence models are not likely to yield flow predictions which are accurate in detail.

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

1985-06-01

411

Coupling of magnetopause-boundary layer to the polar ionosphere  

SciTech Connect

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

412

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

413

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

414

Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.  

PubMed

A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvénic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics. PMID:10511515

Pérez-De-Tejada

1999-11-01

415

Perturbed boundary layer diffusion flames. Ph. D. thesis  

SciTech Connect

Thermal cracking is shown to have a significant effect on the temperature profiles in a boundary layer diffusion flame. Measurements of temperature profiles in a sooting free flow flame are compared with classic flame sheet model results. This comparison reveals a large overprediction of temperatures in the region between the fuel surface and the flame. The principle cause of this overprediction is the neglect of thermal cracking in the flame sheet model. The endothermicity of the cracking phenomena is analytically treated in a forced flow flame through the introduction of new Shvab-Zeldovich variables and a simple cracking sheet model, analogous to the flame sheet model. Two new parameters D sub cr and Q' are found which control the temperature at which cracking occurs and the amount of energy absorbed in the process. A second possible cause for the temperature overprediction is the sink effect of radiative heat transfer from soot in the boundary layer. This effect and the effects of wall emission and normal buoyancy on a horizontal boundary layer diffusion flame are studied by perturbing the cracking sheet solution. The principle effect of soot radiation is an increased blowing rate at the wall. This blowing is offset by the radiative wall emission. The postulated sink effect of soot emission is negligible. The major buoyancy effect is primarily the inducement of a velocity overshoot.

Ang, J.A.

1987-03-01

416

An analytical model of capped turbulent oscillatory bottom boundary layers  

NASA Astrophysics Data System (ADS)

An analytical model of capped turbulent oscillatory bottom boundary layers (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The model solutions show that the flow may slip at the top of the boundary layer due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the model predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary layer. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the model, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency.

Shimizu, Kenji

2010-03-01

417

Inner Temperature Scaling for Combined Convection Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

New inner length and temperature scalings are derived for the combined convection turbulent boundary layer. These new scaling are not obtained by the convectional dimensional analysis, but by considering the analogy of the driving and drag force between the momentum and thermal transport phenomena inside a turbulent boundary layer flow. The new thermal length scale and temperature scale are therefore derived using the known classical length and the velocity scale of the turbulent boundary layer. Using the experimental data from T. Tsuji and Y. Nagano (1990) and Blackwell (1972), it has been observed that the temperature profiles combine to form into a single curve when scaled by the new scalings. The inner temperature scaling derived are also compared with the existing natural convection scalings derived by George and Capp (1978) and the forced convection scaling by Wang and Castillo (2003). The existence of Grashoff Number and Stanton number in the inner scalings clearly indicates the possibility of domination of the buoyancy force or the possible effect of forced convection over the natural. A new dimensional less number has been found which consist of the Stanton number and the Richardson number based on which a clear judgment can be done on the type of convection that dominates the combined convection. Hence the new derived scalings appear to give more information regarding the type of flow. Efforts are made to verify the same scalings with a variety of thermal data.

Jaiswal, Ashish

2005-11-01