Unsteady boundary-layer flow of a non- newtonian fluid on a flat plate
Unsteady boundary layer flow of nonnewtonian fluid on flat plate
BOUNDARY LAYER FLOW↗
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Results for “boundary layer”
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Displacement thickness of the boundary layer with blowing
Displacement thickness for two-dimensional or axisymmetric compressible boundary layer with blowing
AXISYMMETRIC FLOW↗
Carbon vaporization into a nonequilibrium, stagnation-point boundary layer
The heat transfer to the stagnation point of an ablating carbonaceous heat shield, where both the gas-phase boundary layer and the heterogeneous surface reactions are not in chemical equilibrium, is examined. Specifically, the nonequilibrium changes in the mass fraction profiles of carbon species calculated for frozen flow are studied. A set of equations describing the steady-state, nonequilibrium laminar boundary layer in the axisymmetric stagnation region, over an ablating graphite surface, is solved, with allowance for the effects of finite rate of carbon vaporization.
Suzuki, T.↗
Simulation of the atmospheric boundary layer in the wind tunnel for modeling of wind loads on low-rise structures
The lower part of the atmospheric boundary layer (strong wind conditions) was simulated in low speed wind tunnel for the modeling of wind loads on low-rise structures. The turbulence characteristics of the turbulent boundary layer in the wind tunnel are compared with full scale measurements and with measurements made at NASA Wallops Flight Center. Wind pressures measured on roofs of a 1:70 scale model of a small single family dwelling were compared with results obtained from full scale measurements. The results indicate a favorable comparison between full scale and model pressure data as far as mean, r.m.s. and peak pressures are concerned. In addition, results also indicate that proper modeling of the turbulence is essential for proper simulation of the wind pressures.
Tieleman, H. W.↗
Wind-tunnel measurements and comparison with flight of the boundary layer and heat transfer on a hollow cylinder at Mach 3
The wind tunnel tests were conducted both with and without boundary layer trips at Mach 3 and nominal free stream Reynolds numbers per meter ranging from 3.3 x 10 the 6th power. Instrumentation consisted of pressure orifices, thermocouples, a boundary layer pitot pressure rake, and a floating element skin friction balance. Measurements from both wind tunnel and flight were compared with existing engineering prediction methods.
Stallings, R. L., Jr.↗
AFM Special Issue Summary - Integrating Surface Flux with Boundary Layer Measurements
To help bridge science topics related to land-atmosphere interactions, we organized a virtual special issue in this journal (Agricultural and Forest Meteorology [AFM]) entitled, “Land-Atmosphere Interactions: Integrating Surface Flux with Boundary Layer Measurements.” The motivation for the special issue was driven by existing disciplinary barriers between research areas that all address land-atmosphere interactions. In particular, it addressed research silos between those who study features of the land surface, surface fluxes (including water, energy, and trace gases), atmospheric boundary layer growth and thermodynamics, and atmospheric composition and aerosols. The special issue sought to bring these communities together to integrate multiple observations across the soil-vegetation-atmosphere continuum with the aim of 1) improving broader understanding of land-atmosphere interactions, feedbacks, and coupling, 2) fostering new collaborations between atmospheric and surface flux scientists, and 3) identifying new paths for integrative research. In this report we provide an overview and synthesis of the special issue.
58 GEOSCIENCES↗
On Parametric Sensitivity of Reynolds-Averaged Navier-Stokes SST Turbulence Model: 2D Hypersonic Shock-Wave Boundary Layer Interactions
Examined is sensitivity of separation extent, wall pressure and heating to variation of primary input flow parameters, such as Mach and Reynolds numbers and shock strength, for 2D and Axisymmetric Hypersonic Shock Wave Turbulent Boundary Layer interactions obtained by Navier-Stokes methods using the SST turbulence model. Baseline parametric sensitivity response is provided in part by comparison with vetted experiments, and in part through updated correlations based on free interaction theory concepts. A recent database compilation of hypersonic 2D shock-wave/turbulent boundary layer experiments extensively used in a prior related uncertainty analysis provides the foundation for this updated correlation approach, as well as for more conventional validation. The primary CFD method for this work is DPLR, one of NASA's real-gas aerothermodynamic production RANS codes. Comparisons are also made with CFL3D, one of NASA's mature perfect-gas RANS codes. Deficiencies in predicted separation response of RANS/SST solutions to parametric variations of test conditions are summarized, along with recommendations as to future turbulence approach.
Hypersonic↗
Ensemble flow reconstruction in the atmospheric boundary layer from spatially limited measurements through latent diffusion models
Due to costs and practical constraints, field campaigns in the atmospheric boundary layer typically only measure a fraction of the atmospheric volume of interest. Machine learning techniques have previously successfully reconstructed unobserved regions of flow in canonical fluid mechanics problems and two-dimensional geophysical flows, but these techniques have not yet been demonstrated in the three-dimensional atmospheric boundary layer. Here, we conduct a numerical analogue of a field campaign with spatially limited measurements using large-eddy simulation. We pose flow reconstruction as an inpainting problem, and reconstruct realistic samples of turbulent, three-dimensional flow with the use of a latent diffusion model. The diffusion model generates physically plausible turbulent structures on larger spatial scales, even when input observations cover less than 1% of the volume. Through a combination of qualitative visualization and quantitative assessment, we demonstrate that the diffusion model generates meaningfully diverse samples when conditioned on just one observation. These samples successfully serve as initial conditions for a large-eddy simulation code. We find that diffusion models show promise and potential for other applications for other turbulent flow reconstruction problems.
17 WIND ENERGY↗
Two-Line Focused Laser Differential Interferometry of a Flat Plate Boundary Layer at Mach 6
Flat plate models are often used in wind tunnel testing to make measurements of the boundary layer, but preclude the use of conventional focused laser differential interferometry (FLDI) measurements, particularly for measurements at the surface of the model. By instead focusing light in only one direction using cylindrical optics, as opposed to two directions using only spherical optics, FLDI measurements can be made without truncating the beam at the model edges. Measurements at discrete points along a line can also be acquired, effectively acting as many individual FLDI instruments in a single measurement. Here, a two-line FLDI system has been constructed that allows for the measurement lines to be easily oriented at any azimuthal angle about the optical axis since the optics are housed in rotation mounts. Velocity measurements at points along a line or between two lines are also possible, since the beams are split similar to the two-point FLDI instrument. The system was first characterized in the laboratory using a laser-induced breakdown spark to provide a well-defined density fluctuation, along with high-speed schlieren measurements for comparison. The system was then installed at the NASA Langley 20-Inch Mach 6 Air Tunnel to make measurements through the boundary layer of a flat plate model and in the tunnel freestream.
Joshua M Weisberger↗
A study of the interaction of a normal shock wave with a turbulent boundary layer at transonic speeds
An asymptotic description is derived for the interaction of a weak normal shock wave and a turbulent boundary layer along a plane wall. In the case studied the nondimensional friction velocity is small in comparison with the nondimensional shock strength, and the shock wave extends well into the boundary layer. Analytical results are described for the local pressure distribution and wall shear, and a criterion for incipient separation is proposed. A comparison of predicted pressures with available experimental data includes the effect of longitudinal wall curvature.
Messiter, A. F.↗
Discussion of the results of the boundary-layer tests of an airfoil fitted with a rotary cylinder
The results of the velocity measurements in the boundary layer described in NACA-TM 411 are here discussed in greater detail. The measurements made were of the velocity distribution in the vicinity of an airfoil model fitted with a rotary cylinder and were undertaken for the purpose of obtaining a closer insight into the phenomena observed in experimenting with this model.
AIRFOILS↗
A critique of some recent second-order turbulence closure models for compressible boundary layers
Computations based on two recently developed second-order turbulence closure models are compared with a series of boundary-layer experiments and with predictions of these experiments using an algebraic mixing length model. One of the models employs an eddy viscosity, whereas the other evaluates components of the Reynolds stress tensor. For flat plates, the computations are compared with the van Driest skin-friction transformation to assess the handling of compressibility. For boundary layers in pressure gradients, four experiments at Mach 4 and one at Mach 6.7 are used as the bases for comparison. In general, both models represent mean velocities and skin friction reasonably well, but represent the turbulence shear stress less accurately.
Rubesin, M. W.↗
Stability of compressible boundary layers over a smooth backward-facing step
An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.
Ragab, S. A.↗
Stability of compressible boundary layers over a smooth backward-facing step
An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.
Ragab, S. A.↗
Shockwave-boundary layer interference heating analysis.
Interference heating correlations have been developed based on existing wind tunnel test data taken with simple configurations such as wedge/flat plate and compression corner models. For turbulent flow, peak interference heating was first correlated with shock strength (pressure ratio across shock wave) and then as a function of Reynolds number. The peak interference Stanton number was found to exhibit the same Reynolds number and Prandtl number characteristics as the Stanton number variation for undisturbed flow over a flat plate. Similar correlations were developed for laminar flow. Results indicated that for laminar flow at higher Reynolds number, the impinging shockwave may act as a boundary layer trip and cause boundary layer transition resulting in high interference heating. The correlations derived in this study can be used to scale wind tunnel model test data to a full-scale space vehicle at supersonic or hypersonic flight conditions.
Hung, F. T.↗
Experimental hydrodynamics of the accelerated turbulent boundary layer with and without mass injection.
Mean velocity-profile data are reported for blown, unblown, and sucked accelerated turbulent boundary layers. The pressure gradients investigated are those corresponding to constant values of the pressure-gradient parameter. The results obtained indicate that acceleration apparently causes an increase in the thickness of the viscous sublayer. Blowing opposes this effect, while suction enhances it. It seems evident that strong acceleration and/or strong suction will lead to a complete laminarization of the boundary layer. An empirical correlation of the data is presented in the form of a tabular correlation of the damping constant in the van Driest (1956) mixing-length hypothesis.
Julien, H. L.↗
Improved Boundary Layer Depth Retrievals from MPLNET
Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, MD since April 2001. However, because of issues with the operational PBL depth algorithm, the data is not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers, and in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System-version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by 410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they diered the most in the winter.
Micropluse Lidar Network↗
Analysis of boundary-layer transition on X-152-2 research airplane
Surface roughness effects on boundary layer transition indicated by thermocouple data from X-15 aircraft flight
BOUNDARY LAYER TRANSITION↗