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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Structural uncertainty assessment for low-Mach wall-resolved large-eddy simulations: Plane Channel and Periodic Hill Use Cases

A structural uncertainty assessment is provided for a set of wall-resolved large-eddy simulations (WRLES) using a turbulent channel flow (𝑅𝑒 𝜏 395) and a periodic hill in the turbulent regime (𝑅𝑒 𝑏 2800) validation suite. The standard one-equation subgrid scale turbulent kinetic energy model (𝑘 𝑠𝑔𝑠 ) using both a static and dynamic coefficient approach along with Wall Adapting Local Eddy Viscosity (WALE) are exercised. The 𝑘 𝑠𝑔𝑠 model activated in this study also allows for a correction that supports theoretical turbulent viscosity and total kinetic energy scaling (cubit and quadratic, respectively) in the near-wall regime. Channel and hill results showcase very good agreement between prediction and simulation for the WALE and the dynamic coefficient 𝑘 𝑠𝑔𝑠 model. The study also demonstrates that near-wall damping improves predictivity for the static coefficient 𝑘 𝑠𝑔𝑠 model, while proving an unnecessary additional contribution for the dynamic coefficient 𝑘 𝑠𝑔𝑠 model as near-wall scaling is naturally captured. Overall conclusions are that this suite of WRLES models are well suited for production usage in the Sierra-based low-Mach codes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

CFD Modeling of an 81" Single Slope Barrier Wall Drainage Window for on Grade and Sag Conditions

The main goal of this study is to design a drainage window in an 81" single slope barrier wall for on-grade and sag conditions that could replace the standard ODOT I-3 barrier catch basin. The ODOT design guidelines are as follows: a) Examine configurations of the opening to the flume behind the wall under the wall section to maximize conveyance of flow to a roadside ditch section. b) Examine window lengths and configurations to maximize hydraulic efficiency on a grade up to an absolute maximum window length of 20 ft. c) Use a minimum opening height of 4 in. and consider tapering to an increased height at the outlet to the flume to reduce the potential for debris clogging beneath the barrier section. On-grade locations are analyzed for longitudinal slope up to 5% and spread up to 10 ft. Sag locations, represented by pavement at zero longitudinal slope, are analyzed for water depths up to 18 in. The roadway cross section consists of a 10-ft shoulder at a 4.0% cross slope and pavement at a 1.6% cross slope. All surfaces are represented with Manning’s n = 0.015. Computational fluid dynamics (CFD) is used to perform the analysis. The modeling approach follows previous studies by the authors. The new design is similar to a slotted inlet: a rectangular opening cut into the bottom of a barrier (e.g., a temporary barrier or single slope barrier wall), which typically has a uniform cross section. Findings from laboratory tests of flow under Florida DOT barrier walls were used for additional validation of the modeling approach used in this study.

42 ENGINEERING↗
DOE OSTI2024

Direct Numerical Simulation Database of High-Speed Flow over Parameterized Curved Walls

This study presents a direct numerical simulation (DNS) database of high-speed turbulent boundary layers (TBLs) subject to pressure gradients due to parametrically varied backward-facing and forward-facing wall curvatures, with an inflow Mach number of 4.9 and a friction Reynolds number of [Formula: see text] immediately before the onset of wall curvature. The Mach and Reynolds numbers are significantly higher than those reported in the literature for the DNS of pressure-gradient TBLs. The flow conditions and baseline wall geometries are representative of experiments in the high-speed blowdown wind tunnel at the National Aerothermochemistry Laboratory at Texas A&M University. The wall steepness of the baseline geometry for both the backward-facing and forward-facing walls was systematically varied to cause attached, incipiently separated, and fully separated flows. Precomputed flow statistics, including turbulent kinetic energy budgets, are available on the website of the Turbulence Modeling Resource of the NASA Langley Research Center, allowing other investigators to query any property of interest.

Engineering↗
NASA NTRS1962

Combined Radiation and Forced Convection for Flow of a Transparent Gas in a Tube with Sinusoidal Axial Wall Heat Flux Distribution

An analysis is made of the influence that radiation exchanges between elements on the inside surface of a tube have on the wall and gas temperature distributions for forced-convection flow. The wall heat generation has a chopped sine distribution with length along the tube, which is a distribution often encountered in nuclear-reactor channels. The flowing gas is assumed transparent to thermal radiation and hence does not participate directly in the radiative exchange process. Axial heat conduction is neglected in the gas and tube wall, and the convective-heat-transfer coefficient and fluid properties are assumed constant. Several numerical examples are given to illustrate the effects of eight independent parameters such as wall emissivity, Stanton number, and length-diameter ratio. In some instances the radiation exchanges reduced the peak wall temperature or caused a reduction in the exit gas temperature because of radiation losses from the tube end openings.

TUBE↗
NASA NTRS1973

Parametric analysis of turbulent wall jets in still air.

An examination has been made of all the data available on incompressible (nominally) plane wall jets in still air, supplementing these when necessary with some additional measurements. For a wall jet in still air, the chief mean flow qualities of interest are the maximum velocity, the inner length scale, and a total thickness, in addition to the wall stress. On the basis of the analysis, a (nominally) plane wall jet flow can be divided into an initial region, a fully developed flow region, and a confined wall jet flow region.

Narasimha, R.↗
NASA NTRS1974

The effect of wind tunnel wall interference on the performance of a fan-in-wing VTOL model

A fan-in-wing model with a 1.07-meter span was tested in seven different test sections with cross-sectional areas ranging from 2.2 sq meters to 265 sq meters. The data from the different test sections are compared both with and without correction for wall interference. The results demonstrate that extreme care must be used in interpreting uncorrected VTOL data since the wall interference may be so large as to invalidate even trends in the data. The wall interference is particularly large at the tail, a result which is in agreement with recently published comparisons of flight and large scale wind tunnel data for a propeller-driven deflected-slipstream configuration. The data verify the wall-interference theory even under conditions of extreme interference. A method yields reasonable estimates for the onset of Rae's minimum-speed limit. The rules for choosing model sizes to produce negligible wall effects are considerably in error and permit the use of excessively large models.

Heyson, H. H.↗
NASA NTRS1974

Performance of a short annular dump diffuser using wall trailing-edge suction

A short annular dump (abrupt flow area change) diffuser was tested with suction through wall trailing-edge slots at inlet Mach numbers of 0.19 and 0.27 and at near ambient inlet temperature and pressure, with suction flow varied from zero to 10 percent of the inlet air mass-flow rate. The overall ratio of diffuser exit area to inlet area was 4.0, and the ratio of length to inlet height was 2.0. By applying suction flow separately on either wall or to both walls simultaneously, the original annular jet profile could be altered to either a hub- or tip-biased profile. Diffuser effectiveness was increased from about 25 percent with no suction to 50 percent at 6 percent outer-wall suction and to 52 percent at a combined suction rate on both walls of 10.25 percent. At the same time, diffuser total pressure loss was reduced by one-fourth.

Juhasz, A. J.↗
NASA NTRS1974

Viscous reacting flows with wall slip and catalysis applied to spheres in arc jets and flight

The influence of wall slip and catalytic atom-recombination on the flow field and wall heat flux are calculated for high altitude flight and arc jet flow conditions. Boundary equations, which include velocity slip, temperature jump, and wall catalytic atom recombination, are coupled to the viscous reacting multicomponent Navier-Stokes equations. These equations are solved using a time-dependent finite difference technique applied to spheres in an arc jet flow (Reynolds number of 550) and a high altitude flight case representative of the Space Shuttle Orbiter (Reynolds number of 450). The results indicate that catalysis strongly influences the temperature jump, but not the velocity slip. Slip increases the atom fraction and temperature at both the wall and the flow field. Likewise, the shock stand-off distance, the wall heat flux, and friction coefficient are increased over the nonslip cases. The reacting gas calculations confirm the chemically frozen nature of the shock layer in arc jet flows.

Scott, C. D.↗
NASA NTRS1974

Some tunnel-wall effects on transonic flutter

Significant effects of wind-tunnel walls were observed on the transonic flutter boundaries of wall-mounted models during two flutter model research studies. In these studies, flutter experiments with cantilevered SST-type wing models were conducted in three different wind tunnels. The experimental results are compared to flutter boundaries calculated for the models in free air. The results indicate that transonic flutter boundaries can be affected by tunnel-wall interference, tunnel resonances, and shock-wave reflections, and that flutter model data accuracy is a function of model/tunnel size and tunnel wall porosity. However, models within the recommended size limits should give accurate results in transonic tunnels with normal ventilation. A flutter trend analysis for a two-dimensional wing-demonstrating tunnel wall and resonance effects on flutter are also presented.

Ruhlin, C. L.↗
NASA NTRS1976

Rocket engine thrust chamber wall temperature distribution calculation and analysis

An analytical computational concept is presented which predicts the temperature profiles along a regeneratively cooled thrust chamber wall on the hot gas side and on the coolant side, and also the coolant bulk temperature profile. The computational model is based upon a coupling of the boundary layer heat transfer process with the heat transfer process through the chamber wall and the coolant flow heat absorption. The calculation is started with approximate temperature distributions for the hot gas side wall and the coolant flow. The iteration process of the computer program is terminated when the total heat transfer rates from the hot gas boundary layer to the wall and from the wall to the coolant are equal. The computer program for the integration of regenerative cooling process to a thrust chamber is kept general such that this program can be used with any boundary layer analysis computer program for temperature profile and heat transfer studies. A sample application of this concept is shown by using a boundary layer analysis program for the RL10 rocket engine thrust chamber.

Saha, H.↗
NASA NTRS1976

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

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

Hebbar, K. S.↗
NASA NTRS1976

Modifications of the law of the wall and algebraic turbulence modelling for separated boundary layers

Various modifications of the conventional algebraic eddy viscosity turbulence model are investigated for application to separated flows. Friction velocity is defined in a way that avoids singular behavior at separation and reattachment but reverts to the conventional definition for flows with small pressure gradients. This leads to a modified law of the wall for separated flows. The effect on the calculated flow field of changes in the model that affect the eddy viscosity at various distances from the wall are determined by (1) switching from Prandtl's form to an inner layer formula due to Clauser at various distances from the wall, (2) varying the constant in the Van Driest damping factor, (3) using Clauser's inner layer formula all the way to the wall, and (4) applying a relaxation procedure in the evaluation of the constant in Clauser's inner layer formula. Numerical solutions of the compressible Navier-Stokes equations are used to determine the effects of the modifications. Experimental results from shock-induced separated flows at Mach numbers 2.93 and 8.45 are used for comparison. For these cases improved predictions of wall pressure distribution and positions of separation and reattachment are obtained from the relaxation version of the Clauser inner layer eddy viscosity formula.

Baldwin, B. S.↗
NASA NTRS1976

Wind tunnel wall interference effects on a supercritical airfoil at transonic speeds

Wind tunnel tests of a 10% supercritical airfoil have been conducted in the Lockheed Compressible Flow Facility at transonic speeds to determine the effects of varying wind tunnel wall porosity on airfoil performance. Wall configurations ranging in porosity from 1.3% to 10% were investigated at Reynolds numbers of 7 to 30 million. Experimental data presented to show the effect of varying wall porosity include airfoil surface pressures, airfoil forces, and wind tunnel wall pressures. Utilizing the experimental results, an assessment of the applicability of current subcritical theoretical methods to predict wall interference corrections in subsonic and transonic flows is made.

Blackwell, J. A., Jr.↗
NASA NTRS1978

Design and Performance Evaluation of Slotted Walls for Two-Dimensional Wind Tunnels

A procedure for designing slotted walls for two dimensional wind tunnels is is presented. The design objective is the minimization of blockage of streamline curvature or the reduction of both. The slotted wall boundary condition is derived both for flow from the tunnel into the plenum and vice versa, and the procedure for evaluating wall interference is described. A correlation of experimental data for the slotted wall boundary condition is given. Results are given for several designs and evaluations of slotted wind tunnel walls.

Barnwell, R. W.↗
NASA NTRS1978

Numerical design of streamlined tunnel walls for a two-dimensional transonic test

An analytical procedure is discussed for designing wall shapes for streamlined, nonporous, two-dimensional, transonic wind tunnels. It is based upon currently available 2-D inviscid transonic and boundary layer analysis computer programs. Predicted wall shapes are compared with experimental data obtained from the NASA Langley 6 by 19 inch Transonic Tunnel where the slotted walls were replaced by flexible nonporous walls. Comparisons are presented for the empty tunnel operating at a Mach number of 0.9 and for a supercritical test of an NACA 0012 airfoil at zero lift. Satisfactory agreement is obtained between the analytically and experimentally determined wall shapes.

Newman, P. A.↗
NASA NTRS1982

Effects of blade loading and rotation on compressor rotor wake in end wall regions

This study was carried out to understand the effects of blade loading and rotation on the rotor end wall flow structure, including the wake. The measurements were taken with a stationary three sensor hot wire located at the exit of a compressor rotor. The signal was ensemble averaged to derive all the three components of velocity and six components of stresses at the exit. Measurements were made at two different rotational speeds (1753 and 1010 rpm) and at two differing blade loadings at several radii near the hub and the annulus wall. The wake decay in the annulus wall region is found to be much more rapid than the mid span regions. Furthermore, both the loading and rotation of the blade have appreciable influence on the end wall flow and wake structure. Interaction of the annulus and hub wall boundary layers (and secondary flow resulting from these) have appreciable influence on the wake structure in the endwall regions.

Lakshminarayana, B.↗
NASA NTRS1982

Experimental investigation of turbulent wall-jets in the presence of adverse pressure gradients in a rectangular diffuser

An experimental study of wall static pressure distributions and mean velocity profiles along a duct and diffuser downstream of wall-jet injection was conducted over a range of diffuser total angles from 15 to 40 deg at injection to core flow mass flux ratios from 0 to 6. Pressure recovery in the diffuser increased with injection ratio and decreased with diffuser total angle. Peak velocities in the wall-jet decayed along the flow and the inner shear layer and outer mixing region grew in thickness along the flow. The inner layer was near similarity condition, but non-similar variations were found in the outer layer. Estimated wall shear stresses depended upon injection mass fluxes, downstream distance and diffuser total angle. Greater decay of peak velocity and larger friction coefficients were found in the diffuser than indicated by correlations from data for a wall-jet without a pressure gradient. At the largest diffuser total angle and the highest injection ratio flow reversal occurred in the core region.

Back, L.↗
NASA NTRS1982

Near-wall similarity in three-dimensional turbulent boundary layers. I - Model review. II - Pressure-driven flow results

Eleven proposed models for near-wall similarity for three-dimensional turbulent boundary layer flows are reviewed. Six of these models are comparatively simple scalar models and five are more complex and/or two-component vector models. Ten of the models can be tested as to their validity or predictive capability with the aid of measured mean velocity field, wall pressure field, and direct wall shear stress field (magnitude and direction) data. One of the models cannot be tested owing to its dependence on two parameters that are at present extremely difficult (if not impossible) to measure. Ten three-dimensional near-wall similarity models are then evaluated with direct wall shear, velocity field, and pressure gradient data from a three-dimensional pressure-driven boundary layer flow. In a primary focus of the interval where y+ is between 50 and 300, graphical results suggest that six simpler models and the freestream component of one complex model are adequate for profiles with monotone increasing skew up to about 15 deg.

Pierce, F. J.↗