Numerical dissipation in F3D thin-layer Navier-Stokes solution for flows with wall transpiration
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Kandula, M.↗
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Simulation of a Wall-Bounded Flow using a Hybrid LES/RAS Approach with Turbulence Recycling
Simulations of a supersonic recessed-cavity flow are performed using a hybrid large-eddy/ Reynolds-averaged simulation approach utilizing an inflow turbulence recycling procedure and hybridized inviscid flux scheme. Calorically perfect air enters the three-dimensional domain at a free stream Mach number of 2.92. Simulations are performed to assess grid sensitivity of the solution, efficacy of the turbulence recycling, and effect of the shock sensor used with the hybridized inviscid flux scheme. Analysis of the turbulent boundary layer upstream of the rearward-facing step for each case indicates excellent agreement with theoretical predictions. Mean velocity and pressure results are compared to Reynolds-averaged simulations and experimental data for each case, and these comparisons indicate good agreement on the finest grid. Simulations are repeated on a coarsened grid, and results indicate strong grid density sensitivity. The effect of turbulence recycling on the solution is illustrated by performing coarse grid simulations with and without inflow turbulence recycling. Two shock sensors, one of Ducros and one of Larsson, are assessed for use with the hybridized inviscid flux reconstruction scheme.
Quinlan, Jesse R.↗
Theoretical and Experimental Studies of the Transonic Flow Field and Associated Boundary Conditions near a Longitudinally-Slotted Wind-Tunnel Wall
A theoretical examination of the slotted-wall flow field is conducted to determine the appropriate wall pressure drop (or boundary condition) equation. This analysis improves the understanding of the fluid physics of these types of flow fields and helps in evaluating the uncertainties and limitations existing in previous mathematical developments. It is shown that the resulting slotted-wall boundary condition contains contributions from the airfoil-induced streamline curvature and the non-linear, quadratic, slot crossflow in addition to an often neglected linear term which results from viscous shearing in the slot. Existing and newly acquired experimental data are examined in the light of this formulation and theoretical developments.
Everhart, Joel Lee↗
Unsteady behavior of a reattaching shear layer
A detailed investigation of the unsteadiness in a reattaching, turbulent shear layer is reported. Laser-Doppler velocimeter measurements were conditionally sampled on the basis of instantaneous flow direction near reattachment. Conditions of abnormally short reattachment and abnormally long reattachment were considered. Ensemble-averaging of measurements made during these conditions was used to obtain mean velocities and Rreynolds stresses. In the mean flow, conditional streamlines show a global change in flow pattern which correlates with wall-flow direction. This motion can loosely be described as a 'flapping' of the shear layer. Tuft probes show that the flow direction reversals occur quite randomly and are shortlived. Streses shown also vary with the change in flow pattern. Yet, the global'flapping' motion does not appear to contribute significantly to the stress in the flow. A second type of unsteady motion was identified. Spectral analysis of both wall static pressure and streamwise velocity shows that most of the energy in the flow resides in frequencies that are significantly lower than that of the turbulence. The dominant frequency is at a Strouhal number equal to 0.2, which is the characteristic frequency of roll-up and pairing of vortical structure seen in free shear layers. It is conjectured that the 'flapping' is a disorder of the roll-up and pairing process occurring in the shear layer.
Driver, D. M.↗
Reduction of fan noise in an anechoic chamber by reducing chamber wall induced inlet flow disturbances
The difference between the flight and ground static noise of turbofan engines presents a significant problem in engine noise testing. The additional noise for static testing has been attributed to inlet flow disturbances or turbulence interacting with the fan rotor. In an attempt to determine a possible source of inflow disturbances entering fans tested in the Lewis Research Center anechoic chamber, the inflow field was studied using potential flow analysis. These potential flow calculations indicated that there was substantial flow over the wall directly behind the fan inlet that could produce significant inflow disturbances. Fan noise tests were run with various extensions added to the fan inlet to move the inlet away from this backwall and thereby reduce the inlet flow disturbances. Significant noise reductions were observed with increased inlet length. Over 5 db reduction of the blade passage tone sound power level was observed between the shortest and longest inlets at 90% fan speed and the first overtone was reduced 9 db. High frequency broadband noise was also reduced.
Dittmar, J. H.↗
Reduction of fan noise in an anechoic chamber by reducing chamber wall induced inlet flow disturbances
The difference between the flight and ground static noise of turbofan engines has been identified as a significant problem in engine noise testing. The additional noise for static testing has been attributed to inlet flow disturbances or turbulence interacting with the fan rotor. In an attempt to determine a possible source of inflow disturbances entering fans tested in the Lewis Research Center anechoic chamber the inflow field was studied using potential flow analysis. These potential flow calculations indicated that there was substantial flow over the wall directly behind the fan inlet that could produce significant inflow disturbances. Fan noise tests were run with various extensions added to the fan inlet to move the inlet away from this backwall and thereby reduce the inlet flow disturbances. Significant noise reductions were observed with increased inlet length. Over 5 dB reduction of the blade passage tone sound power level was observed between the shortest and longest inlets at 90% fan speed and the first overtone was reduced 9 dB. High frequency broadband noise was also reduced.
Dittmar, J. H.↗
Fluctuating wall pressure under a separated supersonic flow.
Fluctuating wall pressure under separated supersonic turbulent boundary layer, showing origins of fluctuations
SEPARATED FLOW↗
Investigation of the Attenuation of Plane Shock Waves Moving over very Rough Surfaces
Experimental measurements of the attenuation of plane shock waves moving over rough walls have been made in a shock tube. Measurements of the boundary-layer characteristics, including thickness and velocity distribution behind the shock, have also been made with the aid of new cal techniques which provide direct information on the local boundary-layer conditions at the rough walls. Measurements of shock speed and shock pressure ratio are presented for both smooth-wall and rough-wall flow over lengths of machined-smooth and rough strips which lined all four walls of the shock tube. A simplified theory based on Von Karman's expression for skin-friction coefficient for flow over rough walls, along with a wave-model concept and extensions to include time effects, is presented. In this theory, the shock-tube flow is assumed to be one-dimensional at all times and the wave-model concept is used to relate the local layer growth to decreases in shock strength. This concept assumes that local boundary-layer growths act as local mass-flow sinks, which give rise to expansion waves which, in turn, overtake the shock and lower its mass flow accordingly.
Huber, Paul W.↗
Nonadiabatic and three-dimensional effects in compressible turbulent boundary layers
A defect stream function formulation for nonadiabatic flow with small crossflow is developed. The first-integral property of this formulation provides for two removal of the streamline curvature term in the governing equation so that the form of the reduced equation for small crossflow is the same as that for two dimensional flow. The combined law of the wall and wake is used in place of the no-slip boundary condition. The tangential velocity equation for law-of-the-wall flow is shown to be the same for three-dimensions as for two when the Boussinesq approximation applies, and a closed form solution for the crossflow angle in the inner region is obtained. Analytic solutions for nonadiabatic, compressible, equilibrium flow with a Clauser outer-region eddy-viscosity model are obtained, and excellent agreement with experimental skin friction and velocity profile data for nonadiabatic, compressible flat-plate flow is achieved. An analytic solution for a linear inner-region eddy-viscosity model is also obtained; the wake function part of this solution is found to be inconsistent with the empirically established law of the wake.
Barnwell, Richard W.↗
Study of Unsteady Flows with Concave Wall Effect
This paper presents computational fluid dynamic studies of the inlet turbulence and wall curvature effects on the flow steadiness at near wall surface locations in boundary layer flows. The time-stepping RANS numerical solver of the NASA Glenn-HT RANS code and a one-equation turbulence model, with a uniform inlet turbulence modeling level of the order of 10 percent of molecular viscosity, were used to perform the numerical computations. The approach was first calibrated for its predictabilities of friction factor, velocity, and temperature at near surface locations within a transitional boundary layer over concave wall. The approach was then used to predict the velocity and friction factor variations in a boundary layer recovering from concave curvature. As time iteration proceeded in the computations, the computed friction factors converged to their values from existing experiments. The computed friction factors, velocity, and static temperatures at near wall surface locations oscillated periodically in terms of time iteration steps and physical locations along the span-wise direction. At the upstream stations, the relationship among the normal and tangential velocities showed vortices effects on the velocity variations. Coherent vortices effect on the velocity components broke down at downstream stations. The computations also predicted the vortices effects on the velocity variations within a boundary layer flow developed along a concave wall surface with a downstream recovery flat wall surface. It was concluded that the computational approach might have the potential to analyze the flow steadiness in a turbine blade flow.
Wang, Chi R.↗
A study of the turbulence structures of wall-bounded shear flows
This project extends the study of the structure of wall-bounded flows using the topological properties of eddying motions as developed by Chong et al. (1990), Soria et al. (1992, 1994), and as recently extended by Blackburn et al. (1996) and Chacin et al. (1996). In these works, regions of flow which are focal in nature are identified by being enclosed by an isosurface of a positive small value of the discriminant of the velocity gradient tensor. These regions resemble the attached vortex loops suggested first by Theodorsen (1955). Such loops are incorporated in the attached eddy model versions of Perry & Chong (1982), Perry et al. (1986), and Perry & Marusic (1995), which are extensions of a model first formulated by Townsend (1976). The DNS data of wall bounded flows studied here are from the zero pressure gradient flow of Spalart (1988) and the boundary layer with separation and reattachment of Na & Moin (1996). The flow structures are examined from the viewpoint of the attached eddy hypothesis.
Chong, M. S.↗
Characteristics of mean velocity in the annulus wall region at the exit of turbomachinery rotor passage
This paper reports the experimental study of the three-dimensional characteristics of the mean velocity in the annulus-wall boundary layer and wake mixing region of a moderately loaded compressor rotor blade. The measurements reported were obtained using a three-sensor hot-wire probe at the exit of the rotor. They consisted of tangential surveys at several axial and radial locations downstream of the compressor rotor blade passage. The variation of the streamwise, normal, and radial velocity profiles and their decay characteristics are derived from this data. The measurements reveal the highly complex and three-dimensional nature of the annulus-wall flow field and the nature of the interaction of the annulus-wall boundary layer, the blade boundary layers and wake, and the secondary flow associated with the annulus-wall region.
Davino, R.↗
Experiments on supersonic turbulent flow development in a square duct
The nature of supersonic, turbulent, adiabatic-wall flow in a square duct is investigated experimentally over a development length of x/D between 0 and 20 for a uniform flow, Mach 3.9 condition at the duct inlet. Initial discussion centers on the duct configuration itself, which was designed specifically to minimize wave effects and nozzle-induced distortion in the flow. Total pressure contours and local skin friction coefficient distributions are presented which show that the flow develops in a manner similar to that observed for the incompressible case. In particular, undulations exist in total pressure contours within the cross plane and in transverse skin friction coefficient distributions, which are indicative of the presence of a well-defined secondary flow superimposed upon the primary flow. The results are analyzed to show that local law-of-the-wall behavior extends well into the corner region, which implies that wall functions conventionally applied in two-equation type turbulence models, when suitably defined for compressible flow, may also be applied to supersonic streamwise corner flows.
Gessner, F. B.↗
Flow and wall-temperature sensitivity in parallel passages for large inlet to exit density ratios in subsonic flow
Analytical investigation of flow and wall temperature sensitivity in heated passages for large inlet to exit density ratios in subsonic flow of nuclear rocket
Reshotko, M.↗
Generalized Wall Function for Complex Turbulent Flows
A generalized wall function was proposed by Shih et al., (1999). It accounts the effect of pressure gradients on the flow near the wall. Theory shows that the effect of pressure gradients on the flow in the inertial sublayer is very significant and the standard wall function should be replaced by a generalized wall function. Since the theory is also valid for boundary layer flows toward separation, the generalized wall function may be applied to complex turbulent flows with acceleration, deceleration, separation and recirculation. This paper is to verify the generalized wall function with numerical simulations for boundary layer flows with various adverse and favorable pressure gradients, including flows about to separate. Furthermore, a general procedure of implementation of the generalized wall function for National Combustion Code (NCC) is described, it can be applied to both structured and unstructured CFD codes.
Shih, Tsan-Hsing↗
Mass-transfer method of measuring wall shear stress in supersonic flow.
Mass transfer method for measuring skin friction from isothermal adiabatic leading-edge flat plate in compressible laminar airflow with negligible pressure gradient
SHEARING STRESS↗
Interference from slotted walls
Wall interference is made predominant in tunnel models and by wall geometries to facilitate the study of slot flow. The viscous effects in slots are studied by two dimensional measurements of flow. Wall interference is assessed by measuring pressure distributions at two levels near the walls. Interference on lifting delta wings is calculated. Pressure distributions at inner boundaries show basis axisymetries between the pressure side and the suction side, pointing to the necessity of having wider slots on the pressure side.
Berndt, S. B.↗