RANS and Hybrid LES/RANS Simulation of the Effects of Micro Vortex Generators Using Immersed Boundary Methods

Ghosh, Santanu; Choi, Jung Il; Edwards, Jack R.

doi:10.2514/6.2008-3728

Cited by 28 publications

(16 citation statements)

References 22 publications

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“…However, there are only a few detailed experimental studies that have examined the impact of these devices on turbulent boundary layers subjected to oblique-shock interactions [4]. Ghosh et al [5] used hybrid Reynolds-averaged Navier-Stokes with large eddy simulations (RANS/LES) with an immersed boundary method (IBM) to study oblique-shock interactions with microramps. Their RANS/LES approach is helpful in that it allows much higher Reynolds numbers than are practical to compute with an LES.…”

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confidence: 99%

Microramps Upstream of an Oblique-Shock/Boundary-Layer Interaction

et al. 2010

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To examine the potential of micro vortex generators for shock/boundary-layer interaction control, a detailed experimental and computational study in a supersonic boundary layer at M 3:0 was undertaken. The experiments employed a flat-plate boundary layer with an impinging oblique shock with downstream total-pressure measurements. The moderate Reynolds number of 3800 allowed the computations to use monotone-integrated large eddy simulations. The monotone-integrated large eddy simulations predictions indicated that the shock changes the structure of the turbulent eddies and the primary vortices generated from the microramp. Furthermore, they generally reproduced the experimentally obtained mean velocity profiles, unlike similarly resolved Reynoldsaveraged Navier-Stokes computations. The experiments and monotone-integrated large eddy simulations results indicate that the microramps, for which the height is h 0:5, can significantly reduce boundary-layer thickness and improve downstream boundary-layer health as measured by the incompressible shape function H. Regions directly behind the ramp centerline tended to have increased boundary-layer thickness, indicating the significant threedimensionality of the flowfield. Compared with baseline sizes, smaller microramps yielded improved total-pressure recovery. Moving the smaller ramps closer to the shock interaction also reduced the displacement thickness and the separated area. This effect is attributed to decreased wave drag and the closer proximity of the vortex pairs to the wall. Nomenclature A sep = separation area a = speed of sound c = cord length of the microramp D = width of the computational domain d = width of the microramp dt = differential time dx = differential length in the streamwise direction dy = differential length in the normal direction dz = differential length in the spanwise direction E = height of the computational domain H = incompressible shape factor h = microramp height L = length of the computational domain M = Mach number P = pressure P o = total pressure Re ref = Reynolds number based on ref s = spacing between adjacent microramps at the centerline T = temperature t = fluid convection time scale U = average streamwise velocity U = frictional velocity u = instantaneous streamwise velocity u 0 = streamwise fluctuation the velocity v = normal velocity w = spanwise velocity W = weighting function x = streamwise distance y = normal distance relative to solid wall z = spanwise distance relative to center of domain = total-pressure recovery factor = frictional velocity ratio = specific heat ratio t = time step x = streamwise length of the computational cell = boundary-layer thickness ref = displacement thickness at x 0 but with no shock effects = k direction in the computational domain = wall normal coordinate normalized by boundarylayer thickness = von Kármán constant = i direction in the computational domain = integration time = integration time normalized by the freestream flow convection time ! = kinematic viscosity at wall = j direction in the ...

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Microramps Upstream of an Oblique-Shock/Boundary-Layer Interaction

et al. 2010

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“…In the present work, a compressible extension [13] of an IB method developed in Choi et al [12] is used. The immersed surface is generated as a cloud of points, which can be structured or unstructured.…”

Section: B Immersed Boundary Methodsmentioning

confidence: 99%

“…The potential advantages of an IB method in this scope include significant economy in the number of mesh points required in the vicinity of the control device (compared to body-fitted meshes), the ease in which different types of control devices can be interchanged and their effects assessed, and the ability to model moving control devices (such as mesoflaps) without mesh adaptation. An IB method that is suitable for these applications has been recently developed for incompressible flows [12] and has been extended to compressible flows in [13]. This approach reconstructs the velocity field near immersed surfaces using a power-law function, which enables the method to approximate the energizing effects of a turbulent boundary layer.…”

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“…This eliminates the need for a highly resolved mesh near the immersed body. The use of the technique to simulate the effects of micro vortex generators in controlling shock/boundary-layer interactions [13] and initiating transition to turbulence in hypersonic boundary layers [14] has been reported. In all cases, the IB method provides predictions similar to those obtained on body-fitted meshes.…”

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Simulation of Shock/Boundary-Layer Interactions with Bleed Using Immersed-Boundary Methods

Ghosh

Choi

Edwards

2010

Journal of Propulsion and Power

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This work uses an immersed-boundary method to simulate the effects of arrays of discrete bleed holes in controlling shock-wave/turbulent-boundary-layer interactions. Both Reynolds-averaged Navier-Stokes and hybrid large-eddy/Reynolds-averaged Navier-Stokes turbulence closures are used with the immersed-boundary technique. The approach is validated by conducting simulations of Mach 2.5 flow over a perforated plate containing 18 individual bleed holes. Computed values of discharge coefficient as a function of bleed plenum pressure are compared to experimental data. Simulations of an impinging-oblique-shock/boundary-layer interaction at Mach 2.45 with and without bleed control are also performed. For the studies with bleed, two different bleed rates are employed. The 68 hole bleed plate is rendered as an immersed object in the computational domain. Wall pressure predictions show that, in general, the large-eddy/Reynolds-averaged Navier-Stokes technique underestimates the upstream extent of axial separation that occurs in the absence of bleed. Good agreement with pitot pressure surveys throughout the interaction region is obtained, however. Flow control at the maximum-bleed rate completely removes the separation region and induces local disturbances in the wall pressure distributions that are associated with the expansion of the boundary-layer fluid into the bleed port and its subsequent recompression. Computed pitot pressure distributions are in good agreement with experiment for the cases with bleed. Swirl-strength probability density distributions are used to estimate the evolution of turbulent length scales throughout the interaction. These, along with Reynolds-stress predictions, indicate that an effect of strong bleed rates is to accelerate the recovery of the boundary layer toward a new equilibrium state downstream of the interaction region. Nomenclature a 1 = model constant for Menter baseline model C f = skin-friction coefficient C M = model constant for mixed-scale model C = model constant for Menter baseline model D = diameter of bleed hole d = distance from nearest-wall/immersed-surface point d ; = normalized distance F 2 = model constant for Menter baseline model f, g = scaling functions G = Heaviside step function based on signed distance function k = turbulent kinetic energy/power law L = length of bleed hole M = Mach number n = coordinate normal to immersed surface P = static pressure P t = pitot pressure Q = sonic flow coefficient or discharge coefficient q 2 = estimate of subgrid kinetic energy R = universal gas constant Re = Reynolds number R n1;l i = residual vector at cell i for time step n 1 and subiteration l r = recovery factor S = characteristic filtered rate of strain T = temperature u = velocity vector, x component of velocity u = friction velocity V = primitive variable vector v = component of velocity in y direction w = component of velocity in z direction X = streamwise distance from leading edge of bleed-plate insert x = streamwise distance from leading edge of computational domain Y = ...

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“…The results presented herein correspond to a trip spacing of S = 0 .081" and a peak height of h = 0 .060". The mean flow is computed with a Navier-Stokes solver, using the immersed boundary technique (see Ghosh et al 2008). Figure 2 shows that the streamwise streaks with strong spanwise boundary-layer displacement in the wake of the trip array would persisit for long distances over the forebody surface if the boundary-layer flow were to remain laminar.…”

Section: Resultsmentioning

confidence: 99%