Santanu Ghosh

Numerical Simulations of Effects of Micro Vortex Generators Using Immersed-Boundary Methods

This work presents an immersed-boundary technique for compressible, turbulent flows and applies the technique to simulate the effects of micro vortex generators in controlling oblique-shock/turbulent boundary-layer interactions. The Reynolds-averaged Navier-Stokes equations, closed using the Menter k-ω turbulence model, are solved in conjunction with the immersed-boundary technique. The approach is validated by comparing solutions obtained using the immersed-boundary technique with solutions obtained on a body-fitted mesh and with experimental laser Doppler anemometry data collected at Cambridge University for Mach 2.5 flow over single micro vortex generators. Simulations of an impinging oblique-shock boundary-layer interaction at Mach 2.5 with and without micro vortex-generator flow control are also performed, considering the development of the flow in the entire wind tunnel. Comparisons are made with experimental laser Doppler anemometry data and surface-pressure measurements from Cambridge University and an analysis of the flow structure is performed. The results show that three dimensional effects initiated by the interaction of the oblique shock with the sidewall boundary layers significantly influence the flow patterns in the actual experiment. The general features of the interactions with and without the micro vortex-generator array are predicted to good accord by the Reynolds-averaged Navier-Stokes/ immersed-boundary model.

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

This work utilizes an immersed boundary (IB) method to simulate the effects of arrays of discrete bleed ports in controlling shock wave / turbulent boundary layer inter actions . Both Reynolds averaged Navier -Stokes (RANS) and hybrid large -eddy / Reynolds -averaged Navier -Stokes (LES/RANS) turbulence closures are used with the IB technique. The approach is validated by conducting simulations of Mach 2.5 flow over a perfo rated plate containing 18 individual bleed holes. Predictions of discharge coefficient as a function of bleed plenum pressure are compared with experimental data. Simulations of an impinging oblique shock / boundary layer interaction at Mach 2.45 with an d without active bleed control are also performed. The 68 -hole bleed plate is rendered as an immersed object in the computational domain. Wall pressure predictions show that, in general, the LES/RANS technique under -estimate s the upstream extent of axi al separation that occurs in the absence of bleed. Good agreement with P itot -pressure surveys throughout the interaction region is obtained, however. Active suction completely removes the separation region and induces local disturbances in the wall pres sure distributions that are associated with the expansion of the boundary layer fluid into the bleed port and its subsequ ent re -compression. Predicted Pitot -pressure distributions are in good agreement with experiment for the case with bleed. Swirl stre ngth probability -density distributions are used to estimate the evolution of turbulence length -sca les throughout the interaction, and the effects of bleed on the amplification of Reynolds stresses are highlighted. Finally, simple improvements to engineerin g-level bleed models are proposed based on the computational results.

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

This work presents an immersed boundary (IB) technique for compressible, turbulent flows and applies the technique to simulate the effects of micro vortex generators (micro VGs) in controlling oblique-shock / turbulent boundary layer interactions. Both Reynolds averaged Navier-Stokes (RANS) and hybrid large-eddy / Reynolds-averaged Navier-Stokes (LES/RANS) turbulence closures are used with the IB technique. The approach is validated by comparing RANS and hybrid LES/RANS solutions obtained using the IB technique with RANS solutions obtained using a body-fitted mesh and with experimental laser Doppler anemometry (LDA) data collected at Cambridge University for Mach 2.5 flow over a single micro VG. Simulations of an impinging oblique shock / boundary layer interaction at Mach 2.5 with and without micro VG flow control are also performed, considering a.) the development of the entire flow in the wind tunnel using a RANS model and b.) an idealized, nominally two-dimensional interaction using both the RANS and the LES/RANS models. Comparisons are made with experimental LDA data and surface pressure measurements from Cambridge University, and an analysis of the flow structure is performed. The results show that three-dimensional effects initiated by the interaction of the oblique shock with the sidewall boundary layers significantly influence the flow patterns in the actual experiment. The general features of the interactions with and without the micro VG array are predicted to good accord by the RANS / IB model. Results for the idealized interaction show the LES/RANS model captures a faster recovery of the separated boundary layer and a broader influence of the vortices generated by the micro VG array, compared with the RANS model.

Numerical Simulation of the Effects of Mesoflaps in Controlling Shock / Boundary Layer Interactions

This work utilizes an immersed-boundary method to simulate the effects of an array of aeroelastic mesoflaps in controlling oblique shock/turbulent boundary-layer interactions. A loosely coupled approach is adopted for the fluid-structure interaction problem, with separate solvers used for the fluid and structural domains. The mesoflaps are rendered as immersed objects for the fluid solver and modeled as cantilevered Euler-Bernoulli beams for the structural solver. Determination of the aerodynamic loads acting on the mesoflap surfaces from the surrounding fluid is done using a nearest neighbor approach combined with a bi-linear interpolation scheme. Simulations are performed for a Mach 2.46 shock / boundary layer interaction with and without control, based on experiments conducted at University of Illinois at Urbana-Champaign. Both Reynolds-averaged Navier-Stokes (RANS) and hybrid large-eddy/Reynolds-averaged Navier-Stokes (LES/RANS) turbulence closures are used. For the computations of the flow with mesoflap control, both 2-D quasi-steady and 3-D dynamic simulations of the fluid-structure interaction problem are performed. Comparisons made with experimental laser Doppler anemometry data and wall pressure measurements for flows with and without control show reasonable agreement, with better predictions away from the separation region. An analysis of the flow indicates that the mesoflap control system does not eliminate axial flow separation. Also, analysis of the frequency content of the mesoflap deflections suggests that a correlation might exist between the dominant frequency of the flap deflection and the low-frequency shock motion observed in separated flows.

Flow Control in Mach 4.0 Inlet by Slotted Wedge-Shaped Vortex Generators

This work makes an attempt to determine an effective streamwise and spanwise arrangement of a relatively novel control device, the sub-boundary-layer slotted vortex generator, having a slot radius ...

An Immersed Boundary Method for General Flow Applications

The development of a direct-forcing immersed-boundary method for general flow applications is outlined in this paper. A cell-classification procedure based on a signed distance to the nearest surface is used to separate the computational domain into cells outside the immersed object (‘field cells’), cells outside but adjacent to the immersed object (‘band cells’), and cells within the immersed object (‘interior cells’). Interpolation methods based on laminar / turbulent boundary layer theory are used to prescribe the flow properties within the ‘band cells’. The method utilizes a decomposition of the velocity field near embedded surfaces into normal and tangential components, with the latter handled using power-law interpolations to mimic the energizing effects of turbulent boundary layers. A procedure for directly embedding sequences of stereo-lithography files as immersed objects in the computational is described, as are extensions of the methodology to compressible, turbulent flows. Described applications include human motion, moving aerodynamic surfaces, and shock / boundary layer interaction flow control.Copyright