An Immersed Boundary Method for Simulating the Effects of Control Devices used in Mitigating Shock / Boundary-Layer Interactions

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Title: An Immersed Boundary Method for Simulating the Effects of Control Devices used in Mitigating Shock / Boundary-Layer Interactions
Author: Ghosh, Santanu
Advisors: Dr. J. R. Edwards, Committee Chair
Dr. H. A. Hassan, Committee Member
Dr. T. Echekki, Committee Member
Dr. M. A. Zikry, Committee Member
Abstract: This work presents an immersed boundary (IB) technique for compressible, turbulent flows and applies the technique to simulate the effects of three different devices used in controlling oblique-shock / turbulent boundary layer interactions – wedge shaped micro vortex generators (VG), an array of bleed holes, and aeroelastically deflecting mesoflaps. 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 solutions obtained using the IB technique with solutions obtained on 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. RANS simulations performed for an impinging oblique shock / boundary layer interaction at Mach 2.5 indicate 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. To assess the effectiveness of this device in the absence of side-wall effects, an idealized, nominally two-dimensional interaction using both the RANS and the LES/RANS models is also done. Results for the idealized interaction show that 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. Simulations of an impinging oblique shock / boundary layer interaction at Mach 2.45 with and without bleed flow control predict Pitot-pressure distributions which are in good agreement with experimental data. Flow control at two different bleed rates is considered, with the maximum bleed rate completely removing the separation region. Swirl strength probability density distributions, and 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. Simulations are also performed for an impinging oblique shock / boundary layer interaction at Mach 2.46, with and without mesoflap control, based on experiments conducted at University of Illinois at Urbana-Champaign. To simulate the flow-control with the mesoflap array, a loosely coupled fluid-structure interaction problem is solved, in which the mesoflaps are modeled as cantilevered Euler-Bernoulli beams. Results indicate that the transpiration caused by the mesoflap system does not eliminate axial flow separation. Analysis of the frequency content of the mesoflap deflection suggests that a correlation might exist between the dominant frequency of the flap deflection and the low-frequency shock motion observed in separated flows.
Date: 2010-04-30
Degree: PhD
Discipline: Aerospace Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/6201


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