Prediction and control of periodic flows

The Applied Computational Engineering Research Group (ACERG) at The Queens University of Belfast has recently carried out a detailed numerical investigation, studying the ability of two "in-house" Navier-Stokes codes to accurately predict and control periodic flow over rigid airfoils. Firstly, an explicit cellvertex-centred full-mass averaged Navier-Stokes code MGENS2D is employed in conjunction with a hyperbolic C-grid generator. Results are then compared with ACERG's 2-D implicit thin-layer Navier-Stokes code NAVIER operating over an identical hyperbolic Cgrid. Turbulence closure is accomplished in both cases using a modified version of the zero equation algebraic Baldwin-Lomax model. In the transonic flow regime both codes accurately predict the shock induced oscillation onset boundary and reduced frequencies for an 18% thick circular-arc airfoil. In addition the explicit code also reproduces the experimentally detected hysteresis region: only by employing the full massaveraged Navier-Stokes equations, operating on a suitably fine grid, can the dynamic shear layers be adequately resolved. Three control methodologies for this flow regime are successfully investigated, namely: passive control, heat transfer and varying length trailingedge splitter plates. In the low-speed high angle-ofattack periodic flow regime MGENS2D accurately reproduces the periodic leading-edge vortex shedding which was experimentally detected for a NACA0012 airfoil. Using Darcy's Law to simulate a 65% chord * Lecturer and Director of CFD Research, ACERG, Department of Aeronautical Engineering, Member AIAA. ** Lecturer and Director of FEA Research, ACERG, Department of Aeronautical Engineering, Member AIAA * Head of Department, Department of Aeronautical Engineering, Member AIAA. § PostGraduate Research Student, Department of Aeronautical Engineering. Copyright © 1997 by Mark A. Gillan. Published by the American Institute of Aeronautics and Astronautics , Inc with permission. upper surface porous region, the code demonstrates the ability of passive control to suppress periodic vortex shedding and therefore alleviate buffet. Finally, suction control applied in the vicinity of 1-10% chord of the airfoil's upper surface is also shown to eliminate buffet.

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