Numerical Investigation of Separation Bubble Characteristics in the Low-Reynolds-Number Airfoil (KSAS EFD-CFD Workshop Case 5) Using Implicit Large Eddy Simulation

초록

Implicit large eddy simulations are undertaken to investigate the flow characteristics over a low-Reynolds-number airfoil, as proposed in the Korean Society for Aeronautical and Space Sciences Experimental and Computational Fluid Dynamics workshop. Laminar separation bubbles emerge on the suction surfaces even at relatively moderate angles of attack within the low-Reynolds-number flow regime, transitioning from the trailing edge towards the leading edge. Non-linear aerodynamics arising from separation are simulated using GPU-accelerated solver PyFR. A parametric study was conducted to assess the effects of solution polynomial order, grid resolution, spanwise domain extent, and computational precision, leading to the identification of optimal simulation conditions. The results confirmed that a fourth-order accurate simulation, a spanwise length of 0.5 times the chord, and single-precision computation provided an effective balance between accuracy and computational efficiency. Comparisons with experimental data from the Mars Wind Tunnel at Tohoku University demonstrate that the simulations predicted the non-linear lift characteristics and stall behavior observed experimentally. Additional simulations incorporating a virtual side wall model accounted for wind tunnel wall interference effects, revealing that wall-induced disturbances significantly reduced the size of the laminar separation bubble near the side walls. This reduction mitigated non-linear lift behavior during leading-edge stall, further aligning simulation results with experimental observations.