Effects of Structural Motion on Separation and Separation Control: An Integrated Investigation using Numerical Simulations, Theory, Wind-Tunnel and Free-Flight Experiments

Abstract

A combined investigative approach which employs high-fidelity numerical simulations, wind & water-tunnel and free-flight experiments is taken to investigate the fundamental flow physics of separation and separation control for wing sections undergoing temporal motions. Detailed investigations of the underlying unsteady flow physics have been carried out for the X-56A airfoil at nominal angles of attack of 10 and 12 degrees for Re = 200k. The reduced frequency of the structural motion is k=0.7 and the plunging amplitude is 3.2% and 4.8% of the chord length. For 10deg AoA, the agreement between the measurements, simulations, and Theodorsen's theory is good even though the instantaneous angles of attack during the airfoil oscillations are outside the linear CL - AoA regime and extend into the region associated with static stall. As the angle of attack is increased to 12deg, the flow over the suction surface of the wing begins to intermittently separate and Theodorsen's theory fails. Experiments and simulations show strong qualitative agreement and both capture "bursting" of the laminar separation bubble near the leading edge of the airfoil. Furthermore, highly resolved Direct Numerical Simulations (DNS) were performed in order to investigate the hydrodynamic instability mechanisms and transition to turbulence in swept laminar separation bubbles.