On the temporal response of active load control devices

Flow around airfoils with deploying microtabs and microflaps (or dynamic Gurney flap) have been numerically simulated by solving the unsteady turbulent compressible 2-D Navier-Stokes equations with the OVERFLOW 2 solver. Microtabs and microflaps on the order of 1%c were installed in the trailing edge region of the symmetric NACA 0012 airfoil using a Chimera or overset grid topology. The devices were deployed on the order of one characteristic time unit, and the unsteady aerodynamic responses of both devices were compared. The two devices appear to affect the flow similarly by creating a low pressure region aft of the device and changing the Kutta condition. While initial transients varied, the post-deployment aerodynamic response showed a very similar temporal evolution towards a mean asymptotic solution. Both devices reached 90% of mean steady-state lift values by approximately nine characteristic time units from the onset of deployment. Drag and pitching moments evolved significantly faster. The temporal development of these devices is not governed by near-body effects, and instead is an advection driven process. Microflap deployment times of 0.25, 0.50 and 1.00 characteristic time units were also examined. The corresponding mean aerodynamic coefficients for the three deployment times were comparable by one characteristic time unit after deployment. Validation studies with experimental results comparing shedding frequencies and Strouhal numbers for static, deployed microtabs and microflaps were also performed to ensure accurate temporal resolution and convergence of the numerical simulations. Copyright (C) 2009 John Wiley & Sons, Ltd.