Numerical investigation of miniature trailing-edge effectors on static and oscillating airfoils

The aerodynamics of deployable devices based on Gurney flaps, miniature trailing-edge effectors, or MiTEs, is explored for rotorcraft applications using computational fluid dynamics (CFD). A Gurney flap is a small aerodynamic device, with a height of only a few percent of the airfoil chord, mounted normal to the airfoil surface near the trailing edge. A MiTE extends the Gurney flap concept by making it deployable. To support future design efforts, and because fully dynamic wind-tunnel experiments would be difficult and costly, the unsteady behavior of MiTEs is studied for a static airfoil and during airfoil-pitch oscillations using the Navier-Stokes numerical solver OVERFLOW2. Static wind-tunnel tests from low-speed wind-tunnel experiments that explore the effects of Gurney flaps at a chord Reynolds number of 1.0×10 ⁶ are used for the calibration and verification of the CFD. The results indicate similar effects along with qualitatively correct behavior, and the trends in the predicted dynamic performance are reasonable in that they agree with unsteady circulatory theory. In addition, wind-tunnel experiments of an oscillating rotorcraft airfoil using Gurney flaps through dynamic stall are also used for validation. These experiments verify the CFD models, allowing the extension of the studies to examine the potential of MiTE for rotorcraft. Much insight is gained on the unsteady aerodynamic behavior through transonic flow conditions, at high angles of attack, and with variations in the chord-wise placement of MiTEs. Additionally, CFD is used to show that MiTEs have the ability to be used as an active stall control device. These studies show that there does not appear to be any significant shortcoming of MiTEs potential for rotorcraft.