Oscillatory Jets – Benefits and Numerical Modeling Issues

Numerical simulations were conducted to demonstrate the benefits of an oscillatory “zero-net mass” jet for improving the static and dynamic stall/post-stall aerodynamic characteristics of the VR-7 helicopter rotor airfoil. Here, a transpiration boundary condition is implemented into the solution for the thin layer Reynolds averaged Navier-Stokes (RANS) equations to emulate the temporal variations in the oscillating jet velocity. Effects of two turbulence models on the accuracy of the resulting solutions are presented and the importance of accurate specification of the points of laminar-to-turbulent transition is demonstrated. Modeling issues relating to the specification of a meaningful jet boundary condition are presented. Difficulties associated with the accurate prediction of the unsteady aerodynamic loads for a pitching airfoil are also discussed. Where applicable, comparisons with two-dimensional wind tunnel data is presented.