Modeling Three Dimensional Effects on Cross Flow Instability from Leading Edge Dimples

Abstract

The formation of shallow dimples near the leading edge of natural laminar flow wings can occur during operation due to impact by hail, potentially changing the stability characteristics and causing an early transition to turbulence downstream of the dimple. Changes in the base flow will be strongly three-dimensional in character putting this problem beyond the capability of the standard strip based approaches founded on conical flow assumptions that are routinely used in the aerospace industry. This paper describes the application of a fully 3d method to a dimple on a wing for flow resembling that on a natural laminar flow wing. Solving the three-dimensional compressible boundary layer equations for the base flow and using a point to point marching scheme for solving the 3d PSE equations, it is shown that high wave-number stationary cross-flow modes can become unstable and grow rapidly in the dimple wake in a region well beyond the leading edge where stationary cross-flow modes would normally be decaying.