On the absolute instability of the triple-deck flow over humps and near wedged trailing edges

The triple-deck equations for the flow over a hump, a corner and a wedged trailing edge are solved numerically using a novel method based on spectral collocation. It is found that for the flow over a corner, separation begins at a scaled angle β of 2.09, and for the wedged trailing edge for a wedge angle of 2.56. Here β is defined in terms of the small physical angle φ by β = Re1/4λ-1/2φ, λ = 0.3320, and Re is the Reynolds number. The absolute instability of the nonlinear mean flows computed is investigated. It is found that the flow over a hump is inviscidly absolutely unstable with the maximum absolute unstable growth rate occurring near the maximum height of the hump, and increasing with hump size. The wake region behind the wedged trailing edge is also found to be absolutely unstable beyond a critical wedge angle, and the extent of the region of absolute instability increases with increasing wedge angle and separation.