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 t railing 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 beta of 2.09, and for the wedged trailing edge for a wed ge angle of 2.56. Here beta is defined in terms of the small physical angle phi by beta = Re(1/4)lambda (-1/2)phi, lambda = 0.3320, and Re is the Reyn olds number. The absolute instability of the nonlinear mean flows computed is investigated. It is found that the flow over a hump is inviscidly absolu tely unstable with the maximum absolute unstable growth rate occurring near the maximum height of the hump, and increasing with hump size. The wake re gion behind the wedged trailing edge is also found to be absolutely unstabl e beyond a critical wedge angle, and the extent of the region of absolute i nstability increases with increasing wedge angle and separation.