The stability of twodimensional wakes and shearlayers at high Mach numbers
Abstract
The stability properties were studied of laminar free shearlayer flows, and in particular symmetric 2D wakes, for the subsonic through the hypersonic regime. Emphasis is given to the use of proper wake profiles that satisfy the equations of motion at high Reynolds numbers. In particular, the inviscid stability of a developing 2D wake as it accelerates at the trailing edge of a splitter plate was studied. The nonparallelism of the flow is a leading order effect, and the undisturbed state is solved numerically. The neutral stability characteristics are computed numerically and the hypersonic stability is obtained by increasing the Mach number. It is found that the neutral stability characteristics are altered significantly as the wake develops. Multiple modes (second modes) are found in the nearwake (they are shown to be closely related to the corresponding Blasius ones), but as the wake develops, mode multiplicity is delayed to higher and higher Mach numbers. At a distance of about one plate length from the trailing edge, there is only one mode in a Mach number range of zero to twenty. The dominant mode emerging at all wake stations and for high enough Mach numbers is the socalled vorticity mode, which is centered around the generalized inflection point layer. The structure of the dominant mode is also obtained analytically for all streamwise wake locations and it is shown how the farwake limit is approached. Asymptotic results for the hypersonic mixing layer given by a tanh and a Lock distribution are also given.
 Publication:

Final Report Institute for Computer Applications in Science and Engineering
 Pub Date:
 May 1990
 Bibcode:
 1990icas.reptQ....P
 Keywords:

 Computational Fluid Dynamics;
 Flow Stability;
 High Reynolds Number;
 Hypersonic Flow;
 Inviscid Flow;
 Laminar Flow;
 Mach Number;
 Shear Layers;
 Two Dimensional Flow;
 Wakes;
 Boundary Layers;
 Flat Plates;
 Inflection Points;
 Mixing Layers (Fluids);
 Trailing Edges;
 Vorticity;
 Fluid Mechanics and Heat Transfer