EFFECT OF BOUNDARY-LAYER TRANSITION ON VEHICLE DYNAMICS

The effect of boundary-layer transition on vehicle dynamics is a well known, but poorly understood, phenomenon. Severe loss of dynamic stability has been observed to result on ablating vehicles when boundary-layer transition moves up over the base onto the aft body. This effect is caused by the increased (turbulent) aft body heating, and is equivalent to changing to a coating with higher ablation rate on the aft body. Another more subtle effect of boundary-layer transition results from the transition sensitivity to body attitude. Dynamic tests of nonablating slender cones have shown that increased damping and decreased static stability results when boundary-layer transition occurs on the aft body. An analysis using previously developed unsteady concepts for separated flow correctly predicts the relation between dynamic and static effects of boundary-layer transition. The dynamic amplification of static effects is twice as large for sharp as for blunted cones because of oscillatory flow acceleration effects on the sharp cone boundary-layer transition. It is found that the boundary- layer transition sensitivity to body attitude has beneficial effects on the vehicle dynamics up to high supersonic speeds. However, at hypersonic speeds nose-bluntness-induced entropy swallowing may cancel and even reverse this trend, greatly aggravating the undamping effect of turbulent aft body (heating and) ablation. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.