Unsteady aerodynamics of an ablating flared body of revolution including effect of entropy gradient.

The dynamics of an ablating, flared re-entry body are complicated by the effects of the shear flow generated by the blunted nose at hypersonic speeds. On a nonablating flared re-entry body, these entropy effects are statically stabilizing but dynamically destabilizing. However, the flow shear has opposite effects on the forces generated by ablative mass addition, and at high ablation rates the total entropy gradient effects on a shallow flare may become statically destabilizing and dynamically stabilizing. In addition to these forces induced by the entropy gradient, the flare experiences the usual forces generated in the reduced average velocity flowfield aft of the bow shock. The nonablating local flare forces are statically and dynamically stabilizing, whereas the local ablation effects are statically stabilizing but dynamically destabilizing. Even for moderate ablation rates, the total local flare forces become dynamically destabilizing. The total effect of an ablating flare will almost always be undamping and could cause the re-entry body to become dynamically unstable even when ablation rates and thermodynamic time lags are of moderate magnitudes.