Plasma Control of Forebody Nose Vortex Symmetry Breaking

Abstract

Flight vehicle forebody vortex symmetry breaking and control of resulting yaw departure by surface plasma discharges are considered. To assess effectiveness of this control concept, stability of the vortex pairing over slender bodies at incidence is analyzed. For this purpose, the stability of the separation saddle point at the origin of the feeding sheet in the cross flow plane is assessed. A discrete point vortex model and slender body theory are used identify key dimensionless parameters and model the basic physics. Computations are performed for a circular cone. The analysis can be extended to arbitrary-shaped bodies using appropriate scaling and conformal mapping. It is shown that the symmetric vortex structure arising in the model is absolutely unstable to small but finite disturbances that are governed by the Ginzburg-Landau equation. Although the vortex system is stable in a linear approximation applicable to infinitesimal perturbations, it is unstable to finite disturbances due to nonlinear effects. Spatial and temporal evolution of the perturbations is studied and critical initial amplitudes of the instability are obtained. Stability of the point vortices to small symmetric and asymmetric displacements is analyzed. Theoretical results are validated against experimental data. Parametric studies show that the vortex structure can be controlled by artificial displacements of the separation locus. A new method to achieve such vortex flow control using a plasma discharge on the body surface is considered. The effect of the discharge is simulated as a volumetric heat source interacting with the turbulent boundary layer. Theoretical estimates from this model indicate that this approach can control stall-spin departure due to forebody symmetry breaking.