Separated flow past smooth slender bodies
Abstract
This dissertation describes an investigation of the separated flow past slender bodies at high angles of attack. Flows of this type occur on aircraft and missile forebodies and can develop large forces which are important when considering stability and control of the vehicle. The objective of this work is to extend the vortex sheet model, which has previously been implemented for slender wings and circular and elliptic cones, to cones of more general crosssection and to nonconical bodies. The crosssections of the bodies studied here are basically square or triangular, but with rounded corners. The model is inviscid, so the separation positions must be prescribed. Two distinct families of solutions have been identified. For laterally symmetric configurations with symmetric separation positions and no yaw, the first family solutions are symmetric, whereas the second family solutions are asymmetric. For elliptic cones, it is known that crosssection thickness affects the degree of asymmetry of the flow and this represents a mechanism for the control of side forces. Square or triangular crosssections with rounded corners are of interest to aerodynamicists and have been investigated to assess the effect on asymmetry of making a circular crosssection 'square' or 'triangular'. For 'square' and 'triangular' cones placed either side, or corner on to the flow, results are obtained which enable the effect of crosssection shape on the degree of asymmetry to be assessed. A nonconical vortex sheet model has been developed for the first time for separation from a smooth body. Previously a nonconical linevortex model was implemented, however lack of representation of vorticity near the separation line limits the applicability of the results. The solution procedure for the nonconical problem consists of a downstreammarching scheme starting from a known solution at the nose. Starting solutions are available if the flow at the nose is assumed conical. With symmetry enforced, solutions have been calculated far downstream, however progress for asymmetric solutions has been more limited. In the asymmetric case the vortex sheet develops inflexions which cause the solution procedure to fail. The nonconical formulation also permitted a stability analysis to be carried out for conical linevortex solutions, which show that where asymmetric solutions exist they are stable and the corresponding symmetric solutions are unstable.
 Publication:

Ph.D. Thesis
 Pub Date:
 February 1991
 Bibcode:
 1991PhDT........63W
 Keywords:

 Aerodynamic Configurations;
 Conical Bodies;
 Separated Flow;
 Slender Bodies;
 Vortex Sheets;
 Angle Of Attack;
 Corners;
 Forebodies;
 Inviscid Flow;
 Mathematical Models;
 Vorticity;
 Fluid Mechanics and Heat Transfer