LOW DENSITY TRANSITIONAL REGIME DRAG COEFFICIENTS FOR SLENDER COLD WALL CONICAL VEHICLES IN HYPERSONIC FLOW

Abstract

Abstract : A survey of numerical results of low-density transitional regime drag coefficients and number density distributions about slender, cold-wall, conical vehicles at hypersonic speeds is presented. The transitional regime results have been obtained from numerical solutions of Rosen's restricted variational principle representation of the Boltzmann equation, which has been shown to be equivalent at Galerkin's method of solution of operator equations. Transitional regime drag coefficients are compared with near free molecule and viscous interaction predictions of drag coefficients. Number density profiles for the transitional regime are also given and compared with known qualitative features of near continuum flow fields to assess the validity of results obtained by the variational method. Results indicate that the drag coefficient varies smoothly from known viscous interaction predictions and reaches the limiting value of 2 when the freestream Knudsen number is on the order of unity for the class of slender cones considered. A decrease of cone-half-angle, with Knudsen number fixed, results in a steeper rise of the drag coefficient curve toward the limiting high Knudsen number value of 2. For cone half-angles on the order of 5 degrees, the drag coefficient curve exhibits an overshoot over the free molecule value.