Influence of the Compressibility of an Axisymmetric Flow Around a Cylinder with Coaxial Disks of Optimum Arrangement for Its Frontal Resistance at Transsonic Flow Velocities

A numerical investigation of the influence of the compressibility of the air flowing around a disk-cylinder-disk set with an outward-projecting disk of diameter 0.4 and a clearance between this disk and the cylinder of 0.98, close to the optimum one as to the profile drag for the movement with a transonic velocity at Mach numbers of 0-2, on the circulation air flow in the clearance and on the frontal resistance of the set has been performed. The adequacy of the numerical estimates made was substantiated by their comparison with the corresponding results of experiments in a wind tunnel. It was established that in the transonic Mach number range 0.7-0.8, the structure of a vortex in the clearance between the outward-projecting disk and the front edge of the cylinder is rearranged. Because of this, unlike the axisymmetric flow of air around a disk-cylinder-disk set optimum for an incompressible medium, normal and oblique shocks are not formed over the shear layer of the detached flow in the indicated clearance, and, at M = 0.9, a lambda-like shock is formed over the side surface of the cylinder. The wave drag of a disk-cylinder-disk set, optimum for transonic velocities, increases at a smaller rate with increase in the Mach number and appear to be smaller by almost two times compared to the wave drag of a disk-cylinder-disk set optimum for the deep subsonic velocities.