Computational Study of Drag Reduction at Various Freestream Flows Using a Counterflow Jet from a Hemispherical Cylinder

Abstract

A computational study of the counterflow drag reduction by a cold supersonic jet from a hemispherical cylinder at four different hypersonic freestream flows is conducted by solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations with the two-equation k-ɛ turbulence model. The investigations focused on two different flow regimes, SPM (short penetration mode) → LPM (long penetration mode) and LPM to ensure that the maximum drag reduction is achieved. For the present configuration, the oscillatory flow regime SPM→LPM remains dominant over the most of the pressure ratios at all the freestream flows investigated. A higher drag reduction is obtained for the higher Mach number flows at a constant pressure ratio which can be attributed to the increase in relative mass flow rate of the jet. The physical mechanism suggests that the drag reduction using a counterflow jet with different oncoming freestream flows can be expressed as a function of mass flow ratio. A relation describing the drag reduction at various freestream flows as a function of the relative mass flow rate is proposed.