Unsteady wave drag reduction in hypersonic flows: Correlations and influences of and location

This paper presents a numerical study on the unsteady wave drag reduction realized through single pulse energy addition in a hypersonic stream. A single energy pulse of sufficient magnitude added to the stagnation line ahead of a 600 apex angle sphere-cone model placed in a Mach 5.75 stream is analyzed. An in-house developed Finite Volume compressible flow solver is tuned to analyze the flow features and time-dependent drag reduction offered by the pulse energy deposition. Two different flow features are found to be responsible for the drag reduction, one is the lens effect induced by the low-density core of blast wave and the second one is the baroclinic vortex created due to the blast wave-shock wave interaction. Propulsive energy savings associated with different combinations of energy addition parameters is quantified. Based on the 30 data sets generated from the current numerical study, scaling laws are proposed. The proposed scaling laws and mathematical framework derived are found to be suitable to judge the energy demand to realize drag reduction in varied flow and geometric conditions. For the sphere-cone model chosen for the current study, a maximum of 5.2% saving in propulsive energy demand is obtained with a single energy pulse 0.5 J added 50 mm upstream of the blunt body.