Applications of a counterflow drag reduction technique in high speed systems

Abstract

Potential applications of a counterflow drag-reduction technique were investigated to assess performance improvements on aerospace vehicles. The motivation for this study was the 30-50% drag reduction achieved by counterflow blowing experiments on hemispherical cylinders at Mach 4 and higher. Exploratory studies indicate that drag improvements by counterflow drag reduction on hemispherical bodies cannot match those of aerodynamically shaped sharp-nosed bodies. Hence, the approach taken in the present study is that for hypersonic Mach numbers: if the nose shape is required to be blunt for considerations other than drag, counterflow blowing can be effective in improving the performance of the system. Although for generic body shapes counterflow blowing is most effective for blunt-nosed bodies, when applied to actual systems, many other factors need to be considered, such as available internal volume and extreme compressed carriage requirements. Depending on the vehicle speed and nose shape, estimated drag reductions of 15-30% were applied to predict the overall performance gains on Space Operations Vehicle, Gun-Launched Rocket, and Pegasus XL configurations. Potential savings in propellant and improvements in burnout velocity and range are reported. For launch systems with high fuel fraction, the payoff with counterflow drag reduction is marginal as the overall effects of aerodynamic drag on performance are small in the upper atmosphere. For the lower fuel fraction vehicle, the Gun Launched Rocket, a range improvement of 7% was achieved for a drag reduction of 30% with 0.3 blunting of nose flying above Mach 3; with greater blunting, however, the volume of fuel cannot compensate for the increase in drag.