Dynamics of Shock Dispersion and Interactions in Supersonic Freestreams with Counterflowing Jets

Abstract

This study describes an active flow control concept that uses counterflowing jets to significantly modify external flowfields and strongly disperse the shock waves of supersonic and hypersonic vehicles to reduce aerothermal loads and wave drag. The potential aerothermal and aerodynamic benefits of the concepts were investigated by conducting experiments on a 2.6%-scale Apollo capsule model in Mach 3.48 and 4.0 freestreams in a trisonic blowdown wind tunnel, as well as pretest computational fluid dynamics analyses of the flowfields, with and without counterflowing jets. The model employed three sonic and two supersonic (with design Mach numbers of 2.44 and 2.94) jet nozzles with exit diameters ranging from 0.25 to 0.5 in. The schlieren images were consistent with the pretest computational fluid dynamics predictions, showing a long penetration mode jet interaction at low jet flow rates of 0.05 and 0.1 Ib m /s, whereas a short penetration mode jet was revealed at higher flow rates. The long penetration mode jet appeared to be almost fully expanded and was unsteady, with the bow shock becoming so dispersed that it was no longer discernible. High-speed camera schlieren data revealed the bow shock to be dispersed into striations of compression waves, which suddenly coalesced to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. Heat transfer results showed a significant reduction in heat flux, even giving negative heat flux for some short penetration mode interactions, indicating that the flow wetting the model had a cooling effect, instead of heating, which could significantly impact thermal protection system requirements and design. The findings suggest that high-speed vehicle design and performance can benefit from the application ofcounterflowing jets as an active flow control.