Study of Restricted Shock Separation Phenomena in a Thrust Optimized Parabolic Nozzle

摘要

An experimental investigation has been carried out on a subscale thrust optimized parabolic nozzle (area ratio ofn30) to study the flow characteristics prevalent during a partially formed restricted shock separation and a fullynformed restricted shock separation condition, each of which are observed to be discrete in nature.Whereas the wallnpressure signal near the nozzle exit randomly alternates between its value in the backflow region and that abovenambient (i.e., flow randomly alternates between a free shock separation and restricted shock separation transitionncondition and vice versa) as a function of time for a partially formed restricted shock separation condition, the wallnpressure in a fully formed restricted shock separation condition fluctuates in values above ambient in the region ofnflow reattachment. Further, the transient conditions of free shock separation to partially formed restricted shocknseparation and end-effect regime are studied in detail.The preceding transitions and retransitions suggest a variationnin the relative axial positions of normal and separation shocks that favors a fully formed restricted shock separationnto occur during shutdown. A second separation bubble is also observed in the restricted shock separation condition,nthe formation and opening of which is seen to contribute toward side-load peaks. Results also indicate that thenseparation shock translates back and forth (flapping motion) and experiences spanwise perturbations (ripplingnmotion). The results are based on simultaneously acquired real-time wall pressure measurements, surface oilnvisualization technique, high-speed schlieren images, and signals from strain gauges installed on the nozzle bendingntube.