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An Experimental Investigation On The Effect Of Laser Energy Deposition In An Over-Expanded Jet

S Syam, Gauresh Raj Jassal, Bryan E. Schmidt

Case Western Reserve University, Cleveland, Ohio, United States


The shock train structure of a supersonic over-expanded jet is the product of the interaction between the jet flow at the nozzle exit and the ambient environment. Although the effect of flow disturbances on the performance of the supersonic inlets has been studied in detail, a limited understanding of the shock train dynamics subject to flow disturbances is available for over-expanded jets. This experimental investigation focuses on understanding the influence of perturbations due to short-duration energy deposition on the shock train structure and its dynamics in an axisymmetric over-expanded Mach 2.52 jet. The flow is perturbed by laser-induced breakdown, creating a shock wave and a high-temperature plasma zone in the shock train. A high-speed self-aligning focusing schlieren system is used to visualize the flow structure variations by measuring the shock angles and Mach disk height and width to characterize the shock train dynamics and the flow structure recovery process. The response of jet flow to the perturbation at the nozzle exit and the pre-reflection point is found to be similar, however, the response of the supersonic jet to the post-reflection energy deposition is significantly different. The damping ratio for the pre-reflection point and nozzle exit cases found are nearly constant for all scenarios whereas it is linearly dependent on the jet chamber pressure for the post-reflection cases. The frequency of the oscillations is found to be the same for all cases and irrespective of the chamber pressure, laser energy, and deposition location, approximately 10 kHz. The transition from Mach to regular reflection and vice versa are observed at a chamber pressure of Pc = 689 kPa. Any perturbation to the shock structure of a supersonic over-expanding jet at close to the steady-state bifurcation condition between Mach and regular reflection will exhibit Mach-to-regular transition or vice versa.

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