Experimental Studies of Scramjet Inlet Restart in a Hypersonic Wind Tunnel

Experimental Studies of Scramjet Inlet Restart in a Hypersonic Wind Tunnel

Scramjet engines hold great promise for hypersonic propulsion, yet a significant design and operational challenge is ensuring the scramjet can resume operation after being unstarted, once the unstarting conditions have been removed — this process is known as restarting. Groundbased testing of inlet restarting requires facilities with sufficient flow duration for the transient f low processes to be completed. This thesis presents results from inlet restart-ability experiments conducted in the University of Southern Queensland’s (UniSQ) hypersonic wind tunnel (TUSQ). To measure the inlet captured mass flow rate in started, unstarted, and restarted states, a mass flow meter utilising a closed-plenum device was developed. This was coupled with a thermal model to estimate the heat transfer from the plenum gas to the vessel walls. Results show that with sufficient internal surface area arranged inside the plenum, heat transfer reaches a limit which eliminates the need to calibrate the meter for different flow conditions. Further work involved commissioning a large-scale vessel, sized to be suitable to measure captured mass flow from inlets tested in the TUSQ facility. Experiments examining rapid backpressure depressurisation as a method for inlet restarting are documented for the first time. This depressurisation restarting method was tested on a two-dimensional scramjet inlet with optical access by rapidly removing air injected normal to inlet flow at the rear of the inlet. Results indicate that if a sufficiently high rate of injection depressurisation is achieved, the inlet temporarily enters a buzz mode before restarting. However, restart is not achieved if the depressurisation rate is too long. To demonstrate the capabilities of the methods developed in this thesis, restart-ability testing was conducted on a 75% scale model of the HIFiRE 7 scramjet engine flow path. Testing the inlet over a range of flight-equivalent Reynolds numbers revealed that the inlet was incapable of restarting once sonic air injection in the combustor was removed. Various uncontrolled experimental parameters that might have influenced the inlet’s restart-ability were identified, including the Tw To which was 4 orders of magnitude greater at the testing conditions compared to flight. Future work should explore the impact of such parameters.

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