Abstract
Comprehensive numerical analyses are conducted to simulate and capture “Buzz” phenomenon in a supersonic mixed compression air inlet. The buzz is an unsteady self-sustained feature that occurs in supersonic inlets, especially when operating in their subcritical condition. In such a situation, the shock waves oscillate along the inlet and cause mass flow fluctuations inside the inlet that will deteriorate the engine performance significantly. An axisymmetric unsteady numerical simulation was used to solve the Navier–Stokes equations combined with the URANS SST k–ω turbulence model. The simulations for two different free-stream Mach numbers of M∞=2.0 and 2.2 and at two specific subcritical conditions of the inlet operation, where the buzz was experimentally detected, were performed. The numerical solution was able to accurately capture the buzz and its oscillation which is seen to be periodic for this specific inlet. The results show that a large separation region on the compression ramp blocks the duct entry and causes conical and lambda shocks, which are formed on the compression ramp, to move upstream and creates the self-sustained oscillation. The predicted buzz frequencies are in a good agreement with the experimental frequencies calculated based on the surface pressure data with a discrepancy of less than 2%. Further, the peak and trough of both total and static pressure fluctuations and, as a result, the amplitude of buzz all are accurately predicted. The inlet performance curve during the buzz cycle indicates that both TPR and MFR values fluctuate about 70% and 60% of their maximum possible values, respectively. In addition, the influence of the Hysteresis-Effect on the inlet operation and its performance curve is beheld clearly.
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