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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 42731 (45)
- University: Sharif University of Technology
- Department: Aerospace Engineering
- Advisor(s): Soltani, Mohammad Reza; Massoud, Afshin
- Abstract:
- Buzz is a phenomenon caused by the self-sustained shock oscillations in most supersonic inlets. When the entering mass flow is reduced below a specific value, inlet buzz occurs and results in variations of both inlet mass flow and pressure. An extensive wind tunnel tests were conducted on an axisymmetric supersonic inlet at Mach numbers from 1.8 to 2.2, at different values of mass flow rates, and at various angles of attack, α=0-10 degrees, to study the inlet buzz phenomenon. For each test, pressure distributions over the inlet cowl and spike were measured and the flow was visualized by means of the shadowgraph system and a high speed camera to obtain main performance characteristics of the inlet during its stable and unstable operation. As the Mach number is increased the pressure recovery is reduced, but maximum value of the mass flow rate grows up. The results of the stable operation of the inlet showed that, variations of the mass flow affects the surface pressure over both the front portion of the cowl and the entire surface of the spike. Further it has changed both pressure and Mach number at the end of the diffuser. When the inlet instability was initiated, two main frequencies for the buzz were seen in the data. For the moderate mass flow rates, small amplitude and high frequency oscillation (little buzz) occurred. In this operation stage both high and low frequency oscillations with irregular period existed, but the higher one was dominant and was very close to the frequency of the second acoustic resonance mode. This phenomenon showed that the acoustic resonance characteristics of the inlet affects the frequency of little buzz. At lower mass flow, however, low frequency and large amplitude oscillation (big buzz) occurrs that has a single frequency with a constant period. At a free stream Mach number of 2.2, the frequencies of these two kinds of instabilities were about 554 Hz and 137 Hz respectively. At this Mach number and for the moderate mass flow an oscillation with high frequency/large amplitude and constant period was observed. The oscillation had the combined characteristics of the little buzz and the big buzz, which is named “added buzz” in this research. It is shown that at fairly constant mass flow the frequency of the buzz is independent of the Mach number. It is further found that the buzz instability affects the external flow as well as the internal one with the same frequency. Increasing the angle of attack decreased the inlet performance and limited the stability margin. At intermediate values of the mass flow, the buzz frequency was seen to be independent of the angle of attack but for the lower mass flow rates and at high angle of attack, the frequency of buzz at front portions of the inlet varied. However, the flow at the diffuser end has still a constant frequency. Total pressure signal had behavior similar to that of the static pressure data with approximately the same frequency
- Keywords:
- Buzz Phenomenon ; Attack Angle ; Supersonic Flow ; Axisymmetric Inlet Performance ; Added Buzz ; Little Buzz ; Supersonic Flow Instability ; Mach Number Effect
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