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An Experimental Study of the Buzz Frequency and its Relation with the Corresponding Eigen Frequency in an Axisymmetric Supersonic Inlet

Asgari Kaji, Mohmmad Hassan | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40449 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza
  7. Abstract:
  8. All supersonic intakes with external compression, having a good level of performance at all the critical poin t. Exhibit a marked instability of flow in subcritical operation below some value of the flow ratio, in the form of an oscillation of the shock system, colloquially known as “buzz", which can lead to thrust loss, engine surge or even structural damages. Therefore the effort to understand the nature and cause of this phenomenon is important in order that the starting of buzz can be predicted and more effectively avoided without losing performance. This phenomenon has been the subject of many studies, mainly experimental. In this research, we design and build an axisymmetric supersonic external compression inlet for a ramjet engine in an applicable size and geometry. The model was installed in the Emam Hossein University's supersonic blow down wind tunnel which had different facilities and accessory equipments that enabled us to conduct the experiment in appropriate runtime to reach the proper conditions for data acquisition. The inlet was richly equipped with steady and unsteady pressure sensors and the tests were conducted in different conditions for the first time in Iran like: AOAs as 0°, 3°, 6° and 10° , Mach numbers as 1.6, 1.8, 2.0, 2.2 and 2.5 and different mass flow rates. Shadowgraph flow visualization was used to capture the external shock formation in front of the inlet. The shadowgraph pictures were taken using a high speed camera operating at 1000 frames per Second. The scope of this study is to investigate the general characteristics of the inlet Buzz at the external design and off-design conditions. Amplitude and frequency of shock waves are obtained from the pictures recorded by Schilerian system in different conditions. The results show that in the same big value of flow rate, in different experiments, the frequency of shock oscillation increased versus Mach number. Also in each Mach number due to the flow rate decrement, the Buzz's frequency decreases and its amplitude increases vice versa. When the inlet operates with a big flow rate, normal shock moves to the inlet entrance and oscillate with a small amplitude. When the free-stream is not parallel to the center body axis, the shock structures becomes asymmetric with respect to the enter body. As a result, a leading conical shock angel increases and the shock becomes weaker on the leeward side compared to the A.O.A. 0°, and vice versa on the windward side.

  9. Keywords:
  10. Input ; Instability ; Supersonic Flow ; Frequencies ; Buzz Phenomenon

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