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Experimental Aeroacoustic Investigation of Transient Impinging Jet Using Shock Tube

Bahman Jahromi, Iman | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50902 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Ebrahimi, Mohammad; Ghorbanian, Kaveh
  7. Abstract:
  8. Supersonic impinging jets, similar to the jet flows exhausted from a nozzle, generate high unsteady pressure and acoustic loads on the rocket payload or the VTOL aircraft structure with possible mission failure during the launch/starting phase. In the past, experimental studies were concentrated on characterizing the steady impingement flow and not the initial transient process. It was shown that one of the main characteristics of supersonic impinging jets is the dominance of the feedback loop mechanism. The present investigation is an attempt to examine the flow characteristics of a high temperature supersonic impinging jet through a convergent-divergent nozzle during the transient starting phase. To be exact, this dissertation is focused on understanding the physical relation between the transient jet flow and its acoustic signature. In this regard, a reflected shock tube is designed and built to reproduce the hot transient supersonic jet of interest. The stagnation temperature of the test gas can be increased up to 1800K by a shock. The jet will impinge on a flat plate, referred as the impingement plate (or deflector), which is larger than the nozzle exit diameter and positioned at a specific distance from the nozzle exit. In this dissertation, experiments at M=1.4 and total temperature of 950 K are reported. The acoustic results of the quasi-steady free jet at the far-field are compared with those from common steady-state facilities at the same test conditions and an excellent agreement is achieved. It is seen that in free jets, the propagation pattern and frequency content of the acoustic waves generated by the staring vortex ring and quasi-steady jets are similar. In case of jet impingment on inclined flat plate, the propagation direction and the frequency content of the type (ii) acoustic wave in quasi-steady jet and that of the starting vortex ring and inclined flate plate at the same microphone position (θ=75°) are similar. Further, the propagation direction and the frequency content of the type (iii) acoustic wave in quasi-steady condition is similar to the free jet at the same condition and microphone angles. Furthermore, the results indicate that the source of type (iii) acoustic wave in quasi-steady impinging jet is the wall jet shear layer downstream of the impinging point
  9. Keywords:
  10. Wavelets ; Impinging Jet ; Wavelet Transform ; Aeroacoustics Waves ; Shocke Tube ; Transition State

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