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Investigation of the Starting Process of a Second Throat Exhaust Diffuser in a High-Altitude Test Stand

Parsa Delivand, Ahmad Reza | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56456 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Farahani, Mohammad; Fouladi, Nematollah
  7. Abstract:
  8. In the present study, the effect of the diffuser inlet-to-nozzle exit area ratio (A_d/A_e ) on the gradual starting performance of a second throat exhaust diffuser has been investigated experimentally. Experiments have been carried out with four conical nozzles with different expansion ratios and considering two approaches of gradual increase and gradual decrease of nozzle chamber pressure by a high-pressure air tank. Investigations show that at high area ratios before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as A_d/A_e increases, the number of oscillatory modes of the vacuum chamber pressure increases and the dominant frequency of the oscillations before starting the diffuser and also when leaving the started state becomes larger. It was also observed that, generally, with the increase of A_d/A_e , the amount of motor pressure corresponding to the start of oscillations and the maximum amplitude of vacuum chamber pressure oscillations before starting the diffuser and also when leaving the started state decreases. In addition, according to the investigations, with the increase of A_d/A_e from 1.27 to 7.81, the minimum starting pressure of STED and the breakdown pressure (minimum operating pressure) increase. This pressure increasing process has led to a significant reduction of the hysteresis range in the performance of the diffuser. By investigating the effect of changing A_d/A_e at a certain motor pressure, it was observed that with the increase of A_d/A_e , the location of shock wave formation after the impingement of supersonic flow to the diffuser wall was moved to the downstream of the flow and as the angle of the shock wave formation becomes more vertical, its strength increases. Also, with the increase of A_d/A_e at a certain motor pressure, the location of flow separation is moved the upstream of the flow
  9. Keywords:
  10. Diffuser Starting ; Exhaust Nozzles ; Hysteresis ; Second Throat Exhaust Diffuser ; High Altitude Test Stand

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