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Numerical Investigation of Flow Oscillation in the Diffuser Inlet & Test Chamber of High-Altitude Simulator

Zahedifar, Fatemeh | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57302 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Farahani, Mohammad; Fouladi, Nematollah
  7. Abstract:
  8. The present research was conducted to numerical simulation and phenomenology of the pressure fluctuations and instability of the diffuser with the ratio of the diffuser inlet to the nozzle outlet of 1.91. The numerical simulation has been done with k-ω-SST and k-ω-GEKO turbulence models with both steady and unsteady methods for the nozzle with an expansion ratio of 30. Validation of the numerical solution has been done with the help of the experimental test data of the high-altitude test simulator available in the Research Institute of Space Transportation Systems. Tests were conducted by cold gas. Investigations indicate that two types of start occur in the system, stable and unstable start. In the stable start process, which occurs in high-pressure tests, the flow is supersonic over much of the length of the diffuser. On the contrary and in the unstable start, the flow detection and study shows that the flow is not supersonic in most of the length of the diffuser and this causes the disturbances downstream of the diffuser to be transferred to the upstream. These disturbances can be environmental disturbances during testing or unstable structures of turbulence separation or etc. The effect of transition disturbances is the fluctuation of the separation zones in the diffuser, which causes the fluctuation of the internal shock train structure. The change in the structure of the shocks as well as the instabilities created in the shock train and their movement upstream creates a flow separation zone at the entrance of the vacuum chamber and mass suction occurs inside the chamber, which results in the diffuser leaving the starting working condition
  9. Keywords:
  10. Numerical Simulation ; Pressure Fluctuation ; High Altitude Test Stand ; Diffusers ; Shock Train Instability ; Supersonic Flow

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