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Numerical Simulations of the Coaxial Shear and Swirl Injectors’ Cryogenic Flowfields under Trans- and Supercritical Conditions

Poormahmood, Ata’allah | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54803 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Farshchi, Mohammad
  7. Abstract:
  8. Characterizing the dynamics dictating injection and mixing of the coaxial shear and swirl injectors is of central importance in the context of space rockets, diesel and direct injection reciprocating engines, and modern turbine gases. Sophisticated with precise thermo-physical models along with high-fidelity turbulence approaches, a computational platform –based on OpenFOAM open source code– is developed to simulate the practical injectors flow-fields under trans- and supercritical conditions. Aiming at providing a deep insight on the underlying physics, the investigations are conducted in a hierarchical manner; the flow complexities are added step-by-step to eventually construct the elaborate problem of a practical transcritical bi-swirl injector. Results reveal that apart from the well-established aero/hydrodynamic instabilities and phenomena, the consequences of severe non-linearities in near-critical thermodynamics play a vital role in the mixing quality. These effects –appearing in terms of the highly stratified transcritical mixing layers as well as the thermal shield encompassing the liquid-like jet– considerably delay the stable transition to a fully turbulent mixing regime. In such circumstances, the well-known aero/hydrodynamic instabilities can no longer justify the present numerical observations –as well as the preceding experimental/numerical findings. Here, a hypothesis is presented to analyze the underlying physics stating that a new mechanism, called the interaction of turbulence and thermodynamics, controls the transcritical jet mixing –particularly in the jet near-field. To support the hypothesis, several statistical examinations and post-process computations have been performed. Moreover, results indicate that under certain operating conditions appropriate measurements should be taken in the numerical solver to fulfill requirements of the interaction of turbulence and thermodynamics. To address this issue, a regime diagram is developed and validated to distinguish the operating conditions under which the numerical solver should be modified to properly model the interaction of turbulence and thermodynamics
  9. Keywords:
  10. Large Eddy Simulation (LES) ; Coaxial Injector ; Swirl Injector ; Supercritical Condition ; Transcritical Conditions ; Turbulence-Thermodynamics Interaction ; Injection and Mixing Processes

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