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Invetigation of Dynamic and Noise of Subsonic Jets Using Stability Analysis

Gohardehi, Siavash | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55099 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farhanieh, Bijan; Afshin, Hossein
  7. Abstract:
  8. With the growing development of the aviation industry, the emitted jet noise from civil and military aircraft has become a challenging issue in the development of this industry. Despite recent advances in simulation methods using for fluid phenomena, understanding the nature and physics of noise generated by jet flows has been a complex puzzle for the last decades. Although numerical methods are currently able to predict the jet noise, it is still not possible to fully understand the physics of this phenomenon and subsequently use it to control the emitted sound. In this research, with the purpose of studying the pressure fluctuation caused by large-scale coherent turbulence structures in the jet flow, linear disturbances entering the base flow are modeled using stability analysis method based on Parabolized Stability Equations (PSE). Proper agreement of the results with the available experimental data illustrates the high capabilities of this method for predicting flow dynamics at much lower costs comparing to the conventional computational methods. The effect of various flow paStrameters such as jet temperature, turbulence intensity and thickness of boundary layer of velocity profile on the growth rate of different eigenmodes has been investigated. Changing above parameters could reduce jet noise in the context of jet flow control mechanisms. In the second part of the research, global stability analysis and non-modal transient growth analysis were performed in order to find the modes which governing the flow dynamics, and initial fluctuations lead to transient growth greater than the exponential growth of unstable modes at limited time horizons. Different flow conditions and different time periods and related effects on the location and type of initial disturbances with maximum transient growth in the jet flow have been investigated. According to the results, when Reynolds number increases, the transient growth intervals in the jet flow are significantly reduced
  9. Keywords:
  10. Turbulence ; Parabolized Stability Equations (PSE) ; Turbulent Jet Noise ; Stability Analysis ; Non-Modal Analysis ; Transient Growth

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