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Numerical ( and Experimental) Investigation of the Acoustic Behaviour of Internal Incompressible Turbulent Flows and the Effect of Obstacles on the Flow

Rasmi, Mahdi | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56333 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Taghizadeh Manzari, Mehrdad
  7. Abstract:
  8. Measuring flow rate in various industries is an operational challenge that requires to be accurate and fast to avoid wasting energy and money. Various flowmeters are employed in different industries using different principles and methods. Sonar flowmeters are one of the acoustic methods of fluid flow measurement, which do this by listening to the sound of the flow via arrays of sensors. Sonar flow measurement can be achieved by finding either the convection velocity of eddies or the speed of sound in the fluid. The first method is suitable for measuring single-phase flows, which is the subject of this thesis. This method needs a detailed study of turbulence. In the present work, this is achieved by Large Eddy Simulations. In the first part of the thesis, the convection of coherent vortices in a semi-infinite channel is studied, and their speed is correlated to the average velocity of flow. In the second part, the effect of an obstacle (representing a valve) in the flow field on the acoustic field is studied. This effect is investigated for three flow parameters; 1) flap length (damper), 2) inlet flow rate, and 3) flap angle. By changing the length of the flap, the dominant acoustic frequency can be shifted, and also by changing the input Reynolds number, the contribution of pressure fluctuations due to compressibility of fluid in the total sound significantly reduces. This observation is confirmed by the Lighthill analogy. Finally, it was observed that as the flap angle increases, the content of the dominant frequency at zero angle spreads over the entire frequency range and the emitted sound level increases. In the third part of this thesis, a set of experimental studies are conducted to examine how the recorded sound pressure levels can be related to the flow rate in a single-phase pipe flow. A linear correlation between the dominant frequency of the flow and the average velocity was established. This correlation matched the results obtained by the flow simulations
  9. Keywords:
  10. Disturbulance ; Large Eddy Simulation (LES) ; Acoustic Field ; Sonar ; Coherent Structures ; Compressible Fluctuations

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