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Investigation of the Effects of Wall Roughness on the Acoustic Field for Flow Inside a Pipe

Yazdian Hosseinpour, Amir | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55738 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Taghizadeh Manzari, Mehrdad
  7. Abstract:
  8. One of the methods of measuring the flow rate in a pipe (channel) is by using the acoustic waves with long wavelenghs in Sonar flowmeters. This flowmeter consists of an array of sensors, mounted on the outer wall of the pipe. These sensors by listening and interpreting the sound waves passing through the fluid, would give a “non-intrusive” measurement of the volumetric flow rate. This means that the flowmeter is not in direct contact with the flow and therefore its repair, relocation or replacement will not disturb the flow. In this project, we will provide a clear understanding of the principles and physics involved in sonar-based acoustic flowmeters, by means of numerical simulation of the turbulent flow and acoustic field of a pipe, using COMSOL Multiphysics software. Subjects like signal processing, optimum number and distance between sensors, stability of the method, etc. will then be discussed. The simulation involves three consecutive steps: )1) Modelling the turbulent flow )2) Coupling between flow and acoustic )3) Solving the aeroacoustic equations also known as convected acoustics (Linearized Euler Equations). This is done using “Multiphysics” capabilities of the software. The results show that by using at least 4 microphones with equal distances, chosen between 10 to 20cm, the flowmeter would be able to measure flowrate for Reynolds numbers up to 100’000 and diameters up to 50cm, with less than 3 percent error. Then the effects of wall roughness on flow and acoustic field inside a pipe will be discussed. These surface irregularities cause changes in the velocity profile and friction factor of the turbulent flow, thus affecting the wave propagation phenomenon. The results show that for smooth and sand-grain roughend pipes, by assuming a uniform profile for velocity, we can measure the flow rate by sonar technique. But in ribbed pipes, due to the secondary flows in the spaces between the ribs, this assumption would not be valid and the microphone array wouldn’t be able to measure the flow rate
  9. Keywords:
  10. Flow Measurment ; Turbulent Flow ; Sonar ; Acoustic Field ; Pipe Roughness

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