Wavenumber-frequency analysis of internal flow noise in simple constriction-expansion pipe

High-pressure gas is produced in the process of oil production in offshore plants. Pressure relief devices such as valves are widely used to protect related systems from it. High-pressure gas in pipe connected to the flare head burns out at the flare stack or is ventilated to the atmosphere if the gas is not toxic. During this process, excessive noise is generated through pressure relief valves used to discharge the high pressure gas to outside quickly. This noise sometimes induces severe acoustic induced vibration of pipe wall. In this study, internal aerodynamic noise in a simple constriction-expansion pipe which is used to model valve flow is investigated by combining the LES technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. First, steady-state flow is numerically simulated, and the result is compared with a quasi-one-dimensional theoretical solution, which confirms the validity of the current numerical method. Then, unsteady simulation is performed to predict the fluctuating pressure inside a pipe. Finally, acoustic pressure modes in the pipe are extracted by applying the wavenumber-frequency transform to the total pressure field. The results showed that the acoustic pressure fluctuations in pipe can be separated from the incompressible ones. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of piping system and thus enable systematic measure for mitigation action of possible acoustic-induced vibration of piping system.