Turbulent noise production in duct systems

Scriptie/Masterproef: Master-after-master

Samenvatting

In high pressure piping systems present in nuclear power plants, leakages across safety valves can become detrimental for the performance of the installation if their mass flow rate exceeds a certain level. This issue gave rise to a non-intrusive method which has as objective to quantify these leaks in terms of mass flow rate, based on the measurement and interpretation of pipe-wall vibrations. The present work addresses the analysis of the aero-acoustics of unsteady confined flows needed for the development of the method. The physical understanding of the structure of the wall pressure fluctuations is of high importance for the interpretation of the measurements. To be able to achieve this, a numerical tool composed of two main parts is set-up. First, the flow parameters of the leakage flow are obtained using Scaled Adaptive flow Simulations performed in ANSYS Fluent. RANS simulations ran beforehand allowed to obtain initial conditions for convergence improvement as well as a mesh dependency and domain length analysis. Then, using the aeroacoustic Curle's analogy the equivalent acoustic sources are extracted from the CFD data and reduced in number by using a source grouping method. Based on this input, a preliminary analysis of the acoustic propagation is realised. For this purpose, Computational Aeroacoustic simulations using BEM and FEM solvers are ran with the software LMS Virtual.Lab. The overall output of the simulation chain are the acoustic levels induced by the leakage flow at different locations along the pipe wall. A global lowering of the SPL is observed over the considered frequency range for increasing listener point w.r.t. the source. On the other hand one can observe convergence of the as the distance w.r.t. the diaphragm increases. Finally, to validate the numerical tool, the analytical expression of the Green's function of an empty duct as well as a ducted diaphragm are compared with the numerically obtained results. A shift in the frequency spectra of the ducted diaphragm is still observed between both analytical and numerical results and needs further investigations to be able to understand its origin. In brief, 80% of the set-up numerical methodology can be considered as validated and the 20 remaining percent needs additional investigations in the future.
Datum prijs2018
Originele taalEnglish
BegeleiderChristophe Schram (Promotor)

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