Jhiin Joo

Large-Eddy Simulation of Turbulent Wall-Pressure Fluctuations Using the Finite Element Method

A Dissertation Presented for the Doctor of Philosophy in Computational Engineering, The University of Tennessee at Chattanooga

Jhiin Joo, August 2019

Abstract:

In the present dissertation, turbulent wall-pressure fluctuations are characterized. To capture the turbulent characteristics of the flow, large-eddy simulation is used to resolve the large scale motions of the flow directly. A wall-adapting local eddy-viscosity model is selected to account for the effect of small scale motions. The streamwise/upwind Petrov-Galerkin method is chosen to discretize the computational domain and a second-order backward difference formula is applied for the time integration. Maintaining turbulent flow throughout the simulation domain to properly characterize turbulence is critical in investigating wall-pressure fluctuations. In order to reduce the size of the simulation domain an inflow generation method, a variant of the recycling and rescaling method, is used. In this method, the turbulent velocity profile from a specific plane within the computational domain is recycled and rescaled appropriately, and re-introduced at the inlet of the domain at every time step iteration. In the proposed method, the mean velocity profile is fixed at the inlet while the velocity fluctuations are recycled and rescaled to obtain the desired turbulent characteristics. This method is simple and effective and maintains the turbulent flow throughout the simulation domain. The non-reflecting boundary conditions with a sponge layer are applied at the top and exit of the computational domain to remove unwanted reflections from the boundary. In order to examine the present inflow generation method and the ability to capture the wall-pressure fluctuations, numerical results are verified on a flat plate with a zero pressure gradient. The mean velocity profile, the RMS velocity fluctuations, and the friction velocity over time are investigated to show the effectiveness of the present inflow turbulent generation method. Computed wall-pressure fluctuations are evaluated using the time-averaged statistics and the spectra, to show that they are characterized well using the present method. 

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