Date of Award

Spring 5-2021

Degree Type

Dissertation-Restricted

Degree Name

Ph.D.

Degree Program

Engineering and Applied Science

Department

Naval Architecture and Marine Engineering

Major Professor

Dr. Kazim M. Akyuzlu

Second Advisor

Dr. Brandon M. Taravella

Third Advisor

Dr. Lothar Birk

Fourth Advisor

Dr. Martin Guillot

Fifth Advisor

Dr. Jairo Santanilla

Abstract

A Computational Fluid Dynamic (CFD) in-house code is developed to study unsteady characteristics of incompressible oscillating boundary layer flow over a flat plate under laminar and intermittently turbulent condition using pseudo-compressible unsteady Reynolds Averaged Navier- Stokes (RANS) model. In the in-house code, the two-dimensional, unsteady conservation of mass and momentum equations are discretized using finite difference techniques which employs second order accurate (based on Taylor series) central differencing for spatial derivatives and second order Runge-Kutta accurate differencing for temporal derivatives. The in-house code employs Fully Explicit-Finite Difference technique (FEFD) to solve the governing differential equations of the mathematical model. In the study two different closure models are adopted, Chien’s (k–epsilon) and Jones and Launder (k–epsilon) turbulence model. For the purpose of validation and verification of the proposed pseudo-compressibility method, flow over a flat plate is chosen as benchmark case. The numerically predicted velocities are compared to experimentally observed velocity fields using Particle Image Velocimetry (PIV) in laminar regime. The verification of the proposed model is performed using Grid Convergence Index (GCI) method. The discretization errors observed are less than 5% which are within the acceptable range. Once verified and validated, the technique of pseudo-compressibility is use to simulate oscillating flow problem. The velocity fields predicted by the in-house code in laminar regime are compared to the one given by the analytical solution to Stokes’ second problem of oscillating flow. An intermittency equation (gamma ) is proposed which couples with Jones and Launder (k–epsilon) along with unsteady RANS equations to simulate intermittently turbulent oscillating boundary flows. Using the proposed unsteady pseudo-compressible NS and RANS models, numerical experiments were conducted for unsteady cases for Reynolds number (based on Stokes’ thickness) corresponding to laminar and intermittently turbulent flows, respectively. Predicted time-dependent velocity profiles and shear stress distributions are compared to LES results and experimental data. Turbulence properties during acceleration and deceleration phases are also predicted. The sudden rise in shear stress during the acceleration phase of the oscillation, indicating the onset of intermittence, is observed and discussed. Comparison of the results shows that the observed deviations between the velocity magnitudes predicted by the in-house code and experimental data are within the acceptable range for laminar and intermittently turbulent flow conditions. Based on the results of the present study, one can conclude that the proposed unsteady pseudo-compressible intermittent RANS model is capable of predicting the characteristics of oscillating external flows successfully.

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The University of New Orleans and its agents retain the non-exclusive license to archive and make accessible this dissertation or thesis in whole or in part in all forms of media, now or hereafter known. The author retains all other ownership rights to the copyright of the thesis or dissertation.

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