Date of Award:

5-2011

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Mechanical and Aerospace Engineering

Advisor/Chair:

Dr. Thomas Hauser

Abstract

The main objective of this study was to evaluate the performance of three Large Eddy Simulation (LES) subgrid scale (SGS) models on a strongly heated, low Mach number upward gas flow in a vertical pipe with forced convection. The models chosen for this study were the Smagorinsky-Lilly Dynamic model (SLD), the Kinetic Energy Transport model (KET), and the Wall-Adaptive Local-Eddy viscosity model (WALE). The used heating rate was sufficiently large to cause properties to vary significantly in both the radial and streamwise directions. All simulations were carried out using the commercial software FLUENT.

The effect of inlet turbulence generation techniques was considered as well. Three inlet turbulence generation techniques were compared, namely, the Spectral Synthesizer Method (SSM), the Vortex Method (VM), and the Generator (GEN) technique. A user-defined function (UDF) was written to implement the GEN technique into the solver; the SSM and VM techniques were already build-in. All simulation and solver settings were validated by performing computational simulations of isothermal fully developed pipe flow and results were compared to available experimental and Direct Numerical Simulation (DNS) data.

For isothermal boundary conditions, among the three inlet turbulence generation techniques, the GEN technique produced results which best matched the experimental and DNS results. All three LES SGS models performed equally well when coupled with the GEN technique for the study of isothermal pipe flow. However, all models incorrectly predicted the behavior of radial and circumferential velocity fluctuations near the wall and the GEN technique proved to be the most computationally expensive. For simulations with longer computational domain, the effect of the inlet turbulence generation technique diminishes. However, results suggest that both the SLD and KET models need shorter computational domains to recover proper LES behavior when coupled with the VM technique in comparison to the WALE SGS model with the same turbulence inlet generation technique.

For high heat flux simulations all SGS models were coupled with the VM technique to decrease the computational effort to obtain statistically steady-state solution. For comparative purposes, one simulation was carried out using the WALE and GEN techniques. All simulations equally significantly underpredicted the streamwise temperature distribution along the pipe wall as well as in the radial directions at various streamwise locations. These effects are attributed to the overpredicted streamwise velocity components and incorrect behavior of both the radial and circumferential velocity components in the near wall region for all subgrid scale models.

Comments

This work made publicly available electronically on May 11, 2011.

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