Masters Theses

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

R. V. Arimilli

Committee Members

M. Parang, J. R. Parsons

Abstract

In this study, turbulent flow and heat transfer characteristics of three two-dimensional and one axisymmetric geometries are modeled using a Finite-Element k-e technique provided in the form of the computational fluid dynamics package FIDAP. The first case studied is a backward-facing step downstream of a developing channel flow with a Reynolds number of 38,800 based on the 3.3 millimeter step height. The surfaces are held at a constant temperature. The time-averaged Navier-Stokes equations are solved in a two-dimensional form and reveal close agreement with experimental measurements of flow and heat transfer characteristics for this case. The second case is a converging duct with low Reynolds number accelerating turbulent flow conditions. A constant heat flux is applied to the lower wall. The experimental data shows a relaminarization of the turbulent boundary layers. The simulation results for this case do not correlate well with the data, due to the low Reynolds number used in the experiment and the overprediction of the turbulent structure. The third case is a fully-developed flow over a two-dimensional ribbed geometry. The periodic nature of the fully-developed regime is identified far downstream of the inlet by the repetition of the velocity and turbulence components' profiles and the temperature profile. The surface temperature is linearly increased in the flow direction as in a counter-flow heat exchanger. Two-dimensional simulations are performed, and friction coefficients and Nusselt numbers are compared to experimental data. The results for this case show the same trends as the data, although the values are underpredicted. The fourth case is an axisymmetric developing flow within concentric cylinders with a small rib located downstream. The measured wall temperatures from the experiment are applied as the boundary conditions in the models. The heat transfer trends for this case follow the experimental data with some overprediction. The predicted heat transfer and flow structure results from the models of the different geometries generally follow the trends of the experimental data. The models are limited by the availability of good measurements of the flow and turbulence structure.

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