Study of boundary layers approaching separation in diffusers

The purpose of this study was to develop and evaluate a numerical technique for predicting the performance of unstalled diffusers for a magnetohydrodynamic power generating cycle being investigated at University of Tennessee Space Institute. The work involved two tasks. The first task was to conduct a survey of literature to find and catalogue families profiles of velocity and temperature for flow near to smooth and rough walls. The second task was to use the appropriate law-of-the-wall to serve as boundary conditions in a diffuser flow computer program developed by Harsha and Glassman (1). The Harsha-Glassman program is based on a one-equation, turbulent kinetic energy model for turbulence transport that uses a prescribed length-scale for kinetic energy dissipation. In this study, the dissipation length scale was modified to account for adverse pressure gradient effects. The modified version of the computer code predicts velocity profile in the boundary layer very close to the standard data. The modified version of the code predicts separation closer to reality than the original version.