Effect of surface roughness on the delayed transition on 9:1 heated ellipsoids

The laminar to turbulent transition of a boundary layer can be affected by many variables, including pressure gradients, mechanical vibrations, and free stream flow disturbances. The present study is concerned with the interaction of two of these variables, taking into account surface roughness and surface heating, as it relates to boundary layer transition. In an effort to quantify the effects of surface roughness on a thermally stabilized boundary layer in water, an experimental investigation was carried out. The goal of the investigation was to acquire experimental data on the effect of three different levels of distributed roughness on the delayed transition of a heated ellipsoidal model in controlled test environment. A traditional criterion for the maximum size of distributed roughness (sand grain) which will effect laminar-to-turbulent transition was found to be invalid for heat stabilized laminar flow.