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

To quantify the effects of distributed surface roughness on the delayed laminar-turbulent transition of a thermally stabilized boundary layer in water, measurements were made on a 50 mm diameter 9:1 fineness ratio ellipsoid for various surface roughness, heating and flow conditions. Boundary-layer transition locations were determined for length Reynolds numbers ranging from 3.0 to 7.0 xlO6. The ellipsoid was tested at three different surface heating levels. For each surface roughness condition (4, 1.9 and 0.15 /*m finish) transition measurements were made for the ellipsoid with no heating; A7=10 and 15°C, where AT7 is the difference between inlet interior water temperature and freestream water temperature. The results can be summarized as follows; for each reduction in surface roughness, the performance of the model, as judged by length of laminar flow, improved for all three heating conditions. Increases in the amount of surface heat addition corresponded to increases in sensitivity of transition location to roughness. For the smoothest body with the largest amount of surface heating an increase of 81% in laminar flow length over the no heating case was achieved at a length Reynolds number of 5.25 x 106.