Measurements of the Effectiveness of Concave Spherical Dimples for Enhancement Heat Transfer

Measurements of the heat transfer enhancement effects of concave spherical dimples have been performed under hydrogen-oxygen hot-fire conditions in a subscale combustion chamber. Seven configurations were tested with a range of area densities from 15-70% and depth-to-diameter ratios of 0.111 to 0.333. Enhancements of 15-82% relative to a smooth surface were measured. The Reynolds number was varied by a factor of 5 and was found to have an insignificant effect on the enhancement factor. Results correlated well with previous studies conducted under cold-flow conditions with similar values of area fraction, depth-to-diameter ratio, and channel height-to-dimple diameter. These results are suitable for use by analysts and designers considering the use of heat transfer enhancement features on hot-gas walls for example in the design of high-performing expander cycle engines. Concave spherical dimples may have advantages over other approaches for enhancing heat transfer, such as protruding ribs with respect to the integrity of the chamber wall and the efficiency of the heat transfer enhancement relative to the associated increase in skin friction.