The study of convective heat transfer from a rotating disc with special emphasis on the effects of disturbing the boundary layer

Abstract

Attempts to predict the operating temperatures of disc brakes have shown the need for an investigation into the heat transfer from a rotating disc when the airflm" induced by rotation is disturbed in a number of ways, each linked with the conditions of the operating environment. A survey of previous work revealed that a considerable body of work existed on the basic systems of a disc rotating in still air and a rectangular flat plate in a uniform stream, which aided the understanding of the effects of more complex flow systems on the heat transfer, such as were studied durirthis investigation. Experiments were made with an electrically heated rotating disc; measurements were made of the surface temperature and heat input when a steady state was reached, and the heat transfer coefficient calculated from these. Experimental data were found for the heat transfer from a disc rotating in still air and in an airflow parallel and adjacent to the disc surface. The effects of masking certain sectors of the disc were found in both of the environments just described. Finally, experiments were made with boundary layer tripping devices and jets of air directed at the disc surfaces to discover the effectiveness of these methods in increasing the heat transfer. The results from the disc rotating in still air agreed with measurements by previous workers and a prediction based on a combination of data for a rotating disc and a stationary surface achieved good correlation with data recorded with the disc rotating in an air crossflow. The other sections of work, with masked sectors, boundary layer trips and air jets, introduced flow patterns which affected the heat transfer in a complex manner. These effects were explained with the aid of flow visualization and general theoretical correlations obtained.