FLOW AND HEAT-TRANSFER MEASUREMENTS IN SUBSONIC AIR FLOW THROUGH A CONTRACTION SECTION

Flow and heat-transfer measurements are presented for heated air flowing subsonically through a contraction section smoothly connecting a tube to a conical section. These measurements spanned a range of cooled wall-to-stagnation temperature ratios, Tw Tto, from 1 3 to 2 3, Reynolds numbers from 2 × 104 to 2 × 105, with data obtained for both laminar and turbulent boundary layers. Unheated air flow measurements were also made. The basic flow field established from measurements along the wall and centerline consists of a turning of the flow through the contraction section that resulted in an adverse pressure gradient (deceleration) along the wall. Flow-visualization results indicated that the flow separated just upstream of the curved contraction section and reattached near its end. The heat-transfer coefficients reached a minimum value near the center of the separation region, increased in the vicinity of the reattachment point, flattened out in the reattachment region, and then increased again downstream. As a consequence of the curved section and the associated separated flow effects, the heat transfer in the separation region under certain operating conditions was reduced below values measured upstream in the tube. Values of the heat-transfer coefficient were higher with thin boundary layers produced by a short, cooled upstream length, and the distribution of the heat-transfer coefficient in the redevelopment region depended on whether the boundary layer was turbulent or laminar. Effects of wall cooling in terms of Tw Tto that were found upstream in the tube were not observable in the separation and reattachment regions. © 1969.