Heat Transfer of Impinging Jet Arrays on a Ribbed Surface

This study investigated the heat transfer of impinging jet arrays fed by a quadrate pipe on a ribbed surface of a high-pressure turbine case. Three models were experimentally analyzed: a row of vertical jets on a flat surface, a row of 45 degrees jets on a ribbed surface, and a row of 45 degrees jets combined with a row of vertical jets on the ribbed surface. Tests were conducted by the jet Reynolds number (2000-20,000), jet-to-plate spacing (6d-10d, where d is the jet diameter), and jet-to-jet spacing (6d-12d). Results indicate that the ribbed surface greatly enhances the local Nusselt number around the impinging stagnation region. A confined channel is formed by the ribbed surface and quadrate pipe, resulting in an asymmetrical Nusselt number distribution. The spanwise-averaged Nusselt number for the combined model is greater than that for a single row of 45 degrees jets. Results also show that the spanwise-averaged Nusselt number increases with decreasing jet-to-jet spacing, but is little affected by the jet-to-plate spacing, which attains the highest value at a jet-to-plate spacing of 9d. The total average Nusselt number over the entire ribbed surface increases considerably (33%) at Reynolds numbers greater than 5000 compared with conventional configurations involving flat surfaces.