UNSTEADY HEAT TRANSFER AND DIRECT COMPARISON TO STEADY-STATE MEASUREMENTS IN A ROTOR-WAKE EXPERIMENT
An experimental effort has been carried out in which circumferentially local and time-resolved neat transfer measurements have been obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. A direct comparison has been made between the time-averaged thin film results and conventional steady-state heat transfer measurements, yielding excellent agreement. Time-averaged wake-induced stagnation heat transfer enhancement levels above the no-wake case (one percent freestream turbulence) were found to be about 10 percent for the four cylinder Reynolds numbers (ranging from 36 000 to 96 000) included in the study. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. These wake-induced heat transfer spikes were observed to have peak magnitudes averaging 30 to 40 percent above the inter-wake heat transfer level.