Unsteady Heat Transfer and Direct Comparison to Steady-State Measurements in a Rotor-Wake Experiment

Abstract

An experimental effort has been carried out in which c1rcumferent1al1y local and time-resolved heat 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-average thin film results and convent10nal steady-state heat transfer measurements, yielding excellent agreement. T1meaveraged 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 d1rect1y 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. I NT RODUCTI ONAs a result of several recent studies (e.g. refs. 1 to 3), the nature and significance of wake-related flow unsteadiness in turbomach1nery b1ad"1ng and its profound effect on heat transfer are beg1nn1ng to emerge~ This type of research represents the next logical step toward a more complete and realistic understanding of the complex flow f1elds assoc1ated with turbomachines.Unsteady heat transfer has been measured in several short-duration facilities by means of platinum thin film heat flux gauges, prov1d1ng detailed t1me-

Semi-infinite solid heat transfer limitation

“…Earlier heat transfer experiments have utilized few methods such as bulky heaters [9] and preheated models [10,11] to induce the step change in air temperature. A heating element, fast response stainless steel mesh heater, was invented to simplify the process of inducing hot air to the working environment [12].…”

Experimental Study of the Unsteady Boundary Layer Behavior on a Turbine Cascade

“…Simoneau et al (1984) developed a similar research facility to investigate blade heat transfer aspects under unsteady flow conditions. This facility also served to investigate the turbulence structure and wake propagation reported by Morehouse and Simoneau (1986), O'Brien and Capp (1989), and O'Brien et al (1986. Using a similar research facility, Schultz et al (1989) and investigated three-dimensional wake decay characteristics within compressor cascades.…”

Progress towards Understanding and Predicting Convection Heat Transfer in the Turbine Gas Path

“…A hybrid between the rotating and nonrotating experiments are the wake simulation experiments. In wake simulation facilities, either a rotating spoked wheel (Ashworth et al 1985;O'Brien et al, 1986;O'Brien and Capp, 1989;O'Bden, 1990) or a rotating squirrel cage of bars (Pfeil et al, 1982;Bayley and Priddy, 1981;Priddy and Bayley, 1988;Schoberei, 1991), is used to produce wakes which impinge on a downstream test surface. This is where the Oxford ILPT has received extensive use.…”