Heat Transfer of Impinging Jet-Row Onto Trapezoidal Channel With Different Effusion and Discharge Conditions

Abstract

Abstract The heat transfer performances of the trapezoidal channel with the impinging row jets normal to the channel apex wall with no effusion and three effusion conditions from one, two and three rows of bleeding holes along the channel apex, or, and, channel sidewalls were studied. At each effusion condition, the airflow extraction from the channel tip were regulated as full open conditions, and 0% (full close), 5%, 10% of the total airflow rate fed into the trapezoidal channel via the impinging row jets. For each effusion and discharge condition, the full-field heat transfer data over the channel apex and sidewalls were measured at channel Reynolds numbers of 5000, 7500, 10000, 12500 and 15000 using the steady-state infrared thermography method. The corresponding axial distributions of the jet mass flow rate at each effusion and discharge condition were measured at all the Reynolds numbers tested. While the crossflow and channel flow confinement significantly affected the axial distribution of the jet flow rate for the channel without effusion, the impact of effusion and discharge conditions on the distribution of the airflow rate through the row jet was negligible for the effusion channels. Without effusion, the strong crossflow effects acted with the weakened jet momentums near the sealed channel hub to substantially reduce the regional heat transfer rates. With effusion, the flow confinement formulated by the cavity-like channel hub and the crossflow developed along the test channel were significantly suppressed, leading to the even distribution of jet flow and the recovered impinging-jet heat transfer properties over the channel hub region. The preferential heat transfer performances among the present test channels with and without effusion gave rise to the channel with three rows of effusion holes. Relative to the heat transfer impacts caused by varying the row number of the effusion holes, the impacts of tip extraction were less evident; but the overall heat transfer performance was improved by reducing tip discharge. With leading-edge cooling applications to a gas turbine blade, three sets of heat transfer correlations that evaluated the regionally averaged Nusselt numbers over the channel apex and side walls with and without effusions at various tip extractions were devised.