Turbine Wheel Relative Temperature at Freerun Conditions

Analytical predictions and laboratory measurements were made for the relative total temperature experienced at the tip diameter of a radial-inflow turbine used in an air turbine starter (ATS). The predictions showed that at freerun conditions the blade tip temperature would be significantly higher than the turbine inlet temperature. Tests to confirm this prediction were performed on an ATS modified to accept an optical pyrometer. The pyrometer was focused on the suction side of the blade at the tip radius. Blade temperature measurements conducted at the maximum attainable speed of the ATS verified the prediction to be within the error of the pyrometer measuring system.