Heat transfer measurements in leading-edge cooling geometry under rotating conditions

A cold-bridge-type leading-edge cooling system has been experimentally investigated in order to determine rotational effects on heat transfer.Aradial channel feeds seven circular holes, which generate impingement jets in the leading-edge cavity. Spent coolant flow is extracted by five rows of extraction holes. Jet Reynolds numbers from 20,000 to 50,000 have been investigated in static and rotating conditions (corresponding to a jet rotation number of 0.008), as has the effect of different jet feeding conditions. A transient technique with thermochromic liquid crystals has been employed. To respect the correct sign of buoyancy forces, the test is performed by heating the test article with a small mass flow rate and then recording the surface response to a sudden decrease in air temperature (down to ambient value) and increase in mass flow rate (up to nominal value). Reynolds number is the main driving parameter of heat transfer, while jet feeding and extraction conditions only affect its pattern shape. Rotational effects on the jets reduce their lateral spreading, while Coriolis forces in the feeding channel seem to disturb jet generation at the blade tip. The combination of these phenomena has a detrimental effect on heat transfer.