The Effect of Incident Wake Conditions on the Mean Heat Transfer of an Airfoil

The flow phenomena of wakes shed by upstream blade rows is a well–known problem in turbomachinery which influences blade forces, vibrations, losses and heat transfer. With respect to the heat load to turbine blades this problem becomes even more complex because of the interaction between wake, potential flow and the boundary layer along the surface of the airfoil. Experimentally evaluated mean heat-transfer coefficients obtained under different unsteady initial conditions are reported. The heat–transfer measurements have been carried out in the cascade test facility at the ITS in Karlsruhe using a rotating bar wake generator placed upstream of the cascade to simulate the wake passing process. The variation of the wake parameters includes different wake passing frequencies, cascade inlet Reynolds numbers and wake inclination angles. In addition, the relevant parameters of the unsteady wake have been measured by means of a fixed hot–wire anemometer using the ensemble average technique. The results are compared to those from the literature for the wake of a cylinder in cross–flow. They also serve as experimental base for parallel theoretical analyses.