Heat transfer in blade cascades at different angles of attack

Results of a mathematical and experimental investigation of the distribution of heat transfer coefficients over turbine blades at different angles of attack are reported for the peripheral, middle, and root cross sections of movable blades. Flows of from Mach 0.16-0.65 and Mach 0.24-1.2 and Reynolds numbers up to 210,000 were examined in wind tunnel trials with different cascades. Measurements were taken with hot-wire anemometry, gauges, and total-pressure tubes. Velocity distributions were calculated, along with evaluations of the conditions of separation, the extent of the thermal boundary layer (the blades were heated), and the heat transfer coefficients. Variation of the Mach or Reynolds number displaced the coordinates of the transition region, while the heat transfer changed uniformly within the boundary layer. Localized separation was found to occur along the blades on the concave side after the peak velocity at the leading edge, and this was explored with shadowgrams. Separation was determined to be inevitable during start-up and shutdown.