HEAT-TRANSFER MEASUREMENTS IN AN ANNULAR CASCADE OF TRANSONIC GAS-TURBINE BLADES USING THE TRANSIENT LIQUID-CRYSTAL TECHNIQUE

Heat transfer measurements have been made in the Oxford University Col d Heat Transfer Tunnel employing the transient liquid crystal techniqu e. Complete contours of the heat transfer coefficient have been obtain ed on the aerofoil surfaces of a large annular cascade of high-pressur e nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach an d Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 X 10 (6)). A novel mechanism is used to isolate five preheated blades in th e annulus before an unheated flow of air passes over the vanes, creati ng a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the color crystal change is recorded during the run with a miniature CCD video camera. T he heat transfer coefficient is obtained by solving the one-dimensiona l heat transfer equation for all the paints of interest. This paper wi ll describe the experimental technique and present results of heat tra nsfer and flow visualization.