Experimental Investigation of Local Heat Transfer in a Rotating Two-Pass Cooling Channel Using the Transient Thermochromic Liquid Crystal (TLC) Technique

Abstract

Abstract A test rig for the investigation of rotating turbine blade internal cooling channel configurations is presented. Local heat transfer distributions are evaluated using the transient thermochromic liquid crystal (TLC) technique. The rig can be operated at rotational speeds of up to 900 rpm, mass flow rates between 3 g/s and 30 g/s, fluid temperatures between −100 °C and +80°C and fluid pressures of up to 10 bar. This allows for a broad range of possible test conditions. The investigated cooling channel model is a two-pass leading edge configuration manufactured out of acrylic glass. It consists of a first pass with a trapezoidal cross-section and radially outward flow, a 180° bend, and a second pass with a rectangular cross-section and radially inward flow. The suction side and pressure side surfaces are equipped with angled ribs. The evaluation method is based on the measurement of TLC indication times. A sudden fluid temperature change is applied to cool down the TLC-coated heat transfer surfaces. This induces a TLC color play which is captured using cameras that are co-rotating with the test model. Assuming 1D heat conduction inside a semi-infinite wall, heat transfer coefficients are then calculated from the TLC indication times and the fluid reference temperature measurements. The data evaluation procedure and the results of a typical experiment are presented. Heat transfer data are shown in contour plots of the Nusselt number distribution. Furthermore, a method to directly compare the results of a rotating with a corresponding non-rotating experiment using normalized Nusselt number ratios is shown. Finally, data reduction methods are described that provide line-averaged values as well as histograms of normalized Nusselt number ratios.