Transient Liquid Crystal Technique for Convective Heat Transfer on Rough Surfaces

Abstract

The local heat transfer coefficients are obtained on a rough planar surface simulating in-service turbine stator vane sections. A transient experimental technique is presented that permits the determination of local heat transfer coefficients for a rough planar surface using thermochromic liquid crystals. The technique involves the use of a composite test surface in the form of a thin foil of stainless steel with roughness elements laminated over a transparent substrate. Tests are conducted on a splitter plate to provide momentum boundary layer thicknesses to roughness heights appropriate for actual turbine stator vanes. Data are reported for two roughness geometries and two free-stream velocities. The range of Reynolds numbers along with the ratio of average roughness value to momentum thickness matches conditions encountered on the pressure side of the first-stage stator vanes in current high performance turbofan engines. A numerical simulation is conducted to validate the test method. Results for the rough surfaces investigated are compared with an available empirical relationship.