HEAT TRANSFER AND PRESSURE DROP IN BLADE COOLING CHANNELS WITH TURBULENCE PROMOTERS.
Repeated rib roughness elements have been used in advanced turbine cooling designs to enhance the internal heat transfer. Often the ribs are perpendicular to the main flow direction so that they have an angle-of-attack of 90 degree . The objective of the project was to investigate the effect of rib angle-of-attack on the pressure drop and the average heat transfer coefficients in a square duct with two opposite rib-roughened walls for Reynolds number varied from 8000 to 80,000. The heat transfer coefficient distribution on the smooth side wall and the rough side wall at the entrance and the fully developed regions were measured. Thermal performance comparison indicated that the pumping power requirement for the rib with an oblique angle to the flow ( alpha equals 45 degree to 30 degree ) was about 20 to 50 percent lower than the rib with a 90 degree angle to the flow for a given heat transfer duty. Semi-empirical correlations for friction factor and heat transfer coefficients were developed to account for rib spacing and rib angle-of-attack. The correlations can be used in the design of turbine blade cooling passages.