An experimental investigation of the heat transfer in a ribbed triangular cooling channel

One of the most challenging aspects of gas turbine cooling is the cooling of the first stages of turbine blades. Here the highest external heat load is seen at the leading edge of the blade. The present study investigates the internal cooling in a triangular channel with a rounded edge as a model of a leading edge cooling channel for a gas turbine blade. A transient liquid crystal method is used to measure the heat transfer. Experimental results are reported for a number of new 3D rib configurations for Reynolds numbers between 50 000 and 200 000. From the experimental results it has been found that 60 deg. ribs provide in general higher heat transfer enhancements than 45 deg. ribs. However, this results in extremely high friction factors for the 60 deg. ribs. Taking the local and mean distributions of the heat transfer coefficients (as well as the increase in friction factors) into consideration, it was found that the most promising rib arrangement for leading edge cooling is a 3D rib with 45 deg. angle and double-sided fully overlapped ribs in the arc area. These ribs provide uniform heat transfer in the arc area as well as a high level of the heat transfer coefficients in the channel. The resulting friction factors are in an acceptable range for these ribs.