Effect of film-hole shape on turbine-blade film-cooling performance
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Detailed coolant jet temperature profiles and film effectiveness distributions on the suction side of a gas turbine blade are measured using a thermocouple probe and a transient liquid crystal image method, respectively. The blade has only one row of film holes near the gill-hole portion on the suction side of the blade. The hole geometries studied include standard cylindrical holes and holes with diffuser-shaped exit portion (i.e., fan-shaped holes and laidback fan-shaped holes). Tests are performed on a five-blade linear cascade in a low-speed wind tunnel. The mainstream Reynolds number based on cascade exit velocity is 5.3 105. Upstream unsteady wakes are simulated using a spoke-wheel-type wake generator. The wake Strouhal number is kept at 0 or 0.1. Coolant blowing ratio is varied from 0.4 to 1.2. Results show that both expanded holes have significantly improved thermal protection over the surface downstream of the ejection location, particularly at high blowing ratios. In general, the unsteady wake tends to reduce film-cooling effectiveness.
