Experimental investigation of heat transfer and pressure drop using combination of ribs and dimples

Modern gas turbines operate at high inlet temperatures to improve thermal efficiency; therefore, it is necessary to cool the turbine blades. Various techniques are used for heat transfer enhancements, such as ribs, protrusions, pin fin, dimples, etc.; the present study focused on compound and rib alone channel. W-shaped, semicircular and multi-semicircular shaped ribs with dimples are studied experimentally to find the optimum configuration for blade cooling. The experiment was carried out at Reynolds numbers 12,600 to 35,000; the ratio of pitch (P) to height (e) of the rib was 8 to 10, the ratio of rib height to channel hydraulic diameter (D-h) was 0.156 and the ratio of dimple depth (delta) to dimple diameter was 0.2. It was observed that the combination of rib and dimple channel (compound channel) performance was higher than the rib channel. The W-shaped rib compound channel shows the highest thermal performance over semicircular and multi-semicircular rib compound channels, and also sees a small rise in friction loss in compound channel. Realizable k-e turbulence model was used for analysis and observed less difference between experimental and CFD results. In the rib channel, semicircular rib performed better than other tested ribs.