EXPERIMENTAL INVESTIGATION ON HEAT TRANSFER CHARACTERISTICS IN AN IMPINGEMENT/EFFUSION COOLING SYSTEM OF A RIBBED TURBINE CASING

The present paper reports an impingement/effusion cooling structure applied to the turbine casing. The structure consists of three rows of jet holes and two rows of effusion holes, both of which are in a staggered arrangement. A high rib exists inside the impinging chamber for structural support, which is connected to the effusion plate and divides the impinging chamber into two interconnected small chambers, one of which is arranged with effusion holes and the other is not. Transient liquid crystal (TLC) experiments were conducted to investigate the influence of the Reynolds number based on the jet hole diameter (ReD), distance between impingement plate and effusion plate(H), hole pith in Y direction(A) and X direction(C), with a parameter range of 1100 <= Re-D <= 5100, 2.5 <= H/D <= 7.5, 4.0 <= A/D <= 14.0 and 8.0 <= C/D <= 14.0, on the heat transfer characteristics of the effusion plate. The results show that the region averaged Nu increases with an increase in ReD for all studied cases and there is a linear relationship between the ReD and the region averaged Nu in the logarithmic coordinate. The change of H/D has an obvious effect on the heat transfer in the 2D-3D region from the stagnation point. As the H/D increases, the entrainment effect that makes the surrounding fluid continuously enter the jet, resulting in the velocity of the jet decreasing, and the enhanced heat transfer at the effusion plate becomes weaker. When 38<Y/D<42 and 0<Y/D<1, the Nu increases with the increase of H/D due to the weakening of the flow separation of the wall jet. The variation of A/D has little effect on the enhanced heat transfer in Region1 (surface without effusion hole), but for Regions2-4 (surface with effusion holes), decreasing or increasing A/D is unfavorable to the uniformity of the Nu distribution. The heat transfer enhancement is mainly influenced by C/D. As C/D decreases, the proportion occupied by the stagnation region gradually increases, thus the surface Nu increases significantly.