Abstract

Gas turbine blades are equipped with serpentine internal cooling channels with 180-degree bends, through which relatively colder air is routed to cool the internal walls. It has been established that under the influence of rotation, pressure and suction side internal wall heat transfer characteristics are very different, which leads to non-uniform metal temperatures, and hence higher levels of thermal stresses. Present study addresses this non-uniformity in heat transfer using parallel rotation to negate Coriolis effect. Further, the blade curvature does not allow rectangular or trapezoidal passages, which are typically studied. In this paper, we have numerically investigated a realistic design for the four-passage channel, where the cooling design can actually be incorporated in a blade. Four-passage configuration also features 90-degree square shaped rib turbulators, and the corresponding baseline case is smooth channel. Numerical simulations have been carried out at Reynolds numbers of 5000, 10000 and 25000 and Rotation numbers were varied between 0 and 0.25. For smooth case, heat transfer enhancement was found to be higher on suction (leading) side compared to pressure (trailing) side under both stationary and rotating conditions. The enhancement levels between stationary and rotation conditions varied marginally in these designs, indicating that buoyancy effects were insignificant. For ribbed case, the effect of 90-degree rib turbulators on local heat transfer was more pronounced on the suction side when compared to smooth case. Under rotating conditions, it was found that the cooling levels were similar to the stationary condition for both pressure and suction side internal walls.

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