Numerical Investigation On The Effects Of Unsteady Wakes On Film Cooling

With the continuous development of space technology and related field at home and abroad, the research and design methods which were originally based on relatively simpler assumption of steady flow could not be satisfied by the higher performance indicators of turbomachinery anymore. Therefore study on unsteady problem in the turbomachinery has gradually become the more attractive research project.Basing on SIMPLE algorithm and discretizing the control equation in finite volume method, SST k-εturbulence model is applied to investigating the effects of unsteady wakes on the first grade cascade. The rotating turbine at different rotor-stator phases in different rotor with 500rpm, 1000rpm and 2000rpm condition were simulated. The temperature contour maps at different time in a period which are under the conditions of 2000rpm were analyzed. And the development process of vortices on different sections was shown in this paper, and the structures mechanism was analyzed. Simulation results showed that the temperature in the rotor cascade rises with the increase of rotation speed of rotor, while the temperature varying with the change of blade height is negligible. With the increase of frequency of wakes, the separation of separation area was inhibited by the turbulence intensity which is brought by wakes, then inhibits the shedding of rotor wakes. The vortex shedding presents obvious periodicity in the leading edge region of first grade cascade. While in the trailing edge region, vortex shedding does not present obvious periodicity anymore, although there also exists the trend of periodic change.Then we simulated the trajectory of jet on the blade head of blade cascade and the variety rule of cooling efficiency was given by the different ratio of jet flow and the spin velocity. The results show that: the cooling jet flows which flow from the jet flow holes in blade head will break away from blade wall after washing the blade head, mix into main flow adequately and have no protection of blade in the influence of the rotation blade stage circumferential speed. In the condition of the same ratio of the jet flow, the high spin velocity will form continuous covering effect on the blade head and get great film cooling effect on blade. In the condition of the same spin velocity, the high ratio of the jet flow will form continuous covering effect on blade head and get great film cooling effect on blade. The jet flows up obviously on the pressure side because of the stator wake but less change occurs on the suction side.