| Film cooling plays a very important role in the cooling configuration of the modern gas turbine engines. With rapid development of aero-turbine engine, film cooling technology is also facing much more challenges. Recently, the influence of periodic unsteady wake, which is from rotor-stator interaction in turbine vane cascade, on the film cooling has attracted a lot of attention around the world. This paper made a corresponding research on this problem.At first, numerical investigations were performed to study the influence of upstream steady wake on the film cooling over a flat plate. By comparing and analysis of the temperature and flow fields downstream the film holes under several cases, the effects of some factors(such as film-hole shape, wake location and wake width) on the film cooling characteristics was acquired. The results show that the upstream wake has double effects on the film cooling. On one hand, the upstream wake forms a low velocity zone near the film hole and increases the turbulent intensity, resulting in the enhanced mixing between the primary flow and cooling air flow. This action is detrimental to the film cooling efficiency. On the other hand, the upstream wake is capable of suppressing the development of kidney-vortices, enhancing the ability of the cooling air to extend downstream and re-attach to the wall. This action is of improving mechanism for the film cooling. In general, the influence of upstream wake on the film cooling is very complicated. The influence of upstream wake on the film cooling is tightly associated with the film-hole shape. For the three film-hole shapes such as circular-shaped hole, the fan-shaped hole and the converging slot hole, it is found that the circular-shaped hole film cooling effectiveness is most likely to be influenced by the upstream wake and the converging-slot hole film cooling effectiveness is the hardest to be effected. When the position of wake generator either in the transverse direction or in the longitudinal direction is changed, the influence of wake on the downstream flow field of cooling film would change. Under low blowing ratio, the wake would lead to decrease of film cooling efficiency. While under high blowing ratio, the upstream wake tends to increase the film cooling effectiveness. The influence of the upstream wake on the film cooling effectiveness is more obvious with the increase of wake width.At the same time, an experimental study was also carried out to verify the effects of upstream wake on the film cooling. It was indicated that the experimental results are in good agreement with the numerical results. Therefore, it is verified that the computational model and numerical method is reasonable.On the basis of the study of flat plate film cooling, a numerical investigation was further performed to study the effect of upstream wake on the turbine blade film cooling. It was indicated that the basic rules of upstream wake on the blade film cooling is similar to the flat plate film cooling. With regards to the location of film holes, the results shows that the film cooling on the blade suction side is more significantly affected by the upstream wake in relative to that on the blade pressure side. Wake phase location of 0% vane pitch influences the flow field downstream nearly the film hole and film cooling effectiveness magnitudes significantly. Wake phase locations from 25% to 75% vane pitch do not attach to the blade surfaces and hence have little impaction on the film cooling effectiveness. |
