A Research On The Effects Of Unsteady Wakes On Film Cooling

Jiang Xue-Hui(Engineering Thermophysics) Directed by Zhao Xiao-LuThe effects of unsteady wakes on film cooling were investigated by experiments and numerical simulation.Firstly, the effects of unsteady wakes on film cooling effectiveness under low speed condition were investigated by experiments. The results showed that unsteady wake made the time-averaged film cooling effectiveness decreased at blowing ratio of 1, rod diameter of 4mm or 6mm. The unsteady wake made the time-averaged film cooling effectiveness decreased at blowing ratio of 0.5, rod diameter of 4mm. While the unsteady wake made the time-averaged film cooling increased at blowing ratio of 0.5, rod diameter of 6mm.Secondly, the effects of unsteady wakes on film cooling at the leading edge of blade were investigated by experiments and numerical simulations. The experimental results under low speed condition showed that unsteady wakes could increased the film cooling effectiveness by 2%-3% on the experiment conditions. The results of numerical simulations also showed that the unsteady wakes increased the film cooling effectiveness on the experimental conditions. The numerical simulations also showed that when the unsteady wakes strike on the leading edge of blade, the stagnant point of main flow moved to the top of the film cooling slit (hole). The flow of film cooling diverged and the film cooling effectiveness of the wall behind film cooling slit decreased sharply under this condition.Thirdly, the effects of unsteady wakes on film cooling were investigated under two-dimension, high-speed conditions by numerical simulations. The results showed that unsteady wakes affected film cooling by two ways. One is to strike the wall directly, disturb the film cooling layers. The other is to affect filmcooling of the wall behind the film cooling holes (slit) indirectly by changed the flow field conditions near the film cooling holes.Fourthly, the effects of unsteady wakes on film cooling were investigated under three-dimension, high-speed conditions by numerical simulations. From the results, a new kind of the unsteady wakes affecting mechanism on film cooling was found. The unsteady wakes made the main flow stagnant point move from the front of the film cooling holes to the back of the film cooling holes. The film cooling flows would diverge, flow adversely under this conditions.From the experimental and numerical simulation results, we concluded that the unsteady wakes affected the film cooling by two ways. One is a direct way. The wake strikes the wall directly, disturbs the film cooling layers, and makes the temperature of the wall changed. The other is an indirect way. The wakes changes the flow field around the film cooling holes, then the film cooling of the wall behind the film cooling holes changes.