Numerical Simulation of Flow and Heat Transfer Characteristics of Asymmetric Blade Leading Edge Structure

Abstract

In consideration of aerodynamic requirements, the leading edge of turbine blade often presents an asymmetric concave structure. In this paper, an asymmetric model was simplified from the leading edge structure of a real turbine blade, and the flow and heat transfer characteristics were then numerically analyzed. Three impingement cooling models (e/d=1.5, 0 and -1.5) were obtained by changing the position of the impingement holes. The inlet Reynolds number(Re) are 10000, 20000 and 30000 respectively. The results shows that the average Nusselt number(Nu) of the impact target surface with e/d =1.5 is the largest, which is 11.7% higher than that of the model with e/d=-1.5 for Re=20000. However, the thermal uniformity of e/d =-1.5 is the best. The transient analysis shows that the flow period is 0.006 seconds and the flow has strong instability. Then, by adding film holes to the model with e/d=1.5, the impingement-film composite cooling structure is obtained. The analysis shows that compared to the structure with impingement holes only, the heat transfer capacity of the composite structure does not change significantly, but the thermal uniformity of the target surface is significantly improved. For Re=20000, the heat transfer non-uniform coefficient decreases by 13.8%. At last, the outflow mass flow ratio was changed to simulate the pressure distribution of the blade under real operating conditions from film holes, and it was found that with the increase of the mass flow gap between the film holes on the pressure surface and the suction surface, the average Nu of the target surface decreases and the heat transfer non-uniform coefficient increases compared with the pressure-outlet. From the results, it can be found that for the asymmetric leading edge structure, the offset impact holes can enhance the heat transfer of target surface and the film holes are beneficial to enhance the thermal uniformity of target surface. However, the asymmetrical outflow is harmful to the overall heat transfer of the structure.