Effects of the inclination angle of oval film holes on the aero-thermal performance of a squealer blade tip

Abstract

The investigation and study on the characteristics of the flow and wall heat transfer on the squealer tip is of vital importance to the safe and durable operation of a turbine rotor. The numerical model of the blade squealer tip with discrete film cooling holes (round and oval holes) was constructed and validated in this paper. The effects of the radial and axial inclination of oval-holes on aero-thermal performance were systematically investigated, which received little attentions in previous studies. The result shows that the streamline deflection produced by negative inclination structures significantly improves the coverage of film, but the development of the jet vortex leads to an enhancement in leakage flow. The lift-off of film is effectively restrained by positive inclination structures, however, the jet outflow contraction limits the expansion of film coverage. Besides, the scraping between tip cavity flow and leakage flow is also an important factor to the leakage flow control, which can reduce the momentum of leakage flow. Overall, the negative radial inclination structure achieves the optimal performance of film cooling, whose tip average cooling effectiveness at 0.5 blowing ratio is even 132% higher than that in the round hole reference at 1.5 blowing ratio. The highest relative reduction of leakage flow is obtained by the positive axial inclination structure with 62.79% at the blowing ratio of 1.5.