Flow and heat transfer characteristics of a squealer tip with bent rail in turbine blades

Squealer tip is an effective method for reducing heat transfer and leakage losses of blade tips in gas turbines and is currently being extensively researched and developed. In this study, the squealer tip has been innovatively developed by introducing bent rails, and three types of squealer structures with bent rails were proposed: the bent pressure-side rail scheme (Case_P), the bent suction-side rail scheme (Case_S), and the bent double-side rail scheme (Case_PS). This study first compared the performance of the proposed novel schemes with the traditional squealer tip scheme with vertical rails (Baseline) in terms of tip heat transfer and flow control by analyzing parameters such as the tip heat transfer coefficient (h), leakage flow rate (LFR), and total pressure loss (Cpt) under fixed bending values (S). Subsequently, the effects of different bending values (S) on the three novel schemes were investigated. The results show that, in terms of heat transfer, both Case_P and Case_S can effectively reduce the tip h, but their mechanisms are entirely different. Case_P primarily relies on the increasing separation bubble size at pressure-side rail edge and gradually expanded low-energy flow region in the pressure-side rail corner. In contrast, in Case_S, it is mainly because the cavity flow enters the suction-side gap more smoothly due to the bent suction-side rail. In terms of aerodynamics, the bent pressure-side rail of Case_P significantly inhibits the entering velocity of leakage flow, thereby reducing the LFR and Cpt; however, Case_S causes the LFR to increase. In Case_PS, the heat transfer and leakage phenomena resemble a combination of Case_P and Case_S. With the increase in S, the tip h in the three schemes all decreases, and the tip heat transfer in Case_PS is more comprehensively reduced because it incorporates all the flow factors that reduce h from the other two schemes. In Case_PS, the rail types that both hinder and increase LFR coexist, resulting in the LFR remaining relatively stable with varied S.