Heat transfer and film cooling effectiveness on the squealer tip of a turbine blade Jun Su Park a , Dong Hyun Lee b , Dong-Ho Rhee c , Shin Hyung Kang d , Hyung Hee Cho a, * a Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Republic of Korea b Korea Institute of Energy Research, Daejeon 305-343, Republic of Korea c Korea Aerospace Research Institute, Daejeon 305-333, Republic of Korea d School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Republic of Korea article info Article history: Received 19 October 2013 Received in revised form 27 April 2014 Accepted 6 May 2014 Available online 11 June 2014 Keywords: Heat transfer Turbine blade Squealer tip Film cooling abstract Detailed heat/mass transfer coefficients and film-cooling effectiveness were measured on the tip and inner rim surfaces of a blade with a squealer rim. The test blade was a two-dimensional version of a modern first-stage gas turbine rotor blade with a squealer rim. The experimental apparatus was equipped with a linear cascade of three blades, and the axial chord length (C x ) was 237 mm with a turning angle of 126  , the mainstream Reynolds number based on the axial chord and inlet velocity was 1.5  10 5 . In addition, three different types of blade tip surfaces were equipped with a single row of film- cooling holes along the camber line, near the pressure and suction-side rim. The blowing ratio was fixed at 1.5. High heat transfer rates were observed near the leading edge on the tip surface due to reattached flow. Furthermore, heat transfer on both inner side surfaces was higher than that on the tip surface. High film cooling effectiveness was observed in the middle region (0.1 < X/C x < 0.6) due to stagnation of the film cooling. Ultimately, a proper cooling system is suggested to reduce the thermal load and enhance the film cooling effectiveness in the squealer tip. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The inlet temperature of turbine engines has been steadily increasing with the development of new engine. Turbine blades experience severe thermal stress and fatigue as a result of exposure to high-temperature gases. In particular, the tips of gas turbine rotor blades are subjected to large thermal loads, resulting in damage to the blade tips. Such thermal loads arise due to tip leakage flow through the gap between the rotating blade tip and the stationary shroud. The hot leakage flow accel- erates due to large pressure differences that exist between the pressure and suction-sides of the blade, resulting in a thin boundary layer and high heat-transfer rates. This flow across the blade tip is also undesirable in terms of efficiency because it increases turbine power losses. Consequently, squealer-type tips are employed to reduce leakage flow. The presence of a rim and groove increase the flow resistance of the leakage flow, resulting in a decreased leakage flow rate. However, thermal loads and stresses are concentrated at the edge of the rotor blade tip and thus, cracking and breakage can occur in this region. Therefore, it is important to understand the flow and heat transfer charac- teristics of the squealer tip cavity. Morphis and Bindon [1] have contributed to the general un- derstanding of tip-gap flow patterns. In particular, they conducted pressure and flow field measurements on an axial turbine blade tip in a linear cascade under low-speed conditions and suggested tip leakage flow characteristics. Metzger et al. [2] and Chyu et al. [3] investigated heat transfer phenomena for rectangular grooved tip models. The researcher performed experiments using cavities with various depth-to-width and tip gap-to-width ratios, and incorpo- rated the effect of relative motion by introducing a moving shroud surface over the grooved tip model. From the obtained results, it was suggested that heat transfer upstream of the cavity was greatly reduced. When compared to a rectangular flat tip, the heat transfer coefficient was higher at the downstream end of the cavity due to flow reattachment inside the cavity. Cho et al. [4] experimentally measured the local heat/mass transfer characteristics on a shroud with various blade tip clearances. The results showed that the heat/ mass transfer characteristics changed significantly with respect to the gap distance between the tip of the turbine blade and the shroud. Rhee and Cho [5,6] also studied the local heat/mass transfer * Corresponding author. Tel.: þ82 2 2123 2828; fax: þ82 2 312 2159. E-mail address: hhcho@yonsei.ac.kr (H.H. Cho). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2014.05.041 0360-5442/© 2014 Elsevier Ltd. All rights reserved. Energy 72 (2014) 331e343