POD analysis of passage-layout effect on unsteady internal flow in a realistic blade serpentine coolant channel with low
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R E G UL A R P A P E R
Jian Pu • Ren-bin Yu • Jian-hua Wang • Bo Wan • Jian-xia Luo • Shu-qing Tian
POD analysis of passage-layout effect on unsteady internal flow in a realistic blade serpentine coolant channel with low aspect ratios Received: 20 March 2020 / Revised: 25 May 2020 / Accepted: 8 June 2020 The Visualization Society of Japan 2020
Abstract Internal serpentine ribbed coolant channel with low aspect ratio (AR) has been widely employed to provide excellent thermal protection for advanced first-stage turbine blades. Various height differences (DHs) of adjacent passages along pressure side can be generated under the restriction of actual blade profile. The present work made an attempt to acquire detailed influences of DH on the time-averaged and transient secondary motions near sharp bends of low-AR coolant channels. An actual blade ribbed three-pass coolant channel with two DHs was chosen as experimental model. Planar time-resolved particle image velocimetry technique was applied to capture the transient flow fields in 21 typical cross sections. Time-averaged results were validated by standard PIV measurements and flow visualizations. Snapshot proper orthogonal decomposition was employed to extract the dominant flow structures and identify the underlying small-scale flow patterns in time-resolved velocity fields. The experimental results indicated the low-AR channel with real blade profile induces a new type of the secondary-vortex superposition downstream of bends, in comparison with the large-AR channels in open literature. The crucial reason is the DH along pressure side leads to an intensive impingement on the bend wall, which weakens the effects of bend, rib and curvature of suction side. Another new discovery is the effect of DH on unsteady internal flow. In the small DH case, the oscillatory frequency of the secondary vortices is nearly similar with the counter-rotating Dean-vortices; however, in the large DH case, the oscillatory frequency is much lower, and the rotating direction of vortices is same and unchanged in a period. Increasing inlet Reynolds number can significantly change the underlying small-scale flow patterns and improve the oscillatory frequency of large-scale structures, although the basic time-averaged flow patterns are nearly same. Effect of injection from auxiliary-hole (AH) on unsteady internal flow is obvious and the optimum mass flow ratio of AH-to-inlet is 5%. Keywords Coolant channel TRPIV POD Unsteady secondary motion Actual blade profile List of symbols AH AR MFR MS
Auxiliary-hole Aspect ratio Mass flow ratio Middle surface
J. Pu R. Yu J. Wang (&) CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Jinzhai Road No. 96, Hefei 230027, Anhui, People’s Republic of China E-mail: [email protected] B. Wan J. Luo S. Tian Aero Engine Corporation of China (AECC) Commercial Aircraft Engine Co., Ltd, Lianhua South Road No. 3998, Shanghai 200241,
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