Abstract
Gas turbine engines are widely used in industrial systems and military vehicles. The working temperature is increased for a higher thermal efficiency. The increasingly high temperature may degrade the blade material and ultimately shorten the turbine blade life. Developing high-performance cooling technology on hot spots of the components is necessary. Inside a rotating heated flow passage, the flow and heat transfer characteristics are not only affected by the main flow but also modified by the Coriolis-induced cross-stream flow and the centrifugal-buoyancy induced radial secondary flow. Heat transfer characteristics are widely different on different side walls of the flow passage.The purpose of this research is to study the convective heat transfer for the internal flow of rotating gas turbine blades. Experiments are conducted on a rotating stand for a four-pass serpentine channel. Parameters cover: 5atm pressure inlet air; Reynolds number Re=20000, 30000 and 36000; rotating speed N=0, 250, 500 and 750 rpm; outlet-inlet bulk air temperature differences of 10 and 20K. There are totally 143 temperature measuring points, with particular carfulness for the bend section (15 points for each bend section) as well as the inlet and outlet regions (18 points each). Numerical simulations are preformed using the commercial package CFX-TASCflow. Two-layer and k-omega turbulence models are used. Simulated cases include a single-pass square channel and an U-bend two-pass square channel. The present numerical results are compared with the experimental data available in the literature and in the present work.Experimental results indicate that: (1) For the stationary cases, the heat transfer rate increased with the increasing Reynolds numbers, with the increasing rate more pronounced in the bend regions; (2) For the rotating cases, due to Coriolis force effect, the heat transfer rate on leading wall is higher than that on trailing wall for the first and third passages, and inversely for the second and four passages; (3) Widely different heat transfer characteristics are shown by the detailed temperature measurements in the bend regions. For the stationary cases, the heat transfer rates among the three bend regions slightly increase sequentially. Among the four straight passages, the third exhibits the lowest heat transfer rates; (4) For the rotating cases, the distributions of NuΩ/Nu0 in the bend regions are greatly higher than for straight passages. Among the three bends, the ratios are enlarged sequentially. Besides, NuΩ/Nu0 ratios for the four straight passages also increase sequentially. The ratios are higher for a higher rotation number. This may be due to the increased turbulence intensity when the flow passes through each of the bends.The simulation results with different turbulence models exhibit qualtitative agreement of the heat transfer with the experiments. Detailed discussion of the heat transfer characteristics in the rotating four-pass serpentine channels are provided with the combined experimental and numerical analysis.