Flow And Heat Transfer Characheristics In The Rotating Serpentine Cooling Channel With Rib Turbulators

The ribbed serpentine channel uses multiple passes to enhance the inner wallsurface heat transfer, which is widely used in a turbine blade for cooling. In order tolearn more about the heat transfer and pressure distribution of the multiple-passribbed serpentine channel wall and master the effect of rotation and outlet fluxdistribution on channel flow and heat transfer characteristics, a rotating ribbedserpentine channel of a gas turbine rotor was studied experimentally and numericallyin this paper.An amplificatory model was adopted and a rotary total surface heat transfermeasurement experiment system was established. According to the structure of theinternal cooling channel, the experiment model of serpentine channel consists ofthree ribbed passes which are connected by two turn segments. The section of thefirst and third radial outflow pass is trapezoidal, and that of the second radial inflowpass is rectangle. The inlet is located in first pass bottom, outlet1is located in thetop of the first turn segment, and outlets2and3are located in the top and side wallof the3rd channel, respectively.14rectangular ribs are interleaved on pressure andsuction surface of the first and second pass, and16wedge ribs are interleaved in thethird pass. The ratio of inlet hydraulic diameter to rib height is0.107:1, that of ribpitch to rib height is12.58:1. The range of Reynolds number is from5000to20000.The flux distribution of outlet1,2and3is27%,49%and24%(when three outletsare outflow),27%,0%and73%(when outlet2is not outflow) and27%,73%and0%(when outlet3is not outflow). The range of rotating number is from0to0.09.The ratio of rotation radius to hydraulic diameter is46.4. The pressure surface heattransfer coefficient is measured by transient liquid crystal measurement technique.The computational domains and working condition of simulation and experimentwere identical. Two additional factors like rotating radius and hydraulic diameterwere investigated numerically compared with experimental study. The brief details of major conclusions are described as below:1. After the breakthrough of some key techniques like the capture, transmissionand recording of rotating image, the total surface heat transfer coefficientdistribution with high resolution was obtained under the rotating internal channeltotal surface heat transfer measurement experiment system by transient liquid crystalmeasurement technique, which is of especial advantage in rotating all surfacemeasurement. The uncertainty of transient liquid crystal measurement technique canbe controlled below10%.2. The pressure coefficient distribution can be affected by rib flow resistance,outlet flux loss and turn effect. The variation law of pressure coefficient is identicalat different Reynolds number, that is the pressure coefficient decreases along theflow direction, and the loss is larger at the low Reynolds numbers. The pressurecoefficient changes a lot in the third pass at different flux distribution of outlet. Thepressure coefficient drop and flow loss are the largest when outlet2is not outflow.Rotatory force changes the pressure coefficient of every segment of serpentinechannel. The pressure coefficient drop decreases in radial outflow pass and increasesin radial inflow pass. The increase of rotatory radius makes the variation range ofpressure coefficient more evident.3. The heat transfer distribution in pressure surface is similar at differentReynolds numbers. The separation and reattachment of mainstream boundary layerin the near surface caused by rib increases the turbulence of wall and thus the heattransfer coefficient between ribs. The downstream heat transfer distribution is noteven due to turn separation effect. The heat transfer is low in the area that is far awayfrom the turn, and high near the turn. Flow distribution only affects the heat transferin third pass wall. The heat transfer distribution uniformity is more serious in thirdpass due to the decrease of flow of outlet2.4. The heat transfer coefficient of the radial outflow pressure surface increasesand the high heat transfer area of the third pass moves inwards with the increase ofrotating number. The heat transfer coefficient of the radial inflow pass pressuresurface decreases. The single high heat transfer area in the left side of pass2turns into double-vortex high heat transfer areas in both sides of pass2. Then thedouble-vortex high heat transfer areas shift toward left side and merge finally. Theheat transfer coefficient is slightly strengthened with the increase of radius, but thedistribution of the coefficient does not change.5. The distribution of spanwise average heat transfer coefficient along flowdirection in each ribbed pass is multiple-peak. The high heat transfer area decreasesgradually along the flow direction. The peak between ribs shifts toward thedownstream of forehead rib. The variation of average heat transfer coefficientbetween ribs is consistent both in flow and spanwise direction.6. Numerical simulation reveals that the local heat transfer coefficient slightlyincreases with the ratio of radius to hydraulic diameter. The heat transfer distributionof each pass is significantly different from single channel which is caused by the turn.The numerical simulation can accurately predict wall heat transfer distribution, theresult of which is lower than the experimental results.