Effect of Discrete Ribs on Heat Transfer and Friction Inside Narrow Rectangular Cross Section Cooling Passage (AR=1:5) of Gas Turbine Blade
Karthik Krishnaswamy1, Srikanth Salyan2
1Karthik Krishnaswamy*, Research Scholar, Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India.
2Srikanth Salyan, Assistant Professor, Department of Aeronautical Engineering, Dayananda Sagar College of Engineering, Bangalore, India. 
Manuscript received on August 17, 2021. | Revised Manuscript received on August 28, 2021. | Manuscript published on August 30, 2021. | PP: 192-209 | Volume-10 Issue-6, August 2021. | Retrieval Number: 100.1/ijeat.F30740810621 | DOI: 10.35940/ijeat.F3074.0810621
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Abstract: The performance of a gas turbine during the service life can be enhanced by cooling the turbine blades efficiently. The objective of this study is to achieve high thermohydraulic performance (THP) inside a cooling passage of a turbine blade having aspect ratio (AR) 1:5 by using discrete W and V-shaped ribs. Hydraulic diameter (Dh) of the cooling passage is 50 mm. Ribs are positioned facing downstream with angle-of-attack (α) of 30° and 45° for discrete W-ribs and discerte V-ribs respectively. The rib profiles with rib height to hydraulic diameter ratio (e/Dh) or blockage ratio 0.06 and pitch (P) 36 mm are tested for Reynolds number (Re) range 30000-75000. Analysis reveals that, area averaged Nusselt numbers of the rib profiles are comparable, with maximum difference of 6% at Re 30000, which is within the limits of uncertainty. Variation of local heat transfer coefficients along the stream exhibited a saw tooth profile, with discrete W-ribs exhibiting higher variations. Along spanwise direction, discrete V-ribs showed larger variations. Maximum variation in local heat transfer coefficients is estimated to be 25%. For experimented Re range, friction loss for discrete W-ribs is higher than discrete-V ribs. Rib profiles exhibited superior heat transfer capabilities. The best Nu/Nuo achieved for discrete V-ribs is 3.4 and discrete W-ribs is 3.6. In view of superior heat transfer capabilities, ribs can be deployed in cooling passages near the leading edge, where the temperatures are very high. The best THPo achieved is 3.2 for discrete V-ribs and 3 for discrete W-ribs at Re 30000. The ribs can also enhance the power-to weight ratio as they can produce high thermohydraulic performances for low blockage ratios.
Keywords: Reynolds number, Discrete W and V-ribs, Nusselt number ratio, Heat transfer coefficient, Friction factor ratio, Thermohydraulic Performance