Sankaranarayanan Vengadesan

Internal cooling of the gas turbine blade is critical for the durability of the blade material. One of the ways to accomplish this is by passing coolant through serpentine passages roughened with surface elements to enhance the heat transfer. In the present study, the traditional square rib (SQ-rib) placed normal to the flow direction is modified to a backward-facing step rib (BS-rib) and a forward-facing step rib (FS-rib). Large-eddy simulation (LES) is carried out for a square duct at Reb = 20000. Results show that the modified rib shapes result in substantial increase in heat transfer over the square rib with only a marginal increase in flow losses. The BS-rib shape produces the highest heat transfer augmentation followed by the FS-rib. The overall heat transfer augmentation for the BS-rib and FS-rib is 18% and 10% larger than the SQ-rib, respectively. Thermal-hydraulic performance is enhanced by 15%.

Cooling of turbine blades is necessary for longer durability and better thermal efficiency of the turbines. Turbine blade cooling is fulfilled by passing a coolant through the serpentine channel roughened with turbulators. In this work, the combined effect of the centrifugal buoyancy and the Coriolis force on heat transfer of a square duct roughened with ribs is studied using Large Eddy Simulation (LES). Simulations are carried for a Reynolds number based on bulk velocity of 20,000 with staggered square (SQ) rib, Backward step (BS) rib, and Forward step (FS) rib on the leading and trailing wall. The heat transfer performance of the square duct roughened with ribs is compared at rotation numbers Ro=0.35,0.67 and Richardson numbers Ri=0.0,12.0,28.0. The heat transfer augmentation for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 4.2%, 8.6% and 14.9%, respectively, higher than that without the effects of buoyancy. The friction coefficient for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 12.8%, 14.8% and 13.3% respectively higher than that without buoyancy.