SASTech - Technical Journal of RUAS

Gas turbine plays a vital role in the present day industrial society as they are being extensively used for land based power generation and in aircraft propulsion. There is constant challenge to increase the efficiency of the gas turbine engines which can be increased by raising the turbine inlet temperature. Present day advanced gas turbine blade inlet temperatures can be as high as 1700°C, here as blade materials are capable of withstanding only 1200°C to 1300°C. Cooling air, extracted from the compressor is around 650°C, is passed through the airfoil sections of the blade which lower the temperature to about 1000° C which is safe and permissible for reliable operation of the engine. It is practically very difficult and costly to obtain experimental data on heat transfer and the pressure losses in thin airfoil turbine blade sections at such temperatures and rotational speeds. Hence data generated from numerical investigations will play vital role in design, development and improving the efficiency of gas turbine engines. Flow tripping geometries like pin fin, and dimples are generally used in the trailing edge regions, where as ribs or tabulators are located at middle of the airfoil to enhance the heat transfer.

In this paper, analysis is carried out on three different combinations which are simple U duct, ribs aligned at 45° to flow direction and combination of ribs and grooves at 45° to flow direction. All turbulators are located on trailing face of duct. The simulations are carried on square duct having hydraulic diameter (Dh) of 0.0127m, Reynolds number of 25, 000, rotational number (Ro) of 0.24, inlet density ratio (Δρ/ρ) of 0.13. Details for relative rib height (e), pitch distance between ribs (P), distance between ribs and groove centre (g), and the groove angle are similar to experimental reference. The numerical analysis has been carried out on Ansys CFX solving 3D compressible Navier Stokes equation along with k-ω turbulence model.

It was observed from the investigation, that the numerical results are in good agreement with the experimental results in validation stages. For the simple U duct and duct with ribs the simulations are carried out for one complete revolution and for rib-grooved case, only partial results are published. The present results for the turbulators show that there is significant enhancement in heat transfer from the heated wall to coolant when compared with simple U tube.