Inthis study, heat transfer and friction factor for various rib shapes were analyzedfor a rectangular cooling channel of a gas turbine blade. Ratios of rib-height,rib-width and rib-pitch to hydraulic diameter of the channel were taken as 0.1,0.
1 and 1.2 respectively. Numerical simulations were performed on various ribshapes for Reynolds number, based upon the hydraulic diameter, ranging from5000 to 20,000 and uniform heat flux of 800 W/m2. K-w turbulencemodel was used to analyze the turbulence. The computational results for smoothsection were validated with Dittus-Boelter relation for Nusselt number, andBlasius equation for the friction factor.
Furthermore, the computationalresults for area-averaged Nusselt number were compared with the experimentaldata under the same conditions. The main aim of this study is to analyze theeffects of rib shapes on the heat transfer and fluid flow characteristics. Simulationswere done using air as the cooling medium but the effect of using steam,instead of air, was also investigated in this study. 1.
IntroductionCooling channels areprovided in machine parts where heat generation occurs and this generated heatneeds to be removed out of the machine. If let to accumulate, the heat producedcan cause damage and result in failure of machine. Internal cooling channelsare found inside the gas turbine blades, high temperature propulsion systems,electric generator coils, cylindrical lining of IC engines and many otherapplications. In the case of gas turbine blades, bypass air bled from the laststages of compressor acts as the coolant. This air bypasses the combustionprocess thus remains cooler and is fed to the internal cooling channels of theturbines blades, where it removes heat from the hot surfaces, keepingtemperatures within the thermal limits of the alloys used. Turbulators, orcommonly known as ribs, are a popular heat transfer augmentation device used inthe internal cooling channels of a gas turbine blade. These ribs break the flownear the wall surface and cause increase in turbulence. The amount of turbulentkinetic energy produced depends upon various factors such as rib shape,rib-height, rib-width and rib-pitch etc.
out of which rib shape is one of themost important factors.