Numerical Investigation on the Cooling Effectiveness Among Air and Steam and Mist/Steam for a Gas Turbine Vane

This paper presents a numerical comparison of the flow and conjugate heat transfer characteristics about the internal cooling of a nozzle guide vane with three kinds of coolants, including air, steam and mist/steam. Five radial cooling channels are established inside the vanes. The Reynolds-averaged Navier–Stokes equations, coupled with a fully-developed Shear Stress Transport (with γ-θ transition) turbulent model, are adopted and solved. Different coolant mass flow rates are examined. Different initial mist diameters and mist concentrations are numerically calculated. The mist tracks in five internal channels and the cooling effectiveness at the mid-span are obtained and compared among different initial mist diameters and mist concentrations. The turbulence kinetic energy and heat transfer coefficient inside the internal channel are used to further investigate the effects of the droplet size. The mean cooling effectiveness of the vane outer surface is obtained at different coolant mass flow rates. Results show that the mist/steam cooling has a best cooling performance compared with that of the air and steam. The influence of the mist concentration is much smaller than the initial mist diameter on the mists evaporation. The mists can evaporate entirely at a relative small initial diameter and the evaporation distance increases about two times with the mist mass flow rate increases from 1% ∼ 5% coolant mass flow rate. With a same mist concentration, the faster the mists evaporate, the higher the cooling effectiveness is obtained. Under a certain coolant mass flow rate, the amplification of the mean cooling effectiveness decreases with the increase of the mist concentration. With the increase of the coolant mass flow rate, the differences of the mean cooling effectiveness among different mist concentrations become larger.