Mist/air Cooling in a Two-Pass Rectangular Rotating Channel with 45-deg Angled Rib Turbulators

Increasing the turbine inlet temperature can increase the gas turbine cycle efficiency. In order to increase the turbine inlet temperature significantly, an advanced cooling system has to be essentially developed. Injection of mist to the coolant fluid is considered a promising technique to protect the hot components such as combustor liners, combustor transition pieces, and turbine vanes and blades. A series of experiments conducted in the past proved the success of mist cooling technology in the laboratory environment. Favorable results from the numerical simulation further encourage continuous exploration of employing mist-cooling technology in the actual gas turbine working environment in various applications. The present study focuses on applying mist cooling to the rotating mist/air internal cooling passage with rib turbulators using numerical simulation. In the first part, the computational fluid dynamics (CFD) models of smooth and ribbed channels without mist and rotation are validated with the experimental results available in literature. The agreement between the predicted and experimental values in the lower Reynolds number (Re) range is within 3% deviation, and, at higher Re range, the deviation is about 10%. For the smooth channel, the agreement with experimental result is good for the entire range of Re values. In the second part, the rotational effect on the smooth and ribbed channels is predicted and analyzed. In the last part, the mist cooling enhancement on the ribbed channel with rotation is simulated. The secondary flows created due to channel bend and rotation are specifically analyzed. The results show that the mist cooling enhancement is about 30% at the trailing surface and about 20% at the leading surface of the first passage with 2% mist injection. In the second passage, 20% enhancement is predicted for both the surfaces. NOMENCLATURE Ap surface area of droplet b slot width (m) C concentration (kg/m) Dh Channel hydraulic diameter GT gas turbine h convective heat transfer coefficient (W/m-K) H height of channel (m) k turbulent kinetic energy (m/s) K thermophoretic coefficient Nu Local Nusselt number, hDh/kc m mass (kg) q wall heat flux (W/m) Re Reynolds number (ρ Vj d / μ ) Ro rotational number, Ω Dh / V Tw wall temperature (C) V inlet bulk velocity (m/s) W width of channel (m) Greek ε turbulence dissipation (m/s) λ thermal conductivity (W/m-K) Ω rotational speed (rad/s) Subscript p, d particle or droplet r riblet s smooth.