Numerical Study of Film Cooling Enhancement in Gas Turbine Combustor Liner

Abstract

Combustion chamber or combustor is one of the hottest parts of a gas turbine. Liner is where the actual flame occurs in a combustor and thus, the hottest part of the combustor. The temperature of working fluid inside a liner is about 1200 to 2000K. Because of the hot fluid, the liner is heated up to a temperature almost impossible for the material to withstand. Although the mechanical stresses experienced by the combustor liner are within acceptable limits, high temperatures and large temperature gradients affect the structural integrity of its components, which makes the liner a very critical component of a gas turbine in structural and thermal designs. Film cooling is a traditional method of cooling the inner surface of liner. In film cooling for a combustor, axial holes are drilled along the surface of the liner at discrete locations, through which cold air is injected axially into the liner to provide a film of cool air that prevents direct contact of hot air, and thus, protects the inner wall surface. The film is destroyed in the downstream to the flow because of mixing of cool and hot air. Though this method provides an acceptable cooling, there is a compromise with the increased net benefits of the gas turbine. Therefore, there is a need for new cooling techniques or enhancing the techniques available. The current work is a numerical simulation of film cooling in a model combustor. The effect of coolant injection angles and blowing ratios on film cooling effectiveness is studied. One innovative method, cooling with mist injection, is explored to enhance the performance of film cooling. The effect of droplet size and mist concentration, which can affect the performance of the mist injection, is also analyzed. Fluent, a commercial CFD software, is used in the current work for numerical simulations.

Simulation of Impinging Cooling Performance with Pin Fins and Mist Cooling Adopted in a Simplified Gas Turbine Transition Piece

“…The size of droplets is uniformly given as 5 microns, and the masses of water droplets are 0.003 kg/s. The similar conditions have been successfully used in film cooling technology by Subbuswamy and Li [22]. The solid walls are assigned as "reflect" boundary condition, which enables the droplets to elastically rebound once hitting the wall.…”

“…The cooling effectiveness ( ) [22] is used to examine the performance of impinging cooling. The definition of is…”