| Combustion chamber (combustor), primarily consisting diffuser casing, flame tube (liner), cowl, atomizer etc., is one of the hottest parts of a gas turbine. The liner is where the actual flame occurs in a combustor and, thus, the hottest part of the combustor. The working temperature of the liner is about 1200K to 2000K, which is very high for the material of liner to withstand. Although, the mechanical stresses experienced by the combustor liner are within acceptable limits compared to other parts, high temperatures and large temperature gradients affect the structural integrity of these components, which makes 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 a liner. In film cooling for combustor, annular holes are drilled along the surface of the liner, through which cool 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. The film is destroyed in the downstream to the flow because of turbulent 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. Thus, there is a need for new cooling techniques or enhancing the current 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 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. Another enhancement technique proposed in this work is providing compound angled holes instead of axial holes. The performance of mist injection in compound angled holes is also analyzed. Fluent, a commercial CFD software, is extensively used in the current work for numerical simulations. |
