Experimental and Numerical Conjugate Flow and Heat Transfer Investigation of the Influence of Density Ratio and Blowing Ratio on the Film-Cooling Efficiency of a First Stage Turbine Guide Vane

Abstract

A modem nozzle guide vane with showerhead cooling is investigated. The showerhead design consists of four rows of ejection holes at the leading edge in the stagnation region and has been worked out on the basis of a former design with only two rows. The experimental analysis is performed in a cold-air test turbine by means of LDV. In order to overcome the thermal limitations of the test rig, the heat transfer analysis is performed with CHT-Flow, a numerical method that has been developed at the Institute of Steam and Gas Turbines and that works in a conjugate manner. This means that no thermal boundary conditions such as heat transfer coefficients have to be described on the vane surface for thermal analysis. The first part of the investigation deals with the aerodynamics. At first, air is used as a cooling fluid leading to a density ratio of Πρ = 1.2. Then, in order to take density effects into account in the experiments. CO2 is used as a cooling gas providing a density ratio Πρ = 1.8 representative for modern engine operating conditions. The results are compared to the simulations. It is shown that the cooling gas does not penetrate the main flow as far under realistic density ratios. Thus, the aerodynamic losses are reduced and there is better attachment of the cooling film to the airfoil. The second part analyses the heat transfer. It is shown that lowering the blowing ratio has different influences on the material temperature locally. On the suction side, the cooling gas film attachment is enhanced and the surface temperature is lowered. In contrast, the surface temperature rises slightly on the pressure side.