Numerical Investigations On The Effects Of Cooling Air On The Aerodynamic Performance Of Cascade

The increasing pressure ratio and turbine inlet temperature of gas turbine have raised higher requirements for the cooling technologies of turbine blades. Film cooling technology can effectively protect the blades at high heat load, but the mixing between film cooling air and mainstream gas is an important source of aerodynamic loss. In this paper, two turbine cascades were investigated separately and a numerical study on the characteristics of jet flow from film cooling holes and trailing edge slots was conducted to reveal the effects of the geometrical and aerodynamic parameters on the mixing process and the loss of cascades.In a linear cascade of low pressure guide vane, an investigation on the effects of the ejection from trailing edge slots on the aerodynamic performance was taken and then the analysis about changes of the cascade aerodynamic loss due to the variable blowing ratios and trailing edge slot widths was made. It was found that the total pressure loss varied in an opposite direction with that of both blowing ratio and slot width; while the thermodynamic loss was in positive correlation with blowing ratio and the relationship between the thermodynamic loss and slot width depended on the value of blowing ratio. In an annular cascade tandem turbine stage, effects of the cooling air ejection from the trailing edge slots of guide vane on the aerodynamic characteristics of downstream cascade were investigated further numerically, it was concluded that the circumferential non-uniformity of the out-flow field from vane cascade could be reduced by the increase of blowing ratio.Taking a three-dimensional annular cascade as an object which was a rotor blade of a gas turbine’s first-stage, the aerodynamic characteristics and impacts of attack angle on the aerodynamic loss of the twisted blade was studied under conditions without film cooling. Comparisons between the effects of cooling air’s mixing with mainstream under conditions with and without film cooling were made to reach the conclusion that the aerodynamic loss generated in occasions with film cooling was smaller than that without film cooling. To analyze the variations of aerodynamic characteristics of rotor blade cascade with film cooling under situations with different aerodynamic parameters, the effects of flow attack angle, rotating speed and cooling air inlet pressure were investigated separately. It was found that blowing ratio was the key factor affecting the aerodynamic and heat transfer characteristics of film cooling and the aerodynamic loss firstly decreased and then increased with the continuing rise of blowing ratios.Investigations on the effects of mixing between film cooling and mainstream on cascade aerodynamics can provide a reference for the experimental study on the relative subjects and design of turbine blade cooling structures.