New Methods Used for the Smoothing of the Three-Dimensional Flow Behind the Turbine Nozzle Cascade

Abstract

To smooth the parameters of the three-dimensional flow behind the nozzle cascade new methods were suggested that allow us to sustain the flow rate, stagnation enthalpy and the axial projection of the moment of momentum for initial-, nonuniform and averaged flows. It was shown that the choice of the fourth integral characteristic (the kinetic energy, the entropy and the quantity of motion) has no particular significance because it has no effect on the complex criterion of the cascade quality, i.e. the velocity coefficient-angle cosine product that characterizes the level of the radial component of velocity. The minimum values of the velocity coefficient and the cosine angle satisfy the method that allows us to sustain the quantity of motion during the smoothing and the maximum values of the specified nozzle characteristics satisfy method 2 that enables the entropy maintenance. To evaluate the aerodynamic efficiency of the nozzle cascade the preference should be given to method 1 that enables the kinetic energy conservation and the velocity coefficient allows for the precise determination of the degree of loss of the kinetic energy that is equal to 3.6 % as for the example given in the scientific paper. As for method 1, the kinematic losses in the cascade are defined by the angle cosine that characterizes the level of the radial component of the velocity behind the cascade. For the example in question, kinematic losses are equal to 1.9 % and the complex criterion of quality equal to 0.972 corresponds to the overall losses of 5.5 %. It was suggested to use the velocity coefficient and the two angles of flow as integral cascade characteristics. The use of these characteristics enables the correct computations of the efficiency factor for the stage within the one-dimensional computation. The incisive analysis was performed for different methods used for the averaging of the parameters of the axially asymmetric flow behind the nozzle cascade. It was suggested to neglect the flow rate factor in the case of thermal computations done for the turbine stage.