Improved Hybrid Methods for Determining the Integral Characteristics of Turbomachine Nozzle Cascades

Abstract

To determine the integral gas-dynamic characteristics of nozzle cascades of turbomachines, it is necessary to average the parameters of the three-dimensional flow behind the cascade that is non-uniform along with the pitch and along with the height of the cascade. Two types of averaging methods are used. For the first type of methods, the flow parameters at the entrance to the cascade are not taken into account when averaging the parameters of a non-uniform flow behind the cascade. For the second type of methods (hybrid), the pressure behind the cascade is found from the condition of maintaining the enthalpy drop in the initial non-uniform three-dimensional and averaged flows. In a cylindrical flow, the hybrid method is usually used to determine the velocity coefficient. The main disadvantage of this method is the significantly overestimated mass flow mass rate and component onto the axial direction of the angular momentum. To improve the methods of the second type, it is proposed to replace the ratio of the components of the momentum with two parameters, namely: mass flow rate and the component of the moment of momentum on the axial direction. It allows determining the velocity coefficient and two angles for the averaged flow. It is shown that the second kinetic energy of the flow can be replaced by entropy and, thus, the velocity coefficient can be adjusted provided the complex quality criterion is kept constant.