Research on the Optimum Clocking Position in Axial-Flow Turbomachinery

Abstract

In this paper, the deflected circumferential distance of wake related to some aerodynamic and geometrical parameters was studied to determine the optimum clocking position in axial-flow turbomachinery. A predicting method on how to calculate the deflected circumferential distance of the wake was also put forward. To verify this method, a 2-D time-accurate, viscous flow solver had been used to analyze unsteady flow associated with different clocking positions. A 1.5 stage turbine was employed to observe the effects of clocking positions on the machine performance and tend to find out the optimum clocking position. It shows that the error of the optimum clocking position between the simulation result from CFD and the result from the predicting method is only 0.361%. In fact, there are three assumptions implied in the predicting method, and their rationality has been understood and explained one by one through analyzing machine efficiency, instantaneous entropy contours and viscous stress on the surface of the stator suction side. In order to get further confirmation, the method was also used in the case of a 1.5 stage compressor and the error between the predicted position and the maximum efficiency position obtained from flow field simulation is as much as 1.2%. Furthermore, based on numerical simulation of a 2.5 stage turbine, it is found that clocking positions of the first stator row have little effect on the incoming wake and free stream turbulence of the third stator. This conclusion should be helpful and beneficial to the designs of the multistage turbomachinery, in which clocking effect has been fully utilized.