Performance estimation of variable geometry turbines

Abstract

The concept of using variable geometry to alter the characteristics of turbomachinery has been in existence for many years. Advanced gas turbine engines, especially for aeronautical and naval applications, will extensively use variable geometry turbines and, therefore, a tool must exist that is capable of evaluating the performance of such turbines right from the conceptual stage. With this in mind, a new method based on the improved flow model originally proposed by Wang is presented. The improvements resolve two aspects of the flow model that restrict its widely used possibility: that is, the flow model can be applied only to turbines that work under a subcritical condition and it cannot be applied to variable geometry turbines. After these improvements, the new method can be applied to both single-stage turbines and multi-stage turbines with variable geometry used in any stage. To prove this, two examples are presented in this article. One example is a single-stage variable geometry turbine; the predicted results are examined against the experimental results and a satisfactory conformity is obtained. The good agreement shows that the new method is capable of predicting the performance of variable geometry turbine accurately. The other example is a four-stage turbine with variable geometry used in the first stage. All the results show that the ‘bottom-up’ method is an effective way to predict the performance of variable geometry turbine and it can be used extensively.