Experimental and Numerical Evaluation of Losses From Turbine Hub Clearance Flow

Abstract

Long-term efforts have been made to understand loss generation and its reduction in the field of axial turbomachines. The traditional approach to losses for an isolated blade row considers the profile and the secondary losses as a result of viscous flow. The additional kinds of losses in the stage are connected with the shear stress in the mixing process. These losses result from the mixing of the main stream flow with 1) the stator leakage injected through the root axial gap and 2) the return of the tip leakage over the bucket shroud. This article focuses on the first type of mixing losses. The leakage to the main stream flow ratio and the root reaction are the two key parameters investigated in this study. The primary data source for this study is the experiment. An experimental single stage air turbine was modified to set and precisely measure the stator leakage flow. Three configurations of the single-stage test rig with different reaction levels were tested. The second data source for this study is CFD computation. These computations are applied to different geometries and conditions from the experiment; they are derived from real steam turbine stages designed in DSPW. The computations simulate multistage configuration and real steam is considered as the working fluid. CFD computations were performed in the commercial software ANSYS CFX. Each configuration task was computed in three iterative steps. Each step takes the distribution of the flow parameters on the boundary domains from the previous iteration. The final results from this ‘repeating boundary conditions’ approach better correspond with the real expansion in a multistage configuration. The two data sources are not directly comparable. The experiment is used for validation of the trends. The computations provide the possibility of a multi-parametric study. The multi-parametric study is necessary to obtain a more general loss model which can be used during turbine design. The evaluation of the experimental and numerical parts focuses on a comparison of the overall stage performance. Stage efficiency and reaction are presented in relation to the ratio between leakage and main stream flow.

Effect of Manufacturing Inaccuracies on the Wake Past Asymmetric Airfoil by PIV

“…Modifications in the stator wheel affect the reaction and efficiency of the entire stage. Data like those mentioned above are used in the numerical optimization [8] of the developed new stage.…”

Preliminary Experimental Investigation of the Design-Overloaded Stage in Two-Stage Axial Turbine Test Rig

“…For this purpose, it is possible to advantageously use a two-stage arrangement in the test rig, where the design-overloaded stage is preceded by another "preparatory" stage. This stage can also be used to change the inlet conditions for tested stage; for example by changing the clearance in the shaft and shroud seal (see previous research at the single?-stage and 1.5-stage test rings presented in [2] and [3]).…”

Experimental Evaluation of Axial Reaction Turbine Stage Bucket Losses

“…The three variants of the stage with different nozzle blade numbers were tested in turn. The results have been published, e.g., in [6][7][8][9][10][11][12][13][14][15]. This development resulted in an efficiency increase of about 2% in the high-pressure (HP) turbine section and 1.5% in the intermediate-pressure (IP) turbine section compared to the conventional prismatic blading.…”