Modification of a Steam Valve Diffuser for Enhanced Full Load and Part Load Operation Using Numerical Methods

Clemens Bernhard Domnick,Christian Musch,Friedrich-Karl Bera,Dieter Brillert

doi:10.3311/ppme.9041

Clemens Bernhard Domnick, Christian Musch + Show 2 more

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https://doi.org/10.3311/ppme.9041

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Abstract

The flow in a steam turbine inlet valve is investigated and improved by numerical methods. From the fluid dynamic point of view two requirements exist: Low pressure losses are desired at the fully opened valve position and dynamic fluid forces acting on the valve plug should be minimized to reduce valve vibration. Usually these undesired dynamic fluid forces occur when the flow is throttled at part load. It is found that these fluid forces are generated by separated jets in the diffuser. The attachment and the separation of the jet are related to the Coanda effect. By understanding the flow physics a way is found to modify the diffuser design in such a way that the flow separations are reduced. Bell-shaped diffusers are able to reduce the flow losses at full load operation. A diffuser contour that fulfils both requirements is developed.

Highlights

Steam turbine inlet valves are used to control the power output of steam turbines
From the fluid dynamic point of view two requirements exist: Low pressure losses are desired at the fully opened valve position and dynamic fluid forces acting on the valve plug should be minimized to reduce valve vibration
These undesired dynamic fluid forces occur when the flow is throttled at part load

Summary

Introduction

Steam turbine inlet valves are used to control the power output of steam turbines. The design of the valve has to meet several requirements. A comparison of different studies shows that an annular wall jet attached to the valve diffuser is the most desired flow topology in terms of pressure fluctuations and vibrations. The knowledge obtained from these studies, shows, that the flow instability and the valve vibrations are reduced when the attached annular wall jet exists in the valve diffuser. In this case the jet is stabilized by the wall and the kinetic energy bearing the potential for pressure fluctuations is gradually dissipated at the wall. To analyze the jet separations and the pressure loss of the flow in the valve diffuser, the valve is investigated at different lift positions The point of intersection between the operating curve of the valve and the curve of attachment is shifted to lower valve lifts and lower pressure ratios

Design constraints for diffuser shape modification

Impact of seat curvature on wall jet separation at part load

Impact of wall curvature on the pressure loss at full valve lift

Numerical investigation on the impact of the modified wall curvature

Findings

Conclusions