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Research Papers: Flows in Complex Systems

Clarifying the Physics of Flow Separations in Steam Turbine Inlet Valves at Part Load Operation and Improved Design Considerations

[+] Author and Article Information
Clemens Bernhard Domnick

Chair of Turbomachinery,
University of Duisburg-Essen,
Lotharstrasse 1,
Duisburg 47057, Germany
e-mail: bernhard.domnick@uni-due.de

Dieter Brillert

Chair of Turbomachinery,
University of Duisburg-Essen,
Lotharstrasse 1,
Duisburg 47057, Germany
e-mail: dieter.brillert@uni-due.de

Christian Musch

Siemens AG,
Rheinstrasse 100,
Mülheim an der Ruhr 45478, Germany
e-mail: christian.musch@siemens.com

Friedrich-Karl Benra

Chair of Turbomachinery,
University of Duisburg-Essen,
Lotharstrasse 1,
Duisburg 47057, Germany
e-mail: friedrich.benra@uni-due.de

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 14, 2016; final manuscript received February 26, 2017; published online June 5, 2017. Assoc. Editor: Matevz Dular.

J. Fluids Eng 139(8), 081105 (Jun 05, 2017) (10 pages) Paper No: FE-16-1748; doi: 10.1115/1.4036263 History: Received November 14, 2016; Revised February 26, 2017

In steam turbine inlet valves used to adjust the power output of large steam turbines, the through-flow is reduced by lowering the valve plug and hence reducing the cross-sectional area between the plug and the seat. At throttled operation, a supersonic jet is formed between the plug and the seat. This jet bearing tremendous kinetic energy flows into the valve diffuser where it is dissipated. Depending on the dissipation process, a certain portion of the kinetic energy is converted to sound and subsequently to structural vibration, which can be harmful to the valve plug. The flow topology in the valve diffuser has a strong influence on the conversion of kinetic energy to sound and hence vibrations. Several studies show that an annular flow attached to the wall of the valve diffuser causes significantly less noise and vibrations than a detached flow in the core of the diffuser. The relation between the flow topology and the vibrations is already known, but the physics causing the transition from the undesired core flow to the desired annular flow and the dependency on the design are not fully understood. The paper presented here reveals the relation between the flow topology in the steam valve and the separation of underexpanded Coandă wall jets. The physics of the jet separations are clarified and a method to predict the flow separations with a low numerical effort is shown. Based on this, safe operational ranges free of separations can be predicted and improved design considerations can be made.

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Figures

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Fig. 1

Three-dimensional model of the interior surfaces of the valve

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Fig. 2

Distribution of the local pressure ratio (upper half) and the Mach number (lower half) of the flow field below the valve plug at 1.8% lift and πVa = 0.08

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Fig. 3

Streamwise pressure gradient at the wall of the valve diffuser

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Fig. 4

Pressure distribution at the wall of the valve seat for different grid spacings

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Fig. 5

Grid resolution in the vicinity of the valve seat

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Fig. 6

Velocity profile of the boundary layer at the valve seat

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Fig. 8

A 90 deg-model of the control valve

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Fig. 9

Distribution of the Mach number in the different models

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Fig. 10

Pressure and Mach number distribution of the flow field below the valve plug at 14% lift and πVa = 0.347. Azimuthal position: 45 deg offset to the flow guide.

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Fig. 11

Pressure and Mach number distribution of the flow field below the valve plug at 14% lift and πVa = 0.267

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Fig. 12

Change of the flow filed downstream the valve gap during the simulation run

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Fig. 13

Dependency of the pressure ratio of attachment and detachment on the valve lift

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Fig. 14

Definition of geometric parameters for basic Coandă wall jet configurations and for the steam valve

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Fig. 15

Pressure ratio of attachment obtained in different experimental studies

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Fig. 16

Pressure ratio of detachment obtained in different experimental studies

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Fig. 17

Axial pressure distribution in the valve seat and the diffuser. Extracted at the center of the diffuser.

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Fig. 18

Radial pressure distribution beneath the valve seat at z/DS =  0

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Fig. 19

Pressure recovery depending on the valve lift

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Fig. 20

Radius to height ratio in dependence of the valve lift

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Fig. 21

Comparison of the calculated pressure ratio of attachment to the experimentally obtained pressure ratio

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Fig. 22

Comparison of the calculated pressure ratio of detachment to the experimentally obtained pressure ratio

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Fig. 23

Geometry of the baseline and the improved diffuser design

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Fig. 24

Reduction of the pressure ratio of attachment by increasing the valve seat diameter

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