Modelling of the droplet size distribution in a low-pressure steam turbine

Petr, Václav; Kolovratník, Michal

doi:10.1243/0957650001538245

Cited by 18 publications

(23 citation statements)

References 2 publications

(3 reference statements)

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“…Steady codes are generally not able to predict the poly-dispersed droplet spectra and the average radius typically measured in the rear stages of steam turbines, and therefore, they cannot provide a good assessment of the losses in these stages. References [40][41][42][43] showed that the effect of unsteadiness due to the interaction of blade wakes with downstream blade rows is to broaden significantly the droplet-size distribution giving a shape and a mean diameter closer to the experimental measurements in real turbines. The authors use a statistical approach to account for the temperature fluctuations produced by the flow unsteadiness and showed very good agreements with measurements.…”

Section: Numerical Analyses Of Relaxation Processes In Lp Flowsmentioning

confidence: 99%

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

Kreitmeier

Greim

Congiu

et al. 2005

Proceedings of the Institution of Mechanical Engineers, Part C:

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Flow fields in low-pressure (LP) steam turbines, starting expansion well above the saturation line, show four pronounced non-equilibrium processes (called relaxation processes). The first one above the saturation line is centred around heterogeneous nucleation/ condensation, the second one around subcooling and the subsequent homogeneous nucleation/ condensation ('Wilson point'), and the third and the fourth ones are characterized by thermodynamic and mechanical effects in the established droplet-loaded part of the flow field.All these relaxation processes are interacting downwards in the progressive expansion in the turbine. In a multistage LP turbine, the most important ones are the second -because it is mainly responsible for the number of droplets (sizes) -and the third -because it creates most of the dissipation. In addition, the first and the fourth ones can damage the flow guiding geometry by corrosion and erosion, respectively.More than 40 years ago, Gyarmathy formulated the first strictly physical basis for these processes. Subsequently, many researchers have contributed to increase the physical understanding using both experimental and numerical methods. The intuition that the one-dimensional treatment of the flow field in multistage turbines cannot explain the measured droplet sizes behind the blading has been particularly relevant. It became clear that especially the temperature fluctuation within the blading has to be included in homogeneous nucleation/condensation considerations. Also of some importance has been the improved understanding of the first relaxation process, which was initially underestimated.This article highlights the current situation seen by a turbomachinery company that has been contributing to and supporting this discipline for many decades. A wide literature survey and a critical appraisal of published Baumann factors are included. High quality experimental tools and procedures are introduced on the basis of two generations of split-shaft model LP turbines and Damköhler numbers. Further, an overview of the in-house numerical tools and processes developed for wet steam applications is given.More recent experimental results on the influence of impurities and conditioning agents in the relaxation processes and newer numerical results on the influence of phase transition in the flow field around a blade row are presented.

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Section: Numerical Analyses Of Relaxation Processes In Lp Flowsmentioning

confidence: 99%

Experimental and Numerical Analyses of Relaxation Processes in LP Steam Turbines

Kreitmeier

Greim

Congiu

et al. 2005

Proceedings of the Institution of Mechanical Engineers, Part C:

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“…The droplet size spectra were found to be broadened by the unsteadiness, and the results predicted a slight bi-modality in the distributions, consistent with optical measurements. 5 Applying a similar method to a 200 MW low-pressure (LP) turbine, Petr and Kolovratnik 6 made comparisons with optical droplet size data, and by tuning the pitch-wise loss profiles, the computed spectra showed respectable agreement with the light extinction measurements.…”

Section: Introductionmentioning

confidence: 99%

Non-equilibrium wet-steam calculations of unsteady low-pressure turbine flows

Chandler

White

Young

2013

Proceedings of the Institution of Mechanical Engineers, Part A:

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Accurate prediction of the droplet size distribution in steam turbines is crucial for the correct analysis of wetness losses and other two-phase effects. Measurements taken in the later stages of low-pressure turbines have shown broader size distributions with larger average sizes than those predicted by numerical methods. One hypothesis is that the broad distributions stem from the unsteady interaction between blade rows. Wake segmentation in successive rows means that fluid particles passing through the machine have different dissipation histories which in turn cause a wider range of nucleation and droplet growth rates. In the present paper, a method for modelling 3D unsteady multistage condensing flows is described and applied to a five-stage model turbine. One-tenth of the annulus of the turbine is modelled, and an integer blade number ratio between rows is achieved by scaling the blade profiles, keeping the pitch-chord ratio and stagger angle constant. The results are compared with pressure measurements and droplet Sauter-mean radii obtained from experimental optical data. Generally, the level of agreement is reasonable, but with some discrepancies in the detailed streamwise and spanwise trends. Calculations of this type are at an early stage of development and improvements in mesh quality and boundary and interface treatments will be required before firm conclusions can be drawn.

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“…The surface tension σ = σ(T ) is corrected by the parameter β according to Petr and Kolovratník [2] to match correctly the start of nucleation. The Figures 1 and 2 show the effect of this correction on pressure distribution and wetness respectively for the flow in the Barschdorf nozzle (more information about Barschdorf nozzle problem see in the section ).…”

Section: Model Of Condensing Steam Flowmentioning

confidence: 99%

“…Presented flow model relies on classical nucleation theory of Becker and Doering [1], which is complemented by certain empirical correction. We use the correction for surface tension proposed by Petr and Kolovratnik [2]. Droplets dispersed in elemental volume (from the point of view of used domain discretization -detail are explained in the section about method of solution) have different sizes.…”

Section: Introductionmentioning

confidence: 99%