Nucleation and Droplet Growth Rate of Homogeneously Condensing Flows within an industrial Steam turbine

2007 ◽  
Author(s):  
Keramat Fakhari ◽  
Theodore E. Simos ◽  
George Psihoyios ◽  
Ch. Tsitouras
Keyword(s):  
Growth Rate ◽  
Steam Turbine ◽  
Droplet Growth ◽  
Condensing Flows

Numerical Simulations of Unsteady Wet Steam Flows With Non-Equilibrium Condensation in the Nozzle and the Steam Turbine

2006 ◽  
Author(s):  
Shigeki Senoo ◽  
Alexander J. White
Keyword(s):  
Heat Release ◽  
Steam Turbine ◽  
Laval Nozzle ◽  
Expansion Rate ◽  
Droplet Growth ◽  
Layer Model ◽  
Pressure Distributions ◽  
Condensing Flows ◽  
Two Layer Model ◽  
Non Equilibrium

Numerical techniques for non-equilibrium condensing flows are presented. Conservation equations for homogeneous gas-liquid two-phase compressible flows are solved by using a finite volume method based on an approximate Riemann solver. The phase change consists of the homogeneous nucleation and growth of existing droplets. Nucleation is computed with the classical Volmer-Frenkel model, corrected for the influence of the droplet temperature being higher than the steam temperature due to latent heat release. For droplet growth, two types of heat transfer model between droplets and the surrounding steam are used: a free molecular flow model and a semi-empirical two-layer model which is deemed to be valid over a wide range of Knudsen number. The computed pressure distribution and Sauter mean droplet diameters in a convergent-divergent (Laval) nozzle are compared with experimental data. Both droplet growth models capture qualitatively the pressure increases due to sudden heat release by the non-equilibrium condensation. However the agreement between computed and experimental pressure distributions is better for the two-layer model. The droplet diameter calculated by this model also agrees well with the experimental value, whereas that predicted by the free molecular model is too small. Condensing flows in a steam turbine cascade are calculated at different Mach numbers and inlet superheat conditions and are compared with experiments. Static pressure traverses downstream from the blade and pressure distributions on the blade surface agree well with experimental results in all cases. Once again, droplet diameters computed with the two-layer model give best agreement with the experiments. Droplet sizes are found to vary across the blade pitch due to the significant variation in expansion rate. Flow patterns including oblique shock waves and condensation-induced pressure increases are also presented and are similar to those shown in the experimental Schlieren photographs. Finally, calculations are presented for periodically unsteady condensing flows in a low expansion rate, convergent-divergent (Laval) nozzle. Depending on the inlet stagnation subcooling, two types of self-excited oscillations appear: a symmetric mode at lower inlet subcooling and an asymmetric mode at higher subcooling. Plots of oscillation frequency versus inlet sub-cooling exhibit a hysteresis loop, in accord with observations made by other researchers for moist air flow.

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines: Part 2 — Turbine Wetness Measurement and Comparison to CFD-Predictions

2014 ◽  
Author(s):  
M. Schatz ◽  
T. Eberle ◽  
M. Grübel ◽  
J. Starzmann ◽  
D. M. Vogt ◽  
...  
Keyword(s):  
Experimental Data ◽  
Steam Turbine ◽  
Physical Models ◽  
Droplet Growth ◽  
Steam Turbines ◽  
Wet Steam ◽  
Validity And Reliability ◽  
Two Phase ◽  
Validation Data ◽  
Subsequent Formation

The correct computation of steam subcooling, subsequent formation of nuclei and finally droplet growth is the basic prerequisite for a quantitative assessment of the wetness losses incurred in steam turbines due to thermal and inertial relaxation. The same basically applies for the prediction of droplet deposition and the resulting threat of erosion. Despite the fact that there are many CFD-packages that can deal with real-gas effects in steam flows, the accurate and reliable prediction of subcooling, condensation and wet steam flow in steam turbines using CFD is still a demanding task. One reason for this is the lack of validation data for turbines that can be used to assess the physical models applied. Experimental data from nozzle and cascade tests can be found in the open literature; however, this data is only partly useful for validation purposes for a number of reasons. With regard to steam turbine test data, there are some publications, yet always without any information about the turbine stage geometries. This publication is part of a two-part paper; whereas part 1 focuses on the numerical validation of wet steam models by means of condensing nozzle and cascade flows, the focus in this part lies on the comparison of CFD results of the turbine flow to experimental data at various load conditions. In order to assess the validity and reliability of the experimental data, the method of measurement is presented in detail and discussed. The comparison of experimental and numerical results is used for a discussion about the challenges in both modeling and measuring steam turbine flows, presenting the current experience and knowledge at ITSM.

Fast and Accurate Analysis of Steam Condensing Flows Using Ideal Gas Equation

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Changhyun Kim ◽  
JaeHyeon Park ◽  
Jehyun Baek
Keyword(s):  
Phase Transition ◽  
Ideal Gas ◽  
Droplet Growth ◽  
Wet Steam ◽  
Accurate Analysis ◽  
Machine Performance ◽  
Condensing Flows ◽  
Droplet Sizes ◽  
Condensation Model ◽  
Non Equilibrium

Abstract When the steam is used in fluid machinery, the phase-transition can occur and it affects not only the flow fields but also the machine performance. Therefore, to achieve accurate prediction on steam condensing flow using computational fluid dynamics, the phase-transition phenomena should be considered and the proper model which can reflect the non-equilibrium characterisic is required. In the previous study of us, a non-equilibrium condensation model was implemented in T-flow, and several cases on nozzles and cascades were under the consideration. The model showed quite good predictions on the pressure variations including condensation shock. However, the pressure discrepancies in downstream regions were found in all nozzle cases, and the use of ideal gas law as equation of state seemed to be responsible for them. Therefore, IAPWS-95 or IF97 are usually adopted for wet-steam codes, but it entails highly increased computational costs. In this study, the wet-steam model is modified to ensure the accuracy of pressure in nozzle’s downstream region while maintaining the usage of ideal gas equation, which has a benefit to solve the problem quickly. The numerical results of the nozzles are compared with those of the previous wet-steam model, and the results of equilibrium condensation model are also appended. As a result, the accurate predictions are feasible by using the modified non-equilibrium condensation model. In addition, the corrections on liquid surface tension and droplet growth rate are carried out for underestimated droplet sizes and enthalpy, entropy changes throughout the nozzles are investigated.

Influence of Turbulence Modelling to Condensing Steam Flow in the 3D Low-Pressure Steam Turbine Stage

2016 ◽  
Author(s):  
Yogini Patel ◽  
Giteshkumar Patel ◽  
Teemu Turunen-Saaresti
Keyword(s):  
Steam Turbine ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Rapid Change ◽  
Low Pressure ◽  
Turbulence Modelling ◽  
Steam Flow ◽  
Droplet Growth ◽  
Steam Turbines ◽  
Turbine Stage

With the tremendous role played by steam turbines in power generation cycle, it is essential to understand the flow field of condensing steam flow in a steam turbine to design an energy efficient turbine because condensation at low pressure (LP) turbine introduces extra losses, and erosion in turbine blades. The turbulence has a leading role in condensing phenomena which involve a rapid change of mass, momentum and heat transfer. The paper presents the influence of turbulence modelling on non-equilibrium condensing steam flows in a LP steam turbine stage adopting CFD code. The simulations were conducted using the Eulerian-Eulerian approach, based on Reynolds-averaged Navier-Stokes equations coupled with a two equation turbulence model, which is included with nucleation and droplet growth model for the liquid phase. The SST k-ω model was modified, and the modifications were implemented in the CFD code. First, the performance of the modified model is validated with nozzles and turbine cascade cases. The effect of turbulence modelling on the wet-steam properties and the loss mechanism for the 3D stator-rotor stage is discussed. The presented results show that an accurate computational prediction of condensing steam flow requires the turbulence to be modelled accurately.

Modelling and Validation of Wet Steam Flow in a Low Pressure Steam Turbine

2011 ◽  
Author(s):  
Jo¨rg Starzmann ◽  
M. Schatz ◽  
M. V. Casey ◽  
J. F. Mayer ◽  
Frank Sieverding
Keyword(s):  
Steam Turbine ◽  
Droplet Size ◽  
Low Pressure ◽  
Numerical Results ◽  
Steam Flow ◽  
Droplet Growth ◽  
Wet Steam ◽  
Test Rig ◽  
Pressure Steam ◽  
Wet Steam Flow

Results of numerical investigations of the wet steam flow in a three stage low pressure steam turbine test rig are presented. The test rig is a scale model of a modern steam turbine design and provides flow measurements over a range of operating conditions which are used for detailed comparisons with the numerical results. For the numerical analysis a modern CFD code with user defined models for specific wet steam modelling is used. The effect of different theoretical models for nucleation and droplet growth are examined. It is shown that heterogeneous condensation is highly dependent on steam quality and, in this model turbine with high quality steam, a homogeneous theory appears to be the best choice. The homogeneous theory gives good agreement between the test rig traverse measurements and the numerical results. The differences in the droplet size distribution of the three stage turbine are shown for different loads and modelling assumptions. The different droplet growth models can influence the droplet size by a factor of two. An estimate of the influence of unsteady effects is made by means of an unsteady two-dimensional simulation. The unsteady modelling leads to a shift of nucleation into the next blade row. For the investigated three stage turbine the influence due to wake chopping on the condensation process is weak but to confirm this conclusion further investigations are needed in complete three dimensions and on turbines with more stages.

Eulerian-Lagrangian Numerical Simulation of Wet Steam Flow Through Multi-Stage Steam Turbine

2013 ◽  
Author(s):  
Yasuhiro Sasao ◽  
Satoshi Miyake ◽  
Kenji Okazaki ◽  
Satoru Yamamoto ◽  
Hiroharu Ooyama
Keyword(s):  
Steam Turbine ◽  
Turbine Blades ◽  
Steam Flow ◽  
Droplet Growth ◽  
Computational Domain ◽  
Steam Turbines ◽  
Wet Steam ◽  
Multi Stage ◽  
Flow Through ◽  
Wet Steam Flow

In this paper, we present an inclusive tracking algorithm for water droplets in a wet steam flow through a multi-stage steam turbine. This algorism is based on the Eulerian-Lagrangian coupled solver. The solver continuously computes water droplet growth, kinematic non-equilibrium between vapor and droplets, capture and kinetics of droplets on turbine blades, departure of large droplets from the trailing edge of blades, acceleration and atomization of large droplets, and recollisions between blades and droplets. Our Eulerian-Lagrangian coupled solver is used to predict wetness in unsteady three-dimensional (3D) wet steam flows through three-stage stator rotor cascade channels in a low pressure (LP) steam turbine model which is developed by Mitsubishi Heavy Industries (MHI). Droplet groups tracked by the discrete droplet model (DDM) are placed in the computational domain according to the predicted wetness. Interference from the gas phase on the droplets is considered, to track their kinetic and behavior, until they reach the outlet of the computational domain. The aim of this research is to investigate those multi-physics phenomena that trigger all forms of loss in steam turbines. In addition, this method will also be applied to multi-physics problems such as erosion in future work. This paper is presented as a first step in the research. Overviews of model of current coupling solver and several test calculations are presented.

Quantification of Stator Blade Shape Influence on Non-Equilibrium Condensation in Low-Pressure Steam Turbine

2017 ◽  
Author(s):  
Giteshkumar Patel ◽  
Yogini Patel ◽  
Teemu Turunen-Saaresti ◽  
Aki Grönman
Keyword(s):  
Steam Turbine ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Droplet Growth ◽  
Condensation Process ◽  
Trailing Edge ◽  
Ansys Fluent ◽  
Pressure Surface ◽  
Blade Shape

The expansion of steam flow and the condensation phenomena in an LP turbine depend on both the flow passage shape and the operating conditions. This paper presents the quantification of the influence of local geometrical details of the steam turbine blade including blade surface tapering, dimple inclusion and trailing edge shapes on flow expansion and condensation phenomena. For this purpose, the wet-steam model of ANSYS FLUENT, based on the Eulerian-Eulerian approach, was used. The mixture of vapor and liquid phases was solved by compressible Reynolds-averaged Navier-Stokes equations. The low inlet superheat case of White et al. [1] which is conducted with planar stator cascade was used as reference for this study. Various modifications including blade trailing edge shapes, blade shape modification via blade pressure and suction surfaces’ tapering, and addition of dimple feature to the blade pressure surface were applied to the blade profile. The presented results revealed that the applied blade shape modifications affected nucleation and droplet growth processes, shock wave structures and entropy generation rates. The influence of blade shape on loss generation was presented by calculating the Markov energy loss coefficients. The presented analysis exhibits that the blade shape alteration influences the overall loss generation that occur due to the irreversible heat and mass transfer during the condensation process.

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