The effect of flow unsteadiness on the homogeneous nucleation of water droplets in steam turbines

1994 ◽  
Vol 349 (1691) ◽  
pp. 445-472 ◽  
Keyword(s):  
Steady Flow ◽  
Homogeneous Nucleation ◽  
Flow Direction ◽  
Previous History ◽  
Fluid Particle ◽  
Droplet Growth ◽  
Steam Turbines ◽  
Water Droplets ◽  
Blade Row ◽  
Fluid Particles

The paper describes a new theory of the formation and growth of water droplets in multistage steam turbines. The essence of the theory is that large-scale static temperature fluctuations caused by the segmentation of blade wakes by successive blade rows have a dominating influence on nucleation and droplet growth in turbines. ‘True’ turbulent fluctuations (due to shear-layer unsteadiness, etc.) are probably less important and are ignored. A Lagrangian frame of reference is adopted and attention is focused on a large number of individual fluid particles during their passage through the turbine. Homogeneous nucleation and growth of droplets in each fluid particle is assumed to be governed by classical theories. All fluid particles are assumed to experience the same pressure variation, but those particles passing close to the blade surfaces suffer greater entropy production and, therefore, have higher static temperatures than those that pursue nearly isentropic paths through the central portions of the blade passages. Particles which suffer high loss therefore nucleate later in the turbine than those that experience little dissipation. Condensation is thus viewed as an essentially random and unsteady phenomenon because the dissipation experienced by a fluid particle in one blade row is assumed to be uncorrelated with its previous history. On a time-averaged basis, the condensation zone is spread over a much greater distance in the flow direction than a simple steady-flow analysis would indicate and may encompass several blade rows, depending on the number of stages in the machine. Predicted droplet size spectra show broad, highly skewed distributions with large mean diameters and sometimes slight bimodality. These are all characteristics of experimentally measured spectra in real turbines. Conventional, steady-flow calculation methods, which predict a fixed Wilson point in a specific blade row and a nearly monodispersed droplet population, cannot reproduce any of these characteristics.

On the Effects of Unsteadiness on the Condensation Process in Low-Pressure Steam Turbines

2009 ◽  
Author(s):  
Keramat Fakhari
Keyword(s):  
Large Scale ◽  
Flow Direction ◽  
Low Pressure ◽  
Droplet Growth ◽  
Condensation Process ◽  
Steam Turbines ◽  
Two Phase ◽  
Condensation Zone ◽  
Scale Temperature ◽  
Pressure Steam

The condensation process in a turbomachine is in reality an essentially random and unsteady phenomenon. On a time-averaged basis, the condensation zone is spread over a much greater distance in the flow direction than a simple steady-flow calculation would indicate. The droplet growth rate also shows different characteristics which are observed in experiments measured in real low-pressure steam turbines. These differences are mainly introduced by the large-scale temperature fluctuations which are caused by the segmentation of blade wakes by successive blade rows. Furthermore, the additional losses by condensation have to be reconsidered for an unsteady simulation. This paper describes a time-accurate Eulerian/Lagrangian two-phase model which is implemented within the DLR in-house code TRACE [1]. The phases are coupled through appropriately generated source terms for heat, mass and momentum. For the subcooled thermodynamic properties of steam the local formulation of IAPWS-IF97 [2, 3] is used. The implementation has been validated in a previous publication of the author [4] using one and two-dimensional experiments of Laval nozzles and a cascade blade from literature. The focus of this work is on the unsteady Phenomena which are investigated in a stage of an industrial low-pressure steam turbine.

Effects of Wake Chopping on Droplet Sizes in Steam Turbines

2005 ◽  
Vol 219 (12) ◽  
pp. 1357-1367 ◽  
Author(s):  
F Bakhtar ◽  
A V Heaton
Keyword(s):  
Size Distribution ◽  
Homogeneous Nucleation ◽  
Review Article ◽  
Size Distributions ◽  
Steam Turbines ◽  
Water Droplets ◽  
Droplet Sizes

This paper is a review article and considers the influence of wake chopping on the size distribution of water droplets formed by homogeneous nucleation in steam turbines. The studies by several investigators are summarized. All the studies show that the fluctuations caused by the wakes can broaden the size distributions of the nucleated droplets substantially and account for the polydisperse nature of the droplet distributions and coarse water observed in turbines. The effect of the presence of impurities in steam on its nucleation behaviour is also discussed.

Sensitivity Analysis of Condensation Model Constants on Calculated Liquid Film Motion in Radial Turbines

2014 ◽  
Author(s):  
Sebastian Schuster ◽  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen ◽  
Sven König ◽  
Uwe Martens
Keyword(s):  
Liquid Film ◽  
Flow Direction ◽  
Sensitivity Study ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Working Fluid ◽  
Droplet Growth ◽  
Water Droplets ◽  
Radial Turbine ◽  
Radial Turbines

In many technical processes, a mixture of gas and steam is used as the working fluid in radial turbines. When condensation occurs during expansion, a portion of the liquid droplets can hit the rotor blades and form a water film, which can move in a radial direction and even against the flow direction. Then, the liquid film separates in the rotor tip clearance or at the leading edge of the rotor and forms coarse water droplets. The presence of coarse water droplets in the gap between stator and rotor can cause damage to the turbine rotor. To design a radial turbine which works under condensation conditions, it is essential to know where and when condensation and film formation occur. With this information, it is possible to take action to remove the liquid or to adjust the required maintenance intervals. To examine the details of condensation and film motion, an existing flow solver is extended to capture condensation effects. Models describing nucleation and droplet growth are added to a particle-tracking algorithm. Droplets impinging on the rotor blades form a liquid film. The motion of this liquid film is calculated with a newly developed thin film solver. The calculation tool is validated against third party test rig experiments as well as numerical experiments. For many parameters, the agreement between the calculation tool and the experiments is quite satisfactory. Some results, however, show larger deviations. One of these parameters is the droplet diameter. The numerical results are generally reliable, but an experimental validation is necessary for detailed understanding of the mechanism. Before expensive experiments are conducted, it is recommended to perform a sensitivity study to emphasize important parameters. This sensitivity study is performed concerning a radial turbine for an operating point at which the liquid film travels into the tip clearance. In this paper it will be shown how the thickness and movement of the liquid film change with variation in influencing parameters. Finally, model constants that have the strongest influence on the calculated film motion are highlighted.

Development of a Last Stage Blade Row Coupled by Damping Elements: Numerical Assessment of its Vibrational Behavior and its Experimental Validation During Spin Pit Measurements

2017 ◽  
Author(s):  
Christian Siewert ◽  
Frank Sieverding ◽  
William J. McDonald ◽  
Manish Kumar ◽  
James R. McCracken
Keyword(s):  
Structural Integrity ◽  
Mechanical Design ◽  
Vibration Response ◽  
Dynamic Loads ◽  
Steam Turbines ◽  
Response Level ◽  
Vibrational Behavior ◽  
Blade Row ◽  
Calculation Results ◽  
Last Stage

Last stage blade rows of modern low pressure steam turbines are subjected to high static and dynamic loads. The static loads are primarily caused by the centrifugal forces due to the steam turbine’s rotational speed. Dynamic loads can be caused by instationary steam forces, for example. A primary goal in the design of modern and robust blade rows is to prevent High Cycle Fatigue caused by dynamic loads due to synchronous or non-synchronous excitation mechanisms. Therefore, it is important for the mechanical design process to predict the blade row’s vibration response. The vibration response level of a blade row can be limited by means of a damping element coupling concept. Damping elements are loosely assembled into pockets attached to the airfoils. The improvement in the blade row’s structural integrity is the key aspect in the use of a damping element blade coupling concept. In this paper, the vibrational behavior of a last stage blade row with damping elements is analyzed numerically. The calculation results are compared to results obtained from spin pit measurements for this last stage blade row coupled by damping elements.

scholarly journals Multisymplectic formulation of fluid dynamics using the inverse map

2007 ◽  
Vol 463 (2086) ◽  
pp. 2671-2687 ◽  
Author(s):  
C.J Cotter ◽  
D.D Holm ◽  
P.E Hydon
Keyword(s):  
Fluid Dynamics ◽  
Conservation Laws ◽  
Fluid Particle ◽  
Hamilton’S Principle ◽  
Hamilton's Principle ◽  
Numerical Integrators ◽  
Fluid Particles ◽  
Infinite Set ◽  
Circulation Theorem

We construct multisymplectic formulations of fluid dynamics using the inverse of the Lagrangian path map. This inverse map, the ‘back-to-labels’ map, gives the initial Lagrangian label of the fluid particle that currently occupies each Eulerian position. Explicitly enforcing the condition that the fluid particles carry their labels with the flow in Hamilton's principle leads to our multisymplectic formulation. We use the multisymplectic one-form to obtain conservation laws for energy, momentum and an infinite set of conservation laws arising from the particle relabelling symmetry and leading to Kelvin's circulation theorem. We discuss how multisymplectic numerical integrators naturally arise in this approach.

A novel method for measuring the coarse water droplets in wet steam flow in steam turbines

2001 ◽  
Vol 10 (2) ◽  
pp. 123-126 ◽  
Author(s):  
Xiaoshu Cai ◽  
Lili Wang ◽  
Yongzhi Pan ◽  
Xin Ouyan ◽  
Jianqi Shen
Keyword(s):  
Steam Flow ◽  
Steam Turbines ◽  
Wet Steam ◽  
Water Droplets ◽  
Novel Method ◽  
Wet Steam Flow

scholarly journals Bidirectional cyclical flows increase energetic costs of station holding for a labriform swimming fish, Cymatogaster aggregata

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Sarah M Luongo ◽  
Andreas Ruth ◽  
Connor R Gervais ◽  
Keith E Korsmeyer ◽  
Jacob L Johansen ◽  
...  
Keyword(s):  
Steady Flow ◽  
Flow Direction ◽  
Energy Budgets ◽  
Constant Flow ◽  
Energetic Costs ◽  
Mean Velocity ◽  
Unidirectional Flow ◽  
In The Wild ◽  
Additional Costs ◽  
Temperate Fish

Abstract Wave-induced surge conditions are found in shallow marine ecosystems worldwide; yet, few studies have quantified how cyclical surges may affect free swimming animals. Here, we used a recently adapted respirometry technique to compare the energetic costs of a temperate fish species (Cymatogaster aggregata) swimming against a steady flow versus cyclical unidirectional and bidirectional surges in which unsteady swimming (such as accelerating, decelerating and turning) occurs. Using oxygen uptake (ṀO2) as an estimate of energetic costs, our results reveal that fish swimming in an unsteady (i.e. cyclical) unidirectional flow showed no clear increase in costs when compared to a steady flow of the same average speed, suggesting that costs and savings from cyclical acceleration and coasting are near equal. Conversely, swimming in a bidirectional cyclical flow incurred significantly higher energetic costs relative to a steady, constant flow, likely due to the added cost of turning around to face the changing flow direction. On average, we observed a 50% increase in ṀO2 of fish station holding within the bidirectional flow (227.8 mg O2 kg−1 h−1) compared to a steady, constant flow (136.1 mg O2 kg−1 h−1) of the same mean velocity. Given wave-driven surge zones are prime fish habitats in the wild, we suggest the additional costs fish incur by station holding in a bidirectional cyclical flow must be offset by favourable conditions for foraging and reproduction. With current and future increases in abiotic stressors associated with climate change, we highlight the importance of incorporating additional costs associated with swimming in cyclical water flow in the construction of energy budgets for species living in dynamic, coastal habitats.

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.

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.

Aerodynamic Analysis of Steam Turbine Feed-Heating Steam Extractions

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Budimir Rosic ◽  
Cosimo Maria Mazzoni ◽  
Zoe Bignell
Keyword(s):  
Steam Turbine ◽  
Rotor Blade ◽  
Feed Water ◽  
Steam Turbines ◽  
Flow Angle ◽  
Steam Extraction ◽  
Heating Steam ◽  
Blade Row ◽  
Circumferential Distribution ◽  
Stator Blade

Feed-heating in steam turbines, the use of steam extracted from the turbine to heat the feed-water, is known to raise the plant efficiency and so is included in most steam turbine power plant designs. The steam is extracted through an extraction slot that runs around the casing downstream of a rotor blade row. The slot is connected to a plenum, which runs around the outside of the turbine annulus. Steam flows to the feed-heaters through a pipe connected usually to the bottom of the plenum. The steam extraction is driven by a circumferentially nonuniform pressure gradient in the plenum. This causes the mass flow rate of steam extracted to vary circumferentially, which affects the main passage flow downstream of the extraction point. The flow in the extraction plenum and the influence of the steam extraction on the mainstream aerodynamics is analyzed numerically in this paper. A complete annulus with the extraction slot and plenum together with the downstream stator and rotor blade rows is modeled in this study. The results reveal a highly nonuniform steam extraction around the annulus with the highest extraction rates from the bottom nearest the extraction pipe and the lowest at the top of the annulus. This difference in extraction rates modifies the flow angle and loss circumferential distribution downstream of the stator blade row. This study finds out that the distribution of steam extraction around the annulus and its influence on the main passage flow could be greatly improved by changing the shape and increasing the volume of the extraction slot and plenum.

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