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

2000 ◽  
Vol 214 (2) ◽  
pp. 145-152 ◽  
Author(s):  
V Petr ◽  
M Kolovratnik
Keyword(s):  
Steam Turbine ◽  
Size Distribution ◽  
Droplet Size ◽  
Droplet Size Distribution ◽  
Theoretical Models ◽  
Low Pressure ◽  
Steam Turbines ◽  
Size Measurement ◽  
Viscous Effects ◽  
Pressure Steam

Realization of numerous tests on the droplet size measurement with extinction probe, in a 200 MW low-pressure steam turbine, provides necessary experimental data for testing the theoretical models of the droplet nucleation process in steam turbines. The earlier computational model accounting for the unsteady and viscous effects given by Bakhtar and Heaton and by Guha and Young, where the steam particles follow randomly chosen different streamlines within the blade rows with prescribed polytropic efficiency distribution in the pitchwise direction, thus undergoing various nucleation conditions, has been extended in this paper to consider to some extent two-dimensional effects. Because several uncertainties still exist in the inversion methods, predicting the size distribution of droplets, this contribution is aimed at direct comparison of the computed and measured transmittance data I/I0.

Sequential vs Multidisciplinary Coupled Optimization and Efficient Surrogate Modelling of a Last Stage and the Successive Axial Radial Diffuser in a Low Pressure Steam Turbine

2014 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Arne Graßmann
Keyword(s):  
Steam Turbine ◽  
Design Process ◽  
Energy Demand ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Low Pressure ◽  
Steam Turbines ◽  
Low Pressure Turbine ◽  
Pressure Steam ◽  
Last Stage

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage and the subsequent diffuser of a low pressure turbine (LP). The aim of such optimization is to minimize the losses due to separations or inefficient blade or diffuser design. In the usual design process, as is state of the art in the industry, the last stage of the LP and the diffuser is designed and optimized sequentially. The potential physical coupling effects are not considered. Therefore the aim of this paper is to perform both a sequential and coupled optimization of a low pressure steam turbine followed by an axial radial diffuser and subsequently to compare results. In addition to the flow simulation, mechanical and modal analysis is also carried out in order to satisfy the constraints regarding the natural frequencies and stresses. This permits the use of a meta-model, which allows very time efficient three dimensional (3D) calculations to account for all flow field effects.

Advanced Water Droplet Erosion Protection for Modern Low Pressure Steam Turbine Steel Blades

2015 ◽  
Author(s):  
Joerg Schuerhoff ◽  
Andrei Ghicov ◽  
Karsten Sattler
Keyword(s):  
Steam Turbine ◽  
Water Droplet ◽  
Precipitation Hardening ◽  
Turbine Blades ◽  
Low Pressure ◽  
Steam Turbines ◽  
Treatment Facility ◽  
Material Loss ◽  
Pressure Steam ◽  
Steam Turbine Blades

Blades for low pressure steam turbines operate in flows of saturated steam containing water droplets. The water droplets can impact rotating last stage blades mainly on the leading edge suction sides with relative velocities up to several hundred meters per second. Especially on large blades the high impact energy of the droplets can lead to a material loss particularly at the inlet edges close to the blade tips. This effect is well known as “water droplet erosion”. The steam turbine manufacturer use several techniques, like welding or brazing of inlays made of erosion resistant materials to reduce the material loss. Selective, local hardening of the blade leading edges is the preferred solution for new apparatus Siemens steam turbines. A high protection effect combined with high process stability can be ensured with this Siemens hardening technique. Furthermore the heat input and therewith the geometrical change potential is relatively low. The process is flexible and can be adapted to different blade sizes and the required size of the hardened zones. Siemens collected many years of positive operational experience with this protection measure. State of the art turbine blades often have to be developed with precipitation hardening steels and/or a shroud design to fulfill the high operational requirements. A controlled hardening of the inlet edges of such steam turbine blades is difficult if not impossible with conventional methods like flame hardening. The Siemens steam turbine factory in Muelheim, Germany installed a fully automated laser treatment facility equipped with two co-operating robots and two 6 kW high power diode laser to enable the in-house hardening of such blades. Several blade designs from power generation and industrial turbines were successfully laser treated within the first year in operation. This paper describes generally the setup of the laser treatment facility and the application for low pressure steam turbine blades made of precipitation hardening steels and blades with shroud design, including the post laser heat treatments.

A generic low-pressure steam turbine test case for aeromechanics and condensation

2019 ◽  
Vol 233 (7) ◽  
pp. 953-958
Author(s):  
Christopher Fuhrer ◽  
Marius Grübel ◽  
Damian M Vogt
Keyword(s):  
Steam Turbine ◽  
Numerical Test ◽  
Low Pressure ◽  
Test Case ◽  
Test Cases ◽  
Steam Turbines ◽  
Aerodynamic Damping ◽  
Spontaneous Condensation ◽  
Pressure Steam ◽  
Turbine Design

At the Institute of Thermal Turbomachinery and Machniery Laboratory (ITSM) a generic test case was designed to investigate aeromechanical phenomena and condensation in low-pressure steam turbines. This test case, referred to as Steam turbine Test case for Aeromechanics and Condensation (STAC) consists of the two last stages of a low-pressure steam turbine and is representative for a modern steam turbine design. STAC is intended to serve as a numerical test case to allow studying the fields of aerodynamic damping and spontaneous condensation in low-pressure steam turbine last stages. The geometry of the turbine is made available online at www.itsm.uni-stuttgart.de/research/test-cases/ .

scholarly journals Comparison of Moment-Based Methods for Representing Droplet Size Distributions in Supersonic Nucleating Flows of Steam

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Ali Afzalifar ◽  
Teemu Turunen-Saaresti ◽  
Aki Grönman
Keyword(s):  
Size Distribution ◽  
Reference Frame ◽  
Droplet Size ◽  
Method Of Moments ◽  
Gaussian Quadrature ◽  
Droplet Size Distribution ◽  
Steam Turbines ◽  
Wet Steam ◽  
Full Spectrum ◽  
The Moment

This paper investigates the performance of moment-based methods and a monodispersed model (Mono) in predicting the droplet size distribution and behavior of wet-steam flows. The studied moment-based methods are a conventional method of moments (MOM) along with its enhanced version using Gaussian quadrature, namely the quadrature method of moments (QMOM). The comparisons of models are based on the results of an Eulerian–Lagrangian (E–L) method, as the benchmark calculations, providing the full spectrum of droplet size. In contrast, for the MOM, QMOM, and Mono an Eulerian reference frame is chosen to cast all the equations governing the phase transition and fluid motion. This choice of reference frame is essential to draw a meaningful comparison regarding complex flows in wet-steam turbines as the most important advantage of the moment-based methods is that the moment-transport equations can be conveniently solved in an Eulerian frame. Thus, the moment-based method can avoid the burdensome challenges in working with a Lagrangian framework for complicated flows. The main focus is on the accuracy of the QMOM and MOM in representing the water droplet size distribution. The comparisons between models are made for two supersonic low-pressure nozzle experiments reported in the literature. Results show that the QMOM, particularly inside the nucleation zone, predicts moments closer to those of the E–L method. Therefore, for the test case in which the nucleation is significant over a large proportion of the domain, the QMOM provides results in clearly better agreements with the E–L method in comparison with the MOM.

The Influence of Lean and Sweep in a Low Pressure Steam Turbine: Throughflow Modelling and Experimental Measurements

2008 ◽  
Author(s):  
Lutz Vo¨lker ◽  
Michael Casey ◽  
John Dunham ◽  
Heinrich Stu¨er
Keyword(s):  
Steam Turbine ◽  
Field Measurements ◽  
Low Pressure ◽  
Companion Paper ◽  
Test Results ◽  
Steam Turbines ◽  
Performance Measurements ◽  
Cfd Simulations ◽  
Pressure Steam ◽  
Throughflow Model

This paper describes experimental and throughflow investigations on two configurations of a model three-stage low pressure steam turbine. A companion paper describes 3D CFD simulations of the same turbine test data. Global performance measurements and detailed flow field measurements with pneumatic flow probes were carried out to quantify the changes in the design due to the introduction of sweep in the last stator nozzle vanes. An existing 2D throughflow code was improved to enable the present calculations to be completed. The test results have been used in this paper to calibrate the 2D throughflow model, by adjustment of empirical correlation data to match the experimental data on one of the configurations. This throughflow model was then used to examine the influence of lean and sweep on the design. The results identify that throughflow calculations can model the global effects of lean and sweep in the last stages of steam turbines. Some insight is gained on the losses across the span for the different configurations and on the benefits of lean and sweep in reducing the hub reaction in such stages.

CFD Modeling of Low Pressure Steam Turbine Radial Diffuser Flow by Using a Novel Multiple Mixing Plane Based Coupling: Simulation and Validation

2015 ◽  
Author(s):  
Peter Stein ◽  
Christoph Pfoster ◽  
Michael Sell ◽  
Paul Galpin ◽  
Thorsten Hansen
Keyword(s):  
Steam Turbine ◽  
Heat Rate ◽  
Low Pressure ◽  
Cfd Modeling ◽  
Steam Turbines ◽  
Multiple Mixing ◽  
Diffuser Flow ◽  
Wide Range ◽  
Pressure Steam ◽  
The One

The diffuser and exhaust of low pressure steam turbines shows significant impact on the overall turbine performance. The amount of recovered enthalpy leads to a considerable increase of the turbine power output, and therefore a continuous focus of turbine manufacturers is put on this component. On the one hand, the abilities to aerodynamically design such components is improved, but on the other hand a huge effort is required to properly predict the resulting performance and to enable an accurate modeling of the overall steam turbine and therewith plant heat rate. A wide range of approaches is used to compute the diffuser and exhaust flow, with a wide range of quality. Today it is well known and understood, that there is a strong interaction of rear stage and diffuser flow, and the accuracy of the overall diffuser performance prediction strongly depends on a proper coupling of both domains. The most accurate, but also most expensive method is currently seen in a full annulus and transient coupling. However, for a standard industrial application of diffuser design in a standard development schedule, such a coupling is not feasible and more simplified methods have to be developed. The paper below presents a CFD modeling of low pressure steam turbine diffusers and exhausts based on a direct coupling of the rear stage and diffuser using a novel multiple mixing plane. It is shown that the approach enables a fast diffuser design process and is still able to accurately predict the flow field and hence the exhaust performance. The method is validated against several turbine designs measured in a scaled low pressure turbine model test rig using steam. The results show a very good agreement of the presented CFD modeling against the measurements.

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.

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