Numerical Analysis of Partial Admission Flow in an Industrial Steam Turbine

2012 ◽  
Author(s):  
Tobias J. Kalkkuhl ◽  
David Engelmann ◽  
Ulrich Harbecke ◽  
Ronald Mailach
Keyword(s):  
Steam Turbine ◽  
Cfd Simulation ◽  
Computational Cost ◽  
Turbulence Models ◽  
Typical Feature ◽  
Control Stage ◽  
Gap Flow ◽  
Partial Admission ◽  
Flow Effects ◽  
Simulation Parameters

A partially admitted control stage is a typical feature of an industrial steam turbine. Its purpose is to provide efficient part-load operation and to reduce losses caused by an adverse blade height to tip gap ratio by closing segmental arcs of the inlet annulus. On the other hand partial admission naturally causes circumferential nonuniformity of the flow, because the flow enters the control stage rotor over only a portion of the annulus. This induces not only unsteady blade forces but also additional losses in comparison to a full-admission turbine. So the advantage of partial admission is reduced. In order to analyze partial admission flow effects a 3D CFD model of an industrial steam turbine needs to be developed. It consists of three parts: i) The nozzle groups covering only a portion of the annulus and the rotor of the impulse-type control stage, ii) a cross-over channel directing the flow to a reduced diameter, and iii) the downstream reaction-type turbine stages. The results show considerable flow nonuniformity downstream of the cross-over channel which affects performance of the adjacent full-admission stages. Different operating points of the turbine are investigated. Circumferential periodicity is utilized to minimize computational cost of the simulation. Customary guidelines to CFD-simulation are taken into account and simulation parameters are carefully checked for their influence on the results: turbulence models, meshing parameters and boundary conditions are varied. The influence of gap flow is checked. The results are finally compared to experimental data to check simulation quality.

Rotordynamic Stability Under Partial Admission Conditions in a Large Power Steam Turbine

2009 ◽  
Author(s):  
Lin Gao ◽  
Yiping Dai ◽  
Zhiqiang Wang ◽  
Yatao Xu ◽  
Qingzhong Ma
Keyword(s):  
Steam Turbine ◽  
Fluid Model ◽  
Rotor System ◽  
System Stability ◽  
Steam Turbines ◽  
Large Power ◽  
Control Stage ◽  
Partial Admission ◽  
The Stability ◽  
Load Conditions

At present, the majority of power steam turbines operate under part-load conditions during most of their working time in accordance with the fluctuation of power supply. The load governing method may cause partial admission in control stage and even some pressure stages, which impacts much on the stability of the rotor system. In this paper, CFD and FEM method were used to analyze the effect of partial admission on rotor system stability. A new approach is proposed to simplify the 3D fluid model for a partial admission control stage. Rotordynamic analysis was carried out to test the stability of the HP rotor of a 600 MW steam turbine under different load conditions. 13 different governing modes on the rotor stability were conducted and data were analyzed. It is found that rotor stability varies significantly with different governing modes and mass flow rates, which is consistent with the operation. Asymmetric fluid forces resulted from partial admission cause a fluctuation of the dynamic characteristics of the HP bearings, which consequently affect the stability of the rotor system. One of the nozzle governing modes in which the diagonal valves open firstly is demonstrated as the optimal mode with the maximum system stability. The optimization has been applied to 16 power generation units in China and result in improved rotor stabilities.

Rotor Dynamic Analysis on Partial Admission Control Stage in a Large Power Steam Turbine

2010 ◽  
Author(s):  
Lin Gao ◽  
Yiping Dai
Keyword(s):  
Steam Turbine ◽  
Phase Angle ◽  
Low Frequency ◽  
Deep Understanding ◽  
Labyrinth Seal ◽  
Steam Turbines ◽  
Large Power ◽  
Stiffness Coefficients ◽  
Control Stage ◽  
Partial Admission

Partial admission is used widely for steam turbines to match their output power to the load demand. The occurrences or thresholds of most self-induced low-frequency vibrations are under partial admission conditions. But the destabilizing forces which cause rotor instability are seldom investigated under partial admission conditions especially for large power steam turbines. Full 3D CFD model is built for the control stage of a 600 MW steam turbine applying commercial codes. N-S equations are solved to investigate the flow fields in the control stage including all the blade passages and the labyrinth seal over the shroud. Interesting flow distributions are observed for the seal spaces at partial admission conditions. A correction formula is presented for partial admission labyrinth seal based on the classical one and a method is discussed for the estimation of partial-admission phase-angle-dependent stiffness coefficients. The destabilizing forces acting on the rotor system are calculated for different eccentricity angles and are compared with those under the concentric condition. The stiffness coefficients are solved under typical partial admission conditions. They are found to change dramatically with the phase angle. The results may be helpful for a deep understanding of the low-frequency variation problems of large power steam turbines under partial admission conditions.

Transient Response of Control Stage Blade Disk due to Partial Admission by a Reduced Method

2015 ◽  
Author(s):  
Xuanen Kan ◽  
Zili Xu ◽  
Yu Zhao ◽  
Baitong Dou ◽  
Wenbin Zhao
Keyword(s):  
Transient Response ◽  
High Frequency ◽  
Degrees Of Freedom ◽  
Shock Loading ◽  
Computational Cost ◽  
Complex Load ◽  
Displacement Response ◽  
Control Stage ◽  
Partial Admission ◽  
Beat Phenomenon

Partial admission can improve the thermal efficiency of steam turbines at low loads, but a non-uniform flow in circumference will be caused inevitably at the same time. That makes control stage blade subject to complex load, leading to the high cycle fatigue. Therefore, it is important to calculate and accurately analyze transient response of control stage blade disk due to partial admission. However, the large number of degrees of freedom of the practical control stage blade disk will lead to an extremely high computational cost when the finite element method is used. A strategy for reducing the number of degrees of freedom based on the component modal synthesis (CMS) method is presented. CMS method is used to generate a super-element of one group of 4 blades. The cyclic symmetric property is used to generate super-elements for other groups of blades through circumferential rotation and coordinate transformation. The total number of degrees of freedom is reduced to 1.21% of the original DOF. When the rotating blades enter and leave the arc of admission under partial admission conditions, they are subject to the effect of shock loading. The length of the effect of shock loading depends on the rotating blade pitch and the peak of effect of shock loading depends on stage pressure ratio. The displacement response of control stage blade disk under different shock coefficients (1.6, 2.5, 4) is calculated. This paper analyses the vibrations of blade disk under high frequency force caused by nozzles under partial admission conditions. The results show that compared to the shock coefficient of 1.6 the maximum displacement response increased by 27.3% and 72.6% for shock coefficients 2.5 and 4. In addition, a beat phenomenon is found in displacement response of blade disk under high frequency force. The FFT of the response and excitation and the ZZENF of blade disk indicate that the composite vibration of 6050Hz, 6000Hz and 4900Hz these 3 kinds of harmonic vibrations is the main reason of the beat phenomenon.

Numerical Optimization of a Steam Turbine Control Stage by Flowpath Profiling Using Evolutionary Algorithm

2011 ◽  
Author(s):  
Nils Moser ◽  
Rene´ Volkert ◽  
Franz Joos
Keyword(s):  
Evolutionary Algorithm ◽  
Steam Turbine ◽  
Rotor Blade ◽  
Positive Influence ◽  
Considerable Effect ◽  
Flow Angle ◽  
Guide Vanes ◽  
Control Stage ◽  
Wide Range ◽  
Flow Effects

The subject of this paper is the optimization of a steam turbine impulse wheel control stage by flow path profiling of the shroud. The investigated control stage is derived from an existing industrial steam turbine design. The shroud contour is varied in radial direction within specified restrictions by an evolutionary algorithm. The algorithm is directly connected to a mesh generator and a CFD solver. The optimization goal is the reduction of the total pressure loss over the guide vanes. The geometry of the rotor blade has been retained unchanged within the presented investigations. The flow field of the varied stage is compared with the baseline geometry. The optimum candidates are further investigated with CFD simulations for different operating point scenarios. Numerical results show that the axisymetric flowpath profiling of the shroud has a considerable effect on the loss behavior of the whole stage over a wide range of pressure ratios. Due to flowpath profiling the boundary layer in the nozzle is significantly affected which results in a more uniformly shaped exit flow angle profile over the nozzle span and a significant reduction of the global secondary flow effects in the guide vanes. Both observations have a positive influence on the flow conditions to the subsequent rotor blade.

scholarly journals The Effect of the Computational Grid Size on the Prediction of a Flammable Cloud Dispersion

2014 ◽  
Author(s):  
Adriana Miralles Schleder ◽  
Marcelo Ramos Martins ◽  
Elsa Pastor Ferrer ◽  
Eulàlia Planas Cuchi
Keyword(s):  
Cfd Simulation ◽  
Complex Geometry ◽  
Computational Cost ◽  
Computational Grid ◽  
Grid Size ◽  
Hazardous Substances ◽  
Gas Dispersion ◽  
Vapor Cloud ◽  
Predicted Values ◽  
Simulation Parameters

The consequence analysis is used to define the extent and nature of effects caused by undesired events being of great help when quantifying the damage caused by such events. For the case of leaking of flammable and/or toxic materials, effects are analyzed for explosions, fires and toxicity. Specific models are used to analyze the spills or jets of gas or liquids, gas dispersions, explosions and fires. The central step in the analysis of consequences in such cases is to determine the concentration of the vapor cloud of hazardous substances released into the atmosphere, in space and time. With the computational advances, CFD tools are being used to simulate short and medium scale gas dispersion events, especially in scenarios where there is a complex geometry. However, the accuracy of the simulation strongly depends on diverse simulation parameters, being of particular importance the grid resolution. This study investigates the effects of the computational grid size on the prediction of a cloud dispersion considering both the accuracy and the computational cost. Experimental data is compared with the predicted values obtained by means of CFD simulation, exploring and discussing the influence of the grid size on cloud concentration the predicted values. This study contributes to optimize CFD simulation settings concerning grid definition when applied to analyses of consequences in environments with complex geometry.

Unsteady Load of Partial Admission Control Stage Rotor of a Large Power Steam Turbine

2004 ◽  
Author(s):  
Piotr Lampart ◽  
Mariusz Szymaniak ◽  
Romuald Rza˛dkowski
Keyword(s):  
Steam Turbine ◽  
Rotor Blades ◽  
Pressure Pulsations ◽  
Unsteady Forces ◽  
Large Power ◽  
Control Stage ◽  
Partial Admission ◽  
Geometrical Imperfections ◽  
Sst Turbulence Model ◽  
2D Model

Partial admission flow in the control stage of a 200MW steam turbine is investigated with the help of a RANS solver with k-ω SST turbulence model in the code Fluent. A 2D model of flow at the mid-span section of the full annulus is assumed. The results exhibit interesting details of the process of expansion in the control stage. Unsteady forces acting on the single rotor blades of the control stage are calculated, and are subject to Fourier analysis. Single blade forces are summed up to obtain the unsteady load at the rotor (forces acting at the rotor disc are neglected due to the assumed 2D model). The calculations take into account pressure pulsations at the entry to the nozzle boxes and rotor blade mistuning / geometrical imperfections.

Numerical Investigations on Aerodynamic Performance of Nozzle Control Stage of a 600MW Steam Turbine Under Different Backing Pressure Conditions

2011 ◽  
Author(s):  
Gangyun Zhong ◽  
Jun Li ◽  
Zhigang Li ◽  
Xin Yan ◽  
Qilin Wu
Keyword(s):  
Steam Turbine ◽  
Control Valve ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Computational Domain ◽  
Aerodynamic Efficiency ◽  
Control Stage ◽  
Backing Pressure ◽  
Partial Admission

Partial admission aerodynamic performance of a nozzle control stage for a 600MW steam turbine was numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solutions. Two inlet main steam pipe, four control valves, four nozzle groups including strengthening ribs and full stator blades, and full rotor blades were considered in the present computational domain. The partial admission with three control vales opening and the fourth control valve closed under five different backing pressures were calculated to analyze the aerodynamic efficiency and total pressure losses distributions. The maximum aerodynamic efficiency of the nozzle control stage was obtained at five different backing pressure operating conditions. The flow fields in the nozzle control stage at specified backing pressure with consideration of the partial admissions effects were also illustrated.

CFD Simulation of a Supercritical Carbon Dioxide Radial-Inflow Turbine, Comparing the Results of Using Real Gas Equation of Estate and Real Gas Property File

2016 ◽  
Vol 846 ◽  
pp. 85-90 ◽  
Author(s):  
Mostafa Odabaee ◽  
Emilie Sauret ◽  
Kamel Hooman
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Computational Cost ◽  
Real Gas ◽  
Table Method ◽  
Radial Inflow Turbine ◽  
Solar Resource ◽  
Supercritical Carbon

The present study explores CFD analysis of a supercritical carbon dioxide (SCO2) radial-inflow turbine generating 100kW from a concentrated solar resource of 560oC with a pressure ratio of 2.2. Two methods of real gas property estimations including real gas equation of estate and real gas property (RGP) file - generating a required table from NIST REFPROP - were used. Comparing the numerical results and time consumption of both methods, it was shown that equation of states could insert a significant error in thermodynamic property prediction. Implementing the RGP table method indicated a very good agreement with NIST REFPROP while it had slightly more computational cost compared to the RGP table method.

Generation of Regular and Irregular Waves in Navier-Stokes CFD Solvers by Matching With the Nonlinear Potential Wave Solution at the Boundaries

2018 ◽  
Author(s):  
Youngmyung Choi ◽  
Benjamin Bouscasse ◽  
Sopheak Seng ◽  
Guillaume Ducrozet ◽  
Lionel Gentaz ◽  
...  
Keyword(s):  
Viscous Flow ◽  
Open Source ◽  
Cfd Simulation ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Wave Fields ◽  
Flow Solver ◽  
Nonlinear Potential ◽  
Simulation Parameters ◽  
2D And 3D

The capability of wave generation and absorption in a viscous flow solver becomes important for achieving realistic simulations in naval and offshore fields. This study presents an efficient generation of nonlinear wave fields in the viscous flow solver by using a nonlinear potential solver called higher-order spectral method (HOS). The advantages of using a fully nonlinear potential solver for the generation of irregular waves are discussed. In particular, it is shown that the proposed method allows the CFD simulation to start at the time and over the space of interest, retrieved from the potential flow solution. The viscous flow solver is based on the open source library OpenFOAM. The potential solvers used to generate waves are the open source solvers HOS-Ocean and HOS-NWT (Numerical Wave Tank). Several simulation parameters in the CFD solver are investigated in the present study. A HOS wrapper program is newly developed to regenerate wave fields in the viscous flow solver. The wrapper program is validated with OpenFOAM for 2D and 3D regular and irregular waves using relaxation zones. Finally, the extreme waves corresponding to the 1000 year return period condition in the Gulf of Mexico are simulated with the viscous flow solver and the wave elevation is compared with the experiments.

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