CFD ANALYSIS Of COMBINED 8-12 STAGES Of INTERMIDIATE PRESSURE STEAM TURBINE

Transcription

1 CFD ANALYSIS Of COMBINED 8-12 STAGES Of INTERMIDIATE PRESSURE STEAM TURBINE 1st Author name : SHIVAKUMAR VASMATE, 2nd Author name : KAMALADEVI ANANDE. 1 Department of Mechanical Engineering, India 2 Department of Civil Engineering, India ABSTRACT Steam Turbines play a vital role in power generation as a prime mover which converts kinetic energy of steam into mechanical energy. Many of the utility steam turbines is the combination of three cylinder construction i.e. High pressure cylinder in which pressure is maximum with minimum specific volume and so blade height is minimum, Intermediate pressure cylinder in which pressure is intermediate and so is the blade height and finally low pressure cylinder which has a minimum pressure level and maximum specific volume and hence maximum blade height. Generally, IP Steam turbine consists of 12 stages; combination of 1-7 stages and 8-12 stages which are divided by the use of the extraction strip. A typical Intermediate Pressure cylinder module is chosen to carry out the project work. The flow in a Turbine blade passage is complex and involves understanding of energy conversion in three dimensional geometries. The performance of the turbine depends on the efficient conversion with minimum amount of flow losses. To improve the performance it is essential to identify the losses generating mechanism and study their influence and effects on performance. The objective of the project is to carry out the CFD analysis of a typical IP utility turbine module considering the hub/shroud sealing between the stages which account for leakage losses. To achieve the above objective we need to model separately the bladed region and attach the hub/shroud seal region to it by General Grid Interface. The flow domain and mesh generation for seal area needs to be accurate to get the correct interface with blades. IDEAS software is used for geometric modeling, CFX-TURBOGRID software is used for meshing the blade region, ICEM-CFD software is used for meshing the hub/shroud region of the seals and CFX is used for physics definition and solving the problem. Initially the analysis is carried out for the 8th stage, subsequently for the combined 8-12 stages. The results are compared with two dimensional (2D) analysis calculations and found. Keywords-Steam turbine, Hub/shroud, General Grid Interface (GGI), IDEAS software, CFX TURBO-GRID software, ICEM-CFD software, CFX software Page 21

2 I. Introduction BHEL is manufacturing a wide variety of turbines over the last 50 years to meet India s growing need for power. Steam turbine plays a vital role in power generation as a prime mover, which converts Kinetic Energy of steam to Mechanical Energy. Many of the utility steam turbines are of three cylinder constructions i.e. High pressure cylinder in which pressure is maximum with minimum specific volume and so blade height is minimum, Intermediate pressure cylinder in which pressure is intermediate so the blade height is intermediate and Low pressure cylinder which has a minimum pressure level & maximum specific volume and hence LP cylinder blade height is maximum. A typical Intermediate pressure Turbine of utility steam turbine is chosen to carry out the CFD analysis. The analysis requires solving of fluid problem in bladed region. This can be done in three approaches, Analytical, Experimental and Numerical. Analytical methods which assume a continuum hypothesis are more suited for simple problems and are not suited for complex fluid flow problems. Experimental methods are suited for complex fluid flow problems but the expenditure for carrying out the analysis is high. The other limitation is that the determination of the fluid characteristics in the interiors becomes complex and difficult. Hence, Numerical approach is more feasible approach for analysis of a particular design because it overcomes the limitations of the two methods and it gives a close approximate for complex form of fluid problems too. Numerical approach involves discretization of the governing mathematical equations gives numerical solutions for the flow problems. The analysis is carried out by identifying the flow domain. The domain is modeled, discretized and governing equations are solved using commercially available software. The results are post processed and compared with 2 dimensional program results which were experimentally verified. A. Elements of Steam Turbine: The bladed region of Steam Turbine consists of the following as shown in Fig 1 1. Stationary Blades. 2. Moving Blades. 3. Labyrinth Seals. Fig1. Elements of Steam Turbine. Page 22

3 B. Aerofoil Blades: An aerofoil blade is a streamlined body having a thick, rounded leading edge and a thin trailing edge in order to achieve a high lift-drag ratio. Its maximum thickness occurs somewhere near the midpoint of the chord. Both the stationary and Rotating blades should be designed such that it should be capable of obtaining the desired pressure drop and turning towards the tangential direction between the driving surface and trailing surface of the vane passage, so that the flow comes out of the stationary blade with a desired velocity both in magnitude and direction. The exit flow will have high velocity with a high tangential component. Thus the flow enters axially in the stationary as well as the moving blades and both the tangential force and torque exerted by the fluid jet on the following rotating blade row depends on the change in the tangential velocity of the fluid. The blade with respect to turbine axis and blade nomenclature is shown in Figure 2 and Figure 3 respectively. Fig 2.blade with respect to turbine axis. Fig 3. blade nomenclature. Page 23

4 C. Labyrinth Seals: The provision of seals is necessary to minimize the leakage whenever there is a clearance between a moving and a stationary part with pressure difference across the clearance. In a steam turbine seals are provided at the two turbine ends where the shaft is taken out of the casing, at the clearance between the diaphragm and the rotor of an impulse stage and on the blade tips when provided with shrouds. Mostly the labyrinth and strip type of seals are used in the turbo machines. The number of strips used and their arrangement depends upon the pressure difference across the clearance and the basic construction arrangements used for sealing the diaphragm are shown in figure 4 and these are generally known as Labyrinth seals. The flexible type of labyrinth seals used on diaphragms of the high pressure stages are as shown. Tip seals to the turbine stage in the CFD models are used for the more accurate stage performance predictions. Fig 4. : Flow Domain at Labyrinth Seal II. Methodology A. Problem Solving Approach in CFD: The basic steps involved in solving any CFD problem are as follows: 1. Identification of flow domain. 2. Geometry construction or Component Modeling. 3. Grid generation. 4. Specification of boundary conditions and initial conditions. 5. Selection of solver parameters and convergence criteria. 6. Results and post processing. The IP Utility Steam Turbine is modeled and analysis is carried out by following steps Page 24

5 1. Identification of Flow Domain: Before constructing grid, it is required to understand the exact flow domain properly. The flow domain in the case of Steam Turbine consists of blade path (both Stationary and Rotating blades fixed to casing and rotor respectively), Labyrinth seals, and steam inlet & outlet. It is therefore required that before going ahead with 3D modeling and grid generation, the common interfaces should be clearly defined between each blade in each stage and seals. The software that is used for generating the geometry and meshing is decided based on nature and complexity of the geometry. For axi-symmetry bladed geometry, the data for hub, shroud and blade profiles are obtained from 2D drawing and subsequently grids are generated using Turbo-Grid software. Though the stage consists of Stationary and Rotating blades, but to get the flow developed to the upstream of the hub a small passage is added and similarly to the downstream of the shroud the flow domain is extended up to some distance, so that realistic boundary conditions can be given at the inlet and outlet surfaces. The boundary wall is the region where no slip condition exists and the velocity gradually increases and reaches to mainstream velocities. That means, velocity gradient exists there and that region close to the boundary wall should have fine grids to capture the boundary wall effects. 2. Geometrical Modeling: In order to analyze the flow and to evaluate the performance, basically three steps are required as follows: 1. Modeling of components. 2. Grid generation. 3. Analysis. 4. As the flow domain consists of blade and seal passages, the modeling is carried out as described below: 1.1. Geometrical Model of Blades: The blade of the Utility IP Steam Turbine is of cylindrical type and blade extends between hub and shroud surfaces. The geometry of blade is extracted from blade profile co-ordinates are shown in figure 5.1 and figure 5.2, given in the form of suction side and pressure side points, which are located along the radial positions of the blade. Page 25

6 Fig 5.1: 8th Stage Guide Blade Fig 5.2: 8th Stage Moving Blade The point data is arranged in order to obtain blade profiles from hub to shroud. IDEAS software is used to generate the solid model, and generally we will be saving the points data in ASCII (.curve) file format for convenience of grid generation of blades directly in ANSYS TurboGrid Software. This process requires some programming skills which have been done in Microsoft Excel sheet using some formulae. 1.2 Geometrical Model of Seals: Labyrinth seals are attached at the hub and shroud surface of the blades to reduce the leakage flow. Modeling of seals has been done in IDEAS by extracting the data from the AutoCAD drawing is shown in figure 6. A typical cross-section drawing is shown below for guide blade. By extruding the seals in either of the directions then the solid model of the seal with the required length is obtained and is shown in figure 6.1. Flow domain Strips Fig 6 Two Dimensional views of Seals Page 26

7 Figure 6.1. Fluid model of the Seals (Hub & Shroud) 2 Grid Generation of Blades using CFX-TurboGrid: The flow inside a Steam turbine passes through the bladed and seal passages, which can be described as periodic passages. Geometrically these passages are rotationally periodic about its axis of rotation. For the CFD analysis, it is assumed that the flow is also rotationally periodic in these passages. Therefore, the flow computation can be made in one of the periodic passage while applying periodic boundary conditions at periodic interfaces. For the purpose of flow domain discretization, one blade passage is considered for 3D-grid generation. The tool used for grid generation is CFX-TURBOGRID software package for the stator and rotor blade passages. Input to this software is given by three Data files namely, hub.curve, shroud.curve, and profile.curve. These files contain the hub, shroud and profile curve data files in global Cartesian coordinates or cylindrical form. Page 27

8 Input Format for Turbo Grid CFX-Turbo grid requires three input data files (profile, shroud and hub) to define the path and blade geometry. Hub Data File The hub curve runs upstream to downstream and must extend of the blade leading edge. The hub data file contains the hub curve data points in Cartesian form and downstream of the blade trailing edge. The profile points are listed, line-by-line, in free format ASCII style in order from upstream to downstream. These data points are used to place the nodes on the hub surface, which is defined as the surface of revolution of a curve joined by these points. Shroud Data File The shroud data file contains the shroud curve data points in Cartesian or cylindrical form the shroud curve runs upstream to downstream and must extend upstream of the blade leading edge and downstream of the blade trailing edge the points are listed, line by line in free format ASCII style in order from upstream to downstream. These data points are used to place the nodes on the shroud surface, which is defined as the surface of revolution of a curve joined by these points. Example: Considering XZ Plane with X as Axis of Rotation is shown in figure 7. Shroud.Curve Hub. curve Hub.curve Shroud.Curve Fig 7: Hub Curve and Shroud Curve Page 28

9 Profile Data File: The profile data file contains the blade profile curves in Cartesian or cylindrical form. The profile points are listed, line-by-line, in free format ASCII style in a closed loop surrounding the blade. The blade profiles should lie on a surface of revolution to facilitate transformation to m-prime, theta conformal space. A minimum of two blade profiles are required, one which lies exactly on the hub surface and one which lies exactly on the shroud surface. The profiles must be listed in the file in order from hub to shroud. Multi bladed geometries are handled by placing multiple blade profile definitions in the same profile. Example for Profile.curve: # profile # profile Single blade fluid Passage Fig 8: Single bladed Passage after using profile.curve Page 29

10 The first step is to check whether the blade profile data obtained from solid model is intersecting hub and shroud curves or not. We use CFX-Turbogrid intersect option for this purpose. Using this option, we have to see that blade profile must lie on the surface of revolution of hub and shroud as shown in fig 8. Turbo grid intersecting capability can convert an existing set of blade profiles that does not necessarily lie on the surface of revolution into one that can be used in a CFXTurbogrid template. Next step is generating grid. Among the various templates available in turbogrid, Multi Block Grid template as shown in figure 9 is used. By the way of adjusting control points in figure 10 a good quality hexahedral grid can be generated. Flip topology is used to correct negative grid volume due to left-handed system. The Create command not only creates grid but also calculates and displays the minimum and maximum skew angle in the grid and the node at which it occurs. The View command in the GUI window can be used to see the different views of the grid like Cartesian view, Meridional view and blade-to-blade view as shown in figure 13. Shroud.curve Profile Curve Hub.Curve Fig 9: Template of 3D Blade in Turbo-Grid In the above template shown in figure 9 is a 3D blade in Turbo-Grid, the right side view shows the blade-to-blade view of the blade and the left view shows the mesh statistics of the blade. Page 30

11 Trailing edge Control Periodicity Control Topology - H-Grid and O-Grid Leading edge Control Points Control Nodes Fig 10: Adjusting the control points at the Leading Edge & Trailing Edge Shroud surface Hub surface Fig11. Circumferential View of Guide Blade Surfaces Fig12. G8 Guide Blades periodically arranged throughout the circumference Page 31

12 The mesh generated by adjusting the control points as shown in Figure 10 and correspondingly Circumferential view of guide blade surfaces & Periodical arrangement of blades throughout the circumference which differ for different stages are shown in Figures 11 and 12. A Cartesian view is also in figure 13. Cartesian View Fig13. Views for 8th Stage Guide Blade The following parameters were considered to check the quality of the grids: Skew angle: It is defined as the internal angle of the octahedron. Ideally, all the angles should be equal to 90 degrees to get a perfect orthogonal grid. However, for practical purposes, the grid is considered to be of high quality if the minimum skew angle is not lower than 15 degrees and the maximum skew angle is not greater than 165 degrees. Grid volume: Negative volume meant overlapping of adjacent grids, which would lead to errors in solver. Care was taken to ensure that there was no negative volume in the grids. Aspect ratio: It is defined as the ratio of the longest side to the shortest side. Its minimum value is 1. For good quality grid creation, the maximum aspect ratio should be less than 200. Page 32

13 The mesh is generated for the stator and rotor blades with the total number of nodes, maximum and minimum skew angle and aspect ratio obtained from TURBOGRID are given in Table 1. TABLE 1: MESH DATA FOR COMPONENTS OF 8th STAGE BLADES S.No Number Component Number of Aspect Hexa Ratio Nodes Elements (Max) of Orthogonality angle (Min) 1 Stator Blade (G8) 2 Rotor Blade (M8) 5.4 Seals Meshing using ICEM-CFD:In a Steam Turbine Labyrinth or strip type of seals are invariably used. The flow domain of the seals is modeled in IDEAS from the 2D drawings and exported into ICEM CFD to generate the mesh. Before generating the hexahedral-mesh the geometry should be repaired in order to get no negative volumes and to get the better quality of the mesh. It is a semi-automated meshing module which present the rapid generation of multi-block structured or unstructured hexahedral volume meshes. In case of hexa meshing the structured volume meshes will be obtained. Blocks can be interactively adjusted by splitting it to the underlying CAD geometry and fitted internal or external, O-grids can be generated by the system automatically. The figure 14 and figure 15 are shown below the seal geometry and mesh generated using ICEM-CFD software. Page 33

14 G8 Seals (Hub and Shroud) G8 Seals with Hexa Mesh Fig 14. Seal Geometry and Mesh Generated for Guide blade M8 Seals (Hub & Shroud) M8 Seals with Hexa Mesh Fig 15. Seal Geometry and Mesh Generated for the Moving Blade Page 34

15 Above figure is hexahedral structured mesh for eighth stage moving blade (M8) generated in Ansys ICEM-CFD software. The lower part is called Hub and the upper part is known as Shroud. This is obtained by blocking, splitting, associating the points, curves etc; in order to get the mesh with required quality. The total number of nodes, maximum and minimum skew angle and aspect ratio obtained from ICEM-CFD are given in Table 2. TABLE 2: MESH DATA FOR 8th STAGE SEALS (HUB AND SHROUD) S.No Component Number of Number of Nodes Aspect Volume Hexa Ratio (Min ) Elements (Max) 1 G8 Seals 68,096 58, M8 Seals 71,864 60, ANSYS CFX: CFD analysis is carried out to understand the flow through the turbine, predict the pressure distribution and velocity profiles on the blades and predict the various losses. Ansys CFX-11 software tool is used for analysis purpose. The Analysis is carried out using CFX-Pre, CFXSolver and CFX-Post modules. Specification of boundary conditions and initial conditions: Specification of boundary condition of simulation is done in CFX-Pre processing. The files with the extensions:.grd,.gci,.bcf of Guide and Moving blades, also the files with having.cfx5 extension of seals of a IP utility steam turbine module are copied into a new folders separately and this grid file are read into pre-processing model of CFX-11 software. The complete softwares flow chart is shown below in figure 16. Page 35

16 IDEAS or MODELLING BLADES & SEALS AUTO CAD CFX TURBO_GRID BLADES GRID (MESH) GENERATION ANSYS ICEM_CFD SEALS PRE PROCESSING CFD ANALYSIS SOLVING ANSYS CFX 11.0 POSTPROCESSING Fig 16 SOFTWARES FOR COMPLETE CFD ANALYSIS Page 36

17 III Result and Discussion A. Results: The analysis is carried out in two stages. First, initially the analysis is carried out for the 8th stage and later combined analysis for all the 5 stages has been carried out. The stage analysis has been carried out for the turbine stages with the constant mass flow and it consists of stator, rotor, and seals. The various performance parameters like pressure, temperature distribution and velocity profiles on the blades, isentropic efficiencies, Power have been computed using the CFX Macros and with the help of Mollier Chart. As the eight stages consisting of Guide blade, Moving blade with a stage interface between the blades is simulated, and the solution is obtained with high resolution convergence up to 1e-5.The analysis is carried out with seals for 8th stage. The results obtained are discussed below: 1. Flow and performance parameters for 8th stag with seal: CFX-PRE Physics Definition (Stage8) Shroud Counterroating Wall Blade-Shroud Interface G8 Blade Periodicity M8 Blade Outlet G8 Guide Blade G8 Blade Inlet Inlet G8M8 Blade Stage Interface Blade-Hub Interface Hub Rotating wall Fig17. Boundary conditions for 8th Stage with Seals In the pre processing the following fluid domains and boundary conditions are shown in figure17 and specified for the eight stage analysis. 1. Simulation 2. Domains G8 blade & Seals M8 blade & Seals 3. Boundary Conditions: Inlet : steady state : Fluid type : 8th Guide blade with hub & shroud seals : 8th Moving blade with hub & shroud seals : Guide blade inlet Page 37

18 Outlet Inlet Mass Flow Inlet Static Temperature Wall Outlet Static Pressure Rotational Speed Reference pressure 4. Fluid Properties: : Moving blade outlet : kg/sec : K : smooth : bar : rpm : 0 bar Working Fluid Dynamic Viscosity Thermal Conductivity 5. Rotation Axis : Steam5 (Dry steam) : e-6 Pa s : W/m. ºc : X - Axis 6. Turbulence Model: Turbulence Model : Standard k-epsilon Model Heat transfer Model : Total Energy 7. Interface between Guide and Moving Blade: Type Frame Change Option 8. Pitch Change: : Fluid -Fluid : Stage Interface(G8M8 Blade stage interface) Option: Specified Pitch Angle Pitch angle side 1: Pitch angle side 2: B. Run the solver monitor. The solver is allowed to run till the required convergence is obtained in figure 18 Fig18. Solver run convergence. Page 38

19 C. POST PROCESSING: 1. Results which are obtained from the CFX macro for the Eighth stage User Input Inlet Region G8 blade inlet Outlet Region M8 blade outlet Blade Row Region M8 blade Default Reference Radius [m] Number of Blade Rows 115 Machine Axis X Rotation Speed [rev min^-1] Gamma 1.3 Reference Pressure 0 [Pa] 2. Mass Averages Quantity Inlet Outlet Ratio (Out/In) Temperature K K Total Temperature K K Pressure e+006 kg m^ e+006 kg m^ s^-2 s^-2 Total Pressure e+006 kg m^ e+006 kg m^ s^-2 s^-2 Page 39

20 3. Results Torque (one blade row) kg m^2 s^-2 Torque (all blades) kg m^2 s^-2 Power (all blades) e+006 kg m^2 s^-3 Total-to-total isen. efficiency Total-to-static isen. efficiency Streamline and vector plots for various parameters have been given for better understanding of flow through the stages. The Pressure Contour shows the pressure variation across the stage. It is clear from the Pressure Contour that the pressure drop occurs across the stage. The pressure is high at the beginning of the stage, decreases across the stage and is low at the exit of the stage. The Pressure Contour is useful to see the variation of pressure across the stage and modify the design if required to get uniform pressure drop. The Velocity Vector Plot shows the velocity variation across the stage is shown in figure 19. It can be seen from the Velocity Contour Plot that the velocity is minimum at the entry of the guide blade and reaches maximum at the exit of guide blade. Similarly for the moving blade also the velocity is minimum at the entry and maximum at the throat. Thus the velocity changes for each blade from minimum at entry to maximum at the throat. The Velocity Streamline Plot is useful to note the streamline motion of the Steam through the Stage. The Streamline motion is very useful to determine the proper flow of the steam through the stage. The proper design of the stage should have the continuous streamline motion of the Steam without any discontinuity. The Velocity Vector Plot is useful to draw the velocity triangles of the stage. The power output of the stage depends upon the velocity triangles. Thus the velocity vector is an important plot to decide the design efficiency of the stage. It is very important design the stage to get the required power output so the velocity vector plot is good indicator of the design of the stage. The Pressure Contour, Mach number Contour, Velocity Streamline and Velocity Vector Plots for 8 Stage with seals are shown below. th 4. Plots for 8th Stage with Hub & Shroud seals: Page 40

21 Fig19. 8th stage streamline vector plot Fig20. 8th stage Pressure contour plot Page 41

22 Fig21. 8th stage Temperature Streamline plot Fig22. 8th Stage Mach number Streamline plot Velocity Vector Profiles Above Mid-Span Below Mid-Span Fig23. 8th stage Velocity vector plot Page 42

23 5. Discussions: Streamline, vector and contour plots for various parameters have been given for better understanding of the flow through the stages. The variation of pressure across the stage is seen in Fig 20, it is a pressure contour plot which is a series of lines linking points with equal values of a given variable pressure. It is shown in the figure that the pressure goes on decreasing from entry to exit of the stage. At the entrance the maximum of bar is observed and a minimum of bar is obtained at the exit is obtained. The Contour plot for the variation of temperature across the 8th stage is shown in Fig 21. From the figure it is clear that the temperature is decreasing from the entry to the exit. At the entrance the temperature is maximum around K, and at the exit the temperature is minimum of K. Fig 22 shows the variation of Mach number across the 8th stage with seals. From the figure it is obvious that Mach number is increasing from the entry to exit and minimum Mach number of the order of occurred at the entrance of the guide blade and a maximum of is occurred at the interface of the guide blade and moving blade. Fig 23 shows the variation of the velocity across the eighth stage. This vector plot, which is a collection of vectors drawn to show the direction and magnitude of a vector variable on a collection of points are defined by arrows. From the figure it is obvious that the velocity is minimum at the entrance which is of 7.51 m/sec and maximum at the interface and at the exit of the stage which is around m/sec. 6. Comparison of CFD values and 2D Values: The CFD analysis results are compared with 2D program output. The program output is verified experimentally. The comparison chart of 2D values and CFD values for 8th stage are shown in the table 3. The values obtained show that the CFD values are closer to 2D program and are within the acceptable limits. Table3. Comparison of CFD values and 2D values. STAGE 8 WITH SEALS Description Temp inlet Temp outlet Unit 2D value CFD Value K K Page 43

24 Pressure inlet Bar Pressure outlet Bar Output Power MW CFX software provides a macro which computes the values of Steam properties like pressure, temperature, and enthalpy at Guide &moving blade inlet& exit. In addition to the above the torque on moving blades and power developed by the stage is also calculated. 7. Combined analysis: The combined analysis is carried out for the subsequent 5 stages consisting of large number of elements 17, 34,379 nodes with many General Grid Interfaces and stage interfaces with multiple frames of reference. IBM Cluster computing server with P615 processor is used to obtain the solution for the simulation using 4 processors with 2GB RAM each. The solution is converged with 1e-5 with high resolution. The results are as below. 7.1Flow and performance parameters for combined 5 stages with seals: Inlet Outlet: Average Static Pressure Fig24. Boundary conditions of Combined 5 Stage. 7.2 Run the solver monitor. Page 44

25 The solver is allowed to run till the required convergence is obtained in figure 25. Fig 25. Solver run convergence. 7.2 Plots for Combined 8-12 Stages With seal Fig26. Pressure Contour Plot in Pascal (pa) Page 45

26 The variation of pressure across the stage is seen in Fig26, which is a Pressure Contour Plot with series of lines linking stages with equal values of a given variable pressure. The variable values can quickly be associated with the colored regions of the plot. It is shown in the figure that the pressure goes on decreasing from entry to exit of the stage. At the entrance the maximum of bar is observed and a minimum of bar is obtained at the exit. Fig27: Temperature Contour Plot in Kelvin (K) The contour plot for the variation of temperature across 5 stages is shown in Fig 27. The assumption of steady state flow is assumed when a streamline is created, even with a transient simulation. From the figure it is clear that the temperature is decreasing from the entry to the exit. At the entrance the temperature is maximum around K and at the exit the temperature is minimum of K. Fig28 Velocity Streamline Plot in m/sec Page 46

27 Fig 28 shows the variation of the velocity streamline across the different stages. Here, the streamlines goes on decreasing as the stages passes, it is because of not proper alignment of the blades accurately as needed around its periphery. Fig 28 Mach number contour Plot Fig 28 shows the variation of Mach number contour plot across 5 stages. From the figure it is obvious that Mach number is increasing from the entry to exit and minimum Mach number of the order of occurred at the entrance of the guide blade and a maximum of is occurred at the throat of the guide blade and moving blade. Fig29 Velocity vector contour plots Page 47

28 Above Figure 29 shows the variation of the velocity across the each stage in the combined 5 stages. This a vector plot, which is a collection of vectors drawn to show the direction and magnitude of a vector variable on a collection of points and are defined by a location. From the figure it is obvious that the velocity is minimum at the entrance which is of m/sec and maximum at the throat of the stage which is around m/sec. 8. Comparison of CFD and 2D Experimental Values: The CFD analysis results are compared with 2D program output. The program output is verified experimentally. The comparison chart of 2D values and CFD values for 5 stages are shown in the table 4. The values obtained show that the CFD values are closer to 2D program and are within the acceptable limits. Table 4: Comparison of 2D value and CFD Value Stage 8 with Seals Description Units 2D Value CFD Value Mass Flow Rate Inlet Kg/s Temperature Inlet K Pressure Outlet Bar Specific Enthalpy Inlet KJ/kg Power MW Stage 9 with Seals Description Units 2D Value CFD Value Mass Flow Rate Inlet Kg/s Temperature Inlet K Pressure Outlet Bar Specific Enthalpy Inlet KJ/kg Power MW Stage 10 with Seals Description Units 2D Value CFD Value Page 48

29 Mass Flow Rate Inlet Kg/s Temperature Inlet K Pressure Outlet Bar Specific Enthalpy Inlet KJ/kg Power MW Stage 11 with Seals Description Units 2D Value CFD Value Mass Flow Rate Inlet Kg/s Temperature Inlet K Pressure Outlet Bar Specific Enthalpy Inlet KJ/kg Power MW Stage 12 with Seals Description Units 2D Value CFD Value Mass Flow Rate Inlet Kg/s Temperature Inlet K Pressure Outlet Bar Specific Enthalpy Inlet KJ/kg Power MW VI. Conclusions CFD study was carried out for evaluating the performance of a utility Steam Turbine IP Module. The flow in a turbine blade passage is complex and involves understanding of energy conversion in three dimensional geometries. The performance of turbine depends on efficient energy conversion and analyzing the flow path behavior in the various components IP Steam Turbine. Page 49

30 The CFD analysis of the turbine flow path helps in analyzing the flow and performance parameters and their effects on performance parameters like temperature, pressure and Power output. The Intermediate Pressure turbine consisting of 5 stages with cylindrical profiles used for stationary and moving blades. The blades are also designed with sealing strips between stationary parts and rotating parts to reduce leakage losses. The flow path of the turbine with blades and seals is modeled and meshed using different software s like IDEAS, ANSYS-ICEMCFD, ANSYS-TURBOGRID, etc. The mesh for the blade region is generated separately with ANSYS-TURBO-GRID and mesh for the seals are generated from ANSYS-ICEM-CFD and attached by General Grid Interface. The analysis is carried out for a single stage initially and subsequently for all the combined 5 stages. The combined analysis consists of large number of elements 17,34,379 nodes with many General Grid Interfaces and stage interfaces between multiple frames of reference. IBM Cluster computing server with P615 processor is used to obtain the solution using 4 processors with 2GB RAM each. The solution is converged with 1e-5 with high resolution. The results are analyzed for mass flow rates, temperature and pressure distributions on blades, power developed by stage and isentropic efficiency of the stage. The results are compared with TwoDimensional program validated by experimentally and found to be in agreement with the 2D analysis. The CFD analysis of the Intermediate Pressure turbine module has helped in predicting the turbine performance and comparing with experimentally verified values. V. References 1. C.W. Haldeman, R.M. Mathison; Aerodynamic and Heat Flux Measurements in a SingleStage Fully Cooled Turbine Part II, Journal of Turbomachinery, vol. 130/021016, April X.Yan, T.Takinuka; Aerodynamic Design Model Test and CFD Analysis for a Multistage Axial Helium Compressor, Journal of Turbomachinery, ASME paper,vol. 130/031018, July Arun K.Saha, Sumanta Acharya, Computations of Turbulent Flow and Heat Tansfer Through a Three-Dimensional Nonaxisymmetric Blade Passage, Journal of Turbomachinery, ASME paper, Vol. 130/031008, July Horloc, J.H., The Thermodynamics Efficiency of the Field Cycle, ASME paper, Vol. no. 57.A.44, Computational Fluid Dynamics, the basics with applications 6. Fluid Mechanics and hydraulic machines - John D. Anderson. Jr - Dr. R. K. Bansal 7. Numerical heat transfer and Fluid Flow - Suhas V. Patankar 8. Steam Turbine Theory and Practice - W. J. Kearton Websites: Page 50

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