INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET)

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1 INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 3, Issue 3, September - December (2012), pp IAEME: Journal Impact Factor (2012): (Calculated by GISI) IJMET I A E M E FLOW SIMULATION (CFD) & STATIC STRUCTURAL ANALYSIS (FEA) OF A RADIAL TURBINE Tarun Singh Tanwar 1, Dharmendra Hariyani 2 and Manish Dadhich 3 1 (Department of Mechanical Engineering, SKIT, Jaipur RTU Kota, India tarun_singh777@rediffmail.com) 2 (Department of Mechanical Engineering, SKIT, Jaipur RTU Kota, India dhariyani12002@gmail.com) 3 (Department of Mechanical Engineering, SKIT, Jaipur, RTU Kota, India scorpion.manish1988@gmail.com) ABSTRACT This paper describes the fluid flow conditions and parameters within a Radial Turbine with regards to each part of the turbine in contact with the working fluid and all working parts of the Radial turbine. The process of obtaining the fluid flow condition and characteristic within the turbine is done by Computational Fluid Dynamics (CFD) simulation with the help of Ansys. In this present work, flow behavior is observed inside the turbine at different guide vane angles and got the maximum Hydraulic efficiency for all cases and comparison is done between theoretical and experimental (CFD) efficiency. Characteristic curve is verified for all the different guide vane angles. For every case inlet velocity is changed as 10m/s, 7m/s, 4 m/s. CFD simulation is done with K-ω (SST) model and simplec algorithm. Before CFD simulation is done, a model of the Radial turbine needs to be selected as there are wide ranges of model ranging from conventional usage. After getting the best efficient model of radial turbine through CFD simulation, structural analysis would be done for runner and guide vanes. Gerber zero based model is used for the static structural analysis. Keywords cfd, flow simulation, static structure analysis, K-ω (SST) model, radial turbine 1. INTRODUCTION Hydroelectric energy is a clean, safe and renewable energy because it only requires water. Hydraulic turbines are the machines that convert the hydraulic energy into electricity, which are produced since many years ago. Mechanical efficiencies of these turbo machines are quite well, it reaches over 95% [8]. However, reaching such efficiencies is a difficult task and it requires a high engineering effort because hydraulic turbines are usually unique products which must be designed for determined local conditions (head and discharge). For this reason, for each 252

2 component of the machine, a specific design is needed. The traditional design process is based on experiments, measurements and model tests, which is too much time and money consuming. But from last two decades FEA and CFD simulation method is developed which are less time consuming and save money also. FEA simulation is basically based on structure simulation, main aim of structure simulation is to find the amount of force or pressure that much a structure can bear and according to that value of force or pressure, factor of safety decided. CFD simulation is required to judge the right flow behavior of fluid inside or outside the structure. It helps to make the necessary changes to improve the design. CFD simulation has many applications like aviation, automobile, hvac, turbo machinery, sports, biomedical, chemical industries etc. For the economical design of turbine it is very important to understand the flow characteristics indifferent parts of the turbine i.e. how energy transfer and transformation take place in the different parts, which help in analyzing their performance in advance before manufacturing them, it saves time and money both [6]. 2. GEOMETRIC MODELING Radial Turbine Geometry is designed with the help of Catia V5R20 and Ansys Blade Gen software. These are the basic component of Radial Turbine 1. Runner 2. Guide vanes 3. Spiral casing 4. Draft tube Runner is designed in Ansys BladeGen software and guide vanes, spiral casing and draft tube is designed in Catia V5R20. Finally these components are assembled in a single radial turbine with the help of Catia Assembly Design. Axis of turbine Types of draft tube Inlet runner diameter Outlet runner diameter No. of blades 10 Vertical Inlet blade angle Outlet blade angle guide vane angle 25 No of guide vanes 18 Blade width at inlet Blade width at outlet Inlet guide vane diameter Outlet guide vane diameter Elbow type mm mm mm 108 mm mm mm Table 2.1: Specification of turbine 253

3 Figure 2.1: Geometry of spiral casing and draft tube Figure 2.2: Geometry of guide vanes and runner Figure 2.3: Complete assembled geometry of radial turbine 254

4 3.MESHING The partial differential equations that govern fluid flow and heat transfer are not usually amenable to analytical solutions, except for very simple cases. Therefore, in order to analyze fluid flows, flow domains are split into smaller sub domains (made up of geometric primitives like hexahedra and tetrahedral in 3D and quadrilaterals and triangles in 2D). The governing equations are then discretized and solved inside each of these sub domains [3]. Typically, one of three methods is used to solve the approximate version of the system of equations: finite volumes, finite elements, or finite differences. Care must be taken to ensure proper continuity of solution across the common interfaces between two sub domains, so that the approximate solutions inside various portions can be put together to give a complete picture of fluid flow in the entire domain. The sub domains are often called elements or cells, and the collection of all elements or cells is called a mesh or grid [9]. The origin of the term mesh (or grid) goes back to early days of CFD when most analyses were 2D in nature. For 2D analyses, a domain split into elements resembles a wire mesh, hence the name. Figure 3.1: Mesh image of radial turbine Type of mesh No. of nodes No. of elements Tetra/mixed Table 3.1: Generated Mesh Detail 4. CFD ANALYSIS OF RADIAL TURBINE The analysis is carried in fluent by importing the meshed file saved in ansys icem cfd. The steps 255

5 that are followed are given below which include all the conditions and the boundaries values for the problem statement. In this project three different cases are taken through changing the guide vane angle and for each angle three different inlet velocities are taken. Results can get through streamlines, vector plot and velocity and pressure contour. Assumptions 4.1 The following assumptions were taken for simulation: The walls of the casing were assumed to be smooth hence any disturbances in flow due to roughness of the surface were neglected. The friction co-efficient for all surfaces were set to 0, hence friction between the walls and fluid was neglected. Steady state conditions and incompressible fluid flow. 4.2 Solution parameters 3-D double precision solver used to solve for simulation. Multiple reference frame technique used to simulate the pump performance. Clear water is taken as working fluid. Standard K-omega (SST) simulation model is used for turbulence modeling. Convergence criteria for continuity, velocity and turbulence parameters was set to 10. Second order scheme is used for pressure correction as well as for solving momentum, turbulent kinetic energy and turbulence dissipation rate. SIMPLEC scheme is used for pressure velocity coupling. 4.3 Stramline and Vector plot of Radial Turbine Figure 4.1: Stramline and vector plot of fluid flow in radial turbine 256

6 4.4 Velocity and Pressure contour for different cases Case 1.1 Velocity and pressure distribution at 10 m/s velocity of fluid flow for 30 degree guide vane angle and rpm at inlet Figure 4.2: velocity and pressure contour of fluid flow for 4 m/s at inlet Case 1.2 Velocity and pressure distribution at 7 m/s velocity of fluid flow for 30 degree guide vane angle and rpm at inlet Figure 4.3: velocity contour of fluid flow for 4 m/s at inlet Case 1.3 Velocity and pressure distribution at 4 m/s velocity of fluid flow for 30 degree guide vane angle and rpm at inlet 257

7 Figure 4.4: velocity and pressure contour of fluid flow for 4 m/s at inlet Case 2.1 Velocity and pressure distribution at 10 m/s velocity of fluid flow for 25 degree guide vane angle and rpm at inlet Figure 4.5: velocity and pressure contour of fluid flow for 10 m/s at inlet Case 2.2 Velocity and pressure distribution at 7 m/s velocity of fluid flow for 25 degree guide vane angle and rpm at inlet Figure 4.6: velocity contour of fluid flow for 7 m/s at inlet 258

8 Case 2.3 Velocity and pressure distribution at 4 m/s velocity of fluid flow for 25 degree guide vane angle and rpm at inlet Figure 4.7: velocity contour of fluid flow for 4 m/s at inlet Case 3.1 Velocity and pressure distribution at 10 m/s velocity of fluid flow for 20 degree guide vane angle and rpm at inlet Figure 4.8: velocity contour of fluid flow for 10 m/s at inlet Case 3.2 Velocity and pressure distribution at 7 m/s velocity of fluid flow for 20 degree guide vane angle and rpm at inlet Figure 4.9: velocity contour of fluid flow for 7 m/s at inlet 259

9 Case 3.3 Velocity and pressure distribution at 4 m/s velocity of fluid flow for 20 degree guide vane angle and rpm at outlet Figure 4.10: velocity contour of fluid flow for 4 m/s at inlet Contours Analysis: These are the different velocity and pressure contours for three cases of velocities for guide vane angle 30, 25 and 20. These contours are showing the distribution of velocity and pressure of fluid inside the radial turbine. According to these contours, it implies that velocity and pressure distribution in radial turbine is under acceptable condition. 4.5 Characteristic curve verification and comparison between theoretical and cfd results At 10 m/s Sr. No. G.V.A RPM Efficiency (T) Efficiency (CFD) % 90.28% % 95.51% % 96.15% Efficiency N (rpm) theoretical Figure 4.11: Graph between N (rpm) and efficiency at 10 m/s velocity At 7 m/s Sr. No. G.V.A RPM Efficiency (T) Efficiency (CFD) % 89.76% % 95.28% % 98.12% CFD 260

10 Efficiency N (r.p.m) Theoritical CFD Figure 4.12: Graph between N (rpm) and efficiency at 7 m/s velocity At 4 m/s Sr. No. G.V.A RPM Efficiency (T) Efficiency (CFD) % 92.13% % 95.47% % 97.97% Efficiency N (r.p.m) Theoretical CFD Figure 4.13: Graph between N (rpm) and efficiency at 4m/s velocity Efficiency curve analysis: These graphs are showing the hydraulic efficiencies of all the three velocity cases for theoretical and cfd. According to these graphs, it implies that our cfd and theoretical results are very close and under acceptable conditions by the characteristics curve. 5. STRUCTURE SIMULATION OF RUNNER Mesh generation of Runner for structural domain Mesh type Element size Physical preference Mapped face/tetra hadrons 5 mm Mechanical Table 7.4: Mesh input detail 261

11 Figure 5.1: Mesh picture of runner blades for structure domain Generated output after applying mesh input conditions No. of nodes No. of elements Table 5.1: Mesh output detail 5.1 Assumptions Number of r/s is constant that is Linear analysis is being done. Static structure analysis is being done. The model taken is Gerber zero based. 5.2 Boundary conditions Applied pressure on blade face is pa. Environmental temperature is 22 C. Figure 5.2: Boundary Condition 262

12 5.3 Results In structure analysis results are achieved through analyzing the von misses stress, total deformation and fatigue tool. Figure 5.3: Equivalent (von-mises) stress and Total deformation in runner blades Figure 5.4: Life and Damage of runner blade The Fatigue Life plot says that if the loading is of constant amplitude type, then the result from life represents the number of cycles till which the structure can withstand until it will fail due to fatigue. So from the above plot we can see that the structure will withstand up till maximum cycles. Fatigue Damage is a contour plot of the fatigue damage at a given design life. Fatigue damage is defined as the design life divided by the available life. For Fatigue Damage, values greater than 1 indicate failure before the design life is reached. In the preset scenario it can be seen that the damage values are less than 1, so the structure will not undergo fatigue damage. 263

13 Figure 5.5: Safety factor of runner blade Fatigue Safety Factor is a contour plot of the factor of safety with respect to a fatigue failure at a given design life. For Fatigue Safety Factor, values less than one indicate failure before the design life is reached. In present case the region below 1 does not exist so factor of safety is maximum for this case. Graph between equivalent (von mises) stress and blade edge length figure 5.6: Graph between equ.(von mises) stress and blade edge length Graph between total deformation and blade edge length Figure 5.7: Graph between total def. and blade edge length 264

14 These graphs are showing the von mises stress and total deformation with blade edge length and according to these graphs it implies that von mises stress and total deformation is varying with respect to blade edge length. 6. STRUCTURE SIMULATION OF GUIDE VANES Mesh Generation of Guide Vanes for Structural Domain Mesh type Element size Physical preference Mapped face/tetrahedron 5 mm Mechanical Table 6.1: Mesh input detail Figure 6.1: Generated mesh of guide vanes Generated output mesh detail for guide vane in structure domain No. of nodes No. of elements Table 6.2: Mesh Output Detail 6.1 Assumptions No rotation is there. Linear analysis is being done. Static structure analysis is being done. The model taken is Gerber zero based. 6.2 Boundary conditions Applied pressure on blade face is pa. Environmental temperature is 22 C. 265

15 Figure 6.2: Boundary conditions 6.3 Results In structure analysis results are achieved through analyzing the von misses stress, total deformation and fatigue tool. Figure 6.3: Equ. (von-mises) stress and Total Deformation in in guide vanes Figure 6.4: Life and Damage in guide vane 266

16 The Fatigue Life plot says that if the loading is of constant amplitude type, then the result from life represents the number of cycles till which the structure can withstand until it will fail due to fatigue. So from the above plot we can see that the structure will withstand up till maximum cycles. Fatigue Damage is a contour plot of the fatigue damage at a given design life. Fatigue damage is defined as the design life divided by the available life. For Fatigue Damage, values greater than 1 indicate failure before the design life is reached. In the preset scenario it can be seen that the damage values are less than 1, so the structure will not undergo fatigue damage. Fatigue Safety Factor is a contour plot of the factor of safety with respect to a fatigue failure at a given design life. For Fatigue Safety Factor, values less than one indicate failure before the design life is reached. In present case the region below 1 does not exist so factor of safety is maximum for this case. Figure 6.5: Safety factor in guide vane Graph for Equ.(von mises) stress and Total Deformation wth guide vane edge length Graph 6.6: Graph for Equ.(von mises) stress and Total deformation(vertical) with guide vane edge length(horizontal) 267

17 These graphs are showing the von mises stress and total deformation with guide vane edge length and according to these graphs according to it von mises stress and total deformation is varying with respect to guide vane edge length. 7. CONCLUSION AND FUTURE SCOPE 7.1 Conclusion This project brought out the validation of CFD results with theoretical results. The maximum efficiency regime indicated by both approaches is nearly same. Reason for slight difference of efficiency computed by theoretically and CFD method can be because of human errors and due to discretisation of domains and solution of differential equations in computational methods. Hence the result obtained are fairly matching, however streamlines flow in some reasons have some turbulence which is due to occurrence of loses and losses are not considered very precisely. Prediction of turbine performance by CFD gives the idea to know the flow behavior inside the turbine model and get the information about the intricacy of flow pattern. After getting best model according to the cfd analysis, stress analysis on runner blades and guide vane blades is being done. In this section fatigue analysis is checked and found the life, damage and factor of safety for that model. According to structure analysis blades are having maximum life and damage is minimum. In other hand factor of safety is also maximum which implies that this model is completely safe. 7.2 Future scope 1. Simulation can be done on the turbine considering losses. 2. Simulation can be done on the other hydraulic turbines like Kaplan turbine, pelton wheel etc. REFERENCE [1] Zhen Wang, Tao Zhang Research on Tangential Type Turbine Flow meter Based on Simulation International Conference on Mechatronics and Automation August 5-8, 2007, Harbin, China [2] Ruchi Khare, Dr. Vishnu Prasad, Dr. Sushil Kumar cfd approach for flow characteristics of hydraulic francis turbine International Journal of Engineering Science and Technology,Vol. 2(8), 2010, [3] Kiran Patel1, Jaymin Desai2, Vishal Chauhan2 and Shahil Charnia2, Evaluation of Hydro Turbine design by Computational Fluid Dynamics 11 th Asian International Conference on Fluid Machinery and 3 rd Fluid Power Technology Exhibition Paper ID: AICFM_TM_016. [4] Zhang Shujia, Zhu Baolin, Hu Qingbo and Li Xianhua, Virtual performance experiment of a centrifugal pump, 16th International Conference on Artificial Reality and Telexistence-- Workshops (ICAT'O6) [5] Helmut Keck, Wolfgang Michler, recent developments in the dynamic analysis of water turbines Scientific Bulletin of the Politehnica University of Timisoara Transactions on Mechanics Tom 52(66), Fascicola 6, [6] Sanjay Jain, R. P. Saini, Arun Kumar, CFD APPROACH FOR PREDICTION OF EFFICIENCY OF FRANCIS TURBINE, IGHEM-2010, Oct 21-23, 2010, AHEC, IIT Roorkee, India. [7] Weidong Zhou, Zhimei Zhao, T. S. Lee and S. H.Winoto, Investigation of Flow Through Centrifugal Pump Impellers Using Computational Fluid Dynamics, International Journal of Rotating Machinery, vol.-9, no.-1, pp ,

18 [8] Santiago Laín1*, Manuel García2, Brian Quintero1, Santiago Orrego2, CFD Numerical simulations of Francis turbine Simulación numérica (CFD) de turbinas Francis Rev. Fac. Ing. Univ. Antioquia N. 51 pp Febrero, [9] Ruprecht, A., Heitele, M., Helmrich, T., Numerical Simulation of a Complete Francis Turbine including unsteady rotor/stator interactions Institute for Fluid Mechanics and Hydraulic Machinery University of Stuttgart, Germany. [10] V.J. Lakhera, S.V. Jain and S.R. Shah, CFD BASED FLOW ANALYSIS OF CENTRIFUGAL PUMP, 37th National & 4th International Conference on Fluid Mechanics and Fluid Power IIT Madras, December [11] Teodor Miloş 1, Romeo Susan-Resiga 2, Alexandru Baya 3, Sebastian Muntean 4, Sandor Bernad 5 Development of francis turbine model with swirling flow control 269