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, Septmebr - December (2012), pp IAEME: Journal Impact Factor (2012): (Calculated by GISI) IJMET I A E M E FLOW SIMULATION (CFD) & FATIGUE ANALYSIS (FEA) OF A CENTRIFUGAL PUMP Manish Dadhich 1, Dharmendra Hariyani 2 and Tarun Singh 3 1 (Department of Mechanical Engineering, SKIT, Jaipur, RTU Kota, India scorpion.manish1988@gmail.com) 2 (Department of Mechanical Engineering, SKIT, Jaipur RTU Kota, India dhariyani12002@gmail.com) 3 (Department of Mechanical Engineering, SKIT, Jaipur RTU Kota, India tarun_singh777@rediffmail.com) ABSTRACT In the present work the CFD analysis of a centrifugal pump is done using k- turbulent modeling and SIMPLEC algorithm. In this work the mass flow rate is varied three times for two different fluids that are water and fuel oil. Firstly the mass flow rate is decreased by 10% from the initial value of mass flow rate and then increased by 10% from the initial value of mass flow rate. Using the results of varying mass flow rate the efficiency at different mass flow rate is calculated. The results are compared with the theoretical results. Then the theoretical and software results are plotted in the operating characteristics curves and are verified. The deviation produced among them nearly 10% to 15 % is permissible. Secondly the number of RPM has been changed by decreasing and increasing by 10% and results are compared with the experimental results and verified through operating characteristics curves. After the complete flow analysis the maximum pressure acting on the blades for the maximum efficiency in case of water and fuel oil is calculated and the fatigue (FEA) analysis of a centrifugal pump is done. Analysis is linear static structural and the model used is Gerber zero based. From fatigue analysis we can determine whether the pump is safe to run in the operating conditions by plotting various curves of the fatigue analysis and design can be improved. Key words: CFD, Fatigue, k- turbulent model and SIMPLEC algorithm. 1. INTRODUCTION Turbo machinery in mechanical engineering describes machines that transfer energy between a rotor and a fluid, machines are governed by the same basic relationships including Newton's second Law of Motion and Euler's energy equation [3] for fluids. Centrifugal pump are also turbo machines that transfer energy from a rotor to a fluid usually a liquid. Pump has very wide 67

2 range of turbo machinery applications; it plays an important role in various sectors of the industries. Many centrifugal pumps types have been constructed e.g. centrifugal slurry pump [20] and are used in different applications in industry and other technical sectors. However, their design and performance prediction process is still a difficult task, mainly due to the great number of free geometric parameters, the effect of which cannot be directly evaluated. For this reason CFD analysis is currently being used in the design and construction stage of various pump types. Using CFD analysis the internal flow conditions of the pump can be predicted and can be analyzed. From the CFD analysis software and advanced post processing tools the complex flow inside the impeller can be analyzed. FEA analysis helps us to know the fatigue life of the pump. Numerical simulation of centrifugal pumps is not easy due to the usual CFD difficulties: turbulence, separation, boundary layer [1] etc. Although there are also specific problems: Complex geometry, Energy transfer is generated mainly by the centrifugal force in the impeller etc.cfd and FEA has probed to be a very useful tools in the analysis of these turbo machines, both in design and performance prediction. Many researches have been done on the flow analysis of the centrifugal pump. The purpose of the present study is to show the flow simulation (CFD) & fatigue analysis (FEA) of a centrifugal pump using the commercial software s like Catia (V5R20) and ANSYS 12. From the past researches it was seen that only the CFD analysis of the pump was done. In the present work the CFD and FEA analysis were coupled to carry out the fatigue analysis of the centrifugal pump. In the CFD analysis the mass flow rate and number of RPM [2] were varied for the flow analysis and results obtained from the CFD analysis were implemented to carry out fatigue (FEA) analysis. From the fatigue (FEA) analysis we can determine whether the pump is safe to run on the operating conditions if not further design can be improved for the long life of the pump. In the CFD analysis results were compared with the experimental results. The results calculated from the CFD analysis were implemented to carry out the FEA analysis. In the CFD analysis two working fluid water and fuel oil were taken and the comparative study was also done. Basically CFD involves the numerical solution of the equations like Navier Stokes equation [20], energy equation etc. 2. MODELLING AND MESHING OF PUMP To study the numerical analysis on the pump, the dimension data of the pump was required to generate a model in the software. The assembly consist the casing and impeller. The modelling was done in two different software s Catia and ANSYS 12. This was because Catia is modelling software and has sophisticated modelling tools that helped in modelling the complex geometries [12]. Apart from the modelling tools the software has features that helped in creating crosssections at different locations which helped in better visualization and understanding of the actual pump geometry and ANSYS 12 software helps us in designing the complex geometry like impeller and other parts of the turbo machinery. 2.1 Dimensions of the pump 1. Head [4] on which the pump is working = 15m 2. Inlet diameter of impeller = 170mm 3. Outlet diameter of impeller = 280mm 68

3 4. No. of RPM on which pump is running = Inlet blade angle = 16 [12] 6. Outlet blade angle = 27 [12] 7. Width of impeller at inlet = 84mm 8. Width of impeller at outlet = 45mm 9. Shaft power of the pump = 25 kw 10. Number of blades (Vanes) on impeller = Blade (Vanes) thickness= 8mm Fig. 2.2 assembly model of pump components 12. Blade height = 47 mm Fig. 2.1 model of impeller Fig. 2.3 final assembly model of pump components 69

4 Fig. 2.4 meshing of pump assembly (tetrahedral) Meshing of the pump assembly is done by using ANSYS 12. Meshing of the pump consist of tetrahedral elements [9]. Meshing consists of following numeric values: Number of elements= Number of nodes= COMPUTATIONAL EVALUATION OF PUMP PERFORMANCE 3.1 Flow Simulation of Pump After meshing of the model of pump assembly commercial CFD code FLUENT [13] is used for simulation of the pump performance.the boundary conditions of mass flow rate given at pump inlet. The performance results are obtained at different mass flow rate conditions with constant operating rotational speed and second case is by varying the operating rotational speed. In both the above mentioned cases the operating fluid is changed from water to fuel oil. Numerical (Software) performance results compared with the theoretical results at the same operating conditions [16] Assumptions 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 and pump is vibration free [10]. The friction co-efficient for all surfaces were set to 0, hence friction between the walls and fluid was neglected and wall boundary with no slip boundary condition [19]. Steady state conditions and incompressible fluid flow [15] Solution parameters 3-D double precision solver used to solve for simulation [17]. Multiple reference frame [8] technique used to simulate the pump performance. Clear water [11] and fuel oil are taken as working fluid. Standard K-Epsilon [6] simulation model is used for turbulence modelling. Convergence criteria [5] for continuity, velocity and turbulence parameter was set to10. 70

5 Second order scheme is used for pressure correction as well as for solving momentum, turbulent kinetic energy and turbulence dissipation rate [18]. SIMPLEC [7] scheme is used for pressure velocity coupling. 3.2 Streamline and Vector Plot of Pump in Case of Water Fig. 3.1 streamline plot of pump in case of water Fig. 3.2 vector plot of pump in case of water 3.3 Velocity and Pressure Distribution of Pump in Case of Water (When changing the mass flow rate) Velocity and pressure distribution of pump at mass flow rate kg/s (initial) Fig. 3.3 velocity distribution at mass flow rate=130.9 kg/s Fig. 3.4 pressure distribution at mass flow rate=130.9kg/s 71

6 3.3.2 Velocity and pressure distribution of pump at mass flow rate kg/s (10% decrease from initial) Fig. 3.5 velocity distribution at mass flow rate=117.8kg/s Fig. 3.6 pressure distribution at mass flow rate=117.8kg/s Velocity and pressure distribution of pump at mass flow rate kg/s (10% increase from initial) Fig. 3.7 velocity distribution at mass flow rate=143.9kg/s Fig. 3.8 pressure distribution at mass flow rate=143.9kg/s 72

7 3.4 Velocity and Pressure Distribution of Pump in Case of Water (Changing the RPM of pump) Velocity and pressure distribution of pump at 1150 RPM (initial) Fig. 3.9 velocity distribution at 1150 RPM Fig pressure distribution at 1150 RPM Velocity and pressure distribution of pump at 1035 RPM (10% decrease) Fig velocity distribution at 1035 RPM Fig pressure distribution at 1035 RPM 73

8 3.4.3 Velocity and pressure distribution of pump at 1265 RPM (10% increase) Fig velocity distribution at 1265 RPM Fig pressure distribution at 1265 RPM 3.5 Performance Characteristic of Pump using Water The performance characteristic of the centrifugal pump has been predicted experimentally and through software handling water. Efficiency, discharge, mass flow rate and number of RPM characteristics of the pump are predicted by CFD analysis [14]. The numerical simulation on pump performance handling water by varying the mass flow rate and number of RPM three times and the efficiency and discharge are calculated by using turbulent modelling namely as K- Epsilon. The parameters namely efficiency and discharge rate are tabulated for a constant head pump of 15m. Table 3.1 Result of pump performance by experimental and simulation at different mass flow rate (kg/s) Table 3.2 Result of pump performance by experimental and simulation at different number of RPM (N) From the above mentioned theoretical and software results we see that there is only slight variation nearly about 1% to 2% which is permissible up to 10%. So we conclude that our results are satisfactory. 74

9 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME 3.6 Characteristic Curves of the Pump using Water Fig efficiency vs. discharge curve for the Fig discharge vs. number of RPM curve for case of water the case of water From the characteristics curves we see that there is only slight variation between theoretical and software results and characteristics curves are verified which means that simulation through software is correct. 3.7 Streamline and Vector Plot of Pump in Case of Fuel Oil Fig streamline plot of pump in case of fuel oil Fig vector plot of pump in case of fuel oil 3.8 Velocity and Pressure Distribution of Pump in Case of Fuel Oil (When changing the mass flow rate) Velocity and pressure distribution of pump at mass flow rate kg/s (initial) Fig velocity distribution at mass flow rate=125.6kg/s Fig pressure distribution at mass flow rate=125.6kg/s 75

10 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Velocity and pressure distribution of pump at mass flow rate kg/s (10% decrease from initial) Fig velocity distribution at mass flow Fig pressure distribution at mass flow rate=113.0kg/s rate=113.0kg/s Velocity and pressure distribution of pump at mass flow rate kg/s (10% increase from initial) Fig velocity distribution at mass flow rate=138.2kg/s Fig pressure distribution at mass flow rate=138.2kg/s 3.9 Performance Characteristic of Pump using Fuel Oil The performance characteristic of the centrifugal pump has been predicted experimentally and through software handling fuel oil. Efficiency, discharge and mass flow rate characteristics of the pump are predicted by CFD analysis. The numerical simulation on pump performance handling fuel oil by varying the mass flow rate three times and the efficiency is calculated by using turbulent modelling namely as K- Epsilon. The parameter namely efficiency is tabulated for a constant head pump of 15m.The results for the number of RPM is same as case of water. 76

11 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Table 3.3 Result of pump performance by experimental and simulation at different mass flow rate (kg/s) Fig efficiency vs. discharge curve for the case of fuel oil 3.10 Characteristic Curves of the Pump using Fuel Oil From the above mentioned theoretical and software results we see that there is only slight variation nearly about 1% to 2% which is permissible up to 10%. So we conclude that our results are satisfactory. From the above mentioned characteristics curves we see that there is only slight variation between the theoretical and software results and characteristics curves are also verified which means that simulation through software is correct. But when the comparison is made between the water and fuel oil we see that is case of fuel oil the efficiency is decreased this happen because of the decrease of the density. The discharge vs. RPM curve remains the same in case of fuel oil because there is no impact of the density in the calculations Structural Simulation of Pump (Impeller and Blades) After the completion of the flow analysis the structural analysis of the pump is being done. Structural analysis includes the fatigue testing of the impeller of the pump. The fatigue testing on the impeller of the pump is done by applying the pressure on the impeller. The pressure applied on the impeller is calculated from the pressure contour of the maximum efficiency in case of water and fuel oil respectively. The pressure applied is somewhat less than that of the maximum pressure coming in the contour Assumption Number of RPM is constant that is Linear analysis is being done. Static structure analysis is being done. The model taken is Gerber zero based 3.12 Meshing of the Impeller of the Pump Meshing of the impeller of the pump is being done by using ANSYS workbench software by applying various meshing techniques. The meshing of the impeller is shown below in the figure. 77

12 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Number of elements=46382 Number of nodes= Fig structural meshing of the impeller of the pump 3.13 Structural Simulation in Case of Water From the contour plot of pressure of maximum efficiency we calculate the pressure just below the maximum pressure which is acting on the impeller and we apply that pressure in the structural analysis and we get the contour of total deformation, equivalent stress, fatigue life, fatigue damage and fatigue factor of safety and then we analyse the results for the fatigue failure of the impeller of the pump. The pressure acting in the case of water is Pa Total Deformation and Equivalent Stress in Case of Water Fig total deformation of impeller in case of water Fig equivalent stress of impeller in case of water 78

13 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Fatigue analysis results of impeller in case of water Fig fatigue life of impeller in case of water Fig fatigue damage of impeller in case of water Fig fatigue safety factor of impeller in case of water From the above three fatigue analysis diagram we observe that when a pressure of Pa is applied on the impeller the impeller is safe to use and it will run through maximum life cycle (material cycle) without any failure. The fatigue life plot says that if the applied pressure is of constant amplitude type then from the results from life represents the number of life cycles with 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. Damage is defined as the design life divide by available life. Fatigue damage shows that no damage is there when the impeller is working under this operating pressure and number of RPM. Fatigue safety factor is a contour plot of the factor of safety with respect to fatigue failure at given design life. From the above figure it is shown that factor of safety is 15.Generally the factor of safety is taken as 3 to 5 and figure shows 15 which means impeller is safe to use at particular operating conditions Structural Simulation in Case of Fuel Oil The pressure acting in the case of fuel oil is Pa 79

14 6340(Print), ISSN (Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Total Deformation and Equivalent Stress in Case of fuel oil Fig total deformation of impeller in case of Fig equivalent stress of impeller in case of fuel oil fuel oil Fatigue analysis results of impeller in case of fuel oil Fig fatigue life of impeller in case of fuel oil Fig fatigue damage of impeller in case of fuel oil Fig fatigue safety factor of impeller in case of fuel oil 80

15 From the above three figure of fatigue analysis we observe that these figure resemble with the figure of the water. So we can say that pump is safe to use in case of fuel oil under the operating conditions of applied pressure and number of RPM Curves of Total Deformation and Equivalent Stress Fig curve of total deformation acting on hub (water and fuel oil) Fig curve of total deformation acting on blade tip (water and fuel oil) Fig curve of equivalent stress acting on hub (water and fuel oil) Fig curve of equivalent stress acting on blade tip (water and fuel oil) From the above graphs of total deformation and equivalent stress acting on the hub and blade tip a comparison of the results of the water and fuel oil is being done and from the above graphs we can observe that only a slight variation is there between water and fuel oil in total deformation and equivalent stress acting on the hub and blade tip respectively. In both the cases structure is safe to use. 4. CONCLUSION AND FUTURE WORK The geometry of pump (impeller and casing) is modelled using ANSYS 12 and Catia. The mesh is generated successfully using ANSYS 12. Complex internal flow field, pressure and velocity 81

16 distribution investigated using FLUENT commercial computational code. The simulation results are obtained at different operating mass flow rates and three different number of RPM for transportation of clear water and fuel oil. The simulation was performed by using turbulent model k-epsilon and SIMPLEC algorithm. Software performance results at different conditions are compared with the theoretical results. Characteristics curves were plotted using software results and theoretical results. Results obtained were satisfying the characteristics curves and there was only a slight variation among the software and theoretical results nearly 1% to 2% for both the cases of water and fuel oil. But when we compare the efficiency of water and fuel oil we see that is case of fuel oil the efficiency is decreased this happen because of the decrease of the density of the fuel oil. In the structural analysis the fatigue analysis of the pump was done by applying the pressure on the pump. The analysis was linear static structural and the model used was Gerber zero based. The pressure was calculated from the pressure contour of the flow analysis. From the results of the fatigue analysis of the pump for both the cases i.e. water and fuel oil the conclusions were that pump was safe to run on the operating conditions without any damage or distortion. The factor of safety of the pump was also acceptable. Certain graphs of total deformation and equivalent stress acting on the hub and blade tip were plotted and the comparison of the results of the water and fuel oil was being done. From the graphs it was observed that only a slight variation was there between water and fuel oil in total deformation and equivalent stress acting on the hub and blade tip respectively. In both the cases structure was safe to use. Future Scope 1. Pressure and velocity distribution can be calculated for a centrifugal slurry pump by multiphase modelling. 2. Losses can be considered for the computational simulation of centrifugal pump. 3. Computational simulation models can also be used for analyzing the pressure, velocity and stress distribution of the other turbo machines like turbines, compressor, fan and blower. 4. Modal analysis of the centrifugal pump can also be done for the vibration analysis. REFERENCES [1] Blanco-Marigorta, Eduardo and Fernández-Francos, Numerical Flow Simulation in a Centrifugal Pump with Impeller -Volute Interaction, ASME 2000 Fluids Engineering Division Summer Meeting, June [2] B.K Gandhi, S.N. Singh and V. Seshadri, Effect of Speed on the Performance Characteristics of a Centrifugal Slurry Pump, Journal of fluid Engineering, February [3] E. Cezmi Nursen and Erkan Ayder, Numerical Calculation of the Three-Dimensional Swirling Flow inside the Centrifugal Pump Volutes, International Journal of Rotating Machinery, vol.-9, pp , [4] 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 , [5] Miguel Asuaje, Farid Bakir, Smaiıne Kouidri, Frank Kenyery and Robert Rey, Numerical Modelization of the Flow in Centrifugal Pump: Volute Influence in Velocity and Pressure Fields, International Journal of Rotating Machinery, vol.-3, pp ,

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