DESIGN AND CFD ANALYSIS OF A CENTRIFUGAL PUMP 1 CH.YADAGIRI, 2 P.VIJAYANAND 1 Pg Scholar, Department of MECH, Holymary Institute of Technology, Ranga Reddy, Telangana, India. 2 Assistant Professor, Department of MECH, Holymary Institute of Technology, Ranga Reddy, Telangana, India. Abstract Centrifugal blowers play an important role in many industries. This project presents a design methodology to examine various parameters of the centrifugal blower using computational fluid dynamics approach and Finite Element Analysis concept. The effects of blower geometry, blower speed, impeller geometry, and blade design and fillet radius have been assessed. Total discharge and blower total efficiency are the output parameters calculated. The blower is modeled and simplification the modeled blower is meshed in Gambit CFD. The solution is obtained using FLUENT. The post processing is carried out using ANSYS and the results are presented and discussed in detail. Based upon the ANSYS results once again blower parameters are changed and examined. Finally the optimum values of the parameters are obtained. These obtained values need to be implemented into the design for better performance of the blower. KEY WORDS: Centrifugal blower, Computational Fluid Dynamics (CFD), Optimization. I INTRODUCTION A pump is a machinery or device for compressing or transferring liquid. The fluid can be gas or liquid. Pumps are the most often sold and used mechanical devices that can be used in almost every industry. In general, the family of pumps can be segregated as positive displacement pumps and kinetic pumps. A sub-category of kinetic pumps are centrifugal pumps which are again segregated as radial pumps, mixed flow pumps, axial pumps. But even at the axial end of the spectrum there is a part of energy coming from centrifugal force unless most of the energy is generated by vane action. There are several other pumps which combine the principles of both placed in between the two extremes of the centrifugal pump which are known as the mixed flow impellers. Characteristic for centrifugal pump are low specific speeds. Principle of centrifugal pumps: A centrifugal pump is a roto dynamic pump that uses the pressure of the rotating impeller to increase the pressure of the fluid. The fluid enters the pump at the rotating axis, streaming into the rotating impeller. The impeller consists of several vanes attached to it. The vanes normally slope backward away from the direction of rotation. When the fluid enters the impeller at certain velocity due to suction system, it is captured by the rotating impeller vanes. The fluid is accelerated by pulse transmission while following the curvature of the impeller vanes from the eye of the impeller outwards. It reaches its maximum velocity at the impeller s outer diameter and leaves the impeller into a diffuser or volute chamber. So the centrifugal force assists the accelerating fluid particles because the radius at which the particles enter the impeller is smaller than the radius at which the individual particles leave the impeller. Now the fluid s energy is converted into static pressure assisted by the shape of diffuser or the volute chamber. The process of energy conversion in fluid mechanics follows Bernoulli s principle which shows that the sum of all forms of energy in a streamline is same on the two points of the path. The total head energy in a pump system is the sum of potential head, static pressure head and velocity head.
for various velocities, thus, increasing the rate of flow or discharge of the centrifugal pump and to optimize its hydraulic efficiency. The operating conditions which are considered for the analysis are -: LITERATURE REVIEW: Many researchers have been examined on centrifugal pumps.patel and Radhakrishnan carried out research on mixed flow pump (NSQ = 46) at duty point and also at part load conditions. Muggli et al,1997 applied Navier- Stokes code with the standard k-turbulence for CFD analysis of highly loaded pump diffuser flows. Hamkins and Bross,2002 have shown how modern image analysis methods allow quantitative predictions of the corresponding pressure distributions by analyzing surface flow patterns. They mentioned that the surface flow patterns can also be used to adjust boundary conditions for CFD simulations by trial and error method. Medvitz et al,2002 used multiphase CFD method to analyze centrifugal pump performance under cavitating conditions. They used homogeneous TWO-PHASE RANS equations wherein mixture momentum and volume continuity equations were solved along with vapor-volume fraction.zhou et al 2003 carried out numerical simulation of internal flow in three different types of centrifugal pumps. A commercial three dimensional Navier-Stokes code called CFX with a standard k-two-equation turbulence model was used. They found that the predicted results relating to twisted blade pumps were better than those relating to straight pumps which suggests that the twisted blade pump will be better than that of a straight blade pump. BachaRoudis et al,2008 carried out parametric study of impellers with same outlet diameter having different outlet blade angles. The numerical solution of the discretized 3-D incompressible Navier-Stokes equations over an unstructured grid was accomplished with a commercial CFD code.spence and Teixeira,2009 used multi-block structured grid CFD code to carry out parametric study of double entry, double volute centrifugal pump. The cut water gap and vane arrangement were found to exert greatest influence across various monitored locations and flow range. SCOPE OF THE PROJECT: This technical work on the centrifugal pump with various number of blades is considered and Computational Fluid Dynamics (CFD) is used to analyze its operating conditions Varying the velocities at different boundary conditions of the 2-D centrifugal pump with for 5number of blades. Varying the velocities at different boundary conditions of the 2-D centrifugal pump with for 6number of blades. Varying the velocities at different boundary conditions of the 2-D centrifugal pump with for 7number of blades. Varying the velocities at different boundary conditions of the 2-D centrifugal pump with for 8number of blades. With this variation of mass flow rates, the behavior of the following properties is analyzed -: Pressure Velocity Turbulence The CFD principles which are made use in this technical work are effective and appropriate methods that using finite volumes to solve the processes that consist of transport phenomena. The necessary numerical computations are accomplished by FLUENT12.1 (the CFD solver program) and the results are given in graphical representation. The velocity, pressure profiles and turbulence zones in centrifugal pump are very useful aids for reliable, high efficiency and economical design or optimization. Although the most existent designs use experimental methods, but as a outcome of growth and development of numerical methods and the softwares which can solve the PDE, the tendency for analyses of fluid flow are appeared. The different velocities employed for the analysis of the centrifugal pump are -:
5m/s, 10m/s, 15m/s, 20m/s, 25m/s. Volume 3, Issue 3 AUG 2015 CFD SIMULATION OF THE CENTRIFUGAL PUMP GEOMETRICDETAILS METHODOLOGY: The research methodology adopted is as shown in figure. Initially a literature survey was conducted for the topic of interest and suitable literature regarding the topic was collected. Then from the collected literatures the scope for future work and the modifications that can be made was studied. Then the problem was completely defined based on the literature survey. The problem was to analyze a heat pipe which consisted of a rectangular flat plate twisted comprising of orifice(holes) within the twist insert. The modeling and meshing of the geometry was carried out using GAMBIT2.4.6. Three-dimensional axi-symmetric model of the heat pipe was created and meshed. The boundaries were defined in GAMBIT and then the meshed model was exported to FLUENT12.1 for analysis. The analysis was carried out in FLUENT with different boundary conditions. The results obtained were compared with experimental results obtained for validation. The analysis was also carried out for different mass flow rates with and without the orifice and thereby the results obtained were used to predict the operating conditions. In any CFD analysis, the fluid domain creation plays an important role as the solution convergence depends on the mesh quality which in turn depends on the geometry of the domain. The three-dimensional model was created using bottom-up approach. As the impeller blade profile is complex enough care was taken in creation of impeller domain in GAMBIT CFD which is a pre-processor of FLUENT. Casing, which is relatively simple in construction, was also created in GAMBIT CFD in a simplest way so as to get a better as the quality of mesh depends on the complexity of the geometry. The centrifugal pump is modeled by using a CFD technique GAMBIT 2.4 with the following specifications: Model of the Centrifugal Pump:
The boundary conditions employed to compare the performance of the centrifugal pump geometry are: Meshing of Centrifugal Pump : Meshing technique is employed in CFD analysis for solving the problems in Finite Volume Method. In this technique, the component is divided into discrete elements each of which consists of several nodes. While analyzing a problem, each element is considered and hence enhancing the accuracy of the result obtained. The model is then meshed using GAMBIT and the mesh near to the wall was refined using boundary layer meshing. The simulations were carried out over a 11 different operating points with two different turbulence models namely renormalization group (RNG) k-model and shear stress transport (SST) k- model. Mass flow rate correspond to different operating points was specified at the suction of impeller while total pressure was defined at the casing outlet. The flow in the impeller was computed in the moving reference frame, while the flow in the casing was calculated in the stationary reference frame. Between impeller and casing grid interface was used. Different boundary conditions for the computational domain are 1) INLET 2) Blades Velocity=5 m/s Temperature=298 K Rotating blades at 800 r.p.m 3) Point1 At distance of X = -3.272, Y = 170.37 4) Point2 At distance of X = -53.451, Y = -84.515 5) Point3 At distance of X = 83.653, Y = 132.268 6) Point4 At distance of X = 46.727, Y = 170.372 7) Point5 Boundary Conditions: The impeller inlet is taken as velocity inlet and the delivery pipe is taken as pressure outlet. The casing and the rotating blades of the impeller is defined as the wall. The interior of the centrifugal pump is however considered as the wall boundary type. At distance of X = 36.972, Y = 92.914 8) Point6 At distance of X = 38.234, Y = 96.084 9) Outlet
NUMERICAL ANALYSIS OF THE CENTRIFUGAL PUMP Volume 3, Issue 3 AUG 2015 Contours Configuration Study of the static pressure contours help in understanding of energy conversion taking place in different parts of the centrifugal pump. Also it is possible to locate the regions of low pressure which may be subjected to cavitation. In the centrifugal pump, it is seen that the pressure continuously decreases. It was also observed that the pressure fall was quite gradual and uniform Pressure Contours at 5 m/s Pathline Configuration Pathline represents the trace of trajectory of a fluid particle over a period of time. Their study helps in understanding of particle movement identification of zones of vortex formation and secondary flow. Pressure Pathlines
Turbulence Pathlines:
Velocity Pathlines
Pressure contoursat 10 m/s: Turbulence contours at 10m/s:
Velocity contours at 10 m/s:
Pressure Pathlines at 10m/s:
Turbulence Pathlines at 10m/s:
Velocity pathlines at 10m/s:
At inlet velocity 15m/s: RESULT ANALYSIS Results of Numerical Analysis of Centrifugal Pump: At inlet velocity 5m/s The pressure and velocity are found to gradually improve from the points nearer to inlet to the points at outlet region. However, the turbulence is found depleting with the increasing number of blades and hence indicating that the more number of blades causes vortex flow. At inlet velocity 10m/s: The pressure and velocity are found to gradually improve from the points nearer to inlet to the points at outlet region. However, the turbulence is found depleting with the increasing number of blades and hence indicating that the more number of blades causes vortex flow. At inlet velocity 20m/s The pressure and velocity are found to gradually improve from the points nearer to inlet to the points at outlet region. However, the turbulence is found depleting with the increasing number of blades and hence indicating that the more number of blades causes vortex flow. The pressure and velocity are found to gradually improve from the points nearer to inlet to the points at outlet region. However, the turbulence is found depleting with the increasing number of blades and hence indicating that the more number of blades causes vortex flow. At inlet velocity 25m/s
Velocity Variation at all positions The pressure and velocity are found to gradually improve from the points nearer to inlet to the points at outlet region. However, the turbulence is found depleting with the increasing number of blades and hence indicating that the more number of blades causes vortex flow. Graphs drawn showing the variation of pressure, velocity & turbulence Pressure Variation at all positions Turbulence Variation at all positions
Additional blades can be mounted upon the impeller to improve the efficiency of the pump. The speed of the rotor can be varied and thereby optimizing its efficiency REFERENCES: [1]. Yahya S M. 1998. Turbines Compressors and Fans. Tata Mc-Graw Hill Edition. [2]. Anderson J.D. 2012. Computational fluid dynamics. Tata Mc-Graw Hill Edition. [3]. Bogdam Gherman, Cristina Silivestru and Marian Draghici, Aerodynamic geometry optimization of a centrifugal blower. [4]. Asad Said Jama Al Zadjali and G.R Rameshkumar, Condition monitoring of centrifugal blower using vibration analysis. [5]. B.A Kardile, Bearing life improvement of centrifugal blowers by vibration analysis. CONCLUSION: Based on the computational investigation to analyze the performance of centrifugal pump, the following conclusions were made: The CFD code k- turbulence model is capable of predicting the performance of the centrifugal pump. The pressure at th outlet is found to gradually increase. The velocity in the heat pipe is found to gradually increase while the turbulence is found to gradually decrease at the outlet. [6]. D.W Tryhorn Manager Sir W.G Armstrong Whitwort & Company Ltd., Blower noise and solution - An introduction in the A.W. Convel blower. [7]. P.R Baviskar & V.B Tungikar, Analysis of crack in shaft of blower using finite element analysis and experimental technique. [8]. C.N Jayapragasan, Sumedh J.Suryawanshi and K. Janardhan Reddy, Design optimization of centrifugal fan of travelling cleaner. FUTURE SCOPE The present study considered the performance of the centrifugal pump by comparing various operating conditions and different boundary conditions. In future, the work can be extended to the following -: