International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) ...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) ...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Vo...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Vo...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Vo...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Vo...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Vo...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) ...
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Numerical analysis on effect of exit blade angle on cavitation in centrifu

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Numerical analysis on effect of exit blade angle on cavitation in centrifu

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 359 NUMERICAL ANALYSIS ON EFFECT OF EXIT BLADE ANGLE ON CAVITATION IN CENTRIFUGAL PUMP Shalin Marathe Rishi Saxena M.E. (CAD/CAM) Assistant Professor Mechanical Engineering Department Mechanical Engineering Department Sardar Vallabhbhai Patel Institute Sardar Vallabhbhai Patel Institute of Technology, VASAD of Technology, VASAD ABSTRACT This paper presents the effect of outlet blade angle on cavitation in centrifugal pump. The experiment is performed on a centrifugal pump test rig consisting of backward bladed impeller at different operating conditions and characteristics of the pump are predicted. Modeling of the centrifugal pump along with the different configuration of the impeller having different exit blade angles is carried out using Creo Parametric. Numerical simulation is carried out using ANSYS CFX and standard k-ߝ turbulence model is implemented for the analysis purpose. Cavitation is clearly predicted in the form of water vapor formation inside the centrifugal pump from the simulation results. Analytical analysis is carried out in order to find out NPSHr of the pump and Cavitation number (σc) which indicates the cavitation phenomenon in the centrifugal pump. From the results it has been found that the pump having low value of the blade exit angle will have less chances of getting affected by the cavitation phenomenon. KEY WORDS: ANSYS CFX, Cavitation, Cavitation number, Centrifugal pump, NPSHr, Numerical Simulation, Turbulence Model k-ߝ. 1 INTRODUCTION In centrifugal pump, an increase in the fluid pressure from the pump inlet to its outlet occurs during operation. This pressure difference developed in the pump drives the fluid through the system. The centrifugal pump creates an increase in pressure by transferring INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 3, May - June (2013), pp. 359-366 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 360 mechanical energy from the motor to the fluid through the rotating impeller as shown in figure 1. Centrifugal pump faces a problem of cavitation. In general, cavitation occurs when the liquid pressure at a given location is reduced to the vapor pressure of the liquid. Cavitation begins when the absolute pressure at the inlet falls below the vapor pressure of the water. This phenomenon may occur at the inlet to a pump and on the impeller blades, particularly if the pump is mounted above the level in the suction reservoir. Under this condition, vapor bubbles form at the impeller inlet and when these bubbles are carried into a zone of higher pressure, they collapse abruptly and hit the vanes of the impeller, near the tips of the impeller vanes causing damage to the pump impeller, violet vibrations and noise, reduce pump capacity, reduce pump efficiency. Figure 1 Centrifugal pump W.G.Li [1] stated that the blade discharge angle has a strong but equal influence on the head, shaft power and efficiency of the centrifugal oil pump for various viscosities of liquids pumped. The rapid reduction in the hydraulic and mechanical efficiencies is responsible for the pump performance degradation with increasing viscosity of liquids. E.C.Bacharoudis et al [2] found that as the outlet blade angle increases the performance curve becomes smoother and flatter. But M.H.S.Fard et al [3] stated that pump performance goes down when the pump handles high viscosity working fluids because high viscosity results in disc friction losses over outside of the impeller. SHI Weidong et al[4] investigated that the oversize impeller outlet width leads to poor pump performances and increasing shaft power. Cavitation also affect the performance of the pump and it must be avoided. D.Somashekar et al [5] suggested that in order to avoid the cavitation available NPSH of the system must be equal to or greater than the NPSH required by the centrifugal pump and similar recommendations were given by the M.K.Abbas [6]. A.Stuparu et al [7] performed numerical investigation of the multiphase flow inside the storage pump which underlines the fact that the pumping head drops due to the development of cavitation phenomena. A.Goto et al [8] found that at the high flow rate cavitation bubbles appear at the leading edge on pressure side incipiently and the head drops gradually. J.B.Jonker et al [9] suggested that cavitation inception for the forward swept impellers occurs at half-span of the leading-edge, while it occurs close to the shroud for the backward-swept impeller. Also It has been found that the backward bladed impeller gives the highest efficiency to the centrifugal pump in compare to the forward and radial bladed impeller. But the energy transfer is less for the backward bladed impeller in comparisons of radial and the forward bladed impeller.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May 2 EXPERIMENTATION Experiment is carried out having the backward bladed impeller. and table 1 shows the specification of Figure 2 Centrifugal pump test rig 3 MODELING AND SIMULATION Creo Parametric 1.0 version is used for geometric modeling of the impeller having different blade angles and the casing. The figure 3 and figure 4 shows the Creo model of the Impeller and the casing of the centrifugal pump Figure 3 Creo model of Table 1 Centrifugal Test rig specification Pump Total Head Discharge Speed Motor Measuring Tank Sump tank International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 361 Experiment is carried out at different operating conditions on the centrifugal pump impeller. The figure 2 shows the test rig of the centrifugal pump cification of the pump test rig. Figure 2 Centrifugal pump test rig SIMULATIONS Creo Parametric 1.0 version is used for geometric modeling of the impeller having different blade angles and the casing. The figure 3 and figure 4 shows the Creo model of the Impeller and the casing of the centrifugal pump respectively. Creo model of impeller Figure 4 Creo model of casing Table 1 Centrifugal Test rig specification Pump Total Head 12 m Discharge 1.5 lps Speed 2900 rpm Motor 1 HP Measuring Tank 400 400 450 mm Height Sump tank 600 900 600 mm Height International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME on the centrifugal pump shows the test rig of the centrifugal pump Creo Parametric 1.0 version is used for geometric modeling of the impeller having different blade angles and the casing. The figure 3 and figure 4 shows the Creo model of the Figure 4 Creo model of casing
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May ANSYS CFX (14.0) is the simulation tool which is used for the numerical analysis of the centrifugal pump. Meshing is carried out using the Auto Mesh feature of the ANSYS WORKBENCH, which is shown in the figure 5 which as the elements and the number of nodes and the elements generated are respectively during the mesh. To predict the complex behavior of the flows standard k- model is adopted. Figure 5 Meshing of the model One of the major advantages of the ANSYS is that the user can give the boundary conditions close to the actual operating conditions. Analysis is carried out in a Steady state condition taking 1 atmospheric as the reference pressure. Rotating velocity is provided to the impeller along the Z direction. Two fluids namely as Water and Water vapor are selected in order to determine the formation of vapors inside the pump. At inlet a conditions are provided and the discharge of the pump is determined from the simulation in order to match with the experimental. 5 NUMERICAL RESULTS AND After the completion of the solver part of the simulation, results like and the water vapor formation contours are generated as shown in the figure for the different discharge conditions like 1.5, 5 and 10 lps, for all the configurations of the impellers. (a) 20 degree bladed impeller (d) 60 degree bladed impeller Figure 6 Water vapor contours at 1.5 lps International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 362 ANSYS CFX (14.0) is the simulation tool which is used for the numerical analysis of the centrifugal pump. Meshing is carried out using the Auto Mesh feature of the ANSYS which is shown in the figure 5 which indicates that the tetrahedrons a he number of nodes and the elements generated are 77542 and 419333 respectively during the mesh. To predict the complex behavior of the flows inside the pump Figure 5 Meshing of the model One of the major advantages of the ANSYS is that the user can give the boundary conditions close to the actual operating conditions. Analysis is carried out in a Steady state condition taking 1 atmospheric as the reference pressure. Rotating velocity is provided to the impeller along the Z direction. Two fluids namely as Water and Water vapor are selected in order to determine the formation of vapors inside the pump. At inlet and outlet pressure conditions are provided and the discharge of the pump is determined from the simulation in order to match with the experimental. AND DISCUSSIONS After the completion of the solver part of the simulation, results like pressure contours and the water vapor formation contours are generated as shown in the figure for the different discharge conditions like 1.5, 5 and 10 lps, for all the configurations of the impellers. (b) 30 degree bladed impeller (c) 40 degree bladed impeller (e) 70 degree bladed impeller (f) 80 degree bladed impeller Figure 6 Water vapor contours at 1.5 lps International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME ANSYS CFX (14.0) is the simulation tool which is used for the numerical analysis of the centrifugal pump. Meshing is carried out using the Auto Mesh feature of the ANSYS indicates that the tetrahedrons are used 77542 and 419333 inside the pump One of the major advantages of the ANSYS is that the user can give the boundary conditions close to the actual operating conditions. Analysis is carried out in a Steady state condition taking 1 atmospheric as the reference pressure. Rotating velocity is provided to the impeller along the Z direction. Two fluids namely as Water and Water vapor are selected in nd outlet pressure conditions are provided and the discharge of the pump is determined from the simulation in pressure contours and the water vapor formation contours are generated as shown in the figure for the different discharge conditions like 1.5, 5 and 10 lps, for all the configurations of the impellers. (c) 40 degree bladed impeller (f) 80 degree bladed impeller
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May Figure 6 and 8 shows respectively It indicates that at higher exit blade angle, the volume occupied by the water vapor is more as compare to lower exit blade angle. particular blade angle the volume occupied by the water vapor a lps. As the density of the water is competitiv are settled on the upper side of the casing and the impeller Figure 7 and 9 shows the pressure variat 5 lps. On analyzing the pressure contours, higher pressure is observed at the discharge section (a) 20 degree bladed impeller (d) 60 degree bladed impeller Figure 7 Pressure contours at 1.5 lps (a) 20 degree bladed impeller (d) 60 degree bladed impeller Figure 8 Water vapor contour International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 363 phenomenon of water vapor formation at 1.5 lps that at higher exit blade angle, the volume occupied by the water vapor is more as compare to lower exit blade angle. Also thing should be noted that for a particular blade angle the volume occupied by the water vapor at 5 lps is more than the 1.5 s the density of the water is competitively higher than the water vapor, the are settled on the upper side of the casing and the impeller. shows the pressure variation across the centrifugal pump at 1.5 lps and On analyzing the pressure contours, higher pressure is observed at the discharge section (b) 30 degree bladed impeller (c) 40 degree bladed impeller (e) 70 degree bladed impeller (f) 80 degree bladed impeller Figure 7 Pressure contours at 1.5 lps (b) 30 degree bladed impeller (c) 40 degree bladed (e) 70 degree bladed impeller (f) 80 degree bladed impeller Figure 8 Water vapor contours at 5 lps International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME ater vapor formation at 1.5 lps and 5 lps that at higher exit blade angle, the volume occupied by the water Also thing should be noted that for a t 5 lps is more than the 1.5 ely higher than the water vapor, the water vapors ion across the centrifugal pump at 1.5 lps and On analyzing the pressure contours, higher pressure is observed at the discharge section c) 40 degree bladed impeller (f) 80 degree bladed impeller (c) 40 degree bladed impeller bladed impeller
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May on varying the blade angle from 20 degree to 80 degree in both the condition of 1.5 lps and 5 lps. Due to the increased discharge there is no pressure difference in 2 impeller from inlet section to discharge section. T lps is less than the 1.5 lps for pump pressure development inside the centrifugal pump as we lead to the low pressure regions and also to the in pressure from inlet section to outlet section for all Since in the impeller section there is no change recirculation and back flow will continue until the desired pressure is attainable. A low pressure region is observed near the (a) 20 degree bladed impeller (b) 30 degree bladed impeller (d) 60 degree bladed impeller (g)70 degree bladed impeller Figure 9 Pressure Contour Figure 10 Result comparison Figure 10 shows the good results. Figure 11 shows the effect Suction Head required). It indicates 0 0.5 1 1.5 2 2.5 0 2 4 6 8 DISCHARGE(lps) EXPERIMENT NUMBER EXPERIMENTATION SIMULATION International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 364 gle from 20 degree to 80 degree in both the condition of 1.5 lps and 5 lps. Due to the increased discharge there is no pressure difference in 20 degree bladed impeller from inlet section to discharge section. The pressure developed inside the pump having 20 degree impeller. So there is a decrease in pressure development inside the centrifugal pump as we increases the discharge. So that may lead to the low pressure regions and also to the cavitation phenomenon. There is gradual rise in pressure from inlet section to outlet section for all other configuration of the blade angles. ion there is no change in pressure, it will lead to the phenomenon of recirculation and back flow will continue until the desired pressure is attainable. A low pressure region is observed near the tongue section of the casing due to formation of eddies. (b) 30 degree bladed impeller (c) 40 degree bladed impeller (g)70 degree bladed impeller (h) 80 degree bladed impeller Figure 9 Pressure Contours at 5 lps comparison Figure 11NPSHr vs. Discharge shows the good agreement of the simulation results with the effect of discharge on to the value of NPSHr ed). It indicates that as the value of the discharge increases the NPSH 10 12 EXPERIMENT NUMBER EXPERIMENTATION 0 1 2 3 4 5 6 7 8 0 0.002 0.004 NPSHr Q (DISCHARGE) (m3/sec) International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME gle from 20 degree to 80 degree in both the condition of 1.5 lps and 5 0 degree bladed he pressure developed inside the pump at 5 . So there is a decrease in increases the discharge. So that may There is gradual rise configuration of the blade angles. in pressure, it will lead to the phenomenon of recirculation and back flow will continue until the desired pressure is attainable. A low section of the casing due to formation of eddies. (c) 40 degree bladed impeller (h) 80 degree bladed impeller Figure 11NPSHr vs. Discharge experimental (Net Positive he discharge increases the NPSHr 0.006
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May will also increase and that will lead to the cavitation phenomenon. So all the pump should be operated with in its range of design flow discharge conditions on to the cavitation the cavitation number increases and that is nothing but the indication of cavitation phenomenon. Also with increase in the cavitation number the head of the pump will decrease along with the performance. For all the configurations of the blade exit angles similar behavior is observed. Figure 12 Cavitation number vs. Discharge For Different blade CONCLUSIONS It can be concluded from the results that the use of impeller angle is much efficient than the impeller having higher exit blade angle because the phenomenon of the cavitation is identified for higher exit blade angles in the obtained from the simulation. Since the cavitation phenomenon will lead to the erosion of the impeller material, that will reduce head in a drastic manner. Hence, if we use the blade angle in a range of 20 degree to 30 degree it provides efficient conditions REFERENCES [1] Wen-Guang LI “Blade Exit Angle Effects on Performance of a Standard Industrial Centrifugal Oil Pump”- Department Of Civil And Environmental Engineering Cvng 1001: Mechanics Of Fluids. [2] E.C. Bacharoudis, A.E. Filios, M.D. Mentzos And D.P. Margaris Of A Centrifugal Pump Impeller By Varying The Outlet Blade Angle” In The Open Mechanical Engineering Journal, 2008, 2, 75 [3] M.H.S.Fard And F.A.Bhoyaghchi Outlet Angles In A Centrifugal Pump When Handling Viscous Fluid" In American Journal Of Applied Science 2007. -5 0 5 10 15 20 25 30 35 0 2 CAVITATIONNUMBER International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 365 l lead to the cavitation phenomenon. So all the pump should be operated with in its range of design flow rate. Figure 12 shows the effect of different cavitation number which shows that as the discharge increases the cavitation number increases and that is nothing but the indication of cavitation Also with increase in the cavitation number the head of the pump will decrease e performance. For all the configurations of the blade exit angles similar Figure 12 Cavitation number vs. Discharge For Different blade configuration It can be concluded from the results that the use of impeller having low exit blade angle is much efficient than the impeller having higher exit blade angle because the phenomenon of the cavitation is identified for higher exit blade angles in the obtained from the simulation. Since the cavitation phenomenon is undesirable for the pump it will lead to the erosion of the impeller material, that will reduce the efficiency, discharge, in a drastic manner. Hence, if we use the blade angle in a range of 20 degree to 30 degree it provides efficient conditions for operating the centrifugal pump. Guang LI “Blade Exit Angle Effects on Performance of a Standard Industrial Department Of Civil And Environmental Engineering Cvng 1001: Mechanics Of Fluids. , A.E. Filios, M.D. Mentzos And D.P. Margaris- " Parametric Study Of A Centrifugal Pump Impeller By Varying The Outlet Blade Angle” In The Open Mechanical Engineering Journal, 2008, 2, 75-83. M.H.S.Fard And F.A.Bhoyaghchi –” Studies On The Influence Of The Various Blade Outlet Angles In A Centrifugal Pump When Handling Viscous Fluid" In American Journal Of Applied Science 2007. 4 6 8 10 12 DISCHARGE (LPS) 20 DEGREE 30 DEGREE 40 DEGREE 60 DEGREE 70 DEGREE 80 DEGREE International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME l lead to the cavitation phenomenon. So all the pump should be effect of different number which shows that as the discharge increases the cavitation number increases and that is nothing but the indication of cavitation Also with increase in the cavitation number the head of the pump will decrease e performance. For all the configurations of the blade exit angles similar Figure 12 Cavitation number vs. Discharge For Different blade having low exit blade angle is much efficient than the impeller having higher exit blade angle because the phenomenon of the cavitation is identified for higher exit blade angles in the contours is undesirable for the pump it the efficiency, discharge, in a drastic manner. Hence, if we use the blade angle in a range of 20 degree to 30 Guang LI “Blade Exit Angle Effects on Performance of a Standard Industrial Department Of Civil And Environmental Engineering Cvng " Parametric Study Of A Centrifugal Pump Impeller By Varying The Outlet Blade Angle” In The Open f The Various Blade Outlet Angles In A Centrifugal Pump When Handling Viscous Fluid" In American 20 DEGREE 30 DEGREE 40 DEGREE 60 DEGREE 70 DEGREE 80 DEGREE
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 366 [4] SHI Weidong, ZHOU Ling*, LU Weigang, PEI Bing, and LANG Tao-" Numerical Prediction and Performance Experiment in a Deep well Centrifugal Pump with Different Impeller Outlet Width"- CHINESE JOURNAL OF MECHANICAL ENGINEERING Vol. 26,No.-2013 [5] Mr. D. Somashekar1, Dr. H. R. Purushothama –”Numerical Simulation Of Cavitation Hysteresis On Radial Flow Pump" In IOSR Journal Of Mechanical And Civil Engineering (Iosrjmce) Issn : 2278-1684 Volume 1, Issue 5 (July-august 2012), Pp 21- 26 Www.iosrjournals.Org [6] Stuparu, Romeo Susan-resiga, Liviu Eugen Anton And Sebastian Muntean-" A New Approach In Numerical Assessment Of The Cavitation Behavior Of Centrifugal Pumps” In International Journal Of Fluid Machinery And Systems Vol. 4, No. 1, January-march 2011. [7] Motohiko Nohmi , A. Goto – “Cavitation CFD In A Centrifugal Pump” Fifth International Symposium On Cavitation (Cav2003),osaka, Japan, November 1-4, 2003. [8] J.B. Jonker, M. J. Van Os , J. G.H. Op De Woerd "A Parametric Study Of The Cavitation Inception Behavior Of A Mixed-flow Pump Impeller Using A Three- dimensional Potential Flow Model" In The 1997 ASME Fluids Engineering Division Summer Meeting Fedsm’97 June 22–26, 1997. [9] Manish Dadhich, Dharmendra Hariyani and Tarun Singh, “Flow Simulation (CFD) & Fatigue Analysis (Fea) of a Centrifugal Pump”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 67 - 83, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [11] V. Muralidharan, V.Sugumaran and Gaurav Pandey, “Svm Based Fault Diagnosis of Monoblock Centrifugal Pump using Stationary Wavelet Features”, International Journal of Design and Manufacturing Technology (IJDMT), Volume 2, Issue 1, 2011, pp. 1 - 6, ISSN Print: 0976 – 6995, ISSN Online: 0976 – 7002. [12] V. Muralidharan, V. Sugumaran, P. Shanmugam and K. Sivanathan, “Artificial Neural Network Based Classification for Monoblock Centrifugal Pump using Wavelet Analysis”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 1, Issue 1, 2010, pp. 28 - 37, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.

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