SIMULATION OF FLOW INSIDE CENTRIFUGAL PUMP
1.AIM :
TO MODEL AND SIMULATE FLOW INSIDE A CENTRIFUGAL PUMP
2.OBJECTIVE :
- To create a 3D model of a centrifugal pump and simulate the flow inside for various velocities using Soildworks flow simulation.
- To plot performance diagram(relationship between Pressure ratio and mass flow rate).
3.INTRODUCTION :
Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor.
The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.
Flow simulation inside a centrifugal pump can be performed through computational fluid dynamics (CFD), a powerful and convenient tool to perform CFD is Solidworks flow simulation.
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free stream flow of the fluid, and the interaction of the fluid with surfaces defined by boundary conditions.
In simple words to perform CFD following steps are performed in order:-
- A computational model is made using computer aided designing and the domain of fluid is extracted.
- Further the domain is divided into discrete cells called mesh.
- Next the Boundary conditions are defined, which is specifying the fluid behaviour and properties at all bounding surfaces of the fluid domain.
- Next the calculations are performed and the equations are solved iteratively till the convergence is achieved.
- Finally the analysis and visualization of the calculations performed can be seen.
Here in this work a centrifugal pump is modeled using Solidworks and further the flow inside is simulated for various velocities.
The simulation for each velocity is performed till 500 iterations and the performance diagram is obtained for the pump. Performance diagram gives the relationship between Pressure ratio and mass flow rate.
where `"Pressure ratio" = "Outlet total pressure"/" Inlet total pressure"`
4.PROCEDURE :
1)At first the centrifugal pump is modelled using Soildworks.
2)Lids are applied at the inlet and outlet to make model watertight.
3)Using the Wizard option in Solidworks flow simulation a new project is created. The analysis type selected is Internal and rotation analysis is selected.
4)Water is selected as the working fluid, further the initial and ambient conditions are kept as default.
5)The rotating part (impeller) is removed from the input data (input data -> component control -> deselect the rotating part) as we do not want it to act as a wall.
6)Further by clicking the Rotating region the part rotating part of the body (impeller) is selected and the angular velocity is set as 1000 rad/s.
7)At inlet the environment pressure is given as the boundary condition and at outlet the velocity is set as 10 m/s.
8)A basic mesh is defined, surface goals for mass flow rate and total pressure at inlet and outlet is created.
9)Finally parametric study is done for 10, 14, 18, 22, 26 and 30 m/s outlet velocity and performance diagram is made.
5.RESULTS :
Velocity : 10m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Velocity : 14m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Velocity : 18m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Velocity : 22m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Velocity : 26m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Velocity : 30m/s
Cut plot for velocity contour
Flow trajectories showing pressure variation
Explanation
The velocity contours shows the variation of velocity inside centrifugal pump showing high velocity of fluid at the impeller area due to high rotation speed of impeller and as the fluid enters outlet pipe there is a decrease in velocity.
As visible from the flow trajectories showing pressure variation, inside the inlet pipe, around negative pressure (vaccum) can be seen which helps to suck more fluid inside. With increase in velocity in impeller there is an increase in pressure and at the outer radius of impeller comparatively more pressure can be seen.
Performance diagram
Obtaining relationship between Pressure ratio and mass flow rate.
where `"Pressure ratio" = "Outlet total pressure"/" Inlet total pressure"`
Where SG Av Total Pressure 1 represents pressure at outlet and SG Av Total Pressure 2 represents pressure at inlet.
| VELOCITY (m/s) | 10 | 14 | 18 | 22 | 26 | 30 |
| OUTLET PRESSURE (Pa) | 2370045.51 | 2707149.72 | 3405448.64 | 4153529.90 | 1911524.80 | 2125894.78 |
| INLET PRESSURE (Pa) | 246867.34 | 295886.84 | 386289.55 | 497273.63 | 201574.73 | 245438.40 |
| PRESSURE RATIO | 9.60048223 | 9.14927382 | 8.81579282 | 8.3526044 | 9.4829585 | 8.6616225 |
| MASS FLOW RATE (Kg/s) | 0.4965 | 0.6950 | 0.8915 | 1.0870 | 1.2904 | 1.4880 |
It can be seen from the performance diagram that with increase in mass flow rate the pressure ratio reaches peak and starts decreasing till a point and again starts increasing.
6.CONCLUSIONS :
The simulation inside a centrifugal pump for different velocities was completed successfully using Solidworks flow simulation.
With increase in mass flow rate the pressure ratio reaches peak and starts decreasing till a point and again starts increasing.
At the impeller portion due to high velocity of fluid beacuse of rotating impeller there is an increase in pressure too.
7.REFERENCES :