Simulation of Flow through a Centrifugal Pump

AIM

To simulate the Flow through a Centrifugal Pump

OBJECTIVES

• To create a 3D model of a centrifugal pump and run a flow analysis
• To perform a Parametric Study for different velocities.
• To obtain relationship between Pressure Ratio and Mass Flow rate.

INTRODUCTION

Computational Fluid Dynamics or CFD is a technique that deals with the solution of fluid flow fields through numerical analysis. SOLIDWORKS Flow Simulation is a CFD software designed for the everyday SOLIDWORKS user and analyst. It provides dynamic feedback on the fluid flow and Thermal performance of their products. With Parametric optimization capabilities, users can automate the design and analysis process to discover the best iteration of their design within the familiar SOLIDWORKS environment.

Centrifugal pump is a hydraulic machine that is used to transport fluids by the conversion of rotational kinetic energy of impeller into the hydrodynamic energy of the fluid flow. The double-suction centrifugal pump are used for conveyance of a large quantity of water and have wide application due to its stable running, for the balance of axial thrust through by the double suction in impeller, and for a convenient maintenance.So, this simulation helps in understanding the flow and its relations for the Centrifugal Pump.

THEORY

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. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. 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.

Generally a pump is a hydraulic machine which converts mechanical energy into hydraulic energy. The rotational energy typically comes from an electric motor, an engine or a steam turbine. As the impeller and blades rotate, they transfer momentum to incoming fluid.

The fluid accelerates radially outward from the pump chasing and a vacuum is created at the impellers eye that continuously draws more fluid into the pump. As the fluid’s velocity increases obviously its kinetic energy increases and the fluid is forced out of the impeller . In the volute the fluid flows through a continuously increasing cross-sectional area, where the kinetic energy is converted into fluid pressure (according to the Bernoulli’s principle). The impeller blades are usually backward-curved.

Mass Flow Rate

The mass flow rate is the rate at which mass flows through a reference cross-section per unit of time. For centrifugal pumps, this is defined as the mass flow pumped through the outlet cross-section and any tapping cross-sections of the pump with respect to this unit of time.

Pressure Ratio is the ratio between Outlet and Inlet Pressure

CASE SETUP

1. The 3D model is created taking approximate dimensions .
2. The rotation zone for the impeller is defined.
3. Then using the ‘Flow Simulation’ option lids are created at open ends. These lids help us to define the boundary condition.
4. Then using the ‘Wizard’ option in‘Flow Simulation’, features and required conditions are set.
5. The Analysis type is set to Internal,the ‘Rotation’ option is checked and Fluid is chosen as Water. All other parameters are set as default.
6. Then the rotation zone made for the impeller is unchecked(not a part of simulation) by using Component Control’ from ‘Rotating Regions’ option.
7. Then the rotation zone is provided rotation of 1000 rad/sec by using ‘Insert rotating Region’ from ‘Rotating Regions’ option.
8. After this, the ‘Boundary Conditions’ are set using the ‘Insert Boundary Condition’ option. The boundary conditions: Environmental Pressure at Inlet, and Outlet Velocity of 10 m/s at outlet.
9. A mesh level of 3 is used with ‘Advanced Channel Refinement’.
10. Surface Goals were set as Mass Flow Rate,Total Pressure on the Inlet and Outlet.
11. A Cut plot was also made on the Top Plane for observing Velocity Contours.
12. Flow Trajectory is inserted by selecting Inlet and Outlet faces taking 200 input points.
13. Then a new Parametric Study was done taking Input Parameter as Outlet velocity and varying it from 10 m/s to 30 m/s using the ‘Range with Numbers’ option;and Output Parameter as the Cut Plot,Flow trajectory and Goals.
14. Five different scenarios are set upand the simulation is Run.
15. Then the results were obtained.

RESULTS

• For Outlet Velocity 10 m/s

Velocity Cut Plot

Flow Trajectory

• For Outlet Velocity 15 m/s

Velocity Cut Plot

Flow Trajectory

• For Outlet Velocity 20 m/s

Velocity Cut Plot

Flow Trajectory

• For Outlet Velocity 25 m/s

Velocity Cut Plot

Flow Trajectory

• For Outlet Velocity 30 m/s

Velocity Cut Plot

Flow Trajectory

Results:

Variation of Mass Flow Rate with Velocity

Variation of Pressure Ratio with Velocity

Variation of Pressure Ratio with Mass Flow Rate

OBSERVATIONS

• Mass flow rate increases with increase in velocity
• Pressure ratio first increases with increase in velocity upto 20 m/s then decreases.

CONCLUSION

Therefore, the Flow Simulation of the Centrifugal Pump is successfully completed and the results are studied.