Flow simulation inside a Centrifugal Pump

Aim:

To model and simulate flow inside a centrifugal pump in Solidworks and plot it’s performance diagram.

Objective:

• To simulate the flow inside a centrifugal pump.
• To obtain the relationship between pressure ratio and mass flow rate.

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.

Most centrifugal pump manufacturers publish "Head-Flow" Curves for each model, impeller diameter, and rated speed (RPM) for the centrifugal pumps they manufacture. A key point regarding these Head-Flow Curves is that all centrifugal pumps will always run along their Head-Flow Curve and the resulting flowrate will always be at the intersection of the pump's Head-Flow Curve and the "System" Curve which is unique for each piping system, fluid and application.

System curves can be developed quite easily using Hydraulic Modelling Software and compared to various pump Head-Flow Curves in order to properly select centrifugal pumps that meet each user's unique system and flowrate requirements.

Setup Explanation:

1. First, the centrifugal pump is modelled using appropriate dimensions as shown. The rotor and casing should be a separate bodies. This is done by deselecting the merge result option while extruding the rotor inside the casing.

2. A separate cylinder is modelled encompassing the rotor as shown. This will be set as the rotating region in the simulation. Make sure this is a separate body from the rotor.

3. Apply lids to the inlet and outlet ports to make the geometry watertight.
4. Then, under flow simulation option click on wizard tool and create a new setup with default options, internal flow steady state study with water as the working fluid. Select the rotation option with default settings.
5. Keep the computational domain and mesh setting to default.
6. In order to notify SolidWorks to remove the rotating zone from the model, it has to be excluded which can be done by Clicking on Input Data -> Component control and excluding the model.
7. Set the rotating region with a speed of 1000 rad/s clockwise.
8. Set boundary condition with inlet pressure as atmospheric.

9. Set boundary condition with outlet velocity as 10 m/s.

10. Set a surface goal of total pressure at the outlet lid.
11. Insert a velocity cut plot perpendicular to the rotor axis.
12. Insert a surface parameter value of mass flow rate at the outlet lid.
13. To avoid the solution from converging to end quickly we have to increase the number of Iterations by clicking on Input Data -> Calculation control points -> Enable only Iterations and set it to 500.
14. Do a parametric study with the outlet velocity as as variable going from 10 to 20 m/s with 11 total values.

Results:

1. Velocity:

• For 10 m/s:

• For 11 m/s:

• For 12 m/s:

• For 13 m/s:

• For 14 m/s:

• For 15 m/s:

• For 16 m/s:

• For 17 m/s:

• For 18 m/s:

• For 19 m/s:

• For 20 m/s:

2. Pressure Ratio vs Mass flow rate:

Conclusions:

1. From the performance diagram it is clear that with increase in mass flow rate or outlet velocity, the pressure ratio increases first, reaches a peak value and then starts decreasing again due to increase in losses.
2. The peak point is the design point and the pump should be run at that state for minimum losses.

File Link:

https://drive.google.com/drive/folders/1yQwzYWQecgpfuohXQd7szJP4rwkcIrEH?usp=sharing