Cavitating Centrifugal Pump

Introduction

The Purpose of the tutorial is to model cavitation in a centrifugal pump, which involves the use of a rotation domain and the cavitation model.

The problem consists of a five blade centrifugal pump operating at 2160 rpm. The working fluid is water and flow is assumed to be steady and incompressible.

Due to rotational periodicity a single blade passage will be modeled.

The initial flow-field will be solved without cavitation. It will be turned on later.

Workbench

1. Start Workbench and save the project as centrifugalpump.wbpj
2. Drag CFX into the Project Schematic from the Component Systems toolbox
3. Start CFX-Pre by double clicking Setup
4. When CFX-Pre opens, import the mesh by right-clicking on Mesh and selecting Import Mesh > ICEM CFD
5. Browse to pump.cfx5
6. Keep Mesh units in m
7. Click Open

Creating Working Fluids

Modifying the material properties:

1. Expand Materials in the Outline tree
2. Double-click Water
3. On the Material Properties tab change Density to 1000 [kg/m3]
4. Change Dynamic Viscosity to 0.001 [kg m^-1 s^-1] under Transport Properties
5. Click OK

Setting up the Fluid Domain

1. Set the Reference Pressure to 0 [Pa]
2. Set Domain Motion to Rotating
3. Set Angular Velocity to 2160 [rev min^-1]
4. Switch on Alternate Rotation Model
5. Make sure Rotation Axis under Axis Definition is set to Global Z

1. Switch to the Fluid Models tab, and set the following:
2. Turn on Homogeneous Model in the Multiphase section
3. Under Heat Transfer set the Option to Isothermal, with a Temperature of 25 C
4. Set Turbulence Option to Shear Stress Transport
5. Click OK

Inlet Boundary Condition

1. Insert a boundary condition named Inlet
2. On the Basic Settings tab, set Boundary Type to Inlet
3. Set Location to INLET
4. Set Frame Type to Stationary
5. Switch to the Boundary Details tab
6. Specify Mass and Momentum with a Normal Speed of 7.0455 [m/s]
7. Switch to the Fluid Values tab
8. For Water Liquid, set the Volume Fraction to a Value of 1
9. For Water Vapour, set the Volume Fraction to a Value of 0
10. Click OK

Outlet Boundary Condition

1. Inset a boundary condition named Outlet
2. On the Basic Settings tab, set Boundary Type to Opening
3. Set Location to OUT
4. Set Frame Type to Stationary
5. Switch to the Boundary Details tab
6. Specify Mass and Momentum using Entrainment, and enter a Relative Pressure of 600,000 [Pa]
7. Enable the Pressure Option and set it to Opening Pressure
8. Set Turbulence Option to Zero Gradient
9. Switch to the Fluid Values tab
10. For Water Liquid, set the Volume Fraction to a Value of 1
11. For Water Vapour, set the Volume Fraction to a Value of 0
12. Click OK

Periodic Interface

1. Click to create an Interface, and name it Periodic
2. Set the Interface Type to Fluid Fluid
3. For Interface Side 1, set the Region List to DOMAIN INTERFACE 1 SIDE 1 and DOMAIN INTERFACE 2 SIDE 1 (use the “…” icon and the Ctrl key)
4. For Interface Side 2, set the Region List to DOMAIN INTERFACE 1 SIDE 2 and DOMAIN INTERFACE 2 SIDE 2
5. Set the Interface Models option to Rotational Periodicity
6. Under Axis Definition, select Global Z
7. Set Mesh Connection Option to 1:1
8. Click OK

Wall Boundary Conditions

1. Insert a boundary condition named Stationary
2. Set it to be a Wall, using the STATIONARY location
3. On the Boundary Details tab, enable a Wall Velocity and set it to Counter Rotating Wall
4. Click OK

5.In the Outline Tree, right-click on the Default Domain Default boundary and rename it to Moving

-The default behavior for the Moving boundary condition is to move with the rotating domain, so there is nothing that needs to be set

Initialization

1. Click to initialize the solution
2. On the Fluid Settings form, set Water Liquid Volume Fraction to Automatic with Value, and set the Volume Fraction to 1
3. Set Water Vapour Volume Fraction to Automatic with Value, and set the Volume Fraction to 0
4. Click OK

Solver Control

1. Double click Solver Control in the Outline tree
2. Set Timescale Control to Physical timescale

A commonly used timescale in turbomachinery is 1/omega, where omega is the rotation rate in radians per second. You can use an expression to determine a timestep from this. In this case, 2/omega will be used to achieve faster convergence.

1. Enter the following expression in the Physical Timescale box:
   1/(pi*2160 [min^-1])
2. Set Residual Target to 1e-5
3. On the Advanced Options tab, turn on Multiphase Control, then turn on Volume Fraction Coupling and set the Option to Coupled
4. Click OK

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