Cavitation in a Radial Flow Pump CFD Simulation, ANSYS Fluent Training
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The present problem simulates the cavitation phenomenon inside a radial flow pump using ANSYS Fluent software.
This ANSYS Fluent project includes CFD simulation files and a training movie.
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Description
Project Description
The present problem simulates the cavitation phenomenon inside a radial flow pump using ANSYS Fluent software. This pump is of the centrifugal pump (radial flow) type; In this way, the desired fluid enters it parallel to the central axis and exits it radially or perpendicular to the inlet path. These types of pumps are commonly used to create high pressures at low flow rates and are also the most common type among pumps. The working fluid used in this pump is liquid diesel; Thus, it has a density equal to 830 kg.m-3 and a viscosity equal to 0.00332 kg.m-1.s-1.
Since pumps are devices that work inherently based on pressure changes, in this modeling, the pressure boundary condition at the inlet and outlet boundaries of the pump is used. Thus, the liquid diesel flow enters the pump axially with a pressure of 0 pascal and exits it radially with a pressure of 109872 pascal. Also, to define the rotation of the fluid inside the pump, a frame motion tool with a rotational speed equal to 20 rad.s-1 has been used. The purpose of this work is to investigate the cavitation phenomenon inside the pump.
Project Description
The cavitation phenomenon occurs when the pressure of a liquid falls below its vapor pressure at a constant temperature. In this case, the particles turn from liquid to vapor and form a bubble. This process is called cavitation. Now, if these bubbles are transferred to the high-pressure parts of the pump, they will collapse. This collapse of the bubble creates a vacuum locally, as a result of which the liquid particles around the bubble move towards the empty space at a very high speed and pressure.
This process in areas close to the inner walls of the pumps and especially in the areas adjacent to the blades causes liquid particles to hit the walls and blades with high force and as a result, lead to damage to the pump and eventually shorten its life. Therefore, one of the most important issues in the industry is to investigate the possibility of cavitation inside the pumps and solutions to reduce it. So in the present model, another fluid is defined as diesel vapor with a density equal to 9.4 kg.m-3 and a viscosity equal to 0.000007, and also the multi phase VOF model is used.
Thus, the base fluid of diesel is liquid and the secondary fluid is vapor diesel, and between these two fluids, a mass transfer is defined in the form of cavitation, the vapor pressure required for cavitation is defined as 50900 pascal.
Radial Flow Pump Geometry & Mesh
The present model is designed in three dimensions using Bladegen software. Since the present model is radially symmetrical, only one piece of it can be drawn radially and then expanded around the central axis. Therefore, the model consists of a single piece which, on the one hand, has an axial flow input section and, on the other hand, has a radial output output section. On both sides of this piece, the periodic boundary type is used and in the middle of it, a blade is drawn as a curve. If we expand this piece around the central axis, a radial flow pump with seven blades will be created. The following figure shows a view of the geometry.
The meshing of the present model has been done using Turbogrid software. The mesh type is structured and the element number is equal to 63308. The following figure shows an overview of the mesh.
Cavitation CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is steady.
- The gravity effect on the fluid is ignored.
A summary of the defining steps of the problem and its solution is given in the following table:
Models | ||
Viscous | k-epsilon | |
k-epsilon model | RNG | |
near wall treatment | standard wall functions | |
Multi phase Model | VOF | |
number of Eulerian phases | 2 (diesel liquid & vapor) | |
formulation | implicit | |
interface modeling | sharp | |
Boundary conditions | ||
Inflow | Pressure Inlet | |
gauge pressure | 0 pascal | |
volume fraction for liquid | 1 | |
volume fraction for vapor | 0 | |
Outflow | Pressure Inlet | |
gauge pressure | 109872 pascal | |
volume fraction for liquid | 1 | |
volume fraction for vapor | 0 | |
Wall | Wall | |
wall motion | stationary wall | |
Methods | ||
Pressure-Velocity Coupling | Coupled | |
Pressure | PRESTO | |
momentum | second order upwind | |
volume fraction | compressive | |
turbulent kinetic energy | first order upwind | |
turbulent dissipation rate | first order upwind | |
Initialization | ||
Initialization methods | Standard | |
gauge pressure | 0 pascal | |
x-velocity & y-velocity | 0 m.s^{-1} | |
z-velocity | 10.1673 m.s^{-1} | |
vapor fraction for vapor | 0 |
Results
At the end of the solution process, we obtain three-dimensional contours related to pressure, velocity, vapor phase volume fraction, liquid phase volume fraction gradient, and mass transfer rate gradient. We also present 3D velocity vectors.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.
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