Centrifugal Pump CFD analysis

This study shows a smooth workflow of performing a deep CFD analysis
of a mixed flow water pump using TCFD.

TCFD Main Page - Download This Tutorial - Pump Results Report

TCFD - Turbomachinery CFD scheme automated workflow

TCFD is automated workflow

CFD SUPPORT introduces the new generation of CFD simulations. TCFD brings an extreme increase of productivity to CFD simulations. TCFD is extremely popular project, because it sucessfully merged benefits of an open-source (perpetual, unlimited users, jobs, and cores, customizable, ...) with benefits of commercial codes (professional support, well tested, ready for the industry, robust, accurate, automated, GUI, ...).

TCFD - Turbomachinery CFD scheme automated workflow

TCFD is fully automated, it can run the whole workflow by a single command: data input, new case is written down, mesh is created, case is set-up, case is simulated, results are evaluated and the results report is written down. Both GUI and batch mode. Data in - data out. TCFD is mainly focused on supporting the engineers in their real value added work. TCFD is fully automated and the beauty of TCFD is that it is the user who decides how deep to dive into a CFD or not at all. And all the options remain open at the same time.

The input data

This particular pump model is designed in CFturbo®. CFturbo® is a modern, powerful software for interactive design of turbomachinery. It's easy to use and enables the designer to either start from scratch or redesign existing geometries.

CFturbo mixed flow water pump z+ view      CFturbo mixed flow water pump general view      CFturbo mixed flow water pump z- view

The designed model data is exported from CFturbo® directly in TCFD format. The surface model data in .stl file format together with physical inputs are loaded in TCFD. Other option would be loading an external mesh in OpenFOAM® mesh format, or loading an MSH mesh format (Fluent mesh format). This CFD methodology employs a multi component approach, which means the model is split into a certain number of regions. In TCFD each region can have its own mesh and individual meshes comunicate via interfaces.

CFturbo mixed flow pump meridian view      CFturbo mixed flow pump periodic view

The Mesh

In this particular, case the pump model is split into three components. The Inlet tube, the Impeller, and the Volute. Each component has its own mesh. All the meshes are created automatically for each component within snappyHexMesh. Any number of model components is allowed.

CFturbo mixed flow water pump z+ view STL model      CFturbo mixed flow water pump general view STL model      CFturbo mixed flow water pump z- view STL model

Periodic segment or not?

The computational mesh can be either created for the whole impeller as well as for a single blade periodic segment of the impeller. Periodic segment approach can save a reasonable amount of the mesh cells, which is resulting in the reduction of the simulation CPU time.

CFturbo mixed flow water pump z+ view STL model

Mesh Boundary Layer or not?

Another decision to take is adding a "boundary layer" or not. The boundary layer is several layers of cells close to the walls to catch the velocity gradient at the wall. Boundary layer in the mesh usually gives more accurate results but is paid by a higher CPU time. By the experience, the mesh with no boundary layer typically over-predicts the total efficiency in the order of 1% - and saves about 40% of CPU time.

Fine Mesh?

In any CFD simulation, there is always big question how fine mesh is needed for certain level of CFD results. In rotating machinery there is usually clear trend observed: the finer mesh leads to slightly higher efficiency.

CFD pump blockmesh block volute spiral    CFD mesh pump volute spiral snappyHexMesh

Easy to test the mesh sensitivity

In practice, the rough mesh with no boundary layer (CPU time: 4 core*hours/single point) can give the same results as the fine mesh with boundary layer (CPU time: 20 core*hour/point). So finally, the rough mesh effect can eliminate the lack of boundary layer. Anyway, with a fully automated workflow it is easy to make many sensitivity tests to callibrate to actual data.

CFD pump mesh blockmesh impeller    CFD mesh pump impeller full wheel    CFD mesh pump impeller periodic segment wheel

The component graph

Any project simulated in TCFD has its component graph. The component graph shows how the components are organized - the model topology. What is the inlet, the outlet and how the components are connected via interfaces.

CFD pump tcfd tutorial component graph

CFD Simulation Set-up

  • Incompressible flow model
  • Steady-state flow model
  • Medium: Water
  • Viscosity: ν = 8.899e-7 [m2/s]
  • Rotation speed: 1770 [RPM]
  • Flow Rate: 0.126 [m3/s]
  • Interface: mixingInterface (radial averaging)
  • Turbulence Model: k-ω SST
  • Mesh: snappyHexMesh, hexadominant
  • Mesh Cells (full/segment): 3119524/867306
  • Mesh Average y+ (full/segment): 16/16 [-]
  • CPU time (full/segment): 15/4 [core.hours]

For more details of CFD Simulation Set-up see TCFD Manual.

Running CFD Simulation

The simulation can be run on any number of parallel processors. Immediately after the simulation is started, the user can follow the progress of all the important quantities in a HTML report: flow rates, residuals, efficiency, torque, pressure difference and many others. These run-time functions give the user valuable information of the simulation convergence and also the availability to stop the simulation before its expected end.

CFD pump run time convergence monitor flow rate efficiency segment    CFD pump run time residual convergence segment

Every simulation performed in TCFD has its own report in .html format: Pump Simulation Report Example.

Visual Postprocessing using Turbo Blade Post

The simulation results are examined in ParaView. ParaView is CFD postprocessing tool providing all standard features for analyzing CFD data.

TCFD pump Turbomachinery CFD Cull frontface view      CFD pump Turbomachinery STL impeller streamtraces view      CFD pump impeller volute interface

CFD Support developed a special extension to ParaView for visual postprocessing rotating machinery: Turbo Blade Post, which is special set of filters for ParaView to enable for example blade-to-blade view, or meridional average. Turbo Blade Post detailed manual is available on-line: Turbo Blade Post Manual

TCFD Turbo Blade Post Meridian Average      TCFD Turbo Blade Post Unwraped Blade To Blade View Pressure around blade

Within the Turbo Blade Post the impeller mesh can be unwrapped to be able to slice the computed quantities of the same height along the blade - spans between hub and shroud. With such an unwrapped mesh it is also possible to plot all the quantities along the blade at the certain height. Another Turbo Blade Post function is the Meridional Average which creates a special meridional plane of circumferential averages of simulated quantities.

TCFD Turbo Blade Post Unwraped Wheel View      TCFD OpenFOAM Turbo Blade Post Unwraped Wheel Slice      TCFD OpenFOAM Turbo Blade Post Unwraped Blades Slice      TCFD OpenFOAM Turbo Blade Post Pressure along blade

See also other TCFD simulation examples:

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