Node127 – CFD SUPPORT

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Step by step guide

Step 1 — Load the rotor part of an OpenFOAM case into ParaView using the command paraFoam -region rotor. Avoid loading the whole mesh; choose only the blade walls and the hub and shroud patches. Choose some non-zero simulation time, select appropriate components (“Mesh parts”) and fields (“Volume fields”) and press “Apply”. This will load the necessary patches, figure

Step 2 — First, the blades need to be transformed from the cylinder- or disk-like arrangement to a straight rectangular block. This is done by the filter Turbo Unwrap. You should see the icon of the filter in the toolbar. Note that the filter is available (i.e. coloured and clickable) only when the data selected in “Pipeline browser” are of the type “Multi-block Dataset” (see panel “Information”, section “Statistics”).

Either use this button, or select the filter Turbo Unwrap in the Filters > Turbomachinery (or Filters > Alphabetical) menu, or use the search box from Filters > Search. This will add the filter into the “Pipeline browser”.

Step 3 — The basic properties of the filter Turbo Unwrap are shown in the figure

. When the advanced options are hidden, there are only a few options to define. First of all, it is necessary to choose the blade wall patch, that will be transformed, and the hub and shroud patches, which will serve as a leaders to define the transformation. After the transformation is done, hub and shroud will be perfectly flat and parallel to each other, conformly deforming the mesh in between. If multiple mesh parts are selected in the “Unwrap mesh” window or multiple patches are selected in “Hub” or “Shroud” windows then they will be internally merged into a single entity before proceeding. In this example the mesh is well prepared and we can just select the three items that we loaded in the first step.

Step 4 — Set the direction and position of the rotating axis using the parameters “Axis” and “Origin”. In our case we use

-axis, which is the default option.

Step 5 — Unlike in the case of the blade-to-blade view, when constructing the pressure profile it is mostly not necessary to specify a non-zero “Clip out radius”, because the blades do not reach all the way to the axis in the middle. We will leave the parameter having its default zero value.

Step 6 — Click on “Apply”. The transformation should be relatively fast, because the sufrace mesh of the blades is orders of magnitude easier to process than the full volume mesh. It may be necessary to zoom in or out a little (depending on the geometry) to make the result fit to window. Outcome of this step is shown in the figure

, where the blades are coloured by pressure.

Step 7 — Having the blades transformed we can now cut them at a specific height (

-axis) using the filter Slice. This will result in several two-dimensional intersection contours.

Step 8 — Add the filter Plot Data from Filters > Alphabetical or using Filters > Search. Unselect all fields but pressure (see figure

). Above the field selection box use “Points_Y” as the “X Array Name”. This will use points’ Y coordinates as the data for the horizontal axis. Below the field selection box use “None” as “Line Style” and “Circle” as “Marker Style”. This will only show one bullet per a mesh point, making the result independent on the order of the projected points. Now press “Apply”. You should obtain a similar figure to

Figure: Settings of the Turbo Blade Post / Turbo Unwrap filter for transformation of blades of the pump.

Note — The plot will contain data from all blades. As the blades are equivalent, it doesn’t hurt the visualization. If just a single blade profile was required, it would be necessary to separate one of the contours using a pair of the Clip filters .

Figure: Pressure distribution around the blade for a given height (i.e. relative distance from the hub to the shroud) constructed with the aid of the plugins of Turbo Blade Post toolset. The horizontal axis shows the transformed Y axis, which corresponds to the normalized inlet-to-outlet direction position (for given hub-to-shroud distance and angular position). The vertical axis displays the value of the pressure as computed by TCFD using OpenFOAM.

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