Node129 - 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 separate the chosen blade from the rest. This is done by the filter Clip. Adding the Clip filter will provide the user with an interactive positioning tool consisting of a ball in the origin, clipping plane and its normal. Use the ball to position the plane. Use the axis to orient the plane; see figure

. Once you have placed the clipping plane to one side of the chosen blade so that it doesn’t intersect any blade, click apply.

Step 9 — Append the filter Contour. In the drop-down list “Contour By” select the pressure field. Use the red cross button to erase suggested contour values (right bottom of the box “Value Range”) and then press grid button (right top) to populate the list of contour values by equidistant values covering the whole pressure range. Do not modify the suggested minimal (“From”) and maximal (“To”) values, and use e.g. 20 samples (“Steps”). See the figure

Step 10 — Pressing “Apply” will calculate the contour data and display the contours, hiding the blade geometry. Click on the eye symbol in “Pipeline Browser” to show the blade again. The results are in the figure

Figure: Interaction with the interactive Clip manipulator when separating a single blade of a pump transformed by Turbo Blade Post / Turbo Unwrap filter. The blades are colored by static pressure calculated by TCFD using OpenFOAM.

Figure: Settings of the filter Contour applied on a isolated pump blade transformed by Turbo Blade Post / Turbo Unwrap filter.

Figure: Static pressure field and contours on an isolated blade transformed by Turbo Blade Post / Turbo Unwrap filter. The pressure data have been calculated by TCFD using OpenFOAM. Left is the pressure side, right the suction side of the blade.