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Using Paraview to visualise vortex by lambda2, vortexity and QcriterionBy Qingfeng Xia, 2015-12-311. Install Paraview install the 64bit V5.0, 64bit is indispensable for large dataset processing2. export data from CFD softwareFrom CFX, export result as CGNS file (single zone or multiple zone should be fine), and load into paraviewCreate a new spreadsheet view, to lookup velocity vector variable name.CFD result could be exported as pointData(result value at the grid point) or cellData(value at cell centre), In the following tutorial, “Attribute Mode”“point Data” is used, but “cellData” is applicable. Paraview has a “CellDataToPointData” filter, which could be used to convert cellData into PointData for further visualisation. first of all, you need "velocity" vector, which is not present in your data file.Creating vectors from 3 scalarsFilters → Common → Calculator Build the vector equation using the iHat, jHat and kHat buttons on the calculator.Result Array Name → “Velocity” Expression: VelocityX*iHat+VelocityY*jHat+VelocityZ*kHatThe “gradient” filter, the result variable is “Gradients” by default, it is a tensor 3X33. Calculate lambda2After load the data file cgns, create a “Python Calculator” from “Filters->Alphabetical” menuPaste” eigenvalue(strain(Velocity)**2 + (Gradients - strain(Velocity)**)2)” Into Expression text box: Result name could be any text, here “Lambda” is used, Check “Spreadsheet view” for velocity vector variable name, it is assumed it is “Velocity”strain(Velocity)? is S tensor,calc the Gradient of velocity, it is D tensor,? "strain(Velocity)**2" will do "element-wise square" :? S_square_ij = S_ij*S_ijvorticity(Velocity)? is NOT the omega tensor, but a vector!? insteadomega = Gradients - SLambda_X >Lambda_Y>Lambda_Z is clearly shown in spread sheet, as Create a “Calculator” filter to extract the 2nd scaler of lambda vector, it is just another name for Lambda_Y, Switch to 3D view to plot lambda2, using contour filter (default to the mean of lambda2 ), the contour surface could be colored by any scaler, like T, pressure, etc. 4. Calculate Vorticity or Q-criterion to compare with lambda2You must click the gear icon button to activate advanced options.Tick the checkbox, “vorticity” and “Qcriterion”, after click “apply”, “vorticity” and “Qcriterion” appear in spreadsheet view. ................
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