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External Flow – CFDA and Variable Calculation


This video demonstrates how to properly define the Tecplot 360 CFD Analyzer (CFDA) settings in a data set, and how to use those settings to calculate velocity from momentum.

In this video we will be using the ONERA M6 Wing and CFD Analyzer to calculate variables that don’t exist in the incoming data set.

The CFD Analyzer allows the conversion between the velocity and momentum. For this direct conversion, we must supply the fluid properties of the air and the field variables already present in the data set. In this video we will include additional properties not strictly required for this calculation; however they will be required for other uses of the CFD Analyzer. These additional properties include the reference values as they approach infinity and overall case properties (with alpha, the angle of attack, at 0).

The data set used for this video is the ONERA M6 Wing, which can be found in the examples folder of the Tecplot 360 installation (or link above).

The first step will be determining the reference values at the inlet. One method is to Probe at the far field of our fluid volume to find the necessary variable values.

In the Surfaces tab of the Zone Style dialog, select Exposed cell faces under Surfaces to Plot for the fluid volume. Then select the Probe Tool and probe near the inflow. From here we can see the Reference Values for Mach, Density, and Temperature.

Enter the appropriate Reference Values from the Analyze menu, including the Angle of Attack at 0.

Next, select Fluid Properties from the Analyze menu and ensure that the toggle for Incompressible flow is toggled off. Enter 287 for the gas constant, keep 1.4 for gamma, and toggle on Use Field Variable for viscosity to choose Eddy Viscosity from the data set. Leave the default value of conductivity at 1.

Finally, open the Field Variables dialog. Use the assigned Momentum vectors with U, V, W as the convective variables. Select Density and Stagnation energy as the State Variables, and assign Density and Energy respectively from the variables in the data set.

To save these settings select Analyze > Save Settings… At any point the saved file can be loaded back in and the settings just configured will be restored.

Now, we can finally open the Calculate Variables dialog and select Velocity (vector). Keep the defaults and select Calculate to generate the velocity vector variables. Having Calculate on

Demand toggled on will defer loading of the new variable until it is needed in the plot

To visualize these new variables, Toggle off the Surfaces for the fluid volume, and select Plot > Vector > Variables… to reassign the vector variables. Place a slice and draw a rake of streamtraces to inspect the quality of the calculated velocity.

This concludes the tutorial on Variable Calculation and the CFD Analyzer.

Thanks for watching!

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