# Transient Series 4: Calculating Variables and Using Contour Color Cutoff

## Description

This video demonstrates how to calculate a new variable, Vorticity Magnitude, using the built in CFDA Functions of Tecplot 360 from the existing variables in a dataset. Then shows use of the Contour Color Cutoff property to isolate a specific region of Contour levels in a plot.

In this video, we will be demonstrating how to calculate new variables from the CFDA Analyze menu, as well as using the Contour Color Cutoff feature to isolate interesting regions of our plot.

For the same data set we have used in previous videos, we now want to visualize the vortices shed from the blade movement evolve over time. To do this, we will calculate a new variable, Vorticity Magnitude, to show the strength of the vortex.

1. Before performing any calculation(s), we first need to ensure that the required existing variables are properly assigned in the Field Variables dialog. For this data set we can see that the Convective Variables (Velocity) and the State Variables (Pressure and Density) have already been assigned.
2. Next, from the Analyze menu, choose Calculate Variables, then click Select to bring up a list of Functions built into Tecplot 360. For this exercise, select Vorticity Magnitude as the new variable to calculate. Keep all the defaults, and click Calculate. Having Calculate on Demand toggled on will defer loading of the new variable until it is needed in the plot.
3. Vorticity Magnitude has now been added to our data set as a new variable, and we can select it as the active Contour Variable in the Contour Details dialog. Readjust the Contour levels from 0 to 50 over 21 levels, to make even levels and a more interesting plot. Then utilize the Cutoff property to hide any values of Vorticity Magnitude below 7. This isolates and emphasizes the vortex shedding values in our plot. We can make several other quick adjustments to the legend and clean up the plot.
4. Then click Animate.
5. The initial animation moves slowly because we selected Calculate on Demand when calculating Vorticity Magnitude. Now that we are stepping through each time step, Vorticity Magnitude is being called to Load the variable value at each Zone as we animate. Toggling off Calculate on Demand will skip this process during the first animation, and instead load all the variable values upon the initial calculation. Once the initial loading for all the Zones has completed, the animation will perform much more smoothly.

Thanks for watching!