Animations of Flow Visualization

The vector field in any visualization is dependant on the relative velocity of the observer. Traditionally, the average value of the streamwise component of the global vector field is calculated and subtracted from each vector. However, the resulting LIC image, critical points, and vector field features are greatly influenced by the magnitude of the value subtracted from the streamwise velocity. Examples of this phenomenon are shown here.

Use the slider at the bottom of the applet to select different magnitudes to be subtracted. The number in the lower left hand corner is the percentage of the average value of the steamwise component that is being subtracted from each vector in the field.

In this mpeg animation, LIC is applied to experimentally acquired PIV data and superimposed in color is the swirl strength, which corresponds to vortex cores. The animation runs through a sequence of LIC images in which the magnitude subtracted from the streamwise velocity is gradually incremented. At different moments during the animation, the swirling eddies of the flow field are only apparent because we are viewing a frame convecting at a speed that matches the convection velocity of those eddies. Swirl strength, however, is Galilean invariant and does not vary with the magnitude subracted from the streamwise velocity as can be seen when a different magnitude is subtracted.