POD as tool for comparison of PIV and LES data

Both Particle Image Velocimetry (PIV) and Large Eddy Simulation (LES) provides instantaneous velocity fields which can contain dynamical flow structures that occur systematically. Turbulent flows also contain random flow structures, and therefore there is a need for tools that can identify the systematic dynamic flow structures.

We show how Proper Orthogonal Decomposition (POD) based on snapshots (instantaneous flow realizations) can be used for this purpose. As a test case, we use PIV measurements and LES calculations on the same turbulent jet in cross flow. The Reynolds number based on the crossflow velocity and pipe diameter is 2400 and the jet to crossflow velocity ratio is R = 3.3.

The POD is able to identify two dynamic flow structures: jet shear-layer vortices and wake vortices. A good agreement for the dynamical content is found between PIV and LES.