Experimental Validation of the Modified Holmén Vortex Identification Method

Abstract

The iterative vortex identification method originally proposed by Holmén was modified to improve its performance and to add the ability to distinguish between counter-rotating vortices. Then, the resulting modified Holmén method (MHM) was evaluated using experimental data from five different experiments, including planar and three-dimensional flowfield data. The Q, λ2, and Γ2 criteria were used for comparison. No currently available vortex identification method is perfect (otherwise, proposing a new scheme would be a pointless exercise), and the MHM is no exception; however, the MHM was found to accurately identify vortical structures when the number of passes is chosen correctly while minimizing the experimental noise. In particular, it was found to be useful in capturing large vortical structures occurring in a noisy or high-shear region, cases where the Q and Γ2 criteria sometimes fail. On the other hand, the method is limited by the spatial resolution of the experimental data with respect to the structure’s size and its inability to resolve rotating structures near the edges of the measurement domain.