vortexidentifikaation

Vortexidentifikation is a set of methods used in fluid dynamics to locate and characterize vortices within a flow field. It is applied to three-dimensional numerical simulations and experimental velocity data, such as particle image velocimetry (PIV). The aim is to identify regions where rotational motion is dominant and to quantify attributes such as strength, size, and orientation, enabling analysis of turbulent structures, wakes, and jet flows.

Several criteria are commonly employed. The vorticity magnitude highlights regions of high rotation but can misidentify shear layers. The Okubo–Weiss criterion distinguishes rotation-dominated from strain-dominated regions in two-dimensional flows. The Q-criterion identifies vortices where rotation overcomes strain. The Lambda-2 criterion uses the eigenvalues of the velocity gradient’s symmetric and antisymmetric parts to locate vortices. The swirling strength (lambda_ci) measures the local rate of rotation from the complex eigenvalues of the velocity gradient and provides a scalar measure of vortex intensity. Each method has its own sensitivity to noise, resolution, and the presence of multiple vortices. The concept has been developed and refined since the 1990s, with the Q-criterion and related approaches becoming standard tools in CFD visualization.

Applications span aerospace and mechanical engineering (aircraft wakes, turbine and rotor flows), automotive aerodynamics, combustion, and atmospheric and oceanic sciences where coherent vortices influence transport and mixing. Limitations include dependence on threshold values, data quality, and the fact that different criteria may reveal different structures in the same field; therefore, vortex identification is often used in combination with visualization techniques and interpreted within the broader flow physics.