Vortex identification in the wall region of turbulence channel flow

Four widely-used techniques for vortex detection in turbulent flows are investigated and compared. The flow of a viscous incompressible fluid in a plane channel is simulated numerically by means of a parallel computational code based on a mixed spectral-finite difference algorithm for the numerical integration of the Navier-Stokes equations. The DNS approach (Direct Numerical Simulation) is followed in the calculations, performed at friction Reynolds number Reτ = 180. A database representing the turbulent statistically steady state of the velocity field through 10 viscous time units is assembled and the different vortex-identification techniques are applied to the database. It is shown that the method of the "imaginary part of the complex eigenvalue pair of the velocity-gradient tensor" gives the best results in identifying hairpin-like vortical structures in the wall region of turbulent channel flow.