Studying Burgers' models to investigate the physical meaning of the alignments statistically observed in turbulence

The alignments between the vorticity, the vortex stretching vector, the pressure Hessian eigenvectors and the strain rate eigenvectors are computed and discussed in the case of the Burgers' vortex and the Burgers' layer. It is shown that the main physical properties of these models can be deduced from these alignments. Following this example, the alignments between these vectors in turbulent flows are interpreted as dominated by stretched, coherent and locally quasi-bidimensional regions. This induces a new and safer classification for the strain rate and the pressure Hessian eigenvalues. (C) 1997 American Institute of Physics.