[Nitin Minocha]

Hello Foamers
I am performing DNS of turbulent channel flow to understand the relationship b/w hairpin vortices and heat transfer associated with it. In the literature, the formation of hairpin vortices is explained as follows: First of all, vortices formation in spanwise (z) direction due to gradient of streamwise velocity (du/dy) in wall normal (y) direction. Stretching and lifting of spanwise (z) vortices results in two counter-rotating vortices in streamwise (x) direction. These vortices elongate further in x direction and eventually connect at y+=15 and results in formation of hairpin.
I am not able to understand the driving force behind stretching and lifting?
Please share your experience and understanding.

[FMDenaro]

Originally Posted by Nitin Minocha

Hello Foamers
I am performing DNS of turbulent channel flow to understand the relationship b/w hairpin vortices and heat transfer associated with it. In the literature, the formation of hairpin vortices is explained as follows: First of all, vortices formation in spanwise (z) direction due to gradient of streamwise velocity (du/dy) in wall normal (y) direction. Stretching and lifting of spanwise (z) vortices results in two counter-rotating vortices in streamwise (x) direction. These vortices elongate further in x direction and eventually connect at y+=15 and results in formation of hairpin.
I am not able to understand the driving force behind stretching and lifting?
Please share your experience and understanding.

to understand this issue, start from the Helmholtz equation for the dynamics of the vorticity. The key is in the term (w. Grad v) that is non-vanishing in 3D. Such term (stretching term) is responsible for the alignemnt of the vortex tube along the stream-wise direction and the reduction of the tube section.

[aerosjc]

Originally Posted by FMDenaro

to understand this issue, start from the Helmholtz equation for the dynamics of the vorticity. The key is in the term (w. Grad v) that is non-vanishing in 3D. Such term (stretching term) is responsible for the alignemnt of the vortex tube along the stream-wise direction and the reduction of the tube section.

Mark. Important and interesting question. I'll try to put my notes here later.