Vector vorticty vector, if q bar is the velocity vector of a fluid particle then what will happen, if q is the velocity vector of fluid particle then what will happen curl of q bar. Curl of q bar will be del cross q bar and that also we can write it as i j k then you have del by del x del by del y del by del z that is u v w. And this I call it as omega bar and I call this vector at the vorticity vector, this represents this vorticity vector omega bar represents the velocity of a represents the angular velocity of the fluid particle of the fluid particle.