Hi, I am trying to do turbulent channel flow simulations. I need to use periodic bc in x and z directions. I specify a pressure gradient in the periodic panel. I do not get any flow structures. how do i specify any some disturbances in the flow and make sure that they are sustained?

"any flow structures" What are you looking for?

What turbulence model have you used? What kind of disturbances do you want to initiate? Is their sustaining physical?

Please somewhat more info to work with...

Laika, still orbiting

well I am trying to validate a new hybrid turbulence model with the DNS data of moser et al. at Re_tau of 640. So they use periodic bc in both streamwise and spanwise directions. I generated a case file by implementing periodic bc in both streamwise and spanwise directions and then for the periodic bc, I chose the pressure gradient as driving force. I am unable to get flow structures of any sort. I want to create some velocity diturbances which are sustained. How do I create an initial velocity fluctuation and sustain it? This is a transient simulation. Sunil