Velocity fluctuation.
 

Hi all,

I am doing an LES where I have jets entering my domain (a cylinder) at the left face. The axial component is the dominant component of velocity. The velocity at the inlet boundary is composed of a mean value and random fluctuating component based on an experimental rms.. When I plot the axial velocity in the axial direction I see quiet distinct and significant fluctuation in the velocity....in a zig-zag type manner...similar to a decoupled pressure field. However, I do not see an fluctuations in the pressure....it behaves as I would expect. Can anyone tell me where I may be going wrong? I have never seen this problem before. I use no-slip walls and a onvective outflow for the an annular exit.

Re: Velocity fluctuation.
 

Is this an instantaneous snapshot at a particular time of velocity vs. axial distance? If so, does it alternate on successive time steps? Or is it 'sort of' periodic when viewed over several time steps?

The first things I'd suggest are to look at mesh resolution and time step size. In other words, be sure your stability criteria are being satisfied.

Some of the readers with more LES experience will likely be more helpful.