[wertyfg]

In a 2D pipe flow (Poiseuille flow) Re = U*2R/nu, where R is the radius of the pipe. If I set inlet as U, then I can control the Re by varying viscosity nu.

However, if in the simulation, the pressure inlet and outlet is prescribed, how do I control Re? For example, if I set Re = 100, how should I set nu? nu is supposed to nu = U*2R/Re, however, U is not known a prior as pressure is given in the inlet and outlet.

Thanks

[FMDenaro]

Originally Posted by wertyfg

In a 2D pipe flow (Poiseuille flow) Re = U*2R/nu, where R is the radius of the pipe. If I set inlet as U, then I can control the Re by varying viscosity nu.

However, if in the simulation, the pressure inlet and outlet is prescribed, how do I control Re? For example, if I set Re = 100, how should I set nu? nu is supposed to nu = U*2R/Re, however, U is not known a prior as pressure is given in the inlet and outlet.

Thanks

This is a homework you can find in any textbook. Just as hint, write the momentum along the streamwise direction. You will see a relation between the pressure gradient and diffusive term along r.