[ankgupta8um]

Hello,

I am using coodles solver in OpenFOAM 1.4.1 to simulate flow through a cylinder. The computational domain is very simple and consists of an annular pipe attached to a cylinder. This is an expansion problem where the flow through the annular pipe expands into the cylinder (annular jet expanding into a cylindrical pipe). The boundary conditions I am using are:
- fixed value velocity inlet at the annular cross-section; zero gradient for pressure.
- no-slip walls for annlar pipe and cylindrical pipe; zero gradient for pressure.
- waveTrnasmissive pressure BC at the downstream end of the cylinder; inletOutlet BC for velocity.

I am not able to get a reasonable flow field in the computational domain. It seems to me that the unphysical pressure waves in the domain are destroying the numerical solution. Initially, I used the default solver settings as given in the pitzdaily tutorial. Then I tried using recommended convective discretization schemes (eg, fliteredLinear) for LES but that didn't help. I also tried using upwind scheme with the hope that the increased dissipation will dissipate out the spurious pressure waves, but that also didn't help.
I tried different initializations at the start of the run (starting from the RANS solution, starting from a quiscent medium) but all led to unphysical flow field.

I think that the unphysical pressure waves are destroying the solution. The reason being: I ran a case where instead of using walls for the cylindrical surface, I used pressure transmissive boundaries (i.e., no confinement; annular jet expanding into an eclosure with pressure transmissive boundaries at the cylindrical periphery and at the downstream end). For this case, I could get a physical flow field. That suggests that the numerical disturbances in the form of spurious pressure waves exit the computational domain from the peripheral boundary of the cylinder when pressure Transmissibe BC is used there. When wall is used it reflects back and destroys the solution.

I have been trying to resolve this issue in coodles with the use of walls close to the jet for quite some time now but haven't had any success. I am stuck with this issue and need to resolve it in order to make some progress.

I would really appreciate it if someone can throw some light on what the potential causes for this problem are and how to resolve it. People having similar experiences with coodles are kindly requested to share them with the forum. Any information on getting coodles solver to work is also welcome !!

Thanks!
Regards,
Ankur