- #1

HNB

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Hello

I am trying to validate my model by comparing a simple axisymetric 2D

impacting flow of air on a surface.

The geometry is simple: a cylindrical (diameter d=26.5e-3[m]) jet of air

(debit Speed Ud=13.46[m/s]) is impacting a surface at distance H=0.2833[m].

Flow temp is Tj=20°C Wall temp is Tp=30°C

The input flow profile is either

- a uniform flow with speed Ud and standard length scales It=0.05 and

Lt=0.01

- an established flow profile Ue, ke, epe

- a non-established flow profile Ueb, keb, epeb

The model is very capricious, I'm on it since 2 monthes and it seems to

converge quite rarely...

1) First, I tried to get the turbulent low-Re flow physics to work. The

first file shows my first approach, with a thin wall at the side of the

jet. In that case, the model converge to a solution where the flow in the

dead zone is homogenous, and the shape of the turbulent viscosity seems

correct. But if I try to refine the mesh, then it doesn't converge anymore,

and the 'thin wall' solution is not really practical either.

2) The second file shows a model which converges to a solution where on

can see a (toric) rotation structure in the flow of the dead zone. As a

result, the shape of the turbulent viscosity looks quite bad. Here the mesh

is quite dense, and the model does not converge anymore if I try to enlarge

it in the zones that aren't that interesting. You will see a lot of unused

meshes and functions that come from many tries I made to make this damn

*thing* converge. Oftentimes, the rotation structure goes mad on itself and

creates a wirlpool with growing turbulent energy that makes the model

diverge.

3) Based on that 2nd model, I tried a multiphysics model adding a heat

transfer physics (ht+spf) or using non-isothermal Low-Re turbulent flow

(nitf). Whatever I try (mesh, BC, etc.), there is no convergence.

Please could you help me to understand:

- what makes my first model converge only with large mesh and diverge if

I refine the mesh?

- where do those rotational structures come from? Are they realistic

physics, or artefacts? Maybe the incoming flow from the outputs BC adds

turbulent energy to the system? But changing BC outputs to open frontiers

and specifying k=0 and ep=0 does not seem to help.

- Is there anything wrong in my model (in Discretization or Stabilization

parmeters for instance)

- And finally, are my solver configuration parameters correct?

Thanks a lot in advance!

(All parameters are taken from: "Etude comparative de modeles à bas

nombre de Reynolds dans la prédiction d'un écoulement à point de

stagnation" (in French) R. Hadef, B. Leduc. 5, 2002, Int. Comm. Heat Mass

Transfer, Vol. 29, pp. 683-695.)

I am trying to validate my model by comparing a simple axisymetric 2D

impacting flow of air on a surface.

The geometry is simple: a cylindrical (diameter d=26.5e-3[m]) jet of air

(debit Speed Ud=13.46[m/s]) is impacting a surface at distance H=0.2833[m].

Flow temp is Tj=20°C Wall temp is Tp=30°C

The input flow profile is either

- a uniform flow with speed Ud and standard length scales It=0.05 and

Lt=0.01

- an established flow profile Ue, ke, epe

- a non-established flow profile Ueb, keb, epeb

The model is very capricious, I'm on it since 2 monthes and it seems to

converge quite rarely...

1) First, I tried to get the turbulent low-Re flow physics to work. The

first file shows my first approach, with a thin wall at the side of the

jet. In that case, the model converge to a solution where the flow in the

dead zone is homogenous, and the shape of the turbulent viscosity seems

correct. But if I try to refine the mesh, then it doesn't converge anymore,

and the 'thin wall' solution is not really practical either.

2) The second file shows a model which converges to a solution where on

can see a (toric) rotation structure in the flow of the dead zone. As a

result, the shape of the turbulent viscosity looks quite bad. Here the mesh

is quite dense, and the model does not converge anymore if I try to enlarge

it in the zones that aren't that interesting. You will see a lot of unused

meshes and functions that come from many tries I made to make this damn

*thing* converge. Oftentimes, the rotation structure goes mad on itself and

creates a wirlpool with growing turbulent energy that makes the model

diverge.

3) Based on that 2nd model, I tried a multiphysics model adding a heat

transfer physics (ht+spf) or using non-isothermal Low-Re turbulent flow

(nitf). Whatever I try (mesh, BC, etc.), there is no convergence.

Please could you help me to understand:

- what makes my first model converge only with large mesh and diverge if

I refine the mesh?

- where do those rotational structures come from? Are they realistic

physics, or artefacts? Maybe the incoming flow from the outputs BC adds

turbulent energy to the system? But changing BC outputs to open frontiers

and specifying k=0 and ep=0 does not seem to help.

- Is there anything wrong in my model (in Discretization or Stabilization

parmeters for instance)

- And finally, are my solver configuration parameters correct?

Thanks a lot in advance!

(All parameters are taken from: "Etude comparative de modeles à bas

nombre de Reynolds dans la prédiction d'un écoulement à point de

stagnation" (in French) R. Hadef, B. Leduc. 5, 2002, Int. Comm. Heat Mass

Transfer, Vol. 29, pp. 683-695.)