## Fluids

#### Fluent-VOF-Problems reaching convergence

• wolterj
Subscriber

Hey,

following Problem:
I try to simulate flow throught a nozzel.

Physics:

Transient, Pressurebased

VOF-simulations 2 phases(Water-liquid/Air) Implicit body force, level set, interfacial anti-diffusion. Viscous model is SAS.

With Sufcae Tension and Wall adhesion

Boundryconditons is a profil from Simulations of the inlet-pipe(50mm long with a diameter of 3mm)

Solving:

PISO

SC: 2

NC: 1

N/C coupling

Least Cell....

Pressure:

PRESTO!

Momentum:

Bounded central Differencing

Volume-Fraction:

Geo-Reconstruct

Turbulence Kinetic energy:

Second Order

Rest: first order

Controls:

Pressure: 0.8

Desity: 1

Body Forces: 1

Momentum: 0.7

Turbulence Kinetic Energy: 0.8

Specific Dissipation rate: 0.8

Turbulent Viscousity 1

Level set Funktion 0.3

This setup were copied from an earlier project. in which somebody simulatet sth similar (simpler geometry of the nozzel)

Initialization Hybrid:

1 1.000000e+00

2 1.483658e-03

3 2.464239e-04

4 7.808120e-05

5 1.954829e-05

6 2.758029e-05

7 7.300978e-06

8 1.637179e-05

9 3.304232e-06

10 5.462358e-06

11 1.297115e-06

12 2.780550e-06

13 5.708590e-07

14 1.221940e-06

15 2.387166e-07

Time step size:  5e-5s

im using ANSYS 19.1

If any more data is needed dont mind to ask.

Thanks for ur help

• wolterj
Subscriber

Mesh:

Check:

Domain Extents:

x-coordinate: min (m) = -2.298173e-02, max (m) = 7.017803e-03

y-coordinate: min (m) = -2.199953e-02, max (m) = 8.000000e-03

z-coordinate: min (m) = -1.910000e-01, max (m) = -1.510000e-01

Volume statistics:

minimum volume (m3): 6.296011e-14

maximum volume (m3): 8.751962e-11

total volume (m3): 2.268875e-05

Face area statistics:

minimum face area (m2): 1.152058e-09

maximum face area (m2): 4.271876e-07

• wolterj
Subscriber

Mesh:

Quality:

Minimum Orthogonal Quality = 7.22601e-02 cell 351028 on zone 2 (ID: 2859648 on partition: 7) at location (-5.55571e-03 -7.51119e-03 -1.56400e-01)

(To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,

where Inverse Orthogonal Quality = 1 - Orthogonal Quality)

Maximum Aspect Ratio = 4.45425e+01 cell 354648 on zone 2 (ID: 2850200 on partition: 0) at location (-9.28973e-03 -8.64463e-03 -1.56400e-01)

• DrAmine
Ansys Employee

Check if poor quality is related to some few cells but even some few cells with poor metrics might cause issues. Under solver expert (TUI) enable saving residuals and post-process them to see where they accumulate.

• wolterj
Subscriber

got a better quality but still problems but not as bad as before. Its still converging to slow

Minimum Orthogonal Quality = 2.07948e-01 cell 167471 on zone 2 (ID: 5768309 on partition: 14) at location (-9.47030e-03 -7.19996e-03 -1.59992e-01)

(To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,

where Inverse Orthogonal Quality = 1 - Orthogonal Quality)

Maximum Aspect Ratio = 1.60527e+01 cell 26041 on zone 2 (ID: 5959628 on partition: 14) at location (-6.47500e-03 -8.72246e-03 -1.59122e-01)

• DrAmine
Ansys Employee
What kind of mesh do you have. CLSVOF and surface tension better with structured uniform grid.