[spy_hzdr]

Why in CFX drag coefficient cannot be defined as a function of the wall-distance?

Hi there, I am working on Euler-Euler simulation of bubbly flows in vertical pipes. My aim is to test a new drag force model, according to which the drag coefficient would increase when the bubble is approaching the wall.
I first tested the standard drag force model of Ishii-Zuber and the simulation was ok. I then modified the drag coefficient by multiplying the standard drag coefficient by a prefactor. This prefacor is a function of wall distance normalized by the bubble radius (e.g. prefacor = min(10, (1+0.1*LR^-4)) with LR = Liquid.Wall Distance/1 [mm]). The new simulation crashes in the first loop with the report given below. Can anyone give me a hint?
Best regards,
Pengyu

OUTER LOOP ITERATION = 1 CPU SECONDS = 3.218E+00
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| Wallscale-Liquid | 0.00 | 2.6E-04 | 3.1E-04 | 42.4 2.6E-01 ok|
+----------------------+------+---------+---------+------------------+
----------------------------------
Error in subroutine cal_WALLDIST :
Error calculating WALLDIST_FL2
GETVAR originally called by subroutine cal_CAB_MOM

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine GV_ERROR |

[Gert-Jan]

I think the variable "WALLDIST_FL2" is refering to the second fluid. I would therefore try Gas.Wall Distance in stead of Liquid.Wall Distance.

[spy_hzdr]

Originally Posted by Gert-Jan

I think the variable "WALLDIST_FL2" is refering to the second fluid. I would therefore try Gas.Wall Distance in stead of Liquid.Wall Distance.

thank you for the suggestion. I tried but got the following error:

Error in subroutine cal_WALLDIST :
Error calculating WALLDIST_FL1
GETVAR originally called by subroutine cal_CAB_MOM

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine GV_ERROR |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

[ghorrocks]

I suspect the Wall Distance variable is only calculated if you are using a model which requires it - which is normally a turbulence model in the SST family. So unless you are using an SST based turbulence model the Wall Distance variable will not exist.

[spy_hzdr]

Originally Posted by ghorrocks

I suspect the Wall Distance variable is only calculated if you are using a model which requires it - which is normally a turbulence model in the SST family. So unless you are using an SST based turbulence model the Wall Distance variable will not exist.

thank you Glenn for the kind reply. Indeed, I am using SST. Also, I am pretty sure the Wall Distance variable is available in the setting: I also tried to modify the rest interfacial forces (e.g. lift, virtual mass, turbulent dispersion, wall lubrication) in a similar way as I did for the drag and all these simulations are ok.
So, it seems that one can multiply a function of the wall-distance to any of the interfacial force coefficients except the drag coefficient.

[ghorrocks]

Are you sure the Wall Distance variable is by phase? I mean you have "Liquid.Wall Distance", but is it just "Wall Distance"? The wall distance is the same as a location for all phases.

[spy_hzdr]

Originally Posted by ghorrocks

Are you sure the Wall Distance variable is by phase? I mean you have "Liquid.Wall Distance", but is it just "Wall Distance"? The wall distance is the same as a location for all phases.

yes. this is for sure, although "Liquid.Wall Distance" is the same as "Gas.Wall Distance".

[spy_hzdr]

Hey everyone,
the problem disappears when I switch from CFX19.2 to CFX21.1. So, likely it is a bug with CFX19.2. Thank you veryone for your time.