Alphawater go down abruptly to a small number

Geb1313 · May 7, 2020, 06:00

Hi Foamers,

I am about to use interFoam for mudflow simulations using Herschel-Bulkley rheology. prior to my main job, I am simulating the conventional 3d dambreak by only changing the rheology of the fluid and assuming laminar flow. When I do simulate by varying the parameters tau0 and k, for certain combination of these parameters, I am facing this problem:

- After certain time step the fluid with alphawater=1.0 is disappearing. At some point of time alpha always go down abruptly to a very small number (order of 1.0e-5 even lower).
- I can't understand the physical implication. Does this have anything with my mesh size?

HPE · May 12, 2020, 14:05

Hi,

- Have you correctly inspect the values? Have you inspected them visually?
- Why do you think the value would be problematic?

Geb1313 · May 13, 2020, 13:17

Thank you HPE,

For my case I used a 6 degree inclined flume of length 4m, width 1m and height 1m with a Herschel bulkley fluid of tau0 =0.01, k =9.6e-3, n=0.34 and rho =1350. The dam size was 1mx1mx0.5m. The grid size was 50mm. After running interFoam and visualizing taking the free surface at alphawater=0.5( Contour at alphawater =0.5), it went as normal as the dambreak tutorial for newtonian fluids until the simulation time is 0.4 seconds. Afterwards the fluid disappeared from the flume. I tried to to inspect the results and the alphawater range was between 0.0 to 1.0 until t =0.4 seconds. After that the range went to 0.0 to 1.0e-16 just after t =0.41. I did not know why?

************************************************
What I was expecting was the flow would continue until the applied shear stress due to the weight of the fluid is less than tau0 (yield stress).

May 7, 2020, 06:00	Alphawater go down abruptly to a small number	#1
Geb1313 New Member Join Date: Mar 2020 Posts: 16 Rep Power: 6	Hi Foamers, I am about to use interFoam for mudflow simulations using Herschel-Bulkley rheology. prior to my main job, I am simulating the conventional 3d dambreak by only changing the rheology of the fluid and assuming laminar flow. When I do simulate by varying the parameters tau0 and k, for certain combination of these parameters, I am facing this problem: - After certain time step the fluid with alphawater=1.0 is disappearing. At some point of time alpha always go down abruptly to a very small number (order of 1.0e-5 even lower). - I can't understand the physical implication. Does this have anything with my mesh size?

May 12, 2020, 14:05		#2
HPE Senior Member Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 12	Hi, - Have you correctly inspect the values? Have you inspected them visually? - Why do you think the value would be problematic? __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

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May 13, 2020, 13:17		#3
Geb1313 New Member Join Date: Mar 2020 Posts: 16 Rep Power: 6	Thank you HPE, For my case I used a 6 degree inclined flume of length 4m, width 1m and height 1m with a Herschel bulkley fluid of tau0 =0.01, k =9.6e-3, n=0.34 and rho =1350. The dam size was 1mx1mx0.5m. The grid size was 50mm. After running interFoam and visualizing taking the free surface at alphawater=0.5( Contour at alphawater =0.5), it went as normal as the dambreak tutorial for newtonian fluids until the simulation time is 0.4 seconds. Afterwards the fluid disappeared from the flume. I tried to to inspect the results and the alphawater range was between 0.0 to 1.0 until t =0.4 seconds. After that the range went to 0.0 to 1.0e-16 just after t =0.41. I did not know why? ************************************************ What I was expecting was the flow would continue until the applied shear stress due to the weight of the fluid is less than tau0 (yield stress).