icoFoam Blowup at Farfield Boundary

Deedledot · February 27, 2022, 02:19

Hello,

I am running a transient Karman-Trefftz airfoil case with icoFoam.

Re: 10000
α: 5°
Grid Topology: O
Number of Cells: ~1000000 (almost entirely perfect squares)

Δt: 0.0004

Domain Radius: 20c
Wall BC: zeroGradient Pressure, noSlip Velocity

Farfiled BC: fixedValue Pressure, fixedValue Velocity

I know this isn't the ideal setup for this problem but I am just trying to experiment. The max Courant number starts off a bit high for a few steps near the LE and TE where the cells are smallest, but it quickly settles into about 0.8 as the boundary layer grows. On the downstream boundary, a wavy artifact in the velocity field starts off barely visible and then gradually grows until the solution blows up.

t=0.4s
t04.png

t=6.0s
t6.png

t=7.6s
t76.png

Is there something wrong with my boundary conditions?

Deedledot · February 27, 2022, 10:07

Solved

I managed to stabilize it by changing the farfield boundary conditions to freestreamVelocity and freestreamPressure.

February 27, 2022, 02:19	icoFoam Blowup at Farfield Boundary	#1
Deedledot New Member Daniel Dotson Join Date: May 2020 Posts: 13 Rep Power: 6	Hello, I am running a transient Karman-Trefftz airfoil case with icoFoam. Re: 10000 α: 5° Grid Topology: O Number of Cells: ~1000000 (almost entirely perfect squares) Δt: 0.0004 Domain Radius: 20c Wall BC: zeroGradient Pressure, noSlip Velocity Farfiled BC: fixedValue Pressure, fixedValue Velocity I know this isn't the ideal setup for this problem but I am just trying to experiment. The max Courant number starts off a bit high for a few steps near the LE and TE where the cells are smallest, but it quickly settles into about 0.8 as the boundary layer grows. On the downstream boundary, a wavy artifact in the velocity field starts off barely visible and then gradually grows until the solution blows up. t=0.4s t04.png t=6.0s t6.png t=7.6s t76.png Is there something wrong with my boundary conditions?

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February 27, 2022, 10:07		#2
Deedledot New Member Daniel Dotson Join Date: May 2020 Posts: 13 Rep Power: 6	Solved I managed to stabilize it by changing the farfield boundary conditions to freestreamVelocity and freestreamPressure.