[Suya_94]

Hello,


I've been using IBM method, implemented in foam extend ver 4.0, and lately trying to simulate a flow over a moving airfoil body. The body is oscillating transversely to the incoming flow, with a Reynold number of about 5000.


The flow has been initialized using potentialIbFoam, and a desired initial field is generated across the domain. Thereafter, when the simulation is started using the icoDyMIbFoam solver, I get non physical values of force coefficients (only pressure forces, not viscous) on the surface of the body, in the very first iteration itself, following which the simulation is diverged in the second time step.


I've tried to decrease the time step value from 0.001s to 0.0005s, which is far lower than the value obtained using the CFL condition (around 0.01s), but the simulation again diverges. Following is the simulation timesteps shown:




Create time

Create dynamic mesh for time = 0

Selecting dynamicFvMesh immersedBoundarySolidBodyMotionFvMesh
Selecting solid-body motion function linearOscillation

PIMPLE: Operating solver in PISO mode

Reading transportProperties

Reading field p

Reading field U

Reading/calculating face flux field phi


Starting time loop

Time = 0.0005

solidBodyMotionFunctions::linearOscillation::trans formation(): Time = 0.0005 transformation: ((0 0.00055292 0) (1 (0 0 0)))
Moving immersed boundary points for patch foil
Mesh update1
Create immersed boundary cell mask
Create immersed boundary face mask
Found immersed boundary patch 0 named foil
External flow
Number of IB cells: 2548
Courant Number mean: 6.7455e-07 max: 3.40648e-06 velocity magnitude: 0.000170893
PIMPLE: iteration 1
GAMG: Solving for Ux, Initial residual = 0.213939, Final residual = 1.08026e-13, No Iterations 1
GAMG: Solving for Uy, Initial residual = 2.10262e-05, Final residual = 2.61728e-17, No Iterations 1
GAMG: Solving for Uz, Initial residual = 3.83474e-06, Final residual = 3.88647e-17, No Iterations 1
GAMG: Solving for p, Initial residual = 1, Final residual = 0.00801549, No Iterations 100
IB time step continuity errors : sum local = 4.46747e-07, global = -1.11232e-08, cumulative = -1.11232e-08
GAMG: Solving for p, Initial residual = 0.0840467, Final residual = 0.00234937, No Iterations 100
IB time step continuity errors : sum local = 3.04898e-07, global = 2.2904e-09, cumulative = -8.83276e-09
GAMG: Solving for p, Initial residual = 0.038109, Final residual = 0.00214116, No Iterations 100
IB time step continuity errors : sum local = 2.88859e-07, global = 4.977e-09, cumulative = -3.85575e-09
ExecutionTime = 768.31 s ClockTime = 783 s

triangles: 63246 hit: 2548
forces output:
forces(pressure, viscous)((2556.89 -238.327 -0.299448) (0.00105599 -0.0904754 3.87058e-05))
moment(pressure, viscous)((2686.32 4230.69 -275.721) (-0.11958 -0.140859 0.00575492))

Time = 0.001

solidBodyMotionFunctions::linearOscillation::trans formation(): Time = 0.001 transformation: ((0 0.00110584 0) (1 (0 0 0)))
Moving immersed boundary points for patch foil
Mesh update1
Create immersed boundary cell mask
Create immersed boundary face mask
Found immersed boundary patch 0 named foil
External flow
Number of IB cells: 2548
Courant Number mean: 0.00698439 max: 0.838342 velocity magnitude: 42.0573
PIMPLE: iteration 1
GAMG: Solving for Ux, Initial residual = 0.958781, Final residual = 5.86282e-06, No Iterations 1



So, the simulation stops here, and does not proceed further.



I suspected that the initial residual values are quite higher, but still unable to understand why the simulation diverges during the initial steps itself.



The domain mesh is of around 6 million cells.


The dynamic motion parameters are:


1) Amplitude : 0.88
2) Period: 5s


I've tried changing the solver from GAMG to amgSolver(V-cycle and W-cycle), but I notice a similar divergent result. Also, I've used crankNicolson scheme for time discretization and spatial discretization is also second order accurate.


Really not sure, if there is some problem with the setup, or is it IB mesh concern.



If anyone could point me in a right direction, regarding where to look for the error resolution, I would greatly appreciate that.


Also, please let me know if any other detail is required regarding the setup.