[foamF]

Hi everyone, I am using OpenFOAM to simulate a secondary clarifier, following the geometry and flow condition in a paper "Modelling the Dynamic Response of a Secondary Clarifier to a Sea Water Incursion at the Radford" (which can be searched in Google and downloaded).

I built a 2D model and used driftFluxFoam as solver and buoyantKEpsilon as turbulence model. I can run the model achieving a steady state. The plot of alpha.sludge shows that the sludge can settle.

But, the calculated SS removal efficiency (~ 60%) is much lower than that quoted in the paper. After many many trials, I still can't get the point why the calculation is not in order.

Below are the setup:
(Note: y axis is the gravitational direction and z axis is the direction of "empty")

1. BC
inlet: U fixedValue (0.1 0 0)
p_rgh fixedFluxPressure
alpha.sludge fixedValue
k fixedValue
epsilon fixedValue
nut calculated
outlet: U fixedValue (0 0.020807 0)
p_rgh fixedFluxPressure
alpha.sludge zeroGradient
k zeroGradient
epsilon zeroGradient
nut calculated
sludgeOutlet:
U pressureInletOutletVelocity
p_rgh fixedValue (0)
alpha.sludge zeroGradient
k zeroGradient
epsilon zeroGradient
nut calculated
freeSurface (and the symmetry plane along centreline of the clarifier)
U slip
p_rgh fixedFluxPressure
alpha.sludge slip
k slip
epsilon slip
nut slip
solidWalls
U noSlip
p_rgh fixedFluxPressure
alpha.sludge zeroGradient
k kqRWallFunction
epsilon epsilonWallFunction
nut nutkWallFunction
frontAndBack
empty for all BC

2. transportProperties
sludge:
transportModel: BinghamPlastic
coefficient 0.00023143
exponent 179.26
BinghamCoeff 0.0005966
BinghamExponent 1050.8
BinghamOffset 0
muMax 10
rho 1500
water:
transportModel: Newtonian
nu 1.7871e-6
rho 996
relativeVelocityModel simple
V0 (0 -0.00246 0)
a 405
a1 0
residualAlpha 0

any expert can give me some hints about that's wrong with the setup?

many many thanks.

[ahmmedshakil]

I hope it's not too late to reply to this. Based on my experience, a couple of things you can check. First of all, please check your setting parameter (for the settling velocity), then you may check on the rheological parameters, which have significant effect on hydrodynamics. Finally, you may check the turbulence modelling (I assume buoyant k-epsilon is correct, that's why I put it later). In addition, I assume your boundary conditions are okay.

Hope these will solve your problem.
Note: If you explain elaborately your problem, rather than the link of paper, then people may be more interested in the answering and have a closer look at it.

Cheers,
-S

Originally Posted by foamF

Hi everyone, I am using OpenFOAM to simulate a secondary clarifier, following the geometry and flow condition in a paper "Modelling the Dynamic Response of a Secondary Clarifier to a Sea Water Incursion at the Radford" (which can be searched in Google and downloaded).

I built a 2D model and used driftFluxFoam as solver and buoyantKEpsilon as turbulence model. I can run the model achieving a steady state. The plot of alpha.sludge shows that the sludge can settle.

But, the calculated SS removal efficiency (~ 60%) is much lower than that quoted in the paper. After many many trials, I still can't get the point why the calculation is not in order.

Below are the setup:
(Note: y axis is the gravitational direction and z axis is the direction of "empty")

1. BC
inlet: U fixedValue (0.1 0 0)
p_rgh fixedFluxPressure
alpha.sludge fixedValue
k fixedValue
epsilon fixedValue
nut calculated
outlet: U fixedValue (0 0.020807 0)
p_rgh fixedFluxPressure
alpha.sludge zeroGradient
k zeroGradient
epsilon zeroGradient
nut calculated
sludgeOutlet:
U pressureInletOutletVelocity
p_rgh fixedValue (0)
alpha.sludge zeroGradient
k zeroGradient
epsilon zeroGradient
nut calculated
freeSurface (and the symmetry plane along centreline of the clarifier)
U slip
p_rgh fixedFluxPressure
alpha.sludge slip
k slip
epsilon slip
nut slip
solidWalls
U noSlip
p_rgh fixedFluxPressure
alpha.sludge zeroGradient
k kqRWallFunction
epsilon epsilonWallFunction
nut nutkWallFunction
frontAndBack
empty for all BC

2. transportProperties
sludge:
transportModel: BinghamPlastic
coefficient 0.00023143
exponent 179.26
BinghamCoeff 0.0005966
BinghamExponent 1050.8
BinghamOffset 0
muMax 10
rho 1500
water:
transportModel: Newtonian
nu 1.7871e-6
rho 996
relativeVelocityModel simple
V0 (0 -0.00246 0)
a 405
a1 0
residualAlpha 0

any expert can give me some hints about that's wrong with the setup?

many many thanks.

[Abdi Hussein]

Faced similar problem. I hope ahmmed will explain more on setting parameter and rheological parameters. From where [experimental] can I get the those parameters

[Abdi Hussein]

Originally Posted by ahmmedshakil

I hope it's not too late to reply to this. Based on my experience, a couple of things you can check. First of all, please check your setting parameter (for the settling velocity), then you may check on the rheological parameters, which have significant effect on hydrodynamics. Finally, you may check the turbulence modelling (I assume buoyant k-epsilon is correct, that's why I put it later). In addition, I assume your boundary conditions are okay.

Hope these will solve your problem.
Note: If you explain elaborately your problem, rather than the link of paper, then people may be more interested in the answering and have a closer look at it.

Cheers,
-S

Faced similar problem. I hope ahmmed will explain more on setting parameter and rheological parameters. From where [experimental] can I get the those parameters