Drag Force on a droplet

Mwbadawy · July 22, 2020, 20:55

Hi,

I am simulating the motion of a water droplet inside an oil medium using the VOF Multiphase Model. I want to calculate the drag force exerted on the droplet. My approach was to integrate the pressure and shear stress over the droplet surface (ISO surface) However, I couldn't calculate the shear stress on any non-wall cells.
I have found a parameter in CFD-Post variables called "water. Force X", Does this variable define the drag force directly, if not what does it mean and what might be a good way to calculate the drag force?

P.S. I can provide any images if needed.

Thanks

Mwbadawy · July 23, 2020, 15:22

This is the expression I used to validate the drag force at the walls:

=areaInt(2*Velocity u.Gradient X*Normal X*0.1[N*sec/m^2]+(Velocity u.Gradient Y+Velocity v.Gradient X)*Normal Y*0.1[N*sec/m^2]+(Velocity u.Gradient Z+Velocity w.Gradient X)*Normal Z*0.1[N*sec/m^2])@walls

but it doesn't give the same results as the wall shear built-in parameter.

July 22, 2020, 20:55	Drag Force on a droplet	#1
Mwbadawy New Member Mohamed Wael Join Date: Oct 2019 Posts: 6 Rep Power: 6	Hi, I am simulating the motion of a water droplet inside an oil medium using the VOF Multiphase Model. I want to calculate the drag force exerted on the droplet. My approach was to integrate the pressure and shear stress over the droplet surface (ISO surface) However, I couldn't calculate the shear stress on any non-wall cells. I have found a parameter in CFD-Post variables called "water. Force X", Does this variable define the drag force directly, if not what does it mean and what might be a good way to calculate the drag force? P.S. I can provide any images if needed. Thanks

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July 23, 2020, 15:22		#2
Mwbadawy New Member Mohamed Wael Join Date: Oct 2019 Posts: 6 Rep Power: 6	This is the expression I used to validate the drag force at the walls: =areaInt(2Velocity u.Gradient XNormal X0.1[Nsec/m^2]+(Velocity u.Gradient Y+Velocity v.Gradient X)Normal Y0.1[Nsec/m^2]+(Velocity u.Gradient Z+Velocity w.Gradient X)Normal Z0.1[Nsec/m^2])@walls but it doesn't give the same results as the wall shear built-in parameter.