I am simulating turbulent flow around a vertical circular cylinder partially submerged in water. I have used LES and VOF in Fluent. The Re=2.7e4 and Fr=0.8.
My simulation is converging at drag and lift values lower than the required. (pictures of my graphs are attached)
The required values for mean drag are between 0.9to1.1 and for mean lift between 0.2 to 0.3 (highest peak)
I have checked all my reference values which seems to have no problem. i have used various grids ranging from 0.2 million to 1.4million.
model = multiphase(VOF,implicit,implicit body force)
viscous model=LES(used WALES as well as Smagorinsky-Lilly Model)
My boundary conditions are
air and water inlet= velocity-inlet
air outlet= pressure outlet (zero gauge press)
water outlet= hydrostatic pressure using UDF
cylinder=wall (no slip)
boundary walls= Symmetry
The free surface wave formation is very close to the required. I am also observing vortex formation behind the cylinder below water surface. In one simulation attempt I increased the turbulence intensity upto 10% at the water inlet, but it only increased the convergence time.
I am unable to get the required Drag and Lift.
Q1: What do you mean by the "required Drag and Lift"?
Q2: What is your exact geometry and why "boundarys = symmetry"?
Q3: How far downstream is your outlet boundary?
@Shiuh-Hwa Shyu. Thankyou for viewing and responding my Question.
here are the answers which you asked.
A1. The required Drag and Lift means that at my Re and Fr values i should be getting Mean Drag coefficient upto 1 and Lift coefficient should be between 0.2 to -0.2.
A2. please view the attach file for geometry. i have used boundary condition = symmetry for no shear walls.
A3. 20 times the diameter of cylinder
@Aria Sobhani. Thankyou for viewing and responding my Question.
yes i have set the reference velocity.
I confirmed my simulation Coefficient Drag by obtaining the force in x-direction on cylinder in water, and than calculated Cd by the standard Cd formula.
I'm guessing that your cylinder is inserted into the sea ground, so shouldn't it be no slip condition at z=-4d?
Yes my cylinder is into the ground. because i am interested in air water interface so i made this boundary as no shear. Do you suggest this could be the reason of deviation in my results?
There should be a secondary flow around the sea ground and cylinder. If you specify symmetry BC, I guess that you will not be able to observe that phenomena. This might affect your results.
- Badges
- Science topic