## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Water VOF became fixed per time, although water velocities are increasing

• Walaa Elhamamy
Subscriber
Hello,

I need help to understand the physical meaning of this graph， where there is a mistake that I can't get. I am simulating a flood, my inlet boundary condition is a velocity inlet (transient table). I am simulating 15 minutes of flood.

The velocity is increasing in the boundary condition, so logically, the VOF should be growing as well. Eventually, the water should fill the whole space.

However, when the VOF reached 0.6, at a time of almost 5 minutes (300 sec), it stopped growing and kept almost constant, although, the velocity in the boundary condition table kept growing.

Could anyone help to understand where is the problem?

• Rob
Ansys Employee

Please post some images of the flow field. How did you define the report?

• Walaa Elhamamy
Subscriber

• Walaa Elhamamy
Subscriber

Are these screenshots clear? do you need other information?

• Rob
Ansys Employee

How does the air escape?

• Walaa Elhamamy
Subscriber
I am defining the whole ceiling as a pressure outlet, is this enough? I am not defining any vents.

I made another try to examine if there was a problem in the transient table, I redefined the velocity inlet to a fixed value, however, the same exact behavior happened, at almost VOF=0.6, and kept almost stable.
• Walaa Elhamamy
Subscriber

• Rob
Ansys Employee

That should be fine. How is the inlet defined?

• Walaa Elhamamy
Subscriber

I divided the inlet into two parts (velocity inlet and pressure inlet). I don't want the water to enter from the whole door height (occupied the whole height I mean).

The total door height is 1.7 m, and a part of 0.35 m, near the ground, is the water inlet and I defined it as a velocity inlet, the rest of 1.35 m above I defined as a pressure inlet.

• Rob
Ansys Employee

What mass flow of water is coming out of the pressure inlet?

• Walaa Elhamamy
Subscriber

sorry, I don't understand what you mean.

but I am attaching screenshots of related settings to the pressure outlet.

• Rob
Ansys Employee

Please check the mass flux report on the pressure inlet - specifically for the water phase.

• Walaa Elhamamy
Subscriber

I am sorry, would you help me with how to check this? I can't find it.

• Walaa Elhamamy
Subscriber

Is this what you mean?

• Rob
Ansys Employee

Results (tab) > Reports > Fluxes

I suspect the water is entering the domain through the inlet, and then overflowing back out of the pressure inlet.

• Walaa Elhamamy
Subscriber

oh, does the attached screenshot support what you said? I attached the report of mass flux as you asked.

• Rob
Ansys Employee

Yes, you have 384.67kg/s water leaving through the inlet. I suspect that ties up with the inflow.

• Walaa Elhamamy
Subscriber

I see, thanks for your help. do you have any idea how I can fix this ?

• Rob
Ansys Employee

Maybe turn it into a wall?