Simulating the Behavior of Rotating Fluids: CFD vs ALE

In summary, rotating a basin of fluid will cause two acceleration components - gravity and centrifugal. If you add gravity to both components, the fluid will move to one side. However, if you just speed the basin up, the fluid will not even out at an equilibrium point.
  • #1
exophysix
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If I were to rotate a basin of fluid at a given angular speed, I would have two acceleration components.. one gravity and one centrifugal. What would happen if I added gravity to both components of acceleration (from tilting the basin). The fluid should move to one side correct? But, what if I just speed the basin up? Would the fluid even itself out at an equilibrium point?

Thanks!
 
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  • #2
Two acceleration components on what? The fluid?

The fluid in this drum has a body force due to gravity and also shear forces from friction with the wall of the basin. The relative strength of these two forces will dictate how the fluid settles in equilibrium. When the basin is level and spinning, the fluid has some steady-state angular momentum. This angular momentum will be conserved in the fluid until some torque acts on it. When you tilt the basin you are applying a torque, but this is applied at the boundary of the fluid and not the whole fluid. The result is a big mess where the outer parts of the fluid continue to rotate with the tilted basin, but the inner parts rotate as they did before.

Basically it's a very complicated question, and even the qualitative answer depends on the details of the experiment (i.e. turbulent v laminar flow).
 
  • #3
mikeph said:
Two acceleration components on what? The fluid?

The fluid in this drum has a body force due to gravity and also shear forces from friction with the wall of the basin. The relative strength of these two forces will dictate how the fluid settles in equilibrium. When the basin is level and spinning, the fluid has some steady-state angular momentum. This angular momentum will be conserved in the fluid until some torque acts on it. When you tilt the basin you are applying a torque, but this is applied at the boundary of the fluid and not the whole fluid. The result is a big mess where the outer parts of the fluid continue to rotate with the tilted basin, but the inner parts rotate as they did before.

Basically it's a very complicated question, and even the qualitative answer depends on the details of the experiment (i.e. turbulent v laminar flow).

Thank you mike.

Do you know of a good way to simulate this behavior (CFD versus ALE) [by chance]?
 

1. What is the definition of "rotating fluid" in mechanics?

A rotating fluid is a fluid that is in motion around a central axis or point, creating a circular or spiral pattern. This motion is influenced by forces such as gravity and rotation of the Earth.

2. How does the Coriolis effect impact the behavior of rotating fluids?

The Coriolis effect is a result of the Earth's rotation and causes moving objects in a rotating frame of reference to experience a force perpendicular to their direction of motion. In the context of rotating fluids, this force leads to the formation of vortices and the deflection of fluid flow patterns.

3. What are some real-world applications of studying the mechanics of rotating fluids?

The study of rotating fluids has many practical applications, including weather forecasting, ocean currents, atmospheric circulation, and turbine design. It is also used in industries such as aerospace, energy, and marine engineering.

4. How is the Navier-Stokes equation relevant to the mechanics of rotating fluids?

The Navier-Stokes equation is a fundamental equation in fluid mechanics that describes the motion of a fluid. It is particularly relevant to the study of rotating fluids as it includes terms that account for the effects of rotation and the Coriolis force.

5. What are some challenges in studying the mechanics of rotating fluids?

One of the main challenges in studying rotating fluids is the complex nature of the phenomena, which often involve multiple forces and interactions. This can make it difficult to accurately model and predict the behavior of rotating fluids. Another challenge is the need for sophisticated experimental techniques and computational methods to study these fluids in detail.

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