Froude number in vortex formation

In summary, the conversation discusses the presence of unwanted vortex in stirred vessels and the use of the dimensionless Froude number to determine its significance. The Froude number is defined as a ratio of inertia forces to gravitation force and is typically small at low velocities, indicating the absence of vortex. However, one participant raises the question of whether a large denominator in the Froude number would actually result in the presence of a vortex. The confusion lies in determining if a small or large Froude number indicates the presence of a vortex.
  • #1
engineerings
8
0
Hi,

In a stirred vessels it can occur that a vortex is present which is unwanted because it decreases the mixing.
The dimensionless Froude number is a value that can be used to see if the vortex formation is negligible or not. It is defined as Fr=N^2D/g an you can look at it as a ratio of inertia forces to gravitation force. At low velocities you usually don't have a vortex, so this means that the froude number is small?
But then I wonder, if Froude is small, then the denominator of Froude must be large and thus the gravitation force delivers a large contribution with reference to the inertia forces. I would say a vortex would certainly be present then?
 
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  • #2
So I'm confused, what is true? Is Froude number small when a vortex is absent or present?Thanks in advance.
 

1. What is the Froude number in vortex formation?

The Froude number in vortex formation is a dimensionless parameter used to describe the strength and behavior of vortices in a fluid flow. It is defined as the ratio of the flow's inertial forces to its gravitational forces.

2. How is the Froude number calculated?

The Froude number is calculated by dividing the flow velocity by the square root of the product of the gravitational acceleration and the characteristic length scale of the flow. It is represented by the equation Fr = V/√(gL), where V is the flow velocity, g is the gravitational acceleration, and L is the characteristic length scale.

3. What is the significance of the Froude number in vortex formation?

The Froude number is significant in vortex formation as it determines the type and strength of vortices that will form in a fluid flow. A low Froude number indicates a dominant gravitational force, leading to large, stable vortices, while a high Froude number indicates a dominant inertial force, resulting in smaller, more unstable vortices.

4. How does the Froude number affect vortex shedding?

The Froude number plays a crucial role in vortex shedding, which is the process of vortices being periodically shed from an object in a fluid flow. A critical Froude number, known as the Strouhal number, determines the shedding frequency of vortices. As the Froude number increases, the shedding frequency also increases.

5. Can the Froude number be used to predict vortex behavior?

Yes, the Froude number can be used to predict the behavior of vortices in a fluid flow. A low Froude number indicates a more stable flow, with large, persistent vortices. A high Froude number, on the other hand, indicates a more turbulent flow, with smaller, more irregular vortices. By calculating the Froude number, scientists and engineers can anticipate the behavior of vortices and design systems to mitigate their effects.

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