# Vortex Shedding, Cylinder vs. Cuboid

• the-brammo
In summary: Overall, vortex shedding from a cylinder occurs periodically for Reynolds numbers between 90 and 1000, and it is still possible for vortex shedding to occur at a Reynolds number of 1×104. The specific parameters of the shedding vortices in the sub-critical flow region (Reynolds number < 1.5×105) cannot be accurately defined, but research has shown that vortex shedding does occur at Reynolds numbers in this range.
the-brammo
I have been reading papers now for the last few weeks and I have taken from all the information so far that vortex shedding from a cylinder happens periodically for reynolds numbers anywhere between 90 and 1000. It seems to me that there is no actual way of defining the specific parameters of the shedding vortices in the region of sub-critical flow where the reynolds number is less than 1.5×105. My main question is, does the cylinder still shed vortices at all when the reynolds number is around 1×104? I know that the Strouhal number can be used to find the shedding frequency of vortices for a given diameter and wind speed, but most of the time the Strouhal number is estimated using the Reynolds number and if the Reynolds number is higher but not super-critical can this relationship still be used?

I am currently testing a cylinder in a wind tunnel with a diameter of 16cm with wind speeds ranging from 3-10m/s. This gives me a reynolds number ranging from 3.2×104 to 1.0×105. I have researched that vortex shedding has been known to occur at these Reynolds numbers, if it is that lamp posts (for example) do vibrate due to the shedding of vortices the Reynolds numbers would be of the same order and would suggest that t does indeed occur.

Here's a nice picture
http://img63.imageshack.us/img63/119/82450048.jpg
So in case 4 here is that also classified as vortex shedding but it's just not a Karman vortex street? Also how would the situation vary if a cuboid (square cylinder) was used?

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The image you have provided is an example of a Karman vortex street, which is a particular type of vortex shedding. Vortex shedding will still occur when a cuboid (square cylinder) is used, but the vortices will be slightly different since the shape of the object is different. The Strouhal number can still be used to estimate the shedding frequency for both cylinders and cuboids, but the Reynolds number must be known in order to calculate it accurately.

## What is vortex shedding?

Vortex shedding is a phenomenon that occurs when a fluid flows past an object, causing alternating vortices (swirling patterns) to form on either side of the object. This can create a periodic variation in pressure, which can affect the stability of the object and may lead to vibrations or oscillations.

## What is the difference between cylinder and cuboid in terms of vortex shedding?

In terms of vortex shedding, the main difference between a cylinder and a cuboid is their shape. A cylinder has a circular cross-section, while a cuboid has a rectangular cross-section. This difference in shape can affect the flow of the fluid around the object, resulting in different patterns of vortex shedding.

## Which shape, cylinder or cuboid, is more prone to vortex shedding?

Generally, a cylinder is more prone to vortex shedding than a cuboid. This is because the circular cross-section of a cylinder creates a larger wake (region of disturbed flow behind the object) compared to the rectangular cross-section of a cuboid. This larger wake can result in stronger and more frequent vortices, leading to more pronounced vortex shedding.

## How does the Reynolds number affect vortex shedding in cylinder and cuboid?

The Reynolds number is a dimensionless parameter that represents the ratio of inertial forces to viscous forces in a fluid flow. In the case of vortex shedding, a higher Reynolds number indicates a higher fluid velocity, which can lead to a more intense and unstable shedding pattern. Therefore, for both cylinder and cuboid, a higher Reynolds number can increase the likelihood and strength of vortex shedding.

## Can vortex shedding be controlled in cylinder and cuboid?

Yes, vortex shedding can be controlled in both cylinder and cuboid shapes. This can be achieved through various methods such as changing the shape or size of the object, altering the flow conditions, or using devices such as vortex generators or suppressors. However, the effectiveness of these methods may vary depending on the specific shape and flow conditions.

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