Flow Past Sphere at High Re - Velocity Behavior

In summary, the conversation discusses simulations in Solidworks of the flow of air around a sphere at a velocity of 450 m/s. The results show a cut plot of the velocity in the x direction, with purple representing high velocity and red representing low velocity. The individual is curious about the sudden decrease in velocity and increase in pressure in front of the sphere, and the green zone in between. The expert explains that the sudden change is likely due to the formation of a shock wave, caused by the speed of the air being above the speed of sound. The blunt shape of the sphere results in a bow shock instead of an attached oblique shock.
  • #1
redpepper303
1
0
Hello,
I'm currently working on simulations in Solidworks of the flow of air (v = 450 m/s)
around a sphere (radius = 1.5 cm). The results have been used in a cut plot
representing the velocity in the x direction. The image is similar to this one:
https://www.llnl.gov/str/December01/gifs/Naka3.jpg
(Purple is high velocity and red is low velocity)
I was wondering why the velocity suddenly decreased so far in front of the
sphere and so spaced out (green zone), and then increases again.
Thank you for any answer!
 
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  • #2
That looks a lot more like a plot of pressure than a plot of velocity to me. At any rate, I don't know what conditions these simulations were run at, but 450 m/s is likely above the speed of sound, so the reason you see a sudden increase in pressure (and decrease in velocity) is because a shock wave is going to form. It happens out in front of the sphere because the sphere is rather blunt, and so you get a bow shock instead of an attached oblique shock.
 

FAQ: Flow Past Sphere at High Re - Velocity Behavior

1. What is the Reynolds number for a high-speed flow past a sphere?

The Reynolds number (Re) is a dimensionless quantity used to characterize the type of flow past a sphere at high velocity. It is calculated by dividing the product of the sphere's diameter, fluid density, and velocity by the fluid's dynamic viscosity. In high-speed flow, the Reynolds number is typically greater than 10,000.

2. What is the behavior of the flow past a sphere at high Reynolds number?

At high Reynolds numbers, the flow past a sphere becomes turbulent, with chaotic and irregular motion. This is due to the formation of large vortices and eddies in the wake of the sphere, which create high levels of drag and pressure fluctuations. These effects can significantly impact the performance of objects moving through a fluid, such as airplanes and submarines.

3. How does the velocity affect the flow past a sphere at high Reynolds number?

The velocity of the fluid has a direct impact on the behavior of the flow past a sphere at high Reynolds number. As the velocity increases, the Reynolds number also increases, resulting in a more turbulent flow. This can lead to increased drag, pressure fluctuations, and a larger wake behind the sphere.

4. What factors contribute to the high Reynolds number behavior of flow past a sphere?

There are several factors that contribute to the high Reynolds number behavior of flow past a sphere, including the fluid density, viscosity, and velocity, as well as the sphere's size and shape. Additionally, the presence of any external disturbances, such as rough surfaces or upstream obstacles, can also impact the flow behavior.

5. How can the behavior of flow past a sphere at high Reynolds number be predicted?

The behavior of flow past a sphere at high Reynolds number can be predicted through mathematical models and computational fluid dynamics simulations. These methods take into account the various factors that influence the flow behavior and can provide valuable insights into the behavior of objects moving through a fluid at high speeds.

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