Dynamics and Control of Flow around Circular Cylinder

[@stevejoe2609]

What an amazing explanation!

[@pauljohnson6377]

This video was great, but from a person not trained yet in fluids its hard to understand what you mean by adding suction. To what physical system are we referring to that does this?

[@dylancloonan3903]

Suction occurs through a difference in your pressure distribution. So one side will have a high pressure the other a low pressure. This difference in pressure produces 'suction' or a force (normal to your flow direction) on your lower pressure side. This all comes from the circulation theory of lift. As to what physical system can cause this its through the shape of the object and how the pressure distribution is affected by the shape. Another way of increasing this suction not through a physical change could also be through increasing the circulation by having the object spinning (magnus effect).

[@jjrusty13]

Glad to hear you liked the video. In this case, the suction is "applied" as a mathematical constraint in the computer simulation. In other words, the computer enforces that the fluid must move through the wall at a specified speed wherever the suction is applied. The software then solves what the fluid velocities must be elsewhere in the domain (the area of the flow modelled) in order for this suction velocity to hold and for the physics to be true. Dylan gave some great examples of how this suction might be applied in reality (either by making the wall porous or cutting slots and using a pump to draw the fluid), but in this video the suction is purely imposed in the mathematics of the physics. Source: I'm the James Ramsay who did this research.

[@jacobsss5827]

Wow, ingenous!

[@장경철-z1j]

What a awesome video! thank you so much. could tell me which program you use for describing flow?

[@deamonofshiva]

Great work. Kindly be more specific about fluid type.

[@sudheerlanka1939]

what is the fluid you are using... air or any other fluid?

[@jjrusty13]

In this simulation the fluid has the properties of water, but the same flow could equally be seen with other fluids but at different speeds.

[@deamonofshiva]

@@jjrusty13 Air has little different behavior I guess.

[@TheLoko154]

Great stuff

[@infegfx]

That is why fishes do not use propeller. It is looks like smiler tail motion of fish swimming in water. Maybe this is good way to moving underwater with optimum energy consumption for efficiency.

[@rektangel333]

How do i define characteristic linear dimension in reynolds number? Is it diameter of a cylinder or something else?

[@jjrusty13]

Rektangel usually you choose the length scale to be representative of the geometry. It can, in some cases, be fairly arbitrary. For the cylinder, yes, it is the diameter that is typically used.

[@HaithamAhmed-kr8yl]

Yes, it is the cylinder diameter D

[@TroyeSivanBN]

Tame Impala - Currents

[@abhishekpanjiyar8266]

why we study this thing,I have never understand

[@jjrusty13]

I can understand why studying this flow can seem quite irrelevant, it does seem a bit overdone. One reason that it gets taught a lot is because the dynamics are very interesting to observe, while being relatively easy to understand. However, this flow has many applications. Obviously many things have a cylindrical shape and are exposed to dynamic fluid forces - e.g. bridge cables, buildings, chimney stacks, and more. Even more importantly though, the cylinder is a type of body called a "bluff body", which is basically anybody that is not streamlined for fluid flow. Obviously this group of bodies includes many everyday things from cars to human bodies. The drag that arises on these bluff bodies requires significant energy to overcome or resist, for example in New Zealand, approximately 8% of our greenhouse gas emissions arise from energy burned by road vehicles to overcome drag. Therefore, finding new ways to reduce this is vitally important. We can't really change the shape of trucks, but with CFD and flow control we can improve their aerodynamics despite this constraint.