Flow Past a Circular Cylinder
Fluid Mechanics
Flow Past a Circular Cylinder
The behaviour of flow around and past bodies that are circular in the crosssection is very important, mainly because there are so many matching scenarios out there. Golf balls, over head cables and underwater supports are just a few examples of circular cross-sections and how studying flow in this case is important. Let us take golf balls for example, they have been engineered in such a way from them being perfectly round, to having small indents in them to reduce drag, allowing for maximum distance after the ball has been struck.
Early techniques such as potential flow did not produce particularly useful results, especially in what is now known as D‟Alembert‟s Paradox, who predicted that the lift and drag on any closed body was to be zero due to the assumption made that fluid could be treated as “inviscid” meaning the viscous effects can be negligible.
However it soon arose that this was not the case and in fact, viscosity plays a very large role in finding flow behaviour and resulting forces on a body in a flow.
The main way in which viscosity affects the behaviour of flow is through the
“boundary layer” meaning a thin layer of fluid next to the surface of any body in a moving fluid. The increase and behaviour of the boundary layer destroys the predictions of the potential flow theory by means of it distorting the pressure distribution. With the result that the pressure forces over the body are no longer zero, the body has pressure or “form drag”. Viscosity also produces its own kind of drag, that being “skin friction drag” the name essentially explaining itself.
Inviscous flow over a circular cylinder, below is a pictorial explanation of
D‟Alemberts paradox, if this was possible boats and other floating items would be able to go much faster, as no drag is produced and no wake is made.
Unfortunately, as mentioned earlier this is not possible, at least not yet and this is a pictorial
Flow Past a Circular Cylinder
The behaviour of flow around and past bodies that are circular in the crosssection is very important, mainly because there are so many matching scenarios out there. Golf balls, over head cables and underwater supports are just a few examples of circular cross-sections and how studying flow in this case is important. Let us take golf balls for example, they have been engineered in such a way from them being perfectly round, to having small indents in them to reduce drag, allowing for maximum distance after the ball has been struck.
Early techniques such as potential flow did not produce particularly useful results, especially in what is now known as D‟Alembert‟s Paradox, who predicted that the lift and drag on any closed body was to be zero due to the assumption made that fluid could be treated as “inviscid” meaning the viscous effects can be negligible.
However it soon arose that this was not the case and in fact, viscosity plays a very large role in finding flow behaviour and resulting forces on a body in a flow.
The main way in which viscosity affects the behaviour of flow is through the
“boundary layer” meaning a thin layer of fluid next to the surface of any body in a moving fluid. The increase and behaviour of the boundary layer destroys the predictions of the potential flow theory by means of it distorting the pressure distribution. With the result that the pressure forces over the body are no longer zero, the body has pressure or “form drag”. Viscosity also produces its own kind of drag, that being “skin friction drag” the name essentially explaining itself.
Inviscous flow over a circular cylinder, below is a pictorial explanation of
D‟Alemberts paradox, if this was possible boats and other floating items would be able to go much faster, as no drag is produced and no wake is made.
Unfortunately, as mentioned earlier this is not possible, at least not yet and this is a pictorial