Register to reply

Lift of a Rotating Cylinder in Inviscid Flow

by Red_CCF
Tags: cylinder, flow, inviscid, lift, rotating
Share this thread:
Red_CCF
#1
May11-12, 03:21 PM
P: 504
Hi

I am wondering why a spinning cylinder will produce lift in an inviscid flow. From:
http://www.grc.nasa.gov/WWW/k-12/airplane/cyl.html

one of the mechanisms for lift generation was the sticking of fluid particles to the wall of the cylinder. I thought that the no slip condition only applies to viscous fluids so if the fluid was inviscid I don't see how lift can be generated. However, in the simulations in the link, the flow was simulated inviscid yet there is lift, why is this?

Thanks
Phys.Org News Partner Engineering news on Phys.org
'Smart material' chin strap harvests energy from chewing
Lockheed Martin advances live, virtual, constructive training in flight test
Lockheed Martin conducts flight tests of aircraft laser turret for DARPA
boneh3ad
#2
May12-12, 09:47 PM
PF Gold
boneh3ad's Avatar
P: 1,507
In a truly inviscid flow it won't. When one analyzes a rotating cylinder with potential flow, one is essentially approximating the effect of viscosity through the use of a point vortex.
Red_CCF
#3
May15-12, 11:40 PM
P: 504
Quote Quote by boneh3ad View Post
In a truly inviscid flow it won't. When one analyzes a rotating cylinder with potential flow, one is essentially approximating the effect of viscosity through the use of a point vortex.
Hi

Thanks for the response.

Can you briefly describe what point vortex are? I was never introduced this.

And just to confirm, in the NASA simulation at http://www.grc.nasa.gov/WWW/k-12/airplane/cyl.html they state


This type of flow field is called an ideal flow field. It is produced by superimposing the flow field from an ideal vortex centered in the cylinder with a uniform free stream flow. There is no viscosity in this model (no boundary layer on the cylinder) even though this is the real origin of the circulating flow!
and is the reason that the simulation still shows lift when the cylinder spins because the supposed effect of viscosity is superimposed mathematically to the effect of the flow in the simulation that has no viscosity or boundary layer?

Thanks very much

meldraft
#4
May16-12, 08:34 AM
P: 280
Lift of a Rotating Cylinder in Inviscid Flow

You essentially insert manually the fluid rotation that viscosity would have caused. This breaks the symmetry of the flow, making flow on one side of the cylinder faster than the flow on the other one. Velocity is linked to pressure, which is what creates your lift.


Register to reply

Related Discussions
Inviscid flow around cylinder in presence of wall Classical Physics 0
Inviscid fluid flow past a square cylinder. General Physics 4
Fluid Mechanics: Inviscid flow v.s. Laminar flow Engineering, Comp Sci, & Technology Homework 1
Formulation of flow generated by the rotating cylinder Classical Physics 0
Can an inviscid flow rotational? Potential Flow? Mechanical Engineering 2