CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Physical difference between airfoils flows

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   February 9, 2000, 09:00
Default Physical difference between airfoils flows
  #1
Tim Franke
Guest
 
Posts: n/a
Hello,

I have a general question concerning airfoil flows. With different airfoils at the same angle of attack one gets different lift performance. Can anyone give a physical explanation what flow features change if you take an airfoil with a different profile to have higher lift ?

Thanks,

Tim
  Reply With Quote

Old   February 9, 2000, 10:58
Default Re: Physical difference between airfoils flows
  #2
John C. Chien
Guest
 
Posts: n/a
(1). Flow around a body will create pressure force on the surface of the body. (2). When the fluid flow is not moving, the pressure force on the surface will be the same. (gravitational force not included) Thus no net force is produced. (3). As the fluid flow moves around an airfoil, it will create variable pressure force on the different part of the surface. The resultant force from the integration of the surface pressure force will have a component normal to the flow direction, the so-called lift. (4). This is how a bird can fly , without learning the "physics". (5). The physical explanation is that in order to satisfy the conservation laws (mass, momentum, and energy conservations), different airfoil shape will produce different surface pressure distribution. The resultant lift force is a linear function of the angle of attack for small angles. At high angle of attack, the flow will separate from the upper surface of the airfoil. When that happens, the lift force will drop and the airfoil will stall. (6). So, the surface pressure distribution is a non-linear function of the airfoil shape and the angle of attack, as it should be, because the governing equations (conservation laws) are the highly non-linear Navier-Stokes equations. (7). Sometimes, for limited range of airfoil shapes and angles of attack, it is possible to use simplified equations or linearized equation to predict the pressure distribution and the lift. And thus some simple physical explanations are possible. But in general, we are not much smarter than the birds in understanding and predicting the lift. (8). My interpretation of "physical explanation" is "mathematical equations and solutions based on fluid dynamics". (similar question has been asked related to how the lift is created, check the old messages)
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Superlinear speedup in OpenFOAM 13 msrinath80 OpenFOAM Running, Solving & CFD 18 March 3, 2015 06:36
Difference of multicomponent and multiphase homogenous flows Luk_Fiz CFX 11 April 4, 2013 05:29
physical difference between "turbulence off" and "laminar"? val46 OpenFOAM 0 February 24, 2011 06:08
Oscillating Airfoils in Transonic Flows The Aeroelastician Main CFD Forum 20 August 14, 2006 06:50
LES: Difference between physical space and fourier K.Senthil Kumar Main CFD Forum 3 July 3, 2000 08:36


All times are GMT -4. The time now is 18:16.