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

Flow impinging on axisymmetric disk

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 10, 2001, 15:50
Default Flow impinging on axisymmetric disk
  #1
Chuck Leakeas
Guest
 
Posts: n/a
Hello all, I am currently trying to compute the boundary layer thickness from a normally impinging flow against an axisymmetric disk, also known as Homann Flow. When looking in Schlichting's book on b.l. flows he gives the b.l. thickness as delta=2.4*sqrt(nu/a). Where delta is the b.l. thickness and nu is the kinematic viscosity of the fluid. He says that for potential flow the velocity is U=a*x, and V=-a*y where U and V are far from the plate. My question is, what is the best way to determine a? From a computed run of axisymmetric viscous flow I am very skeptical about computing a value for a. It never seems to be constant for any velocity/distance combination far from the plate. What else can I do?

Thanks, Chuck
  Reply With Quote

Old   March 12, 2001, 05:11
Default Re: Flow impinging on axisymmetric disk
  #2
John C. Chien
Guest
 
Posts: n/a
(1). In the "boundary Layer Theory" book I have, the stagnation in plane flow(Hiemanz flow) was assumed to have U=ax; V=-ay, near the stagnation point. (2). The delta for the boundary layer for this case is 2.4 SQRT(NU/a). (3). On the other hand, Stagnation in 3-D flow was assumed to have U=ar; V=-2az. This solution was given by Homann in the form of a power series. (as stated in the book) (4). It seems to me that the solution you quoted is actually the solution of 2-D plane flow, not the 3-D axisymmetric flow. Why don't you double check the solution in the book? (mine is 1960 fourth edition)
  Reply With Quote

Old   March 12, 2001, 14:17
Default Re: Flow impinging on axisymmetric disk
  #3
Chuck Leakeas
Guest
 
Posts: n/a
John,

I understand what you are saying about the 3D axisymmetric flow. Knowing this, how would you compute the value of a, given that one has the numerical solution for viscous flow impinging on a disk? I'm just interested in comparing out approaches.

Thanks, Chuck

  Reply With Quote

Old   March 12, 2001, 19:08
Default Re: Flow impinging on axisymmetric disk
  #4
John C. Chien
Guest
 
Posts: n/a
(1).At some distance from the center line, plot the U-velocity distribution normal to the wall. (2). From the profile, you should be able to identify the inviscid region, which is outside the boundary layer region next to the wall. (3). Pick a point in the inviscid region and use the computed U-velocity in the equation to derive the unknown parameter "a". (4). Use this "a" to derive the V-velocity, and compare it with the calculation. (5). You can then spot check the U,V velocity field to see whether the assumed inviscid field is consistent with your calculation. (5). You can also derive the boundary layer thickness distribution from the calculation, and check against the analytical result.
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Axisymmetric Flow around a hollow cylinder with an extended flair JLight OpenFOAM 5 January 28, 2013 13:11
how can I Run axisymmetric flow using dsmcFoam ? mechy OpenFOAM 4 September 19, 2011 11:25
can I use cyclic boundary condition to modeling axisymmetric flow ? mechy OpenFOAM 0 July 8, 2011 15:16
2d- axisymmetric pipe flow sara Main CFD Forum 0 October 14, 2008 16:54
Axisymmetric Flow S. Kumar Main CFD Forum 0 November 10, 2001 11:15


All times are GMT -4. The time now is 13:52.