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

A micron-sized laminar model leading to an unnatural solution

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 31, 2012, 12:42
Default A micron-sized laminar model leading to an unnatural solution
  #1
New Member
 
Join Date: Dec 2011
Posts: 9
Rep Power: 5
dixylo is on a distinguished road
My propeller model is 30 microns in diameter and 10 microns in height, and rotates counterclockwise at an angular speed of 50 rad/s. Each blade is even in thickness and is of a twisted surface that twists gradually in counterclockwise direction from hub to edge. What has been puzzling me is that the CFD results using the laminar model (because of Re<<1) are just the opposite to reality. The flow direction is from the top down, whereas it should have been from the bottom up because the blades push the liquid up rather than pull it down. What's more, the static pressure on the upwind surfaces is negative. The results are as follows.

this figure is the propeller geometry

this figure shows the velocity vectors in the y-z plane.

the velocity vectors in z=5 plane (perpendicular to the rotating axis) attest to the counterclockwise direction in which the propeller rotates.

this figure shows the static pressure on the propeller surfaces. Note the pressure on the upwind surfaces, which is negative that contradicts reality.

I have rechecked my settings for times to find no clue that accounts for the odd result. However, I can get an acceptable result when calculating the turbulent model of a centimeter-sized propeller which is 10k times bigger in extent and several times higher in rotation speed.
I have refined the grid, tried slowly increasing the rotation speed from a small value, and using a more precise solver and discretization method, but all have failed to be a solution. Please help if you're interested. Any help would be much appreciated.
dixylo is offline   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
about Subgrid-scale model impecca OpenFOAM Running, Solving & CFD 4 December 20, 2013 11:36
Laminar model - Need some urgent help amoolraina FLUENT 0 September 5, 2010 00:15
DNS always returns to laminar initial solution kat Main CFD Forum 10 September 9, 2007 09:20
About the solution of a simplified two-phase model maximus Main CFD Forum 3 October 25, 2005 12:03
Wall functions Abhijit Tilak Main CFD Forum 6 February 5, 1999 02:16


All times are GMT -4. The time now is 05:09.