CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

association of PDE and 3d object

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

LinkBack Thread Tools Search this Thread Display Modes
Old   October 11, 2014, 04:47
Default association of PDE and 3d object
New Member
Join Date: Oct 2014
Posts: 1
Rep Power: 0
shelodn is on a distinguished road
Hello, I am in a CFD class, and we are already discussing hyperbolic equations. we finished the elliptical, and supposedly that is what I would use to determine the air forces on an object at subsonic speeds.
This is not for a class project, but just to help me understand a little better. I created the 2d profile of a bottle, and I want to theoretically launch this bottle through the air, nose first. I understand that I need continuity and specifically the material derivative, as well as momentum, to determine the flows around this bottle.
I am struggling with plugging the PDEs learned to the application.
could someone please tell me how I would apply the continuity and momentum equations to the bottle?
more specifically, would the mesh be the bottle, or some arbitrary points around the bottle? and also is there some simpler way to determine the velocity profile to apply in the spatial derivatives in the divergence, or do I need to go all the way down to the velocity potential, and vorticity?
any help greatly appreciated, and I apologize if my questions are confusing. all I'm asking is to be pointed in the right direction.
shelodn is offline   Reply With Quote

Old   October 16, 2014, 07:05
Default Mesh the fluid not the solid
Join Date: May 2013
Posts: 46
Rep Power: 12
DaveyBaby is on a distinguished road
Hi, if I have understood your question this might help

You would perform the CFD on the air around the bottle so you would be solving on a mesh in that fluid domain.

To start with, you could essentially draw a large box with a bottle shape missing, apply continuity/conservation of momentum to this fluid domain, while thinking about boundary conditions at the box outer walls and at the interface between the fluid and the bottle surface.

The solution of the NS equations on a suitable mesh (not done by hand!) would give you velocity gradients and hence along with the fluid viscosity would give you viscous stresses up to this fluid/solid interface enabling you to infer the internal stresses at the bottle outer surface (if you are interested in these). In practice, CFD simulations often apply wall functions which give you the velocity gradient near the wall in terms of a normalised velocity and a normalised normal-wall distance.

Kind Regards
DaveyBaby is offline   Reply With Quote


beginner, drag, velocity

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

All times are GMT -4. The time now is 19:08.