Calculate velocity inflow on a 2D surface in 3D

quarkz · May 6, 2009, 21:07

Hi,
I need to calculate velocity inflow on a 2D surface in 3D. I can vaguely recall but I 'm not too sure. i have the coordinates of the 2D surface and the velocity vector

The steps are:
1. using 2 vector on the 2d surface (v1 n v2), calculate its unit cross product vector. this new vector will be perpendicular to the 2d surface

2. do a dot product between the new perpendicular vector and the velocity vector (vel vect). tt 'll give the velocity flowing into the 2D surface.

is this correct? tks!

mettler · May 7, 2009, 09:06

isn't this just the curl?

Rami · May 10, 2009, 06:07

There is one step missing in the suggested process: The v1 x v2 product will indeed create a normal, but you will then have to normalize it to make it a unit normal. Only then do the scalar (dot) product with the velocity vector to have the normal velocity. The direction of the latter (into or out of the domain) will depend on whether v1 x v2 is directed into the domain or outwards.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to calculate gradient of pressure and velocity on an outlet face	skabilan	OpenFOAM Running, Solving & CFD	2	December 8, 2008 18:26
Recover surface from surface mesh in IcemCFD	Jerry Tanner	CFX	0	August 20, 2008 13:48
how to calculate a scale velocity in vectors	ladypowel	FLUENT	0	May 8, 2007 19:40
CFX 4.4 New free surface option	Viatcheslav Anissimov	CFX	0	April 3, 2002 07:27
slip velocity on boundary (V.P.M)	Lee, Juhee	Main CFD Forum	3	October 22, 1998 16:30

May 7, 2009, 09:06		#2
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	isn't this just the curl?

May 10, 2009, 06:07		#3
Rami Senior Member Rami Ben-Zvi Join Date: Mar 2009 Posts: 155 Rep Power: 17	There is one step missing in the suggested process: The v1 x v2 product will indeed create a normal, but you will then have to normalize it to make it a unit normal. Only then do the scalar (dot) product with the velocity vector to have the normal velocity. The direction of the latter (into or out of the domain) will depend on whether v1 x v2 is directed into the domain or outwards.