Drag and Coefficent of Drag in Cosmosfloworks

Drag and Coefficent of Drag in Cosmosfloworks

Post by jameszhao0 » Fri, 26 May 2006 08:30:52


Hi
For one of my projects, I need to test various shapes and designs in
order to caculate Drag and Coefficent of drag. I see an option in
Fluent such as Monitor -> Forces Cd(coeff of drag), but I do not see
any options like this in cosmosfloworks. Please tell me if one in
avaliable in cosmosworks, and if not, any alternatives.

Thanks for all the help.
James :)
 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by Ben Eadi » Fri, 26 May 2006 08:45:53

James

I have done this by taking the reaction force in what ever direction you
want the drag in and then putting in a 'equation goal' (look this up in
the cosmos help) using the formula

D = Cd * 1/2 * rho * v^2 * S where rho is the density of air, v is the
velocity of the fluid, D is the drag force and S is the cross sectional
area seen perpendicular from the direction of flow. So you will need to
rearrange this to get Cd, so you have

Cd = (1/2 rho V^2 S)/D

From cosmos you get D (set it up as a goal and give it a variable name)
next you need to know the cross sectional area (calculated using split
lines and a surface, density of the air and the velocity of the fluid

Punch all this into a equation goal and Viola! It will spit it out into
a spreadsheet nicely.

I cannot send any examples unfortunately as I no longer work at a place
that has a Flow license. This is just from memory. So double check the
formula but I am pretty sure that is it


Ben

 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by jameszhao0 » Fri, 26 May 2006 08:59:41

Thanks for your help.
James
 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by jameszhao0 » Fri, 26 May 2006 09:02:31

One problem.

I think the cross-sectional area assumes a uniform shape. However, this
is an arbitary shape (actually a glider) which is composed of solids
with no 1 cross section.

Thank you.
James
 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by Ben Eadi » Fri, 26 May 2006 11:16:52

It still has a projected area you can use. Remember this is only going
to give you a ball park figure, there are many considerations to take
into account. For an aircraft you will most likely need to include
parasitic drag, deal with the full surface area of the wind sections to
develop the figure more accurately, surface finishes....etc etc. oh and
have one hell of a computer to do the calculations.

If you and your company want some help, I could go into this much much
further but the time involved will be too much to do over a news group
or via emails.

Here is my pride and joy of work in aerodynamics we have this recumbent
bike down to a min of drag the same effort that takes you to 15 KPH on a
mountain bike will get you to 52 KPH on this one...We hope to break a
world record in a month.

http://www.yqcomputer.com/


Also I have done extensive work on this aircrafts' aerodynamics and
structural analysis. and worked on some gliders in the Czech Republic
when I worked there.

http://www.yqcomputer.com/

You can contact me at
www.Mountain-Wave.ca
find the email and phone number in the contact link

Best Regards.
Ben
 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by Jerry Stei » Sat, 27 May 2006 05:40:28


Ben,

You were typing faster than you were thinking and inverted the equation.
Cd=D/(1/2 rho V^2 S).

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"
 
 
 

Drag and Coefficent of Drag in Cosmosfloworks

Post by Ben Eadi » Sat, 27 May 2006 13:30:06

Gahhh! Thanks Jerry, hope this does not mean I am garbage and you just
took me out.... he he Love the signature

Ben