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 :)

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

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

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

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

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

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

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"

Gahhh! Thanks Jerry, hope this does not mean I am garbage and you just

took me out.... he he Love the signature

Ben

took me out.... he he Love the signature

Ben

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