[Raco]

Hello,

I have series of questions regarding lift and lift coefficient. If a 3D wing simulation if set up (for a specific velocity and density), I can then use the monitor lift coefficient CL to calculate the total lift using the equation L=0.5*rho*V^2*A*CL? if so...could I use the same CL for a different velocity and density or just for the values used in the simulation?

Also, is there a direct way to obtain total lift directly from fluent?

I know that these might be pretty basic questions but I'm just having trouble understanding this.

Many thanks for your help

[scipy]

C_L in Fluent is calculated base on the Reference values you've entered in Fluent (Setup -> Reference Values).

For a vehicle, C_D and C_L are calculated based on the frontal area of the vehicle - because people agreed that it would be so.

I think the reference dimension for a wing is wing area (surface area when you look at your wing from above/below). So, enter that under Area in m^2 in Reference values and the C_D & C_L that you get will be correct for your wing (there's no need to calculate by hand).

In order to get the exact forces you should make a Force Report (Results -> Reports -> Forces -> pick a direction vector and a wall/surface you want to calculate the force for (say surfaces of your wing, both lower and upper, end plates etc.. everything that's a part of the wing) -> click Print...

There you will see how viscous forces and pressure forces are divided and the overall force (consisting of viscous and pressure forces) and you can calculate the C_D and C_L by hand just to check. It will be also written in the force report on the right under Coefficients.

Direction vector is pretty obvious.. longitudinal one for drag force (all others 0) and vertical one for lift/downforce (all others 0).

[Radwanma]

Hi all,

I have made the following full geometry for a rotor and a surface in ICEM but when read it in mesh just the rotor appears !!! How can I solve this problem , please?
Thanks,

[Freestream]

Originally Posted by scipy

C_L in Fluent is calculated base on the Reference values you've entered in Fluent (Setup -> Reference Values).

For a vehicle, C_D and C_L are calculated based on the frontal area of the vehicle - because people agreed that it would be so.

I think the reference dimension for a wing is wing area (surface area when you look at your wing from above/below). So, enter that under Area in m^2 in Reference values and the C_D & C_L that you get will be correct for your wing (there's no need to calculate by hand).

In order to get the exact forces you should make a Force Report (Results -> Reports -> Forces -> pick a direction vector and a wall/surface you want to calculate the force for (say surfaces of your wing, both lower and upper, end plates etc.. everything that's a part of the wing) -> click Print...

There you will see how viscous forces and pressure forces are divided and the overall force (consisting of viscous and pressure forces) and you can calculate the C_D and C_L by hand just to check. It will be also written in the force report on the right under Coefficients.

Direction vector is pretty obvious.. longitudinal one for drag force (all others 0) and vertical one for lift/downforce (all others 0).

Every good note by Scipy. it is apparent that drag and lift are evaluated at parallel and perpendicular to free stream velocity.

Can i also ask if the lift force presented by FLUENT is presented in the aerodynamic center (often the quater chord point) or it actually doesn't matter??

[scipy]

Originally Posted by Freestream

Every good note by Scipy. it is apparent that drag and lift are evaluated at parallel and perpendicular to free stream velocity.

Can i also ask if the lift force presented by FLUENT is presented in the aerodynamic center (often the quater chord point) or it actually doesn't matter??

You can report a force in any vector direction that you want (doesn't have to be parallel/perpendicular to free stream direction of flow). You just specify the sin/cos components of a unit vector.

Force is just an integrated value of pressure & viscous forces over all the surfaces of the body. Pressure forces do act at the center of pressure location (you can even report that in FLUENT), but viscous forces do not (so a moment reported around a CoP location will be 0 for pressure forces but it'll have some small value due to viscous forces).

Finding the location where forces are acting can be done either via CoP or some simple statics/mechanics using known forces and a moment around any point of your choosing.

[esha]

Originally Posted by scipy

C_L in Fluent is calculated base on the Reference values you've entered in Fluent (Setup -> Reference Values).

For a vehicle, C_D and C_L are calculated based on the frontal area of the vehicle - because people agreed that it would be so.

I think the reference dimension for a wing is wing area (surface area when you look at your wing from above/below). So, enter that under Area in m^2 in Reference values and the C_D & C_L that you get will be correct for your wing (there's no need to calculate by hand).

In order to get the exact forces you should make a Force Report (Results -> Reports -> Forces -> pick a direction vector and a wall/surface you want to calculate the force for (say surfaces of your wing, both lower and upper, end plates etc.. everything that's a part of the wing) -> click Print...

There you will see how viscous forces and pressure forces are divided and the overall force (consisting of viscous and pressure forces) and you can calculate the C_D and C_L by hand just to check. It will be also written in the force report on the right under Coefficients.

Direction vector is pretty obvious.. longitudinal one for drag force (all others 0) and vertical one for lift/downforce (all others 0).

Hi, I also have this basic question as I am doing 3D simulation first time, also using Fluent . I have used area value in reference value and using force vector for Cd x=1, y=0 z=0 and for Cl x=0, y=1 and z=0. But in a video why is used values for z alongwith other? can you please explain?
thank you!

[scipy]

Originally Posted by esha

Hi, I also have this basic question as I am doing 3D simulation first time, also using Fluent . I have used area value in reference value and using force vector for Cd x=1, y=0 z=0 and for Cl x=0, y=1 and z=0. But in a video why is used values for z alongwith other? can you please explain?
thank you!

I don't quite understand what you meant to say, but vector directions depend on your model orientation inside the coordinate system and/or flow direction in the same system. Sometimes you don't need the Z value at all (if the Z axis comes out of the symmetry plane for example). If this wasn't your question, maybe try to formulate it slightly better.