...
Info |
---|
|
Wiki Markup |
---|
FLUENT report forces in term of pressure force and viscous force. For instance, we are interested in the drag on the airfoil,
(Drag)~total~ = (Drag)~pressure~ + (Drag)~viscous~
!force convention.jpg!
Drag due to pressure:
\\
{latex}
\large
$$
{(Drag)_{pressure}} = {\oint \-P \hat{n}.\hat{e_d}dS}
$$
{latex}
Drag due to viscous effect:
\\
{latex}
\large
$$
{(Drag)_{viscous}} = {\oint \tau_w \hat{t}.\hat{e_d}dS}
$$
{latex}
where
_e{_}{_}{~}d{~}_ is the unit vector parallel to the flow direction.
_n_ is unit vector perpendicular to the surface of airfoil.
_t_ is unit vector parallel to the surface of airfoil.
\\
Similarly, if we are interested in the lift on the airfoil,
(Lift) = (Lift)~pressure~ + (Lift)~viscous~
Lift due to pressure:
{latex}
\large
$$
{(Lift)_{pressure}} = {\oint \-P \hat{n}.\hat{e_l}dS}
$$
{latex}
Lift due to viscous effect:
\\
{latex}
\large
$$
{(Lift)_{viscous}} = {\oint \tau_w \hat{t}.\hat{e_l}dS}
$$
{latex}
where
_e{_}{_}{~}l{~}_ is the unit vector perpendicular to the flow direction.
_n_ is unit vector perpendicular to the surface of airfoil.
_t_ is unit vector parallel to the surface of airfoil.
\\
|
|
...
No Format |
---|
Force vector: (0.99980003 0.02094 0)
pressure viscous total pressure viscous total
zone name force force force coefficient coefficient coefficient
n n n
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
airfoil 3.8125084 0 3.8125084 0.0024897052 0 0.0024897052
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
net 3.8125084 0 3.8125084 0.0024897052 0 0.0024897052
|
...
Cd = (Cd)pressure + (Cd)skin friction
...
Info |
---|
|
In reality, (Cd)skin friction has biggest contribution to drag but ignored because of the inviscid model that we specify. (Cd)pressure should be zero, but it is not zero because of inaccuracies and numerical dissipation during the computation. |
Now, let's look at the lift coefficient.
...