Hey Zhang,
Provided you have a no penetration boundary conditions
for the airfoil, the general expression for the fluid force on an airfoil
can be given as:
F^i_R = \int_{\partial R} (P\hat{n} + \nu \nabla v^i) \cdot \hat{n}
(where R is the airfoil domain, v^i is a unit vector in the i
direction, google "Strict general mathematical definition of drag" for
the complete derivation)
Thanks.
On Mon, Apr 27, 2015 at 4:15 AM, Zhang <[email protected]> wrote:
> Dear Vikram,
>
> Well. Just now I recognized that as for the form pressure force you are
> right.
> Since I want to get the lift and drag which are applied by the air flow
> onto the solid airfoil,
> the pressure form should be of positive. while in the original N-S equation
> there is a negative one which means the force applied from solid to the
> gas, as opposite.
>
> In the same way, I think the contribution of viscosity onto the lift and
> drag
> should also be negative, since in the original N-S form it is positive.
> Right?
>
> -----原始邮件-----
> 发件人: "Vikram Garg" <[email protected]>
> 发送时间: 2015-04-27 16:32:10 (星期一)
> 收件人: Zhang <[email protected]>
> 抄送: libmesh-users <[email protected]>
> 主题: Re: [Libmesh-users] calculation of aerodynamic forces and moments
>
>
> Hey Zhang,
> Yes, the get_normals() function will return the outward
> normal vectors.
>
>
> You had mentioned that force on the airfoil was given by:
> \vec{F}=\sum_{qpface_bound} {\tau*normal -normal*p_{qp}}
> *Jxw_face_bound[qp] . Should that be a \tau*normal + normal*p_{qp}} ?
>
>
> Thanks.
>
>
> On Sun, Apr 26, 2015 at 11:07 PM, Zhang <[email protected]> wrote:
> I just made some correction, say, since pressure is defined in a space one
> order
> lower than velocity. In the last code I put all quadrature computation in
> velocity space by mistake,
> now I put the two integrals, $\int \tau * normal$ and $\int (-p)*normal$,
> into two separate
> sections and finally add their partial integral together.
>
> Here are the comparison (for only pressure forces)
> 1) np=1 // the old one
> step 9, forces: (-1.299297e-01 3.460514e-03 0.000000e+00 )
> step 9, moments: (0.000000e+00 0.000000e+00 7.266930e-05 )
> 2) np=1 // the corrected one
> step 9, forces: (-1.799026e-01 -3.255020e-06 0.000000e+00 )
> step 9, moments: (0.000000e+00 0.000000e+00 -9.115135e-07 )
> 3) np=4 // the corrected one
> step 9, forces: (-1.799026e-01 2.098503e-06 0.000000e+00 )
> step 9, moments: (0.000000e+00 0.000000e+00 5.020619e-07 )
>
> when AOA=0.0 degree, the lift and z-pitching moment are dramatically
> reduced to zero.
>
> Now the question is the negative x-force. In the face quadrature, does
> fe_pres_face->get_normals()
> return all outward normal vector?
>
>
> Zhenyu
>
> ------------------------------------------------------------------------------
> One dashboard for servers and applications across Physical-Virtual-Cloud
> Widest out-of-the-box monitoring support with 50+ applications
> Performance metrics, stats and reports that give you Actionable Insights
> Deep dive visibility with transaction tracing using APM Insight.
> http://ad.doubleclick.net/ddm/clk/290420510;117567292;y
> _______________________________________________
> Libmesh-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/libmesh-users
>
>
>
>
>
>
> --
>
> Vikram Garg
> Postdoctoral Associate
> Predictive Engineering and Computational Science (PECOS)
> The University of Texas at Austin
> http://web.mit.edu/vikramvg/www/
>
>
>
> http://vikramvgarg.wordpress.com/
>
> http://www.runforindia.org/runners/vikramg
>
> ------------------------------------------------------------------------------
> One dashboard for servers and applications across Physical-Virtual-Cloud
> Widest out-of-the-box monitoring support with 50+ applications
> Performance metrics, stats and reports that give you Actionable Insights
> Deep dive visibility with transaction tracing using APM Insight.
> http://ad.doubleclick.net/ddm/clk/290420510;117567292;y
> _______________________________________________
> Libmesh-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/libmesh-users
>
--
Vikram Garg
Postdoctoral Associate
Predictive Engineering and Computational Science (PECOS)
The University of Texas at Austin
http://web.mit.edu/vikramvg/www/
http://vikramvgarg.wordpress.com/
http://www.runforindia.org/runners/vikramg
------------------------------------------------------------------------------
One dashboard for servers and applications across Physical-Virtual-Cloud
Widest out-of-the-box monitoring support with 50+ applications
Performance metrics, stats and reports that give you Actionable Insights
Deep dive visibility with transaction tracing using APM Insight.
http://ad.doubleclick.net/ddm/clk/290420510;117567292;y
_______________________________________________
Libmesh-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/libmesh-users
