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
