# Defining area value in CFX-post

 Register Blogs Members List Search Today's Posts Mark Forums Read

 January 16, 2020, 10:36 Defining area value in CFX-post #1 New Member   Join Date: Jan 2020 Posts: 2 Rep Power: 0 Hello all, I am trying to create a chart in CFX-post that will display the drag coefficient. I've created an expression to determine the drag coefficient: (2*force_x()@airflowdomain )/ (AR*den*(InletVel)^2) where AR is the surface area of the object in question and den is the fluid density. However, the value being returned is a Cd of 0.0038, which seems very very low.It seems to me there must be a mistake I've made in determining the force being exerted over the front of the object, but I'm not sure where. Any suggestions/advice would be greatly appreciated! Last edited by itb7; January 16, 2020 at 12:26. Reason: clarifying issue

 January 13, 2021, 00:25 #2 Senior Member   Join Date: Nov 2020 Location: Canada Posts: 377 Rep Power: 5 Hello, There seems to be an error in your equation. If the velocity is aligned with the x-axis, you could obtain the drag coefficient as Cd = force_x()@Surface / (0.5*Rho*U^2*A) There is also a thread that you could go through to troubleshoot your issue(s); http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

 January 13, 2021, 12:54 #3 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,075 Rep Power: 20 1.) As aero_head states: location for force_x() should be the surface object in question, not the domain. 2.) "AR" should not be the surface area, but instead the cross sectional area normal to the flow direction. aero_head likes this.

 Tags cfx-post, drag coefficient, expressions, variable definition