## Fluids

#### How to work out 3d shape aerodynamic center

• Farrukh Malik
Subscriber

How to work out 3d shape aerodynamic center, how to work out Cm at various angles of attack ? and about various points along the chord ? Is there a way of automating this through "Parameter Sets" ?

Kindly help.

• Akshay Gedam
Subscriber

Hi,

The aerodynamics center (AC) is the point about which pitching moment remains constant with respect to coefficient of lift (angle of attack). Calculating it for the 3d shape is not the straightforward thing, it will require some efforts. As it is the point where pitching moment remain constant wrt angle of attack, the first thing you will need to do is to simulate your 3d object for range of angle of attack (AOA), I would suggest choosing range such that it will include negative, zero and positive angle of attack example (-2 deg to +4 deg). Secondly, calculate pitching moment for each AOA about particular point. Theoretically for aerofoil the AC lies nearly about 0.25% of Chord length form LE, for your 3d shape this could also be your starting point, or you can calculate the moment about CG of your 3d Shape. Then plot the graph of pitching moment coefficient VS angle of attack and if the slop is zero (that is pitching moment is constant) then 0.25%C from LE or CG will be your AC if not then you can easily transfer your moment from one point to other point by simple calculation and again plot the same graph for checking the slop.

To automate this process, you can make the use of the Ansys workbench for doing parametric analysis, where angle of attack and pitching moment being your parameter. For doing this you can refer this video Analyzing more than One Design - Lesson 3 - ANSYS Innovation Courses