[frossi]

Hi, I am conducting a parametric study on the effects of the winglet deflection on the lift to drag ratio of the whole wing.

First, I am analyzing the change in lift/drag at a wing angle of attack of 2.5 deg. I am conducting a different simulation for each winglet deflection (multiples of 3 deg, from 0 to 60 deg). I am getting unexpected results since my L/D ratio increases from 14.0 (winglet at 27 deg) to 14.6 (winglet at 30 deg), and then it decreases back to 13.6 (winglet at 60 deg). It looks like my values are oscillating too much, and think it's unrealistic that such a big difference in L/D can exist if the winglet is deflected only 3 deg.

In particular, I am looking for a pattern, as I expect L/D ration at cruise to be larger when the winglet deflection is 0 deg, while I expect L/D ratio to decrease as the winglet is deflected upward. But so far I am not seeing this pattern, as my results are fluctuating a lot.

I believe it may be a mesh problem, so I will try to run with a finer mesh.
Do you guys have some other suggestions?

Best regards.


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[ghorrocks]

The intention of your simulation is to find small differences in lift/drag. That means you will need to have a simulation methodology which is well validated and verified to the accuracy you are looking for - which in your case would be something like 1%. This is quite a challenging accuracy specification to achieve.

You are going to have to carefully validate and verify you method before you start. This FAQ is a starting point: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F and https://www.cfd-online.com/Wiki/Ansy...publishable.3F