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Negative Drag Values for only some surfaces?? Please help

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Old   May 2, 2020, 06:39
Default Negative Drag Values for only some surfaces?? Please help
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Hi there, my deadline for my senior project is fast approaching and any help would be extremely appreciated right now!

Using Star-CCM I'm modelling an external aerodynamics simulation of a fixed wing UAV (see attached photos). I have run preliminary simulations using the realizable k-epsilon turb model with a target Y+ of 30, all converged nicely.

I have separate surface controls for each of my surfaces, and upon running a drag report for each surface I'm getting some as positive and some as negative?? In this case my fan, hinge point and wing/fuselage joint are fine, but the fuselage, H-Tail, V-Tail and Wing all are producing negative results? I think the report is set up correctly.

To add to it, upon looking at the y+ in a scalar field I notice there are some missing sections of the geometry in the scene which have not appeared anywhere else. (See Photo)

Any ideas please, again any help would be much appreciated.
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negative drag values, star-ccm

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