[ryan298]

Hello everyone,

I have a question regarding the accumulated drag curve shown in the figure below for the CFD simulation of external flow over an automobile

It can be seen in several regions that the accumulated drag curve is dropping (ie., having a negative slope, for instance, as in the region between 2500 and 3500 for the x axis). Now this should mean that in those regions, the drag is negative locally, as only this would bring a reduction in the overall drag. But how is this possible,? How can drag be negative locally in the said region for instance?

Correct me if I'm misinterpreting the curve.

PS: 1) The figure I've posted here is taken from a source which I've referenced below

"Levin, Ridgal, Aerodynamic analysis of drag reduction devices on the underbody for SAAB 9-3 by using CFD, Master's thesis, Chalmers University of technology, 2011"

2) It is kind of urgent, so if someone could help me out ASAP, it would be great

[agd]

The total drag is a combination of pressure drag and viscous drag. The pressure drag can be negative or positive depending on the local pressure relative to free stream.

[ryan298]

Thank you agd!. I understand better now