Achieving Negative Drag in MicroCFD

 

Coefficient of Drag of -0.0074

Of course this is impossible. However, we should learn how this is possible in MicroCFD.

You may say that MicroCFD is unreliable but so are most CFD software. We must learn how to understand their results. Their results are based on the formula that we program into them and the data we feed into them.

MicroCFD, even in 2D, has managed to predict the CD of Lightyear 1 and Tesla Model 3. It is slightly lower than the real CD of these cars which are understandable because it is in 2D only but 2D CD should be higher than 3D. Real cars have extra devices and manufacturing realities that reduce their aerodynamic efficiency.

The Lightyear 1 and Tesla Model 3, was traced usinng Blender to within 5 mm in curved edges so has more thana 40 points in the Shape file fed into MicroCFD. The Transparent SUV used for this is only smoothed around sharp edges but has managed to reduce CD to 0.095, which is lower than even the Stella Vie and CUER Resolution in 2D.

The Transparent SUV with ventillation channel fitted with a cover.

In this simulation, a channel is drawn inside the SUV and a cover fitted in front, opened only slightly. That low pressure creates a vacuum that showhow offsets the high pressure in front of it. The shape creates low pressure regions, not at the back of the car but mostly on top of it. Drag forces are not so high and somehow cancelled by the force created by the vacuum. MicroCFD must have overestimated the effect off the vacuum.

This phenomena is interesting because simulations without any cover creates more drag.