Hemisphere test >:-)

Since low aerodynamic drag is a base of movement in these vehicles, I will post my short study of 15 minutes. This study clearly shows the difference between flat surface vs round surface and reaction in air flow around them. Because the study is not done in scientific manners, I created basic shapes without any details or minor flluctuations on their surfaces, these results are not exactly true offcourse, just giving some quidance of this phenomenon.

The study contains a solid 50cm hemisphere, airflow is 10meters/s and surface is theoretically perfect with roughness of 0. Both hemispheres are equal, only variation is their air flow direction, the other is flat face to wind and the other is round face to wind. The results are: flat face to wind gave 13N of force and round face to wind gave 6N of force, so more than twice of force is generated when flat face is put towards the wind.



Previously made simulation with streamlined body (see previous posts) gave results 7N @ 20m/s, which is nearly the same as 50cm hemisphere but with double speed ! With equation F = ½ s v² A Cv , force of drag will give Cv value of 0.095 with given parameters. But frontal area needs to be rechecked in the process when, for example, the bubble is added. So there is a lot of variables and Cv value is not even close to it's practical and real value.