Question about Reverse Magnus Effect

[robhlee]

Hi,
I was looking at the NASA website's FoilSim application (google it) and for spinning objects, there is a maximum rpm. I was wondering why there were maximum/restricted rpms, so I emailed a NASA guy with the question. He said that the FoilSim App was for middle school students and that higher rpms would create secondary boundary layers, or something like that, too complicated for middle schoolers. He also said that the rpm-lift force relationship remains linear (higher rpm-higher lift force) at higher rpms than allowed in the FoilSim. So then I read about the 'reverse Magnus effect', and now I need a bit of clarification. How would having a rough surface completely negate the reverse magnus effect (according to http://209.85.165.104/search?q=cache:5eXgtFXUgfkJ:maxwell.ucdavis.edu/~cole/phy9b/notes/fluids_ch3.pdf+reverse+magnus+effect&hl=en&ct=clnk&cd=1&gl=us) , and is the NASA guy mistaken when he told me the rpm-lift force relationship remains linear at increasing rpms?

Thanks.

 

[Navin A S]

The reverse Magnus effect is a phenomenon that occurs when a spinning object moves through a fluid, such as air or water. It causes the object to experience a force that is opposite the direction of its spin. This force is known as lift force, and it is generated because of the differences in pressure that exist on the surface of the object due to its spin. The greater the spin rate, the greater the lift force generated. The NASA guy was correct in saying that higher rpm would create secondary boundary layers, or something like that, too complicated for middle schoolers. These secondary boundary layers are caused by the increased turbulence that occurs with higher spin rates. This turbulence can decrease the lift force generated, depending on the surface of the spinning object. If the surface of the object is rough, the turbulence will create eddies along the surface of the object, which will disrupt the flow of the fluid around the object, thus reducing the lift force generated. The NASA guy was also correct in saying that the rpm-lift force relationship remains linear at higher rpms than allowed in the FoilSim App. However, if the surface of the object is rough, the lift force generated will be reduced due to the eddies created by the turbulence. Therefore, the linear relationship between rpm and lift force will not hold true in this case.