Experimental determination of the aerodynamic coefficients of spinning bodies

Abstract

To accurately predict the probabilities of impact damage to aircraft from runway debris, it is important to understand and quantify the aerodynamic forces that contribute to runway debris lofting. These lift and drag forces were therefore measured in experiments with various bodies spun over a range of angular velocities and Reynolds numbers. For a smooth sphere, the Magnus effect was observed for ratios of spin speed to flow speed between 0.3 and 0.4, but a negative Magnus force was observed at high Reynolds numbers as a transitional boundary layer region was approached. Similar relationships between lift and spin rate were found for both cube- and cylinder-shaped test objects, particularly with a ratio of spin speed to flow speed above 0.3, which suggested comparable separation patterns between rapidly spinning cubes and cylinders. A tumbling smooth ellipsoid had aerodynamic characteristics similar to that of a smooth sphere at a high spin rate. Surface roughness in the form of attached sandpaper increased the average lift on the cylinder by 24%, and approximately doubled the lift acting on the ellipsoid in both rolling and tumbling configurations.

Investigation of Reverse Swing and Magnus Effect on a Cricket Ball Using Particle Image Velocimetry

“…(Mittal has speculated in sports journalist articles that this is exploited in a singular fashion, such that the ball pitches further from the batsman than expected.) This inversion effect has been demonstrated computationally and experimentally on smooth rotating spheres [16][17][18] and dimpled golf balls [19]. It is often explained by an effective Re on the advancing and retreating sides based on the velocity difference, which is the combination of Re and α. Sakib and Smith [19] identified that the inverse Magnus effect on a golf ball only occurs when Re is close to the critical regime.…”

Effects of spin rate on the surface pressure distribution of a rotating model

“…At higher Reynolds numbers, the boundary layer becomes turbulent. [8][9][10] At high angles of attack, but at a sufficiently low Reynolds numbers and low spin rates, the boundary layer remains laminar; however, the vortices on the body separate. Please note that for most projectiles the angles of attack where the flow separation and vortex formation occur is relatively small, about five degrees or so.…”