#flow separation

[fuckyeahfluiddynamics]

Flow Over an AT-AT

Having previously examined the re-entry characteristics of an X-Wing, a group of engineers are back to look at Imperial vehicle physics. In this poster, they look at what happens to the AT-AT walker when strong crosswinds, like those seen in the Battle of Hoth, blow across the vehicle's path. (Image credit: Y. Yuan et al.)

[fuckyeahfluiddynamics]

Tokyo 2020: Baseball Aerodynamics

For a long time, people thought baseball aerodynamics were simply a competition between gravity and the Magnus effect caused when a ball is spinning. But the seams of a baseball are so prominent that they, too, have a role to play.  (Image credit: top - Pixabay, others - B. Smith; research credit: B. Smith; see also Baseball Aerodynamics) Today wraps up our Olympic coverage, but if you missed our earlier posts, you can find them all here. Read the full article

[fuckyeahfluiddynamics]

Tokyo 2020: Visualizing the Magnus Effect in Golf

Golf returned to the Olympics in 2016 in Rio and is back for the Tokyo edition. Golf balls -- with their turbulence-promoting dimples -- are a perennial favorite for aerodynamics explanations because, counterintuitively, a dimpled golf ball flies farther than a smooth one. But today we're going to focus on a different aspect of golf aerodynamics, namely, what happens when a golf ball is spinning.  (Image credit: top - M. Spiske, others - N. Sakib and B. Smith; research credit: N. Sakib and B. Smith, pdf) We're celebrating the Olympics with sports-themed fluid dynamics. Learn how surface roughness affects a volleyball serve, see the wingtip vortices of sail boats, and find out how to optimize rowing oars. And don't forget to come back next week for more! Read the full article

[fuckyeahfluiddynamics]

Tokyo 2020: Volleyball Aerodynamics

Like footballs and baseballs, the trajectory of a volleyball is strongly influenced by aerodynamics. When spinning, the ball experiences a difference in pressure on either side, which causes it to swerve, per the Magnus effect. But volleyball also has the float serve, which like the knuckleball in baseball, uses no spin.  (Image credit: game - Pixabay, volleyballs - U. Tsukuba; research credit: S. Hong et al., T. Asai et al.; via Ars Technica) Stick around all this week and next for more Olympic-themed fluid physics! Read the full article

[fuckyeahfluiddynamics]

Vortex Rings on V-Shaped Walls

Vortex ring impacts are eternally fascinating. Here, researchers explore what happens when a vortex ring encounters a V-shaped wall. (Image and research credit: T. New et al.) Read the full article

[fuckyeahfluiddynamics]

Engineers frequently face the challenge of maintaining control of air flow around an object across a wide range of conditions. After all, wind turbines and airplanes don’t always get to choose the perfect weather. To widen their operating ranges, designers can use active flow control to keep air flowing around an airfoil instead of separating and causing stall. One method of flow control uses plasma actuators on the upper surface of an airfoil. When activated, the plasma actuator ionizes air near the wing surface, producing the purplish glow seen above. That ionized air, or plasma, gets accelerated by the electric field of the device. The acceleration adds momentum to air near the wing surface, which helps it stay attached and flowing smoothly despite the unfavorable pressure conditions near the trailing edge of the wing. Compared to other methods of active flow control, plasma actuation is relatively simple to implement and so is actively being researched for applications in aviation and wind energy. (Image credit: I. Brownstein et al., source) 

[fuckyeahfluiddynamics]

Yesterday we discussed some of the basic mechanics of a frisbee in flight. Although frisbees do generate lift similarly to a wing, they do have some unique features. You've probably noticed, for example, that the top surface of a frisbee has several raised concentric rings. These are not simply decoration! Instead the rings disrupt airflow at the surface of the frisbee. This actually creates a narrow region of separated flow, visible in region B on the left oil-flow image. Airflow reattaches to the frisbee in the image after the second black arc, and the boundary layer along region C remains turbulent and attached for the remaining length of the frisbee. Keeping the boundary layer attached over the top surface ensures low pressure so that the disk has plenty of lift and remains aerodynamically stable in flight. A smooth frisbee would be much harder to throw accurately because its flight would be very sensitive to angle of attack and likely to stall. (Image credits: J. Potts and W. Crowther; recommended papers by: V. Morrison and R. Lorentz)

[fuckyeahfluiddynamics]

This flow visualization of a pitching wind turbine blade demonstrates why lift and drag can change so drastically with angle of attack. When the angle the blade makes with the freestream is small, flow stays attached around the top and bottom surfaces of the blade. At large (positive or negative) angles of attack, the flow separates from the turbine blade, beginning at the trailing edge and moving forward as the angle of attack increases. The separated flow appears as a region of recirculation and turbulence. This is the same mechanism responsible for stall in aircraft. (Submitted by Bobby E)