6 ms·
I agree with the importance of the freestream turbulence intensity, but at high Re numbers, it's extremely hard to control it. It can be shown mathematically,
by namirez 8y ago
I agree with the importance of the freestream turbulence intensity, but at high Re numbers, it's extremely hard to control it.
It can be shown mathematically, using a technique called parabolized stability equations (PSE), that small disturbances amplify rapidly thorough non-linear interactions in the frequency space. Hence, although it's possible to create a laminar flow at high Re number in the lab, it's extremely hard to achieve in nature.
One interesting case of this is the Rutan's Voyager airplane in the 80s. It was designed to have a laminar flow over its wing to reduce drag. It worked quite well until it faced rain drops at some point which messed up the aerdynamics of the wing and caused the airplane to stall. At that point, they had to add vortex generators on the wing to prevent the stall.
- Serow225 8y agoThe HondaJet was also designed to take advantage of superlaminar flow over the wings and body. It's why the turbines are mounted on pods held high above the wings, instead of closely slung underneath like a traditional design.
- btrettel 8y agoThanks for the interesting example. You're right that this is unlikely to redeem a scaled up dandelion, but I thought it was still worth mentioning as it's often overlooked. I work in internal and multiphase flows, and changing the turbulence level is much easier there than in aerodynamics. I'll also have to look at the parabolized stability equations as I am not familiar with them. If you have a preferred reference, I'd be interested.