Quote:
Originally Posted by trebuchet03
It's worth pointing out that these large bladed designs have really high tip velocities.... Which leads to an unfortunate limitation of scale as you get nearer to the sound barrier.
High Altitude It's the future  |
At 28.8 r.p.m. you can have a blade diameter of almost 110 meters and have a tip speed of less then mach 0.5. That's a pretty big fan. I suspect stresses might be a problem on a thin airfoil 54 meters long. The A380 wingspan is
not quite 80 meters, so the wing itself might be about 37 meters. I'm not sure about the stress calculations for a wind turbine blade, but I'm guessing that that's the limiting factor. From what I can see googling around, it looks like 100 meter turbines with 49 meter blades are the upper end at this time. Tip speed would be well below mach 0.5 at 28.8 r.p.m.
Here is a picture of a huge turbine with rotor diameter of 126 meters and blade length of 61.5 meters. At 28.8 r.p.m, the tip speed would be about 190 meters/second or a little under mach 0.6. Transonic speed is considered to begin at mach 0.8. So, there is some room to grow.