John Dabiri is not a Caltech aerodynamicist, and has never published on wind energy, propellers or rotors. My thesis was on wing theory at that institute, I taught there for many years, and have published many papers, monographs and bits of books on the subject of wind turbines, including a lot of stuff on design of rotors and arrays. I don't k now what he knows, but I do know sumpin! But validity depends not on pedigrees but results!
The article in Physics is pretty bad, for example, contrary to the author's statement, prop turbines do not shed vortices, but annular vortex sheets, with a lotta turbulence, a very different animal, that I have often analyzed, tested and measured in wind tunnel and field. I was concerned at his naive statement that the power increases because the rotational speed increases. It's elementary dynamics that this is not necessarily so. The power is the product of speed and torque, and for many turbines the power reduc es as the rotational speed is increas ed! In fact, in design studies, we often would feather, causing a unit to speed up and reduc e power output. For example, a prop anemometer spins very fast, extracting no energy from the wind, at essentially zero torque (except bearing friction). If it is braked by a motor, then the spin reduces as the power produc tion goes up. I dunno what John's paper is about, haven't read it. It is always good when an outsider introduces a new idea into a field. S o I'm looking forwards to hearing. I am amazed at folks tenacity to an idea that they don't even understand! But like the sound of, I presume! I have no opinion on the subject, because I haven't seen the pap er. When I recei ve same, I'll discuss for Fria mers. I don't want to waste folks' time on conjecture. Peter Lissaman, Da Vinci Ventures Expertise is not knowing everything, but knowing what to look for. 1454 Miracerros Loop South, Santa Fe, New Mexico 87505,USA tel:(505)983-7728
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