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Old 11-05-2015, 07:02 PM   #34 (permalink)
aerohead
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Quote:
Originally Posted by jamesqf View Post
Why do you need to get 100% efficiency? (Let alone more than 100% :-)) You just need to extract more energy than is needed to overcome the extra drag. And as the examples show, it IS possible to do that, just not practical for daily driving. Rather like the solar cars racing across the Australian Outback.
*The wind-powered race cars are traveling at 11.5-mph.
*At this velocity,the car is at sub-critical Reynolds number.
*A 'real' automobile cannot operate at a sub-critical Reynolds number due to the turbulent boundary layer of Earth in which it is traveling.
*'Sail' effects are the reason the wind-powered race cars can move into the wind.
*The turbines on the race cars are gimballed for yawing,to take advantage of relative wind - induced lift/thrust.
*On the front of an automobile,at the forward stagnation point,embedded within the grille area (?),the Prandtl lines of discontinuity in the streamlines would preclude the turbine from relative wind affects,required to produce the thrust present in the race cars.
*We'd be limited to a standard,garden-variety mechanical efficiency for the turbine.
*In traffic,it would be virtually impossible to produce any power,and you'd be relying on battery-alone,which would have to made made up when back underway.
*A conventional belt-driven,shaft-driven,or flywheel-mounted alternator is electrically as efficient as a wind-powered generator,minus drive losses where applicable.
*The mechanical efficiency of a V-belt,cog-belt,serpentine-belt,etc. exceeds the efficiency of a wind turbines ability to harvest energy from the passing air mass.
*On a calm day,the engine in the car would have to produce all the 'wind' for the turbine,and even with a Diesel TDI,we're talking 43% thermal efficiency,to make wind for a turbine which is 59.3% efficient.
*Now we're down to 25.5% efficiency for the electricity,about as efficient as a trash incinerator.
*I'm uncertain as to the minimum velocity of the air column necessary to even begin power generation with a turbine of such small diameter.
*The turbine sections of turbochargers in a 2016 Ford Shelby Super Snake Mustang might be looking at 280-hp worth of hot gases at their inlet.
*The accomplishment of the students,racing into the wind must be taken in view of a very contextual operational environment.
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