Quote:
Originally Posted by orange4boy
Unfortunately, yes.
A wind turbine creates a lot of drag. They are basically air brakes. The job of a wind turbine is to turn the mechanical energy of air movement into electrical energy. In order to do that it requires a lot of surface area and it has to create a lot of lift or pressure differential which means it creates a lot of drag. The relatively low efficiency of the blades coupled with the low efficiency of an electric motor means a whole lot of energy is lost to drag and heat and that's before it passes the bodywork of the car. If you have ever flown a plane with a variable pitch prop you can immediately feel the huge differences between a free wheeling prop (very high drag), a stalled prop (much lower drag) and a feathered prop (low drag). And remember, this is after you have inefficiently converted energy from fuel to motion already and now you want to change it back again with added inefficiencies.
Then, because the air still flows around the body following flow lines, it does not act like some kind of fairing. The disturbed air flows around the vehicle just like it would have without the turbine, acting on it and creating the same drag as before but now you have to add the drag of the turbine.
The upshot is that a turbine would increase your CD a lot.
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you say yes but do we know that as a fact? I have some doubt about that. lets stay with the semi truck and think about this. flat surface above the cab maybe 4x8. wind hitting it at 50 mph, because its flat you are pushing the air and getting maximum force against the area as the excess is having to push around the sides and top. then you put lets say two 4x4 blades in front of that area. and think about this, weather your moving and pushing the air or the wind is blowing and pushing against you, would there not be the same force? so would not the wind a head of the fan blades be slowing down the wind? and the area behind the fan blades would have to be getting less wind force? sure there will be wind getting through the blades it has to do that for the blades to spin. but what happens to the wind after it gets through the blades? does it get redirected some how a little, I am not sure myself just what happens but I can do a quick test by blowing air into a fan and checking out whats happening behind the blades. I don't think you are going to feel the same wind force that is blowing in front of the blades. if you could you could just keep putting more fan blades behind each other and harvest the same force again. it would be more reasonable to believe that if lets say some how you fan blades could cover the whole 4x8 and you added the force getting by and through the blades you would think they would equal the force of the same wind hitting the 4x8 flat surface. or some where close.
sure the spinning prop idea has more drag because its spinning fast and acting more like a flat surface stopping the wind in an area the size of the circle it makes. effectively blocking the wind for the most part while redirecting it. if it is absorbing most of the energy of the wind then there cannot be much energy left on the other side. and what energy there is if you add that to the energy the fan converted into rotation you should get close to the same energy that would be pushing against the 4x8 flat surface. I believe you would be incorrect in believing that the disturbed air passing through the fan would have the same drag as without the fan. In fact I know that would not be true and could easily test that. so the air pushing on that area already and slowing you down I believe we can still use it to do work since you cant stop that force from slowing you down whether its pushing against a flat surface or pushing against a spinning prop. and if my theory is correct you would have converted part of a force slowing you down into useful energy you could use to delete your alternator or maybe make some HHO to feed into you diesel intake. I will be doing some test.