Charging of Electric Vehicles During Motion Using Wind Energy
The main disadvantage of Electric Vehicle is the lack of capability of storing sufficient energy to run the vehicle for a long time. The operation, performance and efficiency of motor driven electric vehicles are much better than engine driven vehicles, at the same time electric vehicles are very much environment friendly. Still electric vehicles are falling behind in the automobile industries due to the problem of storage of energy. This paper is based on the concept of charging the batteries of an electric vehicle when it is in motion or propelling.
This may be done by using the energy of wind which is caused by the relative motion between the vehicle and the wind surrounding it. Wind turbines can be mounted on the body structure of the vehicle to generate electricity in such a way that it must not create any additional drag force (rather than the existing drag force due to frontal area and skin friction) upon the vehicle. Some techniques and methods are proposed to minimize the drag imposed by the introduction of the turbines as much as possible. With this concept it may be possible to increase the range of an electric vehicle and it will also save the charging time of the battery to a great extent.
When a vehicle moves it experiences wind resistance which are classified in two different forms- frictional drag and form drag. Frictional drag arises due to viscosity of air and form drag arises due to variation of air pressure in the front and rear side of the vehicle. As the vehicle moves forward, it leaves the air stream behind. A turbulence or disturbance is created on the wind when a vehicle moves through it. If it is possible to capture those wind streams within the vehicle itself then it can be used to recover some of energy that has been used to overcome the form drag (aerodynamic drag) of the vehicle.
If this wind energy is used to extract some power in such a way that it does not create any component of force or thrust opposite to the direction of the propulsion of the vehicle, then this gained energy can be used to produce electricity to charge up the battery of the electric vehicle itself. At the same time drag can be expected to be reduced by passing this air to the rear side (Low pressure side) of the vehicle. Air stream sliding over the body of the vehicle cannot enter into the rear side due to vortex shedding. If air streams are allowed to flow in this region by any means then the form drag will be reduced by some amount and at the same time it may be possible to generate electricity using the kinetic energy of wind.
Several studies had been carried out in this field but none of them are proved to be scientific. During the Second World War, wind turbines were used in submarines to charge up the batteries when they remained static and afloat in the water. At present it is also common to use turbines in ships, caravans and vehicles when they are parked. But to extract power from a moving vehicle is quite difficult as the turbine will act as a load for the vehicle. Most of the designs showed that the turbines are placed over the vehicle roof without considering the fact that it will impose an additional load for the vehicle and on the other hand no measures had been taken to reduce it. A design by Rory Handel and Maxx Bricklin showed that it has four tactically placed air intakes which will channel the air flow over the car’s body towards the turbine. No such detailed design was available.
In this project, the topic will be dealt by considering all the scientific facts and laws of energy conversion. A new approach is proposed and simulation of the design shall be carried out to analyse the behaviour of the model. Some theoretical formulas will be used for the purpose of calculations.
It is assumed that the vehicle is moving in a calm and steady wind stream with zero wind velocity. If the vehicle is moving at a constant speed, then we can think a wind stream is flowing around the vehicle. Normally this wind will cause a drag force which is opposite to the direction of the propulsion of the vehicle. At constant speed (zero acceleration) the energy requirements to move the vehicle forward are –To overcome the frictional force (rolling resistance of road) and to overcome wind resistance. At this Condition, if the air stream flowing around the vehicle is allowed to enter inside and let it flow down to the rear side; then it may be possible to use these air streams to generate power.
The vehicle has already interacted with this wind and it deflects the stream of wind at the two sides of it by stagnation at the front. This is the energy that had been lost from the vehicle to overcome the aerodynamic resistance. Now if these stream generated by the interaction of the wind and vehicle is captured within the vehicle in such a way that it would not impose an additional drag at the direction of propulsion of the vehicle, some of the energy can be recovered and fed back to the battery by means of conventional energy conversion processes.
Placing a wind turbine can serve the purpose. At the same time it will help to increase the pressure at the back side (according to Bernoulii’s equation pressure will be increased if velocity is decreased and velocity will be reduced at the back side of the turbine after energy extraction) which will reduce the drag force that existed before with the conventional design of the vehicle. So, vortex shedding will be reduced at the rear side. For this it is necessary to modify the design of a vehicle which gives provision of air flow through the vehicle. On the other hand positioning of the turbines will also be important because they must be placed in such a way that they do not impose or create any additional drag on the vehicle. Symmetrical positioning of the turbine can do the trick as the thrust acting on the turbines will cancel each other.
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