Design Process

Motivation

Common to every car is the wind encountered as the car is being used. The speed of winds encountered by a car are equal to exactly that of the car. With average wind speeds of 30 mph for city, and 60 mph for highway, the winds around a car carry greats amount of energy. This energy is usually lost to the drag force applied to the car by the encountered wind which, in turn, needs to be overcome by the engine in your car. This is the reason car bodies have become more aerodynamic to reduce the air drag force on the car. However, by exploiting areas of an automobile’s body that will inevitably produce high amounts of aerodynamic drag, such as the front of the car where a grill would be for a combustion engine car, we can convert the drag that would otherwise slow the car down, into electrical energy with the implementation of a wind turbine in this location.

Placement

Wind turbines on an electric vehicle are not a new concept. Designs and prototypes have been created and successfully implemented. However, the placement and design of these designs have shown to be either inefficient, or counterproductive. These wind turbines have historically been placed on the roof of the car, where wind velocities are greatest. To mount a wind turbine on the roof of a car that will minimize drag effects, the form factor is required to be small. This is problematic due to the amount of energy that can be captured by fluid flow through a turbine. The maximum amount of power produced by a turbine is calculated using the following power equation:

where P is the power, p (rho) is the density of air, A is the swept area of the turbine blades, and v is the velocity of the wind. Being that the power that can be produced is proportional to the cube of the incoming velocity, it seems obvious that turbines should be placed where the wind velocity is the highest. This location on the roof requires small wind turbines. A smaller wind turbine makes a great impact in the power production of a wind turbine. The circular swept area is proportional to the square of the radius, or the length of the turbine blade. Wind velocity differences between the roof of a car and the front “grill” are not substantial enough to produce power differences greater than what is lost by decreasing the swept area of the turbine.

Placing bigger turbines on the roof of the car would take advantage of the increase swept area and wind velocity resulting in higher power outputs. This, however, would incur large amounts of additional drag forces on the car, requiring the engine to produce more power to overcome those. Essentially, the additional power gained from the turbine would be provided by the additional power generated by the engine to move the car. These two powers, however, are not equal, and thus, don’t create a perpetual motion machine. The engine of a car, although very advanced, is not ideal and suffers inefficiency losses. Therefore, the engine would have to produce more power than what is gained through the turbine to make up for the losses to inefficiencies in the engine and to overcome the additionally incurred drag force by the turbine.

Project Goal and Scope

Unlike other attempts at a car mounted wind turbine, this project aims to increase the overall efficiency of an automobile. Increasing the efficiency of the car includes using less energy to propel the car forwards further. Any increase in efficiency is valued in the automobile industry as automobile companies strive to create the most efficient car.

Morph Chart

Selecting the Final Design

Using the morph chart, it was decided that using a rotary horizontal axis blade design would yield that highest power production. Noise reduction was to be addressed by insulating the housing. However, due to the unique nature of the turbine, a proof of concept for power generation was deemed more imperative for the outcome of this project and this was not implemented in the final prototype. Drag reduction was handled best by selecting correct placement of the turbine. The turbine is to be placed in the front area of the vehicle in order to 'recycle' existing drag forces on the car. Lastly, identification of the product could be easily addressed by the unique housing design that serves as the wind diverter.