# Increasing car efficiency by rerouting airflow?

• rumborak
In summary, the conversation discusses the idea of using a supercharger to reduce air drag on a car by compressing and routing the air around the vehicle. However, there are concerns about the energy balance and cost associated with this method. The conversation also touches on the efficiency of dolphins' skin and its potential application in improving hydrodynamic efficiency in vehicles.
rumborak
This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible.

The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car.
Could one upscale a supercharger, I.e. a compressor, to consume all the incident airflow hitting the front of the car, compress it, route it through the car, and in the back expel it again?
Intuitively this should reduce air drag, since a much smaller section of the car is now "visible" to the air.
However, the compression and the associated own air drag might thwart the energy balance, making it negative overall. But, is that necessarily so?

rumborak said:
This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible.

The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car.
Could one upscale a supercharger, I.e. a compressor, to consume all the incident airflow hitting the front of the car, compress it, route it through the car, and in the back expel it again?
Intuitively this should reduce air drag, since a much smaller section of the car is now "visible" to the air.
However, the compression and the associated own air drag might thwart the energy balance, making it negative overall. But, is that necessarily so?
For your back-of-the-napkin calculation, figure out how many horsepower it would require to do that air pumping, and compare that to the power wasted in the excess air resistance...

EDIT -- Wait, you can write on both sides of a napkin, but only on one side of a used envelope...

sophiecentaur
berkeman said:
how many horsepower it would require to do that air pumping,
Yes - the pump would have to be free of turbulence.

berkeman
Sounds like you're essentially talking about a jet engine designed to generate just enough thrust to cancel out it's own drag, rendering the latter effectively zero.

mrspeedybob said:
Sounds like you're essentially talking about a jet engine designed to generate just enough thrust to cancel out it's own drag, rendering the latter effectively zero.
. . . . . which would cost a fortune to buy and to run, of course.
The aerodynamic design of modern fast cars does exactly what the title of the thread suggests.
On a parallel topic, I have read that the skins of dolphins has small ridges and valleys all over it and is 'deliberately' flexible, which is thought to improve its hydrodynamic efficiency. I wasn't aware of an equivalent in air (but who knows what birds' feathers do for efficiency?) but http://msbusiness.com/2007/12/entrepreneur-mimics-dolphin-skin-for-fuel-efficiency-enhancement/ which mentions the subject. There are dozens of other links about dolphin swimming efficiency being higher than you'd expect.

## 1. How does rerouting airflow increase car efficiency?

Rerouting airflow can increase car efficiency by reducing the aerodynamic drag on the vehicle. When air flows smoothly over the car's surface, it creates less resistance, allowing the car to use less energy and therefore, less fuel. By redirecting the airflow, the car can experience less drag and improve its overall efficiency.

## 2. What are some common methods for rerouting airflow in cars?

Some common methods for rerouting airflow in cars include adding aerodynamic features such as spoilers, air dams, and diffusers. These features are designed to manipulate the airflow around the car, reducing drag and improving efficiency. Additionally, some cars are designed with underbody panels and strategically placed vents to direct airflow in a more efficient manner.

## 3. How can rerouting airflow impact a car's fuel economy?

Rerouting airflow can have a significant impact on a car's fuel economy. By reducing aerodynamic drag, the car can use less energy to move through the air, resulting in improved fuel efficiency. In fact, studies have shown that even small changes in a car's aerodynamics can lead to significant improvements in fuel economy.

## 4. Are there any downsides to rerouting airflow in cars?

While there are many benefits to rerouting airflow in cars, there can also be some downsides. Some aerodynamic features, such as spoilers, can add weight to the car, which can decrease fuel efficiency. Additionally, these features may also increase the cost of the car. Furthermore, if not designed properly, rerouting airflow can also negatively impact the car's stability and handling.

## 5. Can rerouting airflow be applied to all types of cars?

Rerouting airflow can be applied to most cars, but the extent to which it can be done may vary. Some cars may already have efficient aerodynamic designs, making additional changes unnecessary. On the other hand, older or less aerodynamic cars may benefit greatly from rerouting airflow. It is also important to consider the specific needs and design of each car when implementing aerodynamic changes.

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