What is an Air Curtain on a Car?

Aerodynamics is an essential component of a vehicle's performance and efficiency equation, whether it be a sports car or a minivan. This facet of vehicle design helps reduce air friction, also known as wind drag, on a vehicle's body. Engineers and designers use many approaches to manage airflow and optimize aerodynamics. One such development on this front is the air curtain.

Achieving Aerodynamics

Automakers utilize a roster of components and devices for achieving aerodynamic results on a vehicle. These include lip spoilers, front diffusers, air splitters, side skirts, sculpted body panels, and canards. Among the vast array of aero components, the air curtain may be one of the least known.

Overall, air curtains are a relatively new approach to improving aerodynamics. 

From a mainstream standpoint, they first showed up on the Ford Mustang a few years back, but now more carmakers are implementing them as part of their vehicle designs across various segments, from sedans to trucks.

What does an Air Curtain do?

An air curtain is essentially a vent at the vehicle's front corners that allows air to flow beneath the headlamps, into the wheel housings, and around the front wheels. By guiding airflow along this path, an air curtain reduces the air resistance of the vehicle body in a simple yet highly effective way.

Although air curtains can vary from a design standpoint from vehicle to vehicle, they all generally involve an inlet or a series of inlets on the front fascia that allow air to enter, followed by specifically engineered outlets that guide the air around the front wheels.

If you take the front wheel off, you'll find a thin vertical slot in the guardliner that feeds air from ducts in the bumper ahead of the front wheel. You can usually see to the other side if you look through that slot.

Understanding Air Flow

Starting at the front fascia, the air hits the vehicle and finds a way around it. Much of that air flows over the tops of the car and underneath the vehicle. But a significant proportion of air wraps around the sides and flows down the length of the car.

This air coming down the car's sides has a challenging passage because it must go over the front wheels. It's not apparent to the eye, but spinning wheels are a significant source of drag. They disrupt the airflow, making it hard for the air to remain in a continuous stream.

That broken airflow results in turbulence that increases the drag coefficient on the vehicle. By definition, drag coefficient is "a numerical measure of the effectiveness of a streamline aerodynamic body shape in reducing the air resistance to the forward motion of a vehicle." The lower the drag coefficient, the more aerodynamic a vehicle will be. Air curtains help reduce this coefficient.

Not long ago, manufacturers figured out that feeding air through the front of the car through slots that exit just ahead of the front wheels helps mitigate this turbulence. Air is pushed through the duct and flows—like a curtain—across the front wheels and down the side of the car in an uninterrupted manner. Hence, the name.

Since enclosing the wheels in skirts to smooth the airflow isn't necessarily practical or attractive, directing that air across the outer surface of the wheel and tire is the better option. It creates a wall of high-speed air that works much like a side skirt to reduce drag while still leaving the wheels fully exposed.

The Benefits

Theoretically speaking, the air curtain improves the momentum of air and ensures flow reattachment. In other words, it keeps the airflow from breaking up at the wheels due to wheel spin. It also adds energy and speed to the airflow and optimizes its journey rearward.

What does all of this mean in a practical sense? An air curtain helps a vehicle achieve better performance, consume less fuel, and emit fewer CO2 emissions, not to mention less noise, vibration, and harshness (NVH) experienced by the driver and occupants. In other words, the vehicle delivers more agility and speed, more efficiency, more eco-friendliness, and more comfort.

Summary

Aerodynamics is achieved through an aggregate of components and tactics that work together to reduce or eliminate drag while a vehicle is in motion. An air curtain is a simple yet effective measure that can contribute to the overall goal of minimum wind resistance and a better overall driving experience.

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