Understanding the Mysterious Sounds of an Open Rear Window During High-Speed Driving
Understanding the Mysterious Sounds of an Open Rear Window During High-Speed Driving
Have you ever driven a car with the rear window down at high speeds and noticed an odd, pulsating noise that seems to make your stomach queasy? If you have, you're not alone. This phenomenon, often occurring in vehicles like the Volkswagen Passat, is a common issue many drivers face. In this article, we'll explore the science behind why this happens and how it can be managed or mitigated.
What Causes the Pulsating Sound?
The pulsating sound is a result of the air pressure differences and airflow dynamics within the car. As the car moves at a high speed, the air pressure changes periodically, creating a cyclical pattern of air entering and exiting through the open window. This cycle can be likened to blowing across the top of a beer or wine bottle, which produces a characteristic tone.
At high speeds, the car's exterior forces the surrounding air back, causing a buildup of pressure just outside the window. When this pressure peaks, it effectively blocks the airflow, and as the air pressure drops, the cycle repeats. This creates a pulsating sound as the air rushes in and out, resonating within the car.
The Aerodynamics of the Situation
The air rushing in and out through the open rear window is a classic example of laminar and turbulent flow. As the air moves, it encounters resistance due to the car's shape, leading to a complex interplay of pressure waves. These waves can resonate within the car's interior, amplifying the pulsating sound.
How to Reduce or Eliminate the Sound
Fortunately, there are several methods to either reduce or eliminate the annoying pulsating sound:
Window Weather Stripping: Adding weather stripping around the window seals the gap and can significantly reduce the airflow, thereby minimizing the pulsating noise. Air Flaps and Deflectors: Placing small air flaps or deflector devices on the rear window can help to direct airflow and create a more stable pressure environment. Modified Rear Window Angle: Adjusting the angle of the rear window can also help in altering the airflow pattern, leading to a quieter ride. Air Conditioning: Running the air conditioning at a low speed can help in masking the pulsating noise. The conditioned air flow can also help in alleviating the pulsations by introducing a more stable airflow.Conclusion
The pulsating sound from an open rear window during high-speed driving may seem like a minor annoyance, but understanding the science behind it can provide valuable insights into automotive acoustics. By addressing the issue through weather stripping, air flap modifications, or simple air conditioning use, you can enjoy a more comfortable and peaceful ride.