• Zachery L'Italien

What is airflow turbulence, you ask?

By: Zachery L'Italien, MCH Acoustical Consultant

 

As acousticians, we guide HVAC designers to avoid airflow turbulence in their system designs because it often leads to problematic noise.

What is airflow turbulence, you ask?

Simply put, airflow turbulence occurs when an airstream rapidly increases in speed such as by being squeezed through a tight aperture, changes direction, or is interrupted. These conditions cause high irregularity in the airstream’s flow and often results in problematic noise. Contrarily, if the airstream is flowing smoothly, we refer to this as laminar airflow.


Analogy of Turbulent vs. Laminar Flow

A river provides a good visual analogy of turbulent versus laminar flow. Turbulent flow is demonstrated by a river’s rapids, which can result from narrower, shallower, more quickly moving sections, or that perhaps have boulders and other debris that cause interruptions in the water flow.

Turbulent flow - rapids in a river

Laminar flow is demonstrated by the section of the river that flows very slowly and calmly, such that you can easily see through the water to the riverbed below.

Laminar flow - calm section of a river

Takeaway

If you imagine the two river scenarios above, you likely realize that the louder of the two is certainly the river's rapids. While these rapids may be fun on a river raft tour, this concept of turbulence directly applies to airstreams in HVAC systems. Excessive noise from airflow turbulence may be far less amusing for end users.


For HVAC systems, designers should consider appropriate velocities, relatively smooth duct runs, and proper placement of (or entirely avoiding) balancing dampers.


Curiously enough, for Duct “Silencers” to extract noise from an airstream, they necessarily squeeze air through a labyrinth of absorptive baffles and by that, create turbulence noise of their own. Trust your acoustical consultant, select and place these judiciously!

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