Airfoil Noise Explained: Trailing-Edge Noise and Broadband Self-Noise

Self-noise means the airfoil is the source

Airfoil self-noise is the sound the section radiates because of its own boundary layer and wake, even in smooth incoming flow. It is distinct from turbulence-ingestion noise, which is the leading edge answering a gusty inflow, and from machinery noise. On wind turbines, cooling fans, propellers and quiet UAVs, trailing-edge self-noise is often what sets the broadband floor. Brooks, Pope and Marcolini’s classification is the standard map of the mechanisms. You can use the map without turning this page into a prediction code.

The mechanisms worth naming

What designers can actually change

• Trailing-edge thickness. A square, thick edge sheds vortices. A sharp, well-aligned edge pushes the problem back toward ordinary turbulent trailing-edge noise, which is quieter than a blunt-edge tone but not silent.
• Angle of attack and separation. A section that is separated in the “quiet cruise” condition is not in a quiet condition. The Cp plot and the noise tell the same story.
• Trips versus tones. At model scale, a tonal whistle from a laminar layer is sometimes cured by a trip. The trip adds turbulent trailing-edge noise. That trade can still be a win if the tone was the complaint.
• Serrations and porous edges. Trailing-edge serrations are a known way to weaken the scattering efficiency of turbulent trailing-edge noise. They are a detail design with structural and manufacturing costs, not a sticker you add in a polar code.
• Speed and chord. Self-noise scales strongly with flow speed. A slower tip speed is often the most powerful noise reduction on a propeller, a fan or a turbine, and it is an operating choice as much as an airfoil choice.

A section polar does not emit decibels. Use the polar and the Cp curve to see whether the section is attached, how thick the edge is, and whether a laminar run is likely to whistle at this Reynolds number. Use a noise model or a test when the requirement is a sound level. Do not read a low CD as a low dB.

---

Where this sits in the series

In simple words: what this page is for

An airfoil in clean flow still makes noise. The turbulent boundary layer scattering off the trailing edge is usually the main broadband source, and the edge geometry changes it.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Airfoil Noise Explained: Trailing-Edge Noise and Broadband Self-Noise helps you keep a clean trail from shape to polar to choice.

Why the topic matters

Engineers lose time when a title sounds clear but the page only sketches the idea. This article expands Airfoil Noise Explained: Trailing-Edge Noise and Broadband Self-Noise so you can answer three questions without jargon: what is the idea, when do you use it, and how do you check it in a HENDOI product.

Read the sections above for the core definitions. Use the steps below to move from reading into a real project trail you can share with a teammate.

How to apply this in HENDOI

In practice: create a HENDOI account or log in, open HENFOIL, bring a section in (create, import DAT, or digitize), pass the geometry gate, climb the analysis ladder only as far as the decision needs, then compare and archive. Every calculated number should keep its method label.

When the section choice is ready for the aircraft, continue in HENSYNTH for mission, compliance and trades. Same account. Same plans.

What this page will not claim: a teaching polar or geometry note is not a flight-Re certificate. HENFOIL labels methods so you know what you bought. Tunnel data and professional judgement still sit outside any single software run.

Checklist before you leave this page

• Can you state the idea of Airfoil Noise Explained: Trailing-Edge Noise and Broadband Self-Noise in one sentence?
• Do you know which product owns the next action — HENFOIL or HENSYNTH?
• Will every number you keep carry a method label or a stored-run source?
• If you are new here, have you opened Register or Login?

Related reading on this site

• Active Flow Control on Airfoils: Suction, Blowing and Synthetic Jets
• What Is the Aerodynamic Center of an Airfoil? Location, Meaning and Applications
• How to Identify Numerical Convergence Problems in Airfoil Analysis
• How to Build an Airfoil Analysis Database with Consistent Simulation Conditions
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
• Login · Register now

• Previous: How to interpret Cp distributions
• Next: How icing changes lift, drag and stall
• Index: all HENFOIL airfoil lessons

These pages teach the ideas. They are not wind-tunnel data and not a certification analysis. When a number matters, compute it at a stated Reynolds number, Mach number and transition setting, and keep the method label on the result. In HENFOIL that production polar is a VIC polar — see the analysis ladder and the polar field guide.