# An aeroacoustic investigation into the effect of self-oscillating trailing edge flaplets

## TL;DR

This study investigates how self-oscillating flaplets on a NACA 0012 aerofoil influence aeroacoustic properties, showing significant noise reduction, especially when placed on the pressure side, by modifying laminar separation bubbles.

## Contribution

It demonstrates that self-oscillating flaplets can effectively reduce tonal noise and overall sound pressure levels by altering flow separation mechanisms.

## Key findings

- Tonal peaks are eliminated when flaplets are on the pressure side.
- Overall sound pressure level is reduced by 1.5 to 2 dB with flaplets.
- Up to 20 dB reduction in tonal noise when peaks are removed.

## Abstract

The aeroacoustics of a NACA 0012 aerofoil with an array of self-oscillating flexible flaplets attached on the trailing edge has been investigated at low to moderate chord based Reynolds number (50,000 -- 350,000) and at geometric angles of attack from $\alpha_g = 0^\circ$ -- $20^\circ$. When the aerofoil is untripped, tonal peaks are observed on the baseline aerofoil. When the passive flaplets are attached to the pressure side of the aerofoil, the tonal peak is removed. If the flaplets are then placed on the suction side, the tonal peak is reduced, but not removed. It is therefore hypothesised that the flaplets on the pressure side modifies the laminar separation bubble situated on the pressure side of the aerofoil, a key mechanism for tonal noise. Throughout all cases, both tripped and untripped, a low frequency (0.1 kHz -- 0.6 kHz) noise reduction and a slight increase at higher frequencies (>2 kHz) is seen. This gives an average overall sound pressure level (OSPL) reduction of 1.5 -- 2 dB for the flaplets affixed to the pressure side. The cases where the tonal noise component is removed an OSPL reduction of up to 20 dB can be seen.