Noise Measurement

Introduction

A sound-absorbing test section insert has been developed for the Transonic Wind Tunnel (TWT) to enable near-field measurements of propeller noise to be made over a wide range of forward speeds.

The photograph shows the Acoustic Test Section Insert installed in the TWT around a contra-rotating propeller model with a microphone traverse gear that is used in measuring the noise levels in the proximity of the propeller.

Technical Information

The insert is 3.658m (12ft) in length and reduces the test section dimensions to 2.4m  2.1m (8ft  7ft). The insert is equipped with traversing and wall-mounted microphones and is effectively anechoic, enabling inverse-square law behaviour to be established in the far-field. The insert has been commissioned and calibrated to Mach numbers up to 0.8.