Particle image velocimetry study of acoustic field in miniature traveling wave device.

Abstract

Particle imaging velocimetry (PIV) techniques were employed to investigate the flow patterns inside a 2 kHz annular thermoacoustic device. This thermoacoustic device uses air at one atmosphere as its working fluid and smoke for seeding particles. For these measurements, the sound level output of the device was kept to 140 dB to help maintain the suspension of seeding particles. Several types of flow patterns were observed, including Gedeon streaming, start-up noise characterized by instabilities such as vortices, and a traveling wave throughout accompanied by radial standing waves localized near corners. Such measurements are challenging in small high frequency devices. In order to satisfy the Shannon-Nyquist theorem, a 2 kHz engine would need to be sampled at a minimum of 4 kHz; however, a new technique was developed that allows for the measurements to be made using a camera with a maximum frame rate per sec of 300. This new method makes it possible to perform measurements on a flow without the need for more expensive and delicate high speed equipment, thereby, making observation of high speed flows more readily available. [Research supported by the U.S. Army Space and Missile Defense Command/U.S. Army Forces Strategic Command.]