Particle Image Velocimetry
Particle Image Velocimetry (PIV) is a non-intrusive optical technique for the simultaneous measurement of flow velocity fields. The ability to measure velocities at many points in a fluid flow instantaneously allows the detection of large and small scale spatial structures and is especially useful for the study of unsteady flows (eg. acoustic fields, arterial blood flows, etc.).
The Acoustics and Fluids Group has recently acquired a state-of-the-art PIV system, comprising a high repetition rate C-V pulsed laser and a high speed camera, capable of frame capture rates up to 60kHz. This new system should allow qualitative and quantitative measurement of the onset of transient effects in acoustic fields and other situations in which a fine degree of spatial and temporal resolution is required.
Recent work by Dawn Rockliff and David Skulina using PIV has been to investigate acoustic streaming velocities in the vicinity of woodwind tone holes. Acoustic streaming is a non-linear effect caused by the viscous interaction of a fluid with discontinuities in its boundary, in this case single and double tone holes, at high sound intensities. The result of the interaction is the generation of a mean flow velocity.
The images to the right show PIV images obtained using the copper vapour laser as a light source and a digital CCD camera for image acquisition. The animations clearly show the formation and development of jets from the tone holes as the driving frequency is increased. The PIV maps confirm the presence of a mean flow out of the tone hole at near resonance frequencies.
