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The SHRL have been awarded a £1.3m EPSRC research grant to study the deformation of microscopic fuel droplets.
We are seeking to recruit two EPSRC Research Fellows.
We are currently offering a fully funded PhD studentship on laser diagnostics for sprays.
Particle Image Velocimetry (PIV)
Contact: Dr Guillaume de Sercey
Theory
PIV is a laser technique that allows the measurement of the velocity of a fluid in a plane. Through the use of stereoscopy, it also enables the measurement of velocity components perpendicular to that plane.
The principle of PIV is to illuminate with two consecutive bursts of light a plane of the flow seeded with particles. These particles can either be a fine solid powder or very small droplets of a diameter small enough (typically a few micrometres) so that they perfectly follow the flow. A correlation algorithm is used to track the displacement of the particles between the two illuminations.
Typically a double-pulse laser (usually Nd:Yag) beam formed into a sheet is used to illuminate the flow. Both burst of lights are either recorded on the same image or onto different images. In the former case, an auto-correlation algorithm is used, in the later a cross-correlation algorithm. Cross-correlation is preferred as auto-correlation leads to ambiguities in the sign of the velocities, however its setup is usually more expensive as it requires cameras capable of acquiring two frames within a very short span (typically only a few nanoseconds).The separation of the two frames (and laser shots) is dictated by the expected average flow velocity. The particles must only move a few pixels between each shot.
Examples of PIV images (two particles frames, resultant velocities):
