3D PARTICLE IMAGE VELOCIMETRY FLOW TEST RIG

PARTICLE IMAGE VELOCIMETRY PARTICLE

Particle Image Velocimetry (PIV) is a non-intrusive optical technique that measures two velocity vector components simultaneously over an two-dimensional flow area. Tracer particles are introduced into the flow, and their scattered light are imaged by high resolution camera at two points in time close to each other. Short pulse illumination (pulsed laser) is used to “freeze” particle motion. Their displacements are then calculated statistically over a grid, for each grid cell area. Knowing the pulse separation and the image scale, the displacement field can be converted into a velocity vector field.

 

STEREO PARTICLE IMAGE VELOCIMETRY

In stereo PIV two (or more) camera perspectives are used to obtain different projections of three-dimensional particle motion. The projection of three dimensional motion along the different camera perspectives results in measureable particle displacements which may be combined to obtain an unambiguous measurement of three-components of displacement and from this three-components of velocity. The optimal angular separation for measuring all three components of velocity is 90 degrees and for a standard camera arrangement where the image and lens planes are parallel it will not be possible to achieve good focus over the whole of the imaged measurement plane. This problem is rectified by tilting the image plane such that the plane of the light sheet, the lens and the image plane intersect at a point. This is termed Scheimpflug tilt and as well as allowing particles over the whole image plane to be focused properly also introduces a perspective distortion.

 

CHARACTERISTIC NUMBERS

Evaluated numbers from flow test data:

• discharge coefficient (αK)

• ca (average axial velocity)

• Swirl

• Tumble

• Cross-Tumble

• Swirl for y+/y-