Three-component PIV measurements on planar domains

In spite of all its advantages, the PIV method underlies some shortcomings that make further developments on the basis of instrumentation necessary. One of these disadvantages is the fact that the “classical” PIV method is only capable of recording the projection of the velocity vector into the plane of the light sheet; the out-of-plane velocity component is lost while the in-plane components are affected by an unrecoverable error due to the perspective transformation as described in section 2.4.3. For highly three-dimensional flows this can lead to substantial measurement errors of the local velocity vector. This error increases as the distance to the principal axis of the imaging optics increases. Thus it is often advantageous to select a large viewing distance in comparison to the imaged area to keep the projection error to a minimum. This is easily achieved using long focal length lenses.