CIV in multi-planes and volumes:

To get the flow structure in a volume, we have two possibilities.

• Multiplane 2D CIV. The laser sheet position moves at successive positions with regular spacing, and one burst is made at each position. It takes about one second to change position, and about the same to make a burst. Therefore, the total time for scanning is long, about 10 s, depending on the number of levels, and the flow can evolve during that time. The advantage is however that is no practical limitation to the measured velocity (it is like in 2D CIV).
• CIV in volume: in this case the laser sheet is sweeping the volume a first time, come back to its origin, and then sweep it again. Correlation is made between two corresponding images at the same position. In the present state of the technique, the minimum time interval t for the correlation is 2s, so that the method is limited to flows with moderate velocity, less than about 1 cm/s. In contrast the scanning time is short (less than 0.5 s), so we really get an instant scanning of the velocity field, unlike in the multiplane case.