Measurements accuracy with 3D laser velocimetry

Accuracy problems that arise in connection with the simultaneous measurement of the three local velocity components using a 3D laser velocimeter (LV), when the 3rd component is obtained by combining two coplanar components, are examined. The various ways to set up a 3D LV are summarized, and a particular fringe, three-color LV, with signals processed by counters, is described in more detail. Sources of error are analyzed, and ways to minimize them are considered. The successful application of an existing LV to study vortex breakdown downstream of a delta wing is reported.