Flow visualization techniques can give us useful knowledge for understanding of complicated flow field or for practical design of fluid machinery and its elements. New techniques based on recent development of high-functional equipments and light source for visualization have possibility to resolve unsolved flow phenomena. Especially quantitative visualization methods using image processing technique, such as PIV, digital speckle method and LIF, are very useful to analyze complicated flow phenomena. A target of experimental analysis shown here is flow in a centrifugal fan in which 3D turbulent flow is induced. Aero-acoustic noise generation in it is related to the complicated flow field in the fan. The mechanism of noise generation at cut-off of scroll casing of the fan is investigated by using new technique and devices for visualization.
