In the present simultaneous spectral and flow-visualization measurements, the disturbance is visible using a suspension of small aluminium or Kalliroscope polymeric flakes that align with the flow, and the intensity of laser or light-emitting-diode light scattered by the flakes is simultaneously measured. The disturbance structure is clarified and the fundamental frequency of the velocity fluctuation is identified by comparing the results of the visual observation and the spectral analysis of the scattered-light intensity. The present method using simultaneous spectral and flow-visualization measurements is applied to analyse various disturbance appearing in the spherical Couette flow between rotating spheres and the radial flow between two parallel disks with an axial inflow.
A new solid-tracer method for visualizing the secondary flow in curved pipes is developed together with the measuring technique to obtain the velocity vectors of the flow field. In this method, the nylon particles suspended in the water flowing are illuminated by a sheet of a strobo light, and their paths are recorded photographically. This method is applied for steady, oscillating and pulsating flows in the fully-developed region of a circular curved pipe with a curvature ratio of 7.6. The obtained velocity vectors and profiles of the secondary flow are in good agreement with the numerical results. The availability of the present method is confirmed for visualization and velocity measurement of the secondary flow motion in curved pipes.