A flow surveying technique is described which provides a direct and quick output of either flow speed or direction. The computer based system enables ‘contour plots’ of these quantities to be obtained for fixed offset distances from a surface, using a series of surface contacting cylindrical probes. Pre-set values of the signal from the flow sensing system are used to switch a tri-coloured light source which traverses in unison with the probe, while a time exposure photograph is taken. For flow direction measurement, the signal activating the lights is computed from the pressure difference between yaw meter tappings on the cylinder in conjunction with the cylinder base pressure. Flow velocity is obtained from the base pressure alone, or alternatively from a hot wire probe.

Results are presented to show that the method can provide useful and detailed data. It is seen mainly as a complement to other methods available for visualising complex flows.