Development of a spark discharge method of flow measurement

The spark method uses the fact that gas molecules which have been excited by the passage of a spark form a high conductance path for another high voltage pulse following the previous discharge after 10 to 100s. A square pulse high voltage spark of duration adjustable down to 01s is available.To ensure that the first spark of a train is as nearly straight as possible, it is triggered by an alpha particle from a safe radioactive source, the alpha-particle track being finely collimated.Stereoscopic photography of the sparks is used for observation, the pair of photographs being taken on a single 125×100 mm² film. A Saab microdensitometer scanner is used for automatic recording of the co-ordinates of selected points on the stereo photograph and a data reduction computer program is used to obtain the three-dimensional positions of the spark paths and hence determine the flow velocities working from a known boundary condition.