ABSTRACT
The flow visualization method using electric sparks is called the spark-tracing method. This method can obtain the velocity distribution of gas flow by putting electrodes of suitable shape into the gas, supplying high-voltage pulses, and creating the spark lines that move downstream with the gas flow. When an electric spark travels in air, it makes an instantaneous path of ionized air. This path has a very low resistance for a very short period, during which detectable ionization exists. To measure flow velocity by the spark method, electric discharge must be made through the ionized path moving together with the flow, and the timeline must be shown. The minimum required voltage was measured by changing the shape of the electrodes, the spacing or interval of the electrodes, and the flow velocity. When the spark discharge is produced in the air, the spark disappears instantaneously. But the ionized air zone remains for a short time.
