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A path line method utilizing a CCD random shutter camera and a laser light sheet was applied for obtaining the air mass entrained into a transient gas jet. Large, light weight particles and fine particles were used for scattering the path lines of the surroundings and visualizing the approximate shape of the jet, respectively The jet configuration and the entrainment process could be visualized simultaneously, and this path line method was found to be very useful for estimating the air mass entrained because of the good agreement with the value obtained using LDA data. The spatial and temporal change of the ambient air entrainment into the jet was approximately clarified.

A turbulent gas jet impinging on a flat wall was visualized by a laser sheet method. Velocity fields were determined from the images with a high speed video system by processing them in terms of the cross correlation method for the jet and particle tracking method for the ambient air from the same images. The vortex flow near the transient jet tip impinging on the wall was visualized and analyzed successfully. The velocity field obtained from the above methods was compared to that determined with a laser Doppler anemometer. The path line of a certain period which was taken with a CCD camera with controlled shutter was analyzed and the mean rate of air entrainment was determined quantitatively. The spatial and temporal change of the entrainment rate was estimated and it was found that the entrainment rate near the upstream part of the jet tip region is larger because of the vortex.

A new measuring technique of gas stream velocity has been developed, based on the phenomenon that the path of an electric discharge moves downstream under the influence of the gas stream. A probe (a thin conductive wire grounded by a resistance) is placed at a fixed distance downstream from the electrodes. When the discharge path arrives at the probe, the probe voltage rises rapidly. By means of measuring the time interval elapsing between the beginning of the spark and the rising of probe voltage, the stream velocity can be determined by the formula, U = Kℓ/τ, where K is a constant. As the result of preliminary tests, it was confirmed that the constant K is independent of distance ℓ, intensity of turbulence, temperature, and pressure of flowing gases, and depends only on the electrode spacing. The digital measurement of the time interval can be made easily.