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Investigation on the Gas Jet Flow Performance Confined in Round Pipe
Author(s): Han Zhang, Li Jia, Lishui Cui, Chunhui Li
Keywords: Confined jet, confined pipe, Size effec, gas flow measurement
Jet flow performance confined in round pipe was investigated experimentally and numerically. Atmospheric gas jet from a circular symmetrical nozzle into a confined pipe was used to study the confined characteristics based on the multi-scale characterization. Effects of inlet velocity and confined space size on the confined characteristics were discussed. The studied inlet velocity range uc was from 0.98 m/s to 84.72 m/s and the diameter ratios dR of the tested confined space were increased from 1 to 20. The initial velocity profile evolution was observed and recorded by numerical simulation as well as a laser Doppler anemometer (LDA) with the resolution of 0.01 m/s. The characteristics of confined jet related to the initial velocity profile evolution were represented by characteristic parameters, namely the centerline velocity decay VR and the entrainment rate MR. The increased recirculation fluid action caused by the addition of confined space was the chief driving force for the promoted initial velocity profile evolution and advanced the self-similarity of confined jet. It was found the confined space could reduce the maximum absolute entrainment mass flux leading a peak at the center of recirculation region, which was jointly controlled by the inlet velocity and the confined space size. The remarkable effect of confined space size mainly further contributes to the confined characteristics of gas jet flow, representing a shortened flow distance despite similar process by reducing the diameter ratio. In some case, the dispersion of initial velocity profile evolution was not significant displayed throughout the variable inlet velocity range resulted from the miniaturization of confined space size, especially when the diameter ratio was less than dR =2.