Experimental study of the behaviour of plane turbulent jets at low Reynolds numbers

An experimental study has been undertaken to determine the effects of the Reynolds number upon the mean flow and turbulence characteristics of plane turbulent jets. The jets were produced by discharging air through a rounded nozzle, 10 mm high by 580 mm wide, contained between two large parallel side walls. The mean velocity and the turbulence normal and shear stresses were measured with constant temperature hot-wire anemometers. Measurements were taken to a distance of 580 mm downstream of the nozzle. Traverses were undertaken across the jet at six equally spaced distances from the nozzle for discharge Reynolds number values of 700, 1900 and 4200. Measurements were also taken at close intervals along the center line at discharge Reynolds numbers of 700, 1150, 1500, 1900, 2700 and 4200. The Reynolds number was found to have a strong influence upon the magnitude of the turbulence lateral normal and shear stress levels, the rate of jet spread and the rate of center line velocity decay, a minimal influence upon the longitudinal normal stress levels, and essentially none upon the dimensionless mean velocity profiles. The results indicate that plane turbulent jets achieve an invariant state at a Reynolds number slightly greater than 4200.