Near-Field Measurements in an Equilateral Triangular Turbulent Freejet

摘要

The near-field mean flow and turbulence characteristics of a turbulent jet of air issuing from a sharp-edged equilateral triangular orifice into still air surroundings have been examined experimentally using hot-wire anemometry and a pitot-static tube. For comparison, some measurements were made in a round free air jet, also issuing from sharp-edged orifice. The Reynolds number, based on the equivalent diameter, was 1.84 x 10~5 in each jet. The three components of the mean velocity vector, the Reynolds normal and primary shear stresses, the distribution of the autocorrelation coefficients and the one-dimensional energy spectra of the fluctuating velocity signals, and the mean static pressure were measured. The mean streamwise vorticity, the half-velocity widths, mass entrainment into the jet, and the local shear in the mean streamwise velocity were obtained from the measured data. It was found that mixing in the equilateral triangular jet is faster than in the round jet. The mean streamwise vorticity field was found to be dominated by counter-rotating pairs of vortices, which facilitated mixing and entrainment in the equilateral triangular jet. The distribution of the autocorrelation coefficients and the one-dimensional energy spectra results indicated the presence of coherent structures in the near field of the equilateral triangular jet.