Effect of the Orifice Aspect Ratio on the Flow Development in Triangular Jets

Abstract

The results of an experimental study of incompressible, isothermal turbulent free jets issuing from sharp-edged isosceles triangular orifices with the 10°, 70°, and 160° apex angles are presented. The aspect ratios, defined herein as the ratios of the base to the height of the triangular orifices, are equal to 0.18, 1.40, and 11.32 for the 10°, 70°, and 160° orifices, respectively. The results for a round jet, also issuing from a sharp-edged orifice, are presented for comparison. All the orifices had the same exit area of 1613 mm². The Reynolds number, based on the equivalent diameter of the triangular orifices (calculated as \({{D}_{e}} = \sqrt {4A{\text{/}}\pi } \), where A is the orifice exit area) or the diameter of the round orifice, was equal to \(~\left( {1.67 \pm 0.08} \right) \times {{10}^{5}}\). A Pitot-static tube was used to measure the mean streamwise velocities, and a hot-wire probe was used for all other measurements. The mean streamwise centerline velocity decays at the fastest rate in the near field of the 160° triangular jet. The Strouhal number, based upon the preferred mode frequency and initial momentum thickness, in all the jets tested has its highest value in the 160° triangular jet. Also, the inertial subrange in the one-dimensional energy spectra occurs closest to the exit plane in this jet compared to the other jets. The autocorrelation coefficients of the fluctuating streamwise velocities exhibit long tails in the 10° and 160° triangular jets, consistent with the nearly uniform initial mean streamwise velocity profiles in these jets.