Mixing in turbulent free jets issuing from isosceles triangular orifices with different apex angles

This paper reports the results of an experimental investigation on mixing in turbulent free air jets issuing from isosceles triangular orifices with apex angles of 10°, 20° and 30°. The results obtained in a contoured nozzle round jet are also presented for comparison. The measurements were made with an x-array hot-wire probe and a pitot-static tube in isothermal, incompressible jets issuing into still surrounding air. The Reynolds number, based on the equivalent diameter of the triangular orifices (the same as the diameter of the contoured round nozzle), was on average 1.69 × 105 for all jets. The results of the mean streamwise centreline velocity decay, mass entrainment and jet spreading suggest that the 10° jet has the highest mixing rate among all the test jets and that the contoured nozzle round jet has the lowest mixing rate. The high mixing rate of the 10° jet is supported by the jet centreline profile of the streamwise turbulence intensity and the one-dimensional energy spectra, which develop much more rapidly in this jet than in any of the other jets.

► Mean streamwise velocity peaks become more pronounced as the apex angle increases.
► Decrease in apex angle increases centreline velocity decay and mass entrainment.
► One-dimensional energy spectra develop most rapidly in the lowest apex angle jet.
► Jet mixing rates are higher in isosceles triangular jets than in a round jet.
► The lowest apex angle jet has the highest mixing rate among the jets tested.