Investigation on surface wave morphologies of a low-intermediate pressure jet with non-circular nozzles

The high-speed photography, large eddy simulation, and coupled level set and volume-of-fluid methods were used to study the initial flow structures, the wave morphologies, and the instantaneous velocity distributions of three-dimensional jets from non-circular nozzles at different viewing sections under low pressure conditions. Two non-circular nozzles, including square and triangular orifice shapes, were designed based on the principle of the equal flow rate at the same pressure. The results showed that the surface waves of the square and triangular jets increased as the working pressures increased due to the air resistance increments, and more fluid band structures and droplets appeared. For the different viewing sections of the jets from the square and triangular nozzles, the surface wave was distributed symmetrically on both sides of the jets for the square nozzles. The jet flowing from the orifice’s symmetrical angles had better aggregation than the jet flowing from the orifice’s edges. The amount of fluid that moved continuously with the jet increased with the entrainment of the air into the jet, and the jet’s instantaneous velocity gradually decreased. As the jet developed, the vortexes gradually spread and entrained the surrounding medium to transfer energy, causing it to decay exponentially along the jet axis. Moreover, the jet’s instantaneous velocity distributions at different vertical sections along the jet’s direction were completely clear from the three-dimensional view. The shapes of the instantaneous velocity parabola in different vertical sections were analyzed in detail, and zigzag-shaped parabolas from the triangular jet were observed.