Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets

The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.

Simulation of Elliptical Liquid Jet Primary Breakup In Supersonic Crossflow

The study of elliptical liquid jets in supersonic flow in a Mach 2.0 is performed numerically. The primary breakup process of the elliptical liquid jet is simulated for a Weber number 223, liquid/gas flux momentum 4.0. The aspect ratios of elliptical geometries are set to be 0.25, 0.5, 1, 2, and 5. The results show a remarkable difference in liquid jet disintegration morphology at different aspect ratios. Under supersonic crossflow conditions, the elliptical liquid jet shows more breakup characteristics than the round liquid jet. As the aspect ratio grows, the penetration depth decreases. The elliptical liquid jet with AR=0.25 has the largest penetration depth in all cases. Moreover, the round jet has a maximum spreading angle of 50.2°. The changing trends of the column breakup length both x direction and y direction are similar. The elliptical jet at a lower aspect ratio has a shorter breakup length due to the narrower windward area. The liquid jet has a pair of larger horseshoe vortex structure and a wider wake region at a higher aspect ratio. Two pairs of reversal vortex pairs with obvious characteristics can be observed in all the simulations.

The Effect of Elliptical Diesel Nozzles on Spray Liquid-Phase Penetration under Evaporative Conditions

Elliptical diesel nozzles affect the fuel–air mixing process, and thus combustion and exhaust emissions. Experiments were conducted to study biodiesel spray liquid-phase behaviors for elliptical and circular nozzles through the Mie-scattering method under evaporative conditions. Based on the measurements, the results show that the elliptical nozzle spray liquid-phase penetration is smaller than the circular one under steady-state conditions. The deformation and the axis-switching behaviors of the elliptical jet are helpful in accelerating the breakup of the liquid core. Moreover, the injection pressure has little impact on the penetration of the liquid-phase spray for either geometrical orifice. Additionally, increasing the ambient temperature can reduce the penetration of liquid-phase spray, because an increase in temperature increases the rate of evaporation. The differences in steady liquid-phase penetration between circular and elliptical sprays decrease as the ambient temperature increases. Additionally, increasing the backpressure can decrease the liquid-phase penetration. The differences in steady liquid-phase penetration between circular and elliptical nozzles are reduced with the increase in backpressure, probably due to the axis-switching and deformation behaviors of the elliptical jet being restrained under high-backpressure conditions. Finally, the application of an elliptical orifice is beneficial for decreasing the spray liquid-phase penetration, and thus avoiding the fuel impingement in small engine combustion chambers. The lower liquid-phase penetration for elliptical spray indicated higher fuel and air mixture quality, which is helpful for reducing the diesel engine exhaust soot emissions.

Flow field and acoustics characteristics of elliptical jet

Purpose The purpose of this paper is to present the results of mixing promotion and screech frequency of controlled elliptical supersonic jet. Design/methodology/approach Flow field characteristics of low-aspect-ratio elliptical jets are examined at over-expanded, under-expanded and correctly expanded conditions. The tabs are placed at elliptical jet exit along the major and minor axes. Findings The results show that the mixing done by the minor axis is superior to the tabs along major axis. At all pressure ratios, the content of jet noise and the frequency are high for the tabs along the major axis because of increase in the amplitude of screech frequency. Further the tabs along minor axis show a dominance of large-scale vertical structures. In under-expanded conditions, the shock cell shows the rapid change because of the presence of tabs. The tabs along minor axis are making the shock weaker, hence no evidence of axis switching. Practical implications To achieve the greater performance of jet, the authors need to reduce the potential core length of the issuing jet. This can be achieved by implementing different types of tabs at the exit of the nozzle. Originality/value The present paper represents the flow of controlled jet using inverted triangular tabs. By achieving the controlled jet flow, the performance of propulsion systems can be improved. This can be used in systems such as combustion chamber, missile’s noise reduction and thrust vector control.

Study on the Effect of Jets Geometry in Liquid Atomization Based on Nonlinear Stability Analysis

In this paper, nonlinear instability of an elliptical jet is investigated by considering the impacts of orifice geometry variations using regular perturbation method. In the breakup mechanisms, created disturbances on the jet interfaces will grow owing to the nonlinear dynamics of fluid. In this study, a scrutiny of nonlinear cylindrical jet breakup is done initially. Next, Cosserat equations as a low order form of Navies-Stokes equations are solved on the nonlinear form to exert the impacts of orifice deformation on various aspect ratios. These nonlinear equations, Cosserat equations, are linearly solved in the past papers. As a result, the dispersion equation is derived to find the most unstable wavelength as well as the breakup length. Results reveal that the elliptical jet with low aspect ratio is more unstable rather than cylindrical jet with aspect ratio of one. Furthermore, the nonlinear equations can predict the break up length of elliptical jet more accurate than linear equations. The predicted results are shown to be in good agreement with the experimental results.