Mixing properties of coaxial jets with large velocity ratios and large inverse density ratios

Abstract

An experimental study was conducted to better understand the mixing properties of coaxial jets as several parameters were systematically varied, including the velocity ratio, density ratio, and the Reynolds number. Diameters of the inner and outer jet were also varied. Coaxial jets are commonly used to mix fluids due to the simplicity of their geometry and the rapid mixing that they provide. A measure of the overall mixing efficiency is the stoichiometric mixing length (Ls), which is the distance along the jet centerline where the two fluids have mixed to some desired concentration, which was selected to be the stoichiometric concentration for H2/O2 and CH4/O2 in this case. For 56 cases, the profiles of mean mixture fraction, rms mixture fraction fluctuations (unmixedness), and Ls were measured using acetone planar laser induced fluorescence diagnostics. Results were compared to three mixing models. The entrainment model of Villermaux and Rehab showed good agreement with the data, indicating that the proper non-dimensional scaling parameter is the momentum flux ratio M. The work extends the existing database of coaxial jet scalar mixing properties because it considers the specific regime of large values of both the velocity ratio and the inverse density ratio, which is the regime in which rocket injectors operate. Also the work focuses on the mixing up to Ls where previous work focused on the mixing up to the end of the inner core. The Reynolds numbers achieved for a number of cases were considerably larger than previous gas mixing studies, which insures that the jet exit boundary conditions are fully turbulent.

Linear stability and acoustic characteristics of compressible, viscous, subsonic coaxial jet flow

“…The stability characteristics of coaxial jets are not only important for bypass jet engines but also for many other devices in which dual-stream nozzles are used to mix different fluids. 4 The mixing properties of the two streams depend significantly on the disturbance development within the inner and outer shear layer of the coaxial jet flow.…”

Breakup Morphology and Mechanisms of Liquid Atomization

“…With the progress of technology [23], it is found that the properties of breakup morphology and fragment distribution in different regimes are different [24][25][26][27][28]. Coaxial air-blast atomizers have many applications [29][30][31]. In order to obtain the desired results of atomization in the industrial scale, the suitable range of nozzle size and operating condition could be determined with the help of the regime map.…”

Investigation on Asymmetric Instability of Cylindrical Power-Law Liquid Jets

“…For an inviscid ideal gas, substituting Equations (1), (4) and 6into Equations 7and 8, the continuity equation is expressed as:…”

“…Similarly, substituting Equations (1), (4) and 6into Equations 7and 8, and neglecting the nonlinear terms of the disturbance, the momentum equation is obtained as follows:…”

“…The transformation of liquid into spray is important in clean energy combustion, agriculture, meteorology, and many industrial processes. As a common type of atomization, cylindrical jets are utilized in a number of devices, such as liquid fuel rocket, irrigation, meteorology, and burners in industrial furnaces, gasifiers, combustion engines, and gas turbine [1][2][3][4]. Many researchers have investigated the liquid breakup, which could ameliorate efficiency in many real applications.…”