Liquid jet disintegration memory effect on downstream spray fluctuations in a coaxial twin-fluid injector

Abstract

This paper intends to investigate the influence of unsteadiness in the liquid jet disintegration process on downstream fluctuations of spray characteristics in a coaxial twin-fluid injector. Time-resolved high-speed shadowgraphic imaging of the spray was obtained for different axial locations downstream of the injector exit at z = 0, 8Dl, and 30Dl, where Dl is the central liquid tube diameter. The primary jet breakup unsteadiness close to the injector exit was characterized by measuring both shear-driven Kelvin–Helmholtz (KH) instability and flapping instability in addition to jet breakup length fluctuations. Downstream of the liquid jet core region, the liquid shedding rate (fshed) was measured at z = 8Dl. The power spectrum of time series data of instantaneous volume mean diameter (VMD) measured at z = 30Dl indicated periodic variation of the droplet size. The corresponding frequency (fVMD) was obtained. It was found that for lower range of gas-to-liquid momentum flux ratio (M < 4), both fshed and fVMD are larger than the frequency of KH instability. Also, for such conditions, larger temporal variation of the droplet size is realized, and this leads to higher fluctuations of the local liquid mass flux. Proper orthogonal decomposition analysis of the shadowgraph images for different axial locations identified similar topology of the dominant mode that corresponds to flapping instability. The results suggest that even far downstream of the injector exit, some memory of the upstream unsteady jet breakup process is retained, which strongly influences spatio-temporal evolution of droplet characteristics, thereby contributing to local spray fluctuations.

Spray dispersion regimes following atomization in a turbulent co-axial gas jet

“…2019). These processes are often coupled with large-scale instabilities causing strong lateral excursions of the liquid jet known as ‘flapping’ (Delon, Cartellier & Matas 2018) or ‘dilatational waves’, resulting in clustered break-up of a high-momentum liquid core (Engelbert, Hardalupas & Whitelaw 1995; Kumar & Sahu 2020).…”

Effect of orifice size on liquid breakup dynamics and spray characteristics in slinger atomizers

“…This method is discussed in detail in Kumar and Sahu. 32 In this approach, the DoF of droplets of different diameters was obtained using a calibration plate containing a number of dots of different diameters (minimum and maximum diameters of the dots are 50 μm and 1000 μm, respectively), as shown in Figure 4. While all dots are identified in the calibration plate when it is in focal plane, the dots tend to blur when the plate is moved out of the focal plane, followed by non-identification of the smaller dots.…”

Inhibitory Effects of Convergent Annular Nozzles on the Primary Breakup of Discontinuous Shear-Thickening Suspensions

“…Air-blasted atomization is of great importance in scientific research and industrial applications, such as aerospace engineering, − coal gasification, , fuel combustion, − spray cooling, , and medical technology. − The primary breakup of the liquid jet is one of the dominant processes in atomization and plays a vital role in energy and mass conversion. The mechanisms of the primary breakup have gained lots of interest and have been investigated in detail by many researchers. − Through experimental exploration and numerical simulations, the primary breakup process of Newtonian fluids is governed by air–liquid interface instabilities. Many factors affect the performance of primary breakup, such as injection pressure, nozzle geometry, and liquid properties. − To describe the magnitude of surface tension and aerodynamic force, Weber proposed a dimensionless number We = ρ g ( u g – u l ) 2 D l /σ, where ρ g is the air density, u g is the air velocity, u l is the liquid velocity, D l is the exit diameter of the liquid jet, and σ is the surface tension.…”