Two-Phase Characterization for Turbulent Dispersion of Sprays: A Review of Optical Techniques

Abstract

In liquid fueled combustion the interaction of spray droplets with surrounding turbulent air flow is crucial since it influences the evaporation rate of the fuel droplets and the process of air and fuel vapor mixture preparation. For detail understanding on the droplet-turbulence interaction mechanisms as well as to validate numerical simulations of sprays, simultaneous measurement of both dispersed and carrier phases of the spray is essential. This way the vortical interaction of droplets can be fully characterized such that important issues such as local spray unsteadiness and spatio-temporal inhomogeneity of droplet concentration due to droplet clustering, and group evaporation of droplets can be addressed. This review focuses on the advances in the optical diagnostics (especially the planar techniques) in the last few decades to meet these requirements. Due to broad size and velocity distributions of spray droplets, the application of the two-phase measurement techniques to sprays encounters challenges especially in phase discrimination. Additionally, for sprays, it is not sufficient to simultaneously measure two-phase velocities but the droplet size is also important since the dynamic drag on droplets is according to their size and velocity relative to the surrounding gas flow. The techniques with such capability are explored. The sources of uncertainty, and advantages and limitations of different two-phase measurement approaches are analyzed according to their application to dense and dilute sprays.

Measurement in opaque flows: a review of measurement techniques for dispersed multiphase flows

“…Fluorescent tracers have been used to study both phases in bubbly flows [8,21], particle-laden flows [9,29], and sprays [26,30]. These examples show that the technique works for any combination of continuous phase (gas/liquid) and dispersed phase (gas/liquid/solid).…”

Recent advances and applications of digital holography in multiphase reactive/nonreactive flows: a review

“…The comprehensive understanding of multiphase reactive/ nonreactive flows is motivated by a wide range of applications in natural and applied sciences, such as the combustion of atomized liquid droplets [1,2] and solid particles [3,4]. In * Author to whom any correspondence should be addressed.…”

Microscopic Imaging Spray Diagnostics under High Temperature Conditions: Application to Urea–Water Sprays

“…The direct measurement or estimation of the gas velocity is especially challenging in the near nozzle region, where the spray affects the velocity field of the gas phase considerably. Moreover, the simultaneous measurement of droplet size in addition to droplet and gas velocity is necessary in order to deliver detailed validation data for turbulent spray dispersion models [30].…”

“…The combination of Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) is a well-known planar optical diagnostic technique for measuring droplet and gas velocity. However, successful phase discrimination and simultaneous measurement of droplet size are not straightforward, which may cause considerable measurement uncertainty [30]. An alternative way to realise the simultaneous measurement of droplet and gas velocity is the utilisation of the smallest detectable droplets as seeding particles of the gas flow.…”