Droplet spatial distribution in a spray under evaporating and reacting conditions

Abstract

In order to study spray combustion, an experimental test rig was developed at ONERA to partially characterize the flow conditions inside the combustion chamber of a gas turbine. Experimental campaigns using laser-based diagnostics were performed to provide an experimental database under reacting and non-reacting conditions. The paper first describes the Mie scattering image-processing to detect the droplets in the spray, and to calculate 2D maps of droplet number density and mean inter-droplet distance. The method is subsequently used to investigate the spray behavior under both reacting and non-reacting conditions according to global-averaging and phase-averaging methods. Experimental findings on the spatial droplet distribution in the spray are compared to the simple regular grid distribution and the Hertz-Chandrasekhar distribution. Results show that, under both conditions, there is an affine relationship between the inverse square root of the mean droplet number density and the nearest-neighbor inter-droplet distance. Moreover, observations suggest that the droplet spatial distribution fits more closely to a Hertz-Chandrasekhar distribution than a simple regular grid distribution, which may bring new insight for spray modeling.

Simplified Interfacial Area Modeling in Polydisperse Two-Phase Flows under Explosion Situations

“…Many experimental studies aim to describe the size distribution in various applications. Recent works include for instance Chandrakar et al (2016) [20] where the influence of aerosol concentration on a cloud-droplet size distribution is investigated in a laboratory chamber, or Rousseau et al (2021) [21] where spray combustion is studied with the help of an experimental test rig. Some theoretical studies attempt to reproduce favorable experimental data.…”

Experimental analysis of reacting and non-reacting sprays

“…Besides, we also prescribe the surface droplet density numbers. They are fixed to [250 450 3500 4500] droplets per cm² and correspond to the extremal experimental values used for the non-reactive and reactive cases [7]. Finally, the thickness of the slice (laser sheet) is equal to 1 mm which represents around 2 at 6 times larger than the 3 .…”

“…In order to see the influence of the slice thickness in the preferential segregation case, three thickness values were tested: 125, 400 and 600 mm. The first value comes from the experimental work ( [5], [6], [7]) and corresponds to a ratio between the laser sheet thickness and the image dimensions around 0.02. The 400 mm and 600 mm values are based on the preliminary analysis with the Monte-Carlo simulation.…”

“…Usually, distance parameter is calculated according to the mean droplet density number and the droplet spatial distribution is fixed as a simple regular grid distribution, so the droplets are regularly arranged in the spray ( [1], [4]). Experimentally, Vicentini [5], Rouzaud et al [6] and Rousseau et al [7] had studied the behaviour of a spray by means of the test rig PROMETHEE, which provides flow conditions close to those encountered inside aeroengine combustion chamber. They noticed that, for non-reactive and reactive conditions, that a linear relationship between the inverse square root of droplet number density in the spray and the mean inter-droplet distance exists (Fig.…”

Insights on droplet drift and effective utilization of pesticide in “Third Pole”：Qinghai-Tibet Plateau of China

“…However, droplet distortion, collision, and evaporation between the nozzle and the target are absent. Droplet spatial behavior serves as a transitional link that can both represent the potential process of pesticide deposition and serve as feedback for the management of particle size [ [23] , [24] , [25] ]. The highest peak in the world, located in China's Qinghai-Tibet Plateau, is where the Yellow, Yangtze, and Lancang rivers originate.…”