EXP 1-1 Introduction
The subject of the case is a PSA spray exposed to cross-flowing air. A small low-PSA was used for the study. This atomiser was developed for spraying aviation fuel Jet A-1 (kerosene) into the combustion chamber of a small gas turbine (GT) engine. The here documented operation conditions of the atomiser and the flow velocity corresponding to the engine's low-power or steady-flight conditions. The airflow is forced perpendicularly to the main spraying axis, which is considered a cross-flow case. The flow is homogeneous, isothermal and with low turbulence intensity, Tu.
Similar atomisers of this type and size used together with the operating pressure and cross-flow air velocity conditions cover many industrial spray applications ranging from small GT combustors to chemical spray reactors. The conditions are also relevant for agriculture and domestic sprayers.
The processed results of the present case were published in [2], with work carried out in the frame of projects -. GA18-15839S and GA 22-17806S funded by Czech Science Foundation. The present case is one of several cases measured and studied in [2].
The data are relevant to CFD engineers and scientists. They can distinguish the crucial phenomena to be considered in their numerical simulations of that disperse two-phase flow case. The modellers can highlight the important features of the complex two-phase flows and provide data for validation purposes. It is as well as to interesting to engineers dealing with the processes where the gas–liquid energy transfer and droplet transport are important.
The case data can be used for further processing to obtain new findings of the problem, derive empirical models and serve as benchmark data. Main characteristics of the flow and spray
The PSA sprays water (which represents low viscosity liquid) into cross-flowing air with low turbulence. There are several forces relevant to the case. Cohesive and consolidating forces acting on the liquid film are the surface tension force F- and the viscosity force F-. These are counteracted with disruptive compressive and momentum forces Fp and FI. Apart from those also the gravity force applies. We can neglect the other forces possibly acting on the droplets and other liquid structures, such as stochastic force that accounts for Brownian collisions of the droplet with surrounding fluid molecules, or Basset force.
The case can be decomposed into several consequent stages with different relevant phenomena, due to the physical acting of these forces, as shown in Figure 2, left:
· Liquid flow inside the atomiser, its discharge,
· Sheet formation and the primary break-up of the liquid sheet,
· Liquid secondary break-up and spray formation,
· Interaction of the sprayed liquid with surrounding air: gas–liquid mixing, droplet collisions, droplet clustering, and droplet repositioning.
From a thermodynamic point of view, the case is isothermal and isobaric, except for possible evaporation which can modify the droplet size [3]. That can introduce thermal effects, such as the exchange of heat between the discharged liquid and the surrounding air, which are otherwise unimportant. For the purpose of numerical simulations, the case features a two-way to four-way coupling between the gas and liquid phases depending on the position in the spray [4].
Contributed by: Ondrej Cejpek, Ondrej Hajek, Milan Maly, Jan Jedelsky — Brno University of Technology
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