Starting point

 


 Establishment of a model for the water bombing from an aircraft


The subject is quite innovative : a large number of studies about injectors or pressurized jets have been led, but never in case of atmospheric air as the ambient medium.

Thus, we did not have any correlation to rely on, and we had to do a preliminary work on the subject. First, we did some bibliographic research to see if equations could be interesting for us. Then, we evaluated the relevance of the assumptions related to every equation, in order to check for the validity of the upscaling process. Finally, we kept in mind the most relevant formulas, and adapted them to our case.

Yet, we had to do some assumptions, owing to the complexity of the subject. Indeed, our goal was to set up a preliminary study, to highlight the phenomena at stake and to leave a coherent work to our successors.

 

Assumptions :

  • the wind remains constant and uniform, the plane flies at constant speed and height ;
  • the plane releases water through a circular discharge module ;
  • the mean flow rate at the exit of discharge is constant ;
  • the liquid column remains compact until the breakup moment, meaning no droplet is formed by shedding or shearing... ;
  • the Rayleigh-Taylor and Kelvin-Helmholtz instabilities are not considered
  • the first atomization of the column happens instantly at the breakup moment ;
  • the second atomization of the drops happens instantly : the unstable big drops are divided instantly into smaller droplets ;
  • the fall phase only starts with stable drops, meaning a bigger drop will first be divided before moving down to the ground ;
  • during the fall phase, a drop may face both evaporation and wake capture ;
  • once on the ground, the droplets do not explode since they are small enough.

Warning : All these assumptions were made to help us start and work. Nevertheless, anyone working on the subject to dig deeper would be strongly encouraged to reconsider them.

 

See next : Notations

 

 


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