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Trajectory computation of small solid particles released and carried by flowfields of helicopters in forward flight

Pekel, Yusuf Okan
In this thesis, trajectory computations of chaff particles ejected from a medium weight utility helicopter are performed using computational fluid dynamics. Since these chaff particles are ejected from a helicopter and carried by its flow field, it is necessary to compute and include the effects of the helicopter flow field in general and engine hot gases, main and tail rotor wakes in particular. The commercial code FLUENT is used for flow field and trajectory computations. Both main rotor and tail rotor are simulated by the so-called Virtual Blade Model in a transient fashion. Flows through the engine inlets and exhausts are treated via appropriate boundary conditions in the analysis. The generic ROBIN geometry is studied first in order to assess the accuracy of the Virtual Blade Model and various turbulence models. The computational solutions related to the ROBIN geometry are validated against the available experimental data. Flowfield and trajectory computations of chaff particles are done at a forward flight condition at which certain flight data and chaff trajectory data were acquired by ASELSAN, Inc. In the flight test, three successive chaff decoy ejections were conducted, and the chaff cloud distributions were recorded by two high-speed cameras positioned on two different locations on the helicopter. Numerical calculations employ the post-processed camera recordings for setting the initial distributions of the chaff particles. Then, the computational results related to the chaff particle trajectories are validated by comparing to the recorded transient chaff cloud distributions from the ASELSAN flight test. For post-processing of the recorded chaff distributions, an experimental analysis commercial code called TrackEye is used. It is found that the numerical simulations capture the trends of chaff particle distributions reasonably well.