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Modeling of two stage nozzle-flapper type electrohyraulic servovalves

Afatsun, Ahmet Can
In this thesis, a detailed mathematical model for a double stage nozzle-flapper type servovalve is developed focusing on its hydraulics. Such valves must comply with very strict performance requirements of aerospace and military industries. To meet these requirements, parts of such a servovalve must be manufactured within the tolerances as low as a few microns. Considering the servovalve consists of many parts that influence overall performance, it becomes obvious that the servovalve must be designed carefully as a system by understanding the effect of deviations of all parameters related to it. Unfortunately, the relations used to define the behavior of servovalve hydraulics in the literature have shortcomings around the operating point. This study is conducted with the intention of fulfilling the need of a simulation model that offers high accuracy on the entire working range. To create such a model, several CFD analyses are carried out using the commercial software ANSYS Fluent®. Available turbulence models’ and wall treatment functions’ performances are compared with the experimental data to find out which models are most suitable to conduct such analyses. Results of these numerical analyses are used to develop more accurate analytical models for both first and second stages. These models are combined in a system simulation model created by using SimScape® blocks. This final model is tested with a commercial valve’s parameters, provided by the manufacturer. The results are accurate comparing to the datasheet values