| Compared with flapper-nozzle servo-valve, the servo-valve which is droved by a jet-pipe or deflection flap is widely used in the areas of electro-hydraulic servo control systems in industries, aeronautics and astronautics due to their simple constructions and much better resistance to oil contaminations. Because of the instability and the complexity of the jet field, self-sustained high frequency oscillations due to shear layer instability may appear inside the flow field, which may raise the problems of high frequency pressure oscillations and noise inside the servo-valve. Therefore, the servo-valve and the hydraulic control system may lose control. In order to improve the capability of jet-pipe servo-valves, it is important to study the rule of caused self-sustained oscillation inside the jet field.In this paper, the shear layer oscillation mechanism is analyzed producing and impacting which aiming at the flow circs of the jet flow simulation. By using vortex and cavity oscillation principles, the shear layer oscillation frequency equations for the flow field inside the servo-valve are derived. The frequency characteristics of the oscillations are studied. Two piezoelectric pressure transducers are applied to measure the dynamic pressure oscillations in the flow field of the jet-pipe pilot inside the servo-valve and a microphone with high accuracy is used to record the noise signals. Meanwhile, the result which analyzes using the experiment certificated the equations of shear layer oscillation frequency. FFT analysis method is used to analyze the experimental data of the self-sustained oscillations and noise. Then the experimental results are compared with the theoretical analysis results. It shows that the theoretical analysis is reasonable. |
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