Vícefázové proudění v hydraulických systémech

Abstract

The dissertation thesis deals with numerical simulations of multiphase flow and experimental determination of static characteristics during oil flow through the throttle valve where cavitation occurred. Photographic images are taken during the experiment to visually evaluate a flow and verify numerical simulations that are performed in ANSYS Fluent. The intensity of the formation and development of cavitation areas are influenced by two factors. The cavitation region is amplified when the flow velocity is increased in the narrow gap of the throttle valve. Simultaneously, the cavitation region is suppressed when the downstream pressure of the valve is increased. The dissertation thesis also deals with the experimental determination of the amount of released gas due to cavitation at the throttle valve. Depending on the formed cavitation, the released gas phase is entrained into the assembled test device where bubbles are monitored. In this way, it is possible to determine the concentration of the released air bubbles in relation to different intensities of cavitation. Two measurement techniques are used to determine the concentration of the released gas which are based on the optical and acoustic method. The optical method is based on sensing the particular area of a flow in the test device using the high-speed camera. To implement the acoustic method, the commercially available device called Acoustic Bubble Spectrometer from Dynaflow company is used. This device is based on sending short acoustic signals through the measured mixture. The outputs of the experiment are then added into the outputs of numerical simulations of multiphase flow with the implemented cavitation model.