| The hydraulic valve is the control element in the hydraulic transmission system,which controls the fluid pressure,flow rate and flow direction in the system.The hydraulic valve is easy to be produced in the throttle port and downstream due to the complex structure of the flow channel.Cavitation has been the focus and difficulty of research for a long time because of its adverse effects such as noise,vibration and cavitation erosion.In this paper,through theoretical analysis and experimental research method of combining the design of the hydraulic control valve in the unsteady cavitation flow field images and the pressure fluctuation signal synchronization acquisition system,and the collection of information in time domain,frequency domain extract relevant characteristic values,and then to carry out the hydraulic control valve inside the unsteady cavitation pressure fluctuation characteristics of structural evolution and research.Set the cavitation flow test bench and the cavitation flow acquisition system,the cavitation structure change images under different inlet pressure is collected by a high speed camera,and cavitation of the structure of the eigenvalue analysis were extracted by image processing techniques,the results show that the unsteady cavitation flow field change obvious quasi periodicity,cavitation occurs near the throttle opening and downstream,a typical cavitation structure mainly includes three phases: adherent void growth stage;The fracture and shedding stage of the attached cavity;The growth,retraction and collapse stages of the shedding type holes.Based on theoretical analysis and experimental research,the structural variation characteristics of unsteady cavitation flow field in the hydraulic control valve under different inlet pressures were studied.The results show that with the increase of inlet pressure,the end of the attached cavity gradually becomes unstable and the cavity begins to fall off.With the increase of inlet pressure,the area of attached and detached free cavities gradually increases,and the change period of the cavitation area becomes longer and longer.Meanwhile,the change range of the cavity area gradually increases with time,and the degree of cavitation gradually increases.The change of the area of attached and free holes has the same center frequency in the frequency domain as the change of the total area of holes,and the period of development and change is basically the same.Based on hydraulic control valve cavitation flow field synchronous measurement system,the cavitation morphology and synchronous data acquisition of pressure pulsation of hydraulic controlled valve were realized.Thus,the unsteady cavitation flow transient cavitation morphology and the wall pressure pulsation can be analyzed simultaneously,and the hole shape evolution and the relationship of the pressure pulsation will be revealed.The time-domain and frequency-domain characteristics of pressure pulsation with the inlet pressure were obtained.The pressure fluctuation law induced by the quasi-periodic development process of cavitation growth,shedding and collapse was emphatically studied,and the correlation characteristics between the cavitation evolution and the pressure fluctuation in the hydraulic control valve were obtained.The results show that the pressure in the flow field decreases slowly during the growth stage of the cavity area.When the cavity falls off and develops downstream,the cavity area also decreases gradually,and the pressure near the wall increases gradually.When the free holes shrink and collapse,the pressure in the flow field reaches the peak.The change process of the pressure and cavitation structure in the flow field presents an approximate quasi-periodic development process,and the pressure pulsation at each monitoring point has the same dominant frequency as the change of the cavity area.There are 45 figures,1 table and 86 references in this paper. |
PDF Full Text Request