Research On The Inner Flow Of The Offset Fluidic Component And Structural Optimization

The research on the inner flow of the offset fluidic component and its structural optimization is one of the contents of China National Key Technology R&D Program (No.2011AA100506)"Precise sprinkling irrigation technology and products". National Agriculture Science and Technology Achievements Transformation Fund (No.2011GB2C100015)"Perfection and Pilot Test on Variable Light-duty Irrigation Equipment"The fluidic sprinkler controlled by clearance was an original invention of China. The offset effect in the fluidic component drove the sprinkler and controlled its rotating direction, so the fluidic sprinkler was characterized with simple structure, low cost and good hydraulic performance. Based on the current research status of the fluidic sprinkler, the study on the inner flow theory of the fluidic component was the key of the structural optimization of the fluidic sprinkler. The theoretical analysis, experiments and numerical simulations were combined to study the inner flow characteristic of the fluidic component of the fluidic sprinkler and the offset flow law of the fluidic component with small offset ratio. The research results would be adapted into the structural optimization of the fluidic sprinkler and the development of new fluidic component to extend the application range of the fluidic technology.The main research contents and results were as follows:(1) Based on the theories of free turbulence jet and wall attachment jet, the key parameters of the offset flow were analyzed and the source program was written and applied to calculate the offset distance under different offset ratios. The switching performance of the fluidic component of the fluidic sprinkler was analyzed and studied, the switching response time tq, the air velocity of the clearance uj, the offset force Fj and the distance of the max offset force point xf were brought out as parameters of the switching performance.(2) The inner flow of the offset fluidic component with small offset ratio (D/b<1) was investigated with PIV for the first time. The fluidic component inner flow PIV test rig was set up and the visualized prototypes with different structural sizes were designed and processed to measure the offset flow under different flow rates. The test results indicated that:the offset distance rarely change with increasing flow rates, in a certain flow rate, the offset distance increased with the offset ratio; in a certain offset ratio, the value of the offset distance reaches the minimum while the air supplement hole distance is3mm; when Q=3m3/h, the length of the component L=40mm, the jet in prototypes with offset ratio bigger than0.5cannot attach to the wall, so the following research focused on prototypes with offset ratio smaller than0.5. The range of the clearance was achieved by the PIV test:left clearance g1<2mm, right clearance g2<1.5mm.(3) The wall-attachment driving force model was established. Formulas for wall-attachment driving force were deduced. The general sprinkler force test rig was set up, and the jet offset force was indirectly obtained by the testing of the sprinkler driving force and the sliding friction. The test results were compared with the theoretical values and the simulation results.(4) The parameterized design of the offset fluidic component model was brought forward, which including three-dimensional geometric template, mesh generation and numerical simulation, by using the knowledge engineering function of CATIA.Based on the results of the PIV tests, the small offset ratio fluidic two-phase flow numerical model was established. By comparing with the results of the PIV tests, the numerical model with SST model and free surface model has a minimum error of5%on offset distance, the effect of offset ratio and air supplement hole distance on the offset flow simulated by the numerical model agree with that of the PIV test. Which means the numerical model could replace the PIV test to take further research.(5) The impact of key structural parameters of the fluidic sprinkler on the wall-attaching performance was simulated and analyzed numerically. With no changes in other parameters including the air supplement hole distance and the cover clearance, the offset distance increased as the offset ratio rose. But if it was higher than0.5, the working area in the spray body had to be lengthened to70mm in order to achieve the wall attachment in the flow, which was not practical in the sprinklers. In this respect, the offset ratio of the fluidic component was ranged from0.15to0.4. Then the relations between the theoretical and numerical results of the offset distance calculated toward different offset ratios were obtained after the theoretical offset distance was modified in reference to the numerical one. The offset distance first declined, then increased as the air supplement hole distance rose; at the value h=3mm, the length required for a complete water attachment of the jet model was the shortest. The influence of the cover clearance on the wall attaching flow field was significant. The size on the left clearance is within0.5-1.5mm, and that on the right is within0.25-1.25mm.(6) The structural parameter optimization based on orthogonal simulation were carried out and a new fluidic component and sprinkler were developed. The switching response time, offset force and distance of max offset force point were taken as the main factors in the orthogonal evaluation of the performance of fluidic sprinkler, and the premium combination under different offset ratios was figured out. The structure of the fluidic sprinkler was optimized based on the study of the inner flow characteristic of the fluidic component. The PXSBW40two-way stepping fluidic sprinkler with extermination fetching tubes was designed. The characteristics and working principle of the PXSBW40sprinkler were introduced, both working processes of the forward-stepping and the backward-stepping were analyzed. Also, the hydraulic performance was compared with those of the sprinklers typed PXH40and PY40. The results indicated that the new sprinkler PXSBW40outperformed the other two sprinklers in hydraulic performance and operation stability.