Study On Nozzle Configuration And Nozzle Combination Used On Jet Trencher

In recent years, with the flourish of offshore oil, there are many submarine pipelines to be laid. Because of the characteristic advantage, the use of water jet trenching in submerged clays attracts extensive attention, which has the advantage of simple structure,efficient,good adaptability for different clays etc.Based on fully investigation of water jet technology, the nozzle which is an important part in the trenching is studied. Through numerical simulation and experiments, analyzing and summarizing the regularity on the impacting effects caused by changing spraying distance,pressure,distance and angle between two nozzles. We take the rotating nozzle and cone nozzle as the researching target. Using the fluent software, simulate the distance between nozzles from 2 to 8 times exit diameter of the nozzle, and the angle 7,10,15,20,30 degree between nozzles.Different characteristic is found between cone nozzle jet and swirling jet through the numerical simulation, also the effect characteristic of two jets overlap is found out. The simulation shows that potential core of cone nozzle is longer than that of swirling nozzle, but the velocity angle of spread of swirling nozzle is bigger. The results show that there exists critical state at some parameter combinations, for example distance 12mm and angle 15 degrees, in which decay in velocity is little and impacting area increases. These combinations at critical state are taken as perfect results. When critical state appears, increasing the distance or decreasing the angle, there will be no overlap, the flow field could be seen independent. Conversely, flow field overlap will be serious, decay in velocity also will be faster. Some critical combination parameters are found at different distance and angle between the two nozzles. When the angle is larger than fifteen, influence becomes stronger with the angle gets larger, but when it is smaller than fifteen, influence becomes weaker with the angle gets smaller. When the angle gets to ten degrees, there is no influence between the two flow fields, at this time we could take the two flow field as independent. For every distance between two nozzles, we can find a corresponding angle to making the flow field be critical state. Under the experiment condition, impacting depth and volume of combination jet is larger than that of single jet. At the same spraying distance, the width of combination jet is about 1.2times that of single jet. Changing the distance or angle between nozzles makes the depth changed. The depth in the condition of distance 10mm is larger than that of 20mm.The depth of moving jet is larger than that of fixed impacting if the velocity is small. In this experiment, the proper moving velocity is 0.4mm/s～0.9mm/s. Also we get that increasing the moving velocity make the depth reduce. The impacting depth mainly depends on the cone nozzle.To a certain extent the experiment results reflect the effectiveness of numerical simulation. This study provides some arguments for developing water jet trenching machinery in submerged clays.