Abstract:
Spray uniformity is an important index to evaluate the irrigation quality of hard hose traveler. The existed uniformity calculating methods are complicated or show poor calculation accuracy. In this study, a curve fitting based on least square method was used for the radial water application of large flow rate sprinkler gun and a corresponding simplified calculation model was built to attain the mobile spraying uniformity. The model was mainly composed of three parts: the curve fitting of radial water distribution, water overlapping in the moving direction and the calculation of combined spraying uniformity. A spraying experiment was designed to verify the accuracy of the model. A JP75-300 type hard hose traveler was adopted in the experiment, the walking speed of the moving cart was 30 m/h, and the working pressure of the spray gun was 0.2 MPa. In addition, the flow rate of the system was 11.22 m3/h and the sector angle was 180°. The deviation between calculated values and measured values were within 6%, which verified the accuracy of the model. The model was then used to calculate and analyze the relation between operating parameters and mobile spraying uniformity of a hard hose traveler equipped with a 50 PYC vertical impact arm sprinkler gun. The results show that: 1) The mobile spraying uniformity improves slightly with the increase of working pressure. The uniformity coefficient of 50 PYC vertical impact arm sprinkler gun under 0.1, 0.2, 0.3 and 0.4 Mpa are 64.9%, 71.9%, 73.8% and 74.7%, respectively. The application depth of water under each pressure presents a form of trapezoid distribution. The depth close to the cart pathway is relatively low. And this value increases to a stable value with the increase of distance to the pathway, nonetheless this value drop dramatically at the end of spray zone. 2) The radiation sector angle of the sprinkler gun shows a great influence on the spraying uniformity. The mobile spraying uniformity coefficients are 61.4%, 69.9% and 71.9% under a radiation sector angle of 180°, 220° and 270° on the setting conditions. The form of water application depth transform from triangle distribution to trapezoidal distribution with the increase of sector angel. The increase of sprinkler gun sector angle can stretch the length of irrigation duration time effectively, which is prone to a lower average application rate and a lower incidence probability of surface ponding and runoff. 3) The mobile spraying uniformity increases at first and then decreases with the increase of combination space. Under the setting conditions, the mobile spraying uniformity is higher than 85% with a combination space of 1.5 R-1.7 R. When considering the influence of both sprinkler gun sector angle and combination space on the uniformity, the recommended sector angle range is 240°-320° and the combination space between adjacent pathway is 1.4 R-1.7 R under the setting conditions. 4) The mobile spraying uniformity shows no difference under various gun rotation cycles without considering on the influence of water distribution profile caused by the rotation cycle. The spraying jet hydraulic characteristic of sprinkler gun was taken under condition of no wind or slight wind (wind speed<1.5 m/s), and the turbulence caused by wind was not yet considered in the model. The conclusions of this study can provide theoretical basis for the operation optimization of hard hose traveler.