The Lygus bug is the most economically damaging pest in California strawberries. Currently available chemical control methods are inadequate, and the organic market has very few alternative options for control. Additionally, the Lygus bug has few effective natural enemies. This, combined with the low economic threshold for Lygus damage makes substantial investment in mechanical control methods possible.

The current industry standard for Lygus control is the Lygus vacuum. It was initially evaluated to reduce Lygus populations by 4%. After two key modifications, a front plate and perforated baffles, the vacuum was determined to remove 16-18% of Lygus from the field. The relatively simple way the vacuum’s performance was dramatically improved suggests a redesign has high potential to significantly increase efficacy.

To treat the Lygus vacuum like an engineering project, it is important to break the process into components and evaluate each separately. The largest component, and the one most conducive to an engineering approach, is an evaluation of the airflow created by the large axial fans. The creation of the airflow and its effect on Lygus bugs is the major focus of this project.

To solve this airflow problem, the field of Computational Fluid Dynamics was introduced to the project. CFD allows for the rapid testing of different parameter adjustments and the visualization of their effects. The first step in this process is to 3D model the vacuums ducting and fan. The model is then brought into the CFD program and a solution is calculated for the flow field. By adjusting the size and speed of the fan we can calculate and visualize the air movement through the vacuum because of different power inputs. With multiple vacuums designed and tested with the same input power, we can compare their relative performance. A major finding this far was that increasing inlet velocity often decreases the total flowrate. Therefore, airspeed alone cannot always be used as an indicator of predicted efficacy. Another benefit to the CFD approach is the creation of graphics which help visualize airflow data. This visualization is helpful not only to the design team but also in the presentation and explanation of the work to others.

In addition to testing various designs, modifications made to the vacuum have also been tested. The inlet reducer, a plate which decreased the area of the inlet, was found to increase airspeed by 25% but reduced airflow by 23%. This reduction in airflow was likely the reason it was found to be ineffective in field trials. The front plate was shown to slightly increase air velocity at canopy level and has been found to significantly increase efficacy in field trials.

In addition to modeling airflow through the vacuum, Discrete Phase Modeling allows for the placement of particles of different material and size at locations throughout the flow domain. When the particles are defined to have similar weight and aerodynamic properties as a Lygus bug, a virtual environment is created which mirrors conditions in the field.

Meet the Researcher

Jack Wells

Cal Poly Undergraduate Program