# A Method to Study the Influence of the Pesticide Load on the Detailed Distribution Law of Downwash for Multi-Rotor UAV

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## Abstract

**:**

## 1. Introduction

## 2. UAV Research Models and Methods

#### 2.1. Physical Structure Model

#### 2.2. Governing Equations of the Downwash Flow Field

_{r}, H

_{r}, and Q are total internal energy, total enthalpy, and rotational angular velocity vector, respectively; ${\varphi}_{x}$, ${\varphi}_{y}$, and ${\varphi}_{z}$ are sticky terms in three directions; and $\overrightarrow{q}$ and ${\overrightarrow{q}}_{w}$ denote absolute speed and implicated speed.

#### 2.3. Turbulence Model and Solution Method of Downwash Airflow

## 3. Study on the Influence of Load on the Distribution of Downwash Flow Field

#### 3.1. Reliability Verification of Numerical Calculation for Downwash Flow Field

#### 3.2. Effect of Load on Longitudinal and Transverse Wind Speed Distribution of Downwash

#### 3.3. Effect of Load on Flow Characteristics of Downwash

## 4. Conclusions

- (1)
- The errors between the calculated and the experimental values of wind speed in the vertical direction for the critical observation points were within 11%, the calculated values of the rotor pulling force were in good agreement with the design values, and the y+ value of the rotor wall was within a reasonable range.
- (2)
- Spray height of this multi-rotor plant protection UAV was recommended to be 2.5 m or higher, and the influence area of the downwash at the height of 2.5 m was dissipated into the focused circle.
- (3)
- The nozzles were recommended to be installed directly under the two rotors along the y-direction, the centrifugal nozzle with positive y-axis rotate counterclockwise, and the centrifugal nozzle with negative y-axis rotate clockwise, so that the droplets can be induced by the same turning rotor to the underside of the rotorcraft body and effectively dispersed. In addition, further work will focus on the influence mechanism of wind field, droplet, and crop interaction on the canopy deposition.
- (4)
- Compared with the four-rotor plant protection UAV [29], the six-rotor plant protection UAV had obvious inter wing interference. Under the influence of wing interference caused by the opposite velocity of adjacent rotor, the turbulent effect of down wash flow was obvious, and the “airflow inlet” and “airflow outlet” region appeared between the wings area at the cross section.
- (5)
- The results show that the pesticide load had an obvious effect on the longitudinal distribution of downwash airflow. As the load increased, the longitudinal distribution of flow field transited from “shrinkage–expansion–shrinkage” to “shrinkage–expansion”.

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Scanning and reconstruction of crucial components of multi-rotor plant protection UAV: (

**a**) Airframe structure of multi-rotor plant protection UAV; (

**b**) Optimscan5-2015011K05 scanner; (

**c**) Closely markers in places with significant curvature changes; (

**d**) Synthesis of multi-angle surface point clouds by a team member; (

**e**) Schematic diagram of wall structured mesh for vital components; (

**f**) Partially enlarged view of the structured mesh model of the rotor component.

**Figure 4.**Reliability verification of wind field model: (

**a**) Wind speed test preparation; (

**b**) Test of z-direction speed under the rotor; (

**c**) Calculation cloud map of z-direction velocity of the longitudinal section below rotor; (

**d**) Relative error of z-velocity calculation and test; (

**e**) The y+ cloud map of the rotor wall after the wind field calculation is stabilized.

**Figure 5.**Velocity distribution of the ZOY planes of different pesticide load: (

**a**) 0 kg; (

**b**) 1 kg; (

**c**) 2 kg; (

**d**) 3 kg; (

**e**) 4 kg; (

**f**) 5 kg.

**Figure 6.**Velocity distribution of the ZOX planes of different pesticide load: (

**a**) 0 kg; (

**b**) 1 kg; (

**c**) 2 kg; (

**d**) 3 kg; (

**e**) 4 kg; (

**f**) 5 kg.

**Figure 7.**Velocity distribution of the XOY cross-sections for downwash airflow under different loads: (

**a**) Load of 0 kg at z = 0.926 m plane; (

**b**) Load of 0 kg at z = 1.426 m plane; (

**c**) Load of 0 kg at z = 1.926 m plane; (

**d**) Load of 0 kg at z = 2.426 m plane; (

**e**) Load of 0 kg at z = 2.926 m plane; (

**f**) Load of 0 kg at z = 3.426 m plane; (

**g**) Load of 4 kg at z = 0.926 m plane; (

**h**) Load of 4 kg at z = 1.426 m plane; (

**i**) Load of 4 kg at z = 1.926 m plane; (

**j**) Load of 4 kg at z = 2.426 m plane; (

**k**) Load of 4 kg at z = 2.926 m plane; (

**l**) Load of 4 kg at z = 3.426 m plane.

**Figure 8.**Cloud map of lateral flow characteristics for 3 kg load working condition at different heights: (

**a**) Velocity distribution at z = 1.426 m; (

**b**) Streamline diagram on the background of pressure at z = 0.926 m.

**Figure 9.**Velocity distribution of the xoz plane (adjacent rotors) at various heights: (

**a**) z = 1.426 m; (

**b**) z = 1.926 m; (

**c**) z = 2.426 m.

**Figure 10.**Velocity distribution at various longitudinal line under the different loads: (

**a**) Longitudinal line at the geometric center of the UAV; (

**b**) Longitudinal line at the geometric center of the rotor; (

**c**) Longitudinal line at the airflow inlet of the adjacent rotors; (

**d**) Longitudinal line at the airflow outlet of the adjacent rotors.

Load (kg) | Simulated Lift Values of Single Rotors (N) | Total Simulated Lift (N) | Total Designed Lift (N) | |||||
---|---|---|---|---|---|---|---|---|

Rotor 1 | Rotor 2 | Rotor 3 | Rotor 4 | Rotor 5 | Rotor 6 | |||

0 | 9.8827 | 9.8813 | 9.8805 | 9.8755 | 9.8738 | 9.8675 | 59.2613 | 58.8 |

1 | 11.5341 | 11.5359 | 11.5311 | 11.5358 | 11.5276 | 11.5263 | 69.1908 | 68.6 |

2 | 13.0190 | 13.0234 | 13.0279 | 13.0184 | 13.0150 | 13.0049 | 78.1086 | 78.4 |

3 | 14.6091 | 14.6117 | 14.6063 | 14.6111 | 14.5991 | 14.5974 | 87.6347 | 88.2 |

4 | 16.3081 | 16.3037 | 16.3053 | 16.3077 | 16.2957 | 16.2952 | 97.8157 | 98.0 |

5 | 17.9452 | 17.9497 | 17.9487 | 17.9448 | 17.9453 | 17.9487 | 107.6824 | 107.8 |

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**MDPI and ACS Style**

Yang, F.; Zhou, H.; Ru, Y.; Chen, Q.; Zhou, L.
A Method to Study the Influence of the Pesticide Load on the Detailed Distribution Law of Downwash for Multi-Rotor UAV. *Agriculture* **2022**, *12*, 2061.
https://doi.org/10.3390/agriculture12122061

**AMA Style**

Yang F, Zhou H, Ru Y, Chen Q, Zhou L.
A Method to Study the Influence of the Pesticide Load on the Detailed Distribution Law of Downwash for Multi-Rotor UAV. *Agriculture*. 2022; 12(12):2061.
https://doi.org/10.3390/agriculture12122061

**Chicago/Turabian Style**

Yang, Fengbo, Hongping Zhou, Yu Ru, Qing Chen, and Lei Zhou.
2022. "A Method to Study the Influence of the Pesticide Load on the Detailed Distribution Law of Downwash for Multi-Rotor UAV" *Agriculture* 12, no. 12: 2061.
https://doi.org/10.3390/agriculture12122061