**1. Introduction**

According to statistics, China has produced 130,000 tons of hazelnuts in recent years, making it the second largest hazelnut producer in the world, with wild mountain hazelnut production accounting for 23% of the total. The picking and sorting of mountain forest hazelnuts is an important part of hazelnut mechanization, and the design of its cleaning device directly affects the working performance of the harvester. Most of the hazelnut harvesters in other countries are adapted from vibratory forest fruit harvesters for flat orchard operations [1–3]. In China, hazelnuts are grown in mountainous areas, so small hazelnut harvesters are suitable for hazelnut harvesting in mountainous area. At present, the hazelnut harvesting operation is divided into two parts, picking and impurity sorting,

**Citation:** Ren, D.; Yu, H.; Zhang, R.; Li, J.; Zhao, Y.; Liu, F.; Zhang, J.; Wang, W. Research and Experiments of Hazelnut Harvesting Machine Based on CFD-DEM Analysis. *Agriculture* **2022**, *12*, 2115. https:// doi.org/10.3390/agriculture 12122115

Academic Editor: Francesco Marinello

Received: 19 November 2022 Accepted: 7 December 2022 Published: 9 December 2022

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and the manual operation faces problems such as high labor intensity and low operational efficiency. Therefore, the mechanization of hazelnut harvesting can solve the above problems.

The agricultural material cleaning process is typically a combined effect of the gas– solid two-phase flow field [4,5]. It is of great significance to study the air-and-screen cleaning device to analyze the air flow distribution of the cleaning shoe and to explore the motion law of agricultural materials on the screen surface, which not only provide the theoretical basis for designing and optimizing the existing typical cleaning unit, but also give theoretical inspiration to look for new cleaning methods. The use of computational fluid dynamics (CFD) for the computation of turbo machinery flows has significantly increased in recent years [6,7]. Furthermore, combined with measurements, CFD provides a complementary tool for simulating, designing, optimizing, and analyzing the flow field inside a turbo machine [8]. The coupling of DEM and CFD provides a means of momentum and energy exchange between solids and fluids, which, in principle, removes the need for some of the semi-empirical approximations employed in CFD solid–fluid models, and is attracting increasing interest from industries. This enables the investigation of fluidized beds, pneumatic conveying, filtration, solid–liquid mixing, and many other systems. Effective modeling of the solid–fluid flow requires methods for adequately characterizing the discrete nature of the solid phase and representing the interaction between solids and fluids. DEM-CFD models reported in the literature have largely been applied to the simulation of fluidized beds and, more recently, to the pneumatic transport of particles [9–16]. Many industrial processes involve complex geometries, often with moving parts, and complex fluid dynamics. For example, the design of pneumatic seed collecting and discharging devices and horizontal seed supply tubes [17–21] coupled with DEM-CFD techniques have also been used as tools to optimize the design of machine structures [22–27].

The air-absorbing hazelnut harvester designed in this paper includes two parts: a conveying pipeline pick-up box and a scavenging box. Because the gas–solid two-phase flow formed during the pneumatic conveying of hazelnuts is more complicated, and at the same time the structure of the scavenging box has a greater impact on the operating effect of this machine, this paper first measured the suspension velocity of typical hazelnuts and fallen leaves by using a suspension test bench to provide data support for the design of the scavenging device. Then, the discrete element method (DEM), computational fluid dynamics method (CFD), and gas–solid two-phase flow theory were used to simulate the flow–solid coupling analysis of the harvester device from the air flow distribution of the cleaning box and the movement law of the material on the screen, in order to obtain the relationship between the movement characteristics of hazelnuts in the conveying process, the flow field distribution characteristics, and the structural parameters of the cleaning box. By analyzing the motion state of the mixture material during the conveying process and the air flow field distribution law of the hazelnut harvester, the effects of the sieve plate angle, the distance of the sieve plate, and the air flow velocity on the net fruit rate of hazelnut were specifically studied, and the potential mechanism was analyzed. The optimal operating parameters of the harvester were determined, and the performance of the harvester was evaluated by prototype tests.
