Design and Test of the Structure of Extractor Negative Pressure Zone of Sugarcane Chopper Harvester

Abstract

Given the problems of the high trash content and loss rate for mechanized sugarcane harvesting, taking the HN4GDL-194 sugarcane chopper harvester extractor developed by South China Agricultural University as the research object, three types of extractor negative pressure structures were designed and internal flow field simulation analysis was conducted. Simulation results showed that the aerodynamic performance of the flow field in the negative pressure area of the extractor negative pressure structure two is the best and the wind velocity and negative pressure are the largest. The measurement results of wind velocity, wind pressure, and flow showed that the changing trend in the actual value of wind velocity and wind pressure is basically consistent with the simulation value. The relative error between the actual flow of the air outlet and the simulation value is less than 10% under different speeds, indicating that the simulation has high accuracy. Field tests of the original extractor and the optimal extractor were conducted. The test results for the trash content showed that when the feeding rate was 1.5 kg/s, there was no significant difference in the trash content between the optimal extractor and the original extractor under various fan speeds. When the feeding rate increased to 7.5 kg/s and the fan speed was low (950 r/min) and medium (1100 r/min), the trash content of the optimal extractor was significantly lower than that of the original extractor, decreasing 2.5% and 1.63%, respectively. The loss rate test results showed that when the fan speed is low and high (1250 r/min), there is no significant difference between the loss rate of the optimal extractor and the original extractor. When the fan speed was 1100 r/min and the feeding rate was 1.5, 4.5, and 7.5 kg/s, compared with the original extractor, the loss rate of the optimal extractor decreased by 0.53%, 0.21%, and 0.19%, respectively.

1. Introduction

Sugarcane is the most essential sugar crop in the world and is mainly planted in regions, such as Brazil, India, and China. Currently, sugarcane mechanized harvesting technology has the major problems of high trash content and loss rate, which seriously restrict the promotion of sugarcane harvesters [1,2]. As the critical working part of the sugarcane chopper harvester, the extractor has a decisive effect on the operating performance of the whole machine, especially the trash removal performance. Therefore, it is an urgent problem to improve the performance of the extractor and reduce the trash content and loss rate of sugarcane.

Relevant scholars at home and abroad have conducted a series of studies on the extractor. Viator et al. [3], White et al. [4], Wang et al. [5], and Xing et al. [6] concluded that the moisture content of materials, feeding rate, length of billet, and extractor speed significantly affect the trash content and loss rate through the test of the sugarcane chopper harvester. With an increase in material moisture content, both impurity content and loss rate increase. The trash content and loss rate increase with the rise in material feeding rate. With the growth of material billet length, the trash content increases and the loss rate decreases. When the extractor speed increases, the trash content decreases and the loss rate increases. Stuart et al. [7] proposed a method to control the extractor speed by detecting the loss rate. Chen et al. [8] proposed to adopt the regression vector machine (GA-SVR) model based on a genetic algorithm to establish the control strategy, matching the extractor speed and traveling speed to reduce the trash and loss. The above research provides a reference for coordinating various components of the sugarcane harvester and optimizing the operating parameters of the extractor, but it does not involve the analysis of the extractor structure and aerodynamic performance.

Given the above problems, Xie et al. [9] designed a new type of cross-flow extractor and obtained the best operating parameters of the extractor through tests. Wang et al. [10] designed a side-blowing extractor using the isolated blade method and acquired the extractor blade’s basic structure and design parameters. Zillman et al. [11] revised the design standard of axial flow fan to allow for the radial distribution of lift coefficient to reduce the inlet vortex and improve the blade life. Zhong et al. [12] conducted simulation analysis and optimization design on the stress and vibration of the impeller of the side blast-type extractor. Xing et al. [13,14,15] optimized the fan hood and blade of the 4GZQ-180 sugarcane chopper harvester developed by the Guangxi Academy of Agricultural Machinery and proposed the horizontal installation scheme of the axial flow fan. Huang et al. [16] used Fluent soft to conduct a numerical simulation for the speed field and pressure field at different extractor speeds and analyzed the effect of the speed on the extractor’s internal flow field. Zhu [17] conducted a numerical simulation for the extractor internal flow field of the CASS 8000 sugarcane chopper harvester and obtained the variation law for the extractor internal flow field. Yuan [18] simulated the flow field of an axial-flow fan at different speeds and found that the actual variation law for wind velocity and negative pressure inside the fan was similar to the corresponding simulation results, but the closer to the impeller, the greater the error between the actual measurement results and the simulation results. The above research mainly analyzes the fan type, hood structure, blade structure, and aerodynamic performance. The negative pressure zone is an essential zone for sugarcane material separation. There is still a lack of suitable solutions for the design and optimization of the negative pressure structure of the extractor.

In this study, three kinds of negative pressure structures are designed for the HN4GDL-194 sugarcane chopper harvester extractor, developed by South China Agricultural University, and the internal flow field simulation is conducted using a CFD numerical simulation method. The performance evaluation of the original and optimal extractor is conducted with the trash content and loss rate as the index. The purpose of this study is to provide a reference for the design of the negative pressure structure of the sugarcane harvester extractor and the reduction in the sugarcane trash content and loss rate.

2. Structure and Working Principle

The extractor comprises a trash discharge area, fan blade area, negative pressure area, fan blade, transmission shaft, and hydraulic motor. The overall structure is shown in Figure 1. In the trash removal process, the fan sucks air from the inlet of the negative pressure zone into the fan internally by the high-speed rotation of the fan blades and forms a high-speed airflow. At times, the billet and trash are thrown into the wind field of the extractor negative pressure area simultaneously. Trash with low-suspension velocity, such as cane leaves, is discharged from the trash discharge area outlet under negative pressure and materials with high-suspension velocity, such as billet, fall from the inlet of the negative pressure area under the action of gravity.

3. Materials and Methods

3.1. Design of the Negative Pressure Structure

The negative pressure is the critical parameter in the axial-flow fan extract to trash removal, which affects the separation of billet and trash. The structure in the negative pressure zone not only has the function of diversion but also affects the distribution and size of the airflow field in the internal fan, especially the size of the negative pressure in the negative pressure zone. The fan’s negative pressure zone structure was designed with an HN4GDL-194 sugarcane chopper harvester extractor as the research object. Structure 1 was the structure of the negative pressure area of the original fan. The three sides of the fan’s air inlet were cut flat. The parallel distance between the upper and lower plates was 712 mm, as shown in Figure 2a. Compared with structure one, in structure two, the space between the two side plates of the fan’s air inlet was narrowed from 712 mm to 560 mm, as shown in Figure 2b. The three sides of the fan’s air inlet of structure 3 were chamfered. The parallel distance between the upper and lower plates was 750 mm, the largest cross-sectional area of the air inlet among the three structures, as shown in Figure 2c.

3.2. Construction of the Airflow Field Simulation Model

3.2.1. Model Building and Meshing of the Extractor

Flow-field models of three kinds of the negative pressure structure fan were established in SolidWorks 2016 (Figure 3), saved in .step format, and imported into Fluent meshing for mesh generation (Figure 4). The fluid inlet and outlet were defined in Fluent meshing and the surface of the fan blade and the remaining walls were set as a wall. The meshes near the fan blades were encrypted to ensure the accuracy of the calculation. The meshes farther from the blades are sparser to save computer resources. The model surface mesh adopts polyhedral mesh and the volume mesh adopts structured mesh to reduce the number of meshes to speed up the calculation speed. The generated mesh was saved as a .mesh file and imported into Fluent software (Ansys 19.2, Ansys, Inc., Canonsburg, PA, USA).

3.2.2. Control Equations and Boundary Conditions

The airflow was turbulent in the extractor and the flow field near the impeller had strong rotational flow, so a realizable k-ε turbulence model was used to calculate the fan flow field [19,20,21]. The dynamic reference frame (MRF) was used to deal with the blade rotation and set the fan speed. The fan blade area was the dynamic area and the other areas were static. The model’s inlet and outlet were set as pressure inlet and pressure outlet and the pressure values were atmospheric pressure, which was used to calculate the flow field of no load. The boundary condition of the wall surface was no sliding wall surface. The internal interface of the model was set as an interface to realize the data transfer of the contact surface. The second-order upwind discrete model was adopted and solved by the SIMPLE algorithm.

3.3. Verification of Extractor System Simulation Model

The cross-section point method was used to measure the wind velocity, wind pressure, and flow rate on the cross-section of the original extractor’s air outlet and the test measurement values were compared with the simulation values to verify the accuracy of the flow field simulation model.

The nine data points were evenly selected 600 mm away from the air outlet of the extractor, and the wind velocity, wind pressure, and flow rate of the nine data points were measured. The extractor speed was set as 950, 1100, and 1250 r/min, as shown in Figure 5. An intelligent digital tachometer (range: 2.5~9999 r/min, accuracy: 0.1 r/min, Jinxiao Instrument Equipment Co., Ltd., Shanghai, China) was used to measure the fan speed; A JX-2000 intelligent digital pressure anemometer (range: 3000~3000 Pa, accuracy level: 1, Jinxiao Instrument Equipment Co., Ltd., Shanghai, China) was used to measure the wind pressure; a SMARTT SENSOR split anemometer (range: 0~45 m/s, accuracy: 0.1 m/s, Jinxiao Instrument Equipment Co., Ltd., Shanghai, China) was used to measure the wind velocity.

3.4. Flow Field Simulation of the Extractor System

The three extractors’ internal flow field simulation was conducted using Fluent soft and the fan speed was set as 1100 r/min. The CFD-POST software was used to analyze the aerodynamic performance of the negative pressure area on the simulation results. The extractor with better performance was selected for subsequent field test verification by comparing the distribution of wind velocity and pressure in the negative pressure zone of the three extractors.

3.5. The Performance Field Test of the Extractor System

3.5.1. Test Conditions

On 18 March 2021, the test was conducted at the sugarcane test site in Zhanjiang, Guangdong, as shown in Figure 6. The test prototype was the HN4GDL-194 sugarcane chopper combine harvester. The test site was rectangular with an area of 0.57 hm² and there were no hard foreign objects such as weeds, stones, and tree stumps that affect the operation. Detailed information about the test site is shown in

Table 1. Information on test site.

Parameters	Measurement Results
Ridge height/mm	113
Ridge distance/mm	122
Soil moisture content	17%
Soil firmness/KPa	2837
Growth density/Plant·m−1	11
Leaf-stem ratio	29%
Moisture content of sugarcane leaf	9.2%

.

3.5.2. Test Methods

The test was conducted based on JB/T 6275-2019 <sugarcane combine harvester>. The field performance test of the extractor was conducted with the trash content and loss rate as the evaluation indexes. The test factors and levels are shown in

Table 2. Test factors and levels.

Test Factors	Levels
Fan speed/(rad·min−1)	950	1100	1250
Driving speed/(km·h−1)	1	2	3

.

The test areas were divided into the stable area, measurement area, and parking area and the measurement area was 10 m. During the operation, the net bag was used to collect the trash discharged by the extractor and the color shed cloth was used to collect the billet. Each group of tests was repeated three times and the measurement results were taken as the average value. The test indexes are calculated as follows:

(1)

Trash content J_h, as shown in Formula (1).

$$J_h=\frac{W_z}{W_{jz}}\times 100\%$$

(1)

where W_z is the total mass of trash, kg; W_jz is the total mass of samples collected in the determination area, kg; J_h is trash content, %.

(2)

Loss rate S_i, as shown in Formula (2).

$$S_{\mathrm{i}}=\frac{W_i}{W_q}\times 100\%$$

where W_i is the lost mass of broken cane/billet discharged by the fan, kg; W_q is the total weight of full-time billet in the measured area, kg; S_i is the fan loss rate, %.

4. Results and Discussion

4.1. Analyzed Aerodynamic Performance of the Extractor System’s Negative Zone

4.1.1. Wind Pressure Analysis

Figure 7 is a cloud diagram of the static pressure, dynamic pressure, and total pressure for the negative pressure area in the three extractors on the Z = 0 cross-section. The cloud diagram of static pressure distribution in Figure 7a shows that the closer to the fan blade, the greater the negative pressure, that is, the greater the suction generated by the rotation of the fan blade. The negative pressure near the wall surface at the lower end of the blade is significantly higher than in other regions. Among the three structures, the negative pressure in the negative pressure area of structure 2 was the largest, mainly concentrated in −122~−45.4 Pa, and the negative pressure in the negative pressure area of structure 1 was the smallest, mainly concentrated in −92.2~−28 Pa. The cloud diagram of dynamic pressure distribution in Figure 7b shows that the closer to the fan blade, the greater the positive pressure. Further, the positive pressure in the blade-end area was significantly higher than that in other regions. Among the three structures, the positive pressure in the negative pressure area of structure 3 was the largest, mainly concentrated in 23.2~185 Pa, and the positive pressure in the negative pressure area of structure 1 was the smallest, mainly concentrated in 26.8~133 Pa. As the cloud diagram of total pressure distribution in Figure 7c shows that the total pressure in the negative pressure area of structure 2 was the most stable and uniform, mainly concentrated in −5.99~0 Pa in the progress of trash removal, the greater the negative pressure in the negative pressure zone, the more uniform the pressure distribution, which was more conducive to the separation of billet and trash. Compared with the three structures, the pressure distribution in the negative pressure zone of structure 2 was the most uniform and the negative pressure was enormous, which was most conducive to air separation and trash removal.

4.1.2. Analysis of Flow Velocity

The velocity vector diagram of the extractor’s negative pressure at the Z = 0 in Figure 8 shows that the airflow showed good consistency in the central zone of the negative pressure. The design of the three concave negative pressure structures did not produce a vortex at the airflow inlet, but a vortex appeared at the right side of the lower plane of the fan blade. The formation of the vortex is due to the collision between the airflow of the fan’s air inlet and material inlet and encountering the wall. Figure 9 was a cloud diagram of the flow velocity of the negative pressure. As shown in Figure 9, the maximum wind velocity of the flow field of structure 1 was 74 m/s and the wind velocity of the negative pressure mainly concerted at 6~8 m/s. The maximum wind velocity of the flow field in structure 2 was 87 m/s and the wind velocity of the negative pressure was mainly concentrated at 7.5~11 m/s. The maximum wind velocity in the flow field of structure 3 was 57 m/s and the wind velocity of the negative pressure was mainly concentrated at 5.5~8 m/s. Compared with the three structures, the velocity distribution of structure 2 was increased as a whole.

4.2. Verification Results of Simulation Test of the Extractor System

The wind velocity and pressure were tested in HanNiu Machinery Co., Ltd., Conghua, Guangdong (Figure 10) and the steady-state simulation was conducted with fan speeds of 950, 1100, and 1250 r/min. The comparison results between the actual measured values and the simulation values are shown in Figure 11a,b. The change trends of the actual values for wind velocity and pressure were basically consistent with the simulation values. Comparing the air outlet flow at different speeds (Figure 11c), the relative error of the air outlet flow of the fan was less than 10%. The above results showed that the simulation model of the extractor was reasonable, the numerical simulation method was correct, and it could be used to study the internal airflow field.

4.3. Measurement Results of the Trash Content and Loss Rate

Taking the feed rate and fan speed as the test factors, the sugarcane harvester original extractor (structure 1) and optimal extractor (structure 2) were tested with the trash content and loss rate as the test index.

4.3.1. Measurement Results of the Trash Content

The test results of the trash content are shown in Figure 12. When the feed rate was 1.5 kg/s and the fan speed was 1100 r/min, the trash content of the optimal extractor decreased by 0.8%, lower than that of the original fan. When the feed rate was 1.5 kg/s, the trash content between the original extractor and optimal extractor had no significant difference under different extractor speeds because the extractor load was lower at a low feed rate and both extractors could maintain a high-level trash removal ability at this moment. When the feed rate increased to 4.5 kg/s, the fan load increased with the material feed rate. Compared with the original fan, the negative pressure zone of the optimal extractor had higher flow velocity and negative pressure under the same speed, better trash removal ability, and the impurity content was decreased by 1.37% (Figure 12a). When the feed rate was 7.5 kg/s, the trash content of the optimal extractor decreased by 2.5% (Figure 12a), lower than that of the original fan.

When the fan speed increased to 1100 r/min, the difference in trash content between the original extractor and the optimal extractor was significantly smaller. However, the fan load increased with the material feed rate and the difference in trash content between the original extractor and the optimal extractor was significantly increased. When the feed rate increased to 7.5 kg/s, compared with the original fan, the trash content in the optimal extractor decreased by 1.63% (Figure 12b).

When the fan speed increased to 1250 r/min, the difference in trash content between the original extractor and the optimal extractor was slight, because, at high speed, the negative pressure zone of the two extractors generated higher flow velocity and negative pressure, which could be efficiently discharged trash. When the feed rate was 7.5 kg/s, compared with the original fan, the trash content in the optimal extractor decreased by 1.63% (Figure 12c).

Through the analysis of Figure 12, it could be seen that the overall trash removal performance of the optimal extractor was better than that of the original extractor; specifically, at medium (1100 r/min) and low (950 r/min) speeds, the trash content was significantly decreased.

4.3.2. Measurement Results of the Loss Rate

Test results of the loss rate are shown in Figure 13. The two extractors’ loss rate gradually decreased with an increase in feed rate; the two extractors’ loss rate increased with an improvement in fan speed. As shown in Figure 13a, when the fan speed was 950 r/min, there was no significant difference in the loss rate of the two extractors because the flow velocity and air pressure produced by the two extractors were too small to cause a loss of sugarcane. As shown in Figure 13b, when the fan speed was 1100 r/min, compared with the original extractor, the loss rate of the optimal extractor was decreased by 0.53%, 0.21%, and 0.19%, respectively. As shown in Figure 13c, when the fan speed was 1250 r/min, there was no significant difference in the loss rate of the two extractors, but it was significantly higher than the loss rate under the medium (1100 r/min) and low (950 r/min) speeds because when the fan speed was high enough, the wind speed and pressure generated by the fan could draw most of the small pieces of sugarcane or crushed sugarcane into the fan for discharge, causing losses.

5. Conclusions

In order to reduce the trash content and loss rate for mechanized sugarcane harvesting, this study took the HN4GDL-194 sugarcane chopper harvester extractor developed by South China Agricultural University as the object, designed the negative pressure zone structure of the extractor, analyzed the internal flow field, and verified the performance of the original extractor and the optimal extractor. The main conclusions of this study are as follows:

(1)

Based on the negative pressure structure in the original extractor, the structure of the negative pressure zone in the two fans was designed. Through the analysis of the internal flow field of the fan, it is found that the negative pressure zone in fan structure 2 had the best aerodynamic performance, the air pressure distribution was uniform and stable, and it had good consistency in air flow direction, which was conducive to reducing trash content.

(2)

The simulation results were verified by the three indexes of the original extractor’s wind speed, wind pressure, and flow rate. The results showed that the actual values of wind speed and wind pressure were basically consistent with the simulation values and the relative error of outlet flow rate was less than 10% at different speeds. The fan simulation model could be used to study the internal airflow field.

(3)

Test results of trash content showed that when the feed rate was 1.5 kg/s, there was no significant difference in the trash content between the original extractor and the optimal extractor under various fan speeds. When the feed rate was 4.5 kg/s, the trash content in the optimal extractor was reduced by 1.37%, 1.0%, and 0.77%, respectively, compared with the original fan at low (950 r/min), medium (1100 r/min), and high (1250 r/min) speeds. When the feed rate was 7.5 kg/s, the low-speed performance of the optimal extractor was significantly improved and the trash content decreased by 2.5%.

(4)

Test results of the loss rate showed that when the fan speed was 950 r/min, there was no significant difference in the loss rate of the two fans. When the fan speed was 1100 r/min, the loss rate of the optimal extractor was reduced by 0.53%, 0.21%, and 0.19%, respectively, compared with the original fan at low (1.5 kg/s), medium (4.5 kg/s), and high (7.5 kg/s) feed rate. When the fan speed was 950 r/min, there was no significant difference in the loss rate of the two fans, but it was significantly higher than the loss rate under medium and low speeds.