Improvement of Straw Throwing Performance of Harvester Based on Matching Header Width

Abstract

Aiming at the problem wherein a straw crushing and throwing device (SCTD) installed in a rice combine harvester (RCH) has a small throwing width and does not match the harvesting width, this paper proposes an improved plan for installing wind blades (WB) and optimizing the parameters of the deflector. The structural parameters of the WB were determined, and static analysis was carried out. The influence of the number of WB on the airflow field of the crushing chamber (CC) was studied by CFD simulation. The movement of the straw after entering the throwing device (TD) was analyzed. It was determined that the factors affecting the throwing width under the condition of a certain straw speed were the installation angle of the deflector (IAD), and the arc length of the deflector (ALD) through the bench test. The optimal combination of deflectors parameters was determined to match the width of the harvester header. When the straw feeding speed was 4 kg/s, and the straw moisture content was 33.80%, the optimal parameters are that the ALD was 400 mm and the IAD was 9°. The matching degree with the header width (4.50 m) is 98.44%. This study can effectively increase the straw throwing width and create conditions for the smooth implementation of straw returning to the field.

1. Introduction

Straw throwing is an essential part of straw returning [1,2], and its operation quality affects the effect of straw returning and whether subsequent operations can be successfully implemented [3,4,5,6]. Compared with the straw pulverizer matching the tractor [7,8,9,10,11], the SCTD installed in the RCH has the characteristics of high operation efficiency and low operation cost [12,13], both of which have broad prospects for various applications. Due to the large amount of straw in the operation of rice straw throwing, a problem often emerges wherein the width of the straw throwing is small and the width of the header does not match it size, which causes excessively uneven throwing. During the subsequent burial and return to the field, the straw is more likely to block the working parts [14], and the decomposition rate of the straw will also decrease [15].

Scholars at home and abroad have researched the problem of throwing width. Schillinger [16] installed a fan on the original harvester, and this fan was designed with a two-way hose. The hoses were arranged at the straw discharge and grain bran outlets. At the same time, the acceleration of the straw was completed by discharging strong airflow from the air outlet of the hose, thereby increasing the throwing width of the straw. However, this improvement plan dramatically changed the structure of the harvester, and the fan also increased the power consumption of the harvester. Christian [17] developed a double-shaft vertical pulverizer for increasing the width of the harvester header, which can realize the integration of straw and powder throwing (that is, the straw was also thrown at the same time). The width can reach 12 m, but the operation stability was poor, the power consumption was high, and it was still in its initial test stage. Lu Jian [18] designed a double helix auger throwing mechanism suitable for the half-feed harvester. During the mechanism’s operation, the straw can be evenly spread in the working area of the harvester, but the work efficiency was low and the throwing width was small. This was not suitable for axial harvesters. Wang Xin [19] analyzed the influence of the IAD on the throwing width through field experiments but did not systematically study the interaction between the deflector itself and the installation parameters. Most of the existing research on the throwing width is to add a throwing device, which significantly changes the structure of the harvester and has high power consumption, which does not apply to the improvement of the throwing performance of the existing rice combine harvester.

In this paper, the harvester’s dynamic model of straw throwing is constructed, and the factors affecting the throwing width are analyzed. The improvement plan for installing WB and optimizing the deflector is proposed, and the relevant parameters are determined. The influence of the WB installation parameters on the airflow in the crushing chamber is studied, and the related parameters of the deflector are determined through optimization tests.

2. Materials and Methods

2.1. Machine Structure and Working Principle of the SCTD

2.1.1. Structure of the SCTD

The structure and operation effects of the whole machine are shown in Figure 1a. The structure of the SCTD comprised grass receiving plate (2), the crushing device (4), the TD (5), and pulley (3). The crushing device included a crushing chamber (8), crushing knife shaft (9), first-level fixed knife (11), Second-level fixed knife (10) and the moving knife combination (12); the throwing device included the throwing shell (7) and the deflector (6); the movable knife assembly mainly includes the movable knife blade (13) and the wind blade (14), and the structure is shown in Figure 1b.

2.1.2. Working Principle

During operation, the power of the SCTD was transmitted from the RCH to the crushing knife shaft through the belt. The operation process can be divided into three stages. (1) Straw feeding stage: the straw come out of the straw discharge port of the threshing device and slid down along the straw collecting plate to the inlet of the CC. (2) Straw crushing stage: when the straw was fed into the CC of the crushing device, the cutting of the straw was completed with the cooperation of the crushing movable and fixed knives. (3) Straw throwing stage: the crushed straw was thrown to the ground under the action of the TD and its gravity.

2.2. Design and Installation of Wind Blades

The induced draft fan had been widely used in factories and mining areas as ventilation and dust removal equipment. Its main working principle was to use the fan blade-shaped working parts to rotate at high speed to accelerate the airflow and generate negative pressure to exhaust air [20]. The blade can be installed on the moving knife by drawing on the working principle of the induced draft fan so that when the moving knife rotated at high speed, a higher wind speed was generated so that the straw could be discharged from the crushing device at a higher speed.

2.2.1. Determination of Structure Size

The structure of the WB shown in Figure 2 includes a windward side and a mounting side. The windward side was perpendicular to the blade face of the moving knife. As shown in Figure 2a, both the wind blade mounting surface and the moving blade surface are provided with connecting holes. The main working face generates high-speed airflow. Since the moving blade was made of 65 Mn steel, the welding and tensile properties were poor, and the WB should not be welded or formed at one time. Therefore, a mounting side was designed to install the windward side of the WB on the blade face of the moving knife, and the specific connection method was the bolt locking connection. As shown in Figure 2a, the WB mounting side and the moving knife surface provide connecting holes.

In order to avoid affecting the crushing effect, the length of the windward side (l_f) should not overlap with the effective length of the blade of the moving knife. According to the actual test, the l_f was designed to be 70 mm. The width of the windward face (d_f) was designed to consider the swing of the moving knife, and the size was 33 mm. At the same time, in order to avoid the phenomenon of knife jamming when the moving knife combination starts and stops, through the indoor installation test, the structure of the windward side was designed, as shown in Figure 2a, using a 70 mm × 35 mm rectangle to cut a 33 mm × 23 mm rectangle. The thickness was designed to be 3 mm. The length of the mounting side should be consistent with the length of the windward side. In order to better connect with the moving knife, the width of the datum plane should be consistent with the width of the moving knife, which was 50 mm. The installation diagram of the wind blade test is shown in Figure 2b.

2.2.2. Establishment of Finite Element Model of WB

The existence of WB can generate airflow under high-speed rotation, but at the same time, the airflow and straw would also impact the WB. In order to avoid fatigue and stress damage during the operation of the designed WB, it is necessary to obtain the windward stress of the WB during the crushing operation. Therefore, carrying out a static finite element analysis of WB was necessary.

In this paper, Solidworks was used to build a three-dimensional model of a WB, and the model was saved in step format and then opened in ANSYS Workbench. The material of the WB was structural steel Q235. After consulting relevant literature [21], the material performance parameters are shown in

Table 1. Q235 material properties.

Parameters	Value
Mass density	7.85 × 103 kg/m3
Young’s modulus	210 GPa
Poisson’s ratio	0.3
Tensile strength	450 MP
Yield strength	235 MP

. According to the table content, the model’s material properties were defined. The model mesh was divided by tetrahedral mesh [22]. Figure 3 shows the model effect after division. A total of 19,522 nodes were divided, and 35,383 nodes were obtained. The number of meshes meets the analysis requirements.

Since the mounting side of the WB was fixedly connected with the moving knife by bolts, a fixed constraint was imposed on the mounting side to analyze the ultimate stress of the windward side of the WB. Before calculating the load pressure, it was assumed that no vortex occurred during the crushing operation and that the angle of the windward side of the straw collision was the same. When the WB rotated at high speed, it would be subjected to air resistance and straw impact force. Reference [23] showed that the air resistance F_k of an object was related to the area of the object, the speed of airflow, and the air resistance coefficient at the airflow speed. Its expression is as follows:

$$F_k=C_d{S}_1{v}_d^2$$

(1)

where C_d is the air resistance coefficient; S₁ is the windward area of the object, m²; v_d is the relative velocity of the airflow and the windward surface, m/s. According to a literature review, it can be seen that C_d tends to decrease slowly with the increase in speed. According to this research, C_d is selected as 0.80 in this paper.

When calculating the average action force Fc of straw on wind blades, it can be understood that the product of action force and action time equals the change of straw momentum. The formula is:

$$F_c\Delta t=\Delta m{v}_j$$

(2)

where $\Delta t$ is the collision time, s; $\Delta m$ is the mass of broken straw, kg; v_j is the velocity of the straw after the collision, m/s. Refer to the relevant literature [24] for further information. $\Delta m$ value is 3.12 × 10⁻⁴ kg; $\Delta t$ value is 1.75 × 10⁻³ s.

The size of the windward side area S₁ of the WB is 2.31 × 10⁻³ m², and the positional velocity v_f of the center point of the windward side can be expressed as:

$$v_f=\frac{2\pi R_f}{60}\times n$$

(3)

where R_f is the turning radius of the center point of the windward side, m, and the value is 0.125; n is the rotational speed of the cutter shaft, r/min, which was taken as 2600 r/min in this paper. Bringing in the above formula can obtain v_f. The speed of the straw after the collision can be considered to be the same speed as the WB; the WB and the airflow are in relative motion; the WB speed can replace the airflow speed, that is, v_f = v_j = v_d. Put the obtained v_f values into Equations (1) and (2), respectively, to obtain the air resistance F_k as 892.81 N, and the average force F_c of the straw on the WB is 391.87 N. As shown in Figure 4, these two forces are added on the WB’s windward side.

2.2.3. Pre-Processing of CFD Simulation

Driven by the crushing knife shaft, the WB would generate a complex airflow field and pressure field in the CC, and the characteristics of the flow field would affect the airflow in the CC and thus the movement of the straw. In this chapter, the CFD analysis method was used to study the influence of different installation parameters of WB on the flow field characteristics of the CC to reveal the influence of different installation parameters of WB on the flowability and throwing characteristics of straw.

In order to improve the simulation efficiency, the 3D model established by Solidworks needed to be simplified, and the structures or details that had little effect on the simulation accuracy were omitted, such as bearings, bolts, tool seats, and openings. At the same time, a motion split surface was established to facilitate the extraction and segmentation of subsequent fluid domains. The simplified CC structure is shown in Figure 5. We saved the 3D model in Parasolid format and imported it into Design Modeler to extract the CC fluid domain. The fluid domain was meshed in Meshing, and the boundaries were named. In order to improve the mesh quality and reduce the simulation time, after the mesh model was imported into Fluent, and the mesh was optimized through the mesh polyhedron conversion function that comes with the software. The optimized polyhedron mesh is shown in Figure 6.

The fluid domain between the pulverizer shell and the split surface was set as the static domain, the motion domain of the pulverizing knife shaft was set as the rotation domain, and the rotational speed of the rotation domain was set as 2600 r/min. During the simulation, the rotation domain would drive the static domain, and Changes in airflow were generated. The inlet and outlet boundary conditions of the CC were set to pressure type, and the pressure was standard atmospheric pressure. Due to the phenomenon of airflow fluctuation and eddy currents in the process of rotating motion, the realizable k-ε model with high reliability was used to simulate the turbulent flow in the CC [25]; the calculation method adopted was ‘Coupled’. After the simulation calculation was completed, the results were processed in CFD-Post, and three sections, P1, P2, and P3, were selected and established (as shown in Figure 7); the fluid properties of each section were analyzed. Section P1 was located on the left side of the tool axis and passed through the end face of the tool axis; section P2 was located at the center of the tool axis and parallel to the P1 plane; section P3 was located on the right side of the tool axis and passed through the end face of the tool axis.

2.3. Motion Analysis of Straw Entering the TD

Since the crushing device and the TD were closely connected, it can be considered that the straw entered the TD immediately after being discharged from the crushing device. After the straw entered the throwing device, its motion can be divided into an AB stage (non-guided stage) and Bb stage (guided throwing stage), as shown in Figure 8. Motion analysis of these two processes is performed below.

2.3.1. Straw Non-Guided Stage

The crushed straw was discharged from point A of the outlet of the crushing device under the action of centrifugal force and airflow, entered the TD, and then reached point B of the TD under the action of its impulse airflow and gravity. This process was the non-guided stage of straw. At this stage, the airflow velocity gradient was slight, and it can be considered that the straw does not rotate, so the influence of its rotation on its force was ignored [26]. Since the volume of straw was small, the flow velocity of the air flowing around it can be considered almost unchanged, and the fluid pressure difference on both sides of the straw was slight, so the displacement of the straw caused by the pressure difference can be ignored [27].

The designed WB can accelerate the airflow through high-speed rotation. It can be considered that the airflow does positive work on the movement of the straw. After the crushing device worked stably, the straw would reach the maximum value in a short period and then maintain a certain speed to reach point A. In attenuation, the airflow would do negative work on the straw in the AB stage, so it was considered that the airflow velocity v_d1 at point A was less than or equal to the straw velocity v_A at this point. Then, the kinetic equation of straw in the AB stage is

$$-(\Delta mg+F_{kt})=m\frac{d^{2}h}{d{t}^2}$$

(4)

where t is the time when the straw leaves point A, s; $\Delta m$ is the straw weight, g; F_kt is the air resistance when the straw leaves point A at time t, N; h is the height difference between point A and point B, mm.

When the straw moved in the AB stage, the air resistance F_kt received can be expressed as:

$$\{\begin{array}{l}{F}_{kt}=C_d{S}_j{v}_{dt}^2\\ S_j=\frac{1}{4}\pi d_j^2\\ d_j^{}={\left(\frac{6V_j}{\pi }\right)}^{\frac{1}{3}}\\ V_j=\frac{1}{4}\pi {\overline{d_j}}^2{l}_j\end{array}$$

(5)

where S_j is the windward area of the straw, m²; d_j is the equivalent volume diameter of the straw, m; V_j is the equivalent straw volume, m³; $\overline{d_j}$ is the average diameter of the cross-section of the straw, m; $l_j$ is the average length of the straw after crushing, m; $v_{dt}^{}$ is the relative velocity of airflow and straw, m/s.

The initial boundary conditions of the AB segment of the straw movement process are $\frac{dh}{dt}=v_A-v_{d1},h=0$. Then the height difference of the straw moving in the AB segment can be expressed as:

$$h=-\frac{\Delta mg+F_{kt}}{2\Delta m}{t}^2+(v_A-v_{d1})t$$

(6)

When the WB was added, the throwing speed of the straw at point A would increase, and the air resistance after being discharged from the crushing device would also increase. It can be seen that h will be smaller according to Formula (5); that is, the collision point B of the straw would move backwards since the guide of the TD was the process of throwing down, which would increase the collision angle of the straw at point B. The increase in the collision angle would reduce the loss of kinetic energy [28].

2.3.2. Straw Guided Throwing Stage

The straw contacted and collided with the TD at point B. Since the flow velocity of the straw was fast, the collision occurred instantaneously, so the beating and displacement generated in the process can be ignored. After passing point B, the straw entered the deflector area and was thrown under the guidance of the deflector. As shown in Figure 9, the force on the straw in this process had its gravity $\Delta mg$, the centrifugal force F_l guided by the deflector, the friction force F_f with the deflector, and the air resistance $F_k^{\prime }$. It can be seen that the straw was subject to more resistance in this process, and there was a specific energy loss. Assuming that the kinetic energy of the straw thrown at point b is E_b, it can be expressed as:

$$E_b=E_0-E_p-E_z$$

(7)

where E₀ is the kinetic energy when the straw enters the deflector, J; E_p is the collision kinetic energy loss when the straw is in contact with the deflector, J; E_z is the kinetic energy loss of the straw when it drains and slips, J.

Assuming that the speed of the straw entering the deflector was v_c, the kinetic energy of the straw at this time can be expressed as:

$$E_0=\frac{1}{2}\Delta m{v}_c^2$$

(8)

When it was considered that the collision between the straw and the deflector was utterly inelastic, the energy loss during the collision can be expressed as:

$$E_b=\frac{1}{2}\Delta m{v}_c^2\sin \epsilon$$

(9)

where is the collision angle between the straw and the deflector, °. The energy loss of straw when the deflector slips can be expressed as:

$$E_c={\displaystyle \underset{0}{\overset{s_d}{\int }}{F}_d}ds={\displaystyle \underset{0}{\overset{s_d}{\int }}(F_f+F_k^{\prime })}ds$$

(10)

Substituting Equations (8)–(10) into Equation (7), we can get:

$$E_b=\frac{1}{2}\Delta m{v}_c^2-\frac{1}{2}\Delta m{v}_c^2\sin \epsilon -{\displaystyle \underset{0}{\overset{s_d}{\int }}(F_f+F_k^{\prime })}ds$$

(11)

The kinetic energy of straw throwing would affect the throwing width. We can discuss the kinetic energy loss in the Bb stage from the above formula. It can be seen that the kinetic energy loss in this process was related to the collision angle $\epsilon$ and the ALD s_d. When the collision angle $\epsilon$ increased, the kinetic energy loss increased, and the collision angle $\epsilon$ was related to the IAD (the angle between the installation section of the deflector and the y-axis) θ_c. When the arc length s_d of the deflector was longer, the friction of the straw at this stage and the negative work carried out by the airflow were greater. According to the above analysis, the kinetic energy loss of straw in the TD was represented by two collisions and the loss of resistance. In order to achieve a better throwing width under the condition that the installation angle of the TD remained unchanged, two factors, the IAD θ_c of the deflector and the ALD s_d, needed to be optimized.

2.4. Determination of the Structural Parameters of the Deflector

As shown in Figure 9, the structure of the deflector can be divided into an installation part and an arc guide part. The installation part mainly connects the deflector with the throwing shell of the throwing device; it has two mounting holes, which can be adjusted within 0°~15° of the IAD by cooperating with the strip holes on the shell plate. The primary dimension parameters of the arc guide part were the arc radius and arc length. The TD’s basic structure and the deflectors’ arrangement are shown in Figure 10. The deflectors were divided into three types and a total of six according to different sizes. Since the outermost deflector was directly related to the throwing width of the TD, this paper only optimized the structure of the outermost deflectors 1 and 6. Considering the overall size of the TD, the radius R_d of the arc guide part of the deflector should not be too small, which would cause the straw to be thrown out not smoothly. If it were too large, the velocity component in the y-axis direction would be small when the straw was thrown, which was not conducive to increasing the throwing width. According to the actual test and the mapping of the original deflector, the radius Rd of the arc guide part of the improved deflector was determined to be 650 mm. According to the analysis in Section 2.3, it can be seen that if the ALD were too long, it would cause more energy loss of straw. However, the guide effect was not apparent if it was too short. According to deflector installation and diversion requirements, the improved deflector arc length sd was designed to be 360 mm~420 mm. The installation size and width of the improved deflector are the same as the original deflector.

2.5. Parameter Optimization of the Deflector on the Test Bench

In order to further determine the appropriate combination of ALD and IAD when the TD threw rice straw, an optimization test was carried out on the SCTD. In order to avoid the influence of uncertain factors and a complex measurement environment on the measurement results in the field test, the optimization test was carried out on a test bench.

The optimization test of the test bench was carried out in October 2020 at the Harbin Songbei Machinery Factory, Harbin, China. The structural design of the test bench is shown in Figure 11, which mainly includes a straw conveyor belt, a safety box, a motor, a support bench, and SCTD. Through continuous motion, the straw drive belt was used as the straw feeding structure to feed the straw into the crushing device. According to the feed rate of the RCH header and the ratio of grass to grain, it can be determined that the feed rate of straw is 4 kg/s. The existence of the safety box is intended to avoid the unsafe factor when the SCTD operates at high speed. The motor serves as the power source of the crushing device, and the support bench provides a stable support environment for the test bench. The test straw was the unpulverized straw in the nearby farmland with a moisture content of 33.80%, which was collected and used later. The speed of the pulverizer was designed to be 2600 r/min, and the WB was all installed. After being thrown, the straw can be received by the pre-laid roll cloth, and the roll cloth can move backwards at a certain speed under the drive of the reel. This process can simulate the forward speed of the harvester during the field test to avoid repeated spreading of the straw after throwing. The significance of the two factors was analyzed by test. The parameter combination optimization was carried out with the width of the harvester header as the optimization target [29,30]. The test factors and levels are shown in

Table 2. Test factors and levels.

Level	sd/mm	θc/°
$+\gamma$	360	0
1	370	2
0	390	7.5
−1	410	13
$-\gamma$	420	15
$\Delta i$	20	5.5

. After the test, the throwing width (D) was measured and evaluated.

3. Results and Analysis

3.1. WB Statics Results and Analysis

The WB model was solved, and the stress, strain, and deformation cloud diagrams are shown in Figure 12. Different colors in the figure represent different effects after being subjected to force. Blue indicated a smaller value, and red indicated a more significant value. From Figure 12a,b, it can be seen that the maximum stress and strain on the windward side of the WB are 43.73 MPa and 0.023, respectively, which were less than the yield strength of the material. At the same time, it was found that the bending angle of the windward side has a stress concentration phenomenon under the load; a triangular transition can be appropriately made at this position when machining parts to avoid damage in the actual work. Figure 12c showed that the maximum deformation of the windward side under load occurs at one end away from the mounting side. The maximum deformation is 0.0044 mm, which can meet the actual strength requirements.

3.2. Analysis of Installation Parameters of WB Based on CFD

3.2.1. The Influence of the Installation Direction of the WB on the Surrounding Airflow

The WB had two installation forms when it cooperated with the moving knife, forward installation and reverse installation. The installation structure is shown in Figure 13. When the forward installation was adopted, the windward side of the WB was consistent with the rotating front end surface of the moving knife. When the reverse installation was used, the windward side of the WB was consistent with the rotating rear end surface of the moving knife.

In order to more directly and accurately study the airflow conditions around the WB in different installation directions, the rotation model with the WB installed was further simplified, as shown in Figure 14. Forward and reverse installation can be achieved by changing the rotation of the crushing knife shaft in the model. Figure 15 showed the cloud diagram of the surrounding airflow when the WB were installed forward and reverse. The maximum flow velocity of the fluid was 64.35 m/s when the forward installation was adopted and 62.78 m/s when the reverse installation was adopted, and the difference in flow velocity was insignificant. It can be seen from the figure that the streamline in the rotation range of the WB was relatively uniform when the forward installation was adopted. During the reverse installation, there was a significant difference in the number of streamlines before and after the WB, which may cause irregular movement of the straw during the crushing process. The partial enlarged image showed multiple vortex areas formed between the windward side and the moving knife when the reverse installation was adopted. During the actual crushing operation, the local vortex area would cause the straw to flow unsmoothly so that the straw can hang around the WB. Compared to reverse installation, when the WB was installed in the forward direction, the airflow movement near the windward side was relatively smooth since the windward side does not form a fluid motion space with the moving blade. Therefore, according to the above analysis, the forward installation was adopted when the WB and the moving knife were installed to achieve a better wind effect.

3.2.2. The Influence of the Number of WB on the Flow Field

The number of WB installed affects the velocity and pressure of the flow field in the CC, thus affecting the performance of the SCTD [27]. In this paper, referring to the number of moving knives, the installation quantities (E) of WB were set to 0, 20 (half the number of installations), and 40 (all installations), respectively. The installation of WB and moving knives adopted forward installation. When E was 20, the uniformity of airflow distribution was considered, and the spaced distribution of WB was adopted. The structure diagram is shown in Figure 16.

Pressure Change at the Inlet

When the crushing knife shaft rotated at high speed, a negative pressure zone would be formed at the inlet of the CC [25]. The larger the value of the negative pressure zone, the more conducive to feeding straws, which can effectively avoid the problem of straw jam and poor feeding. Figure 17 shows the pressure cloud diagram at the inlet under the installed number of different WB. It is known that whether the WB was installed or not would form a negative pressure area at the inlet of the CC. However, when the number of installed WB increases, the high negative pressure area of the inlet begins to increase. When E = 0, the maximum negative pressure at the chamber inlet was 14.59 pa, when E = 20, it was 17.94 pa, and when E = 40, it was 21.86 pa. Therefore, it can be seen that with the increased number of installed WB, the absolute value of the negative pressure at the feeding inlet of the CC also gradually increased. It can be seen from the above analysis that the WB can improve the negative pressure effect at the inlet of the CC, and the negative pressure effect at the inlet was more significant as the number of installed WB increased.

Analysis of Airflow Fluidity in CC

Figure 18 was the velocity streamline diagram of P1, P2 and P3 sections under different WB installation numbers. It can be seen from the figure that under the same installation parameters, the streamline diagrams between different sections were also different. The airflow streamlines of the P1 and P3 sections on both sides were relatively smooth and stable, and the airflow streamlines of the middle P2 section were relatively fluctuating. The main reason was that the airflow in the CC had a specific axial movement phenomenon., which made the airflow field between the shafts more complicated than the airflow field near the side plate so that the airflow would fluctuate to a certain extent.

It can be seen from Figure 18a that when the number of installed WB increased, the fluid velocity in the rotating domain on the P1 section increased gradually. When E = 0, the maximum flow velocity of the fluid in the P1 section was 55.18 m/s, E = 20 was 62.81 m/s, and E = 40 was 71.60 m/s. When E = 0, fluid chasm and eddy currents appeared at the inlet of the CC. When the installed number of WB increased from 0 to 20, the velocity streamlines chasm at the inlet of the CC, and the eddy current in the upper right corner disappeared. However, the fluid fluctuation in the CC increased, the streamline density at the outlet decreased, and the streamline area increased. When the installed number of WB increased from 20 to 40, the fluid streamline fluctuation in the CC increased. The streamlined area and density at the outlet did not change significantly. The installation of WB increased the fluid velocity in the left area of the CC but also caused fluid instability, which means that when the WB was not installed, the straw was more concentrated and thrown away from the CC along the bottom plate. The straw was thrown from the entire outlet after installation. Therefore, the number of WB significantly influenced the fluid flow in the left area of the CC.

It can be seen from Figure 18b that when the number of installed WB increased, the fluid velocity in the rotating domain on the P2 section increased gradually. When E = 0, the maximum flow velocity of the fluid in the P2 section was 64.82 m/s, E = 20 was 65.77 m/s, and E = 40 was 71.73 m/s. When E = 0, a vortex phenomenon appeared in the fluid at the inlet of the CC. When the number of installed WB increased from 0 to 20, the vortex on the left side of the CC inlet disappeared, and the vortex on the right side still existed. A new vortex appeared on the right side of the rotating domain, and the fluid dynamics at the outlet of the CC remained unchanged. When the installed number of WB increased from 20 to 40, the vortex at the inlet of the CC still existed, the vortex on the right side of the rotating domain was enhanced, and the fluid dynamics at the outlet remained unchanged. The installation of WB increased the fluid velocity in the middle area of the CC but also increased the fluid instability, which had little effect on the outlet fluid flow. Therefore, the number of WB significantly influenced the fluid flow in the middle area of the CC.

It can be seen from Figure 18c that when the number of installed WB increased, the fluid velocity in the rotating domain on the P3 section increased gradually. When E = 0, the maximum flow velocity of the fluid in the P3 section was 49.97 m/s, E = 20 was 64.59 m/s, and E = 40 was 67.22 m/s. When E = 0, fluid chasm and eddy currents appeared at the inlet of the CC. When the number of WB installed was increased from 0 to 20, the vortex of the inlet disappeared. The vortex on the right side still existed and moved down to the right side of the rotating domain, and the fluid dynamics at the outlet of the CC remained unchanged. When the installed number of WB increased from 20 to 40, the vortex in the CC continued to move down, but the range decreased, and the fluid dynamics at the outlet remained unchanged. The installation of WB increased the fluid velocity in the right area of the CC but also increased the fluid instability to a certain extent and had little effect on the outlet fluid flow. Therefore, the number of WB significantly influenced the fluid flow in the right area of the CC.

When a fluid chasm occurred at the inlet of the CC, the fluid would concentrate on the left side of the inlet, which was not conducive to the direct feeding of straw into the CC. The above analysis found that installing WB can improve the fluid chasm phenomenon; the more installations, the better the effect. At the same time, increasing the number of WB may reduce the stability of the chamber’s fluid flow and generate local eddy currents, which would have a particular impact on the flow in the CC. Whether the effect affects the operation performance of the device still needs to be verified by tests.

Variation of Exit Velocity

The fluid velocity at the outlet of the CC directly determined the kinetic energy when the straw was thrown, thus affecting the throwing characteristics of the device. Figure 19 shows the velocity cloud diagram at the outlet under different WB installation numbers. It can be seen from the figure that with the increase in the number of WB, the high-velocity area at the outlet gradually increased. When E = 0, the maximum fluid velocity at the outlet was 9.91 m/s; when E = 20, the maximum fluid velocity at the outlet was 10.59 m/s, and when E = 40, the maximum fluid velocity at the outlet was 11.46 m/s. During simulation, set ten monitoring points at equal intervals on the lower edge of the exit. The average flow velocity at the outlet of different WB numbers was 5.08 m/s, 8.57 m/s and 10.19 m/s, respectively. When E = 20 and E = 40, compared with E = 0, the maximum export speed increased by 6.86% and 15.74%, and the average speed increased by 68.70% and 100.59%. Therefore, installing WB significantly improved the fluid velocity at the outlet, which increased gradually with the number of installations.

Through the flow field analysis of the inlet, outlet, and chamber of the CC, it can be known that installing WB benefits the feeding and throwing of straw; at the same time, it will give the straw a higher discharge speed. Considering a large amount of rice straw and the significant difference between the throwing width of the combined harvester’s original SCTD and the header width, a better straw feeding effect and higher throwing speed are required. Therefore, the number of WB should be fully installed, E = 40.

3.3. Analysis and Optimization of Test Results

The test effect diagram is shown in Figure 20, and the test results are shown in

Table 3. Test results.

Test No.	sd/mm	θc/°	D/m
1	−1	−1	4.05
2	1	−1	4.58
3	−1	1	4.49
4	1	1	4.39
5	$-\gamma$	0	4.11
6	$+\gamma$	0	4.71
7	0	$-\gamma$	3.88
8	0	$+\gamma$	4.38
9	0	0	4.41
10	0	0	4.43
11	0	0	4.34
12	0	0	4.29
13	0	0	4.45

. The test data were processed by the software Design-expert 13.0 [31,32].

Through the analysis of test data, the variance table of straw throwing width (D) is shown in

Table 4. Variance of throwing width.

Variation Source		Sum of Squares	Degree Freedom	Mean Square	F Values	p Values
Model		0.51/0.50	5/4	0.10/0.12	7.98/9.92	0.0083 ***/0.0034 ***
x1		0.20/0.20	1/1	0.20/0.20	16.06/16.33	0.0051 ***/0.0037 ***
x2		0.11/0.11	1/1	0.11/0.11	9.00/9.15	0.0199 **/0.0164 **
x1x2		0.099/0.010	1/1	0.099/0.0010	7.80/7.93	0.0268 **/0.0226 **
x12		0.011	1	0.011	0.87	0.3821
x22		0.070/0.079	1/	0.070/0.079	5.48/6.27	0.0517 */0.0367 **
Residual	Lack of fit	0.071/0.082	3/4	0.024/0.021	5.29/4.59	0.0706/0.0847
	Pure error	0.018/0.018	4/4	0.0045/0.0045
Total sum		0.60/0.60	12/12

Note: The numbers after “/” represent the test analysis results after excluding insignificant items; “***” means extremely significant (p < 0.01); “**” means significant (0.01 < p < 0.05); “*” means significant (0.05 < p < 0.1).

. According to the content in the table, the experimental model was significant (p < 0.01). Among the main factors in the test, the ALD (s_d) had a more significant impact on the measurement index. In the interaction term, the ALD (s_d) and the IAD (θ_c) significantly impacted the test index. The two factors had primary and secondary effects on the throwing width. The order was x₁ > x₂. After excluding the insignificant items in the variance analysis, the analysis was carried out again. The results are shown in 4. The multiple regression fitting of the test results was carried out, and the quadratic regression equation of each factor and the test index was obtained as follows:

$$Y=4.41+0.1598x_1+0.1196x_2-0.1575x_1{x}_2-0.1053x_2^2$$

(12)

where x₁ is the ALD, mm; x₂ is the IAD, °.

According to the regression analysis results, we used Design-expert13.0 software to draw the response surface of the influence of factor interaction on the test index, as shown in Figure 21. It can be seen from the figure that when the ALD and IAD increased, the throwing width first increased and then decreased.

In order to obtain the optimal combination of the two parameters, the optimization module in the Design-expert13.0 software was used to solve the regression equation of the throwing width, and the optimization constraints and objectives were selected according to the constraints of factors and actual operation needs [33]. The constraint function is as follows.

$$\{\begin{array}{l}Y=4.5\\ 360\le x_1\le 420\\ 0\le x_2\le 15\end{array}$$

(13)

After solving, the result was that the ALD was 401.05 mm, and the IAD was 9.21°. For the convenience of testing and adjustment, the factors were rounded: the ALD was 400 mm and the IAD was 9° after rounding.

3.4. Test Verification

In order to verify the reliability of the optimization, a test bench verification test was carried out on the optimized parameter combination in November 2020, and the operating condition test method was consistent with the previous design. The ALD is designed to be 400 mm, and the IAD was 9°. The test was carried out three times, the results are shown in

Table 5. The effect of throwing width after SCTD optimization.

Items	Test Results	Average Value	Matching Degree/%
	4.43
	4.39
Throwing width D/m	4.45	4.42	98.44%

. T The average value of the test results was divided by the harvester’s header width (4.5 m) to obtain the matching degree.

With the optimized SCTD, the throwing width had significantly been improved to 4.42 m, and the matching degree with the John Deere c100 combine harvester’s header width can reach 98.44%, with a high matching degree. Improvement was due to the fact that the WB designed in this chapter increased the speed of the straw when it left the crushing device. On this basis, the related parameters of the deflector of the TD were matched and optimized, thus ensuring the matching degree of straw throwing. During the whole experiment process, the improved device ran smoothly, and there was no straw clogging problem, which showed that increasing the eddy current generated by the WB in the CC had little effect on the smooth operation of the device.

4. Conclusions

In order to improve the matching degree with the header width of the combine harvester, this paper innovatively designed the WB, optimized the relevant parameters of the deflector, and improved the throwing performance of the SCTD.

(1) The structural design of the WB is divided into a windward side and a mounting side. The finite element carried out the static analysis of the WB. It was determined that the maximum stress and strain and the maximum deformation on the windward side were 43.73 MPa and 0.023 and 0.0044 mm, respectively, which could meet the material work requirements. Based on CFD, the influence of WB installation parameters on the CC fluid was analyzed. The study found that with the number of WB installed, the negative pressure effect at the CC’s inlet increased, and the velocity at the outlet increased. However, the fluid stability in the CC tended to deteriorate. There would be eddy currents around the windward side during reverse installation. Finally, the analysis determined that the number of WB to be installed was 40, and the forward installation was adopted.

(2) The non-guided stage and the guided throwing stage of straw entering the TD were analyzed. The analysis showed that the increased straw speed in the non-guided stage would make the collision point of the straw and the TD move backwards, increasing the collision angle and reducing the collision kinetic energy loss. In the guided throwing stage, the IAD (θ_c) and the ALD (s_d) affected the speed direction and kinetic energy loss when the straw was thrown, thereby affecting the throwing width of the straw.

(3) To determine the appropriate combination of IAD (θ_c) and ALD (s_d) when throwing rice straw, an optimization test of the SCTD was carried out. The results showed that when the deflector’s IAD and ALD increased, the throwing width first increased and then decreased. The optimization took the width of the harvester header as the goal to solve the simulation equation. It obtained the optimal solution of the parameters: an ALD of 400 mm and an IAD of 9°. It was verified through tests that the throwing width under the optimal parameter combination was 4.42 m, and the matching degree with the width of the harvester header was 98.44%. The throwing effect was good and met the actual needs. At the same time, it was found in the test that the adjustment of the deflector of the TD was complicated, and the throwing width was easily affected by environmental changes (wind direction changes, terrain changes). The following research should further improve these problems.