*2.3. Simulation*

To better observe the movement of soil and straw in the simulation, we selected the velocity clouds from the simulation with different angles of blade rotation and placed them in Figure 7.

The velocity of the model is represented by the color-changing legend. The velocity ranges from green to red is 0–1 m/s, which means the velocity is the same as the forward direction. The velocity ranges from green to blue is 0–−1 m/s, which means the velocity is opposite to the forward direction. L refers to the whole tillage layer, L0 represents the straw, and L1–L4 represents the soil from 0–50 m, 50–100 mm, 100–150 mm, and 150–200 mm below the horizontal surface, respectively.

It can be seen from L: At 0◦ the rotary blade touches the soil, the soil and straw on the side edge are first disturbed by the force of the rotary blade, L1 soil, and L0 straw splash. The disturbed area has a definite initial velocity and appears yellow, representing a low value; At 90◦, the rotary blade has fully entered the soil. The color of the soil and straw starts to change, which indicates that the number of particles gaining velocity starts to increase. At L, L0, and L1, it is clearly observed that the soil and straw near the rototiller knife are red and dark blue in color, with the majority of blue particles, which indicates that the velocity starts to increase and most of the soil acquires the initial velocity backwards. Concurrently, the color of the soil and straw on the other side was light blue, indicating that the latter was significantly more disturbed than the former, and the velocity was negative. At 180◦, the rotary blade was about to break out of the soil. The soil near the front section of the rotary tiller is dark blue and blue, which means that the rotary tiller throws the soil in the lower part of the plow layer backwards and upwards. The color of the soil near the side edge of the rototiller is red, illustrating that the soil in this position moves forward with the rototiller. At this time, the color of the soil with greater disturbance on the left side changes to yellow, indicating that this part of the soil starts to move forward and gradually returns to its original state. The color of the thrown soil and straw particles changed after the rotary tillage knife came out of the soil, indicating that the soil and straw continued to move in the direction of the speed obtained when thrown and finally fell into the ground. The color of the disturbed area is dark green, demonstrating that the velocity returns to 0.

L0 and L1 received a significant disturbance. The soil close to the center is taken to L2 and L3 when the blade starts to cut the soil, and the soil far from the center is thrown upward and backward and finally falls into L2 and L4. L2 and L3 are disturbed similarly to L1 and L0. The soil far from the center is thrown out and finally falls into L1 and L3; For L4, the soil disturbance is minimal, but a small part of the soil far from the center is still affected by the force and acquires a certain initial velocity and flow.

**Figure 7.** Velocity of soil and straw in different tillage layers during single blade operation.

The migration of the soil between L1 and L4 gives a side view of the mixing state of the tillage layer after rotary tillage. The more the layers migrate, the further they are from their original position and the better the mixing of the tillage layer. When the rototiller knife enters the soil again, it continues to disturb the soil after tillage, causing the straw to rebound and thus causing it to continue to migrate in the direction of the initial velocity. The soil is significantly displaced by the action of the rotary cutter, and the movement of the soil particles causes more significant displacement of the straw as the mechanical properties of the straw material are lower than those of the soil particles. The movement of the soil particles causes the straw to move more significantly due to the lower mechanical

properties of the straw material than the soil particles. When the force is greater than the ultimate strength of the bond, the soil particles are separated and fractured, which means that the soil particles that were originally connected by the bond are separated and move to a different layer; as the tillage continues to advance, some of the particles will be separated by secondary cutting. During the tillage process, the soil is disturbed in different areas of the rototiller, with a clear range of disturbance away from the center. The surface of the tilled soil shows some undulations, mainly due to the fact that the tillage process has changed the surface form of the original soil, and there is a certain friction effect between the soil particles, which makes it difficult to recover the initial form.
