# Numerical Simulation and Optimization of the Airflow Field of a Forage Drum Mower
## 5 Verification Experiments
### Test Bench Verify Experiments  
Although the prediction model has been verified in the above simulation verification experiments, neither the numerical simulation results nor the model prediction results have been compared with the actual airflow around the cutter, so it is necessary to build an actual test bench for measurement to verify the correctness of the above results. According to the optimal structural parameters as determined through the orthogonal test, a double-drum cutter test bench was built (Figure 8). The cutter was equipped with twisted blades, tilting discs, and guide plates. The twist angle was \(8^{\circ}\) for the blade, the tilt angle was \(4^{\circ}\) for the discs, the number of guide plates was 2, and the rotational speed of the discs was adjustable.  
During the test, the disc was adjusted to three different rotational speeds: high, medium, and low. After the disc speed was stabilized, the photoelectric tachometer was used for measurement and recording. Then, according to the position and method of airflow velocity measurement, as shown in Figures 5-7, the handheld hot-wire anemometer (TES-1314) was used to measure the airflow velocity at each measurement point. Then, the velocities of the gathering, lifting, and feeding airflows were calculated. Table 5 shows the results of the comparison between the airflow velocity predicted by the regression model and that as measured by the test bench at different disc speeds.  
By comparing the results in Tables 2, 4 and 5, it can be found out that the airflow velocity measured by the test bench is basically similar to that of the numerical simulation, and the variation trend of the airflow velocity under different disc speeds is also consistent, indicating that the numerical simulation results are reliable. In addition, the values of measured airflow velocity are basically consistent with that obtained by the regression model too, a further calculation was performed to reveal that compared with the results  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Indexes** & **Simulated Values** & **Model Predicted Values** & **Error (\%)** \\  & **(m/s)** & **(m/s)** & **Error (\%)** \\ \hline Gathering airflow velocity \(v_{g}\) & 4.1857 & 4.3355 & \(+3.58\) \\ Lifting airflow velocity \(v_{l}\) & 7.5814 & 6.6416 & \(-12.4\) \\ Feeding airflow velocity \(v_{f}\) & 11.4379 & 10.8584 & \(-5.07\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Predicted value and result of the Verify test.  
Figure 8: Test bench of double-drum cutter. 1. Gearbox 2. Cutter 3. Frame 4. Motor 5. Frequency converter 6. Shaft coupling.  
of airflow velocity measurement, the average error of the regression model is \(-5.83\%\) for the predicted velocity \(v_{g}\) of the gathering airflow, \(2.37\%\) for the predicted velocity \(v_{l}\) of the lifting airflow, and \(4.20\%\) for the predicted velocity \(v_{l}\) of the feeding airflow. These results confirmed the validity of the prediction model. Based on the above comparison and discussion, the airflow parameters in numerical simulations, model predictions, and actual measurements are relatively consistent; both numerical simulation and prediction model can provide support to evaluate the airflow field around the double-drum cutter. However, there are still limitations to the prediction model. Since this study is aimed at a specific structure of cutter (double-drum cutter with tilting disc, twisted blade, and guide plates) and the prediction model is based on this structure, the model could not be used for other structures of cutters, in that case, a new numerical simulation model is needed to analyze the airflow field.