# Optimization of Customized Industrial Pneumatic Nozzle to Reduce Noise Emissions
## 3 Results and Discussion
### CFD Analysis Results
In fact, in the experimental setup, the pressure gauge was not located exactly on the nozzle inlet. Hence, there was a difference between the two flow rates, but the results were coherent: the experimental inlet pressure was slightly lower than 0.5 bar because of the pipe present between the pressure gauge and the nozzle. Hence, the simulated flow rate was a bit higher than the experimental rate. By repeating the same test on models M3 and M6, mass flow rates of 0.0035 and 0.0030 kg/s were obtained. The increase in the flow rate in model M3 can be explained by the fact that shorter final ducts present a lower resistance; consequently, the flow rate increases at the given supply pressure. \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Model No.** & **R** & **M2** & **M3** & **M6** \\ \hline Peak of outlet velocity (m/s) & 242 & 91 & 224 & 234 \\ Absolute peak of turbulent kinetic energy (m\({}^{2}\)/s\({}^{2}\)) & 3.71 \(\times\) 10\({}^{3}\) & 3.77 \(\times\) 10\({}^{2}\) & 3.48 \(\times\) 10\({}^{3}\) & 2.76 \(\times\) 10\({}^{3}\) \\ Peak of turbulent kinetic energy in the mixing zone (m\({}^{2}\)/s\({}^{2}\)) & 3.71 \(\times\) 10\({}^{3}\) & 3.77 \(\times\) 10\({}^{2}\) & 2.60 \(\times\) 10\({}^{3}\) & 2.76 \(\times\) 10\({}^{3}\) \\ Average potential core length (mm) & 8.5 & 17.5 & 11 & 7.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Numerical results of CFD simulations for models M2, M3, and M6. Figure 11: Model M6: turbulence field on the left, velocity field on the right. Based on these results, a match between the experimental outputs and CFD simulations was found. However, the final aim was to develop a CFD model that also reflects the actual functioning of the machinery. The Simcenter Amesim circuit made it possible to reproduce the conditions that were most similar to the actual conditions and calculate the exact supply pressure during the firing of the shots (that is, 1.3 mbar). This value was very low but not unrealistic; in fact, the valve-opening time was 22.5 ms in a period of 0.3 s. The nozzle was very short and in direct contact with the atmosphere; hence, it was likely to have such a low inlet pressure. This pressure was then set as the inlet pressure in the ANSYS model, and the simulation was performed. The shapes of the turbulence and speed domains were not altered when compared with the values in the previous simulations, but their intensities were decreased. For example, in Figure 12, it is possible to see that the results of model M3 obtained under the above conditions are comparable to those in Figure 10.  
With these boundary conditions, it was also possible to compare the ANSYS-simulated speed with that calculated by the Simcenter Amesim software for the reference model to verify whether the two methods were valid and equivalent (Figure 13). The values obtained in the two simulations were very similar: the peak speed obtained with the Simcenter software was equal to 14.7 m/s, whereas that obtained with the ANSYS simulations was 14.5 m/s. Figure 12: Model M3: turbulence field on the left, velocity field on the right (supply pressure: 1.3 mbar). Figure 13: Velocity field for the reference model under actual operating conditions. These values were also consistent with the actual values. The actual velocity was not known, but an average minimum speed of approximately 6 m/s was calculated by dividing the distance between the nozzle and rotating cylinder by the period of operation. Considering that the process is highly impulsive, the peak speeds obtained are realistic. For the reference model, the flow rate calculated by the Simcenter circuit was 0.125 g/s, whereas that obtained by ANSYS was 0.137 g/s. The two flow rates were reasonably close, but the Simcenter flow was impulsive with an opening time of 22.5 ms. Hence, it was not possible to reach the steady-state value; only a lower peak could be attained. ANSYS simulates a steady flow; hence, its value was correctly higher and remained constant. Model M3 was used for further analysis.