## 6 Conclusions  
This research systematically undertakes performance improvements on both the impeller and protective cover of a stand fan through the rigorous numerical simulation approach. The flow features used for evaluation include the total flow rate, the uniformity of the airstream at the outlet, noise generation, and the energy efficiency. With the aid of a comprehensive parametric study, the optimal fan design is obtained by selecting an appropriate set of design parameters regarding the impeller blades and the protective cover. Furthermore, mockups of the optimal impeller and protective cover are fabricated via the CNC technology for testing the fan performance. Later, the simulation results are utilized to compare with the experiment results to validate the accuracy and reliability of the CFD approach. The experiment results are summarized below.  
First of all, based on the measurement, the optimal design fan is obviously superior to the original design by an impressive 54% enlargement on the flow rate while the maximum velocity is slightly smaller than that of the reference fan. It follows that the velocity distribution of the optimal fan is quite uniform, flat shaped, and widely extended. On the other hand, although the redesign fan #1, which is constructed by integrating the optimal impeller and reference protective cover, can increase the flow rate by 47%, the outflow velocity distribution is chaotic and not uniform. Moreover, a comparative analysis of the measurements of the redesign fans #1 and #2 apparently implies that the major influence caused by the impeller redesign is the enlargement of the flow rate, while the change or guiding of the flow direction is the key effect induced by the cover modification. In addition, the trends of the experimental and simulation results are in good agreement, and the deviations between them are found to be within an acceptable range. Besides, the flow field distribution of the CFD calculation is consistent with the experimental result; thus, the accuracy and reliability of the numerical simulation are verified here.  
Consequently, this work successfully designs a superior stand fan for delivering a significantly enlarged airstream with a much more uniform and extended velocity distribution, which enables its average flow velocity to be around 1 m/s, preserving the comfortable feeling for the human being. In summary, this research establishes a reliable and systematic scheme to design the stand fan by integrating the numerical, CNC fabrication, and the experimental tools. Also, the corresponding performance influences caused by several important parameters are analyzed and summarized to serve as the design reference for the stand fan.  
The authors would like to gratefully acknowledge the financial support provided by the Ministry of Science and Technology in Taiwan under the contracts of MOST 104-2221-E-011-095 and 105-2221-E-011-067.  
[PERSON] conceived and wrote the paper; [PERSON] conducted the numerical work and provided useful suggestions for the preparation of the paper; [PERSON] and [PERSON] performed the simulations and measurements, and revised the paper; [PERSON] offered the mockup fabrications for performance measurements and analyzed the data.  
The authors declare no conflict of interest.