**4. Conclusions**

To further apply an unpowered ventilator in different buildings or tunnels and quickly exhaust smoke during building and tunnel fires, in this study, we conducted a series of experiments to investigate its ventilation and smoke exhaust performance. Our conclusions are summarized as follows:


The natural ventilator constructed in this study was a swirling natural ventilator 6. This type of unpowered ventilator was also used in the smoke exhaust experiments. Therefore, we conclude that this type of ventilator is more suitable for selected flow natural ventilators, and the optimized natural ventilator is suitable for smoke exhaust from buildings or tunnels. However, in other scenes (such as factories), the optimized unpowered ventilator has not been tested, which is a future research direction for natural ventilator smoke exhaust.

**Author Contributions:** M.L.: Conceptualization, Methodology; Y.Q.: Formal analysis, Writing-Original Draft; X.W.: Investigation; W.S.: Formal analysis; Y.Z.: Writing-Reviewing and Editing; L.Y.: Supervision, Methodology, Resources. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is funded by the Science and Technology Project of Department of Transportation of Yunnan Province under grant No. [2013]261.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
