Development of a Metasilencer Considering Flow in HVAC Systems

Round 1

Reviewer 1 Report

A silencer based on the labyrinthine structure is designed and its noise reduction performance for a vehicle HVAC system is investigated in this manuscript. In general, the manuscript is well prepared, and the detailed comments are as follows.

(1)  The “inlet”, “outlet”, “suction port duct” and “the discharge port mounting the upper HVAC duct” should be indicated in Fig. 1.  

(2)  The noise spectrum is suggested to be added in Fig. 2 to show more details of the characteristics of the HVAC noise.

(3)  As stated from line 86 ~ line 89, the measured HVAC noise is dominant below 1100 Hz, and the target frequency range is chosen as 800 ~ 1100 Hz. The authors need to explain why the frequency band below 800 Hz is not selected in the target range.

(4)  The authors must explain where the straight pipe in simple model in Fig.3 may be used in the HVAC system shown in Fig. 1. 

(5)  The reason for setting the dimension of the curved inlet as 5 mm and choosing the volume weight of the sound absorbing material as 30g/L should be explained in detail. 

(6)  Fig. 14 should be replaced by Fig. 16 for conciseness, as the two curves in Fig. 14 are also presented in Fig. 16. It is also found that the noise is reduced at most frequencies under investigation in the case of W/ metasilencer 1, and this is achieved by 3 contributors, the metasilencer in Fig.8 (a), the curved inlet structure and the filled sound absorbing material in Fig. 8(b). A new curve should be added (metasilencer with only the curved inlet) to discuss the effect of the filled sound absorbing material.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

1.The silencer was set to reduce noise in the frequency range of 800-1100Hz. Why not set the metasurface target frequencies at 800Hz and 1000Hz.

2.In Figure4. the positions of the metasurface for  900Hz and 1000Hz should be marked in words.

3.The influence of the length of the metasurface along the flow direction on the noise reduction should be discussed.

4. Authors should discuss the influence of the number of unit cells covering 180 deg on the noise reductio.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The review comments have been well replied, and the manuscript is  recommended to be accepted for publication.