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Perforation metal plates with dense holes are often used as external curtain walls of high-rise buildings. When air flow passes through these holes at a high speed, complex vortex is generated and causes a significant issue of wind-induced noise. In this study, both Reynolds-averaged Navier–Stokes (RANS) simulations and large-eddy simulations (LES) were conducted to study flow around high-rise buildings with an external sunshade curtain wall. First, wind speed distributions at the height of a typical level under 16 wind directions were acquired. Then, the maximum wind speed ratio and its corresponding azimuth were identified. Second, the sound pressure levels in the vicinity of the shading devices with two types of perforation plate schemes were calculated to evaluate the acoustic characteristics by using the FW-H equation to simulate sound generation and propagation. The results indicate that the maximum wind speed around the buildings exists at the building corners, and the maximum wind speed ratio is 2.8 observed at 0-degree wind direction. Under two different wind conditions, the aeroacoustic performance of perforation plate is enhanced with reducing end plate size and increasing aperture size. The overall sound pressure level (OSPL) and A-weighted sound pressure level (ASPL) around the shading devices are 80 dB and 68 dB(A), respectively, for the improved perforation plate scheme under the 1-year return period maximum speed, which are changed to 58dB and 45dB(A) under the annual average speed. Therefore, it is believed that perforation plates with small end plate size and large aperture size are desirable for the noise prevention design of shading devices.

Efficient use of energy during the entire life cycle of buildings is imperative due to increasing energy demands in the construction industry [

Curtain wall system with shading devices for energy conservation in high-rise buildings.

Shading devices outside the curtain wall of buildings

Perforated plates and curtain walls

As reported in a number of recent studies, noise pollution continues to be a major health issue in urban area, especially areas close to road traffic[

The research methods for wind-induced noise are similar to other studies in the field of wind engineering, and they are classified into three approaches: field measurement, wind tunnel test, and numerical simulation. Usually, wind-driven ambient noise in the natural environment is generally obtained by the method of field measurement [

Under this background, numerical simulation has become an important approach to study wind-induced noise. With the rapid development of computational fluid dynamics, significant progress has been made in the numerical simulation of wind-induced noise, and its application in the field of engineering is becoming increasingly extensive, such as in the study on aerocrafts [

In this paper, three buildings with a height of about 100m in Guangzhou of China are selected as research objects, shown in Figure

In the field of simulation of the flow around buildings, a Newton fluid with a shear stress is considered as an incompressible fluid. The basic governing equation is the Navier–Stokes equation, including the continuity and momentum equations. The commonly used methods for turbulence simulation include the Reynolds-averaged Navier–Stokes method (RANS) and large-eddy simulation (LES). In view of the two scales of flow phenomena and efficiency of computation, the RANS method is used to calculate the flow field around the buildings. The LES method is used to calculate the flow field around the perforation plates. Among these, formula (

The Fowcs Williams–Hawkings (FW-H) equation has been used to simulate the generation and propagation of sound, and the sound generated by an equivalent noise source is predicted based on the acoustic approximation model of the Lighthill equation. In this method, the near-field flow is directly obtained by the governing equation, and the acoustic pressure data are obtained by solving the integral of the other equations. When the sound pressure is calculated by integration with the FW-H equation, the time delay between the firing and reception is taken into account by the forward projection. Thus, the sound pressure and unsteady flow field are calculated concurrently, and then the sound pressure level is obtained.

The FW-H equation is derived from the continuity equation and Navier–Stokes equation; it is as follows:

The factors determining the flow field and sound pressure field around the external sunshade include two main aspects: the overall flow field around the buildings and local flow around the perforation plate cavity. The building exterior flow field is determined by a wide range of building environments. To obtain detailed and accurate information of the flow, the group building model within a radius of 600 m around was sketched on the ICEM platform in ANSYS FLUENT 14.0, where the dimension of computational domain was 3000 m × 3600 m × 500 m (

Group buildings model and the computational domain.

In addition to dimension of computational domain, simulation workload is determined by grid number, which is in close relation to grid resolution. Meanwhile, grid quality is an important indicator, in relation to simulation convergence and local accuracy. The computational domain is discretized by tetrahedral unstructured grids, the minimum mesh size of the building surface is 1 m, and the total mesh number is approximately 10 million, which is shown in Figure

Grids on the surfaces of the buildings.

The wind profile of large-size wind events in the atmospheric boundary layer (ABL) usually obeys logarithmic law. However, a power law formula that can estimate changes in mean wind speed with height under large-size synoptic winds is commonly used due to its simple expression [

Turbulent kinetic energy

Wind flow in CFD simulation has been considered as turbulent and steady but incompressible viscous fluid, which is characterized by Navier–Stokes equations. RNG

Figure

Schematic of the wind angles.

The wind velocity ratio (VR) is employed to assess the airflow performance of the proposed construction area and the impact between the proposed construction area and its surroundings. VR is defined by the following formula:

The wind speed distribution around the building can be obtained by combining the simulated wind speed ratio with the local wind climate data. Guangzhou is located in the subtropical monsoon area, and its prevailing wind direction changes significantly in the seasons. According to the statistics of the historical records of Guangzhou meteorological station (from 1962 to 2015), the prevailing wind direction in Guangzhou is north azimuth with an occurrence probability of 12.4%, followed by the southeast azimuth with an occurrence probability of 8.6%. Furthermore, wind speeds at a one-year return period under each wind direction can be calculated. Both the occurrence probability of wind directions and wind speeds at a one-year return period under 16 wind directions are shown in Figure

Occurrence probability of wind directions and speeds at a one-year return period under 16 wind directions in Guangzhou.

Occurrence probability of wind directions

Wind speeds(m/s) at the one-year return period

The wind speed distribution of a typical level under 16 wind directions is extracted. Figure

Contours of the wind speed ratio distribution around the buildings at typical wind angles (

The maximum wind speed ratio

Maximum wind speed ratio

| | Speed(m/s) | Location | | | Speed(m/s) | Location |
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0 | 2.80 | | Tower B | 180 | 2.03 | 13.1 | Tower A&B |

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22.5 | 2.33 | 19.8 | Tower A | 202.5 | 0.56 | 3.6 | Tower B |

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45 | 2.07 | 14.4 | Tower B | 225 | 1.35 | 8.6 | Tower B |

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67.5 | 2.05 | 16.9 | Tower A&B | 247.5 | 1.46 | 8.4 | Tower B |

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90 | 1.90 | 15.9 | Tower A | 270 | 1.83 | 10.1 | Tower B |

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112.5 | 1.85 | 13.8 | Tower C | 292.5 | 1.66 | 8.4 | Tower C |

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135 | 1.83 | 14.1 | Tower C | 315.5 | 1.37 | 8.7 | Tower B&C |

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157.5 | 2.11 | 14.9 | Tower B | 337.5 | 1.76 | 15.1 | Tower A |

Based on the results of analysis of the entire flow field around the building, the wind speed information of the typical area with maximum wind speed is extracted and the local perforation plate unit was established in detail. Then the flow field analysis and unsteady LES are performed to obtain the small-scale vortex shedding of flow around the perforation plate. Finally, the FW-H equation is solved to simulate sound generation and propagation, and the wind-induced overall sound pressure levels (OSPL) and A-weighted sound pressure levels (ASPL) are calculated to evaluate the acoustic characteristics.

The vertical sunshade component of the facade of the building curtain is a triangular hollow body surrounded by perforation aluminum plates, and the cross-section of the component is shown in Figure

External sunshade perforation structure diagrammatic sketch.

Cross sectional

Hole arrangements of the perforation plate

A physical model is established according to the actual geometry and size of the sunshade, where the dimension of computational domain was 5.0 m × 1.0 m × 5.0m (L × W × H). The computational domain is discretized by tetrahedral unstructured grids, the minimum mesh size of the perforation plate is 0.001 m, and the total mesh number is approximately 4.63 million, shown in Figure

Computational domain, grid distribution, and sound pressure receiving points' diagrammatic sketch.

Computational domain

Grid distribution

Receiving points

The numerical calculation is performed in two stages. First, the steady-state flow field distribution and noise source location are obtained by the steady-state analysis of the flow field. In the second stage, LES is used to obtain the unsteady results. In the unsteady state simulation, the time step is set at

Each wall of the perforation plate is set as a noise source when the unsteady sound pressure field is simulated, and the sound pressure signal files are stored after every 500 time steps. After the calculation, a series of sound pressure time history data can be obtained. To analyze the noise generated by the flow field around the sunshade, a series of acoustic pressure receiving points (receiver) are defined on the windward side of the perforation plate, inside of the cavity, leeward side, and position of the attachment. The maximum distance between the holes and receivers is 1.25m. The exact location of the receiving points is shown in Figure

OSPL can be obtained by accumulating the sound pressure level produced by all sources at the receiving point. Nevertheless, because the response of the human ear to the sound at different frequencies is different, the OSPL which is obtained by accumulating all the sound pressure at all frequencies cannot fully reflect the nonlinear response of the human ear to the sound frequency. Compared with the overall sound pressure level, A-weighted sound level reflects the human ear frequency response more accurately. When calculating the A-weighted sound level, the sound pressure level is reduced according to the formula before the low-frequency and high-frequency sound pressure levels are added together.

For the maximum wind speed condition at 1-year return period, the OSPL and ASPL at the receiving points near the shading devices under the two schemes are shown in Figures

Comparison with sound pressure level of each receiver for the maximum wind speed condition at 1-year return period.

OSPL

ASPL

For the annual average wind speed condition, the OSPL and ASPL at the receiving points near the shading devices under the two schemes are shown in Figures

Comparison with sound pressure level of each receiver for the annual average wind speed condition.

OSPL

ASPL

To analyze the mechanism of wind-induced noise in the two schemes, the distribution curve of sound pressure intensity in each frequency range could be obtained by fast Fourier transform of the sound pressure time history obtained at each monitoring point. The 1/3 octave sound pressure distributions of the key points R1, R7, and R10 under two schemes are given in Figures

Sound pressure level distribution of typical receivers under scheme 1.

Receiver 1

Receiver 7

Receiver 10

Sound pressure level distribution of typical receivers under scheme 2.

Receiver 1

Receiver 7

Receiver 10

In this study, Reynolds-averaged Navier–Stokes (RANS) simulations, large-eddy simulations (LES), and Lighthill’s acoustic method have been conducted to study flow around high-rise buildings with external sunshade curtain wall. Both the wind speed distributions around the buildings and the sound pressure levels in the vicinity of the shading devices have been analyzed. The main findings are summarized as follows.

(1) According to the statistics of the historical records of Guangzhou meteorological station, the maximum wind occurs in the north azimuth with a speed of 9.21m/s at 1-year return period. The average annual wind speed of Guangzhou is only 1.9m/s.

(2) The maximum wind speed around the buildings exists at the building corners under all simulated 16 wind directions. The maximum wind speed ratio is 2.8, which occurs at 0 degree wind direction.

(3) The overall sound pressure level (OSPL) and A-weighted sound pressure level (ASPL) around the shading devices are 80 dB and 68 dB(A) for perforation plate scheme 2 under the 1-year return period maximum speed, which are reduced to 58dB and 45dB(A) under the annual average speed.

(4) The aeroacoustic performance of perforation plate scheme 2 is better than that of perforation plate scheme 1, because wind-induced noise caused by the shading devices has been reduced effectively. Therefore, it is believed that perforation plates with small end plate size and large aperture size are desirable for the noise prevention design of shading devices.

The data used to support the findings of this study are available from the corresponding author upon request.

The authors declare that there are no conflicts of interest regarding the publication of this article.

This research was funded by the National Natural Sciences Foundation of China (NSFC) (51778199), the Natural Science Foundation of Guangdong Province (2017A030313324), and the National Key Research and Development Program of China (2016YFC0701107).