# On the Effects of Lateral Openings on Courtyard Ventilation and Pollution—A Large-Eddy Simulation Study

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## Abstract

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## 1. Introduction

- What is the effect of lateral openings on courtyard pollution and ventilation within an urban environment?
- How do lateral openings affect maximum concentrations and residence time scales within courtyards?

## 2. Methods

#### 2.1. LES Model and Numerical Experiments

#### 2.2. Balance Term Analysis

#### 2.3. Evaluation of Pollutant Residence Times

#### 2.4. Validation and Grid Sensitivity

## 3. Results

#### 3.1. Mean Flow and Scalar Distribution

#### 3.1.1. Case AR1

#### 3.1.2. Case AR3

#### 3.1.3. Case AR03

#### 3.2. Quantification of Net Scalar Transport

#### 3.3. High Scalar Concentration Events

#### 3.4. Residence Time of Pollutants

## 4. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**(

**a**) 3D view of the building setup used in case AR1 and (

**b**,

**c**) horizontal cross-sections of the simulation domains and building configuration: (

**b**) case AR1 and AR3, (

**c**) case AR03. Different shades of grey indicate building patches with a different courtyard configuration, labelled according to their lateral opening orientation. Red colors indicate locations and strength of the scalar sources. The “front”, “center” and “back” labelling indicates the front-, center-, and back-building row of the staggered building patches.

**Figure 2.**Vertical profiles of normalized (

**a**) u-component of the wind and (

**b**) its standard deviation ${u}^{\prime}$ at the center of the courtyard. The red curve shows the profiles simulated by PALM, the black curve the simulated data by Ryu and Baik [9], and the dots data from the wind-tunnel experiments by Hall et al. [2]. ${u}_{0}$ represents the mean oncoming wind speed at $z=H$ (height marked by horizontal line). The PALM profiles are time-averaged over 3 $\mathrm{h}$.

**Figure 3.**Vertical profiles of normalized (

**a**) u-component of the wind and (

**b**) its standard deviation ${u}^{\prime}$ at the center of the courtyard, as well as horizontal profiles of (

**c**) u and (

**d**) ${u}^{\prime}$ along the center line of the courtyard opening for different grid sizes. ${u}_{0}$ represents the mean oncoming wind speed at $z=H$ (height marked by horizontal line). Profiles are time-averaged over 3 $\mathrm{h}$.

**Figure 4.**$Xz$-cross-section of the mean flow field (vector arrows) and mean scalar concentration (contours) at the courtyard center for case AR1. Scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$ at $z=H$. Please note, due to symmetry, courtyards with southern openings show similar scalar distribution and wind field than those with northern openings and are hence not shown.

**Figure 5.**$Xy$-cross-section of the mean flow field (vector arrows) and scalar concentration (contours) within courtyards at $z=1.8\mathrm{m}$ for case AR1. Scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$ at $z=H$. Please note, due to symmetry, courtyards with southern openings show similar scalar distribution and wind field than those with northern openings and are hence not shown.

**Figure 6.**$Xz$-cross-section of the mean flow field (vector arrows) and scalar concentration (contours) along the center of an x-parallel street for case (

**a**) AR1 and (

**b**) AR3. Scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$ at $z=H$. The black-and-white lines indicate the positions of the buildings along the street.

**Figure 7.**$Xz$-cross-section of the mean flow field (vector arrows) and mean scalar concentration (contours) at the courtyard center for case AR3. Please note, for reasons of space, not all realizations are shown.

**Figure 8.**$Xy$-cross-section of the mean flow field (vector arrows) and mean scalar concentration (contours) within courtyards at $z=1.8\mathrm{m}$ for case AR3. Scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$ at $z=H$. Please note, for reasons of space, not all realizations are shown.

**Figure 9.**$Xz$-cross-section of the mean flow field (vector arrows) and scalar concentration (contours) at the courtyard center for case AR03. Please note, for reasons of space, not all realizations are shown.

**Figure 10.**$Xy$-cross-section of the mean flow field (vector arrows) and scalar concentration (contours) within courtyards at $z=1.8\mathrm{m}$ for case AR03. Scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$ at $z=H$. Please note, for reasons of space, not all realizations are shown.

**Figure 11.**Net transport of scalar into the courtyard volume through the lateral (abscissa) and the top opening (ordinate), for (

**a**) case $\mathrm{AR}=3$, (

**b**) $\mathrm{AR}=1$, and (

**c**) case $\mathrm{AR}=0.3$, averaged over 2 h of simulation time. Net transport is normalized with the background concentration. Positive (negative) values of net transport indicate increasing (decreasing) scalar concentration within the courtyard cavity. The dashed horizontal and vertical lines indicate zero values.

**Figure 12.**Probability density function of scalar concentration at courtyard center at $z=1.8\mathrm{m}$ for (

**a**) case $\mathrm{AR}=3$, (

**b**) $\mathrm{AR}=1$, and (

**c**) case $\mathrm{AR}=0.3$. The scalar concentration is normalized with the background concentration ${s}_{\mathrm{B}}$, which is the domain-averaged concentration at $z=H$.

**Figure 13.**Probability density functions of particle residence times within the courtyard volume, for (

**a**) case AR3, (

**b**) AR1, and (

**c**) case AR03.

**Table 1.**Courtyard aspect ratio (AR) and domain size of the three simulated cases. H indicates the building height (or courtyard depth) and W indicates the courtyard width.

Case | AR | H (m) | W (m) | Domain Size ($\mathit{x}\times \mathit{y}\times \mathit{z}$) (m) |
---|---|---|---|---|

AR1 | 1 | 20 | 20 | $480\times 400\times 531$ |

AR3 | 3 | 60 | 20 | $480\times 400\times 531$ |

AR03 | 0.3 | 20 | 60 | $480\times 600\times 531$ |

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**MDPI and ACS Style**

Gronemeier, T.; Sühring, M. On the Effects of Lateral Openings on Courtyard Ventilation and Pollution—A Large-Eddy Simulation Study. *Atmosphere* **2019**, *10*, 63.
https://doi.org/10.3390/atmos10020063

**AMA Style**

Gronemeier T, Sühring M. On the Effects of Lateral Openings on Courtyard Ventilation and Pollution—A Large-Eddy Simulation Study. *Atmosphere*. 2019; 10(2):63.
https://doi.org/10.3390/atmos10020063

**Chicago/Turabian Style**

Gronemeier, Tobias, and Matthias Sühring. 2019. "On the Effects of Lateral Openings on Courtyard Ventilation and Pollution—A Large-Eddy Simulation Study" *Atmosphere* 10, no. 2: 63.
https://doi.org/10.3390/atmos10020063