Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment
Abstract
:1. Introduction
2. Scaled Outdoor Experiment
2.1. Description of the Experiment Setup
2.2. Experimental Results
3. CFD Methodology
3.1. CFD Models
3.2. Inverse Identification of Source Location Method in Dynamic Airflow Fields
- The unsteady airflow fields at min in the forward simulation are used. In the forward simulation, the airflow field is calculated every 1 min. During min, the airflow fields are simulated 30 times to obtain 30 airflow fields in this period. The start time of the forward simulation is set to . Subsequently, using the 1 min average outdoor wind speed as the inlet boundary condition, the airflow field can be obtained. The final airflow field is obtained after 30 forward simulations at . Subsequently, the forward simulation is completed.
- Probability-based inverse modeling starts from the backward time step and the final airflow field . Release one unit of tracer gas CO2 in the monitored room that exceeds the concentration limit and obtain SALP1 of the final time step .
- The calculation is stopped immediately after the convergence of SALP1 is achieved. The SALP1 values of all the grid nodes in the calculation domain are exported. Subsequently, by inverting the airflow field , airflow field is imported to SALP1 and continuously calculated to obtain SALP2.
- Each SALP is obtained by inverting 30 airflow fields in the forward simulation. The adjoint probability of the final pollution SALPn under a dynamic airflow field is then obtained.
- Finally, the CALP was calculated by combining the SALP with the concentration data from multiple monitoring points.
4. Accuracy of the CFD Simulation
4.1. Simulation Setting
4.2. Grid Sensitivity Test
4.3. Model Validation
5. Results and Discussions
5.1. Airflow Fields
5.2. Temperature Fields
5.3. Pollutant Dispersion inside the Street Canyons under Time-Varying Wind Conditions
5.3.1. Interunit Dispersion on the Leeward Side of Building B
5.3.2. Ventilation Rates of Rooms in the Building B
5.4. Results of Pollutant Source Identification
5.4.1. Case 1: Abnormal Concentration Values in Monitored Rooms BL2, BL3, and CW3
5.4.2. Case 2: Abnormal Concentration Values in Monitored Rooms BL3 and BL4
5.4.3. Case 3: Abnormal Concentration Values in Monitored Rooms BW2 and BW1
6. Conclusions
- The change in the boundary wind speed affects the airflow structure inside street canyons. The wind speed at each position in the street canyon fluctuates with changes in the boundary wind speed. Owing to vortex movement and the centrifugal effect, the wind speed at the top and bottom of the street canyons is greater than that in the middle.
- The outdoor wind with a lower temperature exchanges heat with the air at a higher temperature inside the street canyons, thereby removing part of the heat and reducing the heat of the air inside the street canyons. Moreover, the opening of the room produces some air disturbance, which is conducive to heat exchange between the air near the opening and the outdoor wind.
- The fluctuation of the upper wind speed influences the diffusion of the tracer gas, and the ventilation performance of the rooms in the middle of the street canyon is more stable than those in the top and bottom areas.
- We propose an improved adjoint probability method under dynamic wind conditions. Three cases were tested to verify the applicability of this method. The results showed that with limited pollutant information (two or more), all three cases could successfully identify the source location, indicating that this method can be used to locate pollutant sources in street canyons under time-varying inflows in coupled indoor and outdoor conditions.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Nomenclature
Greek symbols | |||
Turbulent viscous dissipation rate () | |||
Model constant | |||
Model constant | |||
Von Karman constant, 0.41 | |||
Density () | |||
molecular viscosity () | |||
Adjoint probability | |||
Nomenclature | |||
Cross-sectional area () | Denotes time | ||
Constant, 0.09 | turbulence intensity, 4% | ||
Transient concentration | Velocity component | ||
Molecular diffusion coefficient () | Empirical coefficient (0.245) | ||
Pressure (Pa) | Wind velocity at height H (m/s) | ||
Mixing length, 0.4 m | Reference wind speed (2.46 m/s) | ||
Turbulent kinetic energy () | Height of the street canyon (1.2 m) | ||
Scale of strain rate | Standard adjoint location probability | ||
Stain-rate tensor | Conditioned adjoint location probability |
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Period | Room | Time over 10 ppm | Concentration over 10 ppm | Maximum Value | Final Value |
---|---|---|---|---|---|
10:40:05–11:09:55 Source room: BW1 | - | - | - | - | - |
11:32:05–12:01:56 Source room: BW2 | BW1 | 11:34:30 | 10.7 ppm | 58.6 ppm | 40 ppm |
12:27:06–12:56:55 Source room: BW3 | BW2 | 12:28:45 | 30.4 ppm | 88 ppm | 63.5 ppm |
BW1 | 12:31:35 | 10 ppm | 15 ppm | 13 ppm | |
13:19:05–13:48:56 Source room: BW4 | BW3 | 13:21:00 | 30.4 ppm | 49 ppm | 37 ppm |
BW2 | 13:20:10 | 10.2 ppm | 13 ppm | 10.5 ppm | |
14:16:06–14:45:55 Source room: BL1 | BL2 | 14:18:28 | 12.8 ppm | 39.7 ppm | 36.1 ppm |
BL3 | 14:22:20 | 10 ppm | 16 ppm | 12 ppm | |
CW3 | 14:30:58 | 10 ppm | 13 ppm | 8 ppm | |
CW1 | 14:31:34 | 10 ppm | 12.5 ppm | 7 ppm | |
BW2 | 14:42:16 | 10 ppm | 10 ppm | 6 ppm | |
15:11:04–15:40:55 Source room: BL2 | BL3 | 15:12:34 | 16 ppm | 154.6 ppm | 130 ppm |
BL4 | 15:15:05 | 10 ppm | 26.8 ppm | 21.5 ppm | |
16:13:04–16:42:56 Source room: BL3 | BL4 | 16:15:44 | 10 ppm | 90 ppm | 66.3 ppm |
17:09:04–17:39:00 Source room: BL4 | - | - | - | - | - |
Temperature (°C) | Outdoor Air (1.8 m) | Acrylic Wall (0.15 m, 0.45 m, 0.75 m, 1.05 m) | Concrete Wall | Model Roof | Concrete Roof |
---|---|---|---|---|---|
Period | |||||
10:40:05–11:09:55 | 35.0 | 35.4 | 38.5 | 41.8 | 51.5 |
36.0 | |||||
35.5 | |||||
35.4 | |||||
11:32:05–12:01:56 | 35.1 | 35.9 | 39.5 | 40.6 | 45.1 |
36.4 | |||||
35.9 | |||||
35.7 | |||||
12:27:06–12:56:55 | 36.4 | 38.1 | 40.9 | 42.9 | 49.4 |
37.8 | |||||
37.1 | |||||
37.0 | |||||
13:19:05–13:48:56 | 36.0 | 38.2 | 42.2 | 41.2 | 51.2 |
38.3 | |||||
37.5 | |||||
37.3 | |||||
14:16:06–14:45:55 | 36.1 | 39.0 | 42.8 | 41.0 | 49.1 |
38.9 | |||||
37.9 | |||||
37.6 | |||||
15:11:04–15:40:55 | 35.7 | 39.3 | 44.1 | 40.8 | 48.5 |
39.5 | |||||
38.7 | |||||
38.2 | |||||
16:13:04–16:42:56 | 34.6 | 36.9 | 42.5 | 38.4 | 44.5 |
37.6 | |||||
36.8 | |||||
36.2 | |||||
17:09:04–17:39:00 | 33.5 | 34.4 | 37.4 | 35.5 | 38.3 |
34.7 | |||||
34.3 | |||||
33.8 |
Inlet | Velocity Inlet (Wind Speed Values at 1.2 m from the 10 m Wind Mast on 9 June 2019, 14:16:05–14:31:05, as Shown in Figure 5) |
---|---|
Outlet | Pressure outlet |
Near-Wall Treatment | Standard Wall Functions |
Temperature | Average temperature of different areas in the street canyons in different periods (as shown in Table 2) |
Building walls | Non-slip for wall shear stress |
Turbulent kinetic energy | |
Turbulent viscous dissipation rate | |
Constants | = 0.09 |
= 0.9 m | |
= 0.6 | |
= 6.7 m/s |
Room | Time over 10 ppm | Concentration Value over 10 ppm | Maximum Concentration Value | Final Concentration Value | |
---|---|---|---|---|---|
Room 1 | BL2 | 14:18:28 | 12.8 ppm | 39.7 ppm | 36.1 ppm |
Room 2 | BL3 | 14:22:20 | 10 ppm | 16 ppm | 12 ppm |
Room 3 | CW3 | 14:30:58 | 10 ppm | 13 ppm | 8 ppm |
Room | Time over 10 ppm | Concentration Value over 10 ppm | Maximum Concentration Value | Final Concentration Value | |
---|---|---|---|---|---|
Room 1 | BL3 | 15:12:34 | 16 ppm | 154.6 ppm | 130 ppm |
Room 2 | BL4 | 15:15:05 | 10 ppm | 26.8 ppm | 21.5 ppm |
Room | Time over 10 ppm | Concentration Value over 10 ppm | Maximum Concentration Value | Final Concentration Value | |
---|---|---|---|---|---|
Room 1 | BW2 | 12:28:45 | 31.4 ppm | 88 ppm | 63.5 ppm |
Room 2 | BW1 | 12:31:35 | 10 ppm | 15 ppm | 13 ppm |
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Dai, Y.; Hou, M.; Wang, H.; Tu, W. Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment. Buildings 2023, 13, 3121. https://doi.org/10.3390/buildings13123121
Dai Y, Hou M, Wang H, Tu W. Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment. Buildings. 2023; 13(12):3121. https://doi.org/10.3390/buildings13123121
Chicago/Turabian StyleDai, Yuwei, Minzhang Hou, Haidong Wang, and Wanli Tu. 2023. "Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment" Buildings 13, no. 12: 3121. https://doi.org/10.3390/buildings13123121