Numerical Modeling of the Dispersion Characteristics of Pollutants in the Confluence Area of an Asymmetrical River
Abstract
:1. Introduction
2. Mathematical Models and Verification
2.1. Control Equations
2.2. Model Validation
2.2.1. Verification Model Overview
2.2.2. Numerical Method
2.2.3. Model Verification
3. Program Design
3.1. Overview of the River Model
3.2. Measurement Point Placement and Cross-Sectional Monitoring
3.3. Calculation and Setting Conditions
3.3.1. Calculation Conditions
3.3.2. Establishing the Boundary Conditions
4. Analysis of Results
4.1. Analysis of the Horizontal Diffusion Characteristics of Pollutants
4.2. Trajectory Line of Pollutant Mixing Interface Changes along the Path
4.2.1. Influence of the Discharge Ratio on Trajectory Line Variation along the Pollutant Mixing Interface
4.2.2. Influence of the Width-Depth Ratio on Trajectory Line Variation along the Pollutant Mixing Interface
4.2.3. Influence of the Concentration Difference on the Trajectory along the Pollutant Mixing Interface
4.3. Mixing Characteristics of the Pollutant Concentration
4.3.1. Effect of the Discharge Ratio on the Pollutant Mixing Characteristics
4.3.2. Effect of the Width-Depth Ratio on the Mixing Characteristics of Pollutants
4.3.3. Effect of the Concentration Difference on the Mixing Characteristics of Pollutants
5. Discuss
6. Conclusions
- (1)
- The dependability of the numerical model is simulated and assessed. According to the verification findings, the flow rate and pollutant content in each section occur within tolerable limits. The numerical model may be used to explore the diffusion mechanism of contaminants in the asymmetric river junction region and to better capture hydrodynamic and water quality changes in the river intersection area.
- (2)
- The three-dimensional properties of the pollutant concentration distribution in the junction area are analyzed. The findings indicate that the discharge ratio and the aspect-to-width-depth ratio significantly impact the distribution of pollutants in the junction region. This is mostly manifested in the horizontal distribution of pollutants, the trajectory of the mixing interface, and the degree of mixing homogeneity. The horizontal diffusion range of pollutants increases with increasing discharge ratio and width-depth ratio, and the mixing homogeneity in each section increases. Pollutants in the bottom plane Z = 0.05 m are totally mixed in the downstream exit section for R = 0.267 and b/h = 3.75. In general, the trajectory line of the mixing interface of pollutants in the junction region exhibits a logarithmic growth tendency, and it progresses along the direction of water flow development. The mixing interface expands to the center axis point after progressively moving to the other side of the interchange.
- (3)
- The concentration difference affects the horizontal distribution and mixing degree of pollutants. The degree of influence, however, is not as high as that of the discharge ratio or width-depth ratio, with only a slight impact. However, the mixing interface trajectory line still exhibits a logarithmic development pattern, and with increasing concentration difference, the mixing interface slightly deviates to the opposite side of the interchange. Molecular diffusion due to concentration variations causes subtle changes in the mixing interface and inhomogeneity index. In summary, the concentration difference only affects the concentration in the pollution belt, but does not influence its width, length, or size.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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NS Value | Result Evaluation |
---|---|
NSE < 0 | Measured values outperform the simulated values |
0.5 < NSE < 0.65 | Acceptable value |
0.65 < NSE < 0.75 | Improved simulation results |
NSE > 0.75 | Excellent simulation results |
NSE = 1 | Perfect match between the simulated and measured values |
Variables | Cross-Section | MRE (%) | NSE |
---|---|---|---|
Velocity of flow (m/s) | X = 5 cm | 4.13 | 0.899 |
X = 15 cm | 3.20 | 0.998 | |
X = 25 cm | 3.37 | 0.934 | |
Concentration of pollutant (μg/L) | Y = 11 cm | 4.49 | 0.992 |
Y = 32 cm | 4.95 | 0.983 | |
Y = 53 cm | 4.68 | 0.962 | |
Y = 74 cm | 3.16 | 0.959 | |
Y = 116 cm | 4.84 | 0.975 |
Working Conditions | Number | Investigation Factors | Mainstream Flow Q1(m3/h) | Discharge Ratio R | Water Depth h(m) | Width-Depth Ratio b/h | Concentration of Tributary C2 (μg/L) | Concentration Difference Cg (μg/L) |
---|---|---|---|---|---|---|---|---|
1 | 1(a) | Discharge ratio | 136.08 | 0.267 | 0.3 | 3 | 2000 | 2000 |
1(b) | 194.40 | 0.187 | 0.3 | 3 | 2000 | 2000 | ||
1(c) | 272.16 | 0.133 | 0.3 | 3 | 2000 | 2000 | ||
2 | 2(a) | Width-depth ratio | 194.40 | 0.187 | 0.24 | 3.75 | 2000 | 2000 |
2(b) | 194.40 | 0.187 | 0.3 | 3 | 2000 | 2000 | ||
2(c) | 194.40 | 0.187 | 0.36 | 2.5 | 2000 | 2000 | ||
3 | 3(a) | Concentration difference | 194.40 | 0.187 | 0.3 | 3 | 500 | 500 |
3(b) | 194.40 | 0.187 | 0.3 | 3 | 1000 | 1000 | ||
3(c) | 194.40 | 0.187 | 0.3 | 3 | 2000 | 2000 |
Number | Pollutant Concentration Distribution Area (m2) | Proportion of the Intersection Area (%) |
---|---|---|
1(a) | 5.25 | 60.77% |
1(b) | 3.90 | 45.16% |
1(c) | 2.97 | 34.34% |
2(a) | 5.08 | 58.82% |
2(b) | 3.90 | 45.16% |
2(c) | 3.65 | 42.27% |
3(a) | 3.77 | 43.68% |
3(b) | 3.86 | 44.66% |
3(c) | 3.90 | 45.16% |
Number | Investigation Factors | Mainstream Flow Q1 (m3/h) | Concentration of Mainstream C1 (μg/L) | Tributary Flow Q2 (m3/h) | Concentration of Tributary C2 (μg/L) | Average Concentration Cp (μg/L) |
---|---|---|---|---|---|---|
1(a) | R = 0.267 | 136.08 | 0 | 36.29 | 2000 | 421.05 |
1(b) | R = 0.187 | 194.40 | 0 | 36.29 | 2000 | 314.61 |
1(c) | R = 0.133 | 272.16 | 0 | 36.29 | 2000 | 235.29 |
2(a) | b/h = 3.75 | 194.40 | 0 | 36.29 | 2000 | 314.61 |
2(b) | b/h = 3.00 | 194.40 | 0 | 36.29 | 2000 | 314.61 |
2(c) | b/h = 2.50 | 194.40 | 0 | 36.29 | 2000 | 314.61 |
3(a) | Cg = 500 | 194.40 | 0 | 36.29 | 2000 | 78.65 |
3(b) | Cg = 1000 | 194.40 | 0 | 36.29 | 2000 | 157.30 |
3(c) | Cg = 2000 | 194.40 | 0 | 36.29 | 2000 | 314.61 |
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Wang, X.; Yang, J.; Wang, F.; Xu, N.; Li, P.; Wang, A. Numerical Modeling of the Dispersion Characteristics of Pollutants in the Confluence Area of an Asymmetrical River. Water 2023, 15, 3766. https://doi.org/10.3390/w15213766
Wang X, Yang J, Wang F, Xu N, Li P, Wang A. Numerical Modeling of the Dispersion Characteristics of Pollutants in the Confluence Area of an Asymmetrical River. Water. 2023; 15(21):3766. https://doi.org/10.3390/w15213766
Chicago/Turabian StyleWang, Xu, Jiening Yang, Fan Wang, Na Xu, Peixuan Li, and Ai Wang. 2023. "Numerical Modeling of the Dispersion Characteristics of Pollutants in the Confluence Area of an Asymmetrical River" Water 15, no. 21: 3766. https://doi.org/10.3390/w15213766