# Physical Experimentation and 2D-CFD Parametric Study of Flow through Transverse Bottom Racks

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## Abstract

**:**

## 1. Introduction

#### Background

^{2}/year of urban waste and sediments, which passed over the screen without entering, it was recorded. Of the urban waste and sediments that passed over the screen, 40% comprised particles between 0.5 mm and 5 mm, and 60% comprised particles greater than 5 mm of mainly grass and debris. The work concludes that the Coanda-effect screen removes many metals and other contaminants that impair water quality. In addition, the unit did not require maintenance during its operation. The Coanda-effect screen provides the following detailed removal information: debris and sediments 67%, arsenic 47%, cadmium 100%, copper 33%, nickel 39%, zinc 33%, and fecal coliforms 35%.

## 2. Materials and Methods

#### 2.1. Physical Experimentation

#### 2.2. Numerical Experimentation

- Geometry construction
- Discretization
- Boundary conditions
- Configuring numerical simulation parameters
- Validation
- 2D parametric study
- Analysis of the results

#### 2.2.1. Geometry

#### 2.2.2. Discretization

#### 2.2.3. Computational Conditions

#### 2.2.4. Numerical Resolution Method

^{−6}as a criterion for confirming convergence to a steady state with highly accurate solutions.

#### 2.2.5. Validation

#### 2.2.6. CFD Parametric Study

- Screen incline: 20, 35, 45 degrees
- Coanda screen position: top, middle, bottom
- Wire section: triangular, circular
- Triangular wire width: 3, 5, 6.3 mm
- Circular wire diameter: 3, 5, 6.3, 10, 16, 20 mm
- Wire spacing: 2 mm, 1 mm
- Number of slots: 13
- Number of wires: 12

## 3. Results and Discussion

#### 3.1. Physical Experimentation

#### 3.1.1. Clean Water

#### 3.1.2. Water with Sediment

#### 3.1.3. Flow/Sediment Ratio Excluded

#### 3.2. Numerical Experimentation

#### 3.2.1. Simulation Validation

#### 3.2.2. Comparison of the Flow Obtained with Experimental Data vs. Numerical Simulation

#### CFD Results from Triangular Wire Screen

#### CFD Results from Circular Wire Screen

#### 3.2.3. 2D–CFD Parametric Study

- F = Froude number,
- $V$ = mean velocity across the screen,
- $D$ = flow depth,
- θ = slope angle of the screen surface, measured from horizontal,
- g = acceleration due to gravity.

- R = Reynolds number,
- V = mean velocity across the screen,
- s = open slot width between wires,
- ν = kinematic viscosity.

#### Triangular Wire Screen Performance

#### Circular Wire Screen Performance

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Detail of screen geometry and key variables. (Adapted from [4]).

**Figure 2.**(

**a**) Variable-slope screen testing flume; (

**b**) screen installed in the test flume; (

**c**) test screen triangular wire (

**d**) test screen circular wire.

**Figure 3.**Geometry 2D of computational domain: (

**a**) flume; (

**b**,

**c**) triangular wire screen; (

**d**,

**e**) circular wire screen.

**Figure 4.**2D tetrahedrical mesh in the computational domain: (

**a**) triangular wire screen mesh; (

**b**) circular wire screen mesh.

**Figure 11.**Two-phase contour volume fraction: (

**a**) channel domain; (

**b**) A5 test screen; (

**c**) pressure contours; (

**d**) velocity contours.

**Figure 12.**CFD simulation results of the triangular wire screen: (

**a**) two-phase contour volume fraction; (

**b**) vectors velocity and pressure contours.

**Figure 13.**CFD simulation results of circular wire screen; (

**a**) two-phase contour volume fraction; (

**b**) vectors velocity and pressure contours.

Screen | 1 | 2 |
---|---|---|

Section | Triangular | Circular |

Test width (cm) | 9.3 | 9.3 |

Wire tilt angle (degrees) | 5 | - |

Average slot width, s (mm) | 2 | 2 |

Average wire thickness, w (mm) | 5 | 5 |

Number of wires | 12 | 12 |

Positions tested | bottom | bottom |

Model Boundary | Boundary Conditions |
---|---|

Walls | No-slip |

Inlet channel | mass flow inlet |

Inlet screen | velocity-inlet |

Outlet | pressure-outlet |

Atmosphere | pressure-outlet |

Property | Phase 1 | Phase 2 |
---|---|---|

Material | air | water |

Density (kg/m^{3}) | 1.225 | 998.2 |

Dynamic viscosity (kg/ms) | 1.7894 × 10^{−5} | 0.001003 |

Surface tension coefficient (N/m) | 0.072 |

**Table 4.**Numerical Schemes and Solution Methods [7].

Variable | Adjustment |
---|---|

Turbulence model | k–ω SST |

Pressure velocity coupling | Coupled |

Gradient | Least Squares Cell-Based |

Pressure | Body Force Weighted |

Momentum | Second-order upwind |

Volume fraction | Compressive |

Turbulence Kinetic Energy | Second-order upwind |

Turbulence Dissipation rate | Second-order upwind |

Initialization | Standard |

Screen | A5 |
---|---|

Relief angle (λ°) | 10 |

Test width (cm) | 5.08 |

Wire Width, w (mm) | 4.7167 |

Slot Width, s (mm) | 1.985 |

Wire Tilt, φ | 5.25 |

Waste Slots | 5 |

Test Slots | 6 |

Screen Incline θ° | 26.3 |

Test Location | bottom |

Distance down straight chute to first slot (mm) | 1094.978 |

Conditions at the crest (critical depth) (mm) | 58.80 |

Flow in (L/s) | 2.2684 |

Screened flow (L/s) | 0.487 |

Element Mesh Size (mm) | Number of Nodes | Laboratory Flow (L/s) | CFD Flow (L/s) | Relative Error (%) | Relative Error Laboratory Flow vs. CFD Model (%) |
---|---|---|---|---|---|

0.2 | 39,510 | 0.487 | 0.396 | -- | 18.69 |

0.1 | 155,721 | 0.487 | 0.440 | 11.11 | 9.65 |

0.05 | 501,376 | 0.487 | 0.466 | 5.91 | 4.31 |

0.04 | 671,511 | 0.487 | 0.474 | 1.72 | 2.67 |

Screen | Screen Incline (°) | Laboratory Flow (L/s) | CFD Flow k–ω SST Model (L/s) | Relative Error Laboratory Flow vs. k–ω SST Model (%) |
---|---|---|---|---|

Triangular wire | 35 | 1.11 | 1.16 | 4.31 |

45 | 1.1 | 1.14 | 3.51 | |

Circular wire | 20 | 0.51 | 0.505 | 0.99 |

35 | 0.54 | 0.542 | 0.37 |

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**MDPI and ACS Style**

Carrión-Coronel, E.; Ortiz, P.; Nanía, L.
Physical Experimentation and 2D-CFD Parametric Study of Flow through Transverse Bottom Racks. *Water* **2022**, *14*, 955.
https://doi.org/10.3390/w14060955

**AMA Style**

Carrión-Coronel E, Ortiz P, Nanía L.
Physical Experimentation and 2D-CFD Parametric Study of Flow through Transverse Bottom Racks. *Water*. 2022; 14(6):955.
https://doi.org/10.3390/w14060955

**Chicago/Turabian Style**

Carrión-Coronel, Eduardo, Pablo Ortiz, and Leonardo Nanía.
2022. "Physical Experimentation and 2D-CFD Parametric Study of Flow through Transverse Bottom Racks" *Water* 14, no. 6: 955.
https://doi.org/10.3390/w14060955