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A Macroscopic Approach for Simulating Horizontal Convection in a Vegetated Pond

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Abstract

A macroscopic approach for simulating horizontal convection in a vegetated pond is presented. The generated convective currents are due to the differential radiation absorption between the two regions of the pond, one with emergent vegetation up to the free surface and one without vegetation. The Volume-Averaged Navier-Stokes (VANS) equations are used for the simulation of the laminar, unsteady, two-dimensional horizontal convection. The vegetation effects on the motion of the currents are taken into account through additional resistance terms based on the vegetation porosity and permeability. The Volume-Averaged Energy (VAE) equation is also solved with an additional source term accounting for the absorption of radiation which is based on a one-waveband and a three-waveband radiation model. The model setup is based on Beer’s law whereas the incoming radiation is absorbed from the water column. Three types of vegetation porosities φ varying from 0.75 to 0.97 are examined in investigating the motion of the convective currents within the vegetated area. The case without vegetation (φ = 1.0) is also examined for assessing the effectiveness of the radiation model. The numerical current velocity and the water temperature increase are presented and compared against available experimental data.

Highlights

• Absorption of radiation based on one- and three-waveband attenuation models

• Vegetation effects on the characteristics of horizontal convection

• Effect of Grashof number on the motion of horizontal convective currents

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Data Availability

All data are available by the authors upon request.

Abbreviations

a1 :

Empirical coefficient (-)

b1 :

Empirical coefficient (-)

CD :

Drag coefficient (-)

Cf :

Dimensionless parameter (-)

Cp :

Specific heat of water (J/(kg·K))

d:

Cylinder diameter (m)

d50 :

Mean size of porous material (m)

F:

Source term (due to vegetation) (N/m3)

g:

Gravity acceleration (m/s2)

Gr:

Grashof number

h:

Water depth (m)

hI :

Intrusion depth (m)

I0 :

Bulk radiation intensity at the surface (W/m2)

k:

Intrinsic permeability (m2)

L:

Total tank length (m)

Lveg :

Length of the vegetated region (m)

Lop :

Length of the open region (m)

N:

Number of bands (-)

n0 :

Bulk attenuation coefficient (1/m)

P:

Effective pressure (Pa)

R2 :

Regression coefficient (-)

Rp :

Pore Reynolds number (-)

Sh :

Source term (W/m3)

t:

Time (s)

T:

Fluid temperature (K)

tc :

Time to the inertia-buoyancy balance (s)

tΕ :

Time to the energy-limited regime (s)

tv :

Time start of the drag dominated flow (s)

UE :

Energy limited velocity scale (m/s)

Ui :

Fluid velocity in the i direction (m/s)

Ux :

Horizontal velocity (m/s)

Ux,mean :

Mean horizontal velocity (m/s)

UV :

Drag dominated velocity (m/s)

UV,sim :

Drag dominated simulation regime (m/s)

Uvis :

Viscous dominated velocity (m/s)

V:

Volume of a horizontal slab (m3)

Vf :

Volume of fluid contained in volume V (m3)

y:

Distance from the tank bottom (m)

β:

Thermal expansion coefficient (1/K)

ΔΤE :

Temperature difference energy -limited regime (K)

ΔΤV :

Temperature difference drag regime (K)

κ:

Thermal conductivity (W/(m·K))

μ:

Fluid dynamic viscosity (kg/(m·s))

ν:

Fluid kinematic viscosity (m2/s)

ρ:

Fluid density (kg/m3)

φ:

Vegetation porosity (-)

ψ:

General parameter (-)

References

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Acknowledgments

Part of this work has been presented in Greek in the 14th Conference of the Hellenic Hydrotechnical Association, Volos, Greece, 16–17 May 2019.

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Authors and Affiliations

Authors

Contributions

Prinos Panagiotis contributed to the conception and design of the study. Papaioannou Vassilios conducted simulation runs, data collection and analysis. The first draft of the manuscript was written by Prinos Panagiotis, and all authors reviewed early drafts of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Vassilios Papaioannou.

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All the ethical standards were followed.

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Code Availability

The C++ code used in the Fluent’s UDF is available by the authors upon request.

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Papaioannou, V., Prinos, P. A Macroscopic Approach for Simulating Horizontal Convection in a Vegetated Pond. Environ. Process. 8, 199–218 (2021). https://doi.org/10.1007/s40710-020-00484-x

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