Convective currents between open water and vegetation due to solar radiation

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/325594937 Convective currents between open water and vegetation due to solar radiation Conference Paper · June 2018 CITATIONS 0 READS 85 2 authors: Vassilios Papaioannou Centre for Research and Technology Hellas 36 PUBLICATIONS193 CITATIONS SEE PROFILE Panagiotis Prinos Aristotle University of Thessaloniki 194 PUBLICATIONS2,199 CITATIONS SEE PROFILE All content following this page was uploaded by Vassilios Papaioannou on 08 June 2018. The user has requested enhancement of the downloaded file. Convective currents between open water and vegetation due to solar radiation ARISTOTLE UNIVERSITY OF THESSALONIKI Papaioannou Vassilios, PhD Candidate Panayotis Prinos, Professor Hydraulics Laboratory Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki, Greece 5th IAHR Europe Congress “New Challenges in Hydraulic Research and Engineering” 12 - 14 June, 2018, Trento, Italy 1 ARISTOTLE UNIVERSITY OF THESSALONIKI Overview of Presentation 1. Introduction 2. Model Description 3. Governing Equations 4. Numerical Procedure 5. Analysis of the Results 6. Conclusions Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy 2 ARISTOTLE UNIVERSITY OF THESSALONIKI Introduction 3 Convective Currents:  thermally-driven exchange flow due to temperature difference  are observed a) between shallow and deep water b) between open water and aquatic vegetation  vegetation prevents solar radiation from entering into the water body  open water higher temperature Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI Introduction Aquatic Vegetation: present in shallow aquatic systems energy dissipation – additional drag reduces the current velocity common vegetation porosity φ = 0.70 - 0.97 4 Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI Introduction Effect of Vegetation 5 macroscopic approach  additional source term in energy equation a) solar model based on Beer’s Law b) solar model based on Radiative Transfer Equation (RTE)  volume averaged theory  additional resistance terms in momentum equations a) canopy flow theory b) porous media flow theory Effect of solar radiation Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI Introduction Objectives of the Study: Investigate Compare numerical results with experimental data For φ=0.75-0.97 [Zhang & Nepf, 2009] For φ=1 [Coates & Patterson, 1993] 6 effect of differential water heating characteristics of convective currents effect of vegetation porosity on convective currents Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI Model Description 7 2D model in a tank separated into 2 regions (open and vegetated) Open water is heated with constant surface radiation intensity I0 = 157 W/m2 Vegetation consists of cylinders (d = 6mm) φ = 0.97, 0.85, 0.75 Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI Governing Equations 8 CFD commercial code: Fluent 15.0.7 Unsteady Navier – Stokes equations Energy equation (Boussinesq approximation) ( ) ∂ ∂+= ∂∂ 0 i i U tx ρ ρ ( ) ( ) ( ) ρ ρ µ ρβ   ∂ ∂ ∂ ∂∂ ∂ + =−+ + + − +    ∂ ∂ ∂∂ ∂ ∂    0 j i ij i i j ij j i U PU U U U TTg F t x xx x x ( ) ( )   ∂ ∂ ∂∂ +=+    ∂ ∂ ∂∂    pj p h j jj T cT U cT S t x xx ρ ρκ extra source term due to radiation absorption Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy extra source term due to vegetation ARISTOTLE UNIVERSITY OF THESSALONIKI Analysis of the Results 15 2. Effect of grid size tested, φ = 0.97 Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy no significant difference (<1%). grid size used 180,000 cells. ARISTOTLE UNIVERSITY OF THESSALONIKI Analysis of the Results 16 Case studies Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy Case φ Io (W/m2) h (m) k (m2) x 10-6 Cf 1* 1.0 127.5 0.3 - - 2 0.97 157.0 0.1 73.13 0.0323 3 0.85 157.0 0.1 5.04 0.0484 4 0.75 157.0 0.1 1.56 0.0510 5 0.97 157.0 0.15 73.13 0.0323 6 0.85 157.0 0.15 5.04 0.0484 7 0.75 157.0 0.15 1.56 0.0510 • Comparison with experimental data [Coates & Patterson, 1993] * • Comparison with experimental data [Zhang & Nepf, 2009] ARISTOTLE UNIVERSITY OF THESSALONIKI Analysis of the Results 17 3. Differential Heating, φ = 1, Temperature increase (dimensionless form Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy both models reproduce the observed data. the sharp increase is due to side wall effect. RTE model has slower temperature increase. ARISTOTLE UNIVERSITY OF THESSALONIKI Analysis of the Results 18 4. Differential Heating, φ = 0.97, Temperature Increase in dimensionless form Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy temperature difference increases when the current reaches this location  the slope of the numerical results in agreement with experimental data  but in experiments there is heat loss (negative δT) the vertical solid line corresponds to wall impact. ARISTOTLE UNIVERSITY OF THESSALONIKI Analysis of the Results 19 5. Porosity Effect on Temperature Increase Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy both models present the same behaviour  as φ decreases the temperature increase starts later in time.  as φ decreases the temperature increase gets higher values for Beer’s law model. ARISTOTLE UNIVERSITY OF THESSALONIKI 20 Analysis of the Results 6. Horizontal velocity (a) and temperature (b) contours for φ = 0.85 and Beer’s law model (t = 100 s and 500 s) Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI 21 Analysis of the Results 7. Porosity effect on horizontal velocity contours (t = 450 s) with Beer’s law model Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI 22 Analysis of the Results 8. Porosity effect on Temperature contours (t = 450 s) with Beer’s law model Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy ARISTOTLE UNIVERSITY OF THESSALONIKI 23 Analysis of the Results 9. Horizontal velocity for φ = 0.97 at x = -0.09 m both models reproduce the observed data depth increase shows a greater increase on velocity profile based on Beer’s law rather than RTE. Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy h=10 cm h=15 cm ARISTOTLE UNIVERSITY OF THESSALONIKI 24 Analysis of the Results 10. Porosity effect on horizontal velocity (t = 500 s) both models have same behavior RTE generates shallower current than Beer’s law model. Convective currents between open water and vegetation due to solar radiation 5th IAHR Europe Congress, Trento, Italy