Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

PhD seminars: Rainwater runoff on porous building materials

1,017 views

Published on

Progress seminar of my phd on Rainwater runoff on porous building materials due to wind-driven rain. The focus of this presentation was on the experimental work, but also contained an update on the WDR simulations with OpenFOAM.

  • Be the first to comment

PhD seminars: Rainwater runoff on porous building materials

  1. 1. Rainwater runoff on porous building materials: an experimental & numerical study [PhD seminars; Januari 8th, 2014] Thijs Van den Brande, supervisors: Staf Roels, Bert Blocken thijs.vandenbrande@bwk.kuleuven.be Building Physics Section, KU Leuven
  2. 2. Building facades become smoother, details are dropped and harder materials are used
  3. 3. Retrofitting also introduce new problems
  4. 4. Runoff on building facades contributes to: • Aesthetic damage at the outside facade • Rain penetration • Leaching of biocides into the environment
  5. 5. How do we tackle these issues? Rain penetration • • • • Salt efflorescence White washing Self cleaning glass State-of-the-art HAM models (without runoff, splashing, bouncing, …) Labour intensive detailed WDR calculations (CFD: rain droplet tracking) Best practice design guidelines Experienced architects/builders/engineers
  6. 6. Into the models: Current models: • Supplied WDR is absorbed • Excess water is discarded • Continuous moisture fluxes In reality: • Splashing & bouncing of droplets • Adhesion water • Runoff of WDR that wets underlying parts • Discrete droplets Goal of my PhD: • Developing a reliable model to quantify runoff due to WDR • Optimising WDR simulations for HAM-research
  7. 7. Outline of the phd WP1: Wind-driven rain using an Eulerian multiphase approach WP2: Combined HAM-runoff model WP3: Experiments • WP3.1: Small scale validation tests • WP3.2: Full scale measurements WP4: Case studies: simplified church building (in cooperation with Ugent) WP 1: CFD WDR model • OpenFoam model • Eulerian multiphase model • Verification with experiments WP 2: HAM-runoff model • build on HAMFEM • research of surface fenomena • material behaviour • verification • (dragforces on dust particles) WP 3: experimental analysis • 2D - lab experiment • 3D - full scale experiment (SEG) WP 4: Case studies • simplified watervliet case • wind-driven rain in the built environment
  8. 8. In this presentation WP1: Wind-driven rain using an Eulerian multiphase approach WP2: Combined HAM-runoff model WP3: Experiments • WP3.1: Small scale validation tests • WP3.2: Full scale measurements WP4: Case studies: simplified church building (in cooperation with Ugent) WP 1: CFD WDR model • OpenFoam model • Eulerian multiphase model • Verification with experiments WP 2: HAM-runoff model • build on HAMFEM • research of surface fenomena • material behaviour • verification • (dragforces on dust particles) WP 3: experimental analysis • 2D - lab experiment • 3D - full scale experiment (SEG) WP 4: Case studies • simplified watervliet case • wind-driven rain in the built environment
  9. 9. Outline of this presentation 1. Introduction 2. Full scale WDR and runoff measurements o o o Setup First measurement campaign Comparison with the simplified runoff model 3. Detailed runoff measurements o o First experimental setup New experimental setup 4. Wind-driven rain simulations in OpenFOAM Why OpenFOAM o Atmospheric Boundary Layer simulations o WDR simulations 5. Conclusions o
  10. 10. Full scale experiments: Setup First measurement campaign Comparison with the simplified runoff model Conclusions from the experiments
  11. 11. Full scale measurements Requirements (building): • Relative ‘open’ approach (for WDR simulations) • SW-oriented facade • Tall building: WDR loads, even at low Ws • Close to detailed weather measurements Amount of rain Sh (mm) 0° 30% 330° 30° 20% 300° 270° 60° 10% 90° 0% 240° 120° 210° Requirements (experimental setup) • Cladding with known material properties • Detailed positioning of the WDR sensors • ‘Easy’ to remove and change materials 150° 180°
  12. 12. Meteo station low rise buildings Medium rise building Test location 50 m N
  13. 13. Experimental setup To collection tubes, linked to pressure sensors: 5.10-3 mm Horizontal rain gauge: 0.1 mm
  14. 14. First measurement campaign: July ‘13 – November ‘13 1/07/2013 – 24/9/2013: Optimising measurement setup • Period of drought • Optimising workflow: adding electric valves • Additional horizontal rainfall measurement on rooftop 01/07 01/08 01/09 01/10 01/11 01/12 ’13
  15. 15. First measurement campaign: July ‘13 – November ‘13 24/09/2013 – 18/11/2013: First measurement campaign • Total of 65 events: • • 43 with 200 °N < Wdir < 280 ° 12 good measurements 0 m/s < Ws < 8.3 m/s (@10m height) Stopped measurements on 18/11/2013 due to frost risk 3.50 horizontal rainfall intensity (mm/h) horizontal rainfall intensity (mm/h) 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0 2 4 6 avarage wind speed (m/s) 8 10 150 180 210 240 270 avarage wind direction (°N) 300
  16. 16. First measurement campaign: July ‘13 – November ‘13 A selection of two events: • October 23th, 16h50-17u10: 2.7 mm of rainfall (shower) • October 15th, 01h00-02h10: 0.2 mm of rainfall (drizzle) 3.50 horizontal rainfall intensity (mm/h) horizontal rainfall intensity (mm/h) 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0 2 4 6 avarage wind speed (m/s) 8 10 150 180 210 240 270 avarage wind direction (°N) 300
  17. 17. Comparison with the simplified runoff model • No surface tension & vertical wall: = 0 • 2D simulation & absorption = 0 o o qWDR from measurements qevap as a function of Ws and RH • Runoff rate at sensor:
  18. 18. First measurement campaign: detailed results October 23th, 16h50 – 17u40: Ws = 1.98 m/s Wdir = 226 °N RH = 89 % T = 15,4 °C Supplied WDR Measured Runoff Modelled Runoff Adjusted model
  19. 19. First measurement campaign: detailed results October 15th, 01h00 – 02u10: Ws = 2.09 m/s Wdir = 203 °N RH = 98 % T = 9.7 °C Supplied WDR Measured Runoff Modelled Runoff + adhesive water Modelled Runoff Double viscosity Half viscosity  Light rain: less sensible to WDR supply, more to viscosity
  20. 20. First measurement campaign: Conclusions • Reliable sensors needed • Optimisation of the collection reservoir size • Detailed quantification of WDR needed! Towards spatial distribution o Towards time distribution (film reacts almost instantly) • Simplification of the runoff model shows difficulties (at least for non-absorbing facade materials) o & 1 . No matter how hard you plan, you always forget something. 2. You can’t build an experimental setup without colleagues.
  21. 21. Detailed runoff measurements First experimental setup New experimental setup
  22. 22. Small scale experiment: first setup • Fixed amount of water is released at t0 • Measurements: o o o o Front tracking with camera (400fps) Sample weight Excess water Adhesive water (using dry cloth)
  23. 23. Small scale measurements: first setup Film height (m) What we learned from this experiments: • Leveling setup is a tedious task • Initial speed of the liquid film determines flow • Supplied amount should be limited plaster brick wood-fiber board Qsupply (g/m²s) 1.389 3.056 0.556 trunoff (s) 600 1800 800 From: master dissertation G. Ameele: “gevelvervuiling ten gevolge van slagregenbelasting en vochtafloop”, 2013, KU Leuven
  24. 24. Small scale experiment: new setup • New experimental setup: 2 tracks to deliver small supply 1) Needle setup: 2) Small opening: 74 needles (Angiocath®) 21 ml/s supply over 260 mm Discrete (drops of 0.7 ml / ~2s) to reservoir 250mm opening of 0.05mm thick Theoretical flow: ~35 ml/s over 250mm  difficult to get steady flow
  25. 25. Small scale experiment: new setup Water reservoir with adjustable height Flexible tubing Mount for camera Supply device (with 74 Angiocath needles) Tilt surface for samples
  26. 26. Small scale experiment: new setup First results: • No film formation on non-absorbing materials • Film formation present on brick, but breaks up after couple of mm into fingers.  Surface effect or film flow problem?
  27. 27. Small scale experiment: do the assumptions hold? • Thin moisture sheet over a smooth surface: • Assumptions: from [Brenner,1993] o Front region is small: no surface tension o Literature states that film mainly acts as Nusselt film, before instability
  28. 28. Possible solutions to this problem • Include slip model with permeability of material: [Neogi & Miller, 1983] • Contact angle hysteresis on porous media Rodriguez-Valverde et al. Contact angle measurements on two (wood and stone) non-ideal surfaces, 2002 Chow, T. Wetting of rough surfaces, 1998 • Include surface tension: more complex solver needed.
  29. 29. Modelling Wind-driven rain Why OpenFOAM ® Atmospheric Boundary Layer simulations WDR simulations
  30. 30. Methodology: Eulerian multiphase models Previous method 1. Calculate wind field around a building 2. Calculate raindrop trajectories Velocity magnitude of the wind in the middle of a street canyon (RANS simulation) Eulerian multiphase approach • Adv. 1: Continuous rain phases • Adv. 2: Decreased user time spent • Adv. 3: More possibilities for further research (turbulent dispersion, LES, detailed facades, ...) First try in Fluent: • convergence issues in the multiphase model • problems with defining boundary conditions, …
  31. 31. OpenFOAM® : benefits & ABL flow OpenFOAM = open Source package for CFD  Has a mathematical library: gives opportunity to write solvers  Large amount of forums for questions  ‘cheap’ to do parallel solve domains with large amount of control volumes.  Scripted input: automation Conclusions from ABL flow simulations: - RANS simulations fast to implement and calculate. - Inlet profiles and wall functions adjusted to ensure horizontally homogeneous flow (Blocken et al. 2007). - Gambit mesher can still be used
  32. 32. WDR simulations in OpenFOAM® A. Solve wind phase (RANS with realizable κ-ε model)   Results in wind (U ) and pressure field (p) B. Determine raindrop distribution for Rh and divide into rain phases. Solve wind phase for each droplet size k: 1 mass conservation eq. 3 momentum eq. C. Due to small volume ratio of rain phase: negligible influence on the wind phase  one way coupled D. Integrate fluxes at the building surfaces and sum up all phases
  33. 33. WDR simulations in OpenFOAM®: implementation Boundary conditions: @ inlet planes (top and inlet of domain) @ outlet planes (outlet, walls, building) Solver: Iterate between mass conservation equation and momentum equations.  still some issues with the code
  34. 34. Future work: 1. Full scale experiments on absorbing materials are needed and will start in April ’14 2. Small scale experiments are needed to validate the simplified runoff model. 3. WDR distributions have a large impact on runoff flow  focus on OpenFOAM simulations
  35. 35. Discussion thijs.vandenbrande@bwk.kuleuven.be Building Physics Section, KU Leuven FWO G.0448.10N Strategies for moisture modelling of historical buildings in order to reduce damage risks

×