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.

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. Building facades become smoother, details
are dropped and harder materials are used

3. Retrofitting also introduce new problems

4. Runoff on building facades contributes to:
• Aesthetic damage at the outside facade
• Rain penetration
• Leaching of biocides into the environment

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. 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. 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. 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. 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. Full scale experiments:
Setup
First measurement campaign
Comparison with the simplified runoff model
Conclusions from the experiments

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. Meteo station
low rise buildings
Medium rise
building
Test location
50 m
N

14. Experimental setup
To collection
tubes, linked to
pressure
sensors:
5.10-3 mm
Horizontal
rain gauge:
0.1 mm

15. 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

16. 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

17. 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

18. 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:

19. 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

20. 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

21. 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.

22. Detailed runoff measurements
First experimental setup
New experimental setup

23. 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)

24. 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

25. 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

26. 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

27. 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?

28. 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

29. 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.

30. Modelling Wind-driven rain
Why OpenFOAM ®
Atmospheric Boundary Layer simulations
WDR simulations

31. 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, …

32. 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

33. 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

34. 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

35. 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

36. 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