Wind – Analogue or Digital?.

Transcription

CONSULTING ENGINEERS & SCIENTISTS
Wind – Analogue or Digital?
CIBSE Building Simulation Group and Natural Ventilation Group
30th April 2014
Wayne Pearce
Principal, Regional Manager (UK)
[email protected]
David Hamlyn
Senior Engineer
[email protected]
Canada | China | Hong Kong | India | Singapore | UK | USA
C O N S U L TI N G I N TH E S C I E N C E O F B U I L D I N G S , S TR U C TU R E S & E N V I R O N ME N T
rwdi.com
Contents
About RWDI
Wind Engineering – Comparison of CFD and Experimental Methods
Modelling Challenges
Accuracy
Purpose of Analysis
Costs and Time
Regulation
Other Approaches
Case Study Examples
Masterplanning
Exhaust Re-Entrainment
Conclusions
About RWDI
About RWDI
• Headquarters in Guelph, Ontario
• Established in 1972
• 350+ employees
Office Locations
Project Experience
About RWDI – Our Activities
Masterplanning
Structure
External
Spaces
Energy
Consumption
Facades
Comfort
Concept
Design
Internal
Spaces
Detailed
Design
Cladding Wind
Loads
Pedestrian
Comfort
Structural
Wind Loads
Exhaust Reentrainment
Daylighting
Wind Pressure
Ventilation
Sand and
Dust Issues
Aeroacoustics
Snow and
Ice Studies
Glare
Stack Effect
Rain Ingress
Studies
About RWDI… a selection of what we do …
§ Design Advice / Consultation
§ Physical Scale Modeling
(Wind Tunnel / Water Flume)
§ Computer Modelling
§ On-site Monitoring & Measurement
About RWDI
Don’t think of the wind as something that creates
problems that need to be solved …
…consider all the issues at a concept stage and design
to take advantage of the wind
Selected Projects
Wind Engineering
Comparison of CFD and Experimental
Methods
CFD or Experiment in Wind Engineering?
…….OR
BOTH?
CFD or experiment?
Consider APPROPRIATENESS in terms of:
Technical suitability
Purpose of analysis, now and future?
Costs and speed
Regulation and best practice
We use both approaches, but not for the same things!
…….OR
SOMETHING
ELSE?
Modelling Challenges : Scale
weather
Global ~ 10,000 km
CFD
Synoptic ~ 1,000 km
Meso ~ 100 km
City ~ 10 km
wind tunnel
Neighbourhood ~ 1 km
Building ~ 0.1 km
Occupant ~ 0.01 km
11
Modelling
Challenges OF
– Variability
of Wind
CHARACTERISTICS
THE WIND
Wind Roses – Regional Variation
Ca lm
L ig h t a ir
L ig h t b re e ze
90
0
G e n t le b re e ze
16 0 0
330
0
16 0 0
M o d e ra t e b re e ze
330
30
14 0 0
Fre sh b re e ze
30
14 0 0
12 0 0
12 0 0
S t ro n g b re e ze
10 0 0
10 0 0
300
800
270
300
60
600
600
400
400
200
200
0
90
240
12 0
2 10
15 0
18 0
Squires Gate
60
800
270
0
90
240
12 0
2 10
15 0
18 0
London
Annual variability requires modelling full 360° wind environment
Substantial overhead in CFD
Modelling Challenges – Depiction of Wind
Synoptic winds – height profiles
300
Shear
Turbulence
Terrain Roughness
Mean Speed
250
Effective height (m)
Town
200
Country
150
Sea
100
300
50
Gust Speed
250
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Mean wind speed factor
300
0
200
Town
150
Country
Sea
100
250
Town
50
200
Sea
Country
0
1.2
150
1.4
1.6
1.8
1s gust wind speed factor
100
50
0
0.10
Turbulence
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
Turbulence intensity factor
0.20
0.21
0.22
0.23
0.24
2.0
2.2
2.4
Modelling Challenges – Depiction of Wind
Gustiness
15
Gustiness
ORIGINAL
ACTUAL
10
WINDSPEED
5
0
0
0.5
1
1.5
2
2.5
-5
-10
TIME
Variability better represented
in wind tunnel
Critical example: Helipad
studies
3
3.5
4
4.5
5
Accuracy
Wind Tunnel
CFD
An analogue computer
On a digital computer
Unlimited resolution mesh is
automatically generated
Mesh resolution limited and
requires generation process
Full turbulence modelling
Simplified turbulence modelling
Short run times to converge
Convergence times can be long
Required accuracy will depend on purpose of analysis….
Spurious statistics:
Config x θ x locations x Sample = ca. 450,000,000 data points / study
Purpose of Analysis
Scoping Analysis / Parametric Studies
CFD easily altered, can be run quickly to evaluate directions of concern
Purpose of Analysis
CFD convenient for combining wind and other climate modelling
Provides excellent visualisation for early stage parametric analysis
Example: Masterplanning
Purpose of Analysis
Detailed assessment for planning – best practice accuracy needed
Capturing and adjusting fine detail challenging in CFD
Examining statistical wind environment expensive in CFD
Fine Detail
Balconies and Landscaping
Wind Mitigation Measures
Costs and Time
Wind Tunnel
CFD
Model more costly
Lower cost for model
Short and low-cost running times
Longer, more costly running times
Phasing or “Fine tuning” model
adaptations quick to run
Adaptations slow - require remeshing/running
Full 360° wind environment at 10°
resolution quickly
Multiple directions increase cost
very substantially
Wind tunnel experiments often thought of as costly
but
Costs reduced via modern data capture and processing techniques
Cost often less than equivalent CFD for all but simple scoping runs
Regulation
Generally, regulation not prescriptive in terms of methodology
Advantages
Disadvantages
Promotes development of
new techniques
Technologies may be misused
Detailed wind engineering regulatory
requirements more easily proved by
experiment than CFD (e.g. Lawson comfort
criteria for pedestrian wind studies)
Other Approaches - Example
90
91
7
6
5
2
8
9
12
89
15 22
23
19
73
20
17
70
74 72
76
80
16 21
75
11
T99
T93
77
T97
14
13
10
78
4
79
T94
3
92
25
18
T95
69
27
68
35
66
30
31 37
38
34
65
63
33
40
T96
67 62
82
36
T100 32
28
71
29
24
26
81
Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle)
Locations 2 - 92 are on Ground level
43
39
41
61
88
T101
42
64
60
44
45
46
49
54
55
48
51
47
83
53
59
50
52
56
86
57
87
85
58
84
N
Sitting
Standing/Entrances
Leisure walking
Business walking
Car park/roadway
Desk Study – Pedestrian Comfort
LAWSON COMFORT CRITERIA (Worst case season): Proposed Development
90
7
6
5
8
9
12
89
15 22
23
19
73
20
17
70
74 72
76
80
16 21
75
11
T99
T93
77
T97
14
13
10
78
4
T94
3
2
79
25
18
T95
69
27
68
35
66
30
31 37
38
34
65
63
33
40
T96
67 62
82
36
T100 32
28
71
29
24
26
81
43
39
41
61
88
T101
42
64
60
44
45
46
49
54
55
48
51
47
83
53
59
52
56
50
Courtyards
suitable for
sitting in BOTH
studies
91
92
86
57
87
85
58
84
N
Sitting
Standing/Entrances
Leisure walking
Business walking
Car park/roadway
90
7
6
5
8
9
12
89
15 22
23
19
73
20
17
70
74 72
76
80
16 21
75
11
T99
T93
77
T97
14
13
10
78
4
T94
3
2
79
25
18
T95
69
27
68
35
66
30
31 37
38
34
65
63
33
40
T96
67 62
82
36
T100 32
28
71
29
24
26
81
43
39
41
61
88
T101
42
64
60
44
45
46
49
54
55
48
51
47
83
53
59
Corners suitable
for strolling in
BOTH studies
91
92
50
52
56
86
57
87
85
58
84
N
Sitting
Standing/Entrances
Leisure walking
Business walking
Car park/roadway
90
7
6
5
8
9
12
89
15 22
23
19
73
20
17
70
74 72
76
80
16 21
75
11
T99
T93
77
T97
14
13
10
78
4
T94
3
2
79
25
18
T95
69
27
68
35
66
30
31 37
38
34
65
63
33
40
T96
67 62
82
36
T100 32
28
71
29
24
26
81
43
39
41
61
88
T101
42
64
60
44
45
46
49
54
55
48
51
47
83
53
59
52
56
50
Corners suitable
for mix of
business
walking, strolling
91
92
86
57
87
85
58
84
N
Sitting
Standing/Entrances
Leisure walking
Business walking
Car park/roadway
90
7
6
5
8
9
12
89
15 22
23
19
73
20
17
70
74 72
76
80
16 21
75
11
T99
T93
77
T97
14
13
10
78
4
T94
3
2
79
25
18
T95
69
27
68
35
66
30
31 37
38
34
65
63
33
40
T96
67 62
82
36
T100 32
28
71
29
24
26
81
43
39
41
61
88
T101
42
64
60
44
45
46
49
54
55
48
51
47
83
53
59
Predicted
strolling –
calmer in reality
91
92
50
52
56
86
57
87
85
58
84
N
Sitting
Standing/Entrances
Leisure walking
Business walking
Car park/roadway
Case Study Example
Case Study:
Using CFD to Examine Masterplan
Microclimate
Masterplanning - Why Examine Urban Microclimate?
How People Perceive Climate
•
Comfort is a complex phenomena
It varies from person to person
SPMV*
•
•
4
3
Hot
2
Warm
1
Slightly
Warm
Neutral
0
-1
A combination of four environment variables
-2
– Wind speed
-3
– Temperature
-4
– RH
– Radiant temperatures (solar impact, hot surfaces)
•
Plus personal factors
– Clothing levels
– Activity
•
Other parameters like gender, height have a lesser
role.
Slightly
Cool
Cool
Cold
Masterplanning – How to Improve Comfort
Layout & Orientation
Limited cross flow
Broken lines encourage
wind flow into side streets
East-West main streets are
in direct sun all day during
the summer months
This orientation allows
maximum self-shading.
Main streets encourage
penetration of prevailing
winds
Typical Study Requirements - Masterplanning
•
•
•
•
•
Scoping level
Identify main factors, make improvements
Ease of visualisation important for client
High-level decisions
Not for regulatory purposes
Desk-based assessment or CFD appropriate
Berlin – Aerial Image of Site
rwdi.com
Berlin – Development
Modelling carried out combining CFD, solar modelling and statistical meteorological records
rwdi.com
Berlin – Wind Speed
Annual mean wind speed (all directions)
low
high
rwdi.com
Berlin – Solar Exposure
Sky view factors – annual average
low
high
rwdi.com
Berlin – Thermal Comfort
SPMV*
Canada | China | Hong Kong | Indiacomfort
| Singapore | UK | USA
worse
better
rwdi.com
Berlin – Wind Chill
Wind chill
low
high
rwdi.com
Berlin – Wind Energy Potential
Wind energy potential
low
high
rwdi.com
Berlin – Annual Solar
Solar radiation to surfaces (e.g. MWh/m2/yr)
low
high
rwdi.com
Berlin – Façade Illuminance
Annual availability of daylight on facades
low
high
rwdi.com
Case Study Example
Case Study:
What is “Exhaust Re-entrainment”?
• Entry or re-entry of exhaust gases into a building that can lead to
indoor air quality problems
– Building exhausts into own air intakes
– Building exhausts into neighbouring air intakes
– Neighbour’s exhausts into our building air intakes
41
before raising stack height
after raising stack height
CFD Modelling: Exhaust Re-Entrainment
Computational Fluid Dynamics (CFD)
Quickly highlights potential issues
Example Results : Exhaust Re-Entrainment
Wind Tunnel Modeling : Exhaust Re-Entrainment
• Most accurate and reliable
• Accuracy important when
dealing with gases with health
impacts
• Fine-tuning designs
• Includes complex geometry
Wind Direction
Pump
Exhaust Stack
Modeled Air
Flow
Air
Intake
Gas
Analyzer
Results
Tracer
Gas
PC
45
Typical Study Requirements – Exhaust Re-Entrainment
•
•
•
•
•
Scoping level
Identify if a problem is likely
Few wind directions of concern
Lower-impact problem
Not for regulatory purposes
Desk study or CFD appropriate
• Detailed design
• Need to examine full wind
environment
• Higher-impact problem
• Study to demonstrate regulatory
compliance
Wind tunnel study appropriate
Conclusions
Conclusions
Choice of approach dependent on the purpose of the analysis
q CFD useful for scoping problems; less appropriate for final approval and fine
detailing.
q Experimental methods fast to run once model is built; both mean and gust
conditions are simulated; requires expert teams
q Pedestrian comfort and structural regulations generally don’t favour specific
methods but standards more easily met by wind tunnel experiments.
User should define purpose of the study, configurations to be assessed and
required future flexibility before deciding on approach.
q Wind tunnel experiment costs biased towards creation of model, CFD spread
between model creation and run time.
q Costs of experiments can be competitive with CFD (particularly when the
unexpected happens!).
Thank you for your time and attention
Are there any questions ?

Wind – Analogue or Digital?.

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