wind pressure distribution of tall buildings using CFD

PARAMETERS INFLUENCING THE WIND
PRESSURE DISTRIBUTION OF TALL BUILDUINGS
USING CFD
Department of civil engineering
Faculty of engineering
University of Peradeniya
Sri Lanka
Date : 1/4/2019 1
The 9th International Conference on Sustainable Built Environment, Earl’s Regency Hotel, Kandy, Sri Lanka, Dec 13th-15th , 2018
P.L.L.T. Padmasiri
M.A.A. Gayan
Samith Buddika

CONTENTS
 INTRODUCTION
 COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS
 HIGH FREQUENCY BASE BALANCE DATA ANALYSIS(HFBB)
 BUILDING DESCRIPTION
 NUMERICAL MODELLING
 ANALYSIS RESULTS
 CONCLUSION
2
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INTRODUCTION
31/4/2019
Colombo, Sri Lanka

INTRODUCTION
1/4/2019 4
Fort-worth , Texas, US
Peel county , Ontario , Canada
Iniki hurricane ,Hawaii , US

INTRODUCTION
Wind loads on buildings have conventionally been determined through,
 wind tunnel experiments, but It’s expensive and a time consuming
process
 code-based approaches are commonly used in construction industry,
because it’s cost effective process.
Due to the limitations in conventional approaches and complexity of
conducting wind tunnel experiments , the use of Computational Fluid
Dynamics (CFD) simulation in determining wind loads has become a
sophisticated alternative in the construction industry
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CFD Simulation
In numerical modelling many factors should be taken into consideration,
computational domain
boundary conditions
Grid generation & solver settings
• In our study 3 main settings in model establishment are outlined ,
 Inflow boundary condition
 Mesh sensitivity
 Turbulence model
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COMPUTATIONAL DOMAIN
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500m
(56m)
(340m)
(204m)
(340m)
Y
X
Z
Inlet
outlet
PLAN VIEW
END VIEW

BOUNDARYCONDITIONS
• The boundary conditions for inlet, outlet and outer walls should be provided.
These boundary conditions are ,
• Velocity
• pressure
• mass flow rates etc.
• Inviscid wall condition and zero normal velocity flux for the surfaces of the fluid
domain which are parallel to the air flow
• Atmospheric pressure at the outlet.
• No-slip boundary condition at the ground
(bottom wall) and surface of the building
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INFLOWBOUNDARYCONDITION
• Finding actual wind profile is extremely costly, tedious and time
consuming. Therefore wind engineers use simple empirical wind profiles,
– Power low method
– Logarithmic wind profile
• Use logarithmic wind profile for calculating wind velocity (Eurocode 1991,
Part 1-4: Wind actions)
𝑣 𝑚(𝑧) = 0.19.
𝑧0
𝑧0′ 𝑖𝑖
. ln(
𝑧+𝑧0
𝑧0
). 𝑣 𝑏
z0 - the roughness height
Z0,ii -Terrain category
Vb - mean wind speed
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Mesh sensitivity
• Mesh sensitivity depends on various parameters such as,
– number of nodes
– number of elements
– Aspect ratio
• In this study, size control is changed for changing
above parameters. Selected sizes of size control,
– 0.5m , 1m and 2m
If Aspect ratio is too large, it can cause
convergence problems during the analysis
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Turbulence models
• RANS equation cannot be solvable directly, therefore turbulence
models are used for solving
• No single turbulence model is universally accepted as being superior
for all classes of problems.
Choice of turbulence models depends on considerations such as ,
 physics encompassed in the flow
 established practice for a specific class of problem
 level of accuracy required
 available computational resources
 amount of time available for the simulation
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BUILDING DESCRIPTION
 Height- 136m and 198m
 Assumed to be located in Colombo where the 3-second
Mean wind speed was determined as 38 m/s
 They consist of 40 and 60 storeys with an inter storey
height of 3.4 m and 3.3 m respectively.
 The exposure category was chosen as Exposure A (urban) and the
aspect ratios were taken as 3:6:16 and 3:6:20
 building density was taken as 520 kg/m3 and the air density was
taken as 1.25 kg/m3
136m
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High Frequency Base Balance analysis (HFBB)
 High-Frequency Base Balance (HFBB) data analysis has consisted with wind
tunnel test data
 Two kinds of wind tunnel-based procedures have been introduced,
1.an empirical expression for the wind-induced acceleration
(the National Building Code of Canada (NBCC))
2.an aerodynamic-load-based procedure
(Australian Standard (AS) and the Architectural Institute of Japan (AIJ))
 can only be readily applied for buildings with regular geometries
131/4/2019

NatHaz Aerodynamic Loads Database
This interactive database provides users with ,
• the RMS base bending moment coefficients
• the non-dimensionalized power spectra obtained from HFBB
measurements
on rigid building models of various aspect ratios and geometries,
exposed to two typical boundary layers.
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PRESSURE VARIATION FROM HFBB ANALYSIS
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0
20
40
60
80
100
120
140
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
buildingheight/m
pressure / kpa
Along wind pressure distribution for wind
in the y direction for the 136 m building
0
20
40
60
80
100
120
140
160
180
200
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
buildingheight/m pressure /kpa
Along wind pressure distribution for wind
in y direction for the 198 m building

Inflowboundarycondition
– Inlet velocity given to separate domain
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- Inlet velocity given by an equation
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Inflowboundarycondition

0.0 0.2 0.4 0.6 0.8 1.0 1.2
0
20
40
60
80
100
120
140
Buildingheight(m)
Pressure (kPa)
HFBB Analysis
Inlet velocity - Domain
Inlet velocity - Equation
Comparison of results using different inlet velocity input condition
201/4/2019

Comparison of results using different inlet velocity input condition
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-0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
0
20
40
60
80
100
120
140
160
180
200
Buildingheight(m)
Pressure (kPa)
HFBB Analysis
Inlet velocity - Domain
Inlet velocity - Equation

221/4/2019

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Mesh sensitivity
• The meshing was done without having any higher order elements , including
geometric proximity , avoid tetra with all boundary nodes
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Pressure variation with height of the building with different mesh size
control
25
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0
20
40
60
80
100
120
140
Buildingheight(m)
Pressure (kPa)
HFBB Analysis
mesh size = 0.5 m
mesh size = 1.0 m
mesh size = 2.0 m
(a)
1/4/2019

Pressure variation with height of the building with different mesh size
control
1/4/2019 26
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
0
20
40
60
80
100
120
140
160
180
200
Buildingheight(m)
Pressure (kPa)
HFBB Analysis
mesh size = 0.5 m
mesh size = 1.0 m
mesh size = 2.0 m
(b)

Turbulence models
In the study four turbulence models are used,
 Large eddy
 K-w SST
 Standard k-e
 K-w
Above turbulence models are used because of it’s wide
applicability, simplicity, accuracy and also economical
1/4/2019 27

Comparison of pressure distribution along the building height for
difference Turbulence models
28
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0
20
40
60
80
100
120
140
Buildingheight(m)
Pressure (kPa)
HFBB Analysis standard k-e
large eddy k-w
k-w SST
1/4/2019

Comparison of pressure distribution along the building height for
difference Turbulence models
1/4/2019 29
-0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
0
20
40
60
80
100
120
140
160
180
200
Buildingheight(m)
Pressure (kPa)
HFBB Analysis standard k-e
large eddy k-w
k-w SST

CONCLUSIONS
 Regarding mesh sensitivity it is found that the mesh size range from
0.5m – 1.0m is appropriate for the analysis of both buildings.
 When the inflow boundary condition specified as a velocity profile
using an equation the convergence and the time taken for analysis is
greatly improved, in comparison to manual input methods.
 More over the standard k – e turbulence model results in a better
estimation of wind pressure data when compared to HFBB analysis.
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ONGOING WORKS
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331/4/2019

REFERENCES
 Australian and New Zealand standards: Structural Design Actions Part 2: Wind actions; AS/NZS
1170.2:2002, Standards Australia
 British Standard: Eurocode 1: Actions on Structures – Part1- 4: General actions – Wind actions; BS
EN 1991-1-4:2005, British Standard Institution, London
 Kijewski, T., and Kareem, A. (1998). ‘‘Dynamic wind effects: A comparative study of provisions in
codes and standards with wind tunnel data.’’ Wind Struct., 77–109
 Zhou, Y., Kareem, A., and Gu, M. (2002). ‘‘Mode shape corrections for wind load effects.’’ J. Eng.
Mech., 128(1), 15–23
 Blocken, B., Carmeliet, J., Stathopoulos, T.,(2007) “Journal of Wind Engineering and Industrial
Aerodynamics”
 A.U. Weerasuriya ., Computational Fluid Dynamic (CFD) Simulation of Flow around Tall
Buildings.Journal of Institution of Engineers, Sri Lanka ,pp 43 – 54, 2013
 Koliyabandara, N., Wijesundara, K., and Jayasundara, D. (2017). ‘‘Analysis of wind load on an
irregular shaped tall building using numerical simulation.’’ ICSECM, No 456.
https://www.researchgate.net/publication/321719812
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High Frequency Base Balance data analysis(HFBB)
Basic Equation
𝑞(𝑧) - the velocity pressure at height z
𝐺 - the gust effect factor
𝐶𝑝 - the pressure coefficient
𝜌 - the air density
𝑉𝑚(𝑧) - the mean velocity at height 𝑧
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High Frequency Base Balance data
analysis(HFBB)
P(Z)-mean, components of the equivalent
static wind loads
PB(Z)- background components of the
equivalent static wind loads
PR(Z)-resonant components of the equivalent
static wind loads
Where, α=0.35 urban environment
and β=1 linear mode shape
∆H – internal storey height
CD –Drag coefficientESWL =P(z) +√ PB(z)2 +PR(z)2
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High Frequency Base Balance data analysis(HFBB)
M - mean moment,
g - peak factor,
𝜎𝑀 - Root Mean Square (RMS) of
fluctuating base moment/torque response
𝑀 𝐵 - background base moment or torque
component
𝑀 𝑅- resonant base moment or torque
component
SM - The Power Spectral Density (PSD)
|𝐻1(𝑓)|2 - structural first mode transfer
function
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CFD simulations
38
 Main components of CFD Simulation,
1. Computational domain
2. Meshing
3. Boundary conditions for inlet, outlet and walls.
 Numerical simulations,
1. Micro scale
2. Meso scale
 CFD simulation is used micro scale modelling.
 Man made structure are within the Atmospheric boundary layer.
 Therefore governing equation can be applied.
 Governing equations(Navier Stokes equation)
1. Conservations of mass
Eq (1)
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40
2.Conservation of momentum
 a is the acceleration of fluid elements,
and it is given by
 Expanding into its Cartesian components
 There are two types of forces acting on the fluid element: body force (δFB) and surface force (δFS)
δF = δFB + δFS
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41
 The only body force considered here is the weight of the fluid element
δFB = δm g = δm (gx i + gy j + gz k)
 There are two types of stresses applied on the surface:
normal stress (σij) and shear stress (τij).
similarly,
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42
 Apply f=ma
For Newtonian fluids
 μ is the viscosity of the fluid
 For incompressible flow, the term .v is zero based on the continuity equation.
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43
Conservation of momentum
ρ – air density
P - air pressure
μ - dynamic viscosity,
 Neglected Coriolis force and buoyance forces because small length and time scale
 Navier stokes equation was developed for the laminar flow.
 Atmospheric flow is turbulent with three dimension random unsteady motion
Eq (2)
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44
 Rearranged as Reynolds Average Navier stokes equation(RANS)
u = u + u′ , v = v + v′ ,w = w + w’
U – mean velocity
U’– fluctuating velocity
Substituting Equation (3) in Equation (2)
tensor form:
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Mixing Length model
Advantages
 Easy to implement and cheap in
terms of computing resources
 Good predictions for thin shear layers
: jets, mixing layers, wakes and
boundary layers
 Well established
Disadvantages
 Completely incapable of describing
flows with separation and
recirculation
 Only calculates mean flow properties
and turbulent shear stress
k – έ model
Advantages
 Simple turbulence model for which
only boundary conditions need to be
supplied
 Excellent performance for many
industrially relevant flows
 Mostly widely validated
Disadvantages
 More expensive to implement than
mixing length model(two extra PDEs)
 Poor performances in a variety of
important cases such as some
unconfined flows ary layers, swirling
flows)
 Fully developed flows in non circular
ducts 451/4/2019

Reynolds stress equation
model
Advantages
 Potentially the most general of all
classical turbulence models
 Very accurate calculation of mean flow
properties and all Reynold stresses for
many simple and more complex flows
including
 Wall jets ,asymmetric channel and non-
circular duct flows and curved flows
Disadvantages
 Very large computing costs (7 extra
PDEs)
 Not as widely validated as above 2
models mentioned
 Performs just as poorly as the k- έ
model in some flows owing to identical
problems with the έ - equation
modelling
Algebraic stress model
Advantages
 Cheap method to account for Reynolds stress
anisotrophy
 Potentially combines the generality of approach
of the RSM With the economy of the k- έ model
 Successfully applied to iso-thermal and buoyant
thin shear layers
Disadvantages
 Only slightly more expensive than k- έ model (2
PDEs and a system of algebraic equations)
 Not as widely validated as the mixing length and
k- έ model
 Model is severely restricted in flows where the
transport assumptions for convective and
diffusive effects don’t apply- validation is
necessary to define the limits
461/4/2019

What and how are we going
to validate?
471/4/2019

wind pressure distribution of tall buildings using CFD

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