Urban Physics: towards sustainable buildings and cities

Inauguration Event & Mini-Symposium for Prof.dr. Alexey Voinov: SYSTEMS AND SUSTAINABILITY IN TIME AND SPACE Urban Physics: towards sustainable buildings and cities Prof.dr.ir. Bert Blocken Eindhoven University of Technology, NL Department of Civil Engineering Leuven University, Belgium

2. SPATIAL SCALES Question Wind flow between buildings

QUESTION: WIND FLOW BETWEEN BUILDINGS Top view of two high-rise buildings in V arrangement. Wind direction from bottom to top. Which configuration yields the highest wind speed in the passage? wind wind B A CONVERGING DIVERGING

2. SPATIAL SCALES I DEFINITION

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. AIM: Providing an outdoor and indoor built environment that is: healthy comfortable taking into account existing and/or future economical energetic ecological climatic constraints.

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. Urban Heat Island (UHI) effect in metropolitan Atlanta, May 11-12, 1997 (NASA/Goddard Space Flight Center Scientific Visualization Studio)

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. Hurricane Katrina flooding of New Orleans, August 29, 2005 (dannyordes.com/katrina.html)

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. Hunting Lodge St. Hubertus, Hoge Veluwe, Netherlands

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. Builiding facade moisture damage - Hunting Lodge St. Hubertus, Hoge Veluwe, Netherlands

DEFINITION Urban physics is the science and engineering of physical processes in urban areas. Royal Festival Hall, London, UK (White 1967)

2. SPATIAL SCALES II SPATIAL SCALES

SPATIAL SCALES

2. SPATIAL SCALES III BASIC RESEARCH

2. SPATIAL SCALES BRIEF OVERVIEW

BASIC RESEARCH 1. ASSESSMENT METHODS Bluff body aerodynamics is very complex. (Modified from Hosker, 1984)

BASIC RESEARCH 1. ASSESSMENT METHODS Bluff body aerodynamics is very complex.! Bluff body aerodynamics research is performed by: (1) On-site measurements

BASIC RESEARCH 1. ASSESSMENT METHODS Bluff body aerodynamics is very complex.! Bluff body aerodynamics research is performed by: (1) On-site measurements (2) Wind tunnel measurements

BASIC RESEARCH New TU/e Atmospheric Boundary Layer Wind Tunnel Facility

BASIC RESEARCH 1. ASSESSMENT METHODS Bluff body aerodynamics is very complex.! Bluff body aerodynamics research is performed by: (1) On-site measurements (2) Wind tunnel measurements (3) Numerical simulation with Computational Fluid Dynamics (CFD)

BASIC RESEARCH 2. COMPUTATIONAL FLUID DYNAMICS Innovation focus of our group (basic research): 1. Development of consistent CFD simulation formulations for atmospheric boundary layer flow * u outlet plane ABL y + y = 0 U(y) ln κ y0 inlet flow incident flow approach flow inlet plane upstream part of computational domain central part of computational domain downstream part of computational domain U p 2 τ u u * = 1 κ k = S,ABL E u * y p ln ν(1 + Cs k s + ) 9.793 C s y 0 Blocken B, Stathopoulos T, Carmeliet J. 2007. CFD simulation of the atmospheric boundary layer: wall function problems. Atmospheric Environment 41(2): 238-252

BASIC RESEARCH 2. COMPUTATIONAL FLUID DYNAMICS Innovation focus of our group (basic research): 1. Development of consistent CFD simulation formulations for atmospheric boundary layer flow 2. Development of high-quality grid generation techniques 3. Verification and validation studies 4. Application of these developments for new and improved insights in basic flow problems in urban environments (see next slides)

2. SPATIAL SCALES BASIC FLOW PHENOMENA

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION?

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? QUESTION Top view. Two buildings. Wind direction from bottom to top. Which configuration yields the highest wind speed in the passage? wind wind A B CONVERGING DIVERGING Blocken B, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturi-effect in passages between perpendicular buildings. Journal of Engineering Mechanics - ASCE 134(12): 1021-1028.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? QUESTION Top view. Two buildings. Wind direction from bottom to top. Which configuration yields the highest wind speed in the passage? Venturi effect? wind wind A B CONVERGING DIVERGING Blocken B, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturi-effect in passages between perpendicular buildings. Journal of Engineering Mechanics - ASCE 134(12): 1021-1028.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Venturi effect: increase of fluid speed due to a decrease of the flow section (Giovanni Battista Venturi, 1799) Theory (confined flow) Reality (open flow) There is no law in physics that says that all the flow has to go through the narrow passage... Is the Venturi effect present in the non-confined flows in urban physics / wind engineering?

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Venturi effect: increase of fluid speed due to a decrease of the flow section (Giovanni Battista Venturi, 1799) Giovanni Battista Venturi (1746-1822) Special thanks to Sandra Johnson and her colleagues from the Niels Bohr Library of the American Institute of Physics for copying this precious (and fragile) book for me.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Three common types of passages between buildings (a) parallel, side-by-side (b) parallel, shifted (c) perpendicular Typical Venturi configuration Conditions for the occurrence of the Venturi effect (Gandemer 1975): 1) H > 15 m 2) L 1 + L 2 > 100 m 3) Exposed site Maximum flow through the passage when passage width is 2 or 3 times the height

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Wind speed measurements for converging and diverging arrangement

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Wind speed measurements for converging and diverging arrangement Atmospheric boundary layer wind tunnel at the Building Aerodynamics Laboratory, Concordia University, Montreal Blocken B, Stathopoulos T, Carmeliet J. 2008. Wind environmental conditions in passages between two long narrow Department perpendicular of the buildings. Built Environment Journal of Aerospace Engineering ASCE Building 21(4): Physics 280-287. and Services

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? CFD simulations - ANSYS Fluent CFD code - Steady RANS - Realizable k-ε model (Shih et al. 1995) - Standard wall functions with sand-grain-based roughness modification - Equivalent sand-grain roughness k S and roughness constant C S based on aerodynamic roughness length y 0 and equation k S = 9.793y 0 /C S. - SIMPLE for pressure velocity-coupling - Second order discretisation schemes - Pressure interpolation: second order For other computational details, see: Blocken B, Moonen P, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturieffect in passages between perpendicular buildings. Journal of Engineering Mechanics ASCE 134(12): 1021-1028.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? CFD results: wind speed amplification factor K at pedestrian level (z = 2 m) 1.7 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 1.7 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 (a) wind 75 CONVERGING w = 75 m (a) wind wind w = 20 m wind (b) (b) wind wind wind CONVERGING w = 20 m DIVERGING w = 20 m Counter-intuitive result DIVERGING wind w = 75 m

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Counter-intuitive result: wind-blocking effect: upstream wind-speed slow-down

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? CFD results: passage fluxes (flow rates) F P F F Blocken B, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturi-effect in passages between perpendicular buildings. Journal of Engineering Mechanics - ASCE 134(12): 1021-1028.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? Schematic of wind-flow pattern extracted from CFD results Upflow due to windblocking effect causes the decrease in K pcp (wind speed) in the upper part of the passage. Blocken B, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturi-effect in passages between perpendicular buildings. Journal of Engineering Mechanics - ASCE 134(12): 1021-1028.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? There is no Venturi effect in the passage between these buildings because it is not a confined flow. Actually, wind tunnel measurements and CFD simulations show the opposite effect. This is a deeply rooted misunderstanding about wind flow between buildings.

VENTURI EFFECT BETWEEN BUILDINGS: FACT OR FICTION? This work was published in three parts and in three different ISI Journals, received very positive reviews and quite a good number of citations. Blocken B, Stathopoulos T, Carmeliet J. 2008. A numerical study on the existence of the Venturi-effect in passages between perpendicular buildings. Journal of Engineering Mechanics - ASCE 134(12): 1021-1028. Blocken B, Stathopoulos T, Carmeliet J. 2008. Wind environmental conditions in passages between two long narrow perpendicular buildings. Journal of Aerospace Engineering - ASCE 21(4): 280-287. Blocken B, Carmeliet J, Stathopoulos T. 2007. CFD evaluation of the wind speed conditions in passages between buildings effect of wall-function roughness modifications on the atmospheric boundary layer flow. Journal of Wind Engineering and Industrial Aerodynamics 95(9-11): 941-962.

EXAMPLE: BAHRAIN WORLD TRADE CENTER

EXAMPLE: BAHRAIN WORLD TRADE CENTER Bahrain World Trade Center - Opened in 2008 - USD $150 million - 240 m height - Three 29 m wind turbines (225 kw) - Oriented to capture the prevailing on-shore Gulf breeze

EXAMPLE: BAHRAIN WORLD TRADE CENTER Bahrain World Trade Center Prevailing on-shore Gulf breeze - Opened in 2008 - USD $150 million - 240 m height - Three 29 m wind turbines (225 kw) - Oriented to capture the prevailing on-shore Gulf breeze

EXAMPLE: BAHRAIN WORLD TRADE CENTER Prevailing on-shore Gulf breeze CONVERGING CONFIGURATION

EXAMPLE: BAHRAIN WORLD TRADE CENTER The earlier academic/theoretical example CONFIGURATION WITH HIGHEST WIND SPEED A B CONVERGING DIVERGING shows a striking resemblance to the configuration of the Bahrain WTC. CHOSEN CONFIGURATION CONVERGING DIVERGING

EXAMPLE: BAHRAIN WORLD TRADE CENTER Investigation! Detailed study by wind-tunnel testing and Computational Fluid Dynamics simulations.

EXAMPLE: BAHRAIN WORLD TRADE CENTER CFD simulations: amplification factor K in horizontal plane

EXAMPLE: BAHRAIN WORLD TRADE CENTER CFD simulations: yearly wind energy output Conclusion: Bahrain WTC has a good design, but it can be improved significantly.

2. SPATIAL SCALES IV APPLIED RESEARCH PROJECTS

1. NATURAL VENTILATION OF THE AMSTERDAM ARENA STADIUM

1. NATURAL VENTILATION OF THE AMSTERDAM ARENA STADIUM van Hooff T, Blocken B, 2010. Coupled urban wind flow and indoor natural ventilation modelling on a highresolution grid: a case study for the Amsterdam ArenA stadium. Environmental Modelling & Software 25(1): 51-65. van Hooff T, Blocken B, 2010. On the effect of wind direction and urban surroundings on natural ventilation of a large semi-enclosed Department stadium. of the Computers Built Environment & Fluids 39: 1146-1155.

1. NATURAL VENTILATION OF THE AMSTERDAM ARENA STADIUM COMPUTATIONAL GRID van Hooff T, Blocken B, 2010. Coupled urban wind flow and indoor natural ventilation modelling on a highresolution grid: a case study for the Amsterdam ArenA stadium. Environmental Modelling & Software 25(1): 51-65. van Hooff T, Blocken B, 2010. On the effect of wind direction and urban surroundings on natural ventilation of a large semi-enclosed Department stadium. of the Computers Built Environment & Fluids 39: 1146-1155.

1. NATURAL VENTILATION OF THE AMSTERDAM ARENA STADIUM COMPUTATIONAL RESULTS

1. NATURAL VENTILATION OF THE AMSTERDAM ARENA STADIUM ON-SITE MEASUREMENTS Outdoor and indoor measurements of: - wind speed - vapor pressure - air temperature - CO 2 concentration

2. AIR POLLUTANT DISPERSION IN DOWNTOWN MONTREAL PROBLEM STATEMENT Gousseau P, Blocken B, Stathopoulos T, van Heijst GJF. 2011. CFD simulation of near-field pollutant dispersion on a high-resolution grid: a case study by LES and RANS for a building group in downtown Montreal. Atmospheric Department Environment of the 45(2): Built 428-438. Environment

2. AIR POLLUTANT DISPERSION IN DOWNTOWN MONTREAL ON-SITE MEASUREMENTS OF GAS DISPERSION Stathopoulos T, Lazure L, Saathoff P, Gupta A. 2004. The effect of stack height, stack location and roof-top structures on air intake contamination - A laboratory and full-scale study. IRSST report R-392, Montreal, Canada, 2004.

2. AIR POLLUTANT DISPERSION IN DOWNTOWN MONTREAL WIND TUNNEL TEST SET-UP AND HIGH-RESOLUTION CFD GRIDS Gousseau P, Blocken B, Stathopoulos T, van Heijst GJF. 2011. CFD simulation of near-field pollutant dispersion on a high-resolution grid: a case study by LES and RANS for a building group in downtown Montreal. Atmospheric Department Environment of the 45(2): Built 428-438. Environment

2. AIR POLLUTANT DISPERSION IN DOWNTOWN MONTREAL CFD SIMULATIONS: RESULTS

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY PROBLEM STATEMENT Not taking into account potential wind comfort problems in the design of new buildings can have serious consequences for pedestrians around buildings. Many wind comfort and wind safety problems exist in cities worldwide, and also in Eindhoven.

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY PROBLEM STATEMENT High-rise buildings in atmospheric boundary layer flow deviate wind flow down to pedestrian level.

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY PROBLEM STATEMENT

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY PROBLEM STATEMENT Hooligan-proof Hooligan-proof

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY HIGH-RESOLUTION COMPUTATIONAL GRID

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY WIND VELOCITY VECTORS

3. PEDESTRIAN-LEVEL WIND COMFORT AND SAFETY CONSTRUCTION OF LARGE CANOPY

4. WIND CONDITIONS IN HARBORS RESEARCH PROJECT WITH PORT OF ROTTERDAM

4. WIND CONDITIONS IN HARBORS RESEARCH PROJECT WITH PORT OF ROTTERDAM (Janssen, Blocken, van Wijhe 2011)

4. WIND CONDITIONS IN HARBORS RESEARCH PROJECT WITH PORT OF ROTTERDAM (Janssen, Blocken, Building van Wijhe Physics 2011) and Services

4. WIND CONDITIONS IN HARBORS RESEARCH PROJECT WITH PORT OF ROTTERDAM

5. WIND CONDITIONS AT CRUISE TERMINAL

5. WIND CONDITIONS AT CRUISE TERMINAL (Janssen, Blocken, van Wijhe 2014)

5. WIND CONDITIONS AT CRUISE TERMINAL (Janssen, Building Blocken, Physics van and Wijhe Services 2014)

5. WIND CONDITIONS AT CRUISE TERMINAL (Janssen, Blocken, van Wijhe 2014)

Inauguration Event & Mini-Symposium for Prof.dr. Alexey Voinov: SYSTEMS AND SUSTAINABILITY IN TIME AND SPACE THANK YOU Prof.dr.ir. Bert Blocken Eindhoven University of Technology, NL Department of Civil Engineering Leuven University, Belgium