Computational Wind Engineering

Activities at CERN

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ANSYS conference & 21. Schweizer Cadfem Users’ Meeting, 16th June 2016 Winterthur

Aniko Rakai – CERN EN-CV, CFD team

Overview

• CERN and its CFD team

• Computational wind engineering

• Demonstration on CERN Meyrin site

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Overview

• CERN and its CFD team

• Computational wind engineering

• Demonstration on CERN Meyrin site

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CERN:

Organisation européenne pour la recherche nucléaire

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Organisation européenne pour la recherche

nucléaire

Safety first!

“I believe CERN should become a role model

for an environmentally-aware scientific

research laboratory. Risk assessment and

prevention and emergency preparedness

are also key targets.”

Fabiola Gianotti – CERN Director-General

https://cds.cern.ch/journal/CERNBulletin/2016/09/News Articles/2133794

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CFD team at CERN

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• CFD studies have been carried out at CERN

since 1992, the CFD team was created in

2004 in the Cooling and Ventilation group of

the Engineering Department;

• 2-3 persons, fellows or technical students;

• 4-6 projects per year;

• www.cern.ch/cfd.

Overview

• CERN and its CFD team

• Computational Wind Engineering

• Demonstration on CERN Meyrin site

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Computational wind engineering

Use of computational fluid dynamics in wind

engineering

Wind engineering: the rational treatment of

interactions between wind in the

atmospheric boundary layer and man and

his works on the surface of Earth.

(Cermak, J.E. 1975. Applications of fluid mechanics to wind engineering – A Freeman Scholar

Lecture. J. Fluids Engng., ASME, March, 9-38.)

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Potential usage 1

Wind load definition on structures

CFD Challenge: Most important is peak

pressure, not available with RANS.

Safety benefit: Reduce risk

of breaking structures.

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http://www.roofservices.com/Home/RoofingBlog/tabid/100/

entryid/92/Prepare-the-Roof-for-Hurricane-Winds.aspx

Potential usage 2

Wind comfort study

CFD Challenge: Simulation of the extremities,

RANS is questionable.

Safety benefit:

Potentially dangerous

zones located.

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Potential usage 3

Detailed environmental emission model

CFD Challenge: Covering the wind statistics

with sufficient simulations.

Safety benefit: Awareness

of immission close to sources.

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Potential usage 4

Emergency preparedness

CFD Challenge: Identification of probable

scenarios, keeping pre-run data.

Safety benefit: Fast reaction

in case of accident,

risk assessment.

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Overview

• CERN and its CFD team at CERN

• Computational Wind Engineering

• Demonstration on CERN Meyrin site

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Goal of the preparatory project

• Build up a strategy for the calculations;

• Automatize what is possible;

• Identify stakeholders;

• Identify safety benefit for CERN and related

scenarios;

• Raise awareness of the availability of this

method.

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What is around the Meyrin site?

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0.00

0.01

0.02

0.03

0.04

N

NNE

NE

ENE

E

ESE

SE

SSE

S

SSW

SW

WSW

W

WNW

NW

NNW

0.00

0.01

0.02

0.03

0.04

All classes

MSPA41 in 2011,12,14

From CERN’s Wind Atlas

(Pavol Vojtyla)

Geometry input data• Data openly available

from Geneva canton GIS

database (Système d’information

du territoire à Genève – ge.ch/sitg)

• MN95 coordinate system

• ESRI grid raster format

for topography

• GIS shape, 3DS or DXF

format for buildings

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CERN Meyrin site

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Not a typical urban

geometry, but similar, with

important elevation change

Challenges

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• Around 200 buildings for the Meyrin site

(there are other smaller sites as well);

• 1.5km x 2km domain;

• Complex topography.

Building clean-up: Icem

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Building clean-up: SCDM

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Building clean-up: SCDM

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Building clean-up: SCDM

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Building clean-up: SCDM

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Topography clean-up: original stl

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Number of faces:

~ 24 million

Faces over 0.7 quality:

~ 8000

Quality histogram with

skewness, smaller is better

0 10.3

Face

number

count

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Topography clean-up: 1m

resolution shrink wrap

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Number of faces:

~ 7 million

Faces over 0.7 quality:

0

Quality histogram with

skewness, smaller is better

0 10.3

Face

number

count

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Topography clean-up: 3m

resolution shrink wrap

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Number of faces:

~ 0.7 million

Faces over 0.7 quality:

0

Quality histogram with

skewness, smaller is better

0 10.3

Face

number

count

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Combination of topology and

buildings: original

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Combination of topology and

buildings: after shrink wrap

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Number of faces:

~ 12.5 million

Faces over 0.7 quality:

5

Quality histogram with

skewness, smaller is better

0 10.3

Face

number

A. Rakai

Demonstrative calculations on a

smaller domain:Only 17 buildings in the centre:

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Pollutant source next to a building

Far field wind direction

• rke turbulence model

• SIMPLE p-v coupling

• ABL inlet

• UDS passive scalar

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Volume mesh Cell

number

Cell

number

Quality histogram with

skewness

Quality histogram with

skewness

Hexcore: 2.9 million cells in total

Cutcell: 0.9 million cells in total

Pressure load on a structure

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Suction: Potential problem

for equipment on the top

of the building

Far

field

win

d d

irection

Note: this usage is not scope of the project but

data is available after the final computations

Flow field between buildings for

wind comfort assessment

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High wind velocity in

passages

Far field wind direction

Note: this usage is not scope of the project but

data is available after the final computations

Streamlines from hypothetical

sources: local differences

Before building After building

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Local effects

Overview

• CERN and its CFD team

• Computational wind engineering

• Demonstration on CERN Meyrin site

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Conclusions and outlook

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CERN commitment for environment and

safety

Strategy built up

First demonstrative simulations

• Scenario identification

• Calculation campaign

• Validation

• Uncertainty quantification

Thank you for your attention!

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Aniko Rakai, CFD Team, CERN, www.cern.ch/cfd