cfd modeling for helium releases in a private garage without forced ventilation papanikolaou e. a....

CFD Modeling for Helium Releases in a Private Garage without Forced Ventilation

Papanikolaou E. A.

Venetsanos A. G.

NCSR "DEMOKRITOS"

Institute of Nuclear Technology & Radiation Protection

Environmental Research Laboratory

Athens, GREECE

[email protected]

NCSR "DEMOKRITOS"INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTIONENVIRONMENTAL RESEARCH LABORATORY

Summary

Scope: Evaluation of CFD ADREA-HF code capability to assess possible hazards posed by H2 releases in confined spaces

Experimental description Methodology

Computational domain and grid Mathematical formulation Initial and boundary conditions

Details of numerical solution Results of simulations Conclusions Future plans

NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

Scope


Safe future H2 based society

Safe use or storage of H2 systems

inside buildings

CFD models for assessment of

hazards by H2 releases in confined spaces

Scope


Evaluation of CFD ADREA-HF code capability to assess such scenarios

Experimental Description Swain et.al. (1998)

Single car garage and sensors location


Vehicle and leak location 7.200 Lt/hr Helium for 2 hours



Case 1: 2.5 inches (6.35 cm) top and bottom door vents



MethodologyI. Computational Domain & Grid

Domain extends beyond garage boundary


Assumption of x-z plane symmetry due to geometry of facility and location of leak



Sensors located at the same side given the symmetry assumption

Domain extends beyond garage boundary


3-D Cartesian grid Grid refinement close to vents,

source, walls Max. grid expansion ratio: 1.2 Min. grid expansion ratio: 0.84 Classification of cells into fully

active, inactive and partially active DELTA_B Code for geometrical pre-

processing


Grid characteristics Case 1 Case 2 Case 3

Grid dimensions 882648 882650 882644

Number of active cells 101.887 106.218 93.552

Min. and Max. cell size in z-direction (m)

0.04 close to source0.512 at domain’s top



Min. and Max. cell size in x-direction (m)

0.02 close to door0.92 at domain’s end

Minimum and Maximum cell size in y-direction (m)

0.1 close to source and symmetry plane0.401 at domain’s beginning


Grid dimensions 882648 882650 882644











Grid dimensions 882648 882650 882644










MethodologyII. Mathematical Formulation

3-D transient, fully compressible conservation equations Mixture mass

Mixture momentum

Helium mass fraction

Mixture density and mass fractions and

Component densities through ideal gas law

0

i

i

x

u

t


i

j

j

it

ji

ij

iji

x

u

x

u

xg

x

P

x

uu

t

u

0.72 , m

106494.5d , 2

5-111

sx

qd

xx

qu

t

q

j

t

jj

j

2

2

1

11

qq

TRP ii

211 qq

MethodologyII. Mathematical Formulation (continued)

Standard k-ε model for turbulence Turbulent viscosity Turbulent kinetic energy, k

Volumetric production rate of k by shear forces G and buoyancy production (destruction) term GB

Dissipation rate of turbulent kinetic energy, ε

09.0C ,2

k

Ct


0.1 , k

Bjk

t

jj

jGG

x

k

xx

ku

t

k

z

g-G and z

tB

j

i

i

j

j

it x

u

x

u

x

uG

1.0 and 1.92 1.44, 1.3,

,

321

231

CCC

CGCGCkxxx

u

t Bj

t

jj

j

MethodologyII. Mathematical Formulation (continued)


Variables to be calculated Component velocities u, v, w He mass fraction, q1

Pressure, P Turbulent kinetic energy, k Dissipation rate of turbulent kinetic energy, ε

Not calculated variable but supplied by the initialization data Temperature, T

MethodologyIII. Initial & Boundary Conditions

Initial Conditions Zero wind velocity with no turbulence Temperature of 293.15 K and hydrostatic

pressure Boundary Conditions applied to:

1 free building surface as the Helium source 28 solid building surfaces 1 solid domain surface (the ground) 5 free domain surfaces


MethodologyIII. Initial & Boundary Conditions (continued)


Variable Source

u

v

w

q1

k

ε

0

0

zu

u

0

0

zv

v

0

1.0

zw

w

0

1

1

1

zq

q

0

0

zk

k

0

0

z

Inflow boundary conditions at the source



Wall function for velocity:

Wall function for k:

Wall function for ε:

212

Cuk

y

kC

43

43

6.11for y )9ln(1

6.11for y

y

yu

Variable

u Wall function

v Wall function

w Wall function

q1

k Wall function

ε Wall function

Solid building surfaces (28)

01

nq






212

Cuk

y

kC

43

43

6.11for y )9ln(1

6.11for y

y

yu

The wall function for velocity forms the basis of the empirical relationship to describe the shape of the wall boundary layer in non-dimensional terms

Variable

u Wall function

v Wall function

w Wall function

q1

k Wall function

ε Wall function


01

nq






212

Cuk

y

kC

43

43

6.11for y )9ln(1

6.11for y

y

yu

The wall function for velocity forms the basis of the empirical relationship to describe the shape of the wall boundary layer in non-dimensional terms

wall thefrom centre cell near wall of distance:y

wallfrom distance lizeddimensiona-Non

stressshear wall: , velocity Friction w

21

w

yuy

u

Variable

u Wall function

v Wall function

w Wall function

q1

k Wall function

ε Wall function


01

nq






212

Cuk

y

kC

43

43

6.11for y )9ln(1

6.11for y

y

yu

Variable

u Wall function

v Wall function

w Wall function

q1

k Wall function

ε Wall function

Solid domainsurface (ground)

01

nq



Free domain

surface1

Variable West side

u

v *1

w *1

q1 *1

k *1

ε *1

0

xu

Free domain

surface2

Variable East side

u

v *1

w *1

q1 *1

k *1

ε *1

0

xu

Free domain

surface3

Variable South side

u *1

v

w *1

q1 *1

k *1

ε *1

0

yv

Free domain

surface4

VariableSymmetry

plane

u

v

w

q1

k

ε

0v

0

yu

0

yw

01

yq

0

yk

0

y

Free domain

surface5

Variable Top plane

u *1

v *1

w *2

q1 *1

k *1

ε *1

*1 function of the flow direction*2 normal velocity obtained from continuity equation

*1 function of the flow direction

Details of Numerical Solution


CFD Code ADREA-HF for simulation Control volume discretization method, staggered grid

arrangement for velocities First order fully implicit scheme for time integration First order upwind scheme for discretization of the

convective terms Automatic time step selection based on convergence error

Initial time step: 10-3 seconds Maximum permitted time step: 10-1 seconds

Intel® XeonTM CPU 3.60GHz with Windows operating system

Calculations performed for real time of 7.200 seconds

Results: Case 1 (2.5 inches)

Outputs of simulation versus experimental data at sensor locations


Good agreement for sensors 2 and 3 (upper vents)

Overestimation for sensors 1 and 4 (lower vents)

Underestimation of the predicted concentration difference between top and lower sensors

Results: Case 1 (continued)

Bottom vent provides a flow of fresh air, flowing under the vehicle Upper vent provides an exit of the low density gas mixture, near

the ceiling The combustible gas cloud is located under the vehicle, near the

source and extends in the z-direction in front of it The rest of the garage gas remained leaner than the lean limit of

combustion for Hydrogen Flow pattern has reached steady state conditions at least at 3.600

seconds





The vent sizes are almost 4 times broader than in Case 1

The predicted He concentrations are in satisfactory agreement with the experimental data for all sensors


The exiting gas mixture has now a wider column-like shape which broadens with height

Most of the garage gas remained leaner than the lean limit of combustion for Hydrogen (4.1%)

Flow pattern has reached steady state conditions at least at 3.600 seconds





Underestimation for sensors 1, 2 and 3

Small over prediction for sensor 4

The predicted natural ventilation rate is overestimated


The maximum Helium concentration is located at the source and occupies much less space

The column of the outflow gas is now much broader resulting in lower Helium concentrations inside the garage

Flow pattern has reached steady state conditions at least at 3.600 seconds


Conclusions

The ADREA-HF CFD code was successfully applied to simulate 3 full scale Helium release experiments

The predicted results were generally in acceptable agreement with the experimental data

The calculations revealed the mixing patterns Mixing mechanisms reached a near-equilibrium

state resulting in a constant cloud size and shape during the release period

CFD practice is important for evaluation of potential hazards especially under complex release conditions


Future Plans

Evaluation of the performance of other turbulence models under the same experimental conditions

Development of CFD practice guidelines for such kind of flows


Acknowledgements


The authors would like to thank the Greek

Secretariat of Research and Technology as well

as the European Commission for funding

for this work through the 02-PRAKSE-42 and HYSAFE-NoE projects

respectively

• NCSR "DEMOKRITOS"• INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION• ENVIRONMENTAL RESEARCH LABORATORY

Animation (Case 1)


Animation (Case 1continued)


Animation (Case 2)


Animation (Case 3)

MethodologyIII. Initial & Boundary Conditions

*1 normal velocity obtained from continuity equation

*2 function of the flow directionWall function for velocity:



212

Cuk


0

0

zu

u0

x

u0

xu 0

y

u

0

0

zv

v0

y

v0v

0

1.0

zw

w0

y

w

01

nq 01

z

q

0

1

1

1

zq

q01

y

q

0

nP 0

z

P0

101325

zP

PaP

0

xP0

x

P 0

yP0

y

P0

zP

0

nT 0

z

T0

zT 0

x

T0

xT 0

y

T0

yT0

z

T

0

0

zk

k0

y

k

0

0

z

0

y

y

kC

43

43

6.11for y )9ln(1

6.11for y

y

yu

Solid building surfaces

(28)

Solid domain surface

(ground)

Source Free domain surfaces (5)

West side East side South side Symmetry plane Top plane

u Wall function Wall function *2 *2

v Wall function Wall function *2 *2 *2

w Wall function Wall function *2 *2 *2 *1

q *2 *2 *2 *2

P

T

k Wall function Wall function *2 *2 *2 *2

ε Wall function Wall function *2 *2 *2 *2

Details of Numerical Solution

Required CPU time (in seconds) of three cases

649760.6

596784.02

543212.6

400000

500000

600000

700000

Case 1Case 2Case 3


Required time (in seconds) to reach maximum time step

2.771.809 1.25

0.0

2.0

4.0

6.0

8.0

10.0

Case 1Case 2Case 3

Relative error (%) of Cases 1, 2 and 3


cfd modeling for helium releases in a private garage without forced ventilation papanikolaou e. a....

Documents

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leak location

garage boundary slide

sensors location vehicle

experimental description

lthr helium

door vents single car

private garage