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QUANTITATIVE IMAGING OF MULTI-COMPONENT

TURBULENT JETSArash AshSupervisors:Dr. DjilaliDr. OshkaiInstitute for Integrated Energy SystemsUniversity of VictoriaICHS2011 – September 12th 2011

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Safety Standards The integration of a hydrogen gas

storage has not been without its challenges.

Flammable characteristics of Hydrogen results in the requirement of more robust, high pressure storage systems that can meet modern safety standards.

Prior to the development of a hydrogen infrastructure, well-researched safety standards must be implemented to reduce the risk of uncontrolled leaks related to hydrogen storage.

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H2 – Fuel Cell Application

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Project Motivation and Objectives

• Perform series of well-defined experiments to generate data to guide development of engineering turbulence model suitable for rapid discharge simulations

• Objectives– experimentally characterize the effects of

buoyancy and cross-flow in a complex flow structure

– provide a quantitative database that can be used for future concentration measurements and also to validate CFD models

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Introduction• the momentum and buoyancy effects

related to the rapid, uncontrolled release of hydrogen must be studied in detail to accurately determine the resultant dispersion.

• In this study, dispersion of a buoyant, turbulent, round jet in a quiescent and moving ambient at a wide range of Froude numbers was investigated.

• This study focuses on slow leaks which might take place in small-scaled hydrogen based systems.

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Experimental Setup• Jet Apparatus:

– honeycomb settling chamber

– Sharp-edged orifice– Nozzle Diameter =

2mm• Cross-flow assembly:

– 11m/s ± 4%• Laser: Nd YAG 532 nm• CCD camera: 1376 ×

1040 pixels

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Flow ConditionsCase Q (lpm –

H2)Uoc (m/s) Fr Re r

1 64.4 318.33 ~1000 5263 11.22 43.4 248.98 ~750 4196 6.93 35.7 185.23 ~500 3121 6.14 21 94.56 ~250 1593 3.25 12 18.86 ~50 317 0.6

Helium density and viscosity are 0.166 kg/m3 and 1.97E-05 kg/ms, respectively

21jjetoc gDU=Fr

Where Fr – Froude number, Dimensionless; Uoc – Jet centerline exit velocity, m/s; g – acceleration due to gravity, m2/s; D – Jet diameter, mm; , ρ – Ambient air density, kg/m3 and ρj – Jet exit density of helium, kg/m3

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PIV - Cross Correlation

Search Area

Original IA

Particles In image B

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Results and Discussions

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Velocity Fields• Free Jet• Jet in Cross - Flow

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Jet Centerline• New coordinate

system• Jet Centerline

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Jet Centerline (Continue)

Free Jet Jet in Cross-flow

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Scaling FactorsFree JetJet in Cross-flow

Where 2/1

4/3

BMLM

first effects of buoyancy in case of Fr = 250 and 50, happens at approximately x/LM = 0.16 and 0.61 which corresponds to x/D = 43 and 32 respectively.

rD scaling

scalingDr 22

2

UU

r ocj

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Velocity DecaysFree Jet Jet in Cross-flow

Where:Uoc is mean nozzle exit velocity

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Velocity Decay (Continue)

NCF = Free jetWCF = Jet in cross-flow

1. Decay rates are faster in cross- flowing jets2. In jet far-field region decay rates drop for jets in cross-flow3. Decay rate drops in Buoyancy dominated regions

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Turbulence QuantitiesFree jet Jet in cross-flow

Where, Uc is the time-averaged velocity magnitude along the jet centerline

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Conclusion• Effects of buoyancy and cross-flow were

investigated in subsonic release of Helium,• Mean and fluctuation velocity components

were quantified using PIV,• lowering the Froude number led to slower

velocity decays due to the buoyancy-driven acceleration components in buoyancy dominated regions,

• Increasing effects of buoyancy were observed by reducing the Froude number,

• The present data can serve to validate computational models derived for investigating hydrogen safety scenarios.

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Thank you

Questions?

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Appendix• Initial Condition – Sharp-edged

Orifice

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Velocity ProfilesFree Jet Jet in cross-flow

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Seeding - Stokes number• Seeding particles must:

1. Match fluid properties2. Neutrally buoyant3. Short response time to flow motion4. ReflectivityParticle Flow is dominated by Stokes drag:

For St>>1, particles will continue in a straight line regardless of fluid streamline but for St<<1, particles will follow the fluid streamlines closely.

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18U d CUStL L