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Aerobiological Simulations Using Arc 1Aerobiological Simulations Using Arc 1

Dr Cath Noakes; Dr Andy Sleigh; Dr Carl Gilkeson; Dr Cath Noakes; Dr Andy Sleigh; Dr Carl Gilkeson; Dr Miller Camargo-Valero; Dr Amir KhanDr Miller Camargo-Valero; Dr Amir Khan

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OutlineOutline

1)1) Airborne pathogens and natural ventilationAirborne pathogens and natural ventilation2)2) Experimental studyExperimental study3)3) Computational Fluid DynamicsComputational Fluid Dynamics4)4) ResultsResults5)5) ConclusionsConclusions

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PaCE InstitutePaCE Institute Pathogen Control Engineering Institute (PaCE) directed Pathogen Control Engineering Institute (PaCE) directed

by Dr Cath Noakes, School of Civil Engineering. by Dr Cath Noakes, School of Civil Engineering.

Aerobiology and Infection ControlAerobiology and Infection Control ExperimentalExperimental

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www.engineering.leeds.ac.uk/pacewww.engineering.leeds.ac.uk/pace

ComputationalComputational

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Airborne PathogensAirborne Pathogens Great threat to human health:Great threat to human health:

Swine flu campaign…Swine flu campaign… Effective ventilation can reduce Effective ventilation can reduce

• Spanish Influenza (1918-1920) 50 - 100 million deathsSpanish Influenza (1918-1920) 50 - 100 million deaths• Asian flu (1957-1958) 1.5 - 2 million deathsAsian flu (1957-1958) 1.5 - 2 million deaths

infection risk in indoor infection risk in indoor environments. environments.

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Natural VentilationNatural Ventilation

• Nightingale wards characterised by:Nightingale wards characterised by:1900 1910

High ceilings, Large windows for natural ventilation.High ceilings, Large windows for natural ventilation.• Many of these wards exist within the UK.Many of these wards exist within the UK.

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St. Lukes HospitalSt. Lukes Hospital

AnemometerAnemometerPartitionedPartitionedOpen wardOpen ward

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Ventilation Tests – Pulse InjectionVentilation Tests – Pulse Injection

CO2 sensorsCO2 sensors

3 x latex balloons 3 x latex balloons

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Measured Ventilation RatesMeasured Ventilation Rates

0

100

200

300

400

500

600

0 10 20 30

Elapsed time (minutes)

CO

2 C

once

ntra

tion

(pp

mv)

PulsePulse

Delayed peak Delayed peak

Decay – freshDecay – freshair mixingair mixing

Typical Results:Typical Results:

Low wind speed 0.4 m/sLow wind speed 0.4 m/sACH = 2/h (~30 mACH = 2/h (~30 m33/h)/h)

High wind speed 5.0 m/sHigh wind speed 5.0 m/sACH = 30/h (~450 mACH = 30/h (~450 m33/h)/h)

where e is the age of air (h); and C(t) is tracer gas concentration as a function of time (t), according to Bonthoux et al.(1999). Indoor Air, 9, 57-62.

; ;

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Flow Visualisation: InletFlow Visualisation: Inlet• TurbulenceTurbulence• Pulsating flow Pulsating flow

of varying of varying durationduration

• Ingestion Ingestion followed by followed by extractionextraction

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Flow Visualisation: OutletFlow Visualisation: Outlet• Less turbulentLess turbulent• Controlled Controlled

extractionextraction• Efficient even Efficient even

for small wind for small wind speedsspeeds

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Flow Visualisation: InternalFlow Visualisation: Internal• High-velocity High-velocity

air entryair entry• Rapidly Rapidly

decaying air decaying air velocitiesvelocities

• Range of Range of length and length and time scalestime scales

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Modelling Challenges Modelling Challenges Natural ventilation unpredictable, flows are time-Natural ventilation unpredictable, flows are time-

dependent, turbulent and reliant on ambient weather dependent, turbulent and reliant on ambient weather conditions.conditions.

Simulations in large 3D air volumes are computationally Simulations in large 3D air volumes are computationally expensive.expensive.

Necessitates a steady-state approach – transient Necessitates a steady-state approach – transient simulations unfeasible. simulations unfeasible.

Boundary conditions (inlets/outlets/walls) require Boundary conditions (inlets/outlets/walls) require careful consideration. careful consideration.

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Computational Fluid Dynamics Computational Fluid Dynamics CFD is a powerful tool for indoor airflow simulations.CFD is a powerful tool for indoor airflow simulations. Utilizes the speed and power of computers to solve governing Utilizes the speed and power of computers to solve governing

fluid flow equations. fluid flow equations.

Step 1 = CAD Step 1 = CAD Step 2 = Mesh Step 2 = Mesh

Step 3 = Solve... Step 3 = Solve...

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2D Coupled Flow2D Coupled Flow

2 m/s2 m/s

2 m/s2 m/s

Velocity contoursVelocity contours

Pressure contoursPressure contours

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3D Model3D Model

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1.3 M 3.3 M 9.9 M1.3 M 3.3 M 9.9 M

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3D Model – Open-plan Ward3D Model – Open-plan Ward

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3D Model – Partitioned Ward3D Model – Partitioned Ward

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Pathogen Transport TestsPathogen Transport Tests

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Windward Release – ExperimentWindward Release – Experiment

P1P1

P2P2P3P3

HW2HW2SourceSource

HW1HW1

Open ward: Even spread, dilution.Open ward: Even spread, dilution. Partitioned ward: Cross infection reduced (P1, P2), higher Partitioned ward: Cross infection reduced (P1, P2), higher

concentrations in central bays .concentrations in central bays .

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Windward Release – CFDWindward Release – CFDOpen-wardOpen-ward Partitioned-wardPartitioned-ward

Pathogen containedPathogen containedMixing smears the Mixing smears the pathogenpathogen

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Leeward Release – ExperimentLeeward Release – Experiment

P2P2

P1P1

P3P3

HW2HW2SourceSource

HW1HW1

Open ward: Even spread, average 15% reduction.Open ward: Even spread, average 15% reduction. Partitioned ward: Lower average infection risk. Concentration Partitioned ward: Lower average infection risk. Concentration

76% lower for healthcare worker by source.76% lower for healthcare worker by source.

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Leeward Release – CFDLeeward Release – CFDOpen-wardOpen-ward Partitioned-wardPartitioned-ward

Partition channelling Partition channelling effect hinders progress effect hinders progress of pathogenof pathogen

Efficient extraction, Efficient extraction, prevents spread of prevents spread of infectioninfection

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ConclusionsConclusions CFD simulations complement the experimental results.CFD simulations complement the experimental results. Qualitative and quantitative comparison good, further model Qualitative and quantitative comparison good, further model

validation required. validation required. Arc1 facilitates significantly improvement compared with Arc1 facilitates significantly improvement compared with

previous machines (Abax, Everest, White Rose Grid).previous machines (Abax, Everest, White Rose Grid). Simulation times up to 4 x faster.Simulation times up to 4 x faster. Larger and more complex problems can now be undertaken:Larger and more complex problems can now be undertaken:

Time-dependent simulations.Time-dependent simulations. Higher-fidelity models (more cells)Higher-fidelity models (more cells)

Enables computation on ever larger air indoor air spaces such Enables computation on ever larger air indoor air spaces such as hospitals/offices.as hospitals/offices.

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Thank you for ListeningThank you for Listening

Questions?Questions?

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