Fighting the spread of pathogens in passenger aircraft cabins: an approach using computer simulations
Presented byValerio Viti, PhDKishor RamaswamyAnsys, Inc.
ContributorsKringan Saha, PhDMuhammad Sami, PhDOmkar ChamphekarMatthieu PaquetWalt Schwarz, PhD
Marc Horner, PhDAkira FujiiVivek KumarAleksandra Egelja-Maruszewki, PhD
Kishor Ramaswamy
Manager Application Engineer,Ansys, Inc.
Technical panel
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Valerio Viti, PhD
Aerospace and Defense Industry Lead,Ansys, Inc.
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Webinar outline
• Introduction‐ Coronavirus: the basics
• The Ansys solution to help reduce the spread
• Airliner cabin case studies:
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Webinar outline
• Introduction‐ Coronavirus: the basics
• The Ansys solution to help reduce the spread
• Airliner cabin case studies:
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Coronavirus – A Highly Contagious Airborne Disease
• The current global pandemic caused by COVID-19 has impacted people around the world and has caused many industries to come to a halt due to the risks of transmission.
• One key reason for the pandemic is the highly contagious nature of the virus particles. The three primary routes of coronavirus transmission are:‐ Airborne particles‐ Droplets from a cough or sneeze‐ Touching a surface with infected particles
• Air travel in particular has been greatly affected by the pandemic because of:‐ close proximity of passengers in an enclosed environment and ‐ the relatively long duration of flights
Develop best-practices and solutions for new-normal
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Multiple solutions will be required to ensure our safety
• All routes of transmission will have to be considered as there is no single solution to disinfect the air we breathe and the surfaces we touch
HVAC in transportation systems will need to be studied and optimized
Surface disinfection via mobile or installed UV systems or sprays
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Multiple solutions will be required to ensure our safety
• All routes of transmission will have to be considered as there is no single solution to disinfect the air we breathe and the surfaces we touch
HVAC systems in public spaces will need to be studied and optimized
Surface disinfection via mobile or installed UV systems or sprays
Computer simulation can provide guidanceHigh-fidelity, physics-based engineering analysis can help optimize the
design and operation of existing ventilation systems as well as UV disinfection system of air and surfaces.
Ansys solution for pathogens neutralization in an enclosed environment
Cabin HVAC System- Analyze flow patters- Minimize recirculation- Optimize vent operation- Minimize spread of
pathogens through air via scrubbing
UV Sterilization- Use UV light to sterilize
recirculating air in HVAC- Design system for efficient
surface disinfection- Ensure proper dosage to
neutralize virus load
Spray disinfection- Spray formation- Evaluate spray dispersion and coverage- Optimize transfer efficiency via electrostatics
PPE effect- Cough/sneeze droplets suppression- Detail deposition pattern- Dispersion
Case studies
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Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV light
Disinfection of cabin via electrostatic sprays
Case studies
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Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV light
Disinfection of cabin via electrostatic sprays
Example of problem setup for CFD analysis: air cabin
Inlet VentsVin = 1 m/s
Outlet Vents (On Both Sides)Pout = 0 Pa (Gauge)
Outlet (Door)Pout = 0 Pa (Gauge)
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Case 1: cough simulation without masks
• Simulation set up with two people coughing in the cabin
• Cough times are staggered
• Coughing parameters are same for both the coughs‐ Rosin Rammler droplet size distribution with a min size: 2 mm,
max size: 75 mm, mean size: 20 mm
‐ Cough velocity: 11m/s directed straight outward from mouth
‐ Cough spray modeled as water, using a cone injection with a cone angle of 24o
‐ Mass flor rate of cough: 1.95e-3 kg/s
‐ DPM simulation solved in a frozen air flow field
Ref: Bourouiba, L., Dehandschoewercker, E., & Bush, J. (2014). Violent expiratory events: On coughing and sneezing. Journal of Fluid Mechanics, 745, 537-563. doi:10.1017/jfm.2014.88
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Case 2: cough simulation with mask
• Add effect of mask on Row 2 (front) passenger
• Mask is generic type‐ Mask modeled using porous media and UDF for filtering
cough droplets
• All coughing parameters same as before
Ref: Bourouiba, L., Dehandschoewercker, E., & Bush, J. (2014). Violent expiratory events: On coughing and sneezing. Journal of Fluid Mechanics, 745, 537-563. doi:10.1017/jfm.2014.88Vivek Kumar,et al., On the utility of cloth facemasks for controlling ejecta during respiratory events., arXiv: Medical Physics, 2020.
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Animation: Streamlines
Analysis of airliner cabin HVAC system: air patterns only
Analysis of airliner cabin HVAC system: coughing without mask
Analysis of airliner cabin HVAC system: coughing with mask
Ref: Vivek Kumar et al., On the utility of cloth facemasks for controlling ejecta during respiratory events., arXiv: Medical Physics, 2020.
Effect of pathogen spread with and without masks
No masks worn, 2 passengers coughing 1 mask worn, 2 passengers coughing
Particle size x10 for person with mask for visualization purposes
• CFD can predict the comfort of occupants in closed environments such as:• aircraft • space capsule (low-gravity)• automobile• auditoriums• hospital rooms
• Key outputs from CFD simulation:• Velocity, Temperature, Humidity• Local Mean Age of Air / Ventilation Effectiveness• Predicted Mean Vote (PMV)• Predicted Percentage Dissatisfied (PPD)• Contaminant/Pollutant dispersion
Other modeling of HVAC systems and human comfort
Solar Load [W/m^2]
Complex geometryHumidity Unsteady velocity
Heat generation from human body
Radiation
Solar Load
➢ Reduce calculation costs for complex situations ➢ Complex geometry : sheet, human body…➢ Unsteady simulation: heat up, cool down…➢ Non-linear physics: natural convection, radiation, humidity, solar load …
Temperature
Natural convection
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System-level simulation of aircraft cabin: Ansys ROMs
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Velocity
Temperature PMV
Solar Load[W/m^2]
PMV is an index showing
the thermal comfort. It is
defined as a function of
temperature, velocity,
humidity and radiation.
Example: Typical airliner cabin output
48hours@20 cores In a second
2 minutes unsteady simulation
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Ansys ROM Technology
Validation: prediction(ROM) vs. correct answer(Fluent)
Temperature Velocity PMV
Point-1
Point-2
Point-3
Point-1
Point-2
Point-3
Point-1
Point-2
Point-3
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Outline
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Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV light
Disinfection of cabin via electrostatic sprays
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How to kill micro-organisms using UV light
• Disinfection efficiency depends on:‐ Wavelength & Intensity: Lamp output
‐ Exposure time: design of disinfection system
• Disinfection efficiency is defined as “UV Dosage”‐ UV Dosage: Amount of received radiation in micro-organisms, either from
continuous exposure or during the flow path in reactor
DNA
flow path of micro-organism
( )t dtIntensityUVDoseUV *:
flow
dt
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Challenges for UV light surface disinfection systems
• Choosing the optimal lighting system
• Ensuring complete exposure and irradiation of all relevant surfaces including line of sight challenges
• Understanding the dosage requirements
• Optimizing the design and motion of a mobile system
Case study: UV Disinfection for transportation industry
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A Step by Step Workflow
1. Create 3D model of area under test (e.g. aero cabin)
2. Apply optical properties to all surfaces in the area
3. Define light delivery system
4. Define motion path ** for mobile solution only
5. Run simulations
6. Calculate cumulative irradiation on all relevant surfaces
7. Determine necessary exposure requirements (or speed requirements for mobile solution)
8. Verify that there are no missed surfaces
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Aero cabin case study
• Three model comparisons‐ Installed lights vs. two robot designs
• Optical properties‐ Robot: ~80% reflectance‐ Floor: ~50% reflectance‐ Ceiling: ~80% reflectance‐ Rest: ~40% reflectance
• Light delivery system‐ Output power: 100W in all cases‐ Intensity distribution: Lambertian‐ Spectrum: Gaussian around 253.7nm
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Installed lights vs. Robot designs
Installed lights Robot design 1 Robot design 2
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Cumulative irradiation & dosage requirements
Installed lights Robot design 1 Robot design 2
Lowest irradiance surface: ~1 uW/cm2
Lowest irradiance surface: ~6 uW/cm2
Lowest irradiance surface: ~4 uW/cm2
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Cumulative irradiation & dosage requirements
Installed lights Robot design 1 Robot design 2
Exposure time required: 600s
Speed required: 0.034 m/s
Exposure time required: 100s
Speed required: 0.204 m/s
Exposure time required: 150s
Speed required: N/A
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Aero cabin case study
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Train cabin example
• Moving to a new (but similar) environment, are we able to re-use the same robot design?
➔Let’s test through simulation, using the same model setup as for the aero cabin example
• Optical properties
‐ Robot: ~80% reflectance
‐ Floor: ~50% reflectance
‐ Ceiling: ~80% reflectance
‐ Rest: ~40% reflectance
• Light delivery system
‐ Output power: 100W in all cases
‐ Intensity distribution: Lambertian
‐ Spectrum: Gaussian around 253.7nm
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Train cabin example
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Train cabin example
Original robot from airplane
Good lighting of seating area
Poor lighting of luggage area
Modified robot with added LEDs
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Train cabin example
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Mask disinfection example
Apply the 3D irradiance sensor on the Mask parts
Gasket
Screws
Body Mask
Filter cover
Filter Gasket 1
Filter Gasket 2
Inner Filter
Outer Filter
Mask Explosion
Import the geometry in Ansys Speos
Analyse the radiometric resuts
In-door ambient lighting
LED array
UV-C Transparent support
UV-C coating
Reflective walls
Define the materials propreties and sources1
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Mask disinfection example
The radiometric analysis shows minimum irradiance of 0.74 W.m-2 to achieve minimum criteria of 20 W.s.m-2. Desinfection process takes 27 seconds.
UV disinfection of cabin HVAC air
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• Model radiation with particle tracking method to simulate UV disinfection system
• Some functions are customized by UDF(User Defined Function)
Disinfection
efficiency
Ansys CFD
Particle UV dosage[mJ/cm2]
US disinfection of HVAC air
Modeling of micro-organisms
• Micro-organisms can be modeled by Ansys Fluent DPM(Discrete Phase Model)• Lagrangian method used to compute
• Virus/droplet trajectories• UV dosage on droplets
Particle paths through ducting
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Residence time (s)
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count
(%)
Min =1.78 s
Average =3.70 s
Std = 1.47 s
Statistics of virus residence time and radiation
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Irradiation dose (Ws/m2)
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mb
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Min =1.00 Ws/m2
Average =184.3 Ws/m2
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Irradiation dose (Ws/m2)
Nu
mb
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(%)
e=0.7
e=1.0
Min =0.50 Ws/m2
Average =128.2 Ws/m2
Average =184.3 Ws/m2
Live, 0.78%
Neutralized,
99.22%
< 7000 μW/cm2
> 7000 μW/cm2
ε=1.0
Outline
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Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV light
Disinfection of cabin via electrostatic sprays
Electrostatic sprays to disinfect airliner cabins in between flights
Cumulative mass
distribution
Courtesy: The Houston chronicle
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Cabin Air
Target Surface
FE
Spray gun
Compressed Air
Fg
FD, cabin air
FD, compressed Air
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Basic Model: Forces Acting on Droplets
FE
Spray gun
Sprayer Air
Cabin Air Target
Surface
Fg
FD, Cabin Air
FD, Sprayer air
EvaporationmEvaporationm
Evaporationm
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2t=p
q
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p
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t
Rayleigh Split
1t=p
q
m
0t=p
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mRayleighq
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Basic spray droplet physical model: forces acting on spray droplets
Particle Size Distribution: experimental or computed
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Droplet Diameter [mm]
Fre
qu
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Number Count
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0 50 100 150Droplet Diameter [mm]
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uen
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Rosin-Rammler
Experimental
Size distribution
Cumulative mass
distribution
Experimentally measured Computed using VOF/DPM
Effect of the electrostatic field on spray droplet trajectories
No Electrostatic Field
Transfer ~ 20%
With Electrostatic Field
Transfer ~ 78%
Droplet diameter = 40mm Particle charge density = 0.874x10-3 C/kg
No e-field 90 kV, no space charge 90 kV, with space
Disinfectant film thickness on target surface
Results: Averaged “Wet” Film Thickness on Target
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r/R
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ilm
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90 kV, No Space Charge
90 kV, With Space Charge
No E-field
Thank you
[email protected] (NASA Account Manager)
Craig [email protected] (NASA Enterprise Account Manager)
