Fighting the spread of pathogens in passenger aircraft cabins: an approach using computer simulations
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Fighting the spread of pathogens in passenger aircraft cabins: an approach using computer simulations Presented by Valerio Viti, PhD Kishor Ramaswamy Ansys, Inc. Contributors Kringan Saha, PhD Marc Horner, PhD Muhammad Sami, PhD Akira Fujii Omkar Champhekar Vivek Kumar Matthieu Paquet Aleksandra Egelja-Maruszewki, PhD Walt Schwarz, PhD
Technical panel
Valerio Viti, PhD Kishor Ramaswamy
Aerospace and Defense Industry Lead, Manager Application Engineer,
Ansys, Inc. Ansys, Inc.
2
Webinar outline
• Introduction
‐ Coronavirus: the basics
• The Ansys solution to help reduce the spread
• Airliner cabin case studies:
3
Webinar outline
• Introduction
‐ Coronavirus: the basics
• The Ansys solution to help reduce the spread
• Airliner cabin case studies:
4
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:
Develop best-practices
‐ Airborne particles and solutions for new-normal
‐ 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
5
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 Surface disinfection via mobile or
need to be studied and optimized installed UV systems or sprays
6
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
Computer simulation can provide guidance
High-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.
HVAC systems in public spaces will Surface disinfection via mobile or
need to be studied and optimized installed UV systems or sprays
7
Ansys solution for pathogens neutralization in an enclosed environment
Cabin HVAC System
UV Sterilization
- Analyze flow patters
- Use UV light to sterilize
- Minimize recirculation
recirculating air in HVAC
- Optimize vent operation
- Design system for efficient
- Minimize spread of
surface disinfection
pathogens through air
- Ensure proper dosage to
via scrubbing
neutralize virus load
Spray disinfection PPE effect
- Spray formation - Cough/sneeze droplets suppression
- Evaluate spray dispersion and coverage - Detail deposition pattern
- Optimize transfer efficiency via electrostatics - Dispersion
Case studies
Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV
light
Disinfection of cabin via electrostatic sprays
9
Case studies
Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV
light
Disinfection of cabin via electrostatic sprays
10Example of problem setup for CFD analysis: air cabin
Outlet (Door) Inlet Vents
Pout = 0 Pa (Gauge) Vin = 1 m/s
Outlet Vents (On Both Sides)
Pout = 0 Pa (Gauge)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
12Case 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.2014.88
Vivek Kumar,et al., On the utility of cloth facemasks for controlling ejecta during respiratory events., arXiv: Medical Physics, 2020.
13Animation: Streamlines 14
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 purposesOther modeling of HVAC systems and human comfort
• 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
Solar Load [W/m^2]System-level simulation of aircraft cabin: Ansys ROMs
➢ 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 …
Complex geometry
Humidity Unsteady velocity
Natural convection
Temperature
Heat generation
from human body
Solar Load
Radiation
21Example: Typical airliner cabin output Solar Load[W/m^2]
Velocity
Temperature PMV
PMV is an index showing
the thermal comfort. It is
defined as a function of
temperature, velocity,
humidity and radiation.
22Ansys ROM Technology
2 minutes unsteady simulation
48hours@20 cores In a second
23Validation: prediction(ROM) vs. correct answer(Fluent)
Temperature Velocity PMV
Point-1 Point-1
Point-1
Point-2 Point-2
Point-2
Point-3 Point-3
Point-3
24Outline
Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV
light
Disinfection of cabin via electrostatic sprays
25How to kill micro-organisms using UV light
• Disinfection efficiency depends on:
‐ Wavelength & Intensity: Lamp output
‐ Exposure time: design of disinfection system
flow path of
micro-organism
flow
UV Dose : (UV Intensity ) * dt
t
dt
DNA
• 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
26Challenges 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 27
Case study: UV Disinfection for transportation industry
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
29Aero 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
30Installed lights vs. Robot designs
Installed lights Robot design 1 Robot design 2
31Cumulative irradiation & dosage requirements
Installed lights Robot design 1 Robot design 2
Lowest irradiance Lowest irradiance Lowest irradiance
surface: ~4 uW/cm2 surface: ~1 uW/cm2 surface: ~6 uW/cm2
32Cumulative irradiation & dosage requirements
Installed lights Robot design 1 Robot design 2
Exposure time required: 150s Exposure time required: 600s Exposure time required: 100s
Speed required: N/A Speed required: 0.034 m/s Speed required: 0.204 m/s
33Aero cabin case study 34
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
35Train cabin example 36
Train cabin example
Original robot from airplane Modified robot with added LEDs
Poor lighting of
luggage area
Good lighting of
seating area
37Train cabin example 38
Mask disinfection example In-door ambient
LED array
lighting
Gasket UV-C
Body Transparent
Mask support
Screws Reflective walls
Inner Outer
Filter Filter
Filter UV-C coating
cover
Mask Explosion
Filter Filter
Import the geometry in Ansys Speos Gasket 2 Gasket 1
1 Define the materials propreties and sources
Analyse the radiometric resuts
4 3
Apply the 3D irradiance sensor on the Mask parts
39Mask 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.
40UV disinfection of cabin
HVAC air
41US disinfection of HVAC air
• Model radiation with particle tracking method to simulate UV disinfection system
• Some functions are customized by UDF(User Defined Function)
Ansys CFD
Disinfection
efficiency
Particle UV dosage[mJ/cm2]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
Statistics of virus residence time and radiation
30%
Average =3.70 s
ε=1.0
Number count (%)
20%
Std = 1.47 s
40%
Average =184.3 Ws/m2
10%
Live, 0.78%
30%
Number count (%)
Min =1.78 s 40%
Average =128.2 Ws/m2
0% e=0.7
20%
e=1.0
25
75
25
75
25
75
25
75
25
75
25
75
25
75
25
75
25
30%
0.
0.
1.
1.
2.
2.
3.
3.
4.
4.
5.
5.
6.
6.
7.
7.
8.
Number count (%)
Residence time (s)
Neutralized,
10% Average =184.3 Ws/m2
Min =1.00 Ws/m2 20%
99.22%
0%
10%
25
75
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
12
17
22
27
32
37
42
47
52
57
62
67
72
77
82
Irradiation dose (Ws/m2) Min =0.50 Ws/m2
< 7000 μW/cm2 0%
> 7000 μW/cm2
25
75
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
12
17
22
27
32
37
42
47
52
57
62
67
72
77
82
Irradiation dose (Ws/m2)Outline
Cabin HVAC system studies
Disinfection of cabin surfaces and HVAC air via UV
light
Disinfection of cabin via electrostatic sprays
46Electrostatic sprays to disinfect airliner cabins in between flights
Cumulative mass
distribution
Courtesy: The Houston chronicleBasic Model: Forces Acting on Droplets
-
-
-
Cabin Air -
Target Surface
Compressed Air
-
+ -
+ + + +
+ +
+
+
FE + + -
+ +
+ + + +
+ +
+
+ +
+
+ -
+ + FD, compressed Air q + +
q mp
+ + q -
Fg +
mp mp -
FD, cabin air
Spray gun -
-
-
-
-
-Basic spray droplet physical model: forces acting on spray droplets
-
-
-
Cabin Air Target
m Evaporation -
m Evaporation Surface
-
Sprayer Air
+
-
+ + + + + + + m Evaporation
+ +
+
+ FE + + -
+ + + +
+
+
+ + +
+ +
+
+
+
-
+ + FD, Sprayer air + +
-
q +
+
+
q
q Fg mp + + -
Spray gun mp t =1 mp
t =0 qRayleigh t =2
FD, Cabin Air -
-
-
Rayleigh Split
-
q
-
mp
t -Particle Size Distribution: experimental or computed
Experimentally measured Computed using VOF/DPM
Size distribution
30%
25%
Number Count
20%
Cumulative mass
Frequency
15%
distribution
10%
5% 100% 100%
0% Rosin-Rammler
80% Experimental 80%
1 10 30 50 70 90 110 130 0
15
Droplet Diameter [mm]
60% 60%
Frequency
40% 40%
20% 20%
0% 0%
0 50 100 150
Droplet Diameter [mm]Effect of the electrostatic field on spray droplet trajectories
Droplet diameter = 40mm Particle charge density = 0.874x10-3 C/kg
No Electrostatic Field With Electrostatic Field
Transfer ~ 20% Transfer ~ 78%Disinfectant film thickness on target surface
No e-field 90 kV, no space charge 90 kV, with spaceResults: Averaged “Wet” Film Thickness on Target
0.03 0.03
90 kV, No Space Charge
90 kV, With Space Charge
Normalized Film Thickness
No E-field
0.02
Normalized Film Thickness
0.02
0.01
0.01
0.00
0 0.2 0.4 0.6 0.8 1
r/R
0.00
0 0.2 0.4 0.6 0.8 1
r/RThank you Justin.klass@ansys.com (NASA Account Manager) Craig Diffie@ansys.com (NASA Enterprise Account Manager) Valerio.viti@ansys.com Kishor.Ramaswamy@ansys.com
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