Fundamental Ice Crystal Accretion Physics Studies

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Fundamental Ice Crystal Accretion Physics Studies

• Peter Struk, Paul Tsao, Mario Vargas
• NASA Glenn Research Center
• Tom Currie, Dan Fuleki, Danny Knezevici
• National Research Council of Canada
• with additional sponsorship by
• Federal Aviation Administration
• Transport Canada

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Ice-Crystal Icing Aspects

• Atmospheric Characterization
• Particle size distributions, morphology
• Concentrations
• Where specifically in the engine could
  ice-crystal icing occur?
• Internal conditions?
• Changes to particle size due to impact with
  rotating blades?
• Concentrations as flow area changes?
• Mixed phase conditions?

Graphic NASA (www.ueet.nasa.gov)

• We need to understand the conditions leading to
  ice-crystal icing.
• Can we simulate these conditions in an
  experimental facility to better understand the
  fundamental aspects of ice-crystal icing?

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Previous Studies

• Ice Crystal Testing on a Flat Plate (MacLeod
  2007)
• Demonstrated rapid ice buildup on a heated plate
  with stagnation blocks exposed to ice crystals.
• Ice appeared to not adhere but rather was held
  against the stagnation point until it grew larger
  and shed due to aerodynamic forces.
• Mixed-phase ice-crystal testing on an airfoil
  in a S-duct (Mason, Chow, Fuleki, 2010)
• Demonstrated that ice can form on the airfoil and
  other surfaces of the S-duct at air temperatures
  significantly warmer than freezing.

Images NRC, with permission
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Fundamental Ice Crystal Accretion Studies

• Subject to operating limits of the facility,
  focus on conditions representative of those found
  in a low pressure compressor
• Research Approach
• Simple test geometry (i.e. wedge airfoil)
• Utilizes NRC Research Altitude Test Facility
  (RATFac)
• Can inject ice crystals into a warm environment
  from near SL to 30,000 ft.
• Test over a range of conditions
• Identify study parameters governing accretion
  initiation growth
• Document time evolution of ice accretions -
  initiation, growth, shedding
• Summary of testing to date (2 entries)
• Nov. 2010 focused on identifying onset
  conditions for ice-crystal accretion
• Began to establish the envelope bounding the
  onset of accretion events
• Noticed that the temperature, altitude and
  humidity all could play a role
• Mar. 2011 further investigated combined effect
  of temperature, altitude, and humidity (i.e. the
  air wet bulb temperature or TWB) on the onset and
  growth rate of ice crystal accretion

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Wedge Airfoil in RATFac Cascade Tunnel
Dimensions mm
Top view (normal to icing surface)
Connection to exhauster
Rectangular inlet bellmouth
Airfoil
Large front window
Side view (end view of leading edge)
Graphics NRC, with permission
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Wedge Airfoil Test Conditions Results

• Conditions
• Mach number 0.2?0.4 (primarily 0.2 0.25)
• Total pressure 6.5 and 13.5 psia
• Injected IWCi 0 ? 20 g/m3
• Supplemental LWCi 0 ? 3 g/m3
• Total air temperature 5 ? 23C
• Ice MMD 90-200µ (estimated)
• Water MVD 40µ
• IWC, LWC measured with SEA multi-element probe
  150mm upstream of airfoil? IWCm , LWCm

• Preliminary results showed there are two types of
  ice accretion
• Ice accumulates and is very slushy with frequent
  shedding when
• evaporation cooling is weak, i.e. TWB gt 0?C
• 2. Ice accretion is firm and little shedding when
  evaporation cooling is strong, i.e. TWB lt 0C.

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Slushy Ice Accumulation with Frequent Shedding
Video shown at 8x real time
Run 522 IWCi, LWCi(17,0.5) g/m3, 6.5psia,
M0.25, To20C, RH 13, TWB 2.7C
Video NASA
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Firm Ice Accretion with Little Shedding
Video shown at 8x real time
Run 543, IWCi, LWCi (7,1.5) g/m3, 6.5psia,
M0.25, To13C, RH8, TWB-2C
Video NASA
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Energy Balance to Better Understand Physics

• Convection to / from air
• Conduction to / from solid
• Water Flow In
• Surface Flow
• Impinging water mass
• ice, water, mixed phase
• Freezing or melting
• Water Flow Out
• Surface Run Back
• Bounce / Splash
• Erosion / shed
• Evaporation/Sublimation

IWC, LWC
Tsurf
U T P
Control volume on icing surface
PW?
Graphic NASA
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Wet Bulb Temperature

• TWB ? balance convection with evaporative cooling
  and no conduction to solid
• Wetted surface evaporates cools down
• Convection provides energy to surface
• Surface temperature can approach TWB in these
  idealized conditions
• The wet bulb temperature represents the humid air
  energy transfer (function of T, P, Pw)
• Lower humidity or lower pressure ? more
  evaporative cooling lower TWB

IWC, LWC
Tsurf
U T P
no conduction
Control volume on icing surface
PW?
Graphic NASA
TWB helped us identify onset of one type of ice
accretion (not complete answer to identifying all
ice accretion conditions)
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Planned Future Work

• Scaling work to include ice-crystal and mixed
  phase conditions
• Identify scaling parameters that govern the ice
  crystal accretion process
• Multi-wire probe characterization in mixed phase
  conditions (Apr. 2012)
• Addition of imaging upstream of probe
• Investigate pooling in multi-wire probe
• Develop melt-ratio correlation for ice-crystals
  scaling condition calculation
• NACA0012 airfoil experiments to validate scaling
  methods (Dec. 2012)
• Measuring ice shape profile along mid-span of
  model
• Addition of heater tape along model root and rip

Heater Tape
132 mm
Thermocouples (13)
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Challenges in Ice Crystal Icing Research

• Can be broadly summarized in these categories
• Understanding generating internal-to-engine
  environmental conditions
• Measuring conditions
• Ice accretion measurements
• Understanding physics

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Challenge Understanding Simulating Environment

• Are the conditions we are simulating relevant to
  a LPC?
• Pressures (6.5 13.5 psia)
• Temperatures (TAT gt 0 to 20?C)
• Mach numbers (0.2 ? 0.4)
• Ice crystal / mixed phase characteristics
• Size distribution (90-200 µm MMD)
• Particle thermal phase distribution (not well
  understood)
• We need to know the above conditions in an
  internal engine environment.
• Can we effectively generate these conditions ?
• Injecting ice into warm environment is difficult
• Uniformity of conditions?
• Importance of heated or cooled surfaces?

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Challenge Measuring Conditions

• Phase of particles
• Can be fully glaciated, fully melted, partially
  melted
• Using hot-wire technique (SEA multi-wire)
• Needs known calibration source (okay for LWC
  alone)
• Under-reads IWC and LWC in mixed-phase, possible
  pooling _at_ high IWC
• Temperature of particles
• Unknown but important to accurately model physics
• Not likely the same temperature as environment in
  ice-crystal engine icing
• Particle size distributions (see next slides)
• Small particles moving at high velocities
• Using imaging methods
• Need good resolution stop-action capability
• Work underway using backlit laser sheet methods

SEA Multi-wire Probe
Image NASA
All Vapor Out
Graphic NASA
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Challenge Ice Shape Measurement (1 of 2)

• Ice shape and morphology required to compare to
  simulations
• Traditional methods (tracings castings) not
  easily adaptable
• NASA developed technique to measure leading edge
  ice growth (1D) from images (Struk, et al. 2012).

Clean Airfoil
ROI 1
ROI 11
Asymmetric ice growth (test 515)
Images NASA
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Challenge Ice Shape Measurement (2 of 2)

• 2D 3D Ice Shape Profiles from images desired
• Preliminary work underway

Far wall accumulation profile (outer white)
Near wall accumulation profile (outer white)
Mid-plane profile (inner white)
Heater tape to prevent ice accumulation near
endwall
Images NASA
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Summary

• Fundamental ice-crystal accretion physics studies
  underway
• Demonstrated that ice accretions can occur when
  ice-crystals are injected onto an airfoil in warm
  conditions.
• Observed ice accretion is firm and little
  shedding when evaporation cooling is strong, i.e.
  TWB lt 0C.
• Ice accumulates and is very slushy with frequent
  shedding when evaporation cooling is weak, i.e.
  TWB gt 0C
• TWB may be able to help identify locations
  susceptible to icing
• However, it is not the complete answer (i.e.
  LWC/TWC ratio, others?)
• Challenges exist for fundamental experiments
• Understanding generating internal-to-engine
  environmental conditions
• Measuring conditions
• Ice accretion measurements
• Understanding physics