NASA Technical Reports Server (NTRS) 20090030607: NASA Airframe Icing Research Overview Past and Current

National Aeronautics and Space Administration

NASA Airframe Icing Research Overview

Past and Current

Cleveland, Ohio

Airframe Icing Workshop
NASA Glenn Research Center

June 9, 2009

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National Aeronautics and Space Administration

NASA Airframe Icing Research

Objective

The objective of fundamental research in airframe icing has been to provide the aviation
community with the design and analysis tools needed to accomplish better and safer
designs of aircraft and aircraft sub-systems, with respect to operations in icing
conditions.

Approach

• Development of new experimental methods and advanced icing simulation software

• Highly integrated, multi-disciplinary effort

- examination of the underlying physics of icing

- analytical model development

- software development and maintenance

- experimental methods development

- creation of experimental databases related to ice formation and its effects

The tools developed in the NASA Glenn Icing Branch are used for a variety of purposes
including but not limited to, ice accretion shape prediction, ice protection system
performance evaluation, and examination of the effects of ice accretion on aircraft
aerodynamics.

These tools have an impact in design, testing, construction, and certification and
qualification of aircraft and aircraft sub-systems.

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NASA Airframe Icing Research Overview
Past and Current

Outline

• Experimental Methods

• Computational Methods

• Flight Dynamics

• Experimental Databases

Historical timeline
Highlights

Development of major products

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Historical Progress in Technology

Experimental Methods

1980s

1990s

2000s

• Ice shape tracing methods

• Development of accurate ice
shape casting technique

• Scaling laws identified and tested

• De-icing fluid aerodynamic tests
conducted in IRT

• Aircraft performance testing with
artificial ice shapes using Twin
Otter

• Icing cloud droplet size and
liquid water content probes
tested in IRT and in flight

• Development of methods for
measurement of collection
efficiency on clean airfoils

3D laser scanner for ice shape
measurement

Significant progress in extension
of scaling laws to greater range
of sizes and conditions

Investigations of Reynolds
number effects on iced airfoil
performance using cast ice
shapes

Tailplane Icing Project develops
methods for evaluation of
stability and control parameters
for iced aircraft

Shed ice particle tracking with
high speed cameras

Development of SLD simulation
capability in IRT

Extension of scaling laws to SLD
icing conditions

Investigations of SLD droplet
splashing, break-up and associated
mass loss

Development of methods for sub-
scale aero testing of complete
aircraft with artificial ice shapes

Full scale iced airfoil performance
testing at flight Reynolds numbers in
ONERA FI pressurized wind tunnel

Swept wing ice shape generation
and performance testing on
representative business jet model

Extension of collection efficiency
measurement methods to iced airfoil
geometries

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Experimental Methods

In-Flight Testing Projects

- Icing cloud characterization

- Ice shape measurements

- Instrumentation development

- Aircraft performance measurements with simulated ice shapes

- Aircraft handling and stability & control characteristics with simulated ice shapes

Flight No. 9768 ; Flight Date: 12/11/97; Time: 15:05:51 ; Span= 18

Particle sizing probe
mounted on Twin Otter

Stereoscopic
imaging for ice
shape

documentation

LWC histogram for Twin-
Otter flight in SLD

Blended LWC Histogram, (g/m3/dLogD)

\

ir 1

1 10 100 1000

Droplet Size, (pm)

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Experimental Methods

Ice Accretion Studies

Research needed to de-construct ice growth stages into micro-physical phenomena

from roughness to ice feathers to ice shape ► new physical models &

improved CFD tools

IRT Test - ice shape growth Click to play movie

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Experimental Methods

Ice shape Measurement Methods

- Ice shape tracing

- Ice shape molds and castings

- Utilization of 3D scanner technology

* L_ '

Iced Airfoil Profile - Run 31

0.05 0.1

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Experimental Methods

Ice shape Measurement Methods

- Ice shape tracing

- Ice shape molds and castings

- Utilization of 3D scanner technology

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Experimental Methods

Advanced Measurement Techniques

- Fluid-thermal measurements in the region near the
ice/water/air interface

- Non-intrusive liquid water and droplet diameter
measurement methods for regions upstream and
surrounding test targets

- Unsteady, high-speed velocity measurements in the
entire flow surrounding the iced geometry

- Automated ice shape measurement techniques

Images

From

DrIFT

Click to play movie

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Experimental Methods

Microphysical Studies

- Multi-phase region at the ice surface: water film
thickness and velocity, the ice surface topology,
detailed airflow temperatures and velocities

Scalloped Ice
Shape Studies

Vertical Icing Studies Tunnel

'| Ret ~“ Roughness
, , . L Modeling

Droplet Splashing Imaging

Re -1 / 2

Re ' 1 / 2

condensed-layer

triple-deck

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Experimental Methods

Aerodynamic Performance Measurements

- Pressure and force measurements on airfoils and wings with leading
edge artificial ice shapes

- Ice shapes can be 3D castings, extrusions from 2D ice shape
tracings, or geometric shapes representing ice shapes (e.g. spoiler
shapes used to simulate ice horns)

- Most testing has been at moderate Reynolds numbers using 2D ice
shapes on airfoil models; some 3D testing and high Reynolds number

Two-Minute Glaze Ice Shape 202

16.7-Minute Rime Ice Shape 212

22.5-Minute Glaze Ice Shape 904

22.5-Minute Glaze Ice Shape 944

Effect of Reynolds number
at constant Mach number
on performance for the
clean GLC-305 airfoil.

ff(des)

Reynolds Number Effects on
22.5-minute Glaze Ice Shape
(944 casting) at Ma = 0.12

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Experimental Methods

High Re Aerodynamic Performance Measurements at ONERA FI Facility

a (deg)

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Experimental Methods

Iced Aircraft CFD Modeling Validation - near-stall condition flow field
research

- Regions containing vortex shedding, vortex interaction from several
regions of interest, flow separation and reattachment, separation
bubble reattachment unsteadiness, and extended regions of boundary
layer transition

Contour plot of the average velocity field at
mid-span for the NACA0012 airfoil with 2D
glaze ice simulation at Re = IxlO 6 and a = 2.7°

■■ C

Contour vector and streamline plots of
an instantaneous velocity field at mid-
span for the NACA0012 airfoil with 2D
glaze ice simulation at Re = IxlO 6 and
a = 2.7°

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Experimental Methods

Scaling Methods

- Geometric and physical parameter scaling methods have been
developed and used when models are too large for the experimental
facility or the icing conditions of interest cannot be obtained in the facility

C,

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LWC,

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in

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kt

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10 6

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160

1.50

9.7

95

1.6

0.43

1.2

10.5

11

200

40

1.00

2.4

93

1.8

0.40

1.4

Scaling to App C for MVD’s up to 160pm has been demonstrated

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Historical Progress in Technology

Experimental Methods - In-flight Testing

1983-1992

1994-1997

1997-1999

2000

2001

2001-2002

Natural ice cloud characterization, icing instrumentation
development, ice detection & protection systems evaluations

N AS A/FAA Tail plane Icing Program: explored factors that lead to
ice contaminated tailplane stall; developed and evaluated flight test
methods and recovery procedures

NASA/FAA/NCAR SLD Icing Flight program: cloud
characterization, ice shape & performance measurements. Data
used to develop SLD icing certification envelope.

Alliance Icing Research Study: Icing remote sensing validation

Piloted Icing Flight Simulator: flight data used to validate an ice
contamination effects flight training simulator

Smart Icing Systems Flight Tests: flight data to develop and
evaluate systems identification methods for isolating icing effects
on airplane performance, stability & control

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National Aeronautics an

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d Space Administration

Historical Progress in Technology w?

Experimental Methods - Ground-based Testing

* 1989

Developed methods for testing aerodynamic penalties resulting from
application of de-icing fluids

1985-1990

Developed ice casting methods for creation of realistic ice shape
models to be used in dry-air wind tunnel performance testing

1985-Present Developed methodology for collection efficiency measurements on

airfoils, wings, engine inlets and other aircraft surfaces

1990-1995

Developed visualization methods for shed ice particle tracking

1995

Adapted laser sheet flow visualization methods for use in icing cloud;
examined effects of ice growth on delta wing leading edge vortices

1990-Present Developed procedures for aero-testing of ice shape geometries

ranging from castings to simplified representations of ice shape
features; examination of Reynolds and Mach number effects

2003-2006 Development of methods for simulation of SLD icing conditions

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1982

1990

1993

2000

2003

2006

Historical Progress in Technology
Experimental Methods - Icing Scaling

1 989 Preliminary tests of methods to scale model size or test conditions
using combinations of matched similarity parameters

1993 Experimental evaluation of early scaling methods; scaling for rime
ice demonstrated; ability to scale LWC shown using Olsen method

1999 Importance of surface phenomena demonstrated; demonstrated
significant improvement by including Weber number in scaling
methodology

present Preliminary study of scaling for intercycle ice accretion performed;
scaling methods incorporating water-film thickness proposed and
evaluated; scaling for SLD conditions begun; effect of drop MVD on
ice shape being mapped

Release of Icing Scaling Manual

Addendum to Icing Scaling Manual to include SLD scaling

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Historical Progress in Technology

Computational Methods

1980s

1990s

2000s

]

• LEWICE development

• Early 2D performance
analysis studies

• LEWICE3D development

• Release of LEWICE 2.0

• 2D grid sensitivity and
turbulence model evaluations

• Early 3D performance
analysis studies

• Development of stand alone
thermal IPS simulation
methods

• Release of LEWICE3D version 2

• Collaboration with Boeing on use
of LEWICE3D for 787 analysis

• Release of LEWICE 3.2.2; includes
initial modifications for SLD

• International release of LEWICE

• Automated grid generation for
LEWICE

• Release of SmaggICE 2.0

• Unsteady DES methods for iced
performance analysis

• Thermal IPS model in LEWICE 2.2

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Ice Accretion Modeling

Feather

growth

Examine the physics of ice
accretion to understand:

- Droplet impact dynamics
(splashing, break-up, re-
impingement)

Re ^“ Roughness

Modeling

condensed-layer

Re -1 / 2 triple-deck

- Surface water transport

- Heat transfer

- Roughness formation

©

a) pre-existng surface water structure

- Phase change kinetics

- Scallop ice (swept wing)
shape formation

b) highly disruptive local impact

c) residual of local impact

d) return to surface water structure

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Ice Accretion Computational Modeling

LEWICE - 2D Ice Accretion Code

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O

Ice Shape Tracing; Validation Database

s 50

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1 40

X

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4 -

□ LEWICE Difference
■ Experiment Variation

if m ri

rime mixed glaze

Example of Ice Shape Prediction at
Average %Difference from Experimental Data

x(in)

Ice Shape Comparison Results Comp. vs. Exp.

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Ice Accretion Computational Modeling

LEWICE3D - 3D Ice Accretion Code

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Iced Aircraft CFD Modeling

to

to

Ice feature effects
Identification of critical ice shapes
Surface modeling and grid generation
Turbulence modeling and multi-phase flow
Time dependent/adaptive gridding
CFD modeling for 3D surfaces
Roughness effects (unsteady, multi-scale) scanned solid to cfd grid
3D particle tracking through unsteady/separated flow

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CFD Studies

1 .) Ice feature effects,
identification of critical
ice shapes

Iced Aircraft CFD

6 deg

Q

oj -1

5

Exp. Data (Run 41 )

3D PANS (refined mesh)

■ 3D DES (refined mesh, dt = 0.000075s)
3D PANS (baseline mesh)

3D DES (baseline mesh, dt = 0.0001 5s)
3D DES (baseline mesh dt = 0.000075s)

O

2.) Turbulence
modeling and time
dependent/ adaptive
gridding for icing
topology

Turbulence
generation
behind a leading
edge ice shape

3.) CFD modeling for
3D surfaces

- 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

M/C

4.) Roughness effects (unsteady,
multi-scale)

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Historical Progress in Technology
Computational Methods - LEWICE

1991 - Release of LEWICE version 1 .0; capable of predicting rime ice
accretion

1993 - Release of LEWICE 1 .3; enhancements to glaze ice accretion
capability

1995 - Release of LEWICE 1 .6; improved ability to simulate long duration ice
accretions, enhancements to usability

1998 - Release of LEWICE 2.0; major overhaul to improve accuracy, reliability,
and robustness; implemented industry-standard software development
and maintenance methods; transition from research tool to production
tool

2002 - Release of LEWICE 2.2; added capability to analyze thermal ice
protection systems

2004 - Release of LEWICE 3.0; added capability to use LEWICE with an
adaptive grid Navier-Stokes code

2006 - Release of LEWICE 3.2.2; added SLD capabilities

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Historical Progress in Technology
Computational Methods - LEWICE3D

1991 Initial version of LEWICE3D with integrated 3D Hess-Smith Panel Code

1993 Initial version of grid based LEWICE3D for body fitted grids

1 994 Support for unstructured flow solutions added.

1995 Support for simple cartesian grids added for 3D panel code interface

1996 Support for Oct-tree type grids add for improved 3D panel code interface.

ICEGRID3D developed to generate Oct-tree type grids about panel
models.

1997 Monte-Carlo trajectory algorithm developed for complex regions such as

ducts, radomes, wing roots

1998 Capability to handle Navier-Stokes based grids added.

1999 Developed simpler, faster, Oct-tree type grid code for 3D panel code

interface (PATCHGRID).

2001 Development of LEWICE3D post-processor to generate off-body

concentration ratios (CONFAC3D)

2002-Present Parallelization of LEWICE3D, with both Open MP and MPI, leads to

significant decreases in turn around time

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Historical Progress in Technology

Computational Methods - Performance Analysis

K>

1983 - 1991 Examined use of existing 2D and 3D CFD tools; results indicated

that methods could be used for pre-stall conditions; difficult to
generate grids for ice shape geometries; identified approach for
analysis of rotorcraft performance losses due to icing

1995 - 1999 Investigated use of new turbulence models and began

development of tools to aid in grid generation for ice shape
geometries; use of new turbulence models improved capability to
determine stall behavior however will require move to unsteady
analysis and LES/DES methods; grid sensitivity studies indicate
that some smoothing of surface geometry to allow easier grid
generation is allowable

2000 - present First release of SmaggICE, computational tool to aid in

development of grids for ice shape geometries

Current

Use 3D unsteady methods to identify stall behavior of iced aircraft

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Historical Progress in Technology

Flight Dynamics

1980s

1990s

2000s

• Initial testing of stability &
control parameters on NASA
Twin Otter

• Classic longitudinal flight test
techniques with artificial ice
shapes

• Application of digital inertial data
system for stability and control
derivative estimation for artificial
ice and natural conditions

• Tailplane Icing Project develops
methods for evaluation of
stability and control parameters
for iced aircraft

Refinement of analysis
techniques and flight test
techniques with artificial ice
shapes

Tailplane Icing Project builds
upon prior experience to quantify
iced tailplane effects

Investigations of scale model
tailplane performance parameters

Investigation of effects of
tailplane icing using scaled and
full-scale wind tunnel tests.

Subscale model testing of Twin Otter
in Bihrle Applied Research spin
tunnel

Iced aircraft state assessment
research at UTSI supported through
NRA

Flight testing to develop parameter
ID methods in support of Smart Icing
Systems studies and Systems
Technology, Inc. SBIR.

Development of Ice Contamination
Effects Flight Training Device
(ICEFTD) to train pilots on effects of
ice accretion.

Development of iced aircraft flight
simulation model of Twin Otter and
Cessna business jet.

Dynamic wind tunnel testing of iced
S-3B Viking to obtain data for
simulation model.

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K>

00

Icing Effects on Aircraft Controllability

Preventing Iced Flight Dynamics Loss of Control

• Technical Approach

- Develop understanding of how “clean” aero-performance and
S&C models are affected by ice accretions

• Analysis of flight data (existing and future) using PID methods

- Simulated and natural ice records with flight dynamics package

• Develop and use iced aerodynamic CFD tools to predict aircraft
response

- Develop onboard vehicle state assessment technologies to
determine the S&C authority margins as ice accretes on
airframe or as flight conditions lead to upset

• Alert pilots through IIFD products to exit icing conditions and/or
change flight condition

- Develop modified control laws to prevent LOC or manage
recovery

• Limit flight envelope to enable recovery and safe landing

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Fligth Dynamics

Tailplane Icing Effects

- Various artificial ice shapes tested

- Static testing performed to determine
degradation on performance parameters

- Dynamic testing performed using zero-G
pushover maneuver

Elevator Deflection Required for Speed
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o

Icing Effects on Aircraft Controllability

Iced Flight Dynamics Loss of Control (LOC)

• Multiple incidents and fatal accidents have occurred recently in which ice
accretions were a causal factor

- IPS usually operating, autopilot masked control changes

• Aircraft icing LOC research areas

- Identification and modeling: premature stall and control authority margin

- Reconfigurable controls for recovery

- Envelope limiting methodology for continued flight through landing

1994 - ATR-72.
Roselawn, /A/

• 68 fatalities

• Aileron hinge moment
reversal with ridge of ice
beyond the deicing boots

Click to play movie

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Research in Iced Flight Dynamics

• Smart Icing Systems (SIS)

- Concept that senses the presence of ice, activates and
manages the IPS, provides the pilot with information on
aircraft performance and S&C

- PID methods were researched to characterize
aerodynamic state of the vehicle. Flight envelope and
autopilot models were developed. Flight management
systems were examined for control response automation

• Aero-performance CFD

- GRC iced aero CFD tools identified premature stall and
subsequent roll-off in aircraft trajectory consistent with

Final NTSB report on Comair Flight
3272 released on November 4, 1998

• The Findings state: “The accident
airplane’s left roll tendency was
precipitated by a thin layer of
rough ice” and may have been
further affected by an asymmetric
ice shed or aileron deflection

10 5.0 10.0 150 20 0 uu D.u iu.u io.u *u.u

Angle ol attack (deg) A0A (degrees)

DFDR data

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Historical Progress in Technology

Experimental Databases

1980s

1990s

2000s

• Ice shape profiles from various
airfoils obtained in the IRT

• Ice shape profiles and icing cloud
conditions from in-flight
measurements on the NASA Twin
Otter

• Iced airfoil performance
characteristics using simplified
artificial ice shape geometries

• Iced airfoil performance
characteristics using complex
casts of actual ice shape
geometries

• Scaled ice shape data covering
an extensive range of App. C
conditions

• Collection efficiency data
covering a range of airfoil and
engine inlet geometries

• Icing cloud data for
characterization of SLD icing
environment

• Ice shape castings and photos
from swept wing geometries used
to identify mechanism of
scalloped ice shape formation

• Extension of ice shape profiles
and collection efficiency
databases to include SLD
conditions

• Scaling databases extended to
include SLD conditions

• Creation of droplet splashing and
ice mass databases; aid in
identification of SLD conditions
and in validation of SLD
computer simulation codes

• Performance degradation data for
finite swept wing with scallop ice
shape castings

• Stability and control data from
sub-scale and full scale iced Twin
Otter models

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Historical Progress in Technology
Experimental Database Development

3 1983 -present

Ongoing accumulation of ice shape tracings provides extensive
data for use in validation of ice shape simulation methods;
Database made available to public via Web

1985-2001

Development of collection efficiency database in collaboration with
Wichita State University

- 1995-2000

Modern Airfoil Project develops ice shape and associated airfoil
performance database on airfoils representative of current usage

1996

Electro-thermal ice protection system model tested to provide
database for validation of thermal ice protection system simulation
software

1999-2002

Tailplane Icing effects on sub-scale & full-scale business jet T-Tail

2002

Testing of swept wing model to determine effects of sweep on ice
shape development and resulting performance losses

2007

Development of SLD ice shape database for validation of
simulation tools

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Summary of Airframe Icing Goals

S Continue to meet customer needs for icing simulation tools and
databases

S Reduce costs of icing certification through use of simulation
methods

S Enhance safety of flight by allowing simulation of conditions
unattainable through flight testing

S Improve accuracy, reliability, range, and usability of simulation tools
through creation of comprehensive validation databases

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