Aircraft anti-icing: improved design and certification
Submitting InstitutionCranfield University
Unit of AssessmentAeronautical, Mechanical, Chemical and Manufacturing Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Mathematical Sciences: Applied Mathematics
Engineering: Electrical and Electronic Engineering, Interdisciplinary Engineering
Summary of the impact
Cranfield's understanding and modelling of aircraft icing, a critical
part of the safety, operation and design protocols for all types of
aircraft, has changed the way in which aerospace companies approach the
design of new aircraft. Cranfield's research has produced high quality
predictive software and an extensive experimental validation database the
impact of which is its use in the design, optimisation and certification
of aircraft and their components.
The impact of Cranfield's icing research is in the design processes for:
- All major Airbus programmes, including A350, A400M, A320 (new engine
- All current Rolls-Royce large civil aircraft projects up to and
including the Trent XWB
- Airframe & UAV (Unmanned Air Vehicle) applications for BAE Systems
and its customers.
Understanding aircraft icing is a critical part of the safety, operation
and design protocols for all aircraft. At temperatures below -30°C there
is no significant liquid water on an aircraft. At temperatures up to 5°C,
ice and liquid water exist on an aircraft's surfaces. It is important to
understand the flow patterns of impacting water, where the ice forms and
how much ice forms. Knowing this, aircraft designers can then decide where
to incorporate heating to prevent the formation or build-up of ice.
Until the mid-1990s, aircraft designers used an ad hoc model that did not
correctly capture the momentum balance of the flowing water. Cranfield
developed an improved mathematical system which accurately models the
energy, momentum and conservation laws for water and ice.
The underlying model uses lubrication theory. Cranfield's researchers
enhanced this to include the freezing and melting processes and the
geometry of the airframe and its components [P1]. The boundary conditions
associated with these systems are complex, the system of differential
equations degenerates. Surface tension effects were modelled using a
pre-cursor film approach.
The nature of the flow fields observed in this class of flows are
characterised by very sharp gradients. Cranfield undertook significant
work to devise Total Variation Diminishing (TVD) schemes which provided
accurate and reliable predictions [P2-P4].
Other aspects of the research include:
- A formulation which supports rotating frames of reference (for
helicopter rotors and turbine blades).
- Automatic error estimation and grid adaptivity for error control.
These features improve the usability of the code.
- Support for structured grids (ICECREMO 1) and unstructured grids
(ICECREMO 2), this meant that the code could be used more easily with
- ICECREMO 2 included Cranfield work on ice protection — the inclusion
of heat sources used to protect critical areas. The computational model
was extended to include heating and conduction in the airframe.
A key aspect of this work is that the code(s) developed at Cranfield have
been integrated into the design and certification processes. This forced
obvious requirements on software development standards. Moreover, the code
had to be compatible with the design codes of various collaborating
organisations. Cranfield developed number of data format translators to
support integration with commercial and in-house codes for computational
fluid dynamics; this was important to make the code accessible to industry
Following problems in service, the US Federal Aviation Authority (FAA)
led an activity to expand icing requirements to force aircraft
manufacturers to address icing due to larger droplets such as freezing
drizzle. To support this activity, Cranfield undertook research projects
to provide experimental data and analysis on large droplet icing. This
work has shown how larger droplets impact different areas of the airframe
and have different splash characteristics. This data has allowed ice
prediction codes, such as ICECREMO, to be adapted to improve their
accuracy for larger droplets. This capability is helping to underpin the
industry's response to the FAA's new requirements [P5, P6].
||Post details and dates
|Dr D. Hammond
||Experimental icing research
|Dr O. Harireche
||Research Fellow (RF)
|Modelling of ice protection
|Dr T. Myers
||Mathematical modelling of freezing & thin film flows
|Mathematical & computational modelling of icing
|Dr P. Verdin
|Mathematical & computational modelling of icing
References to the research
Evidence of quality — Peer reviewed publications
P1* Myers T G, Charpin J P F and Thompson C P, Slowly
accreting ice due to supercooled water impacting on a cold surface,
Phys. Fluids 14, p. 240-256, 2002.
P2 Quero, M, Hammond, D W, Purvisa, R, Smithb, F T,
Analysis of supercooled water droplet impact on a thin water layer and
ice growth, AIAA 2006-466, 2006.
P3* Harireche O, Verdin P, Thompson C P, and Hammond D W, Explicit
Finite Volume Modeling of Aircraft Anti-Icing and De-Icing, Journal
of Aircraft, 45, pp. 1924-1936, 2008.
P4 Verdin P, Charpin J P F, and Thompson C P, Multistep Results in
ICECREMO2, Journal of Aircraft, 46, pp. 1607-1613, 2009.
P5 Lou D and Hammond D W, Heat and Mass Transfer for Ice Particle
Ingestion Inside Aero- Engine, J. Turbomach., 133, 031021 (5
P6* Alègre N, Hammond D W, Experimental Setup for the
Study of Runback Ice at Full Scale Journal of Aircraft, 48,
pp. 1978-1983, 2011.
* 3 identified references that best indicate the quality of the research
Key to publications
a) University of East Anglia, Norwich; b) University College, London
Evidence of quality — underpinning research grants
G1 ICECREMO I, 1996-2000 (DERA, Rolls-Royce, GKN Westland Helicopters,
BAE Systems, Cranfield University), Approx. Funding-Total £1M,
Cranfield-150k, PI: C P Thompson.
G2 ICECREMO II, Jan 2003 - Dec 2005, (Rolls-Royce, GKN Westland
Helicopters, BAE Systems, Cranfield, Dunlop Aerospace/Meggitt)(Approx.
Funding-Total £1M, Cranfield-£160k), PI: C P Thompson.
G3 EU FP6 EXTICE, 2008-2012 (CIRA, ONERA, CEPR, Dassault, Airbus
(ES), Alenia, Uni. Di Napoli, INTA, Piaggio, Cranfield Uni., Technical Uni
of Darmstadt, Uni. Of Twente, Eurocopter) (Overall budget: €429k,
Cranfield Budget: € 115k), PI: D Hammond
Details of the impact
The Cranfield icing research programme has comprised mathematical models,
high quality computer code and experimental validation data which has
become part of the design and certification processes for major parts of
the UK/European aerospace industry. Specific details are company
confidential, since they form part of the core business processes; three
statements from the technical leads in major organisations explain how the
work has had impact.
Airbus uses the computational and experimental aircraft icing programmes,
including developments of the ICECREMO programs, as part of all major
development programmes. The annual expenditure of these programmes is
several billion euros. The codes support design decisions relating to ice
risks associated with regions where air flow is strongly three
dimensional. The certifying authorities accept this type of analysis as
part of the certification documentation [C2].
Since 2008, Airbus programmes where ICECREMO derivatives have been
extensively employed include A350, A400M and the A320 (new engine option).
In the case of the A400M, Airbus used the work by Hammond and Alègre [P6]
to justify how ice formed by runback water (runback ice) is represented on
a sub-scale wind tunnel model. In 2006, Airbus performed the final A400M
Wind Tunnel test, which included runs to investigate the sensitivity to
the aircraft handling qualities to runback ice. Those wind tunnel tests
demonstrate the most critical ice shape and also justify that the wing
performance is acceptable even when degraded by the icing degraded wing
anti-icing performance is acceptable, in terms of the effect of any
runback ice on an aircraft's handling qualities. Runback ice shapes were
generated in the Cranfield Wind Tunnel and the experiments showed that
using surface roughness alone resulted in a similar disturbance to the
boundary layer as the moulding of runback ice taken from the wind tunnel
validating the experimental approach. Airbus also used this work to show
that for the A350 it was appropriate to apply roughness elements smaller
than 3mm to runback ice shapes. The European Aviation Safety Agency (EASA)
gave icing clearance certification by June 2013.
A further example of the use of ICECREMO is in a response to a challenge
Airbus received from the airworthiness authorities. The US FAA asked
Airbus to justify the use of 2D icing codes to predict ice on the A350
wing. The FAA suggested that Airbus could make comparisons against a 3D
code. Airbus compared the droplet catch efficiencies with another code
(from ONERA) and ice shapes with those from ICECREMO, demonstrating good
agreement between both codes. This satisfied the FAA that in using 2D
icing codes we were adequately capturing the 3D effects of ice accretion
on a swept/tapered/twisted wing. The ICECREMO comparisons were presented
to EASA and the FAA on 2nd March 2010. They were satisfied with
the Airbus response. This was a key milestone in the certification
process: type certification is expected in the middle of 2014.
BAE Systems [C3]
BAE Systems has made extensive use of technology and software developed
within ICECREMO 2, to support internal programmes and to provide
consultancy to outside organisations.
Internal programmes to BAE supported by this technology include:
- Herti UAV (sensor placement and airframe icing analysis), 2011
- Mantis UAV (sensor placement and airframe icing analysis), 2011
- Support to general research activities, including novel ice protection
Code use and support for external customers including icing analysis of
- Fuel tank vents
- Intake ducts
- Deployed slats and flaps
These are examples of business which would not have been possible without
the original ICECREMO technology development. Direct contract work
undertaken by BAE Systems associated with these programmes is estimated to
be approximately £600,000.
Although the business impact is difficult to quantify, the technology has
provided a capability, through its 3D modelling ability, for assessment of
aspects of airframe design and performance not otherwise readily
achievable. ICECREMO codes have been used to provide design guidance, e.g.
specification of ice protection systems and location of icing sensors. In
addition to providing design guidance, this has a direct impact on risk
and safety assessment.
Rolls-Royce has found the modularity and clear methodology of the
ICECREMO code especially useful in developing its own in-house analysis
tools and methods. In one form or another, the main elements of code have
been used in all current large civil aircraft projects up to and including
the Trent XWB. The methods have proved to be very valuable in supporting a
shift of emphasis of the certification process away from expensive,
on-wing and simulated altitude testing, to analysis and numerical
simulation backed up with ground testing.
It is difficult to put a figure on the economic benefit as this
capability is one of many essential to how Rolls-Royce currently works. In
essence, the level of fidelity of the company's current analysis methods
is high enough that, whilst it spends more time on analysis, the
dependence on experimental work is reduced, resulting in significant
Sources to corroborate the impact
C1 Contact: Wing Integration & Icing Skill Group Leader, Airbus UK
C2 "ICECREMO is a great example where Airbus has turned University
research into tools of applied practical value." Wing Integration &
Icing Skill Group Leader, Airbus UK
C3 Contact: Group Leader, Fluid Dynamics, BAE SYSTEMS
C4 Contact: Icing and inclement weather specialist, Rolls Royce