456
B. Arizmendi et al.
15.1 Introduction
The requirement for aircraft to be able to safely operate in diverse flight conditions
has never been more prominent than it is now with increasing demand for fast
and reliable transport. With this, the industry faces major dilemmas, that to this
day, have yet to be resolved. For instance, aircraft and helicopters are occasionally
exposed to atmospheric conditions which lead to the accumulation of ice, namely
ice accretion. In-flight icing occurs when an aircraft or rotorcraft goes through a
supercooled cloud at a temperature below 0 ◦ C containing supercooled liquid water
droplets. The droplets might freeze when impacting with the surface of the aircraft
depending on the values of the influencing variables such as the temperature and the
size of the droplets. The formation of ice on the surfaces is problematic because it
alters the shape of control surfaces dropping their performance. In addition, it can
cause the gathering and provision of inaccurate data to the pilot and the blockage of
the mechanisms of control moving parts when accreted in those. Consequently, ice
accretion presents a major threat to safety and performance of aircraft and rotorcraft
which could lead to catastrophic accidents as it happened in the past.
In-flight icing has introduced a new challenge for manufacturers because they
need to ensure safety and performance over different flight conditions. To this purpose, nowadays flying crafts are equipped with ice protection systems to eliminate
or avoid the formation of ice in critical parts of the aircraft. The adequate design of
these systems requires a holistic understanding of the icing phenomena and icing
environments. Furthermore, the design must comply with existing regulation. Over
the years, several research methods were utilized for understanding and predicting
the process of ice accretion. Experimental tests were performed both in-flight and
in wind and ice tunnels. The icing conditions are often replicated by spraying
supercooled droplets into aircraft surfaces. The characterization of icing conditions
is limited due to the vast amount of different icing scenarios and the resources
available for these purposes. Physical models and their corresponding numerical
models help understand the physics of the phenomena. These models need a
thorough experimental validation in order to extrapolate the obtained conclusions
into reality.
There are large uncertainties on the understanding and characterization of the ice
accretion phenomenon. The replication of real icing conditions presents a major
challenge due to the variability of the aforementioned conditions, to the large
number of influencing parameters, to diverse icing conditions, and to the ability
of the experimental facilities available to reproduce them. This would require a
very large number of tests which would imply infeasible costs. In addition, flying
under icing conditions exposes the flight crew and passengers to unwanted risk
situations. These uncertainties lead to ambivalence on the replication of these
conditions in icing wind tunnel tests and the consequent ice shapes accreted in the
aircraft components. They also influence the data for experimental validation of the
numerical models whose input is also subject to uncertainty. To conclude, there are
many and large sources of uncertainties in the study of in-flight icing. Collaborations
B. Arizmendi et al.
15.1 Introduction
The requirement for aircraft to be able to safely operate in diverse flight conditions
has never been more prominent than it is now with increasing demand for fast
and reliable transport. With this, the industry faces major dilemmas, that to this
day, have yet to be resolved. For instance, aircraft and helicopters are occasionally
exposed to atmospheric conditions which lead to the accumulation of ice, namely
ice accretion. In-flight icing occurs when an aircraft or rotorcraft goes through a
supercooled cloud at a temperature below 0 ◦ C containing supercooled liquid water
droplets. The droplets might freeze when impacting with the surface of the aircraft
depending on the values of the influencing variables such as the temperature and the
size of the droplets. The formation of ice on the surfaces is problematic because it
alters the shape of control surfaces dropping their performance. In addition, it can
cause the gathering and provision of inaccurate data to the pilot and the blockage of
the mechanisms of control moving parts when accreted in those. Consequently, ice
accretion presents a major threat to safety and performance of aircraft and rotorcraft
which could lead to catastrophic accidents as it happened in the past.
In-flight icing has introduced a new challenge for manufacturers because they
need to ensure safety and performance over different flight conditions. To this purpose, nowadays flying crafts are equipped with ice protection systems to eliminate
or avoid the formation of ice in critical parts of the aircraft. The adequate design of
these systems requires a holistic understanding of the icing phenomena and icing
environments. Furthermore, the design must comply with existing regulation. Over
the years, several research methods were utilized for understanding and predicting
the process of ice accretion. Experimental tests were performed both in-flight and
in wind and ice tunnels. The icing conditions are often replicated by spraying
supercooled droplets into aircraft surfaces. The characterization of icing conditions
is limited due to the vast amount of different icing scenarios and the resources
available for these purposes. Physical models and their corresponding numerical
models help understand the physics of the phenomena. These models need a
thorough experimental validation in order to extrapolate the obtained conclusions
into reality.
There are large uncertainties on the understanding and characterization of the ice
accretion phenomenon. The replication of real icing conditions presents a major
challenge due to the variability of the aforementioned conditions, to the large
number of influencing parameters, to diverse icing conditions, and to the ability
of the experimental facilities available to reproduce them. This would require a
very large number of tests which would imply infeasible costs. In addition, flying
under icing conditions exposes the flight crew and passengers to unwanted risk
situations. These uncertainties lead to ambivalence on the replication of these
conditions in icing wind tunnel tests and the consequent ice shapes accreted in the
aircraft components. They also influence the data for experimental validation of the
numerical models whose input is also subject to uncertainty. To conclude, there are
many and large sources of uncertainties in the study of in-flight icing. Collaborations