15 In-flight Icing: Modeling, Prediction, and Uncertainty
461
might bounce off the surface and then are eventually removed by aerodynamic
forces. In contrast, wet ice is formed when ice crystals fall into a higher temperature
atmospheric layer and they partially melt. The range of temperatures in which wet
ice can occur is between −7 ◦ C and 3 ◦ C. Adhesion forces are higher than in the
case of the dry ice and therefore ice accretion is possible [19]. The formed ice
consists of a porous mixture of ice, liquid water, and air that presents a low density.
The impinging water can travel through the pores and freeze generating complex
accretions.
Wet snow accretion in power lines has been an active field of research. Its effects
include high mechanical stresses that can produce overload and failure with the
potential risk of blackout or collapse [18–20]. On a different note, limited research
was found in the field of aircraft snow accretion, and only very recently the topic
is being addressed. Nevertheless, in order to comply with the icing regulations
for certification, aircraft must be protected against snow icing envelopes which is
presented in the Sect. 15.4.3.
15.2.2 Icing Relevant Parameters
Aircraft icing entails very complex physical processes which are highly dependent on many interrelated parameters. Those describe characteristics of the icing
environment, the aircraft design and operation, and the interaction between those
two. In addition, the duration of the icing encounter determines its severity being
the longer the encounter the more severe. This section presents the environmental
parameters (cloud liquid water content, ambient temperature, and droplet size), and
the operational parameters (flight speed and altitude) that dictate the characteristics
and severity of the icing encounter together with typical values for those parameters.
15.2.2.1 Outside Air Temperature
The main parameter influencing the accretion of ice from supercooled clouds is the
steady ambient air temperature termed the outside air temperature (OAT) [12]. It
is relatively easy to monitor but it implicitly only represents part of the accretion
physics. Its value influences several phenomena: the convective heat transfer from
the impinging droplets to the aircraft surface and the temperature of the aircraft
surface. The convective heat loss over a control volume ˙
Q can be calculated as
follows:
˙
Q = h c A(T s − T ∞ ),
(15.1)
where h c is the convective heat transfer coefficient, A is the surface area, T s is the
surface temperature, T ∞ is the freestream temperature or Outside air temperature
(OAT), and A is the surface area considered. As it is shown in Eq. (15.1), low OAT
461
might bounce off the surface and then are eventually removed by aerodynamic
forces. In contrast, wet ice is formed when ice crystals fall into a higher temperature
atmospheric layer and they partially melt. The range of temperatures in which wet
ice can occur is between −7 ◦ C and 3 ◦ C. Adhesion forces are higher than in the
case of the dry ice and therefore ice accretion is possible [19]. The formed ice
consists of a porous mixture of ice, liquid water, and air that presents a low density.
The impinging water can travel through the pores and freeze generating complex
accretions.
Wet snow accretion in power lines has been an active field of research. Its effects
include high mechanical stresses that can produce overload and failure with the
potential risk of blackout or collapse [18–20]. On a different note, limited research
was found in the field of aircraft snow accretion, and only very recently the topic
is being addressed. Nevertheless, in order to comply with the icing regulations
for certification, aircraft must be protected against snow icing envelopes which is
presented in the Sect. 15.4.3.
15.2.2 Icing Relevant Parameters
Aircraft icing entails very complex physical processes which are highly dependent on many interrelated parameters. Those describe characteristics of the icing
environment, the aircraft design and operation, and the interaction between those
two. In addition, the duration of the icing encounter determines its severity being
the longer the encounter the more severe. This section presents the environmental
parameters (cloud liquid water content, ambient temperature, and droplet size), and
the operational parameters (flight speed and altitude) that dictate the characteristics
and severity of the icing encounter together with typical values for those parameters.
15.2.2.1 Outside Air Temperature
The main parameter influencing the accretion of ice from supercooled clouds is the
steady ambient air temperature termed the outside air temperature (OAT) [12]. It
is relatively easy to monitor but it implicitly only represents part of the accretion
physics. Its value influences several phenomena: the convective heat transfer from
the impinging droplets to the aircraft surface and the temperature of the aircraft
surface. The convective heat loss over a control volume ˙
Q can be calculated as
follows:
˙
Q = h c A(T s − T ∞ ),
(15.1)
where h c is the convective heat transfer coefficient, A is the surface area, T s is the
surface temperature, T ∞ is the freestream temperature or Outside air temperature
(OAT), and A is the surface area considered. As it is shown in Eq. (15.1), low OAT