CRANFIELD UNIVERSITY ICING TUNNEL DESCRIPTION
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Closed-circuit with return duct on top.
Heat exchanger behind spray rake and fan on the other end. The fan is in suction mode
sucking in the air into the tunnel.
Spray rake with nozzles on one end that injects water into the flow. The spray rake
also makes the tunnel flow turbulent and thus aerodynamic studies can’t be conducted
within the tunnel like a standard tunnel.
The flow with the supercooled water reaches the test section and the model in question
accretes ice on impact.
Tunnel convergence is shallower compared to the other wind tunnels in order to avoid
accretion of ice on the tunnel walls – the idea is for the SWD to actually get mixed with
the air and reach the model in the test section for impact.
Hot air supplied from a main compressor in the B35 at 7 bar to heat up the bars before
we inject the water into the tunnel.
Cooling capacity of 0.5MW with a motor of 250kW capacity.
100m/s max. speed, 0.2 – 4.0 g/m3 LWC range and -30 °C minimum temperature in
the tunnel.
Instrumentation includes a Scanivalve (+/- 1 PSI gauge pressure) for pressure
scanning using static pressure ports on a model within the test section, standard
thermocouples, and pressure sensors, IKP and Malvern. High-speed camera, Thermal
camera etc. have also been used in the past for various projects.
Tunnel monitoring instrumentation includes RTDs for temperature measurements,
static pressure ports at two points synced with a differential pressure sensor to
ascertain tunnel speed and mass flow.
Using impact of SWD we can have rime, glaze or mixed ice that can be accreted on
the model. Rime is obtained at usually low LWC, low temperature and low speeds.
Glaze is the opposite.
Vertical tunnel uses a droplet generator on top to create large droplets to impact on
the model in the test section. The droplet sizes can range from 100-2500 microns.
LWC is not usually consistent enough to be used as a requirement.
Air input in VT is from the top and the direction of the flow can be controlled by the air
valves underneath to make the droplets biased in one direction.
Used more for fundamental research but can also be used for commercial applications
like droplet impact on superhydrophobic or icephobic coatings.
The usual studies undertaken by the university generally includes a Mode I and Mode
II or shear test on various substrates to determine their adhesion strength.
The tunnel is modular so different sections can be changed – like an octagonal section
with a rotating rig and a different configuration that has been used in the past to study
helicopter intakes and their anti-icing system.
The tunnel can also generate anti-icing bleed supply using a separate setup installed
on the far side.
The tunnel is a closed-circuit type with spray rake on the upstream end along with the heat
exchanger and the fan on the downstream end operating in suction mode. The test section is
76cmx76cm. The speed of airflow can range from 20-100m/s, the LWC can range from 0.24.0 g/cub.m. and the temperature can range from +5 to -30 deg C. The tunnel is designed in
a way such that convergence is much shallower than conventional wind tunnels in order to
ensure the SWD reach the test section for impact and do not hit the walls and start accreting
ice. The types of ice that can be built in the tunnel ranges from rime to glaze and mixed ice as
well. For rime ice, the conditions usually are low speed, low LWC and low temperatures and
CRANFIELD UNIVERSITY ICING TUNNEL DESCRIPTION
it is opposite for the glaze ice. The tunnel design is modular so the sections can be removed
and replaced as per requirement including the test section. There is an octagonal test section
that can be installed with a rotating rig that can simulate the spinner section of the gas turbine
engine intake, there is also an alternate configuration which has been designed specifically to
study helicopter intakes and their anti-icing system but can be modified for other applications
as well. The tunnel instrumentation includes pressure sensors and thermocouples along with
a Scanivalve pressure scanner system to read static pressure over multiple points on a model,
a Malvern system to characterize flow and we have used thermal cameras and High-speed
cameras in the past. There is also an IKP to study the local LWC, usually the tunnel is
caliberated using an icing blade.