THE COLD TESTS IN WIND TUNNELS
The cold wind tunnel facility (CWT-1) at the von Karman Institute for Fluid Dynamics can achieve maximum flow velocities of 65m/s within seconds. Running in a closed-loop configuration, it can work at temperatures as low as -30°C. Additionally, large double-glazing walls at the test section provide optical access for flow visualization.
THE CONCEPT
The CWT-1 is used to investigate the behavior of coatings in terms of anti-sticking and cleanability properties.
By means of a customized venturi pump, fruit flies (Drosophila melanogaster) are injected in the wind tunnel.
The coated samples are installed on a reusable cylinder located in the aft part of the test section, at 1.2 meters from the insect injection.
A high-speed camera, operated at a sampling frequency of 20000 Hz, verifies the distribution of the insects, their speed in the test section and their impact behavior on the samples.
After insect injection, water droplets (LWC = 0,25g/m³; MVD = 15µm) are injected during two minutes at a start temperature of 20°C to investigate the cleanability of the coating.
The surface of the coating is scanned before and after cleaning in order to measure height and area of the insect residues and amount of blockage of the holes in the case of a micro-perforated substrate.
Insects being injected in the CWT-1
Typical image of an insect impact, where teh different types of residues have been identified.
TECHNICAL ADVANTAGE
· Flow velocities up to 65 m/s
· Working temperatures as low as -30°C
· Large double-glazing walls in the test section for optical visualization
· Multiple injection points at the beginning of the test section for different injection devices (insects, water droplets, etc.)
· Automatic program to determine inflow insect conditions from the high-speed videos
· 3D surface scanning for measuring height and area of insect residues and micro-perforated holes blockage on the sample
IN THE CHOPIN PROJECT
The CWT-1 facility is used for testing the best three coatings developed for the CHOPIN project under simulated conditions. These coatings are tested on two different substrates (stainless steel 304 and micro perforated titanium) in terms of anti-sticking and cleanability properties. The best coating is selected based on the results obtained from these tests, and used for further validation.