VKI experiment embarked on the 78th Parabolic Flight Campaign: Contact Angle Sloshing Experiment (CASE)

NEWS

DAY 9 --  FLIGHT 3  --

 Alessia, Domenico and Louis are part of the flyer team. One U tube with distilled water is exposed to LED backlighting measurement technic and the second one with HFE7200 is equipped for PIV.

The test case with distilled water showed the most unexpected but interesting behavior. Despite having the highest surface tension among the tested fluids the motion the interface was less than expected, introducing new parameters to be studied such as the hysteresis phenomena at the contact line.

After months of hard work and these 2 weeks on Novespace site, it is now time to unload the aircraft, pack all the equipment and go back to Belgium. The coming weeks will be dedicated to the analysis of the 15 Terabytes of data on capillary flows and dynamic wetting in micro-gravity conditions.

DAY 8 --  FLIGHT 2  --

Alessia, Pedro and Louis are part of the flyer team. One U tube is exposed to LED backlighting measurement technic and the second one is equipped for PIV (Particle Image Velocimetry) to visualize the velocity field underneath the rising interface. The team had to install the laser in Rack 1, and seed the liquid with fluorescent microsphere particles. HFE7200 will be tested.

HFE7200 with the backlighting system behaved as expected under microgravity conditions. The first post-processed images taken on the PIV setup are nice. At the end of the day, our setup has been fully prepared for the last flight.

DAY 7 --  FLIGHT 1  --

Alessia, Domenico and Michel are part of the flyer team. Two liquids are simultaneously studied in two separate U tube configurations. LED backlighting systems are installed on both U tubes to visualize the capillary rise. HFE7200 and DiPropylene Glycol will be tested.

None of them were sick! First parabolas helped them to familiarize with the 0g conditions and the test bench. They calibrated the amount of liquid within the tubes. Labview data are fine and the first post-processed images are interesting. Formation of precursor films along the wall and formation of a spherical meniscus under microgravity. At the end of the day, our setup has been fully prepared for the next flight.

DAY 6

Miguel Mendez and Alessia Simonini joined the team, so we have had a meeting to review the test matrix and introduce them to the procedures. At the end of the day, our setup has been fully prepared for the flight.

DAY 3-4-5

Now, the whole team is working in the aircraft. The last elements have been installed in the test bench and data acquisitions have been performed on ground to verify the software. During the flight, the VKI team will need to change the position of the cameras, increase the amount of liquid into the U-tubes,... Thus, members were trained for these “in-flight procedures”. Some operations are simplified to decrease the amount of manipulations. Parabolic flights are scheduled for Tuesday 29/03, Wednesday 30/03 and Thursday 01/04.

DAY 2

The electrical and mechanical checks performed by Novespace have been successfully passed, so the 2 Racks have been cleaned to avoid any dust in the plane. They are now on board, fixed on the aircraft rails.

DAY 1

The preparation week for the 78th ESA Parabolic Flight Campaign has started today! The VKI Team is the Experiment 9 - CASE, Contact Angle Sloshing Experiment. The purpose of this experiment is to study the capillary rise in conical channels during the microgravity step reduction. Prof. Miguel Mendez is the Principal Investigator for this campaign.

This experiment is composed of 2 Racks that will be installed in the aircraft. Rack 1 is a metallic containment that confines the main experimental equipment : quartz U tubes, liquids, cameras, backlighting system, laser head… Rack 2 is a Standard Primary Structure made of Bosch profiles where all electronic devices are fixed on.

Louis Carbonnelle, Michel Bavier, Domenico Fiorini and Pedro Marques are working hard since early morning to unload the van, reassemble the equipment inside the racks and undergo conformity checks at the Novespace premises.

Description of the VKI experiments on-board

• SCIENTIFIC OBJECTIVE

The scope of this work is to study the interface dynamics during the motion of a gas-liquid interface in microgravity conditions, strongly dominated by capillary forces. The main goal is to measure the interface evolution with sufficient resolution in space and time to allow for deriving better models for the dynamic contact angle.

The main works in dynamic contact angles under microgravity conditions have been focused on the problem of capillary rise. The most influential study on the subject is the one proposed by Dreyer’s group [1,2], who investigated a large range of configurations in a drop tower. Besides providing an

extensive experimental dataset over a wide range of operating conditions, these works have also developed improved models to predict the evolution of the liquid height during the capillary rise.

These results leave an open question on the role of the contact angle and the interface shape on the motion of the liquid column. In particular, the proposed models feature a quasi-steady correlation for the contact angle dynamics, which is indirectly fitted to the data through the model, without measuring the interface shape: the correlation is calibrated so that the model correctly predicts the interface motion. However, it can be shown that different correlations would lead to similar predictions. In other words, the interface dynamic in the previous experiments is not sufficiently sensitive to the chosen correlation to discern whether inertial effects impact the contact angle dynamics.

This work proposed three novelties over the previous experiments:

1. The main goal is to track and monitor in time the interface within the tube, hence measuring ‘directly’ the interface shape and the contact angle.

2. The range of operating conditions allowed by the parabolic flight and the proposed design will also be broader, leveraging the longer microgravity period and the presence of a hypergravity phase.

3. The processing of the experimental data will include a sensitivity analysis linking interface shape to the expected capillary force.

[1] Dreyer, M. E. (2007), Free Surfae Flows under Compensated Gravity Conditions, Springer Tracts in Modern Physics, Vol 221.

[2] Stange, M., Dreyer, M. E., Rath, H. J. (2003), Capillary Driven Flow in Circular Cylindrical Tubes, Physics of Fluids, Vol 15 (2587)

• TECHNICAL DESCRIPTION OF THE EXPERIMENT

The objectives of the planned experiment are to determine both the liquid/gas interface shape and the fluid velocity during HFE 7200 capillary rise in a U-shaped tube with different diameter on each side. During the parabolic flight test campaign, the accelerations generated by the parabolic maneuver will be used as trigger for the capillary rise of the

interface. Two quantitative visualization techniques will be used: 1) Backlighting imaging technique and 2) The fluorescent Particle Image Velocimetry (fPIV). The combination of these techniques require a colorant (dye) and appropriate microscopic fluorescent particles mixed with the liquid and illuminated by a laser source. Four cameras will record the velocity of the fluid and the position of the gas/liquid interface on each side of two different U-tubes, during microgravity and at ambient temperature.

• APPLICATIONS OF THE RESEARCH

The scientific relevance of the work is twofold, on the theoretical and the applied sides alike. From a fundamental side, the result will address key questions on the contact angle's role on the capillary force distribution next to an interface and the generalization capabilities of contact line correlations. On the applied side, while the final goal of this work is to predict the gas-liquid interface during sloshing in space systems, the simplified configurations developed in the proposed experiments are also relevant to a broader spectrum of capillary driven flows.

Experiment Team