The dynamics of a liquid fuel sloshing back and forth within fuel tanks adds complexity to the flammability and safety of transportation vehicles, and especially an aircraft. ESI researchers have provided clear evidence of the fluid dynamic mechanisms that may arise within such structures and the detrimental effects which occur with and without combustion.
In the first part of this study, the slosh dynamics were examined using water and a transparent tank with dimensions of 1.9 m (73’’) x 1.2 m (48’’) x 0.94 m (37’’) and a volume of 2.1m³.
This tank was installed onto a “six-degrees of freedom” motion simulator which is capable of being individually or collectively activated in any one the following six-degrees of motion:
⦁ Yaw: Rotation about the z-axis in the x-y plane
⦁ Pitch: Rotation about the x-axis
⦁ Roll: Rotation about the y-axis
⦁ Surge: Motion parallel to the y-axis
⦁ Sway: Motion parallel to the x-axis
⦁ Heave: Motion parallel to the z-axis
A high-speed digital camera and in-house image processing was used extensively to capture the liquid dynamics and resulting sprays. This information was then used to evaluate the liquid drop separation which was observed within the tank ullage. The three fluid dynamic modes observed are listed below:
• Wave impacting the tank wall
• Hydraulic jump formations
• Wave-wave interactions
Slosh Tank and Simulator
With a tank filled to 22.5 % of the maximum level the simulator was set to impart a 10% amplitude roll. This resulted in a hydraulic jump that was observed to producing a large number of small droplets.
Furthermore, the location of the jump reflected the oscillating motion of the simulator, but out of phase.
Development of a Hydraulic Jump Causing Droplet Separation
Hydraulic Jump Formation for 22.5%
Fill Depth and 10% Roll Amplitude
Effect of Amplitude on Hydraulic Jump Formation at Roll Frequency 0.35 Hz
There is discernible change in the jump formation if the roll frequency is held constant but the amplitude is allowed to increase.
Droplet separation was also found to occur when two waves were travelling in opposite directions.
The interactions of these waves create a large disturbance on the liquid surface and droplets are released at the peak of the disturbance. After the waves interact, each continues to propagate in its initial direction.
Wave Interactions Leading to Droplet Separation
Various amplitudes and frequencies of roll produced wave separations at different lateral positions within the tank as well as at different depths, most of which were below the rest level of the liquid.
Wave Separation Height at Various Tank Locations