11:00 AM - 11:15 AM
[AOS14-08] Hydraulic model experiments on water flow behavior in an artificial gravity facility
Keywords:artificial gravity facility, hydraulic model experiment, lunar habitat, Martian habitat
The Lunaglass and Marsglass concepts are lunar and Martian habitation facilities utilizing artificial gravity, jointly researched by Kajima Corporation and Kyoto University. The exterior of the Lunaglass and Marsgrass is shaped by rotating a quadratic curve. By rotating around a vertical axis, centrifugal force is generated, creating a 1G region in a part of the inner wall. Plans are underway to create water bodies resembling lakes and artificial channels, but the effects of the Coriolis force caused by the rotation must be considered.
In this study's first phase, multiple preliminary experiments were conducted using a tabletop device. Assuming the Marsgrass, a cooking bowl with a diameter of about 20 cm was used as the rotating body model. This was placed on an electric potter's wheel and rotated at 1 Hz (1 rotation/second = 60 rotations/minute). A video camera was set up above the model to capture the flow conditions from the perspective of the rotating field. For visualization, water colored with paint was added to the model. The flow velocity distribution was evaluated using the Particle Image Velocimetry (PIV) method. In PIV, inspection windows of a certain size are set up in the captured images. The brightness pattern of the inspection window at the measurement point is determined by calculating the correlation coefficient to find where it appears in the image at the next time point. This method allows simultaneous measurement of flow velocities at multiple points, enabling observation and quantitative evaluation of turbulent vortices.
When the bowl is rotated, centrifugal force causes the water to gather at the outer rim, raising the water level on the outside and lowering it on the inside. Under this study's hydraulic conditions, the outer rim's water depth is 2.3 cm when stationary, rising to 4.0 cm during rotation. Conversely, the water level drops at the center. By dispersing floating tracer particles on the water surface, the flow velocity distribution was measured. Five seconds after the start of rotation, a large flow velocity was observed in most of the water surface area. However, over time, the flow near the outer rim nearly stopped. This was due to the bowl dragging the water due to its viscosity. This viscous effect was transmitted to the central part over time, and it was found that the water became stationary over the entire surface after 40 seconds.
In the second experiment, a 5 cm long metal plate was installed inside the model and rotated for an extended period. Observations confirmed that even with such an object, the water appeared stationary from the rotating field's perspective. While the water's surface shape changed due to the centrifugal effect, the water remained stationary.
In the third experiment, a small submersible pump was installed in the bowl. The water flow pump created jets. In the stationary field (non-rotating field), a large symmetric circulation was formed. However, when rotated, circulation in the opposite direction to the rotation became prominent, significantly different from the stationary field. This was due to the Coriolis effect. It is important to note that when a constant velocity flow is generated in the rotating field, the direction of the flow changes due to the Coriolis force. The Coriolis effect is crucial when designing artificial waterways and wave generators inside the rotating body.
The above observations pertain to the surface flow, but in this PIV analysis, surface undulations were not considered. Corrections accounting for the surface shape are necessary and will be addressed in future work. Future developments will use a laser sheet to elucidate the velocity structure below the water surface. By irradiating the laser sheet from above into the water and capturing it with a high-speed camera, it is theoretically possible. Kyoto University's Ujigawa Open Laboratory plans to install a high-speed camera with a wired connection in the rotating field using a slip ring for a large rotating model with a diameter of 2-3 meters.
In this study's first phase, multiple preliminary experiments were conducted using a tabletop device. Assuming the Marsgrass, a cooking bowl with a diameter of about 20 cm was used as the rotating body model. This was placed on an electric potter's wheel and rotated at 1 Hz (1 rotation/second = 60 rotations/minute). A video camera was set up above the model to capture the flow conditions from the perspective of the rotating field. For visualization, water colored with paint was added to the model. The flow velocity distribution was evaluated using the Particle Image Velocimetry (PIV) method. In PIV, inspection windows of a certain size are set up in the captured images. The brightness pattern of the inspection window at the measurement point is determined by calculating the correlation coefficient to find where it appears in the image at the next time point. This method allows simultaneous measurement of flow velocities at multiple points, enabling observation and quantitative evaluation of turbulent vortices.
When the bowl is rotated, centrifugal force causes the water to gather at the outer rim, raising the water level on the outside and lowering it on the inside. Under this study's hydraulic conditions, the outer rim's water depth is 2.3 cm when stationary, rising to 4.0 cm during rotation. Conversely, the water level drops at the center. By dispersing floating tracer particles on the water surface, the flow velocity distribution was measured. Five seconds after the start of rotation, a large flow velocity was observed in most of the water surface area. However, over time, the flow near the outer rim nearly stopped. This was due to the bowl dragging the water due to its viscosity. This viscous effect was transmitted to the central part over time, and it was found that the water became stationary over the entire surface after 40 seconds.
In the second experiment, a 5 cm long metal plate was installed inside the model and rotated for an extended period. Observations confirmed that even with such an object, the water appeared stationary from the rotating field's perspective. While the water's surface shape changed due to the centrifugal effect, the water remained stationary.
In the third experiment, a small submersible pump was installed in the bowl. The water flow pump created jets. In the stationary field (non-rotating field), a large symmetric circulation was formed. However, when rotated, circulation in the opposite direction to the rotation became prominent, significantly different from the stationary field. This was due to the Coriolis effect. It is important to note that when a constant velocity flow is generated in the rotating field, the direction of the flow changes due to the Coriolis force. The Coriolis effect is crucial when designing artificial waterways and wave generators inside the rotating body.
The above observations pertain to the surface flow, but in this PIV analysis, surface undulations were not considered. Corrections accounting for the surface shape are necessary and will be addressed in future work. Future developments will use a laser sheet to elucidate the velocity structure below the water surface. By irradiating the laser sheet from above into the water and capturing it with a high-speed camera, it is theoretically possible. Kyoto University's Ujigawa Open Laboratory plans to install a high-speed camera with a wired connection in the rotating field using a slip ring for a large rotating model with a diameter of 2-3 meters.