Characterizing transverse surface velocity profiles in water table experiments

from qualitative visualization to quantitative analysis

Abstract

Water table experiments have been applied as qualitative tools for natural ventilation assessment in architectural design. However, methodological consolidation for establishing them as quantitative analysis instruments remains incomplete, particularly regarding boundary condition definition and similarity requirements. This study characterizes surface velocity profiles in water table experiments through floater-based measurement, an economically accessible technique grounded in hydrometric standards, to verify whether transverse surface velocity variation conforms to open-channel hydraulic theory predictions. Diverse flow rates and transverse positions were evaluated using cubic and hemispherical test body geometries. Statistical analysis confirmed significant velocity reduction toward channel walls, consistent with boundary layer development principles and secondary current effects documented in open-channel flow theory. The cubic body exhibited more consistent measurement patterns, while the hemispherical body demonstrated higher mean velocities but greater variance, suggesting trade-offs between kinematic representation and measurement reproducibility. Results establish that surface velocity approaches uniformity in the central channel region, enabling identification of appropriate model placement zones and defensible obstruction rates. Integration with hydraulic theory, particularly velocity dip and aspect ratio effects, grounds results in established principles.