Investigation of pressure fluctuations in the hyporheic zone in response to flow around a hydraulic structure.

摘要

Erosion around a cylinders is a well studied field. Particles erode when lift and drag forces overcome a critical threshold. These forces are typically studied from above the water-riverbed interface. This study maps hyporheic pressure fluctuations as they are related to surface water velocity. The pressure map is used to evaluate lift enhancement and destabilization forces on the riverbed. High pressure events in the subsurface help generate a destabilizing force from within the riverbed. This work develops a probability distribution function relating turbulent velocity fluctuations and subsurface pressure fluctuations. A cylinder was fitted with differential pressure transducers such that the pressure ports were flush with the cylinder surface and below the water-sand interface. Three-component velocities were recorded synchronously with differential pressure fluctuations measured over a 18 mm depth. As expected, results show decay in pressure fluctuations as a function of depth. The standard deviation of the pressure fluctuation in the upper hyporheic zone scales well with shear stress.