Vortex induced hydrodynamic impact upstream of sluice gates

Abstract

This investigation concerns three-dimensional ow effects upstream of sluice gates and the in uence on the pressure conditions at the gate leaves. Depending on the gate openings of a weir structure or its location relative to the main ow, asymmetric ow conditions may be established. The piers of the weir structure are a ow obstacle causing a boundary layer to separate and the formation of a vortex, which is elongated and drawn under the gate by the ow. Its intensity and location depends mainly on the geometric parameters determined by the weir structure. The pressure on an under ow gate depends on the local characteristics of the ow. Even in a parallel ow and with no vortex the time mean pressure deviates substantially from hydrostatic. The ow asymmetry and the vortex as well as turbulent uctuations create additional complexity. Using physical hydraulic models, pressure measurements were obtained at ten locations on two geometrically similar gates to obtain the pressure distribution. In order to change the ow inlet conditions, the geometry of the weir structure was altered by varying the gate openings, total hydraulic head and pier head lengths. Tests were performed at two model scales. The quasi-static and the dynamic components of the pressure were determined from the time series obtained in the model, by applying statistical analysis to the random data. Hence a stochastic description of the pressure distribution was obtained. The measurement and modelling techniques were investigated, including the type of pressure sensors and measurement time and rate, alteration of the geometry, and impact of surface waves. Linear wave theory and spectral subtraction was successfully applied in order to filter the contribution of surface uctuations to the pressure uctuations. Dimensional analysis was used in order to obtain characteristic parameters describing the geometry, ow and pressure conditions. Therefore charts could be provided to estimate both the quasi-static pressure and amplitudes of pressure uctuations in prototypes. In addition, amplitude spectra indicate the dynamic aspect of the pressure uctuations. The results allow estimating the location of vortex formation and the determination of the pressure conditions with and without in uence of a vortex. Further a reduction of the discharge capacity due to increasing vortex intensity was identified by comparing the calculated discharge coefficients with data from the literature.