Author(s): Raul A. Lopardo; Jose M. Casado
Linked Author(s): Raúl Antonio Lopardo
Keywords: Boundary layer separation; Macro-turbulent flow; Submerged jump; Pressure fluctuations
Abstract: Experimental surveys of pressure fluctuations in highly turbulent flows have made it possible to gain reasonable knowledge of the statistical parameters that characterize the random function that interprets them. The skewness of the amplitude probability density function (PdF) is a statistical parameter that characterizes certain interesting aspects of the random signals. It should be borne in mind that the transition from positive to negative Sw values seems to imply that there is a boundary layer separation from a rigid wall. The separation phenomenon is closely linked to pressure distribution on the boundary layer, modified by the formation of vortices, so it is reasonable to admit that the phenomenon is somehow reflected in the recorded instantaneous pressures. In the case of macro-turbulent flow, the change of sign of the third moment of the amplitude PdF characterized as “skewness” is proposed as an effective experimental approach to determine flow separation in conditions where it cannot be determined by direct visual observations. Examples of macro-turbulent flows generated by a hydraulic jump with sharpedged boundaries (baffle piers, chute blocks and end sills) show that flow separation coincides with negative skewness records. This is also the case with vertical cylindrical piers downstream from a jump. Experimental results show (using the skewness sign difference) that a free jump downstream of a spillway separates from the bottom at about half the jump length, this distance being slightly longer in case of jumps downstream of a sluice gate. The herein presented analysis focuses on submerged jumps separated downstream from sluice gates, describing the influence of the incident Froude number and submergence factor.
Year: 2007