Measured pressures on the basis of bottom slab with gaps in the flow direction in a channel

Abstract

A study was conducted to determine whether the back edges of the longitudinal gaps of a floor tile fixed to the bottom of a canal with a supercritical flow convert kinetic energy into pressure energy using Froude numbers in the range of 2.84 to 10.12. In each test the pressure was measured on 16 points on the bottom surface of the tile with piezo-resistive transducers along three longitudinal lines: one central line with 8 sensors and two lateral lines with 4 sensors each on either side of the central line. In this manner the distribution of the median pressures under the test tile was determined. The test tile is similar to those used in civil engineering structures for the purpose of avoiding the erosive action of the turbulence of a supercritical flow. The analysis of the measured pressures shows that even when the top surfaces of the canal floor and of the protective block are in the same horizontal plane, the back edges of the longitudinal gaps transform the energy of velocity into pressure energy. In such a way a factor has been identified that intervenes in the production of the hydrodynamic force that lifts revetments of different structures, and that has until now been ignored in the study of this problem.