Integrating-Float Measurements in Turbulent Flows

The effect of turbulence on discharges measured by the integrating-float method is studied. Based on Taylor's classical theory on diffusion of fluid particles by continuous movements, an equation is derived giving the dispersion of floats in a homogeneous turbulence field. It shows that larger errors are expected in using the float technique when the relative intensity and scale of turbulence are large, and when the float used rises rapidly. In the experimental part of the study, the integrating-float technique was used to measure discharges in a laboratory flume. A grid was sometimes placed in the flume to decrease turbulence scale and intensity. Results obtained are compared with discharges measured by a standard sharp-crested weir. For a total of 16 runs taken in flows with turbulence of various intensities and scales, the average errors based on 18 releases are 1% and 3% respectively for cases with and without grid.