Skimming Properties of Sharp-Crested Weirs

Abstract

Weirs are structures that allow uppermost layers of liquids to flow by gravity downstream. They are, therefore, inherently gravity skimmers, and have successfully been used as skimmers in numerous applications, including oil-spill cleanup and various stormwater and wastewater treatment operations. This study examines the hydraulic skimming properties of sharp-crested weirs. The skimming properties of basic rectangular, triangular, and trapezoidal weirs are first characterized with a nondimensional skimming function. The triangular V-notch weir is shown to be a superior skimmer when compared to the other basic weirs. The V-notch weir has a maximum skimming rate qm′=1.44, occurring at an elevation ym′=23. Considerable enhancements of skimming properties are, however, achieved with higher order polynomial weirs. Polynomial weirs of order n>1 have maximum skimming rates qm′>1.44, occurring at desirable elevations ym′>23. The results of this work can be applied to design high performing sharp-crested skimmer weir outlets.