Spatial and temporal variation of turbulence characteristics in combined sewer flow

Flow unsteadiness is a typical feature of both combined and storm sewer flow. The following study therefore deals with both theoretical and experimental investigations of the steady uniform and transient turbulent open-channel flows in a circular conduit with smooth walls as well as over rough sediment deposits. The aim of the study is to define the relationship between flow unsteadiness and selected flow/turbulence characteristics estimated in a circular tube running partially full using the ultrasonic velocity profiler (UVP) method. The temporal/spatial turbulence intensities and the Reynolds stress distribution were identified in the mid-vertical of the pipe. Generally, the absolute values of turbulent characteristics are larger in the rising branch of the hydrograph than in the descending one for the same flow depths. This difference in absolute values is related to the flow equilibrium parameter. Furthermore, the influence of the sediment bed on selected flow/turbulence variables was studied. The results show a strong impact of cross-section geometry on local values of friction velocity, i.e. bottom shear stress, along the wetted perimeter of the channel cross-section. Interestingly, their relative values decreased along with an increase in flow depth.