Double-averaging turbulence characteristics in seeping rough-bed streams

Results of an experimental study on the effects of bed injection (upward seepage from the permeable bed) and suction (downward seepage) on the double-averaged (DA) turbulent flow characteristics over and within the interface of flow gravel beds are presented. The DA Reynolds shear stress within the interfacial sublayer undergoes a higher damping with suction and a lesser damping with injection, as compared to that with no seepage. The form‐induced stress within the interfacial sublayer has a decelerating effect with no seepage and suction and an accelerating effect with injection. The quadrant analysis suggests that within the interfacial sublayer the sweep events in flows with injection and the ejection events with suction are the primary contributors toward the Reynolds shear stress production, while both the events in flows with no seepage are equally prevalent. In the roughness sublayer (form-induced and interfacial sublayers together), the mean duration of bursting increases with suction and decreases with injection, but the bursting events become less frequent with suction and more frequent with injection. The analysis of DA higher-order moments confirms that the seepage affects the Reynolds normal stress flux, the turbulent kinetic energy (TKE) flux, and the TKE budget. A downward-upstream flux of TKE is developed within the roughness sublayer with injection; while an upward-downstream flux of TKE is prevalent over the entire flow depth with suction. The significance of this study lies on the hydrodynamic process in such a physical system that may result in modifying the flow resistance, sediment entrainment, and morphological characteristics of a streambed.