Observations on undular hydraulic jump in movable bed

Abstract

Near-critical flows in rivers and natural streams usually present a wavelike undular free surface, associated with dune-type bed-forms. The formation of this particular bed geometry is related to the shear stress acting on the river bed. The boundary shear stress distribution of undular flows was considered by Engelund and Hansen, stating that standing waves and their associated non-uniform shear stresses are responsible for bed-form generation in rivers. However, observations on movable-bed channels involving transcritical flow were not considered. In this note, an exploratory analysis is conducted to outline the analogy between the boundary shear in fixed-bed undular flows and the bed-form shape. Experimental observations reveal a strong analogy, supporting the original hypothesis of Engelund and Hansen.

Keywords:

• Boundary layer
• hydraulic jump
• shear stress
• transitional flow
• turbulence
• undular flow