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Publication# Secondary flow in sharp open-channel bends: experiments and modelling

Abstract

The dependence of curvature-induced secondary flow on the curvature ratio H/R and the Froude number Fr was systematically investigated in a series of 18 experiments in a sharply-curved laboratory flume. The investigated flow depths were 0.9 m, 0.13 m, 0.19 m and 0.26 m, resulting in H/R values of 0.053, 0.077, 0.112 and 0.153, and the Froude numbers were 0.1, 0.2, 0.3, 0.4 and 0.5. The normalized magnitude of the secondary flow did not increase with H/R, as predicted by commonly used parameterizations for secondary flow, but remained quasi-constant. This confirms observations by Blanckaert (2009), who called this phenomenon the saturation of the secondary flow. The experiments did not reveal any dependence of the secondary flow on Fr. Predictions of the magnitude of the secondary flow with the nonlinear model of Blanckaert and de Vriend ((2003, 2010) agreed very well with the experimental data.

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Related concepts (14)

Related publications (11)

Froude number

In continuum mechanics, the Froude number (Fr, after William Froude, ˈfruːd) is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity). The Froude number is based on the speed–length ratio which he defined as: where u is the local flow velocity, g is the local external field, and L is a characteristic length. The Froude number has some analogy with the Mach number.

Secondary flow

In fluid dynamics, flow can be decomposed into primary flow plus secondary flow, a relatively weaker flow pattern superimposed on the stronger primary flow pattern. The primary flow is often chosen to be an exact solution to simplified or approximated governing equations, such as potential flow around a wing or geostrophic current or wind on the rotating Earth. In that case, the secondary flow usefully spotlights the effects of complicated real-world terms neglected in those approximated equations.

Reynolds number

In fluid mechanics, the Reynolds number (Re) is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers, flows tend to be turbulent. The turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents).

François Avellan, Mohamed Farhat, Philippe Ausoni, Amirreza Zobeiri

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, Re-h = 16.1 . 10(3) - 96.6 . 10(3), where the reference length h is the trailing edge thickness, are reported. The ...

2012Anton Schleiss, Koen Blanckaert, Joris Heyman

The dependence of curvature-induced secondary flow on the curvature ratio H/R and the Froude number Fr was systematically investigated in a series of 18 experiments in a sharply-curved laboratory flume. The investigated flow depths were 0.9 m, 0.13 m, 0.19 ...

2015The dependence of curvature-induced secondary flow on the curvature ratio H/R (H is the average flow depth and R is the centreline radius of curvature), the Froude number Fr, and the dimensionless roughness coefficient Cf was systematically investigated in ...