Vanes are essentially small aspect ratio foils used forguiding sediment, by means of affecting the flow features. Theyare usually placed on the river bed and aligned with an angleof attack to the approach flow, thereby inducing a secondaryflow component that is used for guiding sediment in a desireddirection.
The specific vane related topics studied are, 1) localvortex induced scour, 2) flow physics and optimal angle ofattack for a vane placed on a movable bed, and 3) the functionof the coastal application of vanes, in particular the coastalvanes influence on the longshore velocity and the ability tofunction as a beach protection device.
The Navier-Stokes equations for the, one dimensional, freeboundary problem, of vortex induced scour, is solved byapproximating the tangential flow velocities with a polynomialexpression. The derived model is compared with an experimentusing a Bingham fluid to model the behavior of a fluid flow andboundary material. The model is also expanded to the two andthree dimensional cases, and the results are compared withexperiments conducted with a fluid and grain substrate pair.The comparisons all show a good agreement between the model andthe experimental results.
Flume experiments with a vane placed on a movable bed showthat the optimal angle of attack, (regarding only the strengthof the induced secondary circulation) is approximately40Ε. Four trailing vortices are identified as, the tipvortex, the suction side trailing edge vortex, and the two legsof the horseshoe vortex. Where the tip vortex is the strongestand thus, the main flow feature responsible for theeffectiveness of the vane.
In the coastal vanes application, vanes are placed in theupper part of the water column and aligned with an angle ofattack to the incoming waves direction of propagation. They arethus subjected to an onshore directed net flow that induces alift and drag force on the vane. The vane induced radiationstress component (corresponding to the lift and drag acting onthe vane) is derived and the longshore component of thisradiation stress is incorporated into the momentum flux model.The longshore velocity is quantified and compared withexperiments conducted in a small wave basin on a flat uniformlysloped concrete beach. The results show an order of magnitudeagreement between the calculated and measured longshore flowvelocity. The ability of vanes to create a salient is alsodemonstrated by experiments conducted on a sand beach (wherethe sand beach was subjected to oblique waves that generated alongshore sediment transport). These results are furthercorroborated by initial prototype test results.
Institutionen för anläggning och miljö , 2001. , 55 p.