A simple method to regularize supercritical flow profiles in bends

The present paper illustrates the results of an experimental investigation aimed at defining and verifying the effectiveness of a new method for reducing wave maxima in free surface supercritical flows in bends. This method consists of locating - in correspondence of the inner channel wall, upstream of the curve - \u201cwater flaps\u201d capable of producing a counter-phase disturbance pattern with respect to that induced by the channel planimetric variation. The investigation was carried out using three flumes with rectangular cross-section, and with a deviation angle of 180\u25e6 . The ratio between channel width and mean radius of curvature ranged from 1/8 to 1/4. Design criteria concerning shape, dimension, number and location of water flaps were tentatively developed. Cylindrical water flaps were in particular considered to make the application of the method as simple as possible. Forcing the current through a sluice gate located upstream of the bend allowed to check the method under various flow conditions, with the approach Froude number Fap ranging between 2.00 and 3.25, and the channel ratio \u3b6ap /b ranging from 0.120 to 0.260, with \u3b6ap being the approach flow depth and b channel width. Results show that water flaps induce a reduction from 30 to 80% of wave amplitude, thus leading to a significant regularization of flow conditions. Due to its simplicity, the method appears suitable for application in narrow\u2014already operating\u2014steep artificial channels where a regularization of flow conditions in a curved reach is desired