Hydraulic Performance of Coanda-Effect Screens

Abstract

A theoretically based computational model is presented for predicting the hydraulic performance of Coanda-effect screens. These screens use a tilted-wire, wedge-wire screen panel to remove thin layers of high-velocity flow from the bottom edge of a supercritical flow. Typical slot openings are 1 mm or less, and the screens are self-cleaning with no moving parts. The discharge characteristics of several screen materials were evaluated in laboratory tests, and a relation was developed for computing the discharge through a tiltedwire screening surface as a function of the Froude number, the specific energy, and the Reynolds and Weber numbers. A model for the performance of complete Coanda-effect screen structures predicts the wetted length of screen required to accept a given flow, or the flow rate through the screen and the bypass flow over a screen that does not accept all of the flow. Predictions from the model compare favorably to results from clean-water laboratory tests of several different prototype-size screen structures. The model will allow designers to accurately size screens and evaluate design alternatives.

Design of Stormwater Particle Removal System for Small-Scale Urban Hydropower based on the Vortex and Coandă Effects

“…Thorough literature reviews on flow pattern and performance efficiency of vortex and Coandă effects were carried out prior to the design of the experimental setup ( [7], [17], [12] and [13]). It was then clear that specific hydraulic conditions such as pressure head differences and inlet velocity openings must properly be quantified.…”

Coupling Numerical and Physical Modeling for Analysis of Flow in a Diversion Structure with Coanda-effect Screens

“…Different features of a C-S and illustrations of the structure, related to the present study, can be found in the work of Wahl [1,2]. Figure 1, which is a modified form of Figure 1 in [2], presents side view of a typical C-S with some key elements of it.…”

“…It can be a simple circular arc or follow the shape of the crest of an ogee spillway. Typically, the screen panel is a concave arc with a radius of curvature of approximately 3 m, although planar screen panels can also be used [1]. The flow passing through the screen (screened flow) is collected in a conveyance channel beneath the screen, while overflow and debris pass off the downstream end of the screen.…”

“…The flow passing through the screen (screened flow) is collected in a conveyance channel beneath the screen, while overflow and debris pass off the downstream end of the screen. Flow velocities across the screen are typically 2-3 m/s; they increase toward the toe of the screen, and Froude numbers across the screen surface can vary from approximately 2 to 30 or greater [1]. C-Ss utilize a unique tilted-wire screen panel, where each wire is tilted a few degrees downstream to produce shearing offsets into the flow above the screen.…”

“…C-Ss utilize a unique tilted-wire screen panel, where each wire is tilted a few degrees downstream to produce shearing offsets into the flow above the screen. More detailed information about the C-Ss, typical commercial details and size can be found in [1,2]. Wahl [2] provided a detailed description of the applications, design parameters, design procedure, and design recommendations for this screen.…”