Modeling and validation of a real time flow rate model established from velocity profiles in disturbed open channels

The installation of real time flow rate meters is an important indicator for sewer system management (Taxes, flow regulation, flow to the field …). In such conditions, getting an accurate flow rate in open channels conditions is complex. Sewage is composed of a high quantity of disturbance (junction, bends, sediment ...) especially where the flow rate metering is necessary. Since 2000, new flow rate meters for smaller dimensions based on velocity profile determination (Pulse Doppler, Cross correlation) have been existing. Industrials (here NIVUS GmbH) are producing such devices which are more and more present on the market. From users and industrial points of view, the production of acceptable accuracy is an important aspect. In open channels (high presence in sewer systems), the most accurate method to get flow rate is the grid measurement one (ISO 748): it means that a sample of the velocity information is done at the water section. This method is mostly applied for some campaign conditions and not applicable for real time systems. Based on this observation, coming from single measurement based on ultrasonic technology to flow field through grid measurement technique (without using high number of sampling along the width) is the solution to get accurate flow rate.

The knowledge of the ultrasonic technique, the velocity behavior along the ultrasonic beam (based on 2D Navier Stokes) and the distribution of physical parameters (friction velocity with geometry and secondary currents dependence …) through the water perimeter offers a flow field determination under undisturbed and some disturbed conditions in real time without making additional sampling (measurement campaign).

After the application of the model to the industrial devices and sensors, tests under laboratory and field (with a high of conditions), numerical investigations, with reference values will present the quality, potential and efficiency of the model. It will also show its limits of application

Key words: Volume flow rate measurement, velocity profile, grid measurement, ultra sonic cross correlation, shear stress distribution.