High accuracy volume flow rate measurement using vortex counting

A prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which a two-dimensional bluff body and a strain gauge force sensor are placed. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (Vp). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (Vr) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy.

• A volume flow meter counting the vortices in the wake of a bluff body is studied.
• The generation of vortices and their measurements are done by separated elements.
• The geometrical arrangement is optimized in order to get excellent repeatability.
• The accuracy of the flow-rate measurements is of the order of 1000.
• A dimensionless volume, constant and independent of the aspect ratio is introduced.