CHAM was contacted by an air-technology manufacturer to help them create a PHOENICS CFD model of a vortex flow meter, which could then be used to aid their design studies of this flow-measurement device. The PHOENICS Cartesian cut-cell solver was used to simulate air flow through the flow meter using large eddy simulation. Below is an animation which shows, in terms of the velocity magnitude, the vortices shedding from the trapezoidal shedder housed in the aligning conduit. The frequency of these vortices is used to measure the flow rate on the basis that the Strouhal number remains constant with Reynolds number over the operating range of the device. This means that the shedding frequency is directly proportional to the average flow velocity and flow rate through the conduit. A key advantage of CFD for this application is that it provides a relatively inexpensive and rapid means of reducing design and development costs. For example, CFD can help in the investigation of different shedder geometries, in ascertaining the influence of upstream disturbances on different designs, and also in performing flow-meter calibration studies. In this particular case, the main advantage was that CFD enabled a better understanding of the detailed vortex-generation mechanism, which isn’t easy in the physical model because of the measurement difficulties associated with the very small bluff body and the transient nature of the vortices. With CFD the flow field could be viewed in slow motion to find, for example, a good position for the microphone sensors, which are used to detect the pressure pulses from the vortices.

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