Numerical Analysis and Modeling for the Exhaust Pulsating Flow around a Prism Inserted in a Pipe

For the measurements of flow rate, pressure and/or temperature in an engine exhaust pipe, probes are often inserted into the exhaust pipe depending on the application. These measurement probes differ a lot in terms of their size and shape. The flow around the probes become further complicated due to the pulsation of engine exhaust flow. In this study, computational fluid dynamics (CFD) simulations were carried out and a zero-dimensional (0D) model was constructed to analyze the flow field around the probe and flow rate of a pulsating flow. The simulations and the measurements of the flow rate and pressure were performed on flows around a hexagonal prism inserted in a circular pipe which is intended to be a differential pressure flow meter. The velocity field was also measured using the particle image velocimetry (PIV) technique. The CFD simulation results were validated with the experiments for both steady and pulsating flows. In the 0D model for pulsating flow, the flow acceleration as well as pipe friction and prism drag losses were taken into account. The flow rates calculated using the model agreed well with the CFD simulation results. The relationship between the flow rate and the pressure was analyzed using the CFD and the 0D model. In the low flow rate and low pressure difference period, the relationship between the flow rate and the square root of pressure difference deviated from linear and exhibited hysteresis due to the flow acceleration. The cycle-averaged flow rates calculated using the 0D model were closer to those by the CFD simulations than those of a conventional steady flow correlation.