![]() ![]() The results suggest that many aspects of compressible pulsating flow through flow restrictions are yet to be understood.īackground, Motivation, and Existing Literature The variation in C dwas found to be correlated to two dimensionless variables, η and ξ, defined as the standard deviation of the pulsating pressure signal, σ Δ p, normalized by ρ V ¯ 2 and Δ p ¯ across the orifice, respectively. ![]() A novel pulsating flow measurement apparatus that allowed independent variation of pressure, flow rate and frequency and allowed reproducible measurements independent of transducer characteristics, produced C d's in the range of 0.25–0.60 with a similar square-edge orifice. The discharge coefficient of a square-edged orifice placed in the exhaust stream of a diesel engine produced C d's varying between 0.60 and 0.90 for critical/near-critical flows. It has been shown in this work that this assumption is not accurate for pulsating flow, particularly at large amplitudes and low flow rates. This quasi-steady assumption is based on asymptotically constant C d observed at high Reynolds number for steady (non-pulsating) flow. ![]() Similarly, orifices and flow-nozzles used for real-time EGR flow estimation are often calibrated at a few steady-state points with one single constant C d that minimizes the error over the selected points.
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