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Comparison Between Theoretical CFV Flow Models and NIST s Primary Flow Data in the Laminar, Turbulent, and Transition Flow Regimes



Aaron N. Johnson, John D. Wright


Recent improvements in dimensional measurements of complex geometries have made it possible to accurately characterize the shape and throat size of commercially available small throat diameter critical flow venturis (CFVs). These improvements allow long standing theoretical CFV models based on boundary layer and inviscid flow theory to be assessed by comparing them with high quality experimental data. Dimensional measurements were made on nine CFVs with negligible surface roughness having throat diameters ranging from 5 mm to 25 mm. These CFVs were calibrated in dry air using the NIST 677 L and 26 m3 PVTt flow standards which have expanded uncertainties of 0.05 % to 0.12 %, respectively. The acquired data spans a Reynolds number range from 5 104 to 2.5 106, which includes the laminar, turbulent, and transition flow regimes. Although the overall shapes of the measured CFVs followed ISO specifications, dimensional measurements showed that the local curvature near the throat section of several of the dimensionally measured CFVs did not adhere to these guidelines. Differences between the measured and ISO recommended values of the throat curvature were as large as 100 %. When the measured values of the throat curvature were used in the models, the predicted and measured discharge coefficients agreed to better than 0.17 % over the full range of Reynolds numbers. Even better agreement (better than 0.07 %) was observed over the laminar flow range.
Journal of Fluids Engineering-Transactions of the Asme


critical flow, Critical Flow Venturi, discharge coefficient, FunctionNozzel Boundary Layer, gas flow, nozzle sonic line profile
Created July 1, 2008, Updated February 17, 2017