1998-09-14

Validation of a Non-Isentropic, Pressure Loss, Branched Pipe Junction Model 982055

Previous papers from The Queen's University of Belfast have described a new non-isentropic branched pipe junction model for use in a one-dimensional gas dynamic simulation of a multi-pipe system subject to unsteady gas flow. Such assemblages are commonly found in the intake and exhaust systems of multi-cylinder engines.
The model takes full account of the effect of pressure loss, due to change in flow direction, and tracks the properties and composition of gas mixtures through the junction. Although the validity of the model has previously been inferred by its use in a complete engine simulation, which accurately predicted parameter variation in a firing engine, the independent validation of the junction model by itself is only now demonstrated.
To investigate the performance of the junction model a series of three-pipe junctions were tested by directing a single pressure wave through each of the previously quiescent junctions. The predicted pressure histories at locations in each branch pipe are compared with data recorded during each experiment. Correlation was generally good and certainly an improvement on a simple constant pressure junction model.
To further enhance the model an investigation was carried out to determine whether the loss term coefficient could be refined. It was demonstrated that improved accuracy could be achieved by refining the coefficient. Regrettably, insufficient experimental data was acquired to provide a complete understanding of the mechanism by which the improvements were achieved.

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