A model of flow through an area discontinuity with a discharge coefficient: computation algorithm and validation for unsteady gas flow

This paper presents algorithms for computing gas-dynamic fluxes using a local resistance model with a constant discharge coefficient Cd. Computation of fluxes are based on the solution of the Riemann problem at the junction of pipelines with different cross-sections. The developed Riemann problem solvers enable the embedding of the local resistance model into one-dimensional simulations of unsteady gas flows. For low-speed flows (approximately below Mach number 0.07 in the vena contracta at the discontinuity), a linearized procedure is proposed, which converges within 3–4 iterations. For the general case, an iterative procedure for solving the Riemann problem model equations using gas-dynamic functions is presented. The model has been implemented into the ALLBEA software package and validated against experiments with finite-amplitude waves. The correctness of the computations is confirmed by comparison with measured pressure data in sections of a compound pipeline. This applied development contributes to the advancement of domestic software for simulating gas exchange processes in internal combustion engines and other systems.
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