Non-stationary compressible flow in ducts with varying cross-section

A comparative study of the interaction of shock wave or rarefaction wave with a converging duct separating long constant cross-section segments is presented. Quasi-one-dimensional computations are compared with fully two-dimensional computations. It is observed that in some cases the two-dimensional results approach the respective one-dimensional approximations over long times, while in other cases the two-dimensional computed flow is genuinely two-dimensional and cannot be reduced to a one-dimensional equivalent. In the latter cases, significant errors are incurred by analysing the flow using the quasi-one-dimensional duct flow approximation.