Modelling blockage effects using a spectral element method

Abstract

We employ a two-dimensional spectral element method to investigate the effect of various semi-circular blockages on the laminar flow between two flat plates. This simplified geometry has a general relevance to blocked flows, but more academically, also relates to work on the backward-facing step, presenting a qualitatively similar flow with a single, independent step, or blockage, parameter. The parameter space for Reynolds number between 50 and 3000, and blockage ratio ranging from 0.05 to 0.9 is mapped out. The results with blockage ratio of 0.5 compare favourably with previous work on the flow over a backward-facing step, with the analysis suggesting that the onset of three-dimensionality in the flow is likely to be closely matched. Flow phenomena associated with blockage ratios above and below the customary half-blockage are summarised, including smaller than expected flow separation lengths for lower blockages, and vortex shedding and unusual structures within the recirculation zones for higher blockages.