Flow around a diamond-section cylinder at low Reynolds numbers

Abstract

The steady separated flow past a diamond cylinder at low Reynolds numbers, Re, is associated with diverse separation topologies not resolved for a circular or square cylinder. The present study, conducted for Re≤150, also uncovers three unique separation topologies for the time-averaged flow. In this regard, the most striking observation is the formation of a small sub-wake around the base of the cylinder at certain Re between 80 and 90. While two of these structures were previously captured by some recent studies, these studies did not investigate their origin or kinematics. In the present study, conducted via stabilized finite-element computations in two-dimensions, these wake topologies are analyzed in detail. For secondary separation, the pressure at the reattachment point on the cylinder rear surface exceeds the pressure at the corresponding separation point located upstream. In a similar manner, for primary separation, the pressure at the wake stagnation point(s) surpasses the one at the separation points. Via direct steady and unsteady computations, the value of the critical Re indicating the onset of vortex-shedding is found to be 41, approximately. At this Re, the flow quantities, such as wake length, drag, and pressure coefficients, obtained from the steady and unsteady computations are found to diverge. The presentation of wake length and drag as a function of base suction establishes that the drag and wake length share an inverse relationship.