Effects of cylindrical cruciform patterns on fluid flow and drag as determined by CFD models

Fluid flow around and drag of two cylindrical cruciform patterns, conventional (T0) and rotated 45º in its own plane (T45), were numerically investigated by solving three-dimensional Reynolds-averaged Navier-Stokes equations within the subcritical flow regime over angles of attack (AOA) from 90º to 0º. Firstly, the drag for a one-cruciform element was assessed, followed by analysis of a four-cruciform assembly (‘square mesh’) to take into account the wake effect of tandem elements. For the one-cruciform element, T45 experienced a less prominent streamline separation and consequently lower drag between 90° and 45° AOA, while T0 experienced progressively lower drag below 45° AOA owing to re-establishment of smoother streamlines caused by the gradually reduced circulation momentum from the adjacent vortex that rotates in the off-side direction. For the four-cruciform assemblies, T0 and T45 drag was essentially equal above 45º AOA; while below 45º, T45 had greater drag attributed to more prominent spanwise vortex downstream development. Overall, while the largest relative difference between the two orientations was 26.2% and 33.8% for the one- and four-cruciform configurations respectively at 0° AOA, for 30º and above AOA there were limited drag differences (generally below 10%).