Flow separation on a spheroid at incidence

Abstract

Surface streamline patterns on a spheroid have been examined at several angles of attack. Most of the tests were performed at low Reynolds numbers in a hydraulic flume using coloured dye to make the surface flow visible. A limited number of experiments was also carried out in a wind tunnel, using wool tufts, to study the influence of Reynolds number and turbulent separation. The study has verified some of the important qualitative features of three-dimensional separation criteria proposed earlier by Maskell, Wang and others. The observed locations of laminar separation lines on a spheroid at various incidences have been compared with the numerical solutions of Wang and show qualitative agreement. The quantitative differences are attributed largely to the significant viscous-inviscid flow interaction which is present, especially at large incidences.

Correlations for inclined prolates based on highly resolved simulations

“…That is, the streamlines are stretched at the top and compressed at the bottom side of the wake which is more pronounced for larger aspect ratios. For the cases and 6, the streamlines are inclined at the flank of the body with respect to the major axis, which is qualitatively similar to the potential flow streamlines on the spheroid surface presented by Han & Patel (1979). A smooth distribution of the skin friction can be observed for at the flank of the spheroid.…”

Asymmetries in the wake of a submarine model in pitch

“…A primary pair of streamwise counterrotating vortices are seen to form on the leeward side of the model. Similar flow fields have been observed over a wide range of Reynolds numbers by, for example, Han & Patel (1979) for a 4.3:1 spheroid and Vatsa, Thomas & Wedan (1989), Fu, Shekarriz & Huang (1994), Chesnakas & Simpson (1997), Karlsson & Fureby (2009) and Feymark et al (2012) for a 6:1 prolate spheroid. Werlé (1962), Hornung & Perry (1984) and Bippes (1987) described the separation topologies over similar bodies at low and moderate angles of attack, but here we are concerned with the evolution of the streamwise counter-rotating vortices which comprise the turbulent wake of such bodies in pitch.…”

“…When a submarine manoeuvres, a complex three-dimensional separation can occur over the body, which can lead to strong streamwise-oriented vortices in the wake, and such vortices can have an important effect on the forces and moments acting on the submarine (Han & Patel 1979;Lloyd & Campbell 1986;Chesnakas & Simpson 1997;Bridges et al 2003;Gregory, Joubert & Chong 2004;Karlsson & Fureby 2009;Hess et al 2010). For a body of revolution in pitch, similar vortices ('body vortices') are formed by the roll-up of the boundary layer due to azimuthal pressure gradients, and this formation process is illustrated in figure 1 for a simplified model of a submarine.…”

Exact theory of three-dimensional flow separation. Part 1. Steady separation

“…The lack of a unique separation line and surface in crossflow separation has also been noted by Han & Patel (1979), Yates & Chapman (1992) and Wetzel, Simpson & Chesnakas (1998). As a well-defined separation structure in such problems, one may instead choose the one-dimensional separation profile emanating from the attracting skin-friction zero (see figure 19(c) for an example).…”