Hele-Shaw flow

About: Hele-Shaw flow is a research topic. Over the lifetime, 5451 publications have been published within this topic receiving 151320 citations.

Mean flow deformation in a laminar separation bubble: separation and stability characteristics

Abstract: The mutual interaction of laminar-turbulent transition and mean flow evolution is studied in a pressure-induced laminar separation bubble on a flat plate. The flat-plate boundary layer is subjected to a sufficiently strong adverse pressure gradient that a separation bubble develops. Upstream of the bubble a small-amplitude disturbance is introduced which causes transition. Downstream of transition, the mean flow strongly changes and, due to viscous-inviscid interaction, the overall pressure distribution is changed as well. As a consequence, the mean flow also changes upstream of the transition location. The difference in the mean flow between the forced and the unforced flows is denoted the mean flow deformation. Two different effects are caused by the mean flow deformation in the upstream, laminar part: a reduction of the size of the separation region and a stabilization of the flow with respect to small, linear perturbations. By carrying out numerical simulations based on the original base flow and the time-averaged deformed base flow, we are able to distinguish between direct and indirect nonlinear effects. Direct effects are caused by the quadratic nonlinearity of the Navier-Stokes equations, are associated with the generation of higher harmonics and are predominantly local. In contrast, the stabilization of the flow is an indirect effect, because it is independent of the Reynolds stress terms in the laminar region and is solely governed by the non-local alteration of the mean flow via the pressure. © 2010 Cambridge University Press.

Steady planar straining flow past a rigid sphere at moderate Reynolds number

Abstract: This study focuses on the effect of spatial non-uniformity in the ambient flow on the forces acting on a spherical particle at moderate particle Reynolds numbers. A scaling analysis is performed to obtain conditions under which such effects are important. A direct numerical simulation, based on spectral methods, is used to compute the three-dimensional time-dependent flow past a stationary sphere subject to a uniform flow plus a planar straining flow. The particle Reynolds number, Re, in the range 10 to 300 covering different flow regimes, from unseparated flow to unsteady vortex shedding, is considered. A variety of strain magnitudes and orientations are investigated. A systematic comparison with the potential flow results and axisymmetric strain results is given. Under elongational strain, both the planar and axisymmetric cases are found to stabilize the sphere wake and delay the onset of unsteadiness, while compressional strain leads to instability. In terms of separation angles, length of the recirculation eddy and topology of the surface streamlines, planar and axisymmetric strains yield nearly the same results. The drag force appears to have a linear relation with strain magnitude in both cases, as predicted by the potential flow. However, contrary to the potential flow results, the drag in planar strain is higher than that in axisymmetric strain. The generation of higher drag is explained using the surface pressure and vorticity distributions. Planar strain oriented at an angle with the oncoming uniform flow is observed to break the symmetry of the wake and results in a lift or side force. The variation of the drag and lift forces may be quite complex, and unlike the potential flow results they may not be monotonic with strain magnitude. The direction of the lift force may be opposite to that predicted by the inviscid and low Reynolds number (Re [Lt ] 1) theories. This behaviour is dictated by the presence or absence of a recirculation eddy. In the absence of a recirculation region at low Reynolds numbers (Re < 20), or at a very high strain magnitude when the recirculation region is suppressed, the results follow somewhat the pattern observed in potential flow. However, with the presence of a recirculation region, results opposite to those predicted by the potential theory are observed.

Numerical simulation of flow around a circular cylinder having porous surface

Abstract: Flow around a circular cylinder having porous surface is studied numerically by means of direct numerical simulation and large eddy simulation. The flow in the porous media is represented by a spatially averaged model. First, the properties of the most effective porous media are found from a preliminary two-dimensional parametric test. Subsequently, the dependency of flow modification on the Reynolds number (Re = 100, 1000, 3900, and 1.0 × 105) and the porous layer thickness is investigated in detail. It is found that the porous surface works to suppress the velocity and pressure fluctuations and such effect is more significant at higher Reynolds number. In particular, the vortex shedding is found to be completely suppressed at Re = 1.0 × 105. The mechanism of flow modification is explained by slip velocity and energy dissipation process.