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- Qu, L. X., et al.
(författare)
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Quantitative numerical analysis of flow past a circular cylinder at Reynolds number between 50 and 200
- 2013
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 1095-8622 .- 0889-9746. ; 39, s. 347-370
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Tidskriftsartikel (refereegranskat)abstract
- Results of numerical simulations are presented for flow past a stationary circular cylinder at low Reynolds numbers (Re=50-200). The simulations were carried out using a finite-volume code employing a fractional step method with second-order accuracy in both space and time. A sensitivity study on numerical parameters concerning the domain size, grid independence and time step resolution was carried out in detail for Re=100. Global time-averaged results on force coefficients, non-dimensional velocities and pressures, including their corresponding r.m.s. values, as well as various quantities related to the separation and vortex shedding characteristics are presented. A non-monotonous streamwise velocity recovery in the intermediate wake is observed for Re > 50, a phenomenon that has been grossly overlooked in the past. There are two plateaus along the wake centerline, in particular for Re=200. The first, which is the most distinct, ranges from about x=9 to x=16 at a wake deficit velocity of 0.38, x being counted in diameters behind the cylinder axis; the second one appears from x=25 to x=28 at a wake deficit velocity of 0.54. This phenomenon seems to be related to an associated change-over in the orientation of the von Karman vortices and the merging trends, especially for Re=200 beyond x=25, as observed from instantaneous vorticity fields. Three-dimensional simulations using spanwise lengths of 10 and 12 (diameters) were carried out at Re=200. After a long initial phase with regular three-dimensional mode A flow features increasing very slowly in amplitude, the flow went into a state with distinct pulsating forces acting on the cylinder, the pulsations being seemingly randomly localized across the cylinder span. In this second, much more chaotic, flow state, the time-averaged results were in agreement with previous experiments and with parts of previous numerical studies.
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| 2. |
- Ma, J.M., et al.
(författare)
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A low Reynolds number variant of partially-averaged Navier-Stokes model for turbulence
- 2011
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Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier BV. - 0142-727X .- 1879-2278. ; 32:3, s. 652-669
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Tidskriftsartikel (refereegranskat)abstract
- A low Reynolds number (LRN) formulation based on the Partially Averaged Navier-Stokes (PANS) modelling method is presented, which incorporates improved asymptotic representation in near-wall turbulence modelling. The effect of near-wall viscous damping can thus be better accounted for in simulations of wall-bounded turbulent flows. The proposed LRN PANS model uses an LRN k-epsilon model as the base model and introduces directly its model functions into the PANS formulation. As a result, the inappropriate wall-limiting behavior inherent in the original PANS model is corrected. An interesting feature of the PANS model is that the turbulent Prandtl numbers in the k and epsilon equations are modified compared to the base model. It is found that this modification has a significant effect on the modelled turbulence. The proposed LRN PANS model is scrutinized in computations of decaying grid turbulence, turbulent channel flow and periodic hill flow, of which the latter has been computed at two different Reynolds numbers of Re = 10,600 and 37,000. In comparison with available DNS, LES or experimental data, the LRN PANS model produces improved predictions over the standard PANS model, particularly in the near-wall region and for resolved turbulence statistics. Furthermore, the LRN PANS model gives similar or better results - at a reduced CPU time - as compared to the Dynamic Smagorinsky model.
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