Andrey Travin

Bio: Andrey Travin is an academic researcher from Saint Petersburg State Polytechnic University. The author has contributed to research in topics: Turbulence & Reynolds-averaged Navier–Stokes equations. The author has an hindex of 23, co-authored 54 publications receiving 5812 citations.

A new version of detached-eddy simulation, resistant to ambiguous grid densities

Abstract: Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The depleted stresses reduce the skin friction, which can lead to premature separation.

Detached-eddy simulation of an airfoil at high angle of attack

Abstract: We present the first true applications of Detached-Eddy Simulation (DES), in the sense of being three-dimensional. DES was defined in 1997 with hopes of combining the strengths of Reynolds-averaged methods and of Large-Eddy Simulations, in a non-zonal manner, to treat separated flows at high Reynolds numbers. We first simulate isotropic turbulence, to check the concept in LES mode and set its adjustable constant. Smooth inertial ranges are obtained up to the cutoff in the spectra. We then treat an airfoil in the challenging regime of massive separation and do so very successfully, in that lift and drag are within 10% of the experimental results at all angles of attack, to 90°. Such an accuracy is not achieved with traditional modelling, even unsteady, which gives up to 40% error. Cost puts a pure LES of the same flow (at Reynolds number 105 and beyond) out of reach on any computer, yet we use personal computers for the DES, and about 200,000 grid points. On the other hand, grid refinement, domain-size and Reynolds-number studies have not been completed yet. Hysteresis in the 15 - 25° range has not been addressed.

Turbulence Modeling in Rotating and Curved Channels: Assessing the Spalart-Shur Correction

Abstract: Aunie edapproachtosystem-rotationandstreamline-curvatureeffectsintheframeworkofsimpleeddy-viscosity turbulence models is exercised in a range of rotating and curved channel e ows. The Spalart ‐Allmaras (SA) oneequation turbulence model (Spalart, P. R., and Allmaras, S. R., “ A One-Equation Turbulence Model for Aerodynamic Flows,” AIAAPaper 92-0439, 1992 )modie ed in thismanner is shown to bequitecompetitivewith advanced nonlinear and Reynolds-stress models and to be much more accurate than the original SA model and other eddyviscosity models that are widely used for industrial e ow computations. The new term adds about 20% to the computing cost, but does not degrade convergence.

Physical and Numerical Upgrades in the Detached-Eddy Simulation of Complex Turbulent Flows

Abstract: A new formulation of Detached-Eddy Simulation (DES) based on the k-ω RANS model of Menter (M-SST model) is presented, the goal being an improvement in separation prediction over the S-A model. A new numerical scheme adjusted to the hybrid nature of the DES approach and the demands of complex flows is also presented. The scheme functions as a fourth-order centered differentiation in the LES regions of DES and as an upwind-biased (fifth or third order) differentiation in the RANS and outer irrotational flow regions. The capabilities of both suggested upgrades in DES are evaluated on a set of complex separated flows.

A new version of detached-eddy simulation, resistant to ambiguous grid densities

Abstract: Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The depleted stresses reduce the skin friction, which can lead to premature separation.

Detached-Eddy Simulation

Abstract: Detached-eddy simulation (DES) was first proposed in 1997 and first used in 1999, so its full history can be surveyed. A DES community has formed, with adepts and critics, as well as new branches. The initial motivation of high–Reynolds number, massively separated flows remains, for which DES is convincingly more capable presently than either unsteady Reynolds-averaged Navier-Stokes (RANS) or large-eddy simulation (LES). This review discusses compelling examples, noting the visual and quantitative success of DES. Its principal weakness is its response to ambiguous grids, in which the wall-parallel grid spacing is of the order of the boundary-layer thickness. In some situations, DES on a given grid is then less accurate than RANS on the same grid or DES on a coarser grid. Partial remedies have been found, yet dealing with thickening boundary layers and shallow separation bubbles is a central challenge. The nonmonotonic response of DES to grid refinement is disturbing to most observers, as is the absence of...