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...

Detached-Eddy Simulation

The structure of round jets in cross-flow was studied using flow visualization techniques and flying-hot-wire measurements. The study was restricted to jet to freestream velocity ratios ranging from 2.0 to 6.0 and Reynolds numbers based on the jet diameter and free-stream velocity in the range of 440 to 6200.Flow visualization studies, together with time-averaged flying-hot-wire measurements in both vertical and horizontal sectional planes, have allowed the mean topological features of the jet in cross-flow to be identified using critical point theory. These features include the horseshoe (or necklace) vortex system originating just upstream of the jet, a separation region inside the pipe upstream of the pipe exit, the roll-up of the jet shear layer which initiates the counter-rotating vortex pair and the separation of the flat-wall boundary layer leading to the formation of the wake vortex system beneath the downstream side of the jet.The topology of the vortex ring roll-up of the jet shear layer was studied in detail using phase-averaged flying-hot-wire measurements of the velocity field when the roll-up was forced. From these data it is possible to examine the evolution of the shear layer topology. These results are supported by the flow visualization studies which also aid in their interpretation.The study also shows that, for velocity ratios ranging from 4.0 to 6.0, the unsteady upright vortices in the wake may form by different mechanisms, depending on the Reynolds number. It is found that at high Reynolds numbers, the upright vortex orientation in the wake may change intermittently from one configuration of vortex street to another. Three mechanisms are proposed to explain these observations.

An experimental study of round jets in cross-flow

Traditional geotechnical analyses for landslides involve failure prediction (i.e. onset of failure) and the design of structures that can safely withstand the applied loads. The analyses provide limited information on the post-failure behaviour. Modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs. In this paper, various large-deformation analysis methods are introduced and their applicability for solving landslide problems is discussed. Since catastrophic landslides often involve seepage forces, consideration of the coupled behaviour of soil and pore fluid is essential. Two approaches to model soil–pore fluid coupling in large-deformation analysis using the material point method (MPM) are introduced. An example simulation is presented for each approach; one on a model levee failure and the other on a natural cut slope failure (the Selborne experiment conducted by Cooper and co-workers in 1998). In the levee failure case, MPM simulation was able to capture a complex failure mechanism including the development of successive shear bands. The simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage. The simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post-failure behaviour. In the Selborne case, MPM was able to simulate the progressive failure of brittle, overconsolidated clay. The evolution of shear stresses along the failure surface was also captured by the MPM. The changes in the pore pressure and the actual shape of the failure surface were simulated by the MPM. The importance of accurately modelling the shear band within the MPM framework is highlighted.

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Trends in large-deformation analysis of landslide mass movements with particular emphasis on the material point method

Mixing of multiple jets with a confined subsonic crossflow

Review of numerical simulations for high-speed, turbulent cavity flows

Prediction of the Three-Dimensional Velocity Field of a Deflected Turbulent Jet

Detached Eddy Simulations are performed for unsteady three-dimensional supersonic turbulent flow over an open L/D = 5 cavity at free-stream Mach number of 1.19. Numerical results are obtained from the explicit solution and Shear-Stress-Transport based simulations using the 3 rd order Roe scheme. Computational results are presented for the unsteady vortex and shock structures. The acoustic response of the cavity is presented in the form of pressure fluctuations and sound pressure level spectra. The computational results are compared to existing experimental data and to results obtained from twodimensional Reynolds Averaged Navier Stokes with algebraic turbulence model.

/pdf/detached-eddy-simulations-of-supersonic-flow-over-cavity-1iuatv7q50.pdf

Detached eddy simulations of supersonic flow over cavity

This paper presents a methodology for three dimensional numerical simulations of super cooled water droplet trajectories through aeroengine rotating mac hinery Both flow and droplets’ governing equations are formulated and solved in the reference frame of rotating blades A Eulerian -Lagrangian approach is used for the continuous and discrete phases with one -way interaction model to simulate the aerodynami c effects on the three -dimensional particle trajectories A flux -based collection efficiency model is proposed for internal flows to enable the calculation of the amount of water that impinges the rotating and stationary blade surfaces The methodology is applied to a transonic fan rotor and the computational results for the 3D flow field is compared with available experimental data The computed droplet trajectories, rotor blade impingement locations, and the corresponding water collection efficiency are p resented and compared for different droplet sizes

/pdf/numerical-simulations-of-ice-droplet-trajectories-and-3q0w3ktnes.pdf

Numerical simulations of ice droplet trajectories and collection efficiency on aero - engine rotating machinery

This paper presents computational results for two DES (Detached Eddy Simulation), one hybrid RANS (Reynolds Averaged Navier-Stokes)/ LES (Large Eddy Simulation) and some preliminary results from PANS (Partially Averaged Navier-Stokes) turbulence for simulation of unsteady separated turbulent flows. The models are implemented in a full 3-D Navier Stokes solver and are based on the twoequation k-e model. The formulations of each model are presented and results are analyzed for subsonic flow over a Backward Facing Step (BFS). Simulations are carried out using a 3 rd order Roe scheme. A comparative assessment is made between the predictions from the DES, hybrid and PANS models. The predicted results are compared with the available experimental data for skin-friction coefficient, and different turbulent quantities. The three-dimensionality of the flow field and the separated fine scale structures are presented through the Q iso-surfaces.

/pdf/des-hybrid-rans-les-and-pans-models-for-unsteady-separated-4vvqnighpr.pdf

DES, Hybrid RANS/LES and PANS Models for Unsteady Separated Turbulent Flow Simulations

This paper proposes two DES (Detached Eddy Simulation) model and one hybrid RANS (Reynolds Averaged Navier -Stokes)/ LES (Large Eddy Simulation) model for the simulations of unsteady separated turbulent f lows. The two -equation k -� based models are implemented in a full 3 -D Navier Stokes solver and simulations are carried out using a 3 rd order Roe scheme. The predictions of the models are compared for a benchmark problem involving transonic flow over an ope n cavity and the equivalence between the DES formulations and the hybrid formulation is established. Predicted results for the vorticity, pressure fluctuations, SPL (Sound Pressure level) spectra and different turbulent quantities; such as modeled and reso lved TKE (Turbulent Kinetic Energy) profiles, contours and spectra are presented to evaluate various aspects of the proposed models. The numerical results for the SPL spectra are compared with available experimental results and also with the prediction fro m LES simulations. The grid resolved TKE profiles are also compared with the LES predictions. A comparative study of the CPU time required for the two DES models and the hybrid model is also made.

/pdf/des-and-hybrid-rans-les-models-for-unsteady-separated-4jekiur4pa.pdf

Debashis Basu

Papers

Prediction of the Three-Dimensional Velocity Field of a Deflected Turbulent Jet

Detached eddy simulations of supersonic flow over cavity

Numerical simulations of ice droplet trajectories and collection efficiency on aero - engine rotating machinery

DES, Hybrid RANS/LES and PANS Models for Unsteady Separated Turbulent Flow Simulations

DES and Hybrid RANS/LES models for unsteady separated turbulent flow predictions