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This paper provides a study of the dynamic stall of a pitching NACA 0012 airfoil at 106 Reynolds number by means of numerical simulation. A 2D study is carried out comparing three OES and URANS turbulence models (URANS, URANS k-ω SST and k-ε OES). Then a 3D computation is performed using DES Spalart modelling. URANS k-ω SST is providing the best results for 2D computations. [ABSTRACT FROM AUTHOR]

We present large-eddy simulation (LES) results of the streamwise-periodic hill channel configuration, which is a standard test case for massively separated flows. The Reynolds number (computed with the hill height, the bulk mass flux through the cross-section above the hill crest and the dynamic viscosity at the wall) is chosen as 2800, in accordance with recent DNS data from Peller & Manhart (2004) for incompressible flow. The Mach number (computed with the volumetric bulk velocity and the wall temperature) was varied between 0.2 and 2.5. The numerical simulation code NSMB discretises the compressible Navier-Stokes equations with the finite-volume method on a deliberately-chosen coarse structured mesh. The subgrid-scales are accounted for by the well-proven approximate-deconvolution model (ADM). [ABSTRACT FROM AUTHOR]

Results of large eddy simulation of a flow around a cylinder with a finite aspect ratio (length/diameter) of 6 placed on a ground plane, is presented. The Reynolds number based on the inlet velocity and the cylinder diameter is 2×104. The boundary layer thickness at the position of the cylinder is approximately 7 % of the cylinder's diameter. In addition to the comparison of the time-averaged results with existing experimental data, the instantaneous flow was investigated. The fine mesh LES predicted the vortex shedding frequency in agreement with the experimental observations. Several important flow mechanisms are predicted and explained such as: the downwash of coherent structures from the region above the free end into the near wake or the formation of the alternate vortices in the far wake. Instantaneous flow structures around the cylinder such as horseshoe vortex, Kelvin Helmholtz and hairpin vortices are identified and their influence on the cylinder and the resulting aerodynamic forces is explained. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a new subgrid scale (SGS) model in large eddy simulation (LES) of a high Reynolds number turbulent flow. The traditional approaches are usually based on modeling of the non-resolved velocity field, and are customary invariant on the Reynolds number. When the Reynolds number is high, the flow at subgrid scales is intermittent and its structure is depending on the Reynolds number. To account for this, the new SGS model is focused on simulation of the non-resolved acceleration of fluid particle. With this model, an approximation of unfiltered velocity field is reconstructed by computation of the instantaneous model-equation introduced in the paper. The performed computation of a high Reynolds number stationary homogeneous turbulence reproduced qualitatively the effects of intermittency recently observed in experimental studies. [ABSTRACT FROM AUTHOR]

A novel variant of subgrid dissipation that may be used in LES methods is described and tested. The corresponding mathematical model, based on the quasi-gasdynamic equations differs from the Navier-Stokes system by additional nonlinear dissipative terms. This model is applied to the two-dimensional numerical simulation of the laminar-turbulent transition in a backward-facing step flow in subsonic regime. [ABSTRACT FROM AUTHOR]

This paper reports the predictions of three turbulence modelling schemes in the application to the flow around a circular cylinder in a square duct. A URANS scheme known as the Stress-Strain Lag model has been developed in the DESider project, specifically to capture the effects of stress-strain misalignment observed in unsteady mean turbulent flows (Revell, 2006). Coupling of the Lag model with the popular k -ω SST model, to form the so-called SST-Cas model, has been shown to incorporate some of the advantages of a full Reynolds Stress transport Model (RSM), whilst retaining the efficiency and stability benefits of a eddy viscosity model (EVM) (Revell et al., 2006, 2007). This paper first presents 2-D results of the cylinder case, before examining the fully 3-D case, which is also calculated using the SST-DES approach. [ABSTRACT FROM AUTHOR]

The paper reports on the current state of the SST-based Scale-Adaptive Simulation model (SST-SAS model), and summarises the validation activity performed with this model in the course of the DESIDER project. The turbulence-resolving capability of the SST-SAS model has been validated with the official project test cases, covering both the underlying generic flows as well as practical aerodynamic applications. Among the latter ones are also the two aero-acoustic test cases of industrial interest. The paper includes a brief description of the current state of the SST-SAS model, as well as the illustrating test case results. Potentials of the SAS approach are briefly discussed, as well as its position amongst the other transient simulation methods. [ABSTRACT FROM AUTHOR]

DES solutions for an isolated synthetic jet flow are presented. A cubic-root filter with continuous eddy viscosity variation at the RANS-LES switching point is introduced. The intention is to explore the effects of unstructured grids for such a filtering strategy. Dissipation controlled Roe's scheme is applied and dynamic grid techniques are employed to implement the periodically moving diaphragm. The results obtained are compared with the experiments and a previous study using structured grids. No inferiority is observed for the current unstructured grid result in comparison with the structured ones from the previous study. [ABSTRACT FROM AUTHOR]

The present paper presents a simulation of supersonic inlet buzz on a 20x106 points mesh, using the DDES (Delayed Detached Eddy Simulation) method. This latter approach is a version of DES that ensures the attached boundary layers to be treated in RANS. The results are compared to experimental data obtained during a previous campaign of wind-tunnel experiments. The buzz experimentally observed at Mach 1.8 is well reproduced. The buzz frequency, as well as higher frequencies existing in the experimental pressure signals, are correctly predicted. The functions of DDES prove to be robust and to perform satisfactorily. [ABSTRACT FROM AUTHOR]

Increasingly, design studies rely on numerical tools for more and more complex situations. Unfortunately, for some, if not many, of these complex cases, steady RANS has been unable to meet the challenge and cannot capture some of the most important features. At the same time, the continuing increase in computing power has made the use of unsteady simulations feasible, although not on a day-to-day basis, for a growing number of applications. The present paper reports on the experience of implementing one such unsteady technique known as Detached Eddy Simulation (DES) in a RANS-based industrial solver. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the DES methods implemented at the Institute of Fluid Mechanics and Engineering Acoustics (ISTA) at the TU-Berlin during the course of the European DESider project. As well as the validation of these methods on the basis of simplified, academic flow cases presented in the first part, their suitability and necessity for complex industrial applications is demonstrated using results from other research projects. The methods prove robust and reliable for a wide range of applications, ranging from external to internal flows, from bluff bodies with massive separation to the partial resolution of attached boundary layers. [ABSTRACT FROM AUTHOR]

The prediction of the laminar to turbulence transition is essential in the calculation of turbine blades, compressor blades or airfoils of airplanes since a non negligible part of the flow field is laminar or transitional. In this paper we compare the prediction capability of the Detached Eddy Simulation (DES) with the Large Eddy Simulation (LES) using the high-pass filtered (HPF) Smagorinsky model (Stolz et al., 2003) when applied to the calculation of transitional flows on turbine blades. Detailed measurements from (Canepa et al, 2003) of the well known VKI-turbine blade served to compare our results with the experiments. The calculations have been made on a fraction of the blade (10%) using non-reflective boundary conditions of Freund at the inlet and outlet plane extended to internal flows by (Magagnato et al., 2006) in combination with the Synthetic Eddy Method (SEM) proposed by (Jarrin et al., 2005). The SEM has also been extended by (Pritz et al., 2006) for compressible flows. It has been repeatedly shown that hybrid approaches can satisfactory predict flows of engineering relevance. In this work we wanted to investigate if they can also be used successfully in this difficult test case. [ABSTRACT FROM AUTHOR]

While the flow physics of generic delta wings with sharp leading edges are largely understood, realistic configurations with rounded leading edges and canards are still of scientific and industrial interest. The goal of the presented study is the investigation of such a realistic delta wing configuration at 15° angle of attack and at high Reynolds number in comparison with detailed wind tunnel measurements. [ABSTRACT FROM AUTHOR]

In the framework of the German research project FREQUENZ, a joint effort of industry, research establishment and universities has been undertaken to study the effect of design variations on aeroacoustics of a simplified high lift configuration. The flow past an airfoil with small trailing edge devices (MiniTED) was investigated numerically for the case of a generic landing configuration. Because of the turbulent and separated flow character behind the high lift device a hybrid RANS-LES approach was chosen to investigate the flow phenomena. Furthermore, the noise in the turbulent flow field was investigated by evaluating the pressure distribution. As a large measurement campaign has been undertaken within FREQUENZ, it is possible to validate the aerodynamic and the aeroacoustic results. [ABSTRACT FROM AUTHOR]

This paper presents a transonic buffet simulation on a half wing/body rigid model at a realistic Reynolds number. The modelling approach retained is a Zonal-DES approach which allows attached boundary layers to be protected and a rapid switching into LES mode in the separated areas. Transonic buffet phenomenon is a challenging case for DES type simulations since the separation point is unstable during time and the separation remains closed to the skin of the model. The simulation was performed on an adapted mesh and comparisons with experiments are carried out. It is shown that the mean field is accurately predicted with ZDES while the present RANS calculations failed to reproduce this shape of the separated area. The results also provide an insight into the unsteady nature of the flow. [ABSTRACT FROM AUTHOR]

DES are applied to confined turbulent swirling flows exhibiting vortex breakdown. The DES results are compared with measurements obtained on a water test rig operating at a Reynolds number of 4600, and with further predictions obtained via different modelling strategies such as the Reynolds Stress Model (RSM) based URANS and LES. In the LES, the standard Smagorinsky model, and its modification by Voke are used as the subgrid scale models. DES and LES results are observed to be in better agreement with the experiments, compared to the URANS-RSM predictions. The overall performance of DES is observed to be similar to that of LES computations, though, a slight superiority of DES compared to LES can still be claimed, for the considered test case. [ABSTRACT FROM AUTHOR]

Hybrid RANS/LES methods combine the advantages of RANS models in terms of simulation costs, with the ability of LES to capture unsteady flow structures. A problem encountered in applications of this technique is the transmission of information between the RANS and LES zones: in the RANS region only mean-flow data is available, and the Reynolds shear stresses are entirely supported by the turbulence model; in the LES region, on the other hand, turbulent eddies must be present to support the turbulent momentum transport. The generation of these eddies is a critical ingredient in determining the effectiveness and accuracy of a hybrid method. In this paper we discuss this problem for applications in which the RANS region is below the LES zone, and in cases in which the flow advects from RANS to LES regions. We will also present recent results from our research group. [ABSTRACT FROM AUTHOR]

The accuracy of large-eddy simulations is limited, among others, by the quality of the subgrid parameterisation and the numerical contamination of the smaller retained flow-structures. We review the effects of discretisation and modelling errors from two different perspectives. First, we review a database-approach to assess the total simulation error and its numerical and modelling contributions. The interaction between the different sources of error in the kinetic energy is shown to lead to their partial cancellation. An ‘optimal refinement strategy' for given subgrid model, given discretisation method and given flow conditions is identified, leading to minimal total simulation error at given computational cost. We provide full detail for homogeneous decaying turbulence in a ‘Smagorinsky fluid'. The optimal refinement strategy is compared with the error-reduction that arises from grid-refinement of the dynamic eddy-viscosity model. Dynamic modelling yields significant error reduction upon grid refinement. However, at coarse resolutions high error-levels remain. To address this deficiency in eddy-viscosity modelling, we then consider a new successive inverse polynomial interpolation procedure with which the optimal Smagorinsky constant may be efficiently approximated at any given resolution. The computational overhead of this optimisation procedure is well justified in view of the achieved reduction of the error-level relative to the 'no-model' and dynamic model predictions. [ABSTRACT FROM AUTHOR]

The contributions, lessons, and trends found in the DESider Symposium Proceedings are discussed. Three broad classifications can be made among the papers: The first is between studies which widen the code- and user-base of DES and its range of applications to establish the current level of quality, and those which bring out neighbouring hybrid concepts such as SAS for discussions and improvements.The second is between "natural" uses of DES with boundary layers fully covered by RANS, and uses with RANS only as a wall model in LES.The third is between single-model methods such as DES, and zonal methods even if they are closely related. [ABSTRACT FROM AUTHOR]