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This paper focuses on numerical aspects for hybrid RANS-LES computations using the X-LES method. In particular, the impact of using a high-order finite-volume scheme is considered. The finite-volume scheme is fourth-order accurate on non-uniform, curvilinear grids, has low numerical dispersion and dissipation, and is based on the skew-symmetric form of the compressible convection operator, which ensures that kinetic energy is conserved by convection. A limited grid convergence study is performed for the flow over a rounded bump in a square duct. The fourth-order results are shown to depend only mildly on the grid resolution. In contrast, second-order results require at least half the mesh size to become comparable to the fourth-order results. Additionally, the high-order method is extended with shock-capturing capability in such a way that interference with the subgrid-scale model is avoided. The suitability of this extension is demonstrated by means of a supersonic flow over a cavity. [ABSTRACT FROM AUTHOR]

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]

Experimental data from QinetiQ shows the addition of a saw tooth spoiler at the leading edge of the M219 cavity results in a reduction in edge tone resonances by as much as 13dB compared to the clean cavity. In an effort to predict this and understand the underlying mechanism, a detached eddy simulation has been performed for the clean cavity and cavity with spoiler using FLUENT 6.2. Comparison with experiment indicates that the tone amelioration can be reproduced reasonably well. DES also reveals that the spoiler causes the shear layer over the cavity to rise during the first fifth of the cavity length with consequent greater interaction with the region aft of the cavity trailing edge. The teeth appear to have no lasting impact on the flow and it is thought that the displacement effect alone accounts for the tone amelioration. [ABSTRACT FROM AUTHOR]

In this paper the three-dimensional non-reacting turbulent flow field of a swirl-stabilized gas turbine model combustor is analysed with compressible CFD. For the flow analysis URANS and Hybrid RANS/LES (DES, SAS) turbulence models were applied. The governing equations and the numerical method are described. The simulations were performed using the commercial CFD software package ANSYS CFX-10.0. The numerically achieved velocity components show a good agreement with the experimental values obtained by Particle Image Velocimetry (PIV). Furthermore, a precessing vortex core (PVC) could be found in the combustion chamber. [ABSTRACT FROM AUTHOR]

Several hybrid LES/RANS (LES - Large-Eddy Simulation; RANS - Reynolds- Averaged Navier-Stokes) models have been assessed in computations of separated flows over smooth-contoured, wall-mounted hills, including flow control. The models considered include DES (Detached Eddy Simulation; Spalart et al. 1997, Travin et al. 2002), DDES (Delayed DES; Spalart et al. 2006), a zonal hybrid LES/RANS scheme (HLR; Jakirlic et al. 2006) and an Instability-Sensitized (IS) k-ε model. We report on models performance in the two configurations: periodic flow over a symmetric 2-D hill at moderate Reynolds number (Reb=10595; LES: Fröhlich et al.,2005; Breuer et al., 2005) and flow over a 2-D hump at high Re number( Rec ≈ 106,Exp.: Greenblatt et al., 2004). In the latter case the separation was controlled by steady suction through a narrow opening at the natural separation line in addition to the baseline flow. The computational results obtained confirm a crucial role of the LES/RANS interface treatment. [ABSTRACT FROM AUTHOR]

Using the Detached Eddy Simulation (DES) and an algebraic hybrid RANS-LES model, computations are conducted for the flow over a rectangular cavity at a Mach number of M ∞ =0.85. The emphasis is placed on the prediction of unsteady pressure patterns inside the cavity in terms of pressure fluctuations and deduced acoustic tonal modes in comparison with available experimental data. Furthermore, some resolved cavity flow features are also compared, for which a set of wall-resolved LES data is taken as reference. It is shown that both modelling approaches have produced similar results that are in good agreement with experimental or LES data. The DES modelling has generated somewhat reduced pressure fluctuations on the cavity floor. The hybrid model pronounces a less diffusive mixing layer over the cavity opening, which makes a slightly better prediction for the mean flow field. [ABSTRACT FROM AUTHOR]

The flow around Ahmed car body is studied for a 35° slant angle case and 25° slant angle case. For the steady 35° case, RANS modelling have shown good results but is not efficient in the 25° configuration, beeing unable to capture the detachment of the flow over the slant of the body. Then, DES and DDES modelling are performed on the 25° configuration showing better results. [ABSTRACT FROM AUTHOR]

This paper presents a first industrial attempt at Eurocopter Germany to use DES-like methods to compute the wake behind a helicopter in forward flight. Three codes have been used: TAU (DLR), CFX (Ansys) and HMB (Uni. Liverpool) and four different turbulence models: standard SST and three of its unsteady extensions SAS, DES and XLES. Results for the loads, pressure distribution and skin-friction lines have been compared to each other and against wind tunnel experimental data. These more sophisticated models brought improvements over the base SST but not always markedly and consistently: the drag gets improved although the negative lift on the body departs further form the experimental value. The pressure distribution on the backdoor has been improved by one of the computation. Oil-flow visualisation results show that the mean flow in the region of the backdoor is qualitatively reasonably well captured. [ABSTRACT FROM AUTHOR]

A RANS calculation is connected to an upstream LES via explicit coupling conditions at a pre-defined interface. The role of the interface is to allow for mean flow information to propagate upstream and for fluctuations to leave the LES domain without reflections. To this end, the mean velocity is directly coupled across the domain boundaries whereas the fluctuations at the downstream end of the LES zone are treated using either the so-called enrichment strategy (Quéméré & Sagaut, 2002) or a parameter-free generalization of this method based on a convective condition (von Terzi, Fröhlich & Mary, 2006). For incompressible flows, both techniques require a complementary coupling condition for the pressure or an equivalent variable enforcing continuity. Two distinct techniques are investigated: (i) The instantaneous pressure is computed in a coupled fashion for the union of the LES and RANS domains and (ii) the pressure is completely decoupled and mass conservation across the interface is ensured by an adjustment of the velocities on both sides. The performance of the different methods is scrutinized for turbulent channel flow and the flow over periodic hills. It was found that the convective condition with decoupled pressure fields and an explicit mass flux correction was the most robust technique delivering results of equal or increased quality in comparison to other combinations considered. [ABSTRACT FROM AUTHOR]

A one-equation variant of a previously developed two-equation, renormalization group (RG) based, hybrid RANS/LES model is presented. The model has a transport equation for the mean dissipation rate and an algebraically prescribed length scale. The length scale is proportional to the wall distance in RANS regions of the flow and to the filter width in LES regions. A near-wall formulation is used in the manner of Yakhot and Orszag's RNG modelling. The only free parameter entering the low-Reynolds formulation has been calibrated against channel flow, and the value corresponds well with experimental values for the same parameter obtained for decaying homogeneous isotropic turbulence. Applications to an impinging jet and a plane asymmetric diffuser are presented. [ABSTRACT FROM AUTHOR]

The present paper summarizes the research conducted at the University of Manchester over the course of the Desider project on methods of generation of synthetic turbulence. A random procedure, referred to as the Synthetic Eddy Method (SEM), based on the classical view of turbulence as a superposition of coherent structures was developed and compared with other methods of generation of inflow boundary conditions for LES, for different types of wall bounded flows. Synthetic inflow generation methods always show a transition region downstream of the inlet until the turbulence recovers an equilibrium state. The sensitivity of this transition region to variations in the synthetic inflow turbulence energy, length scale and time scale is studied herein with applications to hybrid RANS-LES methods in mind, as RANS results cannot be expected to provide accurate values for these scales to the LES region. A parameterization of the SEM suitable for hybrid RANS-LES simulations is proposed and tested on hybrid RANS-LES simulations of several wall bounded flows, with an emphasis on the flat plat boundary layer. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of the behaviour of DES-type methods used as Wall-Modelled-Large-Eddy-Simulation (WMLES) and to the treatment of the eddy viscosity in the framework of turbulent inlet conditions. A new method named Stimulated Detached Eddy Simulation (SDES) based on a synthetic turbulence method including pseudo-eddy viscosity synthetization is proposed and assessed on a spatially developing boundary layer. [ABSTRACT FROM AUTHOR]

The paper evaluates a new method for prescribing synthesized turbulent inlet boundary conditions. When making LES, DES or hybrid LES-RANS, a precursor channel DNS is often used. The disadvantage of this method is that it is difficult to re-scale the DNS fluctuations to higher Reynolds numbers. In the present work, synthesized isotropic turbulent fluctuations are generated at the inlet plane with a prescribed turbulent length scale and energy spectrum. A large number of independent realizations are generated. A correlation in time between these realizations is introduced via an asymmetric, non-truncated time filter. In this way the turbulent time scale of the synthesized isotropic turbulent fluctuations is prescribed. [ABSTRACT FROM AUTHOR]

Although LES is a highly promising simulation technique, it still suffers from extremely large resources required for the resolution of the near-wall region, especially for high-Re flows. That is the main motivation for setting up hybrid LES-RANS methods. Whereas RANS suits reasonably well to attached boundary layers, requiring much less CPU-time and memory than LES, the latter is recommended for complex large-scale flow phenomena, which RANS often fails to predict correctly. Both characteristics are combined in hybrid LES-RANS methods to obtain an optimal solution at lower cost. Meanwhile a variety of different hybrid concepts were proposed including DES. In the present study a non-zonal approach based on two different but unique models is preferred. The predefinition of RANS and LES regions is avoided and a gradual transition between both methods takes place which weakens the problem of setting up an appropriate coupling strategy. The new hybrid LES-RANS approach relies on a one-equation model for the turbulent kinetic energy in both modes. At this phase the model is of linear type. In addition to this linear eddy-viscosity model (LEVM), an explicit algebraic Reynolds stress model (EARSM) is applied in the RANS mode in order to account for the Reynolds stress anisotropy. This insertion leads to a non-linear model. The linear version is used for comparison in order to emphasize the advantages of the non-linear formulation. Both model variants have been tested on the basis of the standard plane channel flow and the flow over a periodic arrangement of hills. [ABSTRACT FROM AUTHOR]

Reliability and robustness are two important required features of CFD results. While a huge amount of works address the issue of model and numerical scheme validation, the search for robust models (i.e. models that exhibit a low sensitivity with respect to tuning parameters) and methods which make it possible to measure the sensitivity of the results received much less attention. The present work addresses these two issues. [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]

The need of high order boundary discretization in case of a high order code, e.g. a Discontinuous Gaierkin (DG) Code, has already been demonstrated in the literature. Bassi and Rebay extended the DG method to solve the Navier-Stokes equations for laminar and 3D turbulent flow. In the present paper an extension will be provided to include both three-dimensional flows and curved elements to properly represent three-dimensional bodies with curvature. Some results, like Sows around a sphere and around an Onera M6 wing, are calculated and compared with experiments. [ABSTRACT FROM AUTHOR]

Detailed numerical shape optimization will play a strategic role for future aircraft design. It offers the possibility of designing or improving aircraft components with respect to a pre-specified figure of merit. Optimization methods based on exact derivatives of the cost function with respect to the design variables still suffer from the high computational costs if many design variables are used. However, these gradients can be efficiently obtained by the solution of so-called adjoint flow equations. Furthermore, it is possible to derive these adjoint solvers in an automated fashion by the use of so-called automatic differentiation (AD) tools. In the present paper the efficient and automated differentiation of an entire design chain, including the flow solver, is presented. As test case for AD-generated adjoint sensitivity calculations an inviscid RAE2822 airfoil is chosen under transonic flight conditions for drag reduction. [ABSTRACT FROM AUTHOR]

Flow structure in the annular section of the inlet system of a tuboannular swirl combustor with respect to the swirl intensity influence was investigated computationally complementary to the recent experimental study by Palm et al. [1]. In addition to the non-swirling case, two different swirling configurations corresponding to the swirl numbers S = 0.6 and 1.0 were considered. The simulations were performed by using Large Eddy Simulation (LES) method and a two-layer model scheme hybridizing a near-wall k —ε RANS (Reynolds-averaged Navier Stokes) model covering the wall layer and LES method in the outer layer employing Smagorinsky model. Special attention was devoted to the position of the interface. An in-depth analysis of the mean velocity and turbulence fields reveals an increasingly asymmetric axial velocity profile in the annular pipe and an appropriately shaped profile of the Reynolds stress components corresponding to the enhanced turbulence production in the outer part of the concentric annulus. The present study also aimes at generation of reliable swirling inflow data for future LES of the flow in the combustor flue. [ABSTRACT FROM AUTHOR]

To investigate the development of blade tip vortices under different rotor conditions like thrust and rotational speed, both 2C and 3C PIV measurements were performed on a 40% Mach scaled Bol05 model rotor in hover condition. The vortices were traced from the trailing edge of the blade up to half a revolution behind the blade with azimuth steps between 1° to 10° and different spatial resolutions. [ABSTRACT FROM AUTHOR]

In the present paper we investigate the aeroacoustic characteristics of the flow over a forward facing step. The purpose is to identify relevant regions which are responsible for the noise generation. Correlation measurements are carried out for the pressure fluctuations on the wall, velocity characteristics of the flow and the recorded far-field acoustic pressures. The application of the correlation techniques provides a useful tool in the characterisation of the flow-induced sound sources. For further understanding, flow and acoustic experiments are conducted using different Reynolds numbers and radii of curvature. [ABSTRACT FROM AUTHOR]

Sound generation downstream the nozzle end of a subsonic laminar jet has been investigated using two-dimensional direct numerical simulations (DNS). The nozzle end is modeled by a finite flat plate with Mach numbers of MaI = 0.8 above and MaII = 0.2 below the splitter plate. Behind the nozzle end, a combination of a wake and mixing layer develops. Due to the high amplification rates, disturbances saturate before a pure mixing layer occurs. Non-linear generation mechanisms produce higher harmonic disturbances in the upper boundary layer, resulting in an only quasi periodic solution. The main acoustic sources correspond to the positions of vortex pairing. Broadband noise is emitted instead of tonal noise, known from the pure mixing layer without a splitter plate [4]. [ABSTRACT FROM AUTHOR]

In this study the flow field and the acoustic field over a high-lift configuration consisting of a deployed slat and a main wing is numerically analyzed. The flow parameters are Ma = 0.16, Re = 1.4 * 106, αSlat = 23° and αgeo = 13°. The flow data, which are computed via a large-eddy simulation, provide the distributions being plugged in the source terms of, e.g. the acoustic perturbation equations (APE) or the Ffowcs-Williams and Hawkings (FWH) equation, to compute the acoustic near field. The analysis shows the interaction of the shear layer of the slat trailing edge and the slat gap flow to generate higher vorticity than the main airfoil trailing edge shear layer. Thus, the slat gap is the dominant noise region. [ABSTRACT FROM AUTHOR]

Trailing-edge noise data from an experimental study on a flat-plate and on a two-dimensional NACA 0012-like airfoil are presented. Within extensive measurements in the Aeroacoustic Wind Tunnel Braunschweig various flow-permeable (comb-type) edge modifications were tested with respect to their noise reduction capability. Among numerous design parameters a narrow slit width was identified as major requirement for a low-noise trailing-edge design whereas flexibility of the comb material was found to be not imperative for such edge noise reduction means. Because both boundary-layer tripping and trailing-edge thickness show significant influence on trailing-edge noise, a detailed description of these effects is provided to enable an accurate interpretation of corresponding noise test data. [ABSTRACT FROM AUTHOR]

Direct numerical simulations (DNS) are carried out to investigate the effect of effusion cooling by blowing through spanwise slits and discrete holes in a laminar flat-plate boundary layer at various Mach numbers. The comparison with experimental data for a Mach-2.67 boundary layer with a cool wall and a spanwise slit shows good agreement. For an adiabatic Mach-6 boundary layer, the focus of the study is the effectiveness of various effusion-cooling configurations (slits and holes), the generated vortices and shear-layer systems. In terms of cooling effectiveness slits are preferable over (a few) holes. [ABSTRACT FROM AUTHOR]

A large-eddy simulation using preconditioning is described and applied to investigate continuous tundish flow. The Navier-Stokes equations for compressible flow are approximately solved using an implicit dual-time stepping scheme combined with low Mach number preconditioning and a multigrid acceleration technique. The impact of a turbo-stopper on jet spreading, jet impingement on the wall, wall jets, and steel quality is investigated. The numerical analysis shows the turbostopper flow to generate a more homogeneous tundish flow and as such a higher steel quality can be expected. [ABSTRACT FROM AUTHOR]

In the present study, Detached Eddy Simulation is applied to the supersonic axisymmetric base flow. Computations are done on coarse and fine unstructured grids to examine the influence of grid refinement on flow predictions. The final results are compared with available experimental data of Herrin and Dutton, which includes boundary layer velocity profile, base pressure, centerline velocity profile, Mach and turbulent kinetic energy distributions. The influence of grid refinement is observed and the reasons are discussed. [ABSTRACT FROM AUTHOR]

A Seperation of Variables (SoV) scheme has been developed in order to obtain a direct solution to the Poisson problem arising from Chorin's projection method within rectangular enclosures. The algorithm is compared to the previously used FFT with periodic boundaries and methods to improve the performace of the required transformations are presented. Finally, first results of thermal convection obtained in a closed box geometry are compared to results obtained in a periodic rectangular cell. [ABSTRACT FROM AUTHOR]

This paper deals with the effects of heat release and compressibility on temporally evolving, turbulent mixing layers. Direct Numerical Simulations (DNS) of such layers at two different convective Mach numbers are performed with and without combustion which allows to study the effects of heat release and compressibility separately and combined. It is shown that both, compressibility and heat release, dampen the turbulence activity and lead to a reduced growth of the mixing layer. Alterations in pressure fluctuations are a main reason for the changes. The effects of compressibility are not as strong in the reacting mixing layer as in the inert one. A significant difference between the inert and the reacting mixing layers at high convective Mach number is that entropic density fluctuations prevail over the acoustic ones when reaction takes place while both contribute to nearly equal parts in the non-reacting compressible flow. [ABSTRACT FROM AUTHOR]

Simulations and experiments were performed to capture the spatio-temporal flow field around a finite circular cylinder mounted on a ground plate. In order to provide a combined database and testcase for future simulations and experiments, the flow is investigated using state-of-the-art techniques with a high resolution in time and space, namely Large-Eddy Simulation and Detached-Eddy Simulation for the numerics and time-resolved PIV as well as LDA for the measurements. The predicted time-averaged and unsteady flow field from simulations corroborate well the experiments, giving new insights into the complex turbulent separated flow behind a quite simple geometry. [ABSTRACT FROM AUTHOR]