Zonal Detached Eddy Simulation Research Articles

Numerical Investigation of Stall Characteristics of Common Research Model Configuration Based on Zonal Detached Eddy Simulation Method

A zonal detached eddy simulation (ZDES) method, based on the two-equation k-ω SST turbulence model, was employed to predict stall characteristics and capture small-scale vortex structures in the wake region of the main wing under the post-stall condition of the Common Research Model (CRM) configuration. Additionally, the unsteady Reynolds-averaged Navier–Stokes (URANS) method was utilized for performance comparison in resolving small-scale vortices with ZDES. The results revealed a pronounced lateral flow on the wing, induced by the low-pressure region of the inner wing at post-stall angles of attack. Due to the downwash effect, the horizontal tail was influenced by the vortices in the wake region of the main wing, which the URANS method did not capture adequately. As the angle of attack increased, the separation area on the main wing expanded from the middle of the wing towards the inner wing. Consequently, the vortex structures in the wake region of the main wing became more intricate, and the primary peak of the lift coefficient spectrum shifted to the low-frequency region.

Wake tail plane interactions for a tandem wing configuration in high-speed stall conditions

In this work, wake-tail plane interactions are investigated for a tandem wing configuration in buffet conditions, consisting of two untapered and unswept wing segments, using hybrid Reynolds-Averaged Navier–Stokes / Large Eddy Simulations (RANS/LES) with the Automated Zonal Detached Eddy Simulation (AZDES) method. The buffet on the front wing and the development of its turbulent wake are characterized, including a spectral analysis of the fluctuations in the wake and a modal analysis of the flow. The impact of the wake on the aerodynamics and loads of the rear wing is then studied, with a spectral analysis of its lift and surface pressure oscillations. Finally, the influence of the position and the incidence angle of the rear wing is investigated. For the considered flow conditions, 2D buffet is present on the front wing. During the downstream movement of the shock, the amount of separation reaches its minimum and small vortices are present in the wake. During the upstream movement of the shock, the amount of separation is at its maximum and large turbulent structures are present accompanied by high fluctuation levels. A distinct peak in the corresponding spectra can be associated with vortex shedding behind the wing. The impingement of the wake leads to a strong variation of the loading of the rear wing. A low-frequent oscillation of the lift, attributed to the change of the intensity of the downwash generated by the front segment, can be distinguished from high-frequent fluctuations that are caused by the impingement of the wake’s turbulent structures.

Prediction of wall-pressure fluctuations for separating/reattaching flows applied to space launchers using zonal detached eddy simulation-based convolutional neural networks

Convolutional neural networks (CNNs) are used to predict the fluctuating wall-pressure coefficient and associated single-point pressure spectra in the separating/reattaching flow region around a generic space launcher configuration in the transonic regime. The neural networks are trained on a generic axisymmetric afterbody configuration. A Zonal Detached Eddy Simulation of a semi-realistic launcher geometry [NASA (National Aeronautics and Space Administration) model 11 hammerhead] is performed and validated using available experimental results. This configuration is used as a testing case for the trained models. It is shown that the CNNs are able to identify flow features related to physical phenomena of the flow. From this feature identification, the models are able to predict the evolution of fluctuating wall quantities and locate the regions of high pressure fluctuations. A scaling procedure is proposed to retrieve correct levels of the predicted quantities for a given unknown configuration having different free stream conditions. We also demonstrate that the present models perform well applied on Reynolds-Averaged Navier–Stokes mean flow fields, paving the way for a significant reduction in the computational cost for predicting wall-pressure fluctuations around space launchers.

Numerical investigation of self-sustained oscillations of stall cells around a leading edge-separating airfoil

The flow around a stalled airfoil is investigated using zonal detached-eddy simulation (mode 2), including transition effects through a coupling with the γ−Reθ,t framework. The airfoil exhibits mixed trailing edge-leading edge stall type properties. The chord length-based Reynolds number and Mach number, respectively, amount to 1·106 and 0.16. Two computations with different initial conditions are performed for 40 and 120 chord-passing durations, respectively (or equivalently 0.23 and 0.67 s), allowing the capture of several periods of the low frequency dynamics of the flow—compared to typical von Kármán vortex shedding. A stall hysteresis is observed: the computation initiated from an attached flow remains thus, but the computation which starts from a separated flow yields a quasi-permanent low-frequency oscillatory behavior, which bifurcates to the previously attached topology after 90 chord-passing durations (0.45 s). The oscillatory phase displays events of emergence and disappearance of stall cells. The partly- and fully attached flows are validated against experimental data. The oscillatory bistable flow is then analyzed with regard to the characteristics and frequency contents of both massive separation and partial transient reattachments. It is shown that the low-frequency separated shear layer flapping at the leading edge is forced by high-frequency fluctuations, which travel from the trailing edge upstream, close to the wall in the separated flow. The flapping phenomenon displays a Strouhal number based on the front-section height of the airfoil around St=fc sin (α)/u∞≃0.02. Conversely, the high-frequency fluctuations have Strouhal numbers closer to 3, which is in close agreement with leading-edge shear-layer instability frequencies. The spectral content of the flow is then explored in search of the source of these high-frequency fluctuations. It is proposed that they stem from the instability of the trailing edge shear layer between the pressure side boundary layer and the separated flow from the suction side. Finally, a scenario describing a cycle of the low-frequency oscillation of a stall cell is proposed.

Zonal Detached Eddy Simulation of the Fan-Outlet Guide Vanes Stage of a Turbofan Engine: Part II—Broadband Noise Predictions

Abstract This paper (Part II) presents the broadband noise predictions of a turbofan stage based on a hybrid method proposed by ONERA in the framework of the European project TurboNoiseBB. The numerical approach relies on a ZDES (Zonal Detached Eddy Simulation) strategy that is applied to a fan module at approach conditions and tested in AneCom facility (Wildau, Germany). The ZDES method with main aerodynamic flow features is detailed in a companion paper (Part I), and this one focuses on acoustic analyses. Acoustic codes based on Amiet's theory and FWH (Ffowcs Williams and Hawkings) analogy, both taking into account for duct propagation effects, are briefly described in the article and chained to the computational fluid dynamics to assess the rotor–stator interaction (RSI) noise (focusing on stator sources). The required inputs are the turbulent wake information (issued from either Reynolds Averaged Navier-Stokes (RANS) or ZDES) in front of the stator and the unsteady pressure on the vane wall, respectively. Turbulent velocity profiles and velocity spectra are compared to hot-wire measurements in the interstage region. A nice agreement is globally observed with a clear improvement compared to RANS solutions. Then, sound power spectra in the intake and bypass duct provided by acoustic codes are discussed and compared to the experiment. Reliable numerical predictions are obtained when undesirable additional sources in the rear-chord region (believed to be caused by local flow detachments from the vane leading edge and near the trailing edge) are removed from the FWH surface integration. ZDES + FWH spectra are found to be not so far from RANS + Amiet ones, with a best fitting to the experimental spectrum shape and predicted levels 3 dB below the measurements.

Zonal Detached Eddy Simulation of the Fan-Outlet Guide Vanes Stage of a Turbofan Engine: Part I—Methodology, Numerical Setup, and Aerodynamic Analysis

Abstract This article deals with the zonal detached eddy simulation of the fan module of a modern turbofan engine for the prediction of the broadband noise due to the interaction of the fan turbulent wakes with the stationary outlet guide vanes. The simulation relies on a hybrid RANS/LES approach with a zonal strategy: the core airflow is treated in RANS, while the bypass airflow is solved with the hybrid approach. The simulation was performed during four revolutions, and statistical convergence was reached. Inspections of the flowfields highlight a consistent behavior of the shielding function (border between RANS and LES solving areas) around the blade walls and at the trailing edge for a such complex flow. The fan module was tested in the AneCom facility in which hot wire measurements were made in-between the fan and the outlet guide vanes. The numerical results are compared to this large dataset of measurements. The flow maps are well retrieved by the simulation for both the time-averaged and the turbulent quantities. Comparison of radial profiles shows an excellent agreement for the three root-mean-square (RMS) components of the velocities between zonal detached eddy simulation (ZDES) and the measurements, particularly in the tip gap flow area, in which RANS results do not reproduce correctly the flow quantities. The wake shape, a key feature in the mechanism of generation of rotor–stator interaction noise), is quite well predicted by the ZDES simulation. These numerical results demonstrate the maturity of the approach for the simulation of complex turbomachinery flows.

Outer layer turbulence dynamics in a high-Reynolds-number boundary layer up to recovering from mild separation

The outer layer dynamics of a high-Reynolds-number boundary layer recovering from non-equilibrium is studied utilising the multi-resolution approach of zonal detached eddy simulation mode 3. The non-equilibrium conditions are obtained from a boundary layer separation over a rounded step enhancing the turbulent production, and recovery happens during redevelopment after reattachment at high Reynolds numbers ( $Re_{\theta,max}\approx 24{,}000$ ). Most of the outer layer turbulence is resolved by the simulation, which reproduces accurately the experimental boundary layer relaxation. The spectral analysis of streamwise velocity fluctuations and turbulent kinetic energy (TKE) production evidences the different turbulent content distribution at separation and within the redevelopment region, at which very large-scale motions are identified with streamwise wavelengths up to $\lambda _x = 9\delta$ , where $\delta$ is the boundary layer thickness. The redevelopment of the boundary layer is analysed in terms of the persistence of a secondary peak in the TKE production and the evolution of the wall-shear stress statistics. The skewness and probability density function of the skin friction show a slower relaxation than the downstream flow fraction. This confirms the long-lasting impact of perturbations of the outer layer in high-Reynolds-number wall-bounded flows. This persistent non-equilibrium state is suggested to be the reason for the reported lack of accuracy of the considered Reynolds-averaged Navier–Stokes models in the relaxation region.

A comprehensive framework for high fidelity computations of two-species compressible turbulent flows

A strategy for scale-resolving simulations of bi-species turbulent flows is presented. It relies on a combination of Zonal Detached Eddy Simulation (ZDES) and an original low-dissipative version of the AUSM scheme that adapts its dissipation to capture flow discontinuities while ensuring a low numerical dissipation level in resolved turbulence regions. The corresponding discretized equations are thoroughly detailed. This comprehensive numerical framework is evaluated for the coaxial Air/Argon jet configuration investigated experimentally by Clifton and Cutler [1]. A robust method based on a combination of white noise to generate velocity fluctuations at the inlet of attached turbulent boundary layers together with a dynamic forcing method is applied for the first time in a curvilinear bi-species flow framework with ZDES mode 3. It is shown that the taking into account of resolved turbulence in the incoming attached boundary layers provided by this approach improves the prediction of the mixing process in the early stages of the mixing layer. A good agreement with experiment is also observed with a RANS description of attached boundary layers as permitted by ZDES mode 2 (2020) [2] where the switch between RANS and LES zones is set dynamically by the model itself.

Significance of generating synthetic turbulence for zonal detached eddy simulation of shallow water flows

A zonal detached eddy simulation (ZDES) is suitable for large-scale open-channel flows with a free surface, e.g. river flow. In ZDES, only a local region is required to be investigated using large eddy simulation (LES) to obtain a high resolution of vortical structures in hydraulic engineering. In this study, a fully non-hydrostatic free-surface flow model is developed for a ZDES-type model. The focus is to analyse the critical strategy of the turbulent forcing method, which is very important for the ZDES-type model. A well-validated synthetic eddy method was established using a numerical framework and applied to generate velocity fluctuations. Based on the synthetic turbulent velocity, a new formulation of the body force term was fed into the momentum equations. A test case of a fully developed open-channel flow with a free surface was used to verify the numerical strategy. Then, another common flow problem of a free-surface flow over a fixed dune was adopted to further validate the numerical approach. The results show that the proposed numerical strategy can promote the application of the hybrid Reynolds-averaged Navier–Stokes/LES method in natural large-scale open-channel flow simulation.

On the coupling of wall-model immersed boundary conditions and curvilinear body-fitted grids for the simulation of complex geometries

One of the main limitations in computational aerodynamics lies in the ability of CFD solvers to handle complex geometries while maintaining their accuracy. Among the currently available strategies, the Zonal Immersed Boundary Conditions (ZIBC) has shown its capability to introduce complex geometrical details for the simulations of high Reynolds turbulent flows. In this context, this work aims to extend the ZIBC framework, initially adapted to reproduce blockage effects, to take into account configurations where the influence of spatially developing boundary layers has to be accurately predicted. For this purpose, a compact sharp interface immersed boundary method has been developed for curvilinear grids. Moreover, a Thin Boundary Layer Equations (TBLE) wall model based on one-dimensional RANS Spalart-Allmaras equations is coupled with the IBC to model the inner part of compressible turbulent boundary layers. The coupling with the Zonal Detached Eddy Simulation (ZDES) approach is improved and permits to simulate turbulent flows capturing accurately the wall-normal gradients with a limited grid resolution. This strategy is applied to the simulation of a generic missile configuration (FG5) with an angle of attack of 10∘ using RANS and ZDES approaches. For the first time, wall quantities such as unsteady loads, including the viscous contribution, are accuratly reproduced on surfaces modelled with IBC using hybrid RANS/LES (ZDES) computations and for a realistic configuration at high Reynolds number. Such a reconstruction of physical quantities at the wall is achieved thanks to a precise reconstruction procedure using a TBLE wall model.

Impact of Underlying RANS Turbulence Models in Zonal Detached Eddy Simulation: Application to a Compressor Rotor

The present study focuses on the impact of the underlying RANS turbulence model in the Zonal Detached Eddy Simulation (ZDES) method when used for secondary flow prediction. This is carried out in light of three issues commonly investigated for hybrid RANS/LES methods (detection and protection of attached boundary layer, emergence, and growth of resolved turbulent fluctuations and accurate prediction of separation front due to progressive adverse pressure gradient). The studied configuration is the first rotor of a high pressure compressor. Three different turbulence modelings (Spalart and Allmaras model (SA), Menter model with (SST) and without (BSL) shear stress correction) are assessed as ZDES underlying turbulence model and also as turbulence model of unsteady RANS simulations. Whatever the underlying turbulence model, the ZDES behaves well with respect to the first two issues as the boundary layers appear effectively shielded and the RANS-to-LES switch is close downstream of trailing edges and separation fronts leading to a quick LES treatment of wakes and shear layers. Both tip leakage and corner flows are strongly influenced by the Navier–Stokes resolution approach (unsteady RANS vs. ZDES) but the underlying turbulence modelling (SA vs. SST vs. BSL) impacts mainly the junction flow near the hub for both approaches. ZDES underlying turbulence model choice appear essential since it leads to quite different corner flow separation topologies and so to inversion of the downstream stagnation pressure radial gradient.

Application of a zonal hybrid URANS/LES turbulence model to high and low-resolution grids for engine simulation

A zonal hybrid unsteady Reynolds-averaged Navier–Stokes/large eddy simulation (URANS-LES) Zonal detached-eddy simulation (ZDES) model is applied to internal combustion engine (ICE) simulation and comparisons of predicted flow morphology and variability are carried out against on the transparent combustion chamber (TCC-III) particle image velocimetry (PIV) data set for motored conditions. To this aim, a previously developed model derived from a standard seamless-detached eddy simulation (DES) formulation is adopted for two different grid resolutions. In particular, two zonalization choices are evaluated based on previous single-grid results, in order to assess the model outcomes based on the joint turbulence treatment/grid density: the seamless-DES mode is applied (1) only to the cylinder (TCC-Z1) and (2) to the cylinder and intake port (TCC-Z2). Multi-cycle simulations (50 samples) are carried out and the results are compared to experimental data in terms of PIV images using multiple quality indices on multiple planes ( Y = 0 and X = 0). Finally, comparison of predicted mean flow fields is extended to standard URANS mode. Results show that the use of a cylinder-only seamless-DES treatment on a relatively coarse grid results in a quantitative agreement between simulated and measured (PIV) flow fields, both in terms of average morphology and flow variability, whereas the extension of the DES mode to the intake port does not introduce relevant variations. Quality indicators seem to be moderately sensitive to the grid resolution, thus confirming the adaptive potential of a ZDES–like model and promoting the use of DES–type turbulence modelling even on relatively low-resolution grids. The analysis of average fields compared to URANS simulations highlights the benefit for both grids of a scale-resolving ZDES modelling when the same underlying turbulence model ( k-ε RNG) is used. This study reinforces the recommendation in the use of hybrid URANS-LES models to simulate ICE flows. The adopted ZDES formulation based on the two-equation k-ε RNG model shows that high-quality results can be obtained even on engineering-grade grids, both in terms of average and cycle-to-cycle variation. The numerical results obtained using the two grids with variable resolution are consistent, and this further promotes a wider adoption of this class of models to simulate engine flows in industrial applications.

On the estimation of unsteady aerodynamic forces and wall spectral content with immersed boundary conditions

Immersed boundary conditions (IBC) have become a practical tool to simplify the meshing process for the simulation of complex geometries in CFD. This approach has reached a sufficient level of maturity to allow the simulation of compressible high Reynolds number flows. However, the access of physical quantities at the immersed wall is far from being straightforward. This paper provides two methods for the reconstruction of fluctuating wall quantities relying on the creation of explicit watertight surface meshes of the immersed boundary. These surface meshes are used for the investigation of highly unsteady compressible flows of two generic space launcher afterbody configurations using Zonal Detached Eddy Simulation (ZDES). Since the flows are massively separated, the side load arising from the pressure is mainly responsible for the global load unsteadiness. Therefore, in the present study the focus is put on the accuracy of the wall pressure reconstructed on immersed boundaries and compared to validated numerical simulations using a classical body-fitted approach and experimental data. The numerical results demonstrate the ability of the present approaches to accurately capture the global load fluctuation around both afterbody configurations. Moreover, the IBC surface meshes simplify the overall post-processing operations and allow the extraction of wall quantities for unsteady simulation at low computational cost. This last feature has been used for the spectral analysis on IBC surfaces which reproduced successfully the location and the intensity of the pressure fluctuation.

Advanced simulations of turbulent boundary layers under pressure-gradient conditions

A high-Reynolds-number turbulent boundary layer experiencing pressure gradients is simulated with Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS/LES (Large Eddy Simulation) advanced turbulence modeling approaches, namely, two eddy viscosity models, two Reynolds Stress models (RSMs), and Zonal Detached Eddy Simulation (ZDES) mode 3 which corresponds to a wall-modeled LES approach. Such a study is the first of its kind to the authors’ best knowledge. The test-case considered is the experimental work of Cuvier et al. [“Extensive characterisation of a high Reynolds number decelerating boundary layer using advanced optical metrology,” J. Turbul. 18, 929–972 (2017)]. Some modifications of the top wall geometry have been proposed to take into account the blockage effect of the boundary layers developing over the wind tunnel side walls so that statistically two-dimensional simulations are possible. Comparisons have shown that there are some difficulties in properly predicting the mean skin friction and the Reynolds stresses in the adverse-pressure-gradient region for the ZDES and RSMs. The mean velocity profiles in this region are, however, poorly reproduced by all models. The atypical profiles experimentally observed at the beginning of the favorable-pressure-gradient region are well reproduced by RSMs, one eddy viscosity model, and ZDES for the mean velocity; however, only ZDES is able to satisfactorily predict the Reynolds stresses at this station. A spectral analysis of streamwise velocity fluctuations and Reynolds shear stress by means of ZDES has allowed us to identify external energetic turbulent structures at y ≈ 0.5δ and of size λx ≈ 3δ which are probably responsible for these atypical profiles. The present numerical test-case may constitute a development base for turbulence modeling under pressure gradient effects.

Detached-eddy simulation of turbulent coherent structures around groynes in a trapezoidal open channel

The hydrodynamics in a straight open channel with a multiple-embayment groyne field was investigated using the detached-eddy simulation (DES). A series of short groynes were included on a 1:3 side slope of the channel. This work focuses on the turbulent coherent structures around groynes on an uneven bottom. Flows around groyne fields are characterized by massive separation and highly unsteady vortices. DES can capture a wide spectrum of eddies at a lower computational cost than the large eddy simulation (LES) or direct numerical simulation (DNS). In the present work, a zonal DES model (ZDES) was used to simulate the flow around groynes. The ZDES model is a modified version of the DES designed to overcome the model-stress depletion (MSD) of the RANS/LES hybrid model. The vortex system consists of the horseshoe vortex (HV) formed at the base of the obstructions, the necklace vortex (NV) that wrapped the groyne tips near the free surface, and the shedding vortex (SV) underneath the free surface. The effects of the incident flow and local topography on the vortex evolution were investigated by analyzing the mean flow structures and the instantaneous turbulent flow fields. Some important vortices cannot be captured because of the averaging process, while some flow structures cannot be observed in the instantaneous flow. The mean flow is only a reflection of the averaging process when complex vortices are present.

Detached eddy simulation of flow through a circular patch of free-surface-piercing cylinders

The study carried out a numerical investigation of the open channel flow through a circular array of cylinders piercing the water surface. Unlike a lot of the previous research, this study took into account the influence of the bed friction and free water surface. A Zonal Detached-Eddy Simulation (ZDES) model was developed to simulate the turbulent free-surface flow. The non-hydrostatic model was discretized using the Finite Volume Method (FVM). Within the patch, each individual cylinder was directly modelled by specifying the no-slip boundary condition at the solid surface. The ZDES model was verified to be able to capture the small scale turbulent coherent structures. The instantaneous and average flow fields were analysed in detail with the aid of streamline visualization and vortex identifying technique (Q-criterion). The investigation shed light on the complex interaction between the free surface flow and the cylinder array arranged into a circular patch. The complexity arises from the interplay among the separated flows from individual cylinders, interference between adjacent cylinders and the bulk porous-media effect of the patch. The study highlighted the dependence of the flow characteristics on the key properties of the patch, especially the Solid Volume Fraction (SVF). The work demonstrated the encouraging capability of the established numerical technique for the investigation of vegetated flows.

Modal Decomposition Analysis of Three-Dimensional Transonic Buffet Phenomenon on a Swept Wing

The dominant fluid structures and unsteady behavior of the three-dimensional transonic buffet phenomenon on a swept wing are clarified. This paper focuses on a well-established buffet phenomenon rather than an incipient shock buffet (buffet onset). Zonal detached-eddy simulation reproduced the features of three-dimensional buffet. Three-dimensional fluid structures were extracted as modes with dynamic mode decomposition. To apply dynamic mode decomposition to the large fluid dataset, the dimensionality was reduced using incremental proper orthogonal decomposition bases. Then, dominant modes were identified using the compressed sensing approach. The results showed that the computed flowfield is dominated by two fluid structures. One is a buffet cell structure oscillating at Strouhal numbers 0.2 to 0.6. The buffet cells are spatially periodic in the spanwise direction. They are generated at midspan, where a large flow separation occurs, and they propagate at an angle toward the wing tip. The other main fluid structure has a frequency and represents the disturbances generated by the separation at midspan and propagating toward the wing tip and root. The two-dimensional shock wave at the root is oscillated by this disturbance.

Distortion reconstruction in S-ducts from wall static pressure measurements

PurposeThis paper aims to report the attempts for predicting “on-the-fly” flow distortion in the engine entrance plane of a highly curved S-duct from wall static pressure measurements. Such a technology would be indispensable to trigger active flow control devices to mitigate the intense flow separations which occur in specific flight conditions.Design/methodology/approachEvaluation of different reconstruction algorithms is performed on the basis of data extracted from a Zonal Detached Eddy Simulation (ZDES) of a well-documented S-Duct (Garnier et al., AIAA J., 2015). Contrary to RANS methods, such a hybrid approach makes unsteady distortions available, which are necessary information for reconstruction algorithm assessment.FindingsThe best reconstruction accuracy is obtained with the artificial neural network (ANN) but the improvement compared to the classical linear stochastic estimation (LSE) is minor. The different inlet distortion coefficients are not reconstructed with the same accuracy. KA2 coefficient is finally identified as the more suited for activation of the control device.Originality/valueLSE and its second-order variant (quadratic stochastic estimation [QSE]) are applied for reconstructing instantaneous stagnation pressure in the flow field. The potential improvement of an algorithm based on an ANN is also evaluated. The statistical link between the wall sensors and 40-Kulite rake sensors are carefully discussed and the accuracy of the reconstruction of the most used distortion coefficients (DC60, RDI, CDI and KA2) is quantified for each estimation technique.

A rapid and low noise switch from RANS to WMLES on curvilinear grids with compressible flow solvers

A turbulent inflow for a rapid and low noise switch from RANS to Wall-Modelled LES on curvilinear grids with compressible flow solvers is presented. It can be embedded within the computational domain in practical applications with WMLES grids around three-dimensional geometries in a flexible zonal hybrid RANS/LES modelling context. It relies on a physics-motivated combination of Zonal Detached Eddy Simulation (ZDES) as the WMLES technique together with a Dynamic Forcing method processing the fluctuations caused by a Zonal Immersed Boundary Condition describing roughness elements. The performance in generating a physically-sound turbulent flow field with the proper mean skin friction and turbulent profiles after a short relaxation length is equivalent to more common inflow methods thanks to the generation of large-scale streamwise vorticity by the roughness elements. Comparisons in a low Mach-number zero-pressure-gradient flat-plate turbulent boundary layer up to Reθ=6100 reveal that the pressure field is dominated by the spurious noise caused by the synthetic turbulence methods (Synthetic Eddy Method and White Noise injection), contrary to the new low-noise approach which may be used to obtain the low-frequency component of wall pressure and reproduce its intermittent nature. The robustness of the method is tested in the flow around a three-element airfoil with WMLES in the upper boundary layer near the trailing edge of the main element. In spite of the very short relaxation distance allowed, self-sustainable resolved turbulence is generated in the outer layer with significantly less spurious noise than with the approach involving White Noise. The ZDES grid count for this latter test case is more than two orders of magnitude lower than the Wall-Resolved LES requirement and a unique mesh is involved, which is much simpler than some multiple-mesh strategies devised for WMLES or turbulent inflow.

三次元翼における遷音速バフェット特性のスパン方向変化

Transonic buffet is self-induced oscillation of shock waves appeared on a suction side of a wing. We simulated the transonic buffet over the NASA Common Research Model (CRM) wing, which is an open geometry, generic transport model, and characterized its variation in spanwise direction. The numerical method employed in this simulation was a zonal detached eddy simulation (ZDES), which is a RANS/LES hybrid method. The numerical results indicate that the frequency spectra of oscillation on the surface pressure were varied in spanwise direction and were categorized into three patterns. In the inboard region, buffet exhibits a periodical oscillation having a single dominant frequency equivalent to the 2D wing. At the mid-span of the wing, the wavefront of shock moves due to the existence of the angle of sweepback. In the outboard, the spectrum exhibits multiple dominant modes due to superposition of two difference sources. One is a periodical oscillation similar to the 2D wing. The other is pressure oscillation propagating from the inboard region.