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In this paper, measurements of the stall of a NACA [Formula: see text] airfoil section are presented and compared to a simulation with a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) model with the goal of gaining deeper insight into the flow physics of a stall cell and the turbulent wake in such conditions. Detailed measurements of the evolution of the velocity deficit and turbulence within the wake along with surface pressure measurements and flow visualization provided a comprehensive database for code validation and flow physics studies. The measurements in the Laminar Wind Tunnel of the Institute of Aerodynamics and Gas Dynamics were performed at a Reynolds number of [Formula: see text] and comprised surface pressures, oil flow surface visualizations, and hot-wire measurements of the wake. The results at [Formula: see text] were used as validation data for a hybrid RANS/LES run at the same flow conditions. It was shown that the Bernoulli-based detached eddy simulation (BDES) model, which uses a shielding function based on a localized Bernoulli formulation, combined with effective gray area mitigation can capture the stall cell pattern and the point of flow separation at an angle of attack of [Formula: see text]. Furthermore, the velocity deficit and the Reynolds stresses in the wake show good agreement between simulation and experiment under these conditions.

In order to design vortex generators for modern multi-megawatt wind turbines accurately, the three-dimensional behaviour of the boundary layer has to be considered. Due to the rotation of the blade, the lift-enhancing rotational augmentation has a considerable impact, especially in the inner blade sections. To investigate the interaction of vortex generators and rotational augmentation, high-fidelity computational flow simulations by means of unsteady Reynolds-averaged Navier-Stokes methods are presented for a rotating blade of a generic 2 MW horizontal axis wind turbine. The inner blade section is analysed with and without vortex generators for two different pitch settings including one causing largely separated flow. Two ways of placement of the vortex generators on the blade with different radial starting positions are investigated in order to find out if a coexistence of the two lift-enhancement methods (i.e. rotational augmentation and vortex generators) is beneficial. All simulations are performed with the flow solver FLOWer and the vortex generators are modelled by the introduction of source terms into the computational domain through a BAY-type model. For the case without vortex generators, it is found that the strength of rotational augmentation largely depends on the effective angles of attack (i.e. the pitch setting). For the case with lower effective angles of attack, rotational augmentation is a cyclic phenomenon whereas for the case with higher effective angles of attack it generates large loads in the inner root section due to a constant centrifugal pumping mechanism in time. The results from the cases with vortex generators display a rather destructive interaction of vortex generators and rotational augmentation on the torque. For low effective angles of attack and thus attached flow conditions, vortex generators exhibit slight losses compared to the case without VGs as they inhibit spanwise flow through rotational augmentation. For high effective angles of attack, the vortex generators placed over 30 % of the blade produce an increase of 3.28 % in torque compared to the case without VGs and high centrifugal pumping.

In recent years, helicopter manufacturers have developed an increasing number of nonconventional configurations in order to extend flight envelopes of helicopters towards higher cruise speed. Airbus Helicopters' approach is the compound helicopter RACER, which is equipped with a boxwing and lateral pusher rotors. As the combination of these components with the main rotor induces a variety of mutual interactions, influencing their individual aerodynamic performance depending on the flight conditions, the understanding of these interactions is vital for the evaluation of the overall system. For this reason, the respective mutual influence of main rotor, wings, and lateral rotors is analyzed in this paper for hover. With the help of high-fidelity coupled aerodynamic simulations for the full RACER (Rapid And Cost-Efficient Rotorcraft) configuration as well as for setups omitting individual components, first- and second-order interactions of these components are isolated and analyzed for their effect on the helicopter's aerodynamic performance.

The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.

The aeroelastic response of a 2 MW NM80 turbine with a rotor diameter of 80 m and interaction phenomena are investigated by the use of a high-fidelity model. A time-accurate unsteady fluid–structure interaction (FSI) coupling is used between a computational fluid dynamics (CFD) code for the aerodynamic response and a multi-body simulation (MBS) code for the structural response. Different CFD models of the same turbine with increasing complexity and technical details are coupled to the same MBS model in order to identify the impact of the different modeling approaches. The influence of the blade and tower flexibility and of the inflow turbulence is analyzed starting from a specific case of the DANAERO experiment, where a comparison with experimental data is given. A wider range of uniform inflow velocities are investigated by the use of a blade element momentum (BEM) aerodynamic model. Lastly a fatigue analysis is performed from load signals in order to identify the most damaging load cycles and the fatigue ratio between the different models, showing that a highly turbulent inflow has a larger impact than flexibility, when low inflow velocities are considered. The results without the injection of turbulence are also discussed and compared to the ones provided by the BEM code AeroDyn.

With the pursuit of extending the flight envelopes of helicopters toward higher cruise speed, helicopter manufacturers increasingly have come up with nonconventional configurations in recent years. Among these, Airbus Helicopters' RACER (Rapid And Cost-Efficient Rotorcraft) is a compound helicopter equipped with a boxwing and lateral pusher rotors. In combination with the main rotor, these additional components determine the aerodynamic characteristics of the helicopter. Thereby, depending on the flight conditions, their individual performance is influenced by a variety of interactions. As the understanding of these interactions is vital for the evaluation of the overall system, the respective mutual influence of main rotor, wings, and lateral rotors is analyzed in this paper for cruise flight. For this reason, high-fidelity coupled aerodynamic simulations are conducted not only for the full RACER configuration but also for reduced setups omitting individual components to isolate the effect of these components on the helicopter's aerodynamic performance.

RANS simulations of a generic ultra-high bypass ratio engine high-lift configuration were conducted in three different environments. The purpose of this study is to assess small scale tests in an atmospheric closed test section wind tunnel regarding transferability to large scale tests in an open-jet wind tunnel. Special emphasis was placed on the flow field in the separation prone region downstream from the extended slat cut-out. Validation with wind tunnel test data shows an adequate agreement with CFD results. The cross-comparison of the three sets of simulations allowed to identify the effects of the Reynolds number and the wind tunnel walls on the flow field separately. The simulations reveal significant blockage effects and corner flow separation induced by the test section walls. By comparison, the Reynolds number effects are negligible. A decrease of the incidence angle for the small scale model allows to successfully reproduce the flow field of the large scale model despite severe wind tunnel wall effects., Cleansky2, Projekt DEAL

A highly loaded, high-speed turn flight of Airbus Helicopters' Bluecopter demonstrator helicopter is simulated to investigate dynamic stall using a loose computational fluid dynamics/structural dynamics (CFD/CSD) coupling of the flow solver FLOWer and the rotorcraft comprehensive code CAMRAD II. The rotor aerodynamics is computed using a high-fidelity delayed detached-eddy simulation (DDES). A three-degree-of-freedom trim of an isolated rotor is performed, yielding main-rotor control angles that agree well with the flight-test measurements. The flow field in this flight condition is found to be highly unsteady and complex, featuring massively separated flow, blade–vortex interaction, multiple dynamic-stall events, and shock-induced separation. The computed pitch-link loads are compared to flight-test measurements. This shows that all CFD/CSD cases underpredict the amplitudes of the flight test and yield phase shifts. However, overall trends agree reasonably. Also, varying the computational setup reveals that the shear stress transport–DDES turbulence model performs better than Spalart–Allmaras–DDES, that the consideration of the rotor hub and fuselage improves the agreement with flight-test data, and that the elastic twist plays only a minor role in the dynamic-stall events.

The aerodynamic and aeroacoustic behaviors of the Darrieus vertical axis wind turbine are very complicated. Hence, it is challenging to simulate the real flow behavior using the computational fluid dynamics approach. In the present study, the behavior of two different numerical techniques, Unsteady Reynolds Averaged Navier Stokes and Delayed Detached-Eddy Simulation (DDES), are compared to predict the aerodynamic and aeroacoustic performance. The DDES approach with the higher order scheme is used to investigate the noise mechanisms of Darrieus VAWT at several operating conditions. It is concluded that the dominant noise mechanism, when the turbine operates at low and high speed ratios, is a dipole noise, without any contribution from the monopole sound in the time averaged signal. Moreover, all the blade segments along the chord have a significant contribution to noise production. The leading edge segment is responsible for the noise reflects the load fluctuations by the variation of the effective angle of attack, flow blade relative velocity, and Blade vortex interaction. On the other hand, the rest of the blade segments reflect the load fluctuations by the massively separated flow at low speed ratio, while at high speed ratio it is as the same as the leading edge.

The influence of turbulent inflow, as it occurs in complex terrain, on the unsteady surface pressure distributions on a wind turbine is investigated numerically. A method is presented that enables an accurate reproduction of the inflow to the turbine in the complex terrain in Perdigao, Portugal. For this purpose, a precursor simulation with the steady-state atmospheric computational fluid dynamics (CFD) code E-Wind and a high-resolution Delayed Detached Eddy Simulation (DDES) with FLOWer is performed. The conservation of the flow field is validated by a comparison with measurements from the 2017 field campaign in Perdigao. Then, the resolved fluid-structure coupled generic wind turbine I82 is included in the FLOWer simulation to investigate the impact of the complex terrain inflow on the surface pressure fluctuations on tower and blades. A comparison with simulations of the same turbine in flat terrain with simpler inflows shows that the turbine in complex terrain has a significantly different vortex shedding at the tower, which dominates the periodic pressure fluctuations at the tower sides and back. However, the dominant source of periodic pressure fluctuations on the upper part of the tower, the blade-tower interaction, is hardly altered by the terrain flow. The pressure fluctuations on the blade have a rather broadband characteristic, caused by the interaction of the leading edge with the inflow turbulence. In general, it is shown that a sophisticated DDES of the complex terrain plays a decisive role in the unsteady aerodynamics of the turbine, due to its specific flow characteristic.

The effect of inflow turbulence level on the boundary layer transition on a Natural Laminar Flow (NLF) airfoil is investigated through detailed wind tunnel measurements. The free-stream turbulence level (\( Tu \)) is varied in the range \(0.01\%\le Tu \le 0.11\%\) by employing an active grid. Within the range of amplified TS-frequencies the spectral distribution of the \(u'\)-component could be matched to free flight measurements obtained for a glider at low to moderately turbulent conditions. Transition locations as function of turbulence level are determined for three airfoils with fundamentally different baseflows and the results are compared to the modified \(e^{9}\) method of Mack [6].

Currently, the wind turbine size is increasing dramatically, and the blades are experiencing large deformations. Accordingly, the aerodynamic force distributions over the blades are changed, and hence aeroelastic analysis has become of great importance. The state-of-the-art simulation tools for wind turbines aeroelasticity utilize engineering models to find the aeroelastic response. These tools use simplified methods such as BEM to find the unsteady aerodynamic loads and 1D structural models to determine the deformations. They are computationally cheap, but they are based on different corrections to account for the unsteadiness and the 3D effects. These corrections might lead to a decrease in model accuracy. Therefore, the objective of the present studies is to compare the results of engineering models to CFD-based aeroelastic simulations that do require less empirical modeling. The Multi-Body Simulation (MBS) solver SIMPACK is used to determine the dynamic response of the rotor and the blade aerodynamic loads were calculated by an integrated third-party module (AeroDyn) based on BEM. The block-structured CFD solver FLOWer is utilized to obtain the aerodynamic blade loads based on the time-accurate solution of the unsteady Reynolds-averaged Navier-Stokes equations. The engineering model predicted smaller power and thrust compared to the values obtained using the high-fidelity CFD-based aeroelastic model. Moreover, 1%–1.5% increase in the power and thrust was predicted from the engineering model by increasing the number of polars used along the blade.

The most dominant noise source of modern wind turbines is considered to be trailing edge (TE) noise. TE noise increases with increasing angle of attack of the flow. For wind turbine development it is hence crucial to predict TE noise for high angles of attack up to slightly separated flow. It results from wall pressure fluctuations induced by turbulent vortices in the boundary layer. The source term for the pressure fluctuations consists of two terms, the interaction of the mean shear with the turbulence and the turbulence-turbulence interaction (TTI). TTI is neglected in the commonly used TE noise prediction model by Blake, resulting in a strong dependency of the model on the wall normal mean velocity gradient. With increasing angle of attack this wall normal gradient of the boundary layer diminishes. Hence the TTI of the source equation has to be taken into account in order to achieve reliable predictions towards higher angles of attack. Here a new simplified-analytical model including the TTI, based on the model deduction by Blake, is presented and compared to experimental data. It is found that the prediction quality for high angles of attack and slight TE separation can be improved with the new model.

The aeroelastic response of the generic DTU 10 MW horizontal-axis wind turbine blades is investigated employing a time-accurate CFD–CSD loose coupling approach. An FSI coupling approach is implemented and used to conduct the aeroelastic simulations. The block-structured CFD solver FLOWer is employed to obtain the aerodynamic blade loads based on the time-accurate solution of the URANS equations. The CSD solver Carat++ is utilized to calculate the elastic deformations based on non-linear Timoshenko beam elements. Due to the rotor elasticity, the wind turbine power and thrust are increased by approximately 1% and 0.3% respectively. That increase is due to the large edgewise deformations which make the radial force component contribute to the rotor torque. Due to the presence of the tower in the coupled simulations, the forces and the deformations are reduced while the blades are crossing the tower. A time delay in the structural response due to the forces reduction causes a phase shift of 30°between the deformations reduction and the forces reduction. Also, the 1P amplitude of the wind turbine is reduced due to the blade flexibility by 6%, 12% and 22% at r ∕ R = 0 . 3 , 0.6 and 0.9 respectively.

The present paper investigates the aerodynamic and aeroacoustic characteristics of H-rotor Darrieus vertical axis wind turbine combined with a promising energy conversion technology, namely wind-lens, employing computational approaches. The Darrieus turbine adequate for low wind speed and urban area conditions. However, its aerodynamic and aeroacoustic characteristics are very complicated. Thus, the main scope of the current work is to enhance the aerodynamic performance of the introduced turbine and then assess the noise production accomplished with such enhancement. The studies are taken on two phases, the first phase is parametric 2D CFD simulations, employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach, to optimize the design parameters of the wind-lens. The second phase is a 3D CFD simulation of the full turbine using a higher order numerical scheme employing a hybrid RANS/LES method. An estimate of the aeroacoustic noise of the turbine is quantified using the Ffowcs Williams-Hawkings (FW-H) method. As a result, the optimal design parameters of the wind-lens are achieved and the optimized configuration shows a superior augmentation in power generated of about 82 % increase in the power coefficient at a speed ratio of 2.75. However, the turbine equipped wind-lens produces more noisy operation compared to the non-shrouded turbine.

In this work, scattering and shielding of the tonal noise from contrarotating open rotors by surrounding parts are investigated. The computational tool chain is based on unsteady Reynolds-averaged ...

The Discontinuous Galerkin method is a high-order method in space reducing the amount of cells needed for calculations compared to standard computational fluid dynamics (CFD) solvers. At the Institue for Aerodynamics and Gas Dynamics the CFD code SUNWinT has been developed using a DG method with the aim to apply it to rotor flows. The present study concerns the progress in simulating the flow phenomena of an isolated rotor in hover. The results of the calculations are compared to experimental data and show good agreement. Furthermore, the first phenomenological results of the flow around an isolated rotor in forward flight are presented, which reveal promising results and should serve as a starting point for future investigations.

The influence of atmospheric turbulence on an extruded airfoil of the FNG wing in clean configuration is investigated using numerical simulation. Turbulence is injected into the flow field using a momentum source term. It is shown that the turbulence can be propagated accurately to the airfoil. Spectra of the pressure coefficient at different chordwise positions indicate a correlation between the inflow velocity spectrum and the local \(c_p\) spectra, especially for low to medium wave numbers. Furthermore, the applicability of the simplified Disturbance Velocity Approach (DVA) is evaluated, where the velocities of the atmospheric turbulence are added to the flux balance using superposition. The DVA shows satisfying results for the lift spectrum and the \(c_p\) spectrum at the leading edge over a broad wave number range. An overestimation of the amplitudes for the pitching moment and \(c_p\) spectra at \(x/c=0.2\) occurs at medium to high wave numbers. A scaling test of the TAU code in a development version with the implemented DVA is performed on this test case and shows satisfying scalability.

The discontinuous Galerkin (DG) method is a high-order method in space reducing the amount of cells needed for calculations compared to traditional computational fluid dynamics (CFD) solvers. The present study concerns the implementation of a DG Chimera method and its application to simulations with relative body movements. The chosen test cases of a rotating 2D cylinder and a slowly plunging NACA0012 airfoil deal with body movement and unsteady laminar flow at subsonic Mach numbers. The results obtained agree well with the reference. Furthermore, the flexible application of the DG Chimera method to unstructured grids is demonstrated.

Recent enhancements and applications of the flow solver FLOWer are presented. First, an Adaptive Mesh Refinement technique (AMR) is implemented and an AMR cycle is built around FLOWer. Depending on the application case, the usage of AMR significantly reduces the overall computational cost—and thus increases efficiency—of the flow solution. Exemplary, for a complete helicopter simulation a reduction in computational time of 45% is achieved without any observable loss of accuracy. Second, the implementation of a new shielding approach for detached eddy simulations is shown. This applies a sophisticated communication method to exchange flow variables in wall normal direction. As an application case, the computation of the highly resolved rotor wake in hover highlights the possibilities of high performance computing in combination with advanced numerical methods for rotorcraft flows.

Modern wind turbines are increasingly equipped with vortex generators in the inner part of the rotor blade. On large blades it is usual to install hundreds of these small passive devices to delay flow separation. Therefore, affordable numerical methods to include vortex generators in the design process are required. One very promising method based on the addition of source terms in the flow equations is the BAY model. In this work a BAY-type model is presented and assessed for three different vortex generator shapes (rectangular, delta and cropped-delta) placed on a DU 97-W-300 airfoil and computed with steady-state Reynolds-averaged Navier-Stokes numerical methods. In order to quantify the circulation of the main streamwise vortex, a method to identify the vortex core based on the λ2-criterion is presented and shows good results. The computations reveal very good agreement with the experimental data for attached flow in terms of lift and pressure distribution while drag is inherently underestimated by the BAY model due to the inviscid modelling of the vortex generators. It is displayed that this underestimation is proportional to the vortex generator surface area. Concerning the different shapes, it is shown that the delta shape reveals larger deviations from the fully resolved case than the other geometries and therefore requires higher mesh resolution.

The aero-elastic response of the DANAERO wind turbine and interaction phenomena are investigated by the use of a high-fidelity model. A time-accurate unsteady fluid-structure interaction (FSI) coupling between a computational fluid dynamics (CFD) code for the aerodynamic response and a multi-body simulation (MBS) code for the structural response is used. Different CFD models of the same turbine with increasing complexity and technical details are coupled to the same MBS model in order to identify the impact of the different modeling approaches. The influence of the blade and tower flexibility and of the inflow turbulence is analyzed for a specific case of the DANAERO experiment. Lastly a fatigue analysis is performed from load signals in order to identify the most damaging load cycles and the fatigue ratio between the different models, showing that for low inflow velocities, a high turbulence has a major impact than the flexibility.

A study of transonic buffet on the NASA Common Research Model at flight Reynolds numbers is presented. The ability of two different hybrid RANS/LES models as well as the URANS approach for resolving three-dimensional buffet motion was evaluated by means of spectral analysis. Automated Zonal DES and URANS simulations show similar results in terms of buffet frequency and spanwise propagation of buffet cells, whereas the Delayed Detached Eddy Simulation results indicate a strong interaction between flow separation and shock motion. The extracted characteristic frequencies which are associated with transonic buffet are located in a range of Sr = 0.2-0.65 for URANS and AZDES and are therefore in accordance with findings from related recent research. Furthermore, the simulation time series were investigated and a structure of spanwise moving buffet cells with varying convection speed and wavelength could be observed., Deutsche Forschungsgemeinschaft, Projekt DEAL

In recent years, various helicopter manufacturers have been focusing increasingly on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics or aeroacoustic noise emission, to name only a few. In the following study, the behaviour of RACER in hover under the influence of crosswinds from eight different directions is investigated to support AH at the de-risking of RACER for this flight condition prior to the first flight. Therefore, a multidisciplinary, high-fidelity tool chain for coupled and trimmed aerodynamic simulations of the complete rotorcraft is applied. The presentation of the results is organized in three parts. In the first part, the flight mechanic behaviour is analysed and successful de-risking of ground clearance is shown. The second part focuses on the performance of the main rotor, the lateral rotors and the tail surfaces under wind conditions and shows that minimal power is required for headwind. In the last part, an analysis of the engines is performed, including a closer look at the inflow quality to the core engine and the convection of the hot exhaust gases.

The current study describes analyses of the WINSENT wind energy test site located in complex terrain in Southern Germany by highly resolved numerical simulations. The resolved atmospheric turbulence is simulated with Delayed Detached Eddy Simulations by the flow solver FLOWer without consideration of the research wind turbines. The mean inflow and wind direction of the analysed time period is provided by precursor simulations of project partners. The simulation model chain consists of three codes with different time scales and resolutions. The model chain provides a data transfer from mesoscale WRF simulations to OpenFOAM. As a next step OpenFOAM provides inflow data in the valley of the terrain site for the present FLOWer simulations, the code with the highest resolution in space and time. The mean velocity field provided by OpenFOAM is superimposed with fluctuations that are based on measurements to obtain the small turbulent scales within the FLOWer simulations, which the previous tools of the model chain can not resolve. Comparisons with the two already installed met masts clarify that the current FLOWer simulations provide an adequate agreement with measured data. The results are verified with the application of a second simulation, in which a homogeneous velocity profile is superimposed with turbulence. Thus, comparisons with measured data showed that the benefit of using the inflow data of this model chain is especially evident near the ground.

Hybrid RANS/LES simulations of the flow around the NASA Common Research Model aircraft configuration were carried out with the focus on understanding the interaction of the separated wake with the tailplane in the presence of massively separated flow on the main wing. Validation of the CFD data using PIV data obtained for the flow conditions at \(\alpha =16^{\circ }\), \(\alpha =18^{\circ }\) and \(\alpha =20^{\circ }\) was carried out, confirming the generally satisfactory performance of the DDES simulations observed in earlier publications. As a next step, the wake characteristics and tailplane forces were evaluated for three angles of attack in order to investigate the flow dynamics in low speed stall. The separation characteristics were found to vary over the span. The wake size and downwash direction varied significantly with higher values of \(\alpha \). The altered wing downwash influenced the tailplane inflow, with the load fluctuations on the latter being significantly affected by the amount of turbulent kinetic energy present in the wake.

The present work introduces a method for the design of a boundary-layer suction system for turbulent trailing-edge noise reduction of wind turbines. Since the latter hitherto has been primarily assessed in a two-dimensional framework, the paper is meant to point out whether the predicted improvements carry over to wind turbine flow. Since the processes of trailing-edge noise reduction and effective power alteration are intimately bound together, great emphasis is put on an accurate prediction of pump power requirement, the latter being based on a detailed suction hardware system implying pressure losses across each component. An exemplarily performed design reveals that, within a certain design regime, trailing-edge noise reduction is accompanied by an enhancement of rotor power. However, as of a distinct cross-over point at which the pump power requirement exactly compensates the amelioration of aerodynamic power, a trade-off between aeroacoustics and aerodynamics arises. The method bases on fully-resolved URANS computations and is applied to the generic NREL 5 MW turbine.

In addition to efficient reduction of wave drag in transonic flight, shock control bumps also offer some potential for buffet alleviation. In the present paper, two different approaches for buffet ...

Distributed boundary-layer suction has numerically and experimentally shown great potential to reduce flow-induced trailing-edge noise. The paper aims at the transfer of this potential to an indust...

This work is intended to investigate the aerodynamic responses of a large generic 10-MW offshore wind turbine under turbulent inflow conditions. The nonlinear lifting line free vortex wake simulations approach is employed for this purpose, computed using the QBlade code. In these studies, the effects of a three-dimensional correction model for the airfoil polars were studied in advance. For this purpose, the blade element momentum computations employing the corrected polars are performed and compared to computational fluid dynamics simulations, and a good agreement is obtained between both employed approaches. Background turbulence is then imposed in the QLLT simulations with the turbulence intensities ranging from low to high turbulence levels (3%–15%). Furthermore, the impact of wind shear from different locations (offshore and onshore) is investigated in this work.

The present study investigates the impact of unsteady 3-D aerodynamic effects on a wind turbine blade with trailing edge flap by means of computational fluid dynamics (CFD). Harmonic oscillations are simulated on the DTU 10 MW rotor with a morphing flap of 10 % chord extent ranging from 70 to 80 % blade radius. The deflection frequency is varied in the range between 1 and 6 p. To quantify 3-D effects, rotor simulations are compared to 2-D airfoil computations and the 2-D theory by Theodorsen. It was found that the deflection of the flap on the 3-D rotor causes a complex wake development and induction which influences the loads over large parts of the blade. In particular, the rotor near wake with its trailing and shed vortex structures revealed a great impact. Trailing vorticity, a 3-D phenomenon, is caused by the gradient of bound circulation along the blade span. Shed vorticity originates from the temporal bound circulation gradient and is thus also apparent in 2-D. Both lead to an amplitude reduction and shed vorticity additionally to a hysteresis of the lift response with regard to the deflection signal in the flap section. A greater amplitude reduction and a less pronounced hysteresis is observed on the 3-D rotor compared to the 2-D airfoil case. Blade sections neighboring the flap experience, however, an opposing impact and hence partly compensate for the negative effect of trailing vortices in the flap section with respect to integral loads. Comparisons to steady flap deflections at the 3-D rotor revealed the high influence of dynamic inflow effects.

The present study focuses on the impact of grid for accurate prediction of the MEXICO rotor under stalled conditions. Two different blade mesh topologies, O and C-H meshes, and two different grid resolutions are tested for several time step sizes. The simulations are carried out using Delayed detached-eddy simulation (DDES) with two eddy viscosity RANS turbulence models, namely Spalart-Allmaras (SA) and Menter Shear stress transport (SST) k-ω. A high order spatial discretization, WENO (Weighted essentially nonoscillatory) scheme, is used in these computations. The results are validated against measurement data with regards to the sectional loads and the chordwise pressure distributions. The C-H mesh topology is observed to give the best results employing the SST k-ω turbulence model, but the computational cost is more expensive as the grid contains a wake block that increases the number of cells.

The tonal self-noise emission of a vehicle side mirror and the associated flowfield are investigated experimentally. The relevant surface on the model includes a region of geometry-induced laminar ...

The tonal self-noise emission of a two-dimensional blunt-body side mirror model is investigated experimentally in order to characterize the underlying source mechanism. The two-dimensional side mirror design is closely related to an automotive side mirror model 1 which generates tonal self-noise. The examined flow field and tonal noise emission of the two-dimensional side mirror indicates the existence of an aeroacoustic feedback mechanism comprising convective boundary layer instability waves, their scattering to acoustic waves at the trailing edge and the acoustic receptivity at a dominant feedback point. Fundamental evidence of this concept is found in the typical variation of the discrete-frequency noise emission with the free-stream velocity as well as a laminar flow separation in the vicinity of the trailing edge featuring massively amplified discrete-frequency modes. The existence of an aeroacoustic feedback loop is finally confirmed by the systematic variation of the feedback loop resonance length, which is a crucial loop parameter.

The flow in the near-field wake region of a generic transport aircraft configuration has been studied using both unsteady RANS and delayed detached-eddy simulations. The NASA Common Research Model has been used for this purpose, as experimental data obtained with this model in the cryogenic European Transonic Wind Tunnel during the ESWIRP test campaign were available for comparison and validation. Focusing on high angles of attack of $$\alpha = 16^\circ$$ and $$\alpha = 18^\circ$$ , the results form the basis for the study of flow phenomena occurring at stall conditions. Such flight conditions are characterized by massive flow separation at the wing and highly unsteady flow in the wake. In a first step, the numerical results are compared with available test data using global force coefficients and pressure distributions on the wing. Both show a good agreement of numerical and experimental results, indicating slight deviations of the pressure variable at the inboard wing sections. In a second step, the turbulent structures of the near-field wake are examined using the proper orthogonal decomposition method based on snapshots (two-dimensional instantaneous flow fields). Frequencies of the first mode-pair match the dominant frequencies of the lift and velocity wake spectra very well.

This paper presents recent developments in finding alternative shielding functions in the framework of Delayed Detached-Eddy Simulation (DDES). The weaknesses of the standard shielding function are elaborated for the turbulent flow over a flat plate and an axisymmetric adverse pressure gradient flow. In both cases a small filter width compared to the boundary layer height caused a degeneration of the shielding function and led to severe model stress depletion. To overcome the strong grid dependency of the standard shielding two alternative shielding functions are proposed. The first determines the boundary layer edge by integrating the vorticity in the wall-normal direction, while separated flow is identified based on a comparative analysis of the individual vorticity components. For the second switching function the boundary layer edge is estimated by evaluating a localized formulation of the Bernoulli equation. The shielding disintegrates under resolved turbulent content by a sensor that includes the \(\sigma \)-velocity gradient operator. The novel shieldings are verified for basic canonical test cases. Compared to DDES, a superior protection of attached boundary layers could be demonstrated.