Delayed Detached Eddy Simulation Research Articles

Study on the Applicability of URANS, Large Eddy Simulations, and Hybrid Large Eddy Simulations/RANS Models for Prediction of Hydrodynamics of Cyclone Separator

Abstract Cyclone separators are an integral part of many industrial processes. A good understanding of the flow features is paramount to efficiently use them. The turbulent fluid flow characteristics are modeled using unsteady Reynolds-averaged Navier–Stokes (URANS), large eddy simulations (LES), and hybrid LES/Reynolds–averaged Navier–Stokes (RANS) turbulent models. The hybrid LES/RANS approaches, namely, detached eddy simulation (DES), delayed detached eddy simulation (DDES), and improved delayed detached eddy simulation (IDDES) based on the k−ω SST RANS approaches are explored. The study is carried out for three different inlet velocities (v = 8, 16.1, and 32 m/s). The results from hybrid LES/RANS models are shown to be in good agreement with the experimental data available in the literature. Reduction in computational time and mesh size are the two main benefits of using hybrid LES/RANS models over the traditional LES methods. The Reynolds stresses are observed in order to understand the redistribution of turbulent energy in the flow field. The velocity profiles and vorticity quantities are explored to obtain a better understanding of the behavior of fluid flow in cyclone separators.

Spectral proper orthogonal decomposition of compressor tip leakage flow

To identify the spatiotemporal coherent structure of compressor tip leakage flow, spectral proper orthogonal decomposition (SPOD) is performed on the near-tip flow field and the blade surface pressure of a low-speed compressor rotor. The data used for the SPOD analysis are obtained by delayed-detached eddy simulation, which is validated against the experimental data. The investigated rotor near-tip flow field is governed by two tip leakage vortices (TLV), and the near-tip compressor passage can be divided into four zones: the formation of main TLV (Zone I), the main TLV breakdown (Zone II), the formation of tip blockage cell (Zone III), and the formation of secondary TLV (Zone IV). Modal analysis from SPOD shows that a major part of total disturbance energy comes from the main TLV oscillating mode in Zone I and the main TLV vortex shedding mode in Zone III, both of which are low-frequency and low-rank; on the contrary, modal components in Zones II and IV are broadband and non-low-rank. Unsteady blade forces are mainly generated by the impingement of the main TLV on the blade pressure surface in Zone III, rather than the detachment of the secondary TLV from the blade suction surface in Zone IV. These identified coherent structures provide valuable knowledge for the aerodynamic/aeroelastic effects, turbulence modeling, and reduced-order modeling of compressor tip leakage flow.

Numerical analysis of the wake of complex-shaped snow particles at moderate Reynolds number

Climate model parametrization relies strongly on the prediction of snow precipitation, which in turn depends upon the snowflakes falling motion in air. The falling attitudes of such particles are elaborate because of the particles' irregular shapes, which produce meandering and turbulent wakes and give rise to convoluted trajectories. This also has an impact on the drag experienced by the particle. Especially for large snow particles falling close to the ground, Stokesian dynamics is not applicable, and the dependency of drag coefficient on Reynolds number becomes non-linear. This trend arises from the complex interaction between snowflakes and the surrounding air. We investigate the wake of complex-shaped snow particles using a validated delayed-detached eddy simulation model of airflow around a fixed snowflake, combined with experimental observations of free-falling, 3D-printed snowflake analogs. This novel approach allows us to analyze the wake topology and decompose its momentum flux to investigate the influence of shape and wake flow on the drag coefficient and its implications on falling attitudes by comparison with experiments. At low Re, the presence of separated vortex rings is connected to particle porosity and produces an increase in the drag coefficient. At moderate flow regimes, the particle flatness impacts the shear layer separation and the momentum loss in the wake, while at high Re the drag coefficient has almost the same value among the tested geometries although the contribution of different momentum flux terms differs. These results represent a further step toward a deeper understanding the drag of complex-shaped particles.

Delayed-Detached Eddy Simulations of Film Cooling Effect on Trailing Edge Cutback With Land Extensions

Abstract Film cooling effect on trailing edge cutback with land extensions (i.e., landed case) was numerically investigated with the delayed-detached eddy simulation (DDES) method. At three rib geometries (i.e., inline rib arrays, six-row pin-fin arrays, and five-row pin-fin arrays) and five blowing ratios (i.e., M = 0.5, 0.8, 1.1, 1.5, and 2.0), film cooing effectiveness, coherent vortex structures, and discharge coefficients for the landed cases were analyzed and compared with baseline cases (i.e., cutback without land extensions). The results show that land extensions have significant influences on coherent flow structures, vortex energy levels, film cooling effectiveness, and discharge coefficients in cutback region. Different from the baseline cases, the dominant vortex structures in landed cases exhibit the “double helix” (for cutback with inline rib array) or “strip” pattern (for cutback with pin-fin arrays), and the thickness of mixing region in landed cases is decreased. Among three rib geometries, the trailing edge cutback with six-row pin-fin arrays has the worst cooling effect for both baseline and landed cases. Compared with the baseline cases, the discharge coefficients for the landed cases are decreased by about 21.4%. With land extensions, the overall film cooling effectiveness on cutback is decreased first and then increased with increasing blowing ratio. Among all investigated cases, cutback with five-row pin-fin arrays for the landed case performs the best film cooling effect at M = 0.5.

Numerical investigation of tip-vortex cavitation noise of submarine propellers using hybrid computational hydro-acoustic approach

In this study, the hybrid computational hydro-acoustics (CHA) method is applied to predict hydrodynamic noise due to tip vortex cavitation (TVC) of underwater submarine propellers. The hybrid CHA approach consists of two sequential methods: Delayed Detached Eddy Simulation (DDES) technique with adaptive mesh refinement method and the Ffowcs Williams and Hawkings (FW–H) equation. The former is utilized for accurate prediction of TVC of underwater propellers, and the latter is used for efficient prediction of hydro-acoustic pressure due to cavitating flow. The target submarine and propeller are the DARPA suboff submarine and two high skew propellers with skew angles of 17 and 38°. The propellers are designed to investigate the effects of skew angle on TVC and its noise. The corresponding experiments are performed in the Large Cavitation Tunnel (LCT) of the Korea Research Institute of Ships and Ocean Engineering (KRISO). The two preliminary simulations are carried out to confirm the close reproduction of the experimental conditions in the main simulations. First, the flow through the LCT test section is simulated to confirm the accurate reproduction of the wall boundary layer. Its validity is confirmed by comparing the predicted boundary layer profiles with the measured results. Second, the flow over the DARPA suboff submarine without a propeller in the LCT test section is simulated to confirm the accurate prediction of the inflow distortion originating from the boundary layer flow of the submarine body. Its validity is also confirmed by comparing the predicted nominal wake field with the measured one. After the close reproduction of these two effects is confirmed, the cavitating flow of the propellers installed to the DARPA suboff submarine body is simulated by using the DDES technique combined with adaptive mesh refinement, and the TVC noise is predicted by applying the quadrupole-corrected FW-H equation to the surfaces enclosing the propellers. The predicted TVC of the propeller closely follows the measured one. The numerical and experimental results capture the TVC induced by the wake flows due to the submarine body's rudders and sail. The predicted hydro-acoustic pressure spectra due to the propellers' cavitating flow also show excellent agreements with the predicted ones. Besides, both the numerical and experimental results confirm that the lower noise is generated by the propeller with a higher skew angle.

Entropy production analysis for vortex rope of a Francis turbine using hybrid RANS/LES method

The precessing vortex core in the draft tube of Francis turbine is investigated using entropy production method. The high-fidelity Delayed Detached Eddy Simulation (DDES) method with SST k-ω turbulence model is used to acquire the entropy dissipative components of the flow, and the Q-criterion is selected to evaluate the vortex cores inside the draft tube under different operating conditions, separately. The results show that the numerical simulation is in good agreement with the experimental data obtained from the model test. It is found that the vortex motion, separation flow and shock phenomenon are considered to be hydrodynamic factors for the formation of entropy. Furthermore, draft tube accounts for the greatest proportion of entropy production, which is ascribed to the vortex rope. Vortex rope will rotate in the same direction as the runner, but the rotational speed is lower, resulting in low frequency pressure pulsation with large amplitude in the draft tube. It is concluded that the key reason why great energy dissipation is caused in the draft tube is that the vortex rope is transporting continuously towards the downstream, especially when the turbine deviating from optimum operating point.

Study of wind loading and flow characteristics on an array of parabolic trough collectors

Wind loads and structure of the flow field around an array of parabolic trough collectors (PTCs) were investigated using Delayed Detached Eddy Simulation (DDES) method. A scaled three-dimensional (3D) model was adopted and simulated using the ANSYS-Fluent software. Several pitch angles, including θ = 0°, 45°, 135°, and 180° and the stow mode with the pitch angle, θ = 90°, and flow Reynolds number of 2×105, are considered for numerical solutions. For validation of the numerical model, the mean wind load coefficient on a stand-alone PTC and an array model of PTCs were simulated and compared with the wind tunnel data. Detailed analysis of wind characteristics and wind loading on an array for five-pitch angles was provided. Results demonstrated that except for the stow mode, the first PTC in the array experienced the maximum mean pressure in the upwind side of the PTCs model and corresponded to the maximum mean drag coefficient. Besides, the minimum mean drag coefficient belongs to the second row in the array except for the stow mode. A comparison between flow patterns around the PTCs revealed the high vorticity concentration in front of the collectors for pitch angles θ = 0° and θ = 180°.

Assessing the performance and the wake recovery rate of flapping-foil turbines with end-plates and detached end-plates

Three-dimensional numerical simulations of hydrokinetic flapping-foil turbines with fully-prescribed motions are carried out using a Delayed Detached-Eddy Simulation (DDES) approach. The objective is to assess the efficiency and the wake recovery rate of flapping-foil turbines equipped with either end-plates or detached end-plates. The power coefficient and the mean streamwise velocity recovery in the wake of a turbine with different geometries of end-plates and detached end-plates are analyzed and the results are compared to a high-efficiency reference turbine without end-plates. We show that the turbine efficiency is significantly increased when detached end-plates are used. Indeed, the best configuration simulated in this work has an efficiency value that is 21% larger than that of the reference turbine. Moreover, the main physical mechanisms affecting the wake recovery rate are the same whether or not detached end-plates are used. Interestingly, for a turbine with small detached end-plates, the mean streamwise velocity recovery in the wake is similar to that of the reference turbine, while the efficiency is increased by 15%. This suggests that such detached end-plates could be quite beneficial for flapping-foil turbines operating in turbine farms.

Effects of Blade Pressure Side Modification on Unsteady Pressure Pulsation and Flow Structures in a Centrifugal Pump

Abstract In this paper, the effects of modifying the blade pressure side (PS) on unsteady pressure pulsation and flow structures in a low specific speed centrifugal pump are carried out by experimental and computational fluid dynamics (CFD). Seven monitor points are arranged in the circumferential direction of the impeller outlet to capture the pressure signals in the volute at flow rate of 0.2–1.6Qd. Results show that the blade PS modification introduced here can significantly alleviate the amplitude of pressure pulsation at blade passing frequency (fBPF) in all concerned operation conditions. To study the effects of blade modification on the internal flow field, the volute domain is replaced by an even outlet region for CFD analysis. The shear stress transfer (SST) turbulence model is adopted for steady-state numerical simulation while the delayed detached eddy simulation (DDES) based on the SST approach is adopted for transient simulation. Results show that local unsteady velocity fluctuation is the dominant reason for pressure pulsation in the volute. After blade PS modification, the relative velocity distribution at the impeller outlet is more uniform and the intensity of shedding vortex at the blade trailing edge (TE) decreases significantly. The change of internal flow structure improves the uniformity of circumferential velocity distribution the downstream of the impeller outlet, which leads to the decrease of pressure fluctuation amplitude in the volute. Meanwhile, the local Euler head (LEH) distribution at the impeller outlet and the blade loading of PS are presented and compared. It can be concluded that the reduction of pressure pulsation attributes to a more uniform energy distribution at the impeller outlet which is achieved by actively unloading the PS of the modified blades.

Turbulent flow structure and heat transfer mechanisms over surface vortex structures of micro V-shaped ribs and dimples

Turbulent flow and heat transfer characteristics in the channels with surface vortex structures of micro V-shaped ribs, dimples, and their hybrid structures have been investigated by carrying out delayed detached eddy simulations (DDES) at the Reynolds number of 50,500. It is found that, for the micro V-shaped rib, lower turbulent mixing is produced behind the leeward rib region, while the stronger longitudinal vortex pairs induced by the V-shaped ribs enhance the convective transport of heat. For the dimple, the shed vortices and the shear-layer vortices increase the near-wall turbulent mixing. The complex secondary flows induced by the flow separation, attachment and ejection increase the convective transport of heat. However, the flow separation produces a dead-air zone limiting the further increase of heat transfer enhancement. For the micro V-shaped rib-dimple hybrid structure, the strong downwash flow induced by the micro V rib breaks the recirculation zone inside the downstream dimple and the dimple here works as a vortex amplifier, which produces much stronger longitudinal vortex pairs. This process enhances both the turbulent mixing and convective transport of heat. Therefore, the micro V-shaped rib-dimple hybrid structure provides even more pronounced heat transfer enhancement.

Vortex-induced Vibration and Control of Split Three-Box Girder Bridges

The vortex-induced vibration (VIV) performance and aerodynamic mechanism of VIV control of a split three-box girder bridge were investigated numerically by Computational Fluid Dynamics (CFD). Large-scale section model wind tunnel tests show that the integrated countermeasure combined by 30% ventilation ratio grids and new scheme for maintenance tracks can effectively restrain vertical and torsional VIVs. The reliability of numerical method is verified by comparing static three-component coefficients and Strouhal numbers obtained from CFD and wind tunnel tests. The flow structure and changes of aerodynamic forces were analyzed via delayed detached-eddy simulation (DDES). For the original section, large-scale vortices form with shedding behind the safety barrier of the upstream box and behind the maintenance tracks, as well above the downstream highway box, introducing periodic pulsating lifts and moments that result in severe VIVs. The grids can effectively reduce the size of vortices in the gaps, prevent the flow from fluctuating and reduce the pressure difference between upper and lower surfaces. The torsional VIVs at non-negative attack angles are not controlled because the grids cannot interfere with the vortices behind the maintenance tracks. The new scheme for maintenance tracks, which has grid-like effects, can eliminate the torsional VIVs at non-negative attack angles by preventing the vortices behind maintenance tracks from impacting downstream boxes. The aerodynamic force components are analyzed to find that box 1 mainly contributes the mean values and box 3 mainly contributes the fluctuating values. The integrated countermeasure can reduce the mean and RMS values of aerodynamic forces to varying degrees. The streamlines and RMS pressure contours indicate that the integrated countermeasure effectively reduced the wake height and vortices motion range, which is conducive to VIV control. This work lays a solid foundation for an in-depth understanding of the aerodynamic characteristics and optimization mechanism of split three-box girder bridges.

Numerical study on the supersonic near-wake flow structures of a cylinder at an angle of attack

The supersonic near-wake flow experiment conducted by Dutton on a cylinder with 10 degrees angle of attack was studied numerically with Delayed Detached Eddy Simulation (DDES) method. The wind tunnel test section were included in the geometry model to examine if its omission led to the unsuccessful prediction of several important flow features in previous studies. Flow structures were compared to experiment measurements, Gaitonde's k-ε model results and our previous Monotonically Integrated Large Eddy Simulation (MILES) results. It was revealed that with present geometry model and numerical method, good agreements with wind tunnel experiment result were obtained, including the wave structures, density fields and velocity fields. In particular, the inclusion of wind tunnel test section wall in geometry model reproduces the finite area nozzle exit flow and the expansion wave behind the recirculation zone in the actual experiment setup, which lead to correct prediction of the position of maximum streamwise velocity point. The present simulation also reproduced the uniform pressure profile and value observed in the experiment and the deviation between computation and experiment was within 10%. The flow field data obtained was further analyzed to investigate the vortex surface shape and recirculation region shape in near wake flow with non-zero angle of attack and significant differences were found compared to the zero angle of attack case. The vortex surfaces show a non-axisymmetric slitting movement in the near wake region, which gives an explanation to the non-circular density contour pattern on streamwise flow field slices. The recirculation region shape was identified with zero isosurface of streamwise velocity and was found to be of complex three-dimensional shape with maximum length beside the symmetry plane and a local minimum at windward side of the symmetry plane, which is significantly different from that of zero angle of attack case. The observation that the length of the recirculation zone was greatly reduced on the symmetry plane at non-zero angle of attack in previous study is due to the aforementioned local minimum on the symmetry plane. The reduction of recirculation length is much less if we consider the three-dimensional shape of the region.

Numerical analysis of the flow pattern in convergent vortex tubes for cyclone cooling applications

The use of swirling flows in cyclone cooling systems is a promising method for internal cooling applications for instance in the leading edge of gas turbine blades. However, vortex breakdown can occur in such flows, which is associated with an axial flow reversal.Within the scope of this investigation a numerical parameter study was conducted in order to explore the impact of convergent tube geometries on the flow pattern. For this purpose, Delayed Detached Eddy Simulations (DDES) were conducted for a Reynolds number of 10,000 and a swirl number of 5.3. First of all, the numerically obtained velocity field was compared to experimental data for a reference tube with a constant cross-section. This validation showed overall good agreement. Subsequently, the same reference tube was compared to four convergent tubes. The latter ones comprised three geometries with linearly decreasing diameters reaching convergence angles of 0.42deg., 0.61deg. and 0.72deg., respectively. Furthermore, an additional tube featuring a hyperbolic diameter decrease was considered.The current investigation demonstrates that convergent vortex tubes impose a flow acceleration that suppresses the vortex breakdown phenomenon. Moreover, the axial velocity can be associated to different flow regimes with supercritical and subcritical character. These regimes indicate that the flow field within convergent tubes is less affected by the outlet conditions. Moreover, a physical reason is given that explains the formation of different flow regimes and their associated backflow as pressure-driven phenomenon. Furthermore, a modified Q-criterion illustrates two double helix vortex systems that can both be stabilized by choosing an appropriate geometry.

Computational efficiency of CFD modeling for building engineering: An empty domain study

In computational wind engineering, Large Eddy Simulation (LES) operates with superior accuracy. However, this comes with a higher computational cost compared to Reynolds Averaged Navier-Stokes (RANS) models. We propose multiple strategies to reduce the computational cost without compromising accuracy. The turbulence synthesis approach is adopted for efficient inflow generation. To alleviate the issues with tedious and resource-consuming computations, the concept of ‘interpolation’ is endorsed. This approach allows the usage of identical inflow information for different arrangements of meshing. The effect of employing larger time-step and coarser mesh, on the performance of LES with wall functions, is also investigated. Several LES cases are studied, initially with special near-wall treatment, and later, with three different Subgrid Scale (SGS) models. The profiles of mean velocities, turbulence intensities, and integral length scales are examined, in addition to the velocity spectra. The horizontal homogeneity is assessed for all cases. The results show that the wall-adapting eddy viscosity (WALE) SGS model with LES can reduce the computational time at a lower error range. Besides, among three investigated hybrid models, the Detached Eddy Simulation (DES) and the Delayed Detached Eddy Simulation (DDES) provide a significant reduction in the computational cost, compared to LES with the dynamic one-equation eddy-viscosity SGS model, when the objective is to achieve a similar level of accuracy.

Hybrid RANS–LES Simulation of Turbulent Heat Transfer in a Channel Flow With Imposed Streamwise or Spanwise Mean Temperature Gradient

Abstract Computational fluid dynamics (CFD) results are presented for turbulent flow and heat transfer in a plane channel. This study investigates an idealized fully developed planar channel flow case for which the mean velocity gradient is nonzero only in the wall-normal direction, and the mean temperature gradient is imposed to be uniform and nonzero in the streamwise or spanwise direction. The objective is to evaluate the accuracy of turbulent heat flux predictions using hybrid Reynolds-averaged Navier–Stokes (RANS)–large eddy simulation (LES) models in wall-bounded flows. Results are obtained at Prandtl number of 0.71 and Reynolds number of 180 based on wall friction velocity and channel half-height and are compared to available direct numerical simulation (DNS) data and to a well-validated RANS model (k–ω shear-stress transport (SST)). The specific hybrid RANS–LES (HRL) models investigated include delayed detached eddy simulation (DDES), improved delayed detached eddy simulation (IDDES), and dynamic hybrid RANS–LES (DHRL). The DHRL model includes both the standard formulation that has been previously documented in the literature as well as a modified version specifically developed to improve predictive capability for flows in which the mean velocity and mean temperature gradients are not closely aligned. The modification consists of using separate RANS-to-LES blending parameters in the momentum and energy equations. Results are interrogated to evaluate the performance of the three different model types and specifically to evaluate the performance of the new modified DHRL variant compared with the baseline version.

Comparative assessment of SAS, IDDES and hybrid filtering RANS/LES models based on second-moment closure

The question of which turbulence model is better for a given class of applications is always confusing for the CFD researchers and users. Comparative assessments of scale-adaptive simulation (SAS), improved delay detached-eddy simulation (IDDES) and other hybrid RANS/LES models based on eddy-viscosity models (EVMs) are thoroughly investigated. But how well they perform based on a second-moment closure needs to be answered. In this paper, a widely acclaimed Reynolds-stress model (RSM) in aeronautical engineering, SSG/LRR-[Formula: see text] model, is carried out. The relevant test cases include the NACA0012 airfoil stalled flows and turret separated flow. In order to make a more reasonable comparison, a seventh-order scheme WCNS-E8T7 is adopted to reduce the influence of the numerical dissipation and a symmetrical conservative metric method is used to ensure the robustness. By comparing with the relevant experimental data and the solutions by original SSG/LRR-[Formula: see text] model (etc. URANS), it shows that all of the three hybrid methods (SAS, IDDES and hybrid filtering methods) based on the SSG/LRR-[Formula: see text] model have a good ability to simulate unsteady turbulence. Among them, the IDDES correction has the most potential.

Assessment of Methods for Calculating Liquefied Natural Gas Pump Tower Loads

Abstract This paper presents a comparative numerical study on liquefied natural gas (LNG) pump tower loads, while focusing on two aspects. First, are impact loads relevant for the structural design of LNG pump towers and, second, in which way does fluid–structure interaction influence these loads? Numerical simulations of the multiphase problem were conducted using viscous field methods. First, unsteady Reynolds-averaged Navier–Stokes (URANS) equations, extended by the volume of fluid (VoF) approach, were used to simulate, at model scale, the flow inside a three-dimensional LNG tank without the tower structure. Then, these results were used to validate the numerical method against model test measurements. Afterward, motion periods and amplitudes were systematically varied in the flow simulations. Flow velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations based on the Morison equation. Finally, these load approximations were compared with loads determined from solving the delayed detached eddy simulation (DDES). Time histories as well as statistical measures of global loads acting on the entire and the simplified tower structure were of the same order of magnitude. However, their time evolution differed, especially at their peaks, and this was considered significant for structural design.

New Strategies for Mitigating the Gray Area in Delayed-Detached Eddy Simulation Models

This paper presents a new approach for mitigating the unphysical delay in the Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) transition, often referred to as the gray area, which is a common issue for hybrid RANS–LES turbulence models such as delayed-detached eddy simulation. An existing methodology designed for improving the LES performance in complex flows is adapted and tested. This is based on reducing the numerical diffusion in critical areas for permitting a more accurate development of turbulence. The new formulation comprises both a two-dimensional sensitive velocity gradient model and an alternative definition of the subgrid length scale, which are tested both individually and in tandem, and compared with the other formulations commonly used for addressing the gray area. Four test cases are examined, a flat plate, two variants of the incompressible backward-facing step, and an open jet compressible case, all of which are selected to expose the adverse impact of numerical diffusion that this study seeks to address. Furthermore, the proposed changes are implemented in two different codes for the purpose of cross-validation. Encouraging results are observed, supporting the suitability of the new approach as a candidate for addressing the gray area issue in flows of this kind.

Numerical study on the biomimetic trailing edge in the environment of a high-pressure turbine stage

In this study, the whisker structure of a harbor seal is applied to the trailing edge of a high-pressure turbine stage to reduce energy loss. The method to produce biomimetic geometry is provided. Two cases are studied in this paper including a prototype of a high-pressure turbine stage and this stage with the biomimetic trailing edge. The delayed detached-eddy simulation (DDES) method is used to simulate the flow of the stages. The energy loss coefficient of the turbine stage with the biomimetic trailing edge is significantly reduced. The analysis of the local entropy generation rate shows that the wake loss of the biomimetic stage and the loss in the blade passage are greatly reduced. Two reasons for the widening of the wake of the prototype vane during the downstream movement are analyzed. For the biomimetic stage, the Karman vortices are completely suppressed and transformed into small vortices with strong three-dimensional motion. The wake width of the biomimetic trailing edge is narrowed and the speed recovery becomes faster. This leads to the reduction of the wake loss and the interaction between the wake of the vane and the downstream blade.

A general model for trailing edge serrations simulation on wind turbine airfoils

Trailing edge serrations (TESs) are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade. However, the challenges involved in the dimensional design of serration height 2h, wavelength λ and flap angle φ are yet to be dealt with in a satisfactory manner. To address the problem, a general model for simulating the effects of serrations on the hydrodynamic and aeroacoustic performance is proposed due to its ease of use and relatively low requirements for user input. The solid serrations are replicated by momentum sources calculated by its aerodynamic forces. Then, a case relevant to wind turbine airfoil is examined, a hybrid improved delay detached eddy simulation (IDDES) method coupled with FW-H integration is deployed to obtain the flow features and far-field sound pressure level. It is found that the modeling method could reproduce the flow field and noise as serrated airfoil.