Synthetic Turbulence Generation Research Articles

Aeroelastic analyses of bridges using a Pseudo-3D vortex method and velocity-based synthetic turbulence generation

The accurate representation of aerodynamic forces is essential for a safe, yet reasonable design of long-span bridges subjected to wind effects. In this paper, a novel extension of the Pseudo-three-dimensional Vortex Particle Method (Pseudo-3D VPM) is presented for Computational Fluid Dynamics (CFD) buffeting analysis of line-like structures. This extension entails an introduction of free-stream turbulent fluctuations, based on the velocity-based turbulence generation. The aerodynamic response of a long-span bridge is obtained by subjecting the 3D dynamic representation of the structure to correlated free-stream turbulence in two-dimensional (2D) fluid planes, which are positioned along the bridge deck. The span-wise correlation of the free-stream turbulence between the 2D fluid planes is established based on Taylor’s hypothesis of frozen turbulence. Moreover, the application of the laminar Pseudo-3D VPM is extended to a multimode flutter analysis. Finally, the structural response from the Pseudo-3D flutter and buffeting analyses is verified with the response, computed using the semi-analytical linear unsteady model in the time-domain. Meaningful merits of the turbulent Pseudo-3D VPM with respect to the linear unsteady model are the consideration of the 2D aerodynamic nonlinearity, nonlinear fluid memory, vortex shedding and local non-stationary turbulence effects in the aerodynamic forces. The good agreement of the responses for the two models in the 3D analyses demonstrates the applicability of the Pseudo-3D VPM for aeroelastic analyses of line-like structures under turbulent and laminar free-stream conditions.

A numerical-experimental investigation on the aerodynamic performance of CAARC building models with geometric modifications

This paper presents the results of a numerical-experimental investigation carried out with the purpose to evaluate the aerodynamic performance of CAARC tall building models with different cross-section configurations. A numerical model based on the Taylor-Galerkin two-step scheme and the Finite Element Method is adopted. Turbulence is described using LES and a synthetic inflow turbulence generator. Experimental tests were performed at the Prof. Joaquim Blessmann Boundary Layer Wind Tunnel considering CAARC tall building models with cross-section modifications based on chamfered and recessed corners. Some of the wind tunnel predictions obtained here are compared with results obtained from the numerical model proposed in this work, where two and three-dimensional meshes are utilized. Comparisons are also performed considering results obtained from other authors in similar studies. From the present investigation, it was observed that the wind action on tall buildings is significantly influenced by the geometric configuration of the building corners, which may lead to important reductions in the aerodynamic forces. Through a direct comparison of results between numerical and experimental simulation, we can see that both reach a convergence of results, thus indicating the potential of use of CFD in the modern aerodynamic investigation of buildings.

A systematic approach to the generation of synthetic turbulence using spectral methods

In this paper, a systematic discussion on the generation of synthetic turbulence using spectral methods is presented. After a brief introduction which reviews existing methodologies, the role played by the fulfilment of the divergence-free condition and Taylor assumption is investigated. Special attention is given to the case in which such random fields are applied as inflow condition for Computational Fluid Dynamics simulations. Subsequently, a new methodology of general applicability for the generation of synthetic turbulence is proposed. The strength of the new approach lies in its generality and conceptual simplicity. The obtained random field fulfils the divergence-free condition as well as Taylor assumption and it is approximately characterised by preselected spectral content in each spatial direction, so also providing direct control over all turbulence integral scales. Synthetic turbulent fields characterised by different spectral content are generated confirming the soundness of the proposed approach and showing its ability to target strongly anisotropic fields. Finally, some remarks on the generation of inhomogeneous fields, obtained by combination of homogeneous ones, are provided so generalising the proposed procedure.

Numerical simulation of aeroacoustical noise from a wing-flap configuration

A noise-free volumetric synthetic turbulence generator has been applied for Embedded LES of the flow over the wing-flap configuration experimentally studied by Lemonie et al. Good agreement of CFD results with experimental data provides some evidence for the correctness of the chosen computational strategy, which includes a noise-free volumetric synthetic turbulence generator to create turbulent content, “sponge layers” to avoid the reflection of pressure waves from the external boundaries and the Ffowcs Williams, Hawkings acoustic model for calculating far-field noise.

Unsteady Simulations of a Fan/Outlet-Guide-Vane System: Aerodynamics and Turbulence

The Paper presents the aerodynamic and turbulent aspects of a project devoted to creating and validating a high-fidelity computational-fluid-dynamics-based system for the prediction of the performance and noise associated with the fan/outlet-guide-vane configuration typical of modern turbofan aeroengines. Such a tool will be of significant value for evaluating low-cost analytical methods needed for tradeoff studies and fine tuning of low-order computational models for engine performance and noise prediction. For turbulence representation, the system offers two approaches: the unsteady Reynolds-averaged Navier–Stokes equations, and a zonal approach that treats the part of the flowfield upstream of the fan by unsteady Reynolds-averaged Navier–Stokes and the remaining part (the interstage, outlet guide vane, and exhaust regions) by improved delayed detached-eddy simulation combined with a volume synthetic turbulence generator for triggering the scale-resolving capability of the improved delayed detached-eddy simulation. Details of the proposed methodology are outlined, including problem statements for simplified (“duct-only”) and full (including the entire nacelle and external flow) configurations. The results are presented, demonstrating the capabilities of the methodology and its validation by means of comparison of the mean and unsteady flow characteristics with experimental data for the NASA source diagnostic test. The numerical database will be used for the investigation of noise-generation/propagation phenomena.

Optimizing turbulent inflow conditions for large-eddy simulations of the atmospheric boundary layer

Large-eddy simulations (LES) of the atmospheric boundary layer (ABL) require the specification of a turbulent inflow condition with appropriate turbulence intensities and length scales. When using a synthetic turbulence generator, the statistics obtained downstream of the inlet might deviate considerably from the intended values. In the present work we propose a fully automated approach to modify the input parameters for the turbulence generator such that the desired turbulence statistics are obtained at the downstream location of interest. The method employs a gradient-based optimization in combination with the divergence-free version of the digital filter method developed by Xie and Castro [1, 2]. A sensitivity analysis showed that the spanwise and vertical Reynolds stresses and length scales are the most influential input parameters. Hence, the optimization adjusts these parameters until the desired turbulence statistics are obtained downstream in the domain. The results demonstrate the promising capabilities of the method: the mean velocity profile is correctly maintained using an appropriate wall function, while the optimization results in Reynolds stresses, integral length-scales and turbulence spectra that compare well to ABL wind tunnel measurements.

A Band-Width Filtered Forcing Based Generation of Turbulent Inflow Data for Direct Numerical or Large Eddy Simulations and its Application to Primary Breakup of Liquid Jets

Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) of spatially inhomogeneous flows strongly depend on turbulent inflow boundary conditions. Realistic coherent structures need to be prescribed to avoid the immediate damping of random velocity fluctuations. A new turbulent inflow data generation method based on an auxiliary simulation of forced turbulence in a box is presented. The new methodology combines the flexibility of the synthetic turbulence generation with the accuracy of precursor simulation methods. In contrast to most auxiliary simulations, the new approach provides full control over the turbulence properties and computational costs remain reasonable. The lack of physical information and artificiality attested with pseudo-turbulence methods is overcome since the inflow data stems from a solution of the Navier-Stokes equations. The generated velocity fluctuations are by construction divergence-free and exhibit the non-Gaussian characteristics of turbulence. The generated inflow data is applied to the simulation of multiphase primary breakup.

Generation of divergence free synthetic inflow turbulence with arbitrary anisotropy

The paper presents an improvement to the Turbulent Spot method for generation of synthetic turbulence. Earlier versions of the Turbulent Spot method and the Synthetic Eddy method were only able to produce turbulence which does not obey the continuity constraint in general. This was only possible for special cases (isotropic or near-isotropic turbulence).The proposed extension enables the generation of arbitrary anisotropic turbulence and fulfillment of the continuity constraint at the same time. This is made possible by the introduction of a new type of turbulent structure. The derivation of the internal velocity field is given. Also, expressions for the statistical properties of the new structure are derived.The performance of the proposed extension is illustrated on generic test cases.

Synthetic generation of equilibrium boundary layer turbulence from modeled statistics

An improved synthetic digital filtering method (SDFM) for the generation of equilibrium turbulence is described, with emphasis on the ease of application to complex configurations. This is achieved by facilitating the use of modeled (RANS) statistics for the mean flow and Reynolds stress profiles, instead of simulated (DNS or LES) statistics that are not readily available for three-dimensional flows. The effects on boundary layer relaxation with modeled statistics are first quantified for a well-known canonical situation, specifically, Mach 2 equilibrium turbulent boundary layers over 250 < Reθ < 2220. Various convergence criteria are assessed in terms of the streamwise coordinate (x) normalized by the incoming boundary layer thickness (δ0). These include skin-friction, which requires x/δ0 ≈ 12 for equilibrium, inner scale mean velocity (x/δ0 ≈ 16), inner scale Reynolds stresses (x/δ0 ≈ 18), as well as outer scale mean velocity, Reynolds stresses, and spatio-temporal correlations (x/δ0 ≈ 40–50). Development lengths are shown to be inversely related to Reynolds number. In terms of boundary layer relaxation length, initializing the method with RANS (versus simulated) statistics incurs a negligible penalty in inner coordinates and a mild penalty (x/δ0 ≈ 5–10) in outer coordinates. The effectiveness of this approach is then demonstrated by application to significantly more complex three-dimensional flows, including internal single and multi-stream flows, for which synthetic turbulence generation techniques are necessary, but precursor high-fidelity simulations are not available. Thus, the RANS-initialized SDFM provides a rapidly adaptable method for the synthetic generation of wall-bounded turbulence.

Large-Eddy and Direct Numerical Simulations of the Bachalo-Johnson Flow with Shock-Induced Separation

The Bachalo-Johnson experiment on an axisymmetric bump has been a primary validation case for turbulence models in shock-boundary-layer interactions since the 1980’s. In the present work, Wall-Modelled Large-Eddy Simulations (WMLES) of this flow were conducted using Improved Delayed Detached-Eddy Simulation (IDDES) as the sub-grid-scale (SGS) and wall model, with a synthetic turbulence generator, expecting close enough agreement with experiment. However, the WMLES results are disappointing, even in terms of the shock position, even though the results from two grids with 4.7 × 108 and 1.6 × 109 cells respectively agree well with each other. This failure of grid refinement to warn of an inaccurate simulation is of great concern, and the reasons for it are explored. We then conducted a Direct Numerical Simulation (DNS) embedded in the LES over a reduced domain, with 8 × 109 grid cells. The DNS has a far more accurate shock position and overall pressure distribution. The skin friction in the favourable pressure gradient is also much higher than in the LES; thus, wide differences appear upstream of the shock wave, most probably caused by the rapid acceleration which leads to atypical shear-stress profiles. Other SGS models were tried, and performed worse than IDDES. The DNS essentially fulfils the initial expectations although in a reduced domain and provides data for turbulence-modelling studies, for instance by extracting an effective eddy viscosity from it. The most noticeable remaining disagreement with experiment is over the Reynolds shear stress.

Optimized temperature perturbation method to generate turbulent inflow conditions for LES/DNS simulations

Abstract The temperature perturbation method (TPM) is used as an alternative technique to the classical velocity perturbations to generate inflow turbulence for LES or DNS simulations. The TPM consists in seeding the flow with random temperature perturbations which, through a buoyancy triggered mechanism, will induce the creation of turbulent structures. Naturally, this implies that the physical buoyancy effects need to be sufficiently strong, which has limited up to now its application to atmospheric flows. The proposed modification makes it applicable to a wider variety of wall-bounded flows, that would involve much smaller length scales than in the atmosphere. In this novel approach, a perturbation zone is defined at the entrance of the domain, along which an artificial local Richardson number is applied so that buoyancy effects are sufficiently strong to create turbulence. The TPM is implemented in the incompressible solver of OpenFOAM v2.3 with buoyancy effects and tested on a plane channel flow at R e τ = 395 . Prior to testing, periodic channel flow results are obtained to represent the reference fully developed turbulent state. The perturbation zone is divided into a fully active zone, where buoyancy is maximum, and a transition zone, needed to insure a smooth progression back to zero buoyancy. Several perturbation functions are applied to modulate these artificial effects, in order to identify the function that most efficiently pre-mixes the flow, thus preventing stratification effects from slowing down the flow recovery. Thereafter, the transition length and the artificial local Richardson number are optimized, based on wall shear stress recovery. Moreover, the effect of the perturbation frequency on not only the flow solution but also the energy spectra is examined in order to prevent the technique from contaminating the energy content. The flow development is compared to the synthetic turbulence generator method of Xie and Castro [1] in terms of the recovery distances of both the wall shear stress and the Reynolds stresses. The optimized method appears to be efficient with a flow that reaches equilibrium and a good quality energy spectra after about 15 δ . Although this final length remains similar to that obtained by competing methods, the optimized TPM benefits from a greater flexibility since only first-order statistics are required as input. Therefore, it can be applied without prior knowledge of second order moments or integral length scales, making it directly applicable to a wide variety of flows.

A study of unsteady hydrodynamic effects in the stern area of river cruisers in shallow water

ABSTRACTThe aim of the presented research was to determine, how the fairway depth restriction can influence the hydrodynamic exciters of ship stern vibration. A series of computations of the flow around the inland cruise ship was conducted using the hybrid URANS/LES turbulence modelling methods in conjunction with the synthetic turbulence generation. The computational method was tested for the prediction of the wake of an inland ship in model scale and afterwards applied for a typical river cruiser geometry. A range of the depth-to-draft ratios and the drift angles was studied. The flow around the cruise ship was simulated both with and without propulsors. Based on the simulations, the statistical analysis of the longitudinal velocity field in the propeller plane, thrust fluctuations and pressure pulses on the hull was performed. It was shown that all the hydrodynamic sources of stern vibration are intensified when the ship enters the restricted waters. Under certain conditions, the velocity fluctuations can reach 25% of the ship speed, the thrust fluctuations can be as high as 6.5% of the mean and the amplitude of the pressure pulses can increase to 8 kPa. Analysis of the cavitation inception regions showed that the risk of cavitation can increase in shallow water.Abbreviations: CFD: computational fluid dynamics; (U)RANS: (Unsteady) Reynolds-Averaged Navier–Stokes; LES: Large-Eddy Simulation; SST: shear stress transport; IDDES: improved delayed detached Eddy simulation; SIMPLE: semi-implicit method for pressure-linked equations; PISO: pressure-implicit with splitting of operator; TVD: total variation diminishing; EDF: empirical distribution function

Application of the PITM Method Using Inlet Synthetic Turbulence Generation for the Simulation of the Turbulent Flow in a Small Axisymmetric Contraction

We investigate the turbulence modeling of second moment closure used both in RANS and PITM methodologies from a fundamental point of view and its capacity to predict the flow in a low turbulence wind tunnel of small axisymmetric contraction designed by Uberoi and Wallis. This flow presents a complex phenomenon in physics of fluid turbulence. The anisotropy ratio of the turbulent stresses τ 11/τ 22 initially close to 1.4 returns to unity through the contraction, but surprisingly, this ratio gradually increases to its pre-contraction value in the uniform section downstream the contraction. This point constitutes the interesting paradox of the Uberoi and Wallis experiment. We perform numerical simulations of the turbulent flow in this wind tunnel using both a Reynolds stress model developed in RANS modeling and a subfilter scale stress model derived from the partially integrated transport modeling method. With the aim of reproducing the experimental grid turbulence resulting from the effects of the square-mesh biplane grid on the uniform wind tunnel stream, we develop a new analytical spectral method of generation of pseudo-random velocity fields in a cubic box. These velocity fields are then introduced in the channel using a matching numerical technique. Both RANS and PITM simulations are performed on several meshes to study the effects of the contraction on the mean velocity and turbulence. As a result, it is found that the RANS computation using the Reynolds stress model fails to reproduce the increase of anisotropy in the centerline of the channel after passing the contraction. In the contrary, the PITM simulation predicts fairly well this turbulent flow according to the experimental data, and especially, the “return to anisotropy” in the straight section of the channel downstream the contraction. This work shows that the PITM method used in conjunction with an analytical synthetic turbulence generation as inflow is well suited for simulating this flow, while allowing a drastic reduction of the computational resources.

On the generation of synthetic divergence-free homogeneous anisotropic turbulence

It is well known that the generation of appropriate unsteady boundary conditions represents an important component of successful Large Eddy Simulations in turbulent flows. In particular, when Computational Wind Engineering applications are considered, a recurrent problem consists in imposing turbulent fluctuations characterized by given spectra and length scales at the inlet boundary. In the present contribution, firstly, currently available techniques for the generation of synthetic turbulence are revised with a focus on their mathematical formulation. Then, two new approaches for the generation of homogeneous turbulence are proposed. The first one can be seen as a correction over existing techniques which allows to control the obtained length scales. The second method, conceived to generate anisotropic turbulence characterized by arbitrary harmonic content in both time and space, is designed to be computationally efficient, to guarantee the divergence-free condition and to ensure a good approximation of the resulting turbulence integral scales. Finally, the procedure is validated by synthesizing a homogeneous turbulent field characterized by time and length scales typical of the atmospheric boundary layer showing good results.

Assessment of RANS and DES methods for realistic automotive models

This paper presents a comprehensive investigation of RANS and DES models for the Ahmed car body and a realistic automotive vehicle; the DrivAer model. A variety of RANS models, from the 1-equation Spalart Allmaras model to a low-Reynolds number Reynolds Stress model have shown an inability to consistently correctly capture the flow field for both the Ahmed car body and DrivAer model, with the under-prediction of the turbulence in the initial separated shear layer found as a key deficiency. It has been shown that the use of a hybrid RANS-LES model (in this case, Detached Eddy Simulation) offers an advantage over RANS models in terms of the force coefficients, and general flow field for both the Ahmed car body and the DrivAer model. However, for both cases even at the finest mesh level hybrid RANS-LES methods still exhibited inaccuracies. Suggestions are made on possible improvements, in particular on the use of embedded LES with synthetic turbulence generation. Finally the computational cost of each approach is compared, which shows that whilst hybrid RANS-LES offer a clear benefit over RANS models for automotive relevant flows they do so at a much increased cost.

Zonal RANS–LES approach based on an algebraic reynolds stress model

The zonal RANS–LES approach based on the algebraic EARSM Reynolds stress model is considered. Using the EARSM model makes it possible to increase the accuracy of modeling the turbulent parameters at the RANS–LES interface in the case of flows in asymmetric designs and near dihedrals. This favors the more accurate modeling of vortex structures by the synthetic turbulence generator and, as a consequence, the narrowing of the transition zone behind the RANS–LES interface. The application of this approach is analyzed with reference to the examples of flows in a square channel and an asymmetric diffuser.

A stochastic perturbation method to generate inflow turbulence in large-eddy simulation models: Application to neutrally stratified atmospheric boundary layers

Despite the variety of existing methods, efficient generation of turbulent inflow conditions for large-eddy simulation (LES) models remains a challenging and active research area. Herein, we extend our previous research on the cell perturbation method, which uses a novel stochastic approach based upon finite amplitude perturbations of the potential temperature field applied within a region near the inflow boundaries of the LES domain [Muñoz-Esparza et al., “Bridging the transition from mesoscale to microscale turbulence in numerical weather prediction models,” Boundary-Layer Meteorol., 153, 409–440 (2014)]. The objective was twofold: (i) to identify the governing parameters of the method and their optimum values and (ii) to generalize the results over a broad range of atmospheric large-scale forcing conditions, Ug = 5 − 25 m s−1, where Ug is the geostrophic wind. We identified the perturbation Eckert number, Ec=Ug2/ρcpθ̃pm, to be the parameter governing the flow transition to turbulence in neutrally stratified boundary layers. Here, θ̃pm is the maximum perturbation amplitude applied, cp is the specific heat capacity at constant pressure, and ρ is the density. The optimal Eckert number was found for nonlinear perturbations allowed by Ec ≈ 0.16, which instigate formation of hairpin-like vortices that most rapidly transition to a developed turbulent state. Larger Ec numbers (linear small-amplitude perturbations) result in streaky structures requiring larger fetches to reach the quasi-equilibrium solution, while smaller Ec numbers lead to buoyancy dominated perturbations exhibiting difficulties for hairpin-like vortices to emerge. Cell perturbations with wavelengths within the inertial range of three-dimensional turbulence achieved identical quasi-equilibrium values of resolved turbulent kinetic energy, q, and Reynolds-shear stress, 〈w′u′〉. In contrast, large-scale perturbations acting at the production range exhibited reduced levels of 〈w′u′〉, due to the formation of coherent streamwise structures, while q was maintained, requiring larger fetches for the turbulent solution to stabilize. Additionally, the cell perturbation method was compared to a synthetic turbulence generator. The proposed stochastic approach provided at least the same efficiency in developing realistic turbulence, while accelerating the formation of large-scales associated with production of turbulent kinetic energy. Also, it is computationally inexpensive and does not require any turbulent information.

Anisotropic linear forcing for synthetic turbulence generation in large eddy simulation and hybrid RANS/LES modeling

A general forcing method for Large Eddy Simulation (LES) is proposed for the purpose of providing the flow with fluctuations that satisfy a desired statistical state. This method, the Anisotropic Linear Forcing (ALF) introduces an unsteady linear tensor function of the resolved velocity which acts as a restoring force in the mean velocity and resolved stress budgets. The ALF generalizes and extends several forcing previously proposed in the literature. In order to make it possible to impose the integral length scale of the turbulence generated by the forcing term, an alternative formulation of the ALF, using a differential spatial filter, is proposed and analyzed. The anisotropic forcing of the Reynolds stresses is particularly attractive, since unsteady turbulent fluctuations can be locally enhanced or damped, depending on the target stresses. As such, it is shown that the ALF is an effective method to promote turbulent fluctuations downstream of the LES inlet or at the interface between RANS and LES in zonal hybrid RANS/LES modeling. The detailed analysis of the influence of the ALF parameters in spatially developing channel flows and hybrid computations where the ALF target statistics are given by a RANS second-moment closure show that this original approach performs as well as the synthetic eddy method. However, since the ALF method is more flexible and significant computational savings are obtained, the method appears a promising all-in-one solution for general embedded LES simulations.

Gradual wavelet reconstruction of the velocity increments for turbulent wakes

This work explores the properties of the velocity increment distributions for wakes of contrasting local Reynolds number and nature of generation (a cylinder wake and a multiscale-forced case, respectively). It makes use of a technique called gradual wavelet reconstruction (GWR) to generate constrained randomizations of the original data, the nature of which is a function of a parameter, ϑ. This controls the proportion of the energy between the Markov-Einstein length (∼ 0.8 Taylor scales) and integral scale that is fixed in place in the synthetic data. The properties of the increments for these synthetic data are then compared to the original data as a function of ϑ. We write a Fokker-Planck equation for the evolution of the velocity increments as a function of spatial scale, r, and, in line with previous work, expand the drift and diffusion terms in terms up to fourth order in the increments and find no terms are relevant beyond the quadratic terms. Only the linear contribution to the expansion of the drift coefficient is non-zero and it exhibits a consistent scaling with ϑ for different flows above a low threshold. For the diffusion coefficient, we find a local Reynolds number independence in the relation between the constant term and ϑ for the multiscale-forced wakes. This term characterizes small scale structure and can be contrasted with the results for the Kolmogorov capacity of the zero-crossings of the velocity signals, which measures structure over all scales and clearly distinguishes between the types of forcing. Using GWR shows that results for the linear and quadratic terms in the expansion of the diffusion coefficient are significant, providing a new means for identifying intermittency and anomalous scaling in turbulence datasets. All our data showed a similar scaling behavior for these parameters irrespective of forcing type or Reynolds number, indicating a degree of universality to the anomalous scaling of turbulence. Hence, these terms are a useful metric for testing the efficacy of synthetic turbulence generation schemes used in large eddy simulation, and we also discuss the implications of our approach for reduced order modeling of the Navier-Stokes equations.

Assessing the influence of inflow turbulence on noise and performance of a tidal turbine using large eddy simulations

Large eddy simulations of a model scale tidal turbine encountering inflow turbulence have been performed. This has allowed both unsteady blade loading and hydrodynamic noise radiation to be predicted. The study is motivated by the need to assess environmental impact of tidal devices, in terms of their acoustic impact on marine species.Inflow turbulence was accounted for using a synthetic turbulence generator, with statistics chosen to represent the gross features of a typical tidal flow. The turbine is resolved in a fully unsteady manner using a sliding interface technique within the OpenFOAM® libraries. Acoustic radiation is estimated using a compact source approximation of the Ffowcs Williams–Hawkings equation.It is observed that the long streamwise length scale of the inflow turbulence results in characteristic ‘humps’ in the turbine thrust and torque spectra. This effect is also evident in the far-field noise spectra. The acoustic sources on the blades are visualised in terms of sound pressure level and “Powell's source term”. These measures show that the dominant sources are concentrated at the blade leading edges towards the tip. This results from the high loading of the turbine blades, and causes the sound to radiate more akin to a monopole than a dipole.The full scale source level, obtained from scaling of the simulation results, is found to be lower than comparable measured data reported in the literature; this is attributed to additional sources not included in the present study. Based on the predicted source level, no physical impact on fish is expected.