The Influence of Different Arrangements of Shallow Dimples on the Resistance of Plates Subjected to Relative Fluid Motion

Shallow dimples have long been a scientifically investigated topic to reduce the flow resistance of objects subjected to overflow. Most of the investigations on the influence of dimples on flow resistance have so far been carried out experimentally. Although the arrangements and flow conditions are often similar, different research activities conclude differently concerning the effect of the surface structures. This also leads to disagreement regarding the causes of flow resistance reductions. In this paper, time-resolved Large Eddy Simulations on two different, already experimentally investigated setups of dimples have been carried out to better understand the effects of dimples on the surface being subjected to relative fluid motion. In one case the dimples were examined in overlapping arrangement, in the other case in a non-overlapping arrangement. We were able to show that the formation of streaks near the surface significantly influences the local contribution to the flow resistance. For the overlapping arrangement, only a slight resistance reduction of 0.12% was determined. For the non-overlapping arrangement, the mean resistance reduction was found to be 3.16%. Regardless of the resistance reduction determined, a clear interaction between longitudinal vortices near the plate and local contributions to flow resistance could be demonstrated. Since these longitudinal vortices are directly influenced by the dimples, it is very likely that an optimized arrangement of the dimples, adapted to the flow conditions, can reduce the resistance

Boundary conditions and SGS models for LES of wall-bounded separated flows: an application to engine-like geometries

The implementation and the combination of advanced boundary conditions and subgrid scale models for Large Eddy Simulations are presented. The goal is to perform reliable cold flow LES simulations in complex geometries, such as in the cylinders of internal combustion engines. The implementation of an inlet boundary condition for synthetic turbulence generation and of two subgrid scale models, the local Dynamic Smagorinsky and the Wall-Adapting Local Eddy-viscosity SGS model (WALE) is described. The WALE model is based on the square of the velocity gradient tensor and it accounts for the effects of both the strain and the rotation rate of the smallest resolved turbulent fluctuations and it recovers the proper y(3) near-wall scaling for the eddy viscosity without requiring dynamic pressure; hence, it is supposed to be a very reliable model for ICE simulation. Model validation has been performed separately on two steady state flow benches: a backward facing step geometry and a simple IC engine geometry with one axed central valve. A discussion on the completeness of the LES simulation (i.e. LES simulation quality) is given

Large Eddy Simulation of separating flows from curved surfaces

PhDThe capabilities and limitations of LES in predicting separation from curved surfaces at high Reynolds number are at the centre of this Thesis. Issues of particular interest are mesh resolution, subgrid-scale modelling and near-wall approximations aiming to reduce the computational cost. Two cases are examined: a flow separating in a channel with streamwise periodic constrictions (hills), and the flow around a single-element, high-lift aerofoil at a Reynolds number of 2.1 . 106. Prior to these studies, fully-developed channel-flow simulations are considered. These show substantial differences among subgrid-scale models in terms of the subgrid-scale viscosity magnitude and its wall-asymptotic variation. Modelling and numerical errors appear to counteract each other, thus reducing the total error. Wall functions axe shown to be a cost-effective approach, providing a reasonably accurate approximation in near-equilibrium conditions. Adequate resolution remains critical, however, in achieving successful simulations. In the hill flow, separation occurs downstream of the hill crest, reattachment takes place about half-way between two consecutive hills and partial recovery occurs prior to a re-acceleration on the following hill. A highly-resolved simulation, performed to produce -benchmark data, permits an extensive study of the flow properties. Coarser mesh simulations are then compared with the former. These highlight the influence of the streamwise discretisation around the separation point and the role played by the implementation details of the wall treatments, while the subgrid-scale models influence is less significant. The aerofoil, which features transition and separation, is extremely challenging and at the edge of current LES capabilities. None of the simulations reproduce 2 the experimental data well. Indications on the sensitivity to various parameters, including the numerical scheme, the mesh resolution and the spanwise extent, are extracted, however. The studies indicate the need for a structured mesh of about 80 million nodes to achieve the required accuracy. For the present study, this was unaffordable

On the Simulation of Turbulent Fluid-Structure Interaction

The fluid-structure interaction (FSI) phenomena are relevant in a significant number of naturally occurring as well as industrial applications. Simulations of FSI have gained noteworthy attention with rapid advancements of computational technology in the last decade. Efficiency and accuracy of these simulations are still a concern, specially with a turbulent flow, the challenge is compounded by an additional computational cost for a turbulence modeling approach. Partitioned coupling approaches owing to software modularity and reusability are favored by engineers to solve FSI problems. The turbulence in flow is simulated through models with varying levels of complexity and computational requirements. In industrial applications, the use of Reynolds Averaged Navier Stokes (RANS) modeling of turbulence is dominant, whereas turbulence resolving approaches like Large-Eddy simulation (LES) are still not considered feasible due to computational requirements. To get as much accuracy by using as least as possible computer resources, a reasonable compromise are hybrid RANS-LES of turbulence, which are becoming more and more frequent. The goal of this work is to enable efficient and reliable simulations of FSI in turbulent flow. To this end, validation studies of three different turbulence modeling approaches available in the in-house flow solver FASTEST are performed. The structural subproblem in the coupling environment is solved with the Finite Element Method based code FEAP, while the data transfer and interpolation on non-matching grid interfaces can be handled with MpCCI or preCICE. For this work, the turbulence modeling approaches in FASTEST are extended with an implementation of the Wall Adapting Local Eddy (WALE) viscosity model for LES, and a validation study of the model is performed for a two dimensional periodic hill flow test case. An economical method based on a Poisson equation for the calculation of the nearest wall distance is also implemented, which is required by some turbulence models. The accuracy of the method is assessed with two computations on stationary grids. In turbulent flow simulations with moving grids, the height of cells on a wall changes and it can make a wall treatment approach unsuitable. This issue is addressed with an implementation of wall boundary conditions that work regardless of the first cell position in a boundary layer. The implementation is tested on stationary grids in a channel flow with a variation of the first cell height on the wall. A test of the method with an FSI test case showed satisfactory results. Validation studies of a RANS and a hybrid RANS-LES approach are performed with simulations of two FSI test cases. The two and three dimensional RANS and the hybrid RANS-LES produce a good agreement with the experimental results for oscillation characteristics of the structure. A hybrid RANS-LES and an LES is performed for another FSI test case with a very dense mesh. The LES and the hybrid RANS-LES on two different, but relatively dense meshes produced very similar results with a satisfactory prediction of the structural deflections

Mitigation of Aeroacoustic Noise of a Fixed Wing Using Passive Flow Control

As the world becomes more environmentally conscious, noise pollution is of increasing concern. In this study, shallow dimples are applied to a NACA 0012 airfoil at multiple angles of attack (AoA) with the intent of reducing aeroacoustic noise emissions. Both Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models are used for aerodynamic and aeroacoustic investigations, respectively, at a fixed Reynolds number of 4.8 x 105. Altering the dimple depth to diameter ratio (d/D) from 2.5% to 15% is first investigated, with a d/D of 5% or lower resulting in the least aerodynamic impact. The transition from shallow dimples to dimpled vortex generators is also found to occur at a 7.5% d/D, as defined by differing flow structures. An aeroacoustic analysis shows a 3.3% d/D ratio is optimal for a 5.71 dB Overall Averaged Sound Pressure Level (OASPL) reduction with a 2.66% average drag increase. A staggered array of dimples with this depth covering the latter 20%, 33% and 50% X/c is then investigated. Far-field noise characteristics are reduced up to 7 dB, with broadband noises below 3000 Hz showing the most improvement. The shallow dimpled array application is found to break up the spanwise coherence, shifting the generated noise towards higher frequencies where it can be more easily dissipated. As such, the application of shallow dimples on the latter portion of an airfoil can be considered a potential candidate for passive noise reduction

Numerical simulation of vortex-induced vibration of a vertical riser in uniform and linearly sheared currents

This paper presents a numerical study on vortex-induced vibration (VIV) of a vertical riser subject to uniform and linearly sheared currents. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. A standing wave response is observed for the single-mode in-line (IL) and cross-flow (CF) vibrations. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The majority of the vortex shedding shows a clear 2S pattern, whereas a 2P mode is observed near the position where the maximum vibration amplitude appears. The higher IL fatigue damage in the present study emphasises the importance of the IL fatigue damage especially in the design of low flow velocity or low mode number applications

Numerical resolution of turbulent flows on complex geometries.

This thesis aims at developing a numerical methodology suitable for the direct numerical simulation (DNS) and large-eddy simulation (LES) of turbulent flows in order to be used in complex flows, currently encountered in industrial application. At the same time, the study of such turbulent flows can be an opportunity for gaining insight into the complex physics associated with them. To accomplish these goals, the mathematical formulation, conservative spatial discretization on unstructured grids and time- integration scheme for solving the Navier-Stokes equations are presented. The spatial discretization proposed preserves the symmetry properties of the continuous differential operator and ensure both, stability and conservation of the global kinetic energy balance on any grid. Furthermore, the time-integration technique proposed is an efficient self-adaptive strategy, based on a one-parameter second-order-explicit scheme, which has been successfully tested on both Cartesian staggered and unstructured collocated codes, leading to CPU cost reductions of up to 2.9 and 4.3, respectively. After presenting the general methodology for computing flows in complex geometries with unstructured grids, different LES models and regularization models suitable for these kind of meshes are presented and assessed by means of the analysis of different flows. First, regularization models are tested by means of the simulation of different cases with different level of complexity of the mesh. From a structured grid to a very complex mesh, with zones composed of prism and tetrahedral control volumes. It has been shown, that regularization models are very dependent on the quality of the filtering process. Although good results can be obtained with structured or smooth unstructuredmeshes, their performance is affected under fully irregular unstructured grids. A possible remedy to circumvent this issue is also presented. The main idea is to formulate the C4 model within a LES template. Although preliminary results are promising, further testing is still required. After regularization model assessment, LES models are also tested in a natural convection flow. It is shown that, although first order statistics are well solved for most of the models tested (with the exception of the Smagorinsky model), QR- and dynamic-Smagorinsky models present a better prediction of the second-order statistics. However, if CPU time is considered, then QR model is the best alternative. The second part of the thesis is devoted to the study of turbulent flows past bluff bodies. The cases studied are: the flow past a sphere, the flow past a circular cylinder and the flow past a NACA 0012 airfoil. All these cases shares some characteristics encountered in turbulent flows with massive separations, i.e., flow separation, transition to turbulence in the separated shear-layers and turbulent wakes with periodic shedding of vortices. However there are intrinsic characteristics of the turbulence in each of them, which make them interesting for the studying of the turbulence. Furthermore, the results presented for the flow past a sphere at Re = 3700 and 10000, together with the flow past a NACA 0012 at Re=50000 and AoA = 8 are the first DNS results presented in the literature for both flows. Conclusions drawn from the good results obtained point out that the use of the conservative formulation presented in this thesis, is one of the keys for the success of the SGS models used. This formulation, together with the use of unstructured grids might be a step towards the use of LES models for solving industrial flows on complex geometries at high Reynolds numbers.La present tesi proposa una metodologia apte per a realitzar simulacions directes de la turbulència (DNS) i simulacions de les grans escales (LES) de fluxos turbulents en geometries complexes. Tanmateix també s'estudia detalladament els mecanismes bàsics de funcionament dels fluxos turbulents en diferents situacions d'interès industrial i acadèmic. Per acomplir aquest objectiu s'ha desenvolupat una innovadora formulació matemàtica que permet conservar discretament les propietats continues de les equacions governants en malles no estructurades. La formulació proposada preserva la simetries originals dels operadors diferencials, assegurant així l'estabilitat i la conservació de l'energia cinètica turbulent en qualsevol mallat. Posteriorment s'ha proposat una metodologia d'integració temporal basada en una formulació explicita de segon ordre. Aquesta nova tècnica ha demostrat ser entre 2.9 i 4.3 més rapida que les tècniques anteriorment utilitzades per la comunitat. Un cop presentada la formulació per a simular fluxos turbulents en geometries complexes, s'han validat diferents models LES adaptats a malles no estructurades. Els models s'han testejat usant diferents solucions de referencia de la literatura i simulacions d'alt nivell generades en el context de la present tesi. Finalment s'ha conclòs que la conjunció de la formulació bàsica proposada amb alguns del models LES sorgits en els darrers anys es molt efectiva per a simular fluxos turbulents en situacions complexes, essent el Variational Multiscale WALE i el model QR els més adequats per a simular situacions de interes industrial. La segona part de la tesi es dedicada a l'estudi aerodinàmic del flux turbulent al voltant de diferents perfils. El perfils seleccionats son: el flux al voltant d'una esfera, flux al voltant d'un cilindre i flux al voltant d'un perfil NACA 0012. Els tres casos comparteixen fenomenologies com ara separació massiva de capes límits, esteles turbulentes i desprendiment periòdic de remolins. Tot i així cadascun d'ells es comporta diferent a nivell turbulent així que es d'interès estudiar-los i entendre quins son les causes de les diferencies físiques que es troben. Cal recordar que la física estudiada es la que es pot trobar posteriorment en ales d'avió, perfils de turbines de vent, aerodinàmica de cotxes, etc. Finalment recalcar que els resultats DNS del flux al voltant de l'esfera a Re=3700 i Re=10000 conjuntament amb els DNS del flux al voltant del perfil NACA a Re=50000 i AoA =8 son els primers presentats en la literatura internacional en el seu àmbit. Finalment es pot concloure que la formulació conservativa presentada en la tesis juntament amb els diferents models LES d'última generació testejats en la tesis, han demostrat ser una eina eficaç tan per a resoldre fluxos turbulents d'interès acadèmic com per simular situacions d'interès industrial.Postprint (published version

Vortex-induced vibration of cylindrical structures

Vortex-induced vibration (VIV) of cylindrical structures is a classical topic within fluid-structure interaction (FSI). In offshore engineering, it often causes the fatigue of slender structures, such as risers, mooring lines and pipelines. Detailed understanding of this FSI phenomenon and an efficient prediction of such self-excited and self-sustained oscillations are required for the reliable estimation of the fatigue damage and the development of VIV suppression techniques.Over the past few decades, VIV has been extensively studied and the majority of the existing publications in the literature are experiments or semi-empirical modelling. In contrast, FSI simulations by combining high-fidelity computational fluid dynamics (CFD) and computational structural dynamics (CSD) solvers have received less attention. The main objective of this thesis is to investigate VIV of elastically mounted rigid cylinders and flexible cylinders using fully three-dimensional (3D) FSI simulations. Apart from important VIV aspects, such as response amplitude, response frequency and fatigue damage etc., the present research is also focussed on the aspects which have not been fully addressed by previous studies such as correlation lengths and time-dependent 3D flow structures.Two-degree-of-freedom (2DOF) VIV of an elastically mounted circular cylinder with varying in-line (IL) to cross-flow (CF) natural frequency ratios (f* = fnx/fny) is first studied using a 3D CFD approach. Numerical simulation is carried out for a constant mass ratio m* = 2 at a fixed Reynolds number Re = 500. The reduced velocity Vr ranges from 2 to 12. Three natural frequency ratios are considered, i.e., f* = 1, 1.5 and 2. The structural damping is set to zero to maximise the response of the cylinder. The main objective of the first study is to investigate the effect of f* on the 2DOF VIV responses and the 3D characteristics of the flow. It is discovered that there is a significant increase in the vibration amplitude and the peak amplitude shifts to a higher reduced velocity when f* increases from 1 to 2. A single-peak cross-flow response is observed for the identical in-line and cross-flow mass ratios when f* = 2. Dual resonance is found to exist over the range of f* studied.;The preferable trajectories of the cylinder in the lock-in range are counterclockwise figure-eight orbits, whereas clockwise orbits primarily occur in the initial branch. The number of clockwise orbits decreases as f* increases from 1 to 2. Oblique figure-eight trajectories appear at Vr = 6, 7 and 8 when f* = 1. The third harmonic component which is observed in the lift fluctuation increases with f*. The correlation decreases in the lock-in range and reaches its minimum value around the transition region between the lock-in and post-lock-in ranges. Three vortex shedding modes (2S, P + S and 2P) appear in the present simulation. A dominant P + S mode is associated with the oblique figure-eight trajectories. Variation of vortex shedding flows along the cylinder is observed leading to the poor correlation of the sectional lift forces.Then, a numerical investigation of VIV of a vertical riser subject to uniform and linearly sheared currents is presented. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The majority of the vortex shedding shows a clear 2S pattern, whereas a 2P mode is observed near the position where the maximum vibration amplitude appears. The higher IL fatigue damage in the second study emphasises the importance of the IL fatigue damage analysis especially in the design of low flow velocity or low mode number applications.The third study is on VIV of two tandem flexible cylinders at different spacing ratios (Sx/D) at a fixed Reynolds number Re = 500 using a two-way FSI method. The main objective is to investigate the effect of spacing on the hydrodynamic interactions and the VIV responses of these cylinders. It is found that the responses of the two tandem flexible cylinders are similar to the classical VIV responses when Sx/D is small.;Once Sx/D is large enough for the vortices to be completely detached from the upstream cylinder, the response of the upstream cylinder is similar to the typical VIV response whereas the downstream cylinder undergoes wake-induced vibration (WIV). The characteristics of the response of the downstream cylinder in the present study are similar to those of the first two response regimes. The third response regime is not observed for the flexible downstream cylinder with both ends fixed. The two changes in the phase relation between the cross-flow displacements of the two tandem flexible cylinders are discovered to be linked with the initial-upper branch transition and the upper-lower branch transition, respectively. The correlation lengths of the two tandem flexible cylinders decrease significantly in the transition range between the upper and lower branches. Three vortex shedding modes (2S, P + S and 2P) have been identified in the present study. It is found that the upper-branch 2P mode is associated with large-amplitude vibration of the upstream cylinder and the P + S mode is related to large-amplitude vibration of the downstream cylinder for Sx/D = 3.5 and 5. On the other hand, the lower-branch 2P mode leads to small-amplitude vibration of the downstream cylinder in the post-lock-in range at Sx/D = 2.5. The relative phase shifts of the sectional lift coefficients on different spanwise cross sections can be attributed to the variation of the vortex shedding flow along the flexible cylinders and these phase shifts result in poor phasing between the forces and the displacements which is related to the decrease of the correlation lengths.Vortex-induced vibration (VIV) of cylindrical structures is a classical topic within fluid-structure interaction (FSI). In offshore engineering, it often causes the fatigue of slender structures, such as risers, mooring lines and pipelines. Detailed understanding of this FSI phenomenon and an efficient prediction of such self-excited and self-sustained oscillations are required for the reliable estimation of the fatigue damage and the development of VIV suppression techniques.Over the past few decades, VIV has been extensively studied and the majority of the existing publications in the literature are experiments or semi-empirical modelling. In contrast, FSI simulations by combining high-fidelity computational fluid dynamics (CFD) and computational structural dynamics (CSD) solvers have received less attention. The main objective of this thesis is to investigate VIV of elastically mounted rigid cylinders and flexible cylinders using fully three-dimensional (3D) FSI simulations. Apart from important VIV aspects, such as response amplitude, response frequency and fatigue damage etc., the present research is also focussed on the aspects which have not been fully addressed by previous studies such as correlation lengths and time-dependent 3D flow structures.Two-degree-of-freedom (2DOF) VIV of an elastically mounted circular cylinder with varying in-line (IL) to cross-flow (CF) natural frequency ratios (f* = fnx/fny) is first studied using a 3D CFD approach. Numerical simulation is carried out for a constant mass ratio m* = 2 at a fixed Reynolds number Re = 500. The reduced velocity Vr ranges from 2 to 12. Three natural frequency ratios are considered, i.e., f* = 1, 1.5 and 2. The structural damping is set to zero to maximise the response of the cylinder. The main objective of the first study is to investigate the effect of f* on the 2DOF VIV responses and the 3D characteristics of the flow. It is discovered that there is a significant increase in the vibration amplitude and the peak amplitude shifts to a higher reduced velocity when f* increases from 1 to 2. A single-peak cross-flow response is observed for the identical in-line and cross-flow mass ratios when f* = 2. Dual resonance is found to exist over the range of f* studied.;The preferable trajectories of the cylinder in the lock-in range are counterclockwise figure-eight orbits, whereas clockwise orbits primarily occur in the initial branch. The number of clockwise orbits decreases as f* increases from 1 to 2. Oblique figure-eight trajectories appear at Vr = 6, 7 and 8 when f* = 1. The third harmonic component which is observed in the lift fluctuation increases with f*. The correlation decreases in the lock-in range and reaches its minimum value around the transition region between the lock-in and post-lock-in ranges. Three vortex shedding modes (2S, P + S and 2P) appear in the present simulation. A dominant P + S mode is associated with the oblique figure-eight trajectories. Variation of vortex shedding flows along the cylinder is observed leading to the poor correlation of the sectional lift forces.Then, a numerical investigation of VIV of a vertical riser subject to uniform and linearly sheared currents is presented. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The majority of the vortex shedding shows a clear 2S pattern, whereas a 2P mode is observed near the position where the maximum vibration amplitude appears. The higher IL fatigue damage in the second study emphasises the importance of the IL fatigue damage analysis especially in the design of low flow velocity or low mode number applications.The third study is on VIV of two tandem flexible cylinders at different spacing ratios (Sx/D) at a fixed Reynolds number Re = 500 using a two-way FSI method. The main objective is to investigate the effect of spacing on the hydrodynamic interactions and the VIV responses of these cylinders. It is found that the responses of the two tandem flexible cylinders are similar to the classical VIV responses when Sx/D is small.;Once Sx/D is large enough for the vortices to be completely detached from the upstream cylinder, the response of the upstream cylinder is similar to the typical VIV response whereas the downstream cylinder undergoes wake-induced vibration (WIV). The characteristics of the response of the downstream cylinder in the present study are similar to those of the first two response regimes. The third response regime is not observed for the flexible downstream cylinder with both ends fixed. The two changes in the phase relation between the cross-flow displacements of the two tandem flexible cylinders are discovered to be linked with the initial-upper branch transition and the upper-lower branch transition, respectively. The correlation lengths of the two tandem flexible cylinders decrease significantly in the transition range between the upper and lower branches. Three vortex shedding modes (2S, P + S and 2P) have been identified in the present study. It is found that the upper-branch 2P mode is associated with large-amplitude vibration of the upstream cylinder and the P + S mode is related to large-amplitude vibration of the downstream cylinder for Sx/D = 3.5 and 5. On the other hand, the lower-branch 2P mode leads to small-amplitude vibration of the downstream cylinder in the post-lock-in range at Sx/D = 2.5. The relative phase shifts of the sectional lift coefficients on different spanwise cross sections can be attributed to the variation of the vortex shedding flow along the flexible cylinders and these phase shifts result in poor phasing between the forces and the displacements which is related to the decrease of the correlation lengths

Large eddy simulation of optimal synthetic jet actuation on a SD7003 airfoil in post-stall conditions

Aerodynamic performances may be optimised by the appropriate tuning of Active Flow Control (AFC) parameters. For the first time, we couple Genetic Algorithms (GA) with an unsteady Reynolds-Averaged Navier-Stokes (RANS) solver using the Spalart-Allmaras (SA) turbulence model to maximise lift and aerodynamic efficiency of an airfoil in stall conditions [1], and then validate the resulting set of optimal Synthetic Jet Actuator (SJA) parameters against well-resolved three-dimensional Large Eddy Simulation (LES). The airfoil considered is the SD7003, at the Reynolds number and the post-stall angle of attack . We find that, although SA-RANS is not quite as accurate as LES, it can still predict macroscopic aggregates such as lift and drag coefficients, provided the free-stream turbulence is prescribed to reasonable values. The sensitivity to free-stream turbulence is found to be particularly critical for SJA cases. Baseline LES simulation agrees well with literature results, while RANS-SA would seem to remain a valid model to a certain degree. For optimally actuated cases, our LES simulation predicts far better performances than obtained by suboptimal SJA LES computations as reported by other authors [2] for the same airfoil, Re and a, which illustrates the applicability and effectiveness of the SJA optimisation technique applied, despite using the less accurate yet computationally faster SA-RANS. The flow topology and wake dynamics of baseline and SJA cases are thoroughly compared to elucidate the mechanism whereby aerodynamic performances are enhancedThis work was supported by the Spanish Government under grants FIS2016-77849-R and PID2020-114043GB-I00 and by the Catalan Government under grant 2017-SGR-00785. Computations were performed in the Red Española de Supercomputación (RES), Spanish supercomputer network, under the grants IM-2019-3-0002 and IM-2020-1-0001. F. M. is a Serra-Húnter fellowPostprint (published version