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See detailNumerical and experimental study of the flow around a 4:1 rectangular cylinder at moderate Reynolds number
Guissart, Amandine ULiege; Andrianne, Thomas ULiege; Dimitriadis, Grigorios ULiege et al

in Journal of Wind Engineering and Industrial Aerodynamics (2019), 189

This paper presents the results of investigations into the flow around a rectangular cylinder with a chord-to-depth ratio equal to 4. The studies are performed through wind tunnel dynamic pressure ... [more ▼]

This paper presents the results of investigations into the flow around a rectangular cylinder with a chord-to-depth ratio equal to 4. The studies are performed through wind tunnel dynamic pressure measurements along a cross section combined with two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) and three-dimensional Delayed-Detached Eddy Simulation (DDES). These experimental and numerical studies are complementary and combining them allows a better understanding of the unsteady dynamics of the flow. These studies aim mainly at determining the effects of the rectangle incidence and freestream velocity on the variation of the flow topology and the aerodynamic loads, and at assessing the capability of the industrially affordable URANS and DDES approaches to provide a sufficiently accurate estimation of the flow for different incidences. The comparison of experimental and numerical data is performed using statistics and Dynamic Mode Decomposition. It is shown that the rectangular cylinder involves complex separation-reattachment phenomena that are highly sensitive to the Reynolds number. In particular, the time-averaged lift slope increases rapidly with the Reynolds number in the range 7.8e3 < Re < 1.9e4 due to the modification of the time-averaged vortex strength, thickness and distance from the surface. Additionally, it is shown that both URANS and DDES simulations fail to accurately predict the flow at all the different incidence angles considered. The URANS approach is able to qualitatively estimate the spatio-temporal variations of vortices for incidences below the stall angle alpha = 4°. Nonetheless, URANS does not predict stall, while DDES correctly identifies the stall angle observed experimentally. [less ▲]

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See detailCFD analysis of an exceptional cyclist sprint position
Blocken, Bert; van Druenen, Thijs; Toparlar, Yasin et al

in Sports Engineering (2019), 22:10

A few riders have adopted a rather exceptional and more aerodynamic sprint position where the torso is held low and nearly horizontal and close to the handle bar to reduce the frontal area. The question ... [more ▼]

A few riders have adopted a rather exceptional and more aerodynamic sprint position where the torso is held low and nearly horizontal and close to the handle bar to reduce the frontal area. The question arises how much aerodynamic benefit can be gained by such a position. This paper presents an aerodynamic analysis of both the regular and the low sprint position in comparison to three more common cycling positions. Computational fluid dynamics simulations are performed with the 3D RANS simulations and the transition SST k–ω model, validated with wind-tunnel measurements. The results are analyzed in terms of frontal area, drag coefficient, drag area, air speed and static pressure distribution, and static pressure coefficient and skin friction coefficient on the cyclist surfaces. It is shown that the drag area for the low sprint position is 24% lower than for the regular position, which renders the former 15% faster than the latter. This 24% improvement is not only the result of the 19% reduction in frontal area, but also caused by a reduction of 7% in drag coefficient due to the changed body position and the related changes in pressure distribution. Evidently, specific training is required to exert large power in the low sprint position. [less ▲]

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See detailNumerical and Experimental Investigation of Tandem Wing Flyers
Lambert, Thomas ULiege; Warbecq, Nicolas; Hendrick, Patrick et al

in Proceedings of the AIAA SciTech 2019 Forum and Exhibition (2019, January)

The recent focus on micro-UAV systems and bio-inspired drones has generated interest in tandem wing applications. Dragonfly-based configurations are of significance for very low Reynolds numbers; for ... [more ▼]

The recent focus on micro-UAV systems and bio-inspired drones has generated interest in tandem wing applications. Dragonfly-based configurations are of significance for very low Reynolds numbers; for larger drones, Microraptor-based geometries could prove to be efficient. The present study of tandem wing flyers aims at understanding the basic principles governing the aerodynamic properties of tandem wings in close proximity. The analysis includes both numerical simulations by means of the Unsteady Vortex Lattice Method and wind tunnel experimentation applied to generic rectangular wing geometries. Preliminary conclusions include the facts that increasing the rear wing’s angle of attack results in a bigger increase in lift than increasing the front wing’s angle of attack. The dihedral angles of the two wings also seem to have significant impact on the lift, some configurations leading to an increase in lift coefficient of up to 25%. The insight provided by the results will be used in the future to test and validate different flight configurations for the Microraptor and, hopefully, to shed some light on its preferred in-flight configuration and its flight capabilities. [less ▲]

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See detailOn the effects of crosswinds in tandem aerodynamics: an experimental and a computational study
Mannion, Paul; Toparlar, Yasin; Clifford, Eghan et al

in European Journal of Mechanics. B, Fluids (2019), 74

Aerodynamics has been an important research aspect in cycling science, with aerodynamic apparel and equipment, athlete postures, and race strategies all taking advantage of scientific aerodynamics ... [more ▼]

Aerodynamics has been an important research aspect in cycling science, with aerodynamic apparel and equipment, athlete postures, and race strategies all taking advantage of scientific aerodynamics knowledge. Crosswinds occur when cyclists travel at a non-zero angle to the direction of the wind. Research into crosswinds has yielded race strategies for able-bodied cyclists such as staggered drafting, and wind conditions are recognised as a key factor to consider for cyclist safety. The impact of crosswinds on tandem para-cyclists is less understood. Within the tandem para-cycling discipline, two athletes compete as a team on a single bicycle with a high degree of flow interaction between both athletes. Wind tunnel experiments and computational fluid dynamics were utilised in this research to investigate the drag and lateral forces at yaw angles between 0◦–20◦. No single turbulence model was found superior for all yaw angles investigated, with the SST k-ω and k-kl-ω turbulence models providing good results for separate yaw ranges. The individual drag and lateral forces experienced by both athletes and the tandem bicycle were investigated to provide further clarity on the distribution of wind loads for each yaw angle tested, and to aid in identifying potential locations for aerodynamic optimisation. 15◦ yaw was found to be the critical yaw angle where the maximum drag area of 0.337 m2 was experienced. The lateral force exceeded the drag force by 52.8% at a yaw angle of 20◦. [less ▲]

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See detailMixture model in high-order statistics for peak factor estimation on low-rise building
Rigo, François ULiege; Andrianne, Thomas ULiege; Denoël, Vincent ULiege

in Proceedings of the XV Conference of the Italian Association for Wind Engineering (2018, December 10)

To design reliable structures, extreme pressures and peak factors are required. In many applications of Wind Engineering, their statistical analysis has to be performed taking into account the non ... [more ▼]

To design reliable structures, extreme pressures and peak factors are required. In many applications of Wind Engineering, their statistical analysis has to be performed taking into account the non-Gaussianity of the wind pressures. With the increasing precision and sampling frequency of pressure sensors, large short and local peak events are more usually captured. Their relevance is naturally questioned in the context of a structural design. Furthermore, the increasing computational power allows for accumulation and analysis of larger data sets revealing the detailed nature of wind flows around bluff bodies. In particular, in the shear layers and where local vortices form, it is commonly admitted that the Probability Density Function (PDF) of measured pressures might exhibit two or more significant components. These mixed flows can be modelled with mixture models [Cook (2016)]. Whenever several processes coexist, and when one of them is leading in the tail of the statistical distribution, as will be seen next in the context of corner vortices over a flat roof, it is natural to construct the extreme value model with this leading process and not with the mixed observed pressures. It is therefore important to separate the different processes that can be observed in the pressure histories. Once this is done, specific analytical formulations of non-Gaussian peak factors can be used to evaluate the statistics of extreme values [Kareem and Zhao (1994), Chen (2009)]. The separation of mixed processes is usually done by means of the PDF of the signals [Cook (2016)]. This information is of course essential to perform an accurate decomposition but it might be facilitated by considering higher rank information like auto-correlations and higher correlations like the triple or quadruple correlation. Indeed, the two phenomena that need to be separated and identified might be characterized by significantly different timescales, which are not reflected in the PDF. In this paper, the large negative pressures measured on a flat roof are analyzed and decomposed into two elementary processes, namely, the flapping corner vortex and the turbulent flow detaching from the sharp upstream edge. The full paper will finally show that an accurate decomposition of the recorded pressures into their underlying modes provides a more meaningful evaluation of the extreme pressures. [less ▲]

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See detailAerodynamic analysis of different cyclist hill descent positions
Blocken, Bert; van Druenen, Thijs; Toparlar, Yasin et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 181

Different professional cyclists use very different hill descent positions, which indicates that prior to the present study, there was no consensus on which position is really superior, and that most ... [more ▼]

Different professional cyclists use very different hill descent positions, which indicates that prior to the present study, there was no consensus on which position is really superior, and that most cyclists did not test different positions, for example in wind tunnels, to find which position would give them the largest advantage. This paper presents an aerodynamic analysis of 15 different hill descent positions. It is assumed that the hill slope is steep enough so pedaling is not required to gain speed and that the descent does not include sharp bends necessitating changes in position. The analysis is performed by Computational Fluid Dynamics (CFD) simulations with the 3D RANS equations and the Transition SST k-ω model. The simulations are validated wind tunnel measurements. The results are analyzed in terms of frontal area, drag area and surface pressure coefficient. It is shown that the infamous “Froome” position during the Peyresourde descent of Stage 8 of the 2016 Tour de France is not aerodynamically superior to several other positions. Other positions are up to 7.2% faster and also safer because they provide more equal distribution of body weight over both wheels. Also several positions that allow larger power generation are aerodynamically superior. [less ▲]

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See detailVIV response of a suspended sphere nearby the critical Reynolds number
Andrianne, Thomas ULiege; Rigo, François ULiege; Denoël, Vincent ULiege

Conference (2018, September 10)

The Vortex-Induced Vibration of a sphere connected to a flexible beam is investigated in air for Reynolds numbers including the critical value. For this value (ReC =3e5 ), wake disorganisation is expected ... [more ▼]

The Vortex-Induced Vibration of a sphere connected to a flexible beam is investigated in air for Reynolds numbers including the critical value. For this value (ReC =3e5 ), wake disorganisation is expected in a static configuration. This fundamental fluid-structure interaction characterised by an axisymmetric configuration leads to vibrations in the lateral and longitudinal directions. Similarly to the well-known circular cylinder, a lock-in phenomenon will take place due to the effect of the motion of the body on the shedding process. An experimental aeroelastic model is designed, instrumented and tested in the wind tunnel of University of Liège. The objective is twofold: (i) solve a practical wind-engineering problem (a spherical suspended streetlight) and (ii) propose a fundamental investigation of the VIV of a smooth sphere for sub-critical and critical Reynolds numbers. [less ▲]

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See detailVortex induced vibrations of rectangular cylinders arranged on a grid
Rigo, François ULiege; Andrianne, Thomas ULiege

Scientific conference (2018, September 10)

A grid arrangement made of one hundred rectangular cylinders fixed to the facade of a house generates strong and disturbing mono-harmonic noise. The cross-flow vibration of the rectangular cylinders is ... [more ▼]

A grid arrangement made of one hundred rectangular cylinders fixed to the facade of a house generates strong and disturbing mono-harmonic noise. The cross-flow vibration of the rectangular cylinders is identified as the origin of the noise. The present article proposes a complete investigation of the Vortex Induced Vibration (VIV) combined with a grid effect. It is based on in situ measurements, numerical (finite elements and Computational Fluid Dynamics (CFD)) and extensive wind tunnel (WT) modelling. A comparison between unsteady pressure tap measurements and CFD results allows to understand the vortex shedding process and synchronisation type depending on the wind incidence and spacing of the cylinders. On the basis of this multi-approach parametric investigation, a deep understanding of the VIV-grid phenomenon enables to propose two mitigation techniques. These techniques are tested and their effectiveness is reported in terms of vibration amplitude and acoustic intensity. [less ▲]

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See detailAerodynamic drag in cycling team time trials
Blocken, Bert; Toparlar, Yasin; van Druenen, Thijs et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 182

In a team time trial (TTT), the main strategy is based on drafting, where team members alternately take the lead while others ride behind the leading cyclist. TTTs can contain up to 9 riders of the same ... [more ▼]

In a team time trial (TTT), the main strategy is based on drafting, where team members alternately take the lead while others ride behind the leading cyclist. TTTs can contain up to 9 riders of the same team. To the best of our knowledge, systematic aerodynamic studies of drafting groups from 2 up to 9 riders have not yet been published. Therefore, this paper presents such an analysis for up to 9 drafting cyclists in a single paceline, with wheel-to wheel spacings d ¼ 0.05, 0.15, 0.5, 1 and 5m. A total of 47 Computational Fluid Dynamics (CFD) simulations are performed with the 3D RANS equations, standard k-ε model and scalable wall functions and validated with wind-tunnel measurements. In groups of up to 5 identical riders with d up to 1 m, the last rider has the lowest drag but this is not the case for larger groups. A closely drafting group of 7, 8 or 9 riders has an average drag that is about half that of an isolated rider. However, for much longer theoretical single pacelines, a staggered peloton configuration can yet be about two times more drag efficient. [less ▲]

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See detailAnalysis of crosswind aerodynamics for competitive handcycling
Mannion, Paul; Toparlar, Yasin; Blocken, Bert et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 180

Competitive hand-cycling represents a unique case for cycling aerodynamics as the athletes are in a relatively aerodynamic position in comparison to traditional able-bodied cyclists. There are some ... [more ▼]

Competitive hand-cycling represents a unique case for cycling aerodynamics as the athletes are in a relatively aerodynamic position in comparison to traditional able-bodied cyclists. There are some aerodynamic similarities between both cycling disciplines, including wheel designs and helmets. The lack of research in hand-cycling aerodynamics presents the potential for significant improvements. This research analysed the aerodynamics of competitive hand-cycling under crosswind conditions using wind-tunnel experiments and Computational Fluid Dynamics (CFD) simulations. A range of yaw angles from 0° to 20° in 5° increments were investigated for two separate hand-cycling setups; a road race and a time-trial setup. A maximum drag increase of 14.1% was found from 0° to 15° yaw, for a hand-cyclist equipped for a road race. The three disk wheels used for the TT setup had a large impact on the lateral forces experienced by the TT hand-cyclist. At just 5° yaw and at 15 m/s, the drag and lateral forces for the TT setup matched closely, while this event did not occur until 15° yaw at the same velocity for the road setup. For 20° yaw, the ratio of the lateral force to drag force was 1.6 and 5.6 for the road and TT setups respectively. [less ▲]

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See detailAerodynamic drag in cycling pelotons: New insights by CFD simulation and wind tunnel testing
Blocken, Bert; van Druenen, Thijs; Toparlar, Yasin et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 179

A cycling peloton is the main group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure. Previous studies on small groups of in-line drafting cyclists showed reductions ... [more ▼]

A cycling peloton is the main group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure. Previous studies on small groups of in-line drafting cyclists showed reductions down to 70 to 50% the drag of an isolated rider at same speed and these values have also been used for pelotons. However, inside a tightly packed peloton with multiple rows of riders providing shelter, larger drag reductions can be expected. This paper systematically investigates the drag reductions in two pelotons of 121 cyclists. High-resolution CFD sim- ulations are performed with the RANS equations and the Transition SST-k-ω model. The cyclist wall-adjacent cell size is 20 μm and the total cell count per peloton is nearly 3 billion. The simulations are validated by four wind- tunnel tests, including one with a peloton of 121 models. The results show that the drag of all cyclists in the peloton decreases compared to that of an isolated rider. In the mid rear of the peloton it reduces down to 5%–10% that of an isolated rider. This corresponds to an “equivalent cycling speed” that is 4.5 to 3.2 times less than the peloton speed. These results can be used to improve cycling strategies. [less ▲]

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See detailAerodynamic drag in competitive tandem para-cycling: Road race versus time-trial positions
Mannion, Paul; Toparlar, Yasin; Blocken, Bert et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 179

An athlete's riding posture is a key element for aerodynamic drag in cycling. Tandem cycling has the complication of having two athletes in close proximity to each other on a single tandem bicycle. The ... [more ▼]

An athlete's riding posture is a key element for aerodynamic drag in cycling. Tandem cycling has the complication of having two athletes in close proximity to each other on a single tandem bicycle. The complex flow-field between the pilot and stoker in tandem cycling presents new challenges for aerodynamic optimisation. Aerodynamic drag acting on two tandem road race setups and two track time-trial setups were analysed with computational fluid dynamics (CFD) simulations. For validation purposes, wind tunnel measurements were designed providing drag measurements from both tandem athletes simultaneously using a quarter-scale model. A max drag force deviation of 4.9% was found between the wind tunnel experiments and CFD simulations of the quarter-scale geometry. Full-scale CFD simulations of upright, crouched, time-trial and frame-clench tandem setups were performed. The drag force experienced by individual athletes in all investigated tandem setups was compared to that of solo riders to enhance understanding of the aerodynamic interaction between both tandem athletes. The most aerodynamic tandem setup was found to be the frame-clench setup which is unique to tandem cycling and had a CDA of 0.286m2, and could provide an advantage of 8.1 s over a standard time-trial setup for a 10 km timetrial event. [less ▲]

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See detailVortex induced vibrations of rectangular cylinders arranged on a grid
Rigo, François ULiege; Denoël, Vincent ULiege; Andrianne, Thomas ULiege

in Journal of Wind Engineering and Industrial Aerodynamics (2018)

A grid arrangement of hundred rectangular cylinders fixed to the facade of a house generates strong and disturbing mono-harmonic noise. The cross-flow vibration of the rectangular cylinders is identified ... [more ▼]

A grid arrangement of hundred rectangular cylinders fixed to the facade of a house generates strong and disturbing mono-harmonic noise. The cross-flow vibration of the rectangular cylinders is identified as the origin of the noise. The present article proposes a complete investigation of the Vortex Induced Vibration (VIV) combined with a grid effect. It is based on in situ measurements, numerical (finite elements and Computational Fluid Dynamics (CFD)) and extensive wind tunnel modelling. A comparison between unsteady pressure tap measurements and CFD results allow to understand the vortex shedding process and synchronization type depending on the wind incidence and spacing of the cylinders. On the basis of this multi-approaches parametric investigation, a deep understanding of the VIV-grid phenomenon enables to propose two mitigation techniques. These techniques are tested and their effectiveness is reported in terms of vibration amplitude and acoustic intensity. [less ▲]

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See detailGenerating atmospheric turbulence using passive grids in an expansion test section of a wind tunnel
Vita, Giulio; Hemida, Hassan; Andrianne, Thomas ULiege et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 177

Generating atmospheric turbulence in wind tunnels is an important issue in the study of wind turbine aerodynamics. A turbulent inlet is usually generated using passive grids. However, to obtain an ... [more ▼]

Generating atmospheric turbulence in wind tunnels is an important issue in the study of wind turbine aerodynamics. A turbulent inlet is usually generated using passive grids. However, to obtain an atmospheric-like flow field relatively large length scales (L~30 cm) and high turbulence intensities (I~15%) need to be reproduced. In this work, the passive grid technique has been used in combination with a downstream expansion test section in order to investigate the generation of atmospheric like turbulence, with the possibility of varying both the turbulence intensity and the integral length scale of the flow field independently. Four passive grids with different mesh and bar sizes were used with four wind velocities and five downstream measurement positions. It was found that the flow field is isotropic and homogeneous for distances less than what is recommended in literature (x=M 5). The effect of the expansion on the turbulence characteristics is also investigated in detail for the first time. The study confirms that by adding an expansion test section it is possible to increase both turbulence intensity and integral length scale downstream from the grid with limited impact on the overall flow quality in terms of anisotropy and energy spectra. [less ▲]

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See detailEnergy harvesting from different aeroelastic instabilities of a square cylinder
Andrianne, Thomas ULiege; Aryoputro, Renar; Laurent, Philippe ULiege et al

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 172

This paper presents an experimental and numerical investigation of the power extraction from the oscillations of a square beam due to aeroelastic instabilities. The energy harvesting is performed using a ... [more ▼]

This paper presents an experimental and numerical investigation of the power extraction from the oscillations of a square beam due to aeroelastic instabilities. The energy harvesting is performed using a coil-magnet arrangement connected to a variable resistance load with the target objective to auto-power a remote sensor. Two aeroelastic phenomena are investigated: Vortex Induced Vibration (VIV) and cross-flow galloping. The first instability (VIV) is analyzed on a free-standing vertical structure. A second experimental set-up is developed on a horizontal square cylinder supported by springs, free to oscillate vertically as a rigid body. In this case, both galloping and VIV interact, leading to interesting characteristics in order to harvest energy from the wind. The behavior of each electro-mechanical aeroelastic system is investigated for different reduced wind speeds and load resistances in a wind tunnel. Observed efficiencies are rather low, but large enough to power a remote sensor with an adapted measuring strategy. Both harvesting systems are then studied numerically using a wake oscillator model (for VIV) coupled to a quasi-steady model (for galloping) and an electric model (for the harvester). This mathematical model is used to extend the parametric space and to highlight the effectiveness of the high stable branch of the VIV-galloping curve to harvest energy. [less ▲]

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See detailFirst passage time as an analysis tool in experimental wind engineering
Vanvinckenroye, Hélène ULiege; Andrianne, Thomas ULiege; Denoël, Vincent ULiege

in Journal of Wind Engineering and Industrial Aerodynamics (2018), 177

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See detailImproving CFD prediction of drag on Paralympic tandem athletes: influence of grid resolution and turbulence model
Mannion, Paul; Toparlar, Yasin; Blocken, Bert et al

in Sports Engineering (2017)

Tandem cycling enables visually impaired athletes to compete in cycling in the Paralympics. Tandem aerodynamics can be analysed by track measurements, wind-tunnel experiments and numerical simulations ... [more ▼]

Tandem cycling enables visually impaired athletes to compete in cycling in the Paralympics. Tandem aerodynamics can be analysed by track measurements, wind-tunnel experiments and numerical simulations with computational fluid dynamics (CFD). However, the proximity of the pilot (front) and the stoker (rear) and the associated strong aerodynamic interactions between both athletes present substantial challenges for CFD simulations, the results of which can be very sensitive to computational parameters such as grid topology and turbulence model. To the best of our knowledge, this paper presents the first CFD and wind-tunnel investigation on tandem cycling aerodynamics. The study analyses the influence of the CFD grid topology and the turbulence model on the aerodynamic forces on pilot and stoker and compares the results with wind-tunnel measurements. It is shown that certain combinations of grid topology and turbulence model give trends that are opposite to those shown by other combinations. Indeed, some combinations provide counterintuitive drag outcomes with the stoker experiencing a drag force up to 28% greater than the pilot. Furthermore, the application of a blockage correction for two athlete bodies in close proximity is investigated. Based on a large number of CFD simulations and validation with wind-tunnel measurements, this paper provides guidelines for the accurate CFD simulation of tandem aerodynamics. [less ▲]

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See detailUnsteady pressure distributions on a 4:1 rectangular cylinder: comparison of numerical and experimental results using decomposition methods.
Guissart, Amandine ULiege; Andrianne, Thomas ULiege; Dimitriadis, Grigorios ULiege et al

Conference (2017, July 04)

Detached flows around bluff bodies are ubiquitous in civil engineering applications. In this work, the flow around a static 4:1 rectangular cylinder at moderate Reynolds number and at different angles of ... [more ▼]

Detached flows around bluff bodies are ubiquitous in civil engineering applications. In this work, the flow around a static 4:1 rectangular cylinder at moderate Reynolds number and at different angles of incidence is studied using both Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD). Typically, the integration of EFD and CFD allows a better understanding of the flow of interest by leveraging the complementary of their respective outputs. However, the comparison of computational and experimental results is an important but difficult step of this integration, particularly in the case of local quantities related to unsteady flows. In this work, decomposition methods are used to compare unsteady loads and pressure distributions coming from EFD and CFD. In particular, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to extract the dominant structures of the aerodynamic coefficients. The experimental data are obtained from dynamic pressure measurements in wind tunnel while numerical data come from two-dimensional unsteady Reynolds-Averaged Navier-Stokes (uRANS) simulations and tri-dimensional Delayed-Detached Eddy Simulations (DDES). This work shows that the decomposition methods represent a powerful tool enabling the analysis and the quantitative comparison of the main spatial and temporal characteristics of unsteady flows. Moreover, the accuracy of uRANS and DDES results is analyzed in light of the capacity of both CFD techniques to capture the reattachment occurring on the upper part of the rectangular cylinder. [less ▲]

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See detailEnergy harvesting from galloping of prisms: A wind tunnel experiment
Hémon, Pascal; Amandolèse, Xavier; Andrianne, Thomas ULiege

in Journal of Fluids and Structures (2017), 70

We study the energy harvesting from the galloping oscillations of rigid prisms flexibly mounted in a wind tunnel. A square section and a 2/3 rectangular section are tested and the inclination angle of the ... [more ▼]

We study the energy harvesting from the galloping oscillations of rigid prisms flexibly mounted in a wind tunnel. A square section and a 2/3 rectangular section are tested and the inclination angle of the prisms referred to the flow direction is optimally adapted. The energy harvester is based on magnets moving with the prism in the front of a coil-core at rest. Energy is dissipated in a load resistance for which an optimal value is found. Efficiency of the "prism wind turbine" is weak compared to usual wind turbine due to the physics of the galloping mechanism. However such systems remain interesting for their potential of adaptation to various situations. [less ▲]

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See detailReal-scale observations of vortex induced vibrations of stay-cables in the boundary layer
Denoël, Vincent ULiege; Andrianne, Thomas ULiege

in Procedia Engineering (2017), 199

Abstract This paper shows some records and analysis of evidences of vortex induced vibrations of very long stay cables in the atmospheric boundary layer. The considered structure is a 254-m high ... [more ▼]

Abstract This paper shows some records and analysis of evidences of vortex induced vibrations of very long stay cables in the atmospheric boundary layer. The considered structure is a 254-m high telecommunication antenna whose structural system is made of a light flexible metallic truss, approx. 10×10m square, which is stayed at five different levels by a set of 20 pairs of stay-cables. The exposure of this antenna is category I with a low-turbulence wind flow which results in a high sensitivity to vortex induced vibrations. The fundamental frequency of the longest cable is 0.3 Hz so that several dozens of regularly spaced natural frequencies could be observed with a sampling frequency of 500 Hz. Sufficiently long recordings allowed to distinctly observe the separate peaks corresponding to the various modes of the cables. Among them many are excited by the detachment of vortices, taking place at different frequencies (because of different cable diameters and the change of wind velocity along the height of the antenna) in the range 35-55 Hz. Referring to the so-called spectral model proposed by Vickery and Clark, the detachment of vortices takes place in a certain bandwidth, whose extent is not completely understood yet. This bandwidth is clearly observed with our long stay-cables because of the large density of mode shapes in the range [0, 200] Hz and because of their regular spacing in the spectral domain. To the author’s knowledge this constitutes a first attempt at identifying this parameter of the Vickery and Clark model from full-scale measurements. [less ▲]

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