Aerodynamic drag of a transiting sphere by large-scale tomographic-PIV

Terra, Wouter; Sciacchitano, Andrea; Scarano, Fulvio

doi:10.1007/s00348-017-2331-0

Cited by 37 publications

(41 citation statements)

References 31 publications

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“…As a consequence, the contribution of the Reynolds stress term in the expression for the drag (second term in Eq. 2) is overestimated, thus yielding an underestimation of the aerodynamic drag by approximately 0.15 N. At sufficient distance behind a bluff body, the contribution of the pressure term to the aerodynamic drag decays to zero due to the pressure recovery towards the freestream condition (Terra et al 2017). To understand the contribution of the time-average pressure term to the drag for the present downstream position of the wake plane, the pressure field distribution is investigated.…”

Section: Wake Flow Topologymentioning

confidence: 99%

“…By conducting large-scale PTV measurements and solving the Poisson equation for pressure, Schneiders et al (2016) measured the instantaneous volumetric pressure in the wake of a truncated cylinder over a volume of about 6 liters. Loads determination from large-scale PIV has been attempted for the first time by Terra et al (2017), estimating the drag coefficient of a transiting sphere at Re = 10,000. Load determination from large-scale PIV in wind tunnels, however, has been hampered firstly by the limited HFSB tracers concentration, which has been below 1 bubble/cm 3 , and secondly by the limited size of the seeded stream tube cross-section, not exceeding the order of 0.1 m 2 Jux et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…where ū is the time-average streamwise velocity, u ′ the fluctuating streamwise velocity and p the time-average static pressure. Following Terra et al (2017), the first, second and third term at the right hand side of this equation are referred to as the momentum term, the Reynolds stress term and the pressure term, respectively. Equation 2 allows evaluating the time-average aerodynamic drag from velocity and pressure statistics in the wake of the wind tunnel model.…”

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confidence: 99%

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Aerodynamic drag determination of a full-scale cyclist mannequin from large-scale PTV measurements

2019

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The aerodynamic drag of a human-scale wind tunnel model is obtained from large-scale particle tracking velocimetry measurements invoking the conservation of momentum in a control volume surrounding the model. Lagrangian particle tracking is employed to obtain the velocity and static pressure statistics in a thin volume in the wake of a cyclist mannequin at freestream velocities between 12.5 and 15 m/s, corresponding to Reynolds numbers from 5 × 10 5 to 6 × 10 5 based on the torso length. The spatial distributions of the time-average streamwise velocity and pressure coefficient match well with previous works reported in literature. The streamwise velocity fluctuations in the wake of the cyclist's model are presented, clearly demonstrating the unsteady nature of the main wake flow structures. Furthermore, the obtained aerodynamic drag follows the expected quadratic increase with increasing freestream velocity. The accuracy of this drag estimation is evaluated by comparison to force balance data and corresponds to 30 drag counts. The three terms composing the overall drag force, ascribed to the mean and fluctuating streamwise velocity and the mean pressure, are also evaluated separately, demonstrating that the resistive force is dominated by the contribution of the mean streamwise momentum deficit, whereas the contribution of the pressure term is negligible. Graphical abstractThe data presented in the figures in this work is available online (https ://doi.org/10.4121/uuid:7f42e 060-766d-4bf1-86c4-c648c 79431 7c)

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Section: Wake Flow Topologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Aerodynamic drag determination of a full-scale cyclist mannequin from large-scale PTV measurements

2019

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“…When considering a sufficient distance behind the model, the downstream pressure recovers to the freestream value and the velocity fluctuations decay [12] such that the time-average drag can be written as the difference between the upstream momentum, , and the wake momentum, :…”

Section: Methodsmentioning

confidence: 99%

A Novel Approach for Skin Suit Aerodynamic Optimization Using Local Momentum Deficit

Terra¹,

Sciacchitano²,

Scarano³

2018

The 12th Conference of the International Sports Engineering Association

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Abstract:A new approach is introduced to evaluate the potential drag reduction by skin suit design in speed sport. The approach relies upon local flow information measured in the wake of a cyclist mannequin. Lagrangian Particle Tracking is employed to measure the distribution of time-average streamwise velocity in a cross-plane of 30 × 100 cm 2 behind the stretched leg of the rider at a range of Reynolds numbers (0.4 × 10 5 < Re < 2.4 × 10 5 ). The expected Reynolds number effect is observed: a general wake narrowing at increasing speed. Unexpected local effects are also identified, which may be due to local variations in geometry of the rider's leg. The conservation of momentum within a control volume containing the leg is used showing that the aerodynamic drag of the rider's leg can be decreased by application of surface roughness. This outcome is validated by repeated measurements using zigzag tape on the legs' surface.

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“…PIV is a non-intrusive technique which allows the athlete to freely pass through the measurement region while high-speed cameras image the particles illuminated by a pulsed-light source. This approach provides the desired velocity information and allows to estimate the aerodynamic drag of the moving athlete by a control volume approach invoking the conservation of momentum [12].…”

Section: Introductionmentioning

confidence: 99%

The Ring of Fire for in-Field Sport Aerodynamic Investigation

Spoelstra

Terra

Sciacchitano

2018

The 12th Conference of the International Sports Engineering Association

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A novel measurement system, the Ring of Fire, is deployed which enables the aerodynamic drag estimation of transiting cyclists. The system relies upon the use of large-scale stereoscopic PIV and the conservation of momentum within a control volume in a frame of reference moving with the athlete. The rider cycles at a velocity of approximately 8 m/s, corresponding to a torso based Reynolds number of 3.2 × 10 5 . The measurements upstream and in the wake of the athlete are conducted at a rate of 2 kHz within a measurement plane of approximately 1000 × 1700 mm 2 . The non-dimensional, ensemble-averaged streamwise velocity fields compare well to literature and the ensemble-averaged drag area shows a rather constant value along the wake with an uncertainty of 5%. A comparison with wind tunnel force balance measurements shows discrepancies which may be partly attributed to the bike supports and stationary floor in the wind tunnel measurements. The 25% drag difference measured between a rider in upright and time-trial position, however, matches literature well.

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Aerodynamic drag of a transiting sphere by large-scale tomographic-PIV

Abstract: wake and blockage effects. The above findings can provide practical criteria for the drag evaluation of generic bluff objects with this measurement technique.

Cited by 37 publications

References 31 publications

Aerodynamic drag determination of a full-scale cyclist mannequin from large-scale PTV measurements

Aerodynamic drag determination of a full-scale cyclist mannequin from large-scale PTV measurements

A Novel Approach for Skin Suit Aerodynamic Optimization Using Local Momentum Deficit

The Ring of Fire for in-Field Sport Aerodynamic Investigation

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