Drag Analysis from PIV Data in Speed Sports

Terra, Wouter; Sciacchitano, Andrea; Scarano, Fulvio

doi:10.1016/j.proeng.2016.06.188

Cited by 9 publications

(7 citation statements)

References 18 publications

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“…Energies 2021, 14, 4712 5 of 19 However, there has been a great deal written about the relation of velocity profiles to the drag coefficient, e.g., [14,[24][25][26] and many others.…”

Section: Expanding Boundary Layer Approachmentioning

confidence: 99%

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Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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Several methods of defining and estimating the width of a turbulent wake are presented and tested on the experimental data obtained in the wake past an asymmetric prismatic airfoil NACA 64(3)-618, which is often used as tip profile of the wind turbines. Instantaneous velocities are measured by using the Particle Image Velocimetry (PIV) technique. All suggested methods of wake width estimation are based on the statistics of a stream-wise velocity component. First, the expansion of boundary layer (BL) thickness is tested, showing that both displacement BL thickness and momentum BL thickness do not represent the width of the wake. The equivalent of 99% BL thickness is used in the literature, but with different threshold value. It is shown that a lower threshold of 50% gives more stable results. The ensemble average velocity profile is fitted by Gauss function and its σ-parameter is used as another definition of wake width. The profiles of stream-wise velocity standard deviation display a two-peak shape; the distance of those peaks serves as wake width for Norberg, while another tested option is to include the widths of such peaks. Skewness (the third statistical moment) of stream-wise velocity displays a pair of sharp peaks in the wake boundary, but their position is heavily affected by the statistical quality of the data. Flatness (the fourth statistical moment) of the stream-wise velocity refers to the occurrence of rare events, and therefore the distance, where turbulent events ejected from the wake become rare and can be considered as another definition of wake width. The repeatability of the mentioned methods and their sensitivity to Reynolds’ number and model quality are discussed as well.

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“…Energies 2021, 14, 4712 5 of 19 However, there has been a great deal written about the relation of velocity profiles to the drag coefficient, e.g., [14,[24][25][26] and many others.…”

Section: Expanding Boundary Layer Approachmentioning

confidence: 99%

“…It should be noted that the deficit of velocity is closely related to the drag force, which can be derived solely from the velocity and pressure in a plane in the wake of the object [14].…”

Section: Introductionmentioning

confidence: 99%

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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“…The time-average velocity field behind isolated bluff bodies changes significantly going from the sub-to the super-critical regime [10]; in particular, the wake narrows and the area of reverse flow becomes smaller. As it can also be deduced from Equation (1), these flow field characteristics behind the model correspond to a decrease in aerodynamic drag.…”

Section: Effect Of Reynolds Numbermentioning

confidence: 99%

“…The measurements are conducted downstream of a cyclist's leg, where Reynolds number effects are expected to be important due to its bluff geometry. It is well known that the wake of a bluff body narrows moving from the sub-to super-critical regime and that a reduction of this streamwise velocity in the wake is associated with a drag reduction [10]. The streamwise velocity in the wake is considered to evaluate local drag variations stemming from Reynolds number effects or changes in surface roughness, and to reveal the local drag crisis of the leg only.…”

Section: Introductionmentioning

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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“…In recent years the amount of aerodynamic studies that make use of local flow measurements increased, either by scanning through the measurement area with pressure probes [6,7] or conducting whole-field measurements using particle based velocimetry [8][9][10][11], leading to increased understanding of the human body aerodynamics.…”

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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Drag Analysis from PIV Data in Speed Sports

Cited by 9 publications

References 18 publications

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

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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