Load-estimation techniques for unsteady incompressible flows

Rival, David E.; Oudheusden, B.W. van

doi:10.1007/s00348-017-2304-3

Cited by 41 publications

(31 citation statements)

References 53 publications

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“…In a successive work, the authors extended the use of the PIV wake rake to moving objects for the determination of the aerodynamic loads on an aircraft propeller blade (Ragni et al 2011). Recently, a detailed review of loads estimation approaches from PIV measurements has been carried out by Rival and van Oudheusden (2017) and a set of guidelines is provided for accurate fluid force measurements involving unsteady body motion by Lentink (2018).…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

2019

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“…They have recently gained popularity for use with planar or volume meaurements of fluid velocities (but not pressure) from particle image velocimetry and related techniques, e.g. Rival & van Oudheusden (2017) and Limacher et al (2018). For example, Limacher et al (2019a) tested an impulse equation for thrust against measurements of an impulsively started circular cylinder using PIV data, and this method was then compared by Limacher et al (2019b) to a momentum-based formulation.…”

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confidence: 99%

Derivation of an Impulse Equation for Wind Turbine Thrust

Limacher

Wood

2019

Preprint

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Abstract. Using the concept of impulse in control volume (CV) analysis, we derive a new equation for steady wind turbine thrust in a constant, spatially uniform wind. This equation contains the circumferential velocity and tip speed ratio. We determine the conditions under which the new equation reduces to the standard equation involving only the axial velocity. A major advantage of an impulse formulation is that it removes the pressure and introduces the vorticity, allowing the equation to be used unambiguously immediately behind the blades. Using two CVs with this downwind end – one rotating with the blades, and one stationary – highlights different aspects of the analysis. We assume that the vorticity is frozen relative to an observer rotating with the blades, so the vortex lines follow the local streamlines in the rotating frame and vorticity does not appear explicitly in the impulse equation for force. In the stationary frame, streamlines and vortex lines intersect, and one of the thrust terms can be interpreted as the effect of wake rotation. The impulse analysis also shows the significance of the radial velocity in wind turbine aerodynamics. By assuming both the radial and axial velocities are continuous through the rotor disk, their contributions to the final thrust expression cancel to leave an expression dependent on azimuthal velocity alone. The final integral equation for thrust can be viewed as a generalization of the Kutta–Joukowsky theorem for the rotor forces. We give a proof, for the first time, for the conditions under which the Kutta–Joukowsky equations apply. The analysis is then extended to the blade elements comprising the rotor. The new formulation gives a very simple, exact equation for blade element thrust which is the major contribution of this study. By removing the pressure partly through the kinetic energy contribution of the radial velocity, the new equation circumvents the long-standing concern over the role the pressure forces acting on the expanding annular streamtube intersecting each blade element. It is shown that the necessary condition for blade-element independence of the conventional thrust equation – that which involves the axial induction factor – is the constancy of the vortex pitch in the wake.

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“…If the pressure field cannot be measured, then fluid forces and moments can be determined based on velocity and vorticity fields, which are generally determined either computationally or using particle image velocimetry (PIV) (Protas 2007;Howe 1995;Quartapelle and Napolitano 1983;Ragazzo and Tabak 2007;Magnaudet 2011;Wu 1981). Alternatively, the control volume analysis can be simplified by rewriting it into a control surface analysis (Lentink 2018;Rival and van Oudheusden 2017;Wu et al 2005). Fluid forces can then be recovered by measuring velocity, pressure and shear stress fields on the control surface.…”

Section: Introductionmentioning

confidence: 99%

“…Fluid forces can then be recovered by measuring velocity, pressure and shear stress fields on the control surface. The two main experimental implementations of this control surface analysis are highspeed particle image velocimetry (PIV) (Rival and van Oudheusden 2017), and the aerodynamic force platform (AFP) (Lentink 2018). Lentink (2018) recently derived theory to find the conditions under which the control surface formulation of the Navier-Stokes equations can be used to accurately recover fluid forces based on PIV and AFP measurements.…”

Section: Introductionmentioning

confidence: 99%

Fluid moment and force measurement based on control surface integration

Chin

Lentink

2019

Exp Fluids

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The moments and torques acting on a deforming body determine its stability and maneuverability. For animals, robots, vehicles, and other deforming objects locomoting in liquid or gaseous fluids, these fluid moments are challenging to accurately measure during unconstrained motion. Particle image velocimetry and aerodynamic force platforms have the potential to resolve this challenge through the use of control surface integration. These measurement techniques have previously been used to recover fluid forces. Here, we show how control surface integration can similarly be used to recover the 3D fluid moments generated about a deforming body's center of mass. We first derive a general formulation that can be applied to any body locomoting in a fluid. We then show when and how this formulation can be greatly simplified without loss of accuracy for conditions commonly encountered during fluid experiments, such as for tests done in wind or water channels. Finally, we provide detailed formulations to show how measurements from an aerodynamic force platform can be used to determine the net instantaneous moments generated by a freely flying body. These formulations also apply more generally to other fluid applications, such as underwater swimming or locomotion over water surfaces.

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Load-estimation techniques for unsteady incompressible flows

Cited by 41 publications

References 53 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

Derivation of an Impulse Equation for Wind Turbine Thrust

Fluid moment and force measurement based on control surface integration

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