Experimental and Computational Investigation of the Knoller-Betz Effect

Jones, Kevin D.; Dohring, Claus M.; Platzer, Max F.

doi:10.2514/2.505

Cited by 356 publications

(99 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Fig. 5(b) shows an analogous experimental result obtained by Jones, Dohring and Platzer [69] in a water tunnel. It can be seen that the high-order SD scheme is able to capture very fine vortical structures (observed experimentally) that develop in the wake of the airfoil.…”

Section: Vortex Dominated Flow In the Vicinity Of Flapping Wingssupporting

confidence: 58%

See 1 more Smart Citation

Facilitating the Adoption of Unstructured High-Order Methods Amongst a Wider Community of Fluid Dynamicists

Vincent

Jameson

2011

Math. Model. Nat. Phenom.

View full text Add to dashboard Cite

Abstract. Theoretical studies and numerical experiments suggest that unstructured high-order methods can provide solutions to otherwise intractable fluid flow problems within complex geometries. However, it remains the case that existing high-order schemes are generally less robust and more complex to implement than their low-order counterparts. These issues, in conjunction with difficulties generating high-order meshes, have limited the adoption of high-order techniques in both academia (where the use of low-order schemes remains widespread) and industry (where the use of low-order schemes is ubiquitous). In this short review, issues that have hitherto prevented the use of high-order methods amongst a non-specialist community are identified, and current efforts to overcome these issues are discussed. Attention is focused on four areas, namely the generation of unstructured high-order meshes, the development of simple and efficient time integration schemes, the development of robust and accurate shock capturing algorithms, and finally the development of high-order methods that are intuitive and simple to implement. With regards to this final area, particular attention is focused on the recently proposed flux reconstruction approach, which allows various well known high-order schemes (such as nodal discontinuous Galerkin methods and spectral difference methods) to be cast within a single unifying framework. It should be noted that due to the experience of the authors the review is directed somewhat towards aerodynamic applications and compressible flow. However, many of the discussions have a wider applicability. Moreover, the tone of the review is intended to be generally accessible, such that an extended scientific community can gain insight into factors currently pacing the adoption of unstructured high-order methods.

show abstract

Section: Vortex Dominated Flow In the Vicinity Of Flapping Wingssupporting

confidence: 58%

“…Such configurations act as simple flapping wing models, and also allow comparisons to be made with experimental studies, of which there are several for the 2D configurations in question [69]. Fig.…”

Section: Vortex Dominated Flow In the Vicinity Of Flapping Wingsmentioning

confidence: 99%

Facilitating the Adoption of Unstructured High-Order Methods Amongst a Wider Community of Fluid Dynamicists

Vincent

Jameson

2011

Math. Model. Nat. Phenom.

View full text Add to dashboard Cite

show abstract

“…With increasing Strouhal number, the streamwise spacing of the vortices decreases (figure 10d), and the wake ultimately becomes asymmetrical (figures 10e, f) with an appearance similar to that of the computations by Jones, Dohring & Platzer (1998). The vortices in the asymmetrical wakes become turbulent within about one period.…”

Section: The High-aspect-ratio Panel (Panel 4)mentioning

confidence: 52%

“…DPIV data at St = 0.36 and St = 0.72 (not shown) yield a mean symmetric wake inconsistent with the flow-visualization observations in figures 10(e) and 10 (f). The discrepancy implies the existence of more than one stable vortex pattern under these conditions with selection determined by either a finite asymmetry in the pitching motion or by conditions at the initiation of the pitching motion as observed by Jones et al (1998).…”

Section: The High-aspect-ratio Panel (Panel 4)mentioning

confidence: 90%

The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

2008

View full text Add to dashboard Cite

Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For Re C = O(10 4 ), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9 % and 21 % were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and Re C = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper.

show abstract

“…They observed vortex streets in the wake region which are inclined at an angle pointing upward or downward relative to the neutral position of the airfoil. As mentioned by Lai and Platzer (1999), by applying numerical simulations, Jones, Dohring, and Platzer (1998) found that the mode of the deflected vortex street is determined by the starting condition of the plunging oscillation. Similarly, further computations in this study, starting from a mirrored or another initial flowfield solution, confirmed that the asymmetric force history is dependent on the initial solution of the flowfield.…”

Section: Engineering Applications Of Computational Fluid Mechanicsmentioning

confidence: 99%

Experimental and computational investigations of flapping wings for Nano-air-vehicles

Yuan

Lee

Levasseur

2015

Engineering Applications of Computational Fluid Mechanics

View full text Add to dashboard Cite

This paper presents the finalized results of a recent project which investigated the aeromechanical aspects of aerodynamic force generation by making use of flapping wings. Flapping-wing experiments using small wings have some unique challenges posed by the low force level ( ∼ 1 N) and the cyclic wing motion. A tailored experimental water tunnel facility was developed for flapping wings operating at high reduced frequency with a complex two-dimensional and a three-dimensional motion profile. The experimental capability is demonstrated by the test cases of two-dimensional and three-dimensional flapping wings, designed according to a proposed notional nano-air-vehicle at a hovering condition. The features of the water tunnel, the geometric and kinematic parameters of the airfoils/wings, and the setups of the motion rigs for each test case are described. Measured forces and particle image velocimetry data are analyzed and cross-checked with the numerical results obtained from a code developed in-house. The comparisons of the experimental and numerical results show that the established experimental approach obtained a quantitatively reliable solution for the development of flapping wings and can serve for numerical validation of engineering tool developments. The investigation reveals that the kinematics of a rigid airfoil or wing is the dominant influence in the generation of aerodynamic forces, while the cross-section profile plays a secondary role. An asymmetric-wake-in-time is found behind the single airfoils and wings, which contributes to an asymmetry behavior of the resulting aerodynamic forces. In addition to the findings of single airfoils and wings, further analyses of the numerical and experimental results confirm that wing-wing interaction through the clap-fling mechanism can intensify the generation of the thrust force while accompanied by a small reduction in the overall propulsion efficiency.

show abstract

Experimental and Computational Investigation of the Knoller-Betz Effect

Cited by 356 publications

References 20 publications

Facilitating the Adoption of Unstructured High-Order Methods Amongst a Wider Community of Fluid Dynamicists

Facilitating the Adoption of Unstructured High-Order Methods Amongst a Wider Community of Fluid Dynamicists

The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

Experimental and computational investigations of flapping wings for Nano-air-vehicles

Contact Info

Product

Resources

About