Boundary Layer Stabilization by Distributed Damping

Kramer, Max O.

doi:10.1111/j.1559-3584.1962.tb05568.x

Cited by 122 publications

(49 citation statements)

References 4 publications

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“…The assertion that the thrust generated by a swimming dolphin approaches or is equivalent to the drag of a rigid flat plate with a laminar boundary flow (Gray, 1936;Kramer, 1960a;Kramer, 1960b;Choi et al, 1997;Babenko and Carpenter, 2002;Romanenko, 2002;Nagamine et al, 2004) was not supported by bubble DPIV measurements (Fig. 5).…”

Section: Research Articlementioning

confidence: 99%

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

Fish

Legac

Williams

et al. 2014

Journal of Experimental Biology

109

101

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Attempts to measure the propulsive forces produced by swimming dolphins have been limited. Previous uses of computational hydrodynamic models and gliding experiments have provided estimates of thrust production by dolphins, but these were indirect tests that relied on various assumptions. The thrust produced by two actively swimming bottlenose dolphins (Tursiops truncatus) was directly measured using digital particle image velocimetry (DPIV). For dolphins swimming in a large outdoor pool, the DPIV method used illuminated microbubbles that were generated in a narrow sheet from a finely porous hose and a compressed air source. The movement of the bubbles was tracked with a high-speed video camera. Dolphins swam at speeds of 0.7 to 3.4 m s −1 within the bubble sheet oriented along the midsagittal plane of the animal. The wake of the dolphin was visualized as the microbubbles were displaced because of the action of the propulsive flukes and jet flow. The oscillations of the dolphin flukes were shown to generate strong vortices in the wake. Thrust production was measured from the vortex strength through the Kutta-Joukowski theorem of aerodynamics. The dolphins generated up to 700 N during small amplitude swimming and up to 1468 N during large amplitude starts. The results of this study demonstrated that bubble DPIV can be used effectively to measure the thrust produced by large-bodied dolphins.

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Section: Research Articlementioning

confidence: 99%

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

Fish

Legac

Williams

et al. 2014

Journal of Experimental Biology

109

101

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“…The phenomenal drag reduction as much as 60% by Kramer (1957Kramer ( , 1962 has never been reproduced afterwards. Those attempts were reviewed by Bushnell et al (1977) and Gad-el-Hak (1996), who focused on the experiments employing the "soft" coatings, i.e., either porous material covered by thin film or gel-like substance.…”

Section: Introductionmentioning

confidence: 99%

Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

Бойко¹,

Kulik²,

Hu³

et al. 2011

International Journal of Naval Architecture and Ocean Engineeri

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“…The continuity of uid wall motion is given in the streamwise, normal, and spanwise directions, respectively as @ 1 @t =u 1 + 1 U 0 o 8 @ 1 @t =v 1 9 @ 1 @t =w 1 10 where u 1 ; v 1 ; w 1 are the disturbance velocity components in the streamwise, normal and spanwise directions.…”

Section: Primary Wave Modelmentioning

confidence: 99%

The effect of compliant walls on secondary instabilities in boundarylayer transition

Joslin

Morris

1991

29th Aerospace Sciences Meeting

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For aerodynamic and hydrodynamic vehicles, it is highly desirable to reduce drag and noise levels. A reduction in drag leads to fuel savings. In particular for submersible vehicles, a decrease in noise levels inhibits detection. A suggested means to obtain these reduction goals is by delaying the transition from laminar to turbulent o w in external boundary layers. For hydrodynamic applications, a passive device which shows promise for transition delays is the compliant coating. In previous studies with a simple mechanical model representing the compliant w all, coatings were found that provided transition delays as predicted from the semi-empirical e n method. Those studies were concerned with the linear stage of transition where the instability of concern is referred to as the primary instability. F or the at-plate boundary layer, the Tollmien-Schlichting TS wave is the primary instability. In one of those studies, it was shown that three-dimensional 3-D primary instabilities, or oblique waves, could dominate transition over the coatings considered. From the primary instability, the stretching and tilting of vorticity i n t h e shear ow leads to a secondary instability mechanism. This has been theoretical described by Herbert based on Floquet theory. In the present study, Herbert's theory is used to predict the development of secondary instabilities over isotropic and non-isotropic compliant w alls. Since oblique waves may be dominant o v er compliant w alls, a secondary theory extention is made to allow for these 3-D primary instabilities. The e ect of variations in primary amplitude, spanwise wavenumber, and Reynolds number on the secondary instabilities are examined. As in the rigid wall case, over compliant w alls the subharmonic mode of secondary instability dominates for low-amplitude primary disturbances. Both isotropic and non-isotropic compliant w alls lead to reduced secondary growth rates compared to the rigid wall results. For high frequencies, the non-isotropic wall suppresses the ampli cation of the secondary instabilities, while instabilities over the isotropic wall may grow with an explosive rate similar to the rigid wall results. For the more important l o w er frequencies, both isotropic and non-isotropic compliant w alls suppress the ampli cation of secondary instabilities compared to the rigid wall results. The twofold major discovery and demonstration of the present i n v estigation are: 1 the use of passive devices, such as compliant w alls, can lead to signi cant reductions in the secondary instability growth rates and ampli cation; 2 suppressing the primary growth rates and subsequent ampli cation enable delays in the growth of the explosive secondary instability mechanism.

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Boundary Layer Stabilization by Distributed Damping

Cited by 122 publications

References 4 publications

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

The effect of compliant walls on secondary instabilities in boundarylayer transition

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