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passive and active flow control by swimming fishes and mammals

passive and active flow control by swimming fishes and mammals

Figure 18Comparison of

Figure 18Comparison of relationshipsof propulsive efficiency andthrust coefficient for fourspecies of small whales and atypical marine propeller.Data for the whales wereobtained from Fish (1998),and data for the propeller(EMB 2294) are fromSaunders (1957).Annu. Rev. Fluid. Mech. 2006.38:193-224. Downloaded from arjournals.annualreviews.orgby WEST CHESTER UNIVERSITY on 12/20/05. For personal use only.counter-rotating vortices (i.e., Kármán vortex street) where the optimal position fordrag reduction is directly behind another body (Fish 1994). Although similar in patternto the Kármán vortex street, a thrust-type vortex system has the opposite rotationof the vortices. In this system, which is generated by an oscillating foil, the optimalposition is diagonal in a diamond pattern (Weihs 1973).Thrust-type vortices produced by fish provide drag reduction in diamond-shapedformations (Weihs 1973). Trailing fish experience a relative velocity 40–50% of thefree-stream velocity and a reduction of the force generated for swimming by a factorof 4 to 6. However, the decrease in relative velocity is not maintained with eachsuccessive row of trailing fish due to destructive interference.Small whales often position themselves beside and slightly behind the maximumdiameter of a larger animal (Weihs 2004). Whereas the larger whale experiencesincreased drag, the smaller individual gains an energetic benefit (Lang 1966). Thiseffect is beneficial particularly for young whales in order to maintain speed with theirmothers. A neonate can gain up to 90% of the thrust needed to move alongside themother at swimming speeds up to 2.4 m/s (Weihs 2004).A new locomotor behavior was recently described in which fishes can use vorticesshed by objects in flowing water and radically alter their locomotor kinematicsto maintain station well downstream of any suction region (Liao 2004; Liaoet al. 2003a,b). This locomotor gait, termed the Kármán gait, was observed in fishesswimming 3 to 6 fish body lengths downstream of a cylindrical object in the Kármánvortex street shed by this object. When trout, for example, swim in a Kármán street,body kinematics are altered and large lateral oscillations of the center of mass occuras the body is buffeted from side to side in the vortex street. The amplitude of lateral216 Fish·Lauder

ody movement and body curvature are both much greater than during free-streamlocomotion (Liao et al. 2003b). Trout can maintain position in the central downstreamflow in between vortices with very little activity of body musculature. This reductionin muscle activity when swimming in a Kármán vortex street strongly suggeststhat fishes are experiencing a considerable energy savings compared to free-streamlocomotion.Annu. Rev. Fluid. Mech. 2006.38:193-224. Downloaded from arjournals.annualreviews.orgby WEST CHESTER UNIVERSITY on 12/20/05. For personal use only.4. PROSPECTUSNew insights into aquatic propulsion by animals can be exploited for the developmentof advanced propulsive technologies. These insights will come primarilyfrom understanding the unsteady nature of animal movement, measurement of complexmovement in three dimensions, use of computational methods that model boththe animal’s movement and its effect on the surrounding fluid, physiological andbiomechanical studies of locomotor tissues in relation to thrust production and energyrecycling, and analysis of appendages for thrust production, maneuvering, andstability.ACKNOWLEDGMENTSWe appreciate the use of illustrations from L. Howle, E. Paterson, J. Rohr, J. Liao,and W. Rossiter. The research reported herein was supported in part by grants fromthe National Science Foundation, DARPA, and the Office of Naval Research. We aregrateful to R. Mittal, P. Bandyopadhyay, E. Drucker, and P. Madden for numerousdiscussions related to the fluid dynamics of animal propulsion.LITERATURE CITEDAleyev YG. 1977. Nekton. The Hague: JunkAnderson EJ, MacGillivray PS, DeMont ME. 1997. Scallop shells exhibit optimizationof riblet dimensions for drag reduction. Biol. Bull. 192:341–44Anderson EJ, McGillis W, Grosenbaugh MA. 2001. The boundary layer of swimmingfish. J. Exp. Biol. 204:81–102Anderson JM, Streitlien K, Barrett DS, Triantafyllou MS. 1998. Oscillating foils ofhigh propulsive efficiency. J. Fluid Mech. 360:41–72Askew GN, Marsh RL. 1997. The effects of length trajectory on the mechanicalpower output of mouse skeletal muscles. J. Exp. Biol. 200:3119–31Bainbridge R. 1963. Caudal fin and body movement in the propulsion of some fish.J. Exp. Biol. 40:23–56Bandyopadhyay PR. 2004. Biology-inspired science and technology for autonomousunderwater vehicles. IEEE J. Oceanic Eng. 29:542–46Bearman PW, Owen JC. 1998. Reduction of bluff-body drag and suppression ofvortex shedding by the introduction of wavy separation lines. J. Fluid Struct.12:123–30www.annualreviews.org • Fish and Mammal Locomotion 217

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