TY - JOUR
T1 - Characteristics of vortex formation and thrust performance in drag-based paddling propulsion
JF - The Journal of Experimental Biology
JO - J. Exp. Biol.
SP - 2283
LP - 2291
DO - 10.1242/jeb.050716
VL - 214
IS - 13
AU - Kim, Daegyoum
AU - Gharib, Morteza
Y1 - 2011/07/01
UR - http://jeb.biologists.org/content/214/13/2283.abstract
N2 - Several characteristics of drag-based paddling propulsion are studied with a simple mechanical model and a measurement technique for mapping three-dimensional flow fields. In drag-based propulsion, the temporal change of the vortex strength is an important parameter in the relationship between vortex formation and thrust generation. Our results indicate that spanwise flow behind the paddling propulsor significantly affects tip vortex development and thrust generation. The distribution of spanwise flow is dependent on the propulsor shape and the Reynolds number. A delta-shaped propulsor generates strong spanwise flow compared with a rectangular propulsor. For the low Reynolds number case, spanwise flow is not as strong as that for the high Reynolds number case. Without sacrificing total impulse, the flexible propulsor can smooth out thrust peaks during sudden stroke motions, which is favorable for avoiding structural failures and stabilizing body motion. We also explored the role of stopping vortex shedding in efficient thrust generation by determining the relationship between stroke angles and total impulses generated by paddling propulsors. Aarea on the z=0 planeAplate areacwidth of the platemean width of the plateCqnquasi-steady force coefficient acting normally on the plate surfaceCTthrust coefficientEYoung's modulusEInon-dimensional flexural stiffness per unit widthEIddimensional flexural stiffness per unit widthFhydrodynamic force acting on the objectFqntotal quasi-steady force acting normally on the plate surfacehthickness of the plateI∞non-dimensional total impulse in the x-directionIxnon-dimensional impulse in the x-directionnon-dimensional second moment of plate area with respect to the rotating axissplate span lengthSvector of the surface spanned by the close vortex loopSxarea of S projected on the y–z planetnon-dimensional timeTstroke time of a plate during the power stroketddimensional timeunon-dimensional velocityuddimensional velocityUcharacteristic velocity (=sΩ)V∞infinite flow field volumeVbbody volumexnon-dimensional coordinatexddimensional coordinateαcoordinate along the span of the plate from the baseΓnon-dimensional circulation of a vortexΓddimensional circulation of a vortexθangle between the plate and the x=0 planeρffluid densityρmplate densityτintegral variable for timeφstroke angle of the power strokeωnon-dimensional vorticityωddimensional vorticityΩmean angular velocity of the motor during rotation
ER -