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Paul S Krueger - One of the best experts on this subject based on the ideXlab platform.
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Effect of vehicle configuration on the performance of a submersible pulsed-jet vehicle at intermediate Reynolds number.
Bioinspiration & biomimetics, 2012Co-Authors: J. Tyler Nichols, Paul S KruegerAbstract:Recent results have demonstrated that pulsed-jet propulsion can achieve Propulsive Efficiency greater than that for steady jets when short, high frequency pulses are used, and the pulsed-jet advantage increases as Reynolds number decreases into the intermediate range (∼50). An important aspect of Propulsive performance, however, is the vehicle configuration. The nozzle configuration influences the jet speed and, in the case of pulsed-jets, the formation of the vortex rings with each jet pulse, which have important effects on thrust. Likewise, the hull configuration influences the vehicle speed through its effect on drag. To investigate these effects, several flow inlet, nozzle, and hull tail configurations were tested on a submersible, self-propelled pulsed-jet vehicle ('Robosquid' for short) for jet pulse length-to-diameter ratios (L/D) in the range 0.5-6 and pulsing duty cycles (St(L)) of 0.2 and 0.5. For the configurations tested, the vehicle Reynolds number (Re(υ)) ranged from 25 to 110. In terms of Propulsive Efficiency, changing between forward and aft-facing inlets had little effect for the conditions considered, but changing from a smoothly tapered aft hull section to a blunt tail increased Propulsive Efficiency slightly due to reduced drag for the blunt tail at intermediate Re(υ). Sharp edged orifices also showed increased vehicle velocity and Propulsive Efficiency in comparison to smooth nozzles, which was associated with stronger vortex rings being produced by the flow contraction through the orifice. Larger diameter orifices showed additional gains in Propulsive Efficiency over smaller orifices if the rate of mass flow was matched with the smaller diameter cases, but using the same maximum jet velocity with the larger diameter decreased the Propulsive Efficiency relative to the smaller diameter cases.
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The effect of Reynolds number on the Propulsive Efficiency of a biomorphic pulsed-jet underwater vehicle
Bioinspiration & biomimetics, 2011Co-Authors: Ali Moslemi, Paul S KruegerAbstract:The effect of Reynolds number on the Propulsive Efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of its propulsion system with squid. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and dimensionless frequency (St(L)) in the range 0.2-0.6 in a glycerin-water mixture. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses from the velocity and vorticity fields of the jet flow to calculate the pulsed-jet Propulsive Efficiency, and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 37 and 60. The current results for Propulsive Efficiency were compared to the previously published results in water where Re ranged between 1300 and 2700. The results showed that the average Propulsive Efficiency decreased by 26% as the average Re decreased from 2000 to 50 while the ratio of pulsed-jet to steady jet Efficiency (η(P)/η(P, ss)) increased up to 0.15 (26%) as the Re decreased over the same range and for similar pulsing conditions. The improved η(P)/η(P, ss) at lower Re suggests that pulsed-jet propulsion can be used as an efficient propulsion system for millimeter-scale propulsion applications. The Re = 37-60 conditions in the present investigation, showed a reduced dependence of η(P) and η(P)/η(P, ss)on L/D compared to higher Re results. This may be due to the lack of clearly observed vortex ring pinch-off as L/D increased for this Re regime.
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Propulsive Efficiency of a biomorphic pulsed jet underwater vehicle
Bioinspiration & Biomimetics, 2010Co-Authors: Ali Moslemi, Paul S KruegerAbstract:The effect of the velocity program and duty cycle (StL) on the Propulsive Efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of essential elements of its propulsion system with squid jet propulsion. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2–6 and StL in the range 0.2–0.6 with jet velocity programs commanded to be triangular or trapezoidal. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses to calculate the pulsed-jet Propulsive Efficiency and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 1300 and 2700 for the conditions tested. The results indicated better Propulsive Efficiency of the trapezoidal velocity program (up to 20% higher) compared to the triangular velocity program. Also, an increase in the ratio of the pulsed-jet Propulsive Efficiency to the equivalent steady jet Propulsive Efficiency (ηP/ηP, ss) was observed as StL increased and L/D decreased. For cases of short L/D and high StL, ηP/ηP, ss was found to be as high as 1.2, indicating better performance of pulsed jets. This result demonstrates a case where propulsion using essential elements of a biological locomotion system can outperform the traditional mechanical system equivalent in terms of Efficiency. It was also found that changes in StL had a proportionately larger effect on Propulsive Efficiency compared to changes in L/D. A simple model is presented to explain the results in terms of the contribution of over-pressure at the nozzle exit plane associated with the formation of vortex rings with each jet pulse.
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hydrodynamics of pulsed jetting in juvenile and adult brief squid lolliguncula brevis evidence of multiple jet modes and their implications for Propulsive Efficiency
The Journal of Experimental Biology, 2009Co-Authors: Ian K. Bartol, Paul S Krueger, William J. Stewart, Joseph T. ThompsonAbstract:The dynamics of pulsed jetting in squids throughout ontogeny is not well understood, especially with regard to the development of vortex rings, which are common features of mechanically generated jet pulses (also known as starting jets). Studies of mechanically generated starting jets have revealed a limiting principle for vortex ring formation characterized in terms of a ;formation number' (F), which delineates the transition between the formation of isolated vortex rings and vortex rings that have; pinched off' from the generating jet. Near F, there exists an optimum in pulse-averaged thrust with (potentially) low energetic cost, raising the question: do squids produce vortex rings and if so, do they fall near F, where Propulsive benefits presumably occur? To better understand vortex ring dynamics and Propulsive jet Efficiency throughout ontogeny, brief squid Lolliguncula brevis ranging from 3.3 to 9.1 cm dorsal mantle length (DML) and swimming at speeds of 2.43-22.2 cms(-1) (0.54-3.50 DMLs(-1)) were studied using digital particle image velocimetry (DPIV). A range of jet structures were observed but most structures could be classified as variations of two principal jet modes: (1) jet mode I, where the ejected fluid rolled up into an isolated vortex ring; and (2) jet mode II, where the ejected fluid developed into a leading vortex ring that separated or ;pinched off' from a long trailing jet. The ratio of jet length [based on the vorticity extent (L(omega))] to jet diameter [based on peak vorticity locations (D(omega))] was 3.0 for jet mode II, placing the transition between modes in rough agreement with F determined in mechanical jet studies. Jet mode II produced greater time-averaged thrust and lift forces and was the jet mode most heavily used whereas jet mode I had higher Propulsive Efficiency, lower slip, shorter jet periods and a higher frequency of fin activity associated with it. No relationship between L(omega)/D(omega) and speed was detected and there was no apparent speed preference for the jet modes within the speed range considered in this study; however, Propulsive Efficiency did increase with speed partly because of a reduction in slip and jet angle with speed. Trends in higher slip, lower Propulsive Efficiency and higher relative lift production were observed for squid /=5.0 cm DML. While these trends were observed when jet mode I and II were equally represented among the size classes, there was also greater relative dependence on jet mode I than jet mode II for squid <5.0 cm DML when all of the available jet sequences were examined. Collectively, these results indicate that approximately 5.0 cm DML is an important ontogenetic transition for the hydrodynamics of pulsed jetting in squids. The significance of our findings is that from early juvenile through to adult life stages, L. brevis is capable of producing a diversity of vortex ring-based jet structures, ranging from efficient short pulses to high-force longer duration pulses. Given that some of these structures had L(omega)/D(omega)s near F, and F represented the delineation between the two primary jet modes observed, fluid dynamics probably played an integral role in the evolution of squid locomotive systems. When this flexibility in jet dynamics is coupled with the highly versatile fins, which are capable of producing multiple hydrodynamic modes as well, it is clear that squid have a locomotive repertoire far more complex than originally thought.
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Effect of Stroke Ratio and Duty Cycle on Propulsive Efficiency of a Pulsed Jet Underwater Vehicle
39th AIAA Fluid Dynamics Conference, 2009Co-Authors: Ali Moslemi, Paul S KruegerAbstract:PP , η η ) as L St increased and L/D decreased. For most cases ss P P , η η was found to be less than 1, indicating better performance of steady jets, but for short L/D and high L St , ss P P , η η > 1 appears to be achievable. It was also found that the changes in L St had a larger effect on Propulsive Efficiency when compared to changes in L/D.
Frank E. Fish - One of the best experts on this subject based on the ideXlab platform.
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Propulsive Efficiency of the Underwater Dolphin Kick in Humans
Journal of biomechanical engineering, 2009Co-Authors: Alfred Von Loebbecke, Rajat Mittal, Frank E. Fish, Russell MarkAbstract:Three-dimensional fully unsteady computational fluid dynamic simulations of five Olympic-level swimmers performing the underwater dolphin kick are used to estimate the swimmer’s Propulsive efficiencies. These estimates are compared with those of a cetacean performing the dolphin kick. The geometries of the swimmers and the cetacean are based on laser and CT scans, respectively, and the stroke kinematics is based on underwater video footage. The simulations indicate that the Propulsive Efficiency for human swimmers varies over a relatively wide range from about 11% to 29%. The Efficiency of the cetacean is found to be about 56%, which is significantly higher than the human swimmers. The computed Efficiency is found not to correlate with either the slender body theory or with the Strouhal number.
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POWER OUTPUT AND Propulsive Efficiency OF SWIMMING BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS)
The Journal of Experimental Biology, 1993Co-Authors: Frank E. FishAbstract:Summary The power output and Propulsive Efficiency of swimming bottlenose dolphins (Tursiops truncatus) were determined from a hydromechanica l model. The Propulsive movements were filmed as dolphins swam in large pools. Dolphins swam at velocities of 1.2‐6.0ms21. Propulsion was provided by dorsoventral oscillations of the posterior body and flukes. The maximum angle of attack of the flukes showed a linear decrease with velocity, whereas the frequency of the Propulsive cycle increased linearly with increasing velocity. Amplitude was 20% of body length and remained constant with velocity. Propulsive Efficiency was 0.81. The thrust power computed was within physiological limits. After correction for effects due to swimming depth, the coefficient of drag was found to be 3.2 times higher than the theoretical minimum assuming turbulent boundary conditions. The motions of the body and flukes are primarily responsible for the increased drag. This analysis supports other studies that indicate that bottlenose dolphins, although well adapted for efficient high-performance swimming, show no unusual hydrodynamic performance.
Russell Mark - One of the best experts on this subject based on the ideXlab platform.
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Propulsive Efficiency of the Underwater Dolphin Kick in Humans
Journal of biomechanical engineering, 2009Co-Authors: Alfred Von Loebbecke, Rajat Mittal, Frank E. Fish, Russell MarkAbstract:Three-dimensional fully unsteady computational fluid dynamic simulations of five Olympic-level swimmers performing the underwater dolphin kick are used to estimate the swimmer’s Propulsive efficiencies. These estimates are compared with those of a cetacean performing the dolphin kick. The geometries of the swimmers and the cetacean are based on laser and CT scans, respectively, and the stroke kinematics is based on underwater video footage. The simulations indicate that the Propulsive Efficiency for human swimmers varies over a relatively wide range from about 11% to 29%. The Efficiency of the cetacean is found to be about 56%, which is significantly higher than the human swimmers. The computed Efficiency is found not to correlate with either the slender body theory or with the Strouhal number.
Rajat Mittal - One of the best experts on this subject based on the ideXlab platform.
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Effect of caudal fin flexibility on the Propulsive Efficiency of a fish-like swimmer
Bioinspiration and Biomimetics, 2014Co-Authors: Michel Bergmann, Angelo Iollo, Rajat MittalAbstract:A computational model is used to examine the effect of caudal fin flexibility on the Propulsive Efficiency of a self-propelled swimmer. The computational model couples a penalization method based Navier-Stokes solver with a simple model of flow induced deformation and self-propelled motion at an intermediate Reynolds number of about 1000. The results indicate that a significant increase in Efficiency is possible by careful choice of caudal fin rigidity. The flow-physics underlying this observation is explained through the use of a simple hydrodynamic force model and guidelines for bioinspired designs of flexible fin propulsors are proposed.
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Propulsive Efficiency of the Underwater Dolphin Kick in Humans
Journal of biomechanical engineering, 2009Co-Authors: Alfred Von Loebbecke, Rajat Mittal, Frank E. Fish, Russell MarkAbstract:Three-dimensional fully unsteady computational fluid dynamic simulations of five Olympic-level swimmers performing the underwater dolphin kick are used to estimate the swimmer’s Propulsive efficiencies. These estimates are compared with those of a cetacean performing the dolphin kick. The geometries of the swimmers and the cetacean are based on laser and CT scans, respectively, and the stroke kinematics is based on underwater video footage. The simulations indicate that the Propulsive Efficiency for human swimmers varies over a relatively wide range from about 11% to 29%. The Efficiency of the cetacean is found to be about 56%, which is significantly higher than the human swimmers. The computed Efficiency is found not to correlate with either the slender body theory or with the Strouhal number.
John O. Dabiri - One of the best experts on this subject based on the ideXlab platform.
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Optimal vortex formation in a self-propelled vehicle
Journal of Fluid Mechanics, 2013Co-Authors: Robert Whittlesey, John O. DabiriAbstract:Previous studies have shown that the formation of coherent vortex rings in the near-wake of a self-propelled vehicle can increase Propulsive Efficiency compared with a steady jet wake. The present study utilizes a self-propelled vehicle to explore the dependence of Propulsive Efficiency on the vortex ring characteristics. The maximum Propulsive Efficiency was observed to occur when vortex rings were formed of the largest physical size, just before the leading vortex ring would pinch off from its trailing jet. These experiments demonstrate the importance of vortex ring pinch off in self-propelled vehicles, where coflow modifies the vortex dynamics.
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The `upstream wake' of swimming and flying animals and its correlation with Propulsive Efficiency
Journal of Experimental Biology, 2008Co-Authors: Jifeng Peng, John O. DabiriAbstract:The interaction between swimming and flying animals and their fluid environments generates downstream wake structures such as vortices. In most studies, the upstream flow in front of the animal is neglected. In this study, we demonstrate the existence of upstream fluid structures even though the upstream flow is quiescent or possesses a uniform incoming velocity. Using a computational model, the flow generated by a swimmer (an oscillating flexible plate) is simulated and a new fluid mechanical analysis is applied to the flow to identify the upstream fluid structures. These upstream structures show the exact portion of fluid that is going to interact with the swimmer. A mass flow rate is then defined based on the upstream structures, and a metric for Propulsive Efficiency is established using the mass flow rate and the kinematics of the swimmer. We propose that the unsteady mass flow rate defined by the upstream fluid structures can be used as a metric to measure and objectively compare the Efficiency of locomotion in water and air.
