Optimal vortex formation in a self-propelled vehicle

2013 ◽  
Vol 737 ◽  
pp. 78-104 ◽  
Author(s):  
Robert W. Whittlesey ◽  
John O. Dabiri
Keyword(s):  
Vortex Ring ◽  
Vortex Dynamics ◽  
Vortex Formation ◽  
Vortex Rings ◽  
Near Wake ◽  
Propulsive Efficiency ◽  
Physical Size ◽  
Coherent Vortex

AbstractPrevious 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.

scholarly journals Vortex-enhanced propulsion

2010 ◽  
Vol 668 ◽  
pp. 5-32 ◽  
Author(s):  
LYDIA A. RUIZ ◽  
ROBERT W. WHITTLESEY ◽  
JOHN O. DABIRI
Keyword(s):  
Pressure Field ◽  
Vortex Formation ◽  
Added Mass ◽  
Vortex Rings ◽  
Local Pressure ◽  
Propulsion Systems ◽  
Near Wake ◽  
Propulsive Efficiency ◽  
Flow Unsteadiness ◽  
Vehicle Efficiency

It has been previously suggested that the generation of coherent vortical structures in the near-wake of a self-propelled vehicle can improve its propulsive efficiency by manipulating the local pressure field and entrainment kinematics. This paper investigates these unsteady mechanisms analytically and in experiments. A self-propelled underwater vehicle is designed with the capability to operate using either steady-jet propulsion or a pulsed-jet mode that features the roll-up of large-scale vortex rings in the near-wake. The flow field is characterized by using a combination of planar laser-induced fluorescence, laser Doppler velocimetry and digital particle-image velocimetry. These tools enable measurement of vortex dynamics and entrainment during propulsion. The concept of vortex added-mass is used to deduce the local pressure field at the jet exit as a function of the shape and motion of the forming vortex rings. The propulsive efficiency of the vehicle is computed with the aid of towing experiments to quantify hydrodynamic drag. Finally, the overall vehicle efficiency is determined by monitoring the electrical power consumed by the vehicle in steady and unsteady propulsion modes. This measurement identifies conditions under which the power required to create flow unsteadiness is offset by the improved vehicle efficiency. The experiments demonstrate that substantial increases in propulsive efficiency, over 50 % greater than the performance of the steady-jet mode, can be achieved by using vortex formation to manipulate the near-wake properties. At higher vehicle speeds, the enhanced performance is sufficient to offset the energy cost of generating flow unsteadiness. An analytical model explains this enhanced performance in terms of the vortex added-mass and entrainment. The results suggest a potential mechanism to further enhance the performance of existing engineered propulsion systems. In addition, the analytical methods described here can be extended to examine more complex propulsion systems such as those of swimming and flying animals, for whom vortex formation is inevitable.

Formation regimes of vortex rings in negatively buoyant starting jets

2013 ◽  
Vol 716 ◽  
pp. 470-486 ◽  
Author(s):  
C. Marugán-Cruz ◽  
J. Rodríguez-Rodríguez ◽  
C. Martínez-Bazán
Keyword(s):  
Vortex Ring ◽  
Richardson Number ◽  
Vortex Formation ◽  
Vortex Rings ◽  
Vortex Identification ◽  
Buoyant Flows ◽  
Formation Number ◽  
Secondary Vortices ◽  
Starting Jet ◽  
Negatively Buoyant

AbstractThe formation of vortex rings in negatively buoyant starting jets has been studied numerically for different values of the Richardson number, $\mathit{Ri}$, covering the range of weak to moderate buoyancy effects ($0\leq \mathit{Ri}\leq 0. 20$). Two different regimes have been identified in the vortex formation and the transition between them takes place at $\mathit{Ri}\approx 0. 03$. The vorticity distribution inside the vortex ring after pinching off from the trailing stem as well as the total amount of circulation it encloses (characterized by the formation number, $F$) show different behaviours with the Richardson number in the two regimes. The differences are associated with the different mechanisms by which the head vortex absorbs the circulation injected by the starting jet. While secondary vortices are engulfed by the leading vortex before separating from the trailing jet in the weak buoyancy effects regime ($0\lt \mathit{Ri}\lt 0. 03$), this phenomenon is not observed in the moderate buoyancy effects regime ($0. 03\lt \mathit{Ri}\lt 0. 2$). Moreover it is shown that the formation number of a negatively buoyant vortex ring can be determined by considering that its dynamics are similar to that of a neutrally buoyant vortex but propagating with velocity corresponding to the negatively buoyant one. Based on this simple idea, a phenomenological model is presented to describe quantitatively the evolution of the formation number with the Richardson number, $F(\mathit{Ri})$, obtained numerically. In addition, the limitations of different vortex identification methods used to evaluate the vortex properties in buoyant flows are discussed.

Investigations Of Pressure Pulsations In A Model Of Draft Tube Of Hydraulic Turbine Caused By Vortex Rings

2016 ◽  
Vol 11 (4) ◽  
pp. 25-32
Author(s):  
Sergey Skripkin ◽  
Mikhail Tsoy ◽  
Sergey Shtork ◽  
Pavel Kuibin
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Vortex Rings ◽  
Experimental Investigations ◽  
Visualization Technique ◽  
Vortex Rope ◽  
Hydro Turbine ◽  
Hydraulic Turbines

Current work is devoted to experimental investigations of behavior of precessing vortex rope in a draft tube model of hydraulic turbine. We used combination of stationary and freely rotating swirlers as a hydro turbine model. Such construction provides velocity distribution on the draft tube inlet close to distribution in natural hydraulic turbines operated at non-optimal conditions. The phenomenon of precessing vortex rope reconnection with further formation of vortex ring was founded in this experimental research using high-speed visualization technique. Synchronization of highspeed visualization and pressure measurements allowed us to relate pressure shock on the draft tube wall with vortex ring moving along wall.

scholarly journals Stabilizing effect of flexibility in the wake of a flapping foil

2012 ◽  
Vol 710 ◽  
pp. 659-669 ◽  
Author(s):  
C. Marais ◽  
B. Thiria ◽  
J. E. Wesfreid ◽  
R. Godoy-Diana
Keyword(s):  
Symmetry Breaking ◽  
Vortex Dynamics ◽  
Momentum Balance ◽  
Near Wake ◽  
Low Speed ◽  
Flapping Foil ◽  
Balance Calculation ◽  
Stabilizing Effect ◽  
Dynamical Features ◽  
Regime Transitions

AbstractThe wake of a flexible foil undergoing pitching oscillations in a low-speed hydrodynamic tunnel is used to examine the effect of chordwise foil flexibility in the dynamical features of flapping-based propulsion. We compare the regime transitions in the wake with respect to the case of a rigid foil and show that foil flexibility inhibits the symmetry breaking of the reverse Bénard–von Kármán wake reported in the literature. A momentum balance calculation shows the average thrust to be up to three times greater for the flexible foil than for the rigid foil. We explain both of these observations by analysing the vortex dynamics in the very near wake.

Near wake vortex dynamics of a hovering hawkmoth

2008 ◽  
Vol 25 (1) ◽  
pp. 23-36 ◽  
Author(s):  
Hikaru Aono ◽  
Wei Shyy ◽  
Hao Liu
Keyword(s):  
Vortex Dynamics ◽  
Wake Vortex ◽  
Near Wake

Laminar to Turbulent Buoyant Vortex Ring Regime in Terms of Reynolds Number, Bond Number, and Weber Number

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Xueying Yan ◽  
Rupp Carriveau ◽  
David S. K. Ting
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Weber Number ◽  
High Speed ◽  
Reynolds Numbers ◽  
Bond Number ◽  
Vortex Rings ◽  
Transition Regime ◽  
Turbulent Vortex ◽  
Buoyant Vortex Rings

When buoyant vortex rings form, azimuthal disturbances occur on their surface. When the magnitude of the disturbance is sufficiently high, the ring will become turbulent. This paper establishes conditions for categorization of a buoyant vortex ring as laminar, transitional, or turbulent. The transition regime of enclosed-air buoyant vortex rings rising in still water was examined experimentally via two high-speed cameras. Sequences of the recorded pictures were analyzed using matlab. Key observations were summarized as follows: for Reynolds number lower than 14,000, Bond number below 30, and Weber number below 50, the vortex ring could not be produced. A transition regime was observed for Reynolds numbers between 40,000 and 70,000, Bond numbers between 120 and 280, and Weber number between 400 and 800. Below this range, only laminar vortex rings were observed, and above, only turbulent vortex rings.

Ionic Wind Application to Vortex Ring Generator and its Transportation Efficiency

2019 ◽  
Author(s):  
Kengo Fukunaga ◽  
Masayoshi Satake ◽  
Noboru Maeda ◽  
Kazushi Shikata ◽  
Tomohisa Ezaka
Keyword(s):  
Kinetic Energy ◽  
Mechanical System ◽  
Electric Power ◽  
Vortex Ring ◽  
Energy Conversion Efficiency ◽  
Target Distance ◽  
Vortex Rings ◽  
Experimental Measurements ◽  
Ionic Wind ◽  
External Turbulence

Abstract In this study, ionic wind generated in corona discharge is focused for producing an air flow without having mechanical actuators. First, the kinetic energy conversion efficiency to ionic wind from electric power is experimentally estimated to be 0.32%. Then, it is confirmed that intermittent blows of ionic wind enable to produce vortex rings without using mechanical system. We adopt novel sub-chamber structure to avoid the concentration of the substance in a vortex ring low, so that the substance concentration transported to the target distance of 200 mm increases by 9%. As an application, the efficiency for moisture transportation is evaluated through experimental measurements. As a result, it is shown that the substance (moisture) can be transported at an efficiency of about 85% to target distance of 200 mm under conditions where the influence of external turbulence is small.

scholarly journals Hydrodynamics of Vortex Generation during Bell Contraction by the Hydromedusa Eutonina indicans (Romanes, 1876)

Biomimetics ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 44 ◽  
Author(s):  
John H. Costello ◽  
Sean P. Colin ◽  
Brad J. Gemmell ◽  
John O. Dabiri
Keyword(s):  
Vortex Dynamics ◽  
Swimming Speed ◽  
Momentum Flux ◽  
Energy Transport ◽  
Opposite Sign ◽  
Vortex Rings ◽  
Vortex Generation ◽  
Fish Swimming ◽  
Linear Path ◽  
Hydrodynamic Wake

Swimming bell kinematics and hydrodynamic wake structures were documented during multiple pulsation cycles of a Eutonina indicans (Romanes, 1876) medusa swimming in a predominantly linear path. Bell contractions produced pairs of vortex rings with opposite rotational sense. Analyses of the momentum flux in these wake structures demonstrated that vortex dynamics related directly to variations in the medusa swimming speed. Furthermore, a bulk of the momentum flux in the wake was concentrated spatially at the interfaces between oppositely rotating vortices rings. Similar thrust-producing wake structures have been described in models of fish swimming, which posit vortex rings as vehicles for energy transport from locations of body bending to regions where interacting pairs of opposite-sign vortex rings accelerate the flow into linear propulsive jets. These findings support efforts toward soft robotic biomimetic propulsion.

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