Publications Research

Fluid dynamic drag in animal swimming and flying

On the diverse roles of fluid dynamic drag in animal swimming and flying
R. Godoy-Diana & B. Thiria
Journal of the Royal Society Interface 15 20170715 (2018)

Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. read more »



ESPCI proposes a brand new international doctoral programme – UPtoPARIS: More info here:

The first call closes on February 28th, 2018. Our project on bio-inspired wave-energy conversion is one of the projects selected (project page here).

Bio-inspired elastic structures for ocean wave energy conversion

The purpose of this project is to study a surface wave absorbing system with potential for both coastal erosion control and renewable energy production. The system is inspired by the fluid flow calming effects of aquatic vegetation in near-shore and riverine environments. The system consists of an ensemble of flexible slender structures mimicking an underwater canopy whose collective dynamics is forced by the action of the waves. The reconfiguration of slender structures by their interaction with an external flow has been a vibrant subject of research in the past decade, and applications abound in this archetype of interdisciplinary subject where biology, physics and engineering meet. read more »


Conferences, workshops, etc. 2018

Deadline watch for 2018…

TAU-ESPCI Winter School on Active Matter
Jan. 28 – Feb 1, 2018, Tel Aviv, Deadline: Nov 1, 2017

APS March Meeting 2018
March 5-9, 2018, Los Angeles, CA, Deadline: November 3, 2017
read more »


Marion Segall’s PhD defense. Water as a driver of evolution: the example of aquatic snakes

PhD defense on November 10th, at 2pm, in the auditorium of the Grande Galerie de l’Evolution.

Water as a driver of evolution: the example of aquatic snakes

Marion Segall

1. UMR 7179, CNRS-MNHN, Mécanismes adaptatifs et Evolution, équipe FUNEVOL, Département d’Ecologie et de Gestion de la Biodiversité. Pavillon d’anatomie comparée, 55 rue Buffon, case postale 55, 75231 Paris cedex 5, France.
2. UMR 7636, CNRS, ESPCI Paris–PSL Research University, Sorbonne Université, U Paris Diderot, Physique et Mécanique des Milieux Hétérogènes. 10 rue Vauquelin, 75005 Paris, France


Animal-environment interactions are determinant in driving the evolution of phenotypic variation. Most aquatic animals have developed adaptations to overcome the physical constraints inherent to an aquatic lifestyle and particularly to motion in water. These constraints are the drag and the added mass if an acceleration is involved in the motion, such as during prey capture. The aim of this project is to evaluate the role of water as a potential driver of evolution of aquatic snakes by focusing on morphological and behavioral convergences during underwater prey capture. Snakes are a good model as an aquatic life-style has originated independently in different genera. However, aquatic snakes did not develop a suction feeding system in contrast to most aquatic vertebrates. Prey-capture under water is constrained by the physical properties of the fluid and thus morphological and/or behavioral convergence is expected. By comparing the head shapes and the behavior of different species, we evaluated the impact of water on the evolution of head shape and strike behavior. By using experimental fluid mechanics approaches, we quantified the physical constraints involved in prey capture and evaluated the nature of the evolutionary response in response to these hydrodynamic constraints. This interdisciplinary approach allowed us to bring novel data to our understanding of functional constraints as drivers of phenotypic evolution.


Harvey LILLYWHITE (University of Florida) Rapporteur
Patricia ERN (Institut de Mécanique des Fluides de Toulouse) Rapporteur
Sam VAN WASSENBERGH (Universiteit Antwerpen) Examinateur
Catherine QUILLIET (Université Grenoble-Alpes) Examinateur
Anthony HERREL (Muséum National d’Histoire Naturelle) Directeur de thèse
Ramiro GODOY-DIANA (ESPCI Paris – CNRS) Directeur de thèse

Publications Research

Flapping elastic plates as a model of fish-like swimmers

Modelling of an actuated elastic swimmer
M. Piñeirua, B. Thiria & R. Godoy-Diana
Journal of Fluid Mechanics 829 731-750 (2017)
[doi:10.1017/jfm.2017.570]PDF file

We studied the force production dynamics of undulating elastic plates as a model for fish-like inertial swimmers. Using a beam model coupled with Lighthill’s large-amplitude elongated-body theory, we explore different localised actuations at one extremity of the plate (heaving, pitching and a combination of both) in order to quantify the reactive and resistive contributions to the thrust. The latter has the read more »

Publications Research Video

Synchronisation and pattern formation in fish swimming


Simple phalanx pattern leads to energy saving in cohesive fish schooling
I. Ashraf, H. Bradshaw, T. T. Ha, J. Halloy, R. Godoy-Diana, B. Thiria
PNAS 114 (36) 9599-9604 (2017)
[doi:10.1073/pnas.1706503114]PDF file

Synchronisation and collective swimming patterns in Hemigrammus bleheri
I. Ashraf, R. Godoy-Diana, J. Halloy, B. Collignon, B. Thiria
Journal of the Royal Society Interface 13 20160734 (2016)
[doi:10.1098/rsif.2016.0734] PDF file

The question of how individuals in a population organize when living in groups arises for systems as different as a swarm of microorganisms or a flock of seagulls. The different patterns for moving collectively involve a wide spectrum of reasons, such as evading predators or optimizing food prospection. Also, the schooling pattern has often been associated with an advantage in terms of energy consumption. We use a popular aquarium fish, the red nose tetra fish, Hemigrammus bleheri, which is known to swim in highly cohesive groups, to ana- lyze the schooling dynamics. In our experiments, fish swim in a shallow-water tunnel with controlled velocity, read more »

Publications Research

Hydrodynamic constraints and evolution of aquatic snakes

snakesDoes aquatic foraging impact head shape evolution in snakes ?
M. Segall, R. Cornette, A-C. Fabre, R. Godoy-Diana & A. Herrel
Proceedings of the Royal Society B 283 20161645 (2016).
[doi:10.1098/rspb.2016.1645] PDF file

Evolutionary trajectories are often biased by developmental and historical factors. However, environmental factors can also impose constraints on the evolutionary trajectories of organisms leading to convergence of morphology in similar ecological contexts. The physical properties of water impose strong constraints on aquatic feeding animals by generating pressure waves that can alert prey and potentially push them away from the mouth. These hydrodynamic constraints have resulted in the independent evolution of suction feeding in most groups of secondarily aquatic tetrapods. Despite the fact that snakes cannot use suction, they have invaded the aquatic milieu many times independently. Here, we test whether the aquatic environment has constrained head read more »


Volumetric velocimetry of wake vortices produced by an undulatory swimmer

Our last poster in collaboration with Francisco Huera-Huarte from Universitat Rovira i Virgili presented at the APS Gallery of Fluid Motion in the DFD 2015 Meeting.

poster APS DFD2015_LowRes

Publications Research

Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers

resistive_vs_reactiveResistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers
M. Piñeirua, R. Godoy-Diana & B. Thiria
Physical Review E 92 021001(R) (2015).
[doi:10.1103/PhysRevE.92.021001] arXiv

We address here a crucial point regarding the description of moderate to high Reynolds numbers aquatic swimmers. For decades, swimming animals have been classified in two different families of propulsive mechanisms based on the Reynolds number: the resistive swimmers, using local friction to produce the necessary thrust force for locomotion at low Reynolds number, and the reactive swimmers, lying in the high Reynolds range, and using added mass acceleration (described by perfect fluid theory). read more »

Publications Research

Centrifugal instability of Stokes layers in crossflow

centrifugal_instability_cylinderCentrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake
J. D’Adamo, R. Godoy-Diana & J. E. Wesfreid
Proceedings of the Royal Society A 471: 20150011 (2015).

A circular cylinder oscillating in a viscous fluid produces an axisymmetric Stokes layer, a fundamental flow susceptible to centrifugal instabilities [see e.g. Seminara & Hall, Proc. Roy. Soc. London A 350, 299 (1976)]. In the present work we study such problem in the wake flow around a circular cylinder at Re = 100 performing rotary oscillations. read more »

Publications Research

Four-winged flapping flyer in forward flight

mite4ailes Four-winged flapping flyer in forward flight
R. Godoy-Diana, P. Jain, M. Centeno, A. Weinreb & B. Thiria
In Klapp et al. (eds.), Selected Topics of Computational and Experimental Fluid Mechanics, Environmental Science and Engineering, pp. 147-158. Springer (2015).
[doi:10.1007/978-3-319-11487-3_8] PDF file

We study experimentally a four-winged flapping flyer with chord-wise flexible wings in a self-propelled setup. For a given physical configuration of the flyer (i.e. fixed distance between the forewing and hindwing pairs and fixed wing flexibility), we explore the kinematic parameter space constituted by the flapping frequency and the forewing-hindwing phase lag. read more »

Publications Research

Undulatory swimming near a wall

wall_effect_visuLarge-amplitude undulatory swimming near a wall
R. Fernández-Prast, V. Raspa, B. Thiria, F. Huera-Huarte & R. Godoy-Diana. Bioinspiration and Biomimetics 10 016003 (2015).


[PDF file]

We study experimentally the propulsive dynamics of flexible undulating foils in a self-propelled swimming configuration near a wall. Measurements of swimming speed and propulsive force are performed, together with full recordings of the elastic wave kinematics and particle image velocimetry. read more »


Habilitation à diriger des recherches (HDR)

Bio-inspired swimming and flying – Vortex dynamics and fluid/structure interaction

Ramiro Godoy-Diana
Habilitation à diriger des recherches, Université Pierre et Marie Curie, 2014.

PDF file here (19.4 MB)

The present document, prepared in view of obtaining the Habilitation à diriger des recherches, reviews my main research subject at PMMH since 2006, which concerns the study of swimming and flying inspired by nature. Canonical examples of flapping flight and undulatory swimming are explored using simplified experimental models as a starting point. This allows for the discussion of some fundamental questions related to the physics of bio-inspired locomotion at “intermediate” Reynolds numbers. In particular, we address the strong fluid-structure interactions that arise in these problems, where we have focused on: simplified models of flapping foils in hydrodynamic tunnel experiments, especially in the dynamics of vorticity in the wake of an oscillating foil ; mechanical models of flapping flyers with flexible wings in a self-propelled configuration (in the spirit of the pioneer experiments of Etienne-Jules Marey), as well as novel experimental models of undulatory swimming.
read more »

Publications Research Video

Elastic swimmer on a free surface

Elastic swimmer on a free surface
S. Ramananarivo, B. Thiria & R. Godoy-Diana.
Physics of Fluids, 26: 091112 (2014)
*31st Annual Gallery of Fluid Motion (Pittsburgh, Pennsylvania, USA, 2013)

Publications Research

Drag in undulatory swimmers

vortices_foilsVortex-induced drag and the role of aspect ratio in undulatory swimmers
V. Raspa, S. Ramananarivo, B. Thiria & R. Godoy-Diana. Physics of Fluids, 26 : 041701 (2014).

During cruising, the thrust produced by a self-propelled swimmer is balanced by a global drag force. For a given object shape, this drag can involve skin friction or form drag, both being well-documented mechanisms. However, for swimmers whose shape is changing in time, the question of drag is not yet clearly established. read more »

Publications Research

Propagating waves in bounded elastic media

fig_beamsPropagating waves in bounded elastic media: an application to the efficiency of bio-inspired swimmers
S. Ramananarivo, R. Godoy-Diana & B. Thiria.
EPL, 105 : 54003 (2014).

Confined geometries usually involve reflected waves interacting together to form a spatially stationary pattern. Our recent study on the locomotion of a self-propelled elastic swimmer on a free surface [Ramananarivo et al. 2013], however, has shown that propagating wave kinematics can naturally emerge in a forced elastic rod, even with boundary conditions involving significant reflections. This particular behavior is observed only in the presence of strong damping. read more »


Sophie Ramananarivo’s PhD: Propulsion biomimétique de structures élastiques

PhD defense on January 10, 2014 at ESPCI

Propulsion biomimétique de structures élastiques

Sophie Ramananarivo


Birds and aquatic animals exploit the surrounding fluid to propel themselves in air or water. In inertial regimes, the mechanisms of propulsion are based on momentum transfer; by flapping wings or fins, animals accelerate fluid in their wake, creating a jet that propels them forward. The structures used to move can be flexible, and are thus likely to experiment large bending. Literature showed that those passive deformations can improve propulsive performance, when exploited in a constructive way. The mechanisms at play however remain poorly understood. In the present thesis, we aim at studying how a flapping elastic structure generates thrust, using two experimental biomimetic models. The first setup is a simplified mechanical insect with flexible wings, and the second one is a swimmer whose elastic body mimics the undulating motion of an eel. We show that propulsive performance is significantly influenced by the way the systems passively bend, and that their elastic response can be described by simplified theoretical models of forced oscillators. Those models also bring forward the crucial role of the quadratic fluid damping that resists the flapping motion. This result introduces the counter-intuitive idea that it is sometimes desirable to dissipate part of the energy in the fluid, in order to improve performance.

Christophe Clanet (Rapporteur)
Christophe Eloy (Rapporteur)
Yves Couder (Président)
Emmanuel de Langre (Examinateur)
Jean-Marc Di Meglio (Examinateur)
Ramiro Godoy-Diana (Directeur de Thèse)
Benjamin Thiria (Directeur de Thèse)

Publications Research Video

Passive elastic mechanism to mimic fish-muscles action in anguilliform swimming

nageur_Ramananarivo_etalPassive elastic mechanism to mimic fish-muscles action in anguilliform swimming
S. Ramananarivo; R. Godoy-Diana & B. Thiria.
Journal of the Royal Society Interface 10 : 20130667 (2013).

Abstract: Swimmers in nature use body undulations to generate propulsive and maneuvering forces. The an- guilliform kinematics is driven by muscular actions all along the body, involving a complex temporal and spatial coordination of all the local actuations. Such swimming kinematics can be reproduced artificially, in a simpler way, by using passively the elasticity of the body. Here we present experiments on self-propelled elastic swimmers at a free surface in the inertial regime. read more »

Publications Research

Topology-induced effect in biomimetic propulsive wakes

two_flapsTopology-induced effect in biomimetic propulsive wakes
V. Raspa; R. Godoy-Diana & B. Thiria.
Journal of Fluid Mechanics, 729: 377-387 (2013).

Abstract: It is known that the wake pattern observed in a cross-section behind swimming or flying animals is typically characterized by the presence of periodical vortex shedding. However, depending on species, propulsive wakes can differ according to the spatial ordering of the main vortex structures. We conducted a very precise experiment to analyse the role of the topology of the wake in the generation of propulsion by comparing two prototypical cases in a quasi-two-dimensional view. read more »

Publications Research

Force balance in the take-off of a pierid butterfly

Force balance in the take-off of a pierid butterfly: relative importance and timing of leg impulsion and aerodynamic forces

G. Bimbard, D. Kolomenskiy, O. Bouteleux, J. Casas & R. Godoy-Diana.
Journal of Experimental Biology, 216 : 3551-3563 (2013).

Abstract: Up to now, the take-off stage remains an elusive phase of insect flight relatively poorly explored compared to other maneuvers. An overall assessment of the different mechanisms involved in the force production during take-off has never been explored. Focusing on the first downstroke, we have addressed this problem from a force balance perspective in butterflies taking-off from the ground. read more »

Publications Research

Stabilizing effect of flexibility in the wake of a flapping foil

flex_vs_rig_jetStabilizing effect of flexibility in the wake of a flapping foil
C. Marais; B Thiria; Wesfreid, J. E. & R. Godoy-Diana.
Journal of Fluid Mechanics, 710 : 659-669 (2012).

Abstract: The 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. read more »

Publications Research

Spatiotemporal spectral analysis of a forced cylinder wake

spectral_analysisSpatiotemporal spectral analysis of a forced cylinder wake
J. D’Adamo; R. Godoy-Diana & J. E. Wesfreid.
Physical Review E, 84 : 056308 (2011).

Abstract: The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at $Re=100$. Two-dimensional particle image velocimetry on the mid-plane perpendicular to the axis of cylinder is used to characterize the spatial development of the flow and its stability properties. read more »

Publications Research

Behind the performance of flapping wing flyers

flapping_wingRather than resonance, flapping wing flyers may play on aerodynamics to improve performance
S. Ramananarivo; R. Godoy-Diana & B. Thiria.
Proceedings of the National Academy of Sciences (USA), 108 (15): 5964-5969 (2011).

Abstract: Saving energy and enhancing performance are secular preoccupations shared by both nature and human beings. In animal locomotion, flapping flyers or swimmers rely on the flexibility of their wings or body to passively increase their efficiency using an appropriate cycle of storing and releasing elastic energy. Despite the convergence of many observations pointing out this feature, the underlying mechanisms explaining how the elastic nature of the wings is related to propulsive efficiency remain unclear. Here we use an experiment with a self-propelled simplified insect model allowing to show how wing compliance governs the performance of flapping flyers. read more »


Catherine Marais’ PhD. Dynamique tourbillonnaire dans le sillage d’un aileron oscillant

PhD defense on January 14th, 2011 at Amphi Langevin, ESPCI

Dynamique tourbillonnaire dans le sillage d’un aileron oscillant: Propulsion par ailes battantes biomimétiques

Catherine Marais


This thesis deals with the fundamental mechanisms implied in flapping based propulsion systems. We use a simplified model, which consists of a flapping foil, placed in a hydrodynamic tunnel. This set up allows us to establish a framework for the analyse of wakes produced. Particularly, we are interested with the influence of the foil flexibility on these wakes. We define a 2D phase space (frequency and amplitude of the flapping), in which we identify three main flow regimes, associated with three vortices wake type. The PIV technique allows us to precisely analyse and quantify the physical and geometrical parameters of the observed wakes. The mean force is estimated for each regime, using a standard momentum balance. We localise then the drag-propulsion transition in our phase space. We show that the propulsive performance of flexible foils is superior to that of the rigid foil, and we suggest some explanations to explain this result.


Olivier Doaré (Examinateur) ENSTA, Palaiseau
Marie Farge (Examinatrice) ENS, Paris
Stéphane Popinet (Rapporteur) NIWA, New Zealand
Lionel Schouveiler (Rapporteur) IRPHE, Marseille
José Eduardo Wesfreid (Directeur de thèse) PMMH, Paris
Ramiro Godoy-Diana (Co-Directeur de thèse) PMMH, Paris

Publications Research

Impulse response in the subcritical cylinder wake

impulse_cylinder_wakeConvective instability in inhomogeneous media: impulse response in the subcritical cylinder wake
C. Marais; R. Godoy-Diana; D. Barkley & J. E. Wesfreid.
Physics of Fluids, 23 (1): 014104 (2011).

Abstract: We study experimentally the impulse response of a cylinder wake below the critical Reynolds number of the Bénard-von Kármán instability. In this subcritical regime, a localized inhomogeneous region of convective instability exists which causes initial perturbations to be transiently amplified. The aim of this work is to quantify the evolution resulting from this convective instability using two-dimensional particle image velocimetry in a hydrodynamic tunnel experiment. read more »

Publications Research Video

Bending to fly

How wing compliance drives the efficiency of self-propelled flapping flyers
B. Thiria & R. Godoy-Diana.
Physical Review E, 82 : 015303(R) (2010).
*arXiv preprint blogged in MIT Technology Review (March 2, 2010)
*Also referenced in Vir. J. Bio. Phys. Res. / Volume 20 / Issue 3 / (August 1, 2010)


Abstract: Wing flexibility governs the flying performance of flapping-wing flyers. Here, we use a self-propelled flapping-wing model mounted on a ”merry go roun” to investigate the effect of wing compliance on the propulsive efficiency of the system. read more »

Publications Research

Symmetry breaking of the reverse Bénard-von Kármán vortex street

flap_fluo_BKI_ASYM_smallA model for the symmetry breaking of the reverse Bénard-von Kármán vortex street produced by a flapping foil
R. Godoy-Diana; C. Marais; J. L. Aider & J. E. Wesfreid.
Journal of Fluid Mechanics, 622 : 23-32 (2009).

Abstract: The vortex streets produced by a flapping foil of span-to-chord aspect ratio of 4:1 are studied in a hydrodynamic tunnel experiment. In particular, the mechanisms giving rise to the symmetry breaking of the reverse Bénard-von Kármán vortex street that characterizes fish-like swimming and forward flapping flight are examined. Two-dimensional particle image velocimetry measurements in the mid-plane perpendicular to the span axis of the foil are used to characterize the different flow regimes. read more »

Publications Research Video

Transitions in the wake of a flapping foil

transitions_wakeTransitions in the wake of a flapping foil
R. Godoy-Diana; J. L. Aider & J. E. Wesfreid.
Physical Review E, 77 : 016308 (2008).

Abstract: We study experimentally the vortex streets produced by a flapping foil in a hydrodynamic tunnel, using two-dimensional particle image velocimetry. An analysis in terms of a flapping frequency-amplitude phase space allows the identification of (i) the transition from the well-known Bénard-von Kármán (BvK) wake to the reverse BvK vortex street that characterizes propulsive wakes, and (ii) the symmetry breaking of this reverse BvK pattern giving rise to an asymmetric wake. read more »

Publications Research

Tuning a wave-energy-driven OWC seawater pump to polychromatic waves

polychromatic_signalsOn the tuning of a wave-energy driven oscillating-water-column seawater pump to polychromatic waves
R. Godoy-Diana & S. P. R. Czitrom.
Ocean Engineering, 34 : 2374-2384 (2007).

Abstract: Performance of wave-energy devices of the oscillating water column (OWC) type is greatly enhanced when a resonant condition with the forcing waves is maintained. The natural frequency of such systems can in general be tuned to resonate with a given wave forcing frequency. In this paper we address the tuning of an OWC sea-water pump to polychromatic waves. We report results of wave tank experiments, which were conducted with a scale model of the pump. read more »

Publications Research Video

Internal gravity waves in a dipolar wind

Internal gravity waves in a dipolar wind: a wave–vortex interaction experiment in a stratified fluid
R. Godoy-Diana; J. M. Chomaz & C. Donnadieu.
Journal of Fluid Mechanics, 548 : 281-308 (2006).


Abstract: An experimental study on the interaction of the internal wave field generated by oscillating cylinders in a stratified fluid with a pancake dipole is presented. The experiments are carried out in a salt-stratified water tank with constant Brunt–Väisälä frequency ($N$). Experimental observations of the deformation of the wave beams owing to the interaction with the dipole are presented. read more »

Publications Research

Vertical length scale selection for pancake vortices in strongly stratified viscous fluids


Vertical length scale selection for pancake vortices in strongly stratified viscous fluids
R. Godoy-Diana; J. M. Chomaz & P. Billant.
Journal of Fluid Mechanics, 504 : 229-238 (2004).

Abstract: The evolution of pancake dipoles of different aspect ratio is studied in a stratified tank experiment. Two cases are reported here for values of the dipole initial aspect ratio $\alpha_0 = L_v/L_h$ (where $L_v$ and $L_h$ are vertical and horizontal length scales, respectively) of $\alpha_0 = 0.4$ (case I) and $\alpha_0 = 1.2$ (case II). read more »


The dynamics of pancake vortices in strongly stratified fluids

schmidt I did my PhD at LadHyX during 2000-2004 supervised by Jean-Marc Chomaz. My dissertation was an experimental and theoretical study of the dynamics of pancake vortices and their interaction with internal gravity waves in a strongly stratified fluid.

Abstract. Stably stratified fluids give rise to distinct internal wave modes and potential vorticity modes (PV). The timescales relevant to these two types of motion separate when the stratification is strong: Internal waves propagate on a fast timescale based on the buoyancy frequency (TN = N-1) while a slower timescale in terms of the horizontal advection —TA = Lh/U, where Lh and U are the horizontal length scale and mean velocity of the horizontal motions— characterizes the evolution of vortices. An illustration of the difference between these two modes can be observed in turbulent regions decaying in presence of background stable stratification : As vertical motions are suppressed, energy is either radiated as internal waves, which propagate away from the initially turbulent region, or transferred to horizontal advective motions which are finally organized as patches of potential vorticity. This thesis presents a theoretical and experimental study of the interaction between pancake vortices (representing the PV mode) and internal gravity waves in a strongly stratified fluid, and of the diffusive mechanisms of pancake vortices.

Document indexed at

read more »

Publications Research

Diffusion of pancake-like vortices in cyclostrophic balance

conical_diffuserEffect of the Schmidt number on the diffusion of axisymmetric pancake vortices in a stratified fluid
R. Godoy-Diana & J. M. Chomaz.
Physics of Fluids, 15 : 1058-1064 (2003).

Abstract: An asymptotic analysis of the equations for quasi-two-dimensional flow in stratified fluids is conducted, leading to a model for the diffusion of pancake-like vortices in cyclostrophic balance. This analysis permits one to derive formally the model for the diffusion of an axisymmetric monopole proposed by Beckers et al. [J. Fluid Mech. 433, 1 (2001)], and to extend their results. The appropriate parameter for the perturbation analysis is identified as the square of the vertical Froude number Fv=U/(Lv N), where U is the horizontal velocity scale, N is the Brunt–Väisälä frequency, and Lv the vertical length scale. read more »

Publications Research

Hydrodynamics of an oscillating water column seawater pump

sibeo_colorHydrodynamics of an oscillating water column seawater pump. Part I: Theoretical Aspects
S. P. R. Czitrom; R. Godoy; E. Prado; P. Pérez & R. Peralta-Fabi.
Ocean Engineering, 27 : 1181-1198 (2000).

Abstract: A wave-driven seawater pump, composed of a resonant and an exhaust duct joined by a variable-volume air compression chamber, is studied. The time dependent form of Bernoulli’s equation, adapted to incorporate losses due to friction, vortex formation at the mouths and radiation damping, describes the pump behaviour. A dimensional analysis of the pump equations shows that a proposed scale-model will perform similar to a full-scale seawater pump. read more »

Publications Research

Hydrodynamics of an oscillating water column seawater pump (Part II)

sibeoHydrodynamics of an oscillating water column seawater pump. Part II: Tuning to Monochromatic Waves
S. P. R. Czitrom; R. Godoy; E. Prado; A. Olvera & C. Stern.
Ocean Engineering, 27 : 1199-1219 (2000).

Abstract: Flume experiments with a scale-model of a wave driven seawater pump in monochromatic waves are described. A tuning mechanism optimises the pump performance by keeping it at resonance with the waves. The pumping process itself was found to de-tune the system because of the reduced gravity restoring force due to spilling in the compression chamber. A perturbation analysis of the pump equations shows that performance of the system can be increased by optimising the shape of the pump intake to minimise losses due to vortex formation. read more »

Publications Research

Vortex suppresion in an oscillating flow

conical_diffuserVortex suppresion in an oscillating flow
C. Stern; S. Czitrom; E. Prado & R. Godoy.
Revista Mexicana de Fisica, 46 : 409-410 (2000).

Abstract: The motivation for this work was the reduction of losses due to vortex formation at the entrance of a wave driven seawater pump. Measurements in a wave tank using a prototype had shown a 10% ¡ncrease in the pumping efficiency when a trumpet like shape was added to the intake. This lead us to search for an inlake that would reduce or completely suppress vortex formation. In this experiment a piston produces an oscil1ating flow inside a partly submerged duct. At the end of the duct four different shapes were tested. read more »

Publications Research

Oscillating Flow through a Funnel

vortex_owc_exitOscillating Flow through a Funnel
C. Stern; S. Czitrom & R. Godoy.
Physics of Fluids, 11 : S3 (Gallery of Fluids) (1999).

Abstract: Our interest in vortex suppression at the entrance of a wave-driven seawater pump leads us to study vortex formation at the exit of a diffuser due to an oscillating flow. In the present experiment, a piston produces an oscillating flow inside a partly submerged duct that ends in a diffuser. The diffuser is designed such that a constant relationship between centripetal and inertial forces is maintained along the profile. The flow in the near field of the mouth is visualized by injecting diluted fluorescent water paint just outside the diffuser. read more »