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.

# Tag Archives: vortex dynamics

Research## Volumetric velocimetry of wake vortices produced by an undulatory swimmer

22 November 2015 – 0 h 00 min

## Centrifugal instability of Stokes layers in crossflow

6 May 2015 – 0 h 00 min

** ****Centrifugal 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).

DOI:10.1098/rspa.2015.0011

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

## Undulatory swimming near a wall

5 January 2015 – 0 h 00 min

**Large-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).

doi:10.1088/1748-3190/10/1/016003

## Elastic swimmer on a free surface

8 February 2014 – 14 h 34 min

**Elastic swimmer on a free surface**

S. Ramananarivo, B. Thiria & R. Godoy-Diana.

*Physics of Fluids*, ** 26**: 091112 (2014)

[doi:10.1063/1.4893539]

**31st Annual Gallery of Fluid Motion (Pittsburgh, Pennsylvania, USA, 2013)*

## Drag in undulatory swimmers

8 February 2014 – 14 h 28 min

**Vortex-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).

## Transitions in the wake of a flapping foil

24 January 2008 – 0 h 00 min

**Transitions 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

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

16 April 2004 – 14 h 29 min

**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

19 March 2004 – 12 h 00 min

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 (T_{N} = N^{-1}) while a slower timescale in terms of the horizontal advection —T_{A} = L_{h}/U, where L_{h} 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 https://pastel.archives-ouvertes.fr/tel-00007046/

## Diffusion of pancake-like vortices in cyclostrophic balance

4 March 2003 – 0 h 00 min

**Effect 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

## Vortex suppresion in an oscillating flow

1 July 2000 – 0 h 00 min

**Vortex 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

## Oscillating Flow through a Funnel

1 September 1999 – 0 h 00 min

**Oscillating 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