### Abstract

We establish a general formula for the translational speed of a counter-rotating vortex pair, valid for thick cores, moving in an incompressible fluid with and without viscosity. We extend to higher order the method of matched asymptotic expansions developed by Ting and Tung (1965 Phys. Fluids 8 1039-51). The solution of the Euler or the Navier-Stokes equations is constructed in the form of a power series in a small parameter, the ratio of the core radius to the distance between the core centers. For a viscous vortex pair, the small parameter should be where ν is the kinematic viscosity of the fluid and Γ is the circulation of each vortex. A correction due to the effect of finite thickness of the vortices to the traveling speed makes its appearance at fifth order. A drastic simplification is achieved of expressing it solely in terms of the strength of the second-order quadrupole field associated with the elliptical deformation of the core. For a viscous vortex pair, we exploit the conservation law for the hydrodynamic impulse to derive the growth of the distance between the vortices, which is cubic in time.

Original language | English |
---|---|

Article number | 031401 |

Journal | Fluid Dynamics Research |

Volume | 50 |

Issue number | 3 |

DOIs | |

Publication status | Published - Mar 29 2018 |

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### All Science Journal Classification (ASJC) codes

- Mechanical Engineering
- Physics and Astronomy(all)
- Fluid Flow and Transfer Processes

### Cite this

*Fluid Dynamics Research*,

*50*(3), [031401]. https://doi.org/10.1088/1873-7005/aaa5c8

**Finite-thickness effect on speed of a counter-rotating vortex pair at high Reynolds numbers.** / Habibah, Ummu; Nakagawa, Hironori; Fukumoto, Yasuhide.

Research output: Contribution to journal › Article

*Fluid Dynamics Research*, vol. 50, no. 3, 031401. https://doi.org/10.1088/1873-7005/aaa5c8

}

TY - JOUR

T1 - Finite-thickness effect on speed of a counter-rotating vortex pair at high Reynolds numbers

AU - Habibah, Ummu

AU - Nakagawa, Hironori

AU - Fukumoto, Yasuhide

PY - 2018/3/29

Y1 - 2018/3/29

N2 - We establish a general formula for the translational speed of a counter-rotating vortex pair, valid for thick cores, moving in an incompressible fluid with and without viscosity. We extend to higher order the method of matched asymptotic expansions developed by Ting and Tung (1965 Phys. Fluids 8 1039-51). The solution of the Euler or the Navier-Stokes equations is constructed in the form of a power series in a small parameter, the ratio of the core radius to the distance between the core centers. For a viscous vortex pair, the small parameter should be where ν is the kinematic viscosity of the fluid and Γ is the circulation of each vortex. A correction due to the effect of finite thickness of the vortices to the traveling speed makes its appearance at fifth order. A drastic simplification is achieved of expressing it solely in terms of the strength of the second-order quadrupole field associated with the elliptical deformation of the core. For a viscous vortex pair, we exploit the conservation law for the hydrodynamic impulse to derive the growth of the distance between the vortices, which is cubic in time.

AB - We establish a general formula for the translational speed of a counter-rotating vortex pair, valid for thick cores, moving in an incompressible fluid with and without viscosity. We extend to higher order the method of matched asymptotic expansions developed by Ting and Tung (1965 Phys. Fluids 8 1039-51). The solution of the Euler or the Navier-Stokes equations is constructed in the form of a power series in a small parameter, the ratio of the core radius to the distance between the core centers. For a viscous vortex pair, the small parameter should be where ν is the kinematic viscosity of the fluid and Γ is the circulation of each vortex. A correction due to the effect of finite thickness of the vortices to the traveling speed makes its appearance at fifth order. A drastic simplification is achieved of expressing it solely in terms of the strength of the second-order quadrupole field associated with the elliptical deformation of the core. For a viscous vortex pair, we exploit the conservation law for the hydrodynamic impulse to derive the growth of the distance between the vortices, which is cubic in time.

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U2 - 10.1088/1873-7005/aaa5c8

DO - 10.1088/1873-7005/aaa5c8

M3 - Article

VL - 50

JO - Fluid Dynamics Research

JF - Fluid Dynamics Research

SN - 0169-5983

IS - 3

M1 - 031401

ER -