scholarly journals A study of short wave instability on vortex filaments

1996 ◽  
Author(s):  
Hong Yun Wang
Keyword(s):  
Short Wave ◽  
Wave Instability ◽  
Vortex Filaments

Short Wave Instability on Vortex Filaments

1998 ◽  
Vol 80 (21) ◽  
pp. 4665-4668 ◽  
Author(s):  
Hongyun Wang
Keyword(s):  
Short Wave ◽  
Wave Instability ◽  
Vortex Filaments

Short wave instability of core‐annular flow

1992 ◽  
Vol 4 (1) ◽  
pp. 186-188 ◽  
Author(s):  
Kang Ping Chen
Keyword(s):  
Annular Flow ◽  
Short Wave ◽  
Wave Instability

scholarly journals On the porosity influence on stability of flow over porous medium

2020 ◽  
Vol 30 (1) ◽  
pp. 134-144
Author(s):  
K.B. Tsiberkin
Keyword(s):  
Porous Medium ◽  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Short Wave ◽  
Wave Instability ◽  
Plane Parallel ◽  
Long Wave ◽  
The Stability ◽  
Critical Wavenumber

The stability of incompressible fluid plane-parallel flow over a layer of a saturated porous medium is studied. The results of a linear stability analysis are described at different porosity values. The considered system is bounded by solid wall from the porous layer bottom. Top fluid surface is free and rigid. A linear stability analysis of plane-parallel stationary flow is presented. It is realized for parameter area where the neutral stability curves are bimodal. The porosity variation effect on flow stability is considered. It is shown that there is a transition between two main instability modes: long-wave and short-wave. The long-wave instability mechanism is determined by inflection points within the velocity profile. The short-wave instability is due to the large transverse gradient of flow velocity near the interface between liquid and porous medium. Porosity decrease stabilizes the long wave perturbations without significant shift of the critical wavenumber. Simultaneously, the short-wave perturbations destabilize, and their critical wavenumber changes in wide range. When the porosity is less than 0.7, the inertial terms in filtration equation and magnitude of the viscous stress near the interface increase to such an extent that the Kelvin-Helmholtz analogue of instability becomes the dominant mechanism for instability development. The stability band realizes in narrow porosity area. It separates the two branches of the neutral curve.

A Visual Study of Vortex Instabilities in the Wake of a Rotor in Hover

2012 ◽  
Vol 57 (4) ◽  
pp. 1-8 ◽  
Author(s):  
Christopher V. Ohanian ◽  
Gregory J. McCauley ◽  
Ömer Savaş
Keyword(s):  
Growth Rate ◽  
Exponential Growth ◽  
Linear Growth ◽  
Short Wave ◽  
Linear Growth Rate ◽  
Water Tank ◽  
Vortex Filaments ◽  
Visual Study ◽  
Helical Vortex ◽  
Wave Instabilities

A visual study of the instability characteristics of the helical vortex filaments trailing from the tips of a three-bladed lifting rotor in a water tank is presented. The rotor diameter was 25.4 cm, and its rotation rate ranged from 4 to 12 revolutions per second. Soon after their formation, the vortex filaments developed long- and short-wave instabilities. In the long-wave instability mode, two of the three vortices coming off the rotor orbited around each other and merged in about 0.4 of the theoretical orbit time of equistrength two-dimensional vortices, after which the third vortex joined the merger to form a single, apparently turbulent helical vortex filament. The wavelengths of the short-wave instabilities were about 0.4 of the wake radius, about 17 cycles over the circumference. The short waves exhibited a linear growth rate during the first half of their orbital motion and an exponential growth prior to merging. The linear growth rate was about 0.0034 D/rad. The e-folding time for the exponential growth rate was about 0.52 rad.

Shear-flow instability due to a wall and a viscosity discontinuity at the interface

1987 ◽  
Vol 179 ◽  
pp. 201-225 ◽  
Author(s):  
A. P. Hooper ◽  
W. G. C. Boyd
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Flow Instability ◽  
Short Wave ◽  
Linear Instability ◽  
Wave Instability ◽  
New Type ◽  
Lower Fluid ◽  
Superposed Fluids ◽  
Shear Flow Instability

Consider the Couette flow of two superposed fluids of different viscosity with the depth of the lower fluid bounded by a wall and the interface while the depth of the upper fluid is unbounded. The linear instability of this flow configuration is studied at all values of flow Reynolds number and disturbance wavelength using both asymptotic and numerical methods. Three distinct forms of instability are found which are dependent on the magnitude of two dimensionless parameters β and (α R)1/3, where β is a dimensionless wavenumber measured on a viscous lengthscale, α is a dimensionless wavenumber measured on the scale of the depth of the lower fluid and R is the Reynolds number of the lower fluid. At large β there is the short-wave instability found previously by Hooper & Boyd (1983). At small β and small (αR)1/3 there is the long-wave instability first discovered by Yih. At small β and large (αR)1/3 there is a new type of instability which arises only if the kinematic viscosity of the lower bounded fluid is less than the kinematic viscosity of the upper fluid.

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