86 research outputs found
Attractive internal wave patterns
This paper gives background information for the fluid dynamics video on
internal wave motion in a trapezoidal tank.Comment: 2 pg, movie at two resolutions _low(Low-resolution) and
_hr(High-resolution
Attractive internal wave patterns
This paper gives background information for the fluid dynamics video on
internal wave motion in a trapezoidal tank.Comment: 2 pg, movie at two resolutions _low(Low-resolution) and
_hr(High-resolution
Evolution of the Leading-Edge Vortex over an Accelerating Rotating Wing
AbstractThe flow field over an accelerating rotating wing model at Reynolds numbers Re ranging from 250 to 2000 is investigated using particle image velocimetry, and compared with the flow obtained by three-dimensional time-dependent Navier-Stokes simulations. It is shown that the coherent leading-edge vortex that characterises the flow field at Re~200-300 transforms to a laminar separation bubble as Re is increased. It is further shown that the ratio of the instantaneous circulation of the leading-edge vortex in the accel-eration phase to that over a wing rotating steadily at the same Re decreases monotonically with increasing Re. We conclude that the traditional approach based on steady wing rotation is inadequate for the prediction of the aerodynamic performance of flapping wings at Re above about 1000
Three-dimensional advective--diffusive boundary layers in open channels with parallel and inclined walls
We study the steady laminar advective transport of a diffusive passive scalar
released at the base of narrow three-dimensional longitudinal open channels
with non-absorbing side walls and rectangular or truncated-wedge-shaped
cross-sections. The scalar field in the advective--diffusive boundary layer at
the base of the channels is fundamentally three-dimensional in the general
case, owing to a three-dimensional velocity field and differing boundary
conditions at the side walls. We utilise three-dimensional numerical
simulations and asymptotic analysis to understand how this inherent
three-dimensionality influences the advective-diffusive transport as described
by the normalised average flux, the Sherwood or Nusselt numbers for mass
or heat transfer, respectively. We show that is well approximated by an
appropriately formulated two-dimensional calculation, even when the boundary
layer structure is itself far from two-dimensional. This important result can
significantly simplify the modelling of many laminar advection--diffusion
scalar transfer problems: the cleaning or decontamination of confined channels,
or transport processes in chemical or biological microfluidic devices
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The magic carpet: an arbitrary spectrum wave maker for internal waves
Abstract: We present a novel apparatus for generating internal waves of arbitrary size and shape, including both phase-locked and propagating waves. It is an actively driven, flexible “magic carpet” in the base of a tank. Our wave maker is computer-controlled to enable easy configuration. The actuation of a smooth, flexible surface produces clean waveforms with a predictable spectrum, for which we derive a theoretical model. We demonstrate the versatility of our wave maker through an experimental study of linear and nonlinear, isolated, and combined internal waves, including some that are sufficiently nonlinear to break remote from their source. Graphic abstract
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