 |
| Titel |
Complex Flow Image Velocimetry in Shock Instabilities with Fractal Boundaries |
| VerfasserIn |
Jackson David Tellez Alvarez, Teresa Vila |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137459
|
| Publikation (Nr.) |
 EGU/EGU2017-179.pdf |
|
|
|
|
|
| Zusammenfassung |
| We use an advanced version of Correlation Particle Image Velocimetry used in surface flows
SFIV [1,2] in order to analyze the complex patterns due to the basic instabilities and
boundary conditions, and to relate the production and detection of vortices, advected by
fast flows with cores of low pressure. These coincide with the 3D lines of strong
vorticity or helicity. For example in fast flowing rivers or laboratory experiments of
environmental hydraulics [3] or shocks in compressible mixing [4]. The mixing fronts
interacts with a density interface producing positive or negative baroclinic structures
with varying turbulent cascades[5]. LIF Images of the thickness of the mixing zone
at the centre of a shock tube, allow us to perform Multi-Fractal analysis on the
evolution of the interfaces [6,7]. The interactions of the pressure fronts with balloons
filled with various density gas also allow a wide range of initial conditions. In the
same way, using wakes of fractal grids also modify the cascade proceses[7,8]. The
three-dimensional mixing zone, its thickness and topology are important experimental
measurements. The three basic cases are: when the shock wave passes from a heavy gas to a
light one; from a gas to another of similar densities and from a light gas to a heavy
one.
We consider body forces and the effect of Baroclinic production of vorticity [5]. The
Lagrangian statistics and the characterization of the topology used in SFIV analysis [1,2] is
based on the Okubo-Weiss criterion which is an approximate method of partitioning the
topologically distinct regions, based on the relative values of
Q(x,y) = s(x,y)2 − ω(x,y)2
with s(x,y) the local shear, and ω(x,y) the local vorticity, which is obtained using
DigiFlow [4] in real, or Fourier space. In order to evaluate the scale to scale transfer of
energy, vorticity and helicity; descriptors of great importance in complex flow processes and
intermittency, the data from numerical simulations[5,7] are compared with laboratory
experiments [8] in different types (2D-3D) of the turbulence cascade, using models of relative
scaling exponents which are estimated as functions of the fractal dimension, D and the
spectral slope b. Numerical simulations of Multi-Fractal grids are performed through
OpenFoam or incompact3d software; using either direct numerical simulation (DNS) or
Large Eddy Simulation (LES)[9].
REFERENCES
[1] Tellez, J., M. Gomez, B. Russo, J.M. Redondo Surface Flow Image Velocimetry
(SFIV) for hydraulics applications, 18th International Sym- posium on the Application of |
|
|
|
|
|
|