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Projecte llegit

Títol: Instability mechanisms of fluidic oscillators

Estudiants que han llegit aquest projecte:

Director/a: MELLIBOVSKY ELSTEIN, FERNANDO PABLO

Departament: FIS

Títol: Instability mechanisms of fluidic oscillators

Data inici oferta: 04-02-2017     Data finalització oferta: 04-10-2017


Estudis d'assignació del projecte:
    GR ENG SIST AEROESP
Tipus: Individual
 
Lloc de realització: EETAC
 
Paraules clau:
Active flow control, Fluidic Oscillator, Direct Navier Stokes, Hydrodynamic instability
 
Descripció del contingut i pla d'activitats:
Boundary layer separation results in poor aerodynamic performance of blunt afterbodies and wings at high angles of attack. Active flow control aims at delaying (or even suppressing) separation. This can be achieved by employing periodic perturbation with pulsating jets generated with fluidic oscillators. This project will focus on unveiling the hydrodynamic instability that makes the jet issued by fluidic oscillators pulsate.

The work plan will consist of the following activities

1) Literature review on active flow control, fluidic actuators and fluidic oscillators.

2) Choice of a fluidic oscillator geometry, meshing, spectral-elements computation setup and convergence analysis for domain and mesh optimisation.

3) Parametric exploration of Z2-symmetric flow regimes of the 2D fluidic oscillator at low Reynolds number and characterisation of primary transition.

3) Identification of primary transition upon removal of the Z2-symmetry restriction.

4) Characterisation of the onset of three dimensionality in the stably oscillating regime.

5) Fully 3D DNS simulation of the fluidic oscillator.

6) Conclusions.
 
Overview (resum en anglès):

In this work, direct numerical simulation of the Navier-Stokes equations governing incom-
pressible fluid flow has been employed to analyze the various flow topologies observed in
a two-dimensional fluidic oscillator at the very low Reynolds’s regime (Re ∈ [25,100]), in
order to elucidate the mechanisms by which oscillation begins. The main goal is to find
and classify the characteristics and properties of the jet at the oscillator outlet. The study
has been carried out using software based on spectral elements.
The geometry being fixed and the flow incompressible, the Reynolds’s number is the only
independent parameter. The increasingly complex flow solutions obtained as the Reynolds
is increased have been studied in the light of dynamical systems and bifurcation theory to
explain complex phenomena such as hysteresis or the advent of chaotic dynamics.
An increasing Reynolds’s number turns an initially stationary and reflection-symmetric
jet into non-symmetric, then oscillatory periodic, period doubled and finally chaotic. Sta-
tistical reflection-symmetry is recovered as temporal chaos develops into spatio-temporal
chaos. A few well-known local bifurcations, and possibly some global bifurcation, are
responsible for the transitions.
Additionally, the flow topology of the jet issued from the oscillator exit into the discharge
region has been investigated. The initiation of temporal dynamics is seen to result in
vortex shedding, first periodic, then irregular, from the oscillator outlet diverter.
Finally, a series of discussions on the obtained results will be included that will allow to
finish defining all the elements that make up the study.

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