Abstract:
This Philosophiae Doctor thesis presents the motivation, objectives and reasoning behind
the undertaken project. This research, study the capability of compressible Implicit Large
Eddy Simulation (ILES) in predicting free shear layer flows, under different free stream
regimes (Static and Co-flow jets).
Unsteady flows or jet flows are non-uniform in structure, temperature, pressure and
velocity. Turbulent mixing is of particular importance for the developing of this class of
flows. As a shear layer is formed immediately downstream of the jet exhaust, an early linear
instability involving exponential growth of small perturbations is introduced at the jet
discharge. Beyond this development stage, in the non-linear Kelvin-Helmholtz instability
region large scale vortex rings roll up, and their dynamics of formation and merging become
the defining feature of the transitional shear flow into fully developed regime. This
class of flows is particularly relevant to numerical predictions, as the extreme nature of
the flow in question is considered as a benchmark; however, experimental data should be
selected carefully as some results are controversial. To qualify the behaviour of unsteady
flows, some important criteria have been selected for the analysis of the flow quantities
at different regions of the flow field (average velocities, Reynolds stresses and dissipation
rates). A good estimation of high-order statistics (Standard Deviation, Skewness and
Kurtosis) correspond to mathematical steadiness and convergence of results. From the
physical point of view, similarity analysis between jet’s wake sections reveals physical
steadiness in results. Spectral analysis of the different regions of the flow field could be
used as a sign that the energy cascade is correctly predicted or efficiently enough since this
is where the smallest scales are usually present and which in effect require to be modelled
by the different numerical schemes. Cont/d.
