Abstract:
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Current state-of-the-art supersonic turbines have been conceived to work under supersonic
ow conditions where the inlet axial velocity is subsonic. For the present case,
an extreme
ow situation has been studied, where the inlet axial velocity component
is supersonic. After the literature, it can be stated that the performance achieved by
conventional turbines working under axial supersonic conditions is extremely low (e -
ciencies of the order of 27%).
As an answer to this challenge, this master thesis presents, for the rst time in the
open literature, the aerodynamic performance study of a new supersonic turbine blade
design intended to work under inlet axial supersonic conditions. For this purpose, an
accurate 3-D Navier-Stokes analysis of the blade performance has been conducted, for
both design and o -design conditions .
At rst, the in
uence of the inlet
ow angle on the blade performance at a given
Mach number was parametrized through steady-state simulations. In a second step,
an implicit time-marching method was used to solve the unsteady Reynolds-Averaged
Navier-Stokes equations. This transient analysis of the turbine performance considered
a sinusoidal inlet angle variation at a frequency of 100 Hz. Finally, in order to study the
in
uence of the inlet Mach number on the establishment of supersonic
ow within the
blade passage, a steady state parametrization of the inlet Mach number for the given
geometry was performed.
Steady state results highlight important drawbacks on the blade performance due to
the nature of the inlet supersonic axial
ow. Oblique shocks are created and ingested
by the turbine blade passage. As a result, large stagnation losses occur, due to the
presence of shocks and its interaction with the blade's boundary layers. By the same
way, the transient analysis points out the importance of the frequency at which the inlet
conditions vary. As the frequency rises, increasingly signi cant hysteresis-like behaviour
of the
ow variables is seen at the outlet of the turbine. Finally, the blade passage's
converging geometry has remarked the importance of the inlet Mach number in order
to correctly establish a supersonic
ow within the passage. For the studied geometry,
a lower limit on Mach number is identi ed, below which the turbine enters into an
unstarted condition, where supersonic
ow could not be established in the passage. |