Jet engine spare parts are expensive. Hence, for economic reasons,
as many components as possible should be repaired. For
planning the repair or regeneration process, defects must be identified
early. The present paper explores whether the detection and
examination of inhomogeneities in the temperature distribution in
an exhaust gas stream of a jet engine can be used for the identification
and localization of defects before engine disassembly. In
order to be able to assign the defects to the resulting temperature
non-uniformity in the exhaust gas, the mixing characteristics of the
temperature inhomogeneities in the turbine caused by the defects
are examined. A three-dimensional unsteady CFD-simulation of a
whole turbine with a complex temperature distribution at the inlet is
carried out. The simulations show, that the temperature inhomogeneities
are barely mixed out with the surrounding flow. To
describe the mixing effects a coefficient (turbine mixing factor) is
derived. The factor enables an integral assessment of the mixing
behaviour of inhomogeneities within and outside of turbine stages.
It is a well known fact that turbocharger works
with pulsating exhaust flow in its entire operating
life, hence the need to predict unsteady performance.
This paper presents the unsteady performance
prediction resultof a single entry nozzleless
mixed flow turbine under steady flow and 60
Hz pulsating flow at 43.0 rps/
K operating speed.
The modeling method coupled one-dimensional gas
dynamic modelwith a mean-line model to predict
the turbine efficiency by appropriate losses consideration.
The coupled method assumes that the turbine
volute has a large volume and length, so that
unsteadiness effect of the pulsating flow is significant
while the rotor is assumed to behave quasisteadily.
A pressure drop boundary is used to simulate
pressure drop across the turbine volute. The
coupled method was validated with the experimentally
measured steady state results of the same turbine.
Experimentally measured total conditions of
the flow were used as inlet conditions for the model
during unsteady analysis. The predicted isentropic
power averaged results show convincing match with
the experimental data. This will set forward a systematic
approach for engine designers to evaluate
turbine performance beyond what will be normally
provided by turbocharger manufacturers, which is
the steady state map.
Mixing losses due to cavity related flows in axial steam
turbines contribute considerably to overall aerodynamic losses.
The coherent study presented in this paper examines the
influence of rotor inlet cavity geometry on stage efficiency. The
experimental work is supported by computational analysis. Inlet
cavity geometry has been varied by reducing the axial and radial
cavity lengths along with the volume. Six different configurations
have been examined, focusing mainly on the flow interactions
occurring at the zone between the cavity and main flow and their
impact on stage efficiency. An upper stator-casing platform
prolonged by 17% and 34%, and a radial wall length shortened
by 13% and 25% offered a cavity volume reduction of 14% and
28%, respectively, compared to the initial cavity volume. The
axial cavity wall length reduction impacts drastically on the
vortex formation inside the cavity. A 17% length reduction leads
initially to the bifurcation and re-connection of the vortex during
inflow, whereas the 34% length reduction completely eliminates
the presence of any vortex. On the other hand, the radial cavity
wall length reduction affects the vortex positioning. Generally,
the cases with radial wall length reduction show higher efficiency
relative to the axial cavity length reduction. For the 14% cavity
volume reduction cases this difference rises to 1%, and for the
28% cavity volume reduction the difference is even higher,
attaining a 1.7% efficiency increase.