High-bypass ratio turbofan engines are commonly employed  
in aircrafts. Their usage is essential to guarantee small specific  
fuel consumption, reduced CO2 emissions and low noise levels.  
Such modern aero-engines benefit from high efficiencies by operating  
at turbine inlet temperatures in excess of the melting point  
of the turbine components. To enable this, compressor air is supplied  
to the turbine for cooling and purging purposes. The reintroduction  
of the cooling air back into the mainstream flow is  
known to alter the flow field and to affect the aerodynamic performance  
of the turbine components. A component especially  
susceptible to the interaction between the mainstream and purge  
flow is the Turbine Center Frame, located between high-pressure  
turbine (HP) and low-pressure (LP) turbine. For ever higher bypass  
ratios, this turbine transition ducts need to be designed with  
axial lengths as short as possible and larger radial offsets to avoid  
engine weight penalties while at the same time maintaining aerodynamic  
performance. More detailed experience in the field of  
intermediate turbine ducts is needed to identify further opportunities  
to improve turbofan engine performance, including an indepth  
understanding of the interaction between mainstream and  
purge flows.  
This paper presents a Computational Fluid Dynamics (CFD)  
study of the effect of the purge flow temperature, and hence density,  
on the aerodynamic performance of an engine representative  
Turbine Center Frame (TCF). Several steady-state Reynoldsaveraged  
Navier–Stokes (RANS) simulations were conducted  
for varying purge flow temperatures using an in-house code  
called LINARS. Time-averaged five-hole-probe measurements  
acquired in the Transonic Test Turbine Facility (TTTF) at Graz  
University of Technology were used as inlet boundary conditions  
to impose an engine-relevant flow field. The results obtained  
from two reduced and two increased purge flow temperature  
conditions were compared to a reference case. The reference  
case results showed agreement with static wall pressure measurements,  
hence validating the simulation. Changing the purge flow  
temperature significantly affected the main flow locally as well  
as overall. The position and size of vortices in the TCF were  
changed under the presence of hotter or cooler purge flows. Additionally,  
a flow separation on the outer duct wall observed in  
the baseline case was suppressed in the cold-purged flow case.  
The cold-purged TCF showed a 40% lower total pressure loss  
than the hot-purged one. This indicates that a more aggressive  
TCF design may be feasible in a cold-purged operation.


Influence of Purge Temperature Variation on the Performance of Turbine Center Frames

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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