Aero Engine Intercooling
Doctoral thesis, 2016
Intercooling has the potential to provide a shortcut to the next generation aero engines with
higher bypass ratio (BPR), higher overall pressure ratio (OPR) and higher turbine inlet
temperature (TIT) by lowering the high pressure compressor (HPC) delivery temperature.
To be able to establish a systematic understanding of aero engine intercooling, the heat
transfer and pressure loss characteristics of a given intercooler architecture need to be
known in the parameter range anticipated for the engine optimization. A two-pass cross flow tubular
heat exchanger for aero engine intercooling applications was hence developed by the
means of computational fluid dynamics (CFD). Optimizations with this
intercooler installed were performed by considering the intercooler design parameters and the
engine design simutaneously. A geared variant was adopted to complement the use of intercooling as
it could support high OPR engines better by allowing a lower position installtion of the HPC.
For a flight mission, further optimization of the intercooled engines was acheived by
controlling the amount of intercooling for different engine operating points in two ways.
One is intercooler external flow control by a separate variable nozzle and another one
is intercooler internal flow variable flow path. As the flight altitude strongly influences
the working condition for an aero engine, considerable SFC benefit can be obtained by limiting
intercooling at high altitude operation. Nevertheless, the precondition is to enable a
higher OPR at the take-off operation by intercooling.
Compared to a reference non-intercooled geared engine, an optimal intercooled geared engine with intercooling
control shows a 4.9\% better mission fuel burn under the same engine technology level assumptions. However,
the optimum is still constrained by the last stage compressor blade height. To further explore the potential
of intercooling the constraint limiting the axial compressor last stage blade height is
relaxed by introducing an axial-radial combined HPC. The axial–radial
high pressure ratio configuration allows for an ultrahigh OPR. With an
optimal top-of-climb (TOC) OPR of 140, the configuration provides a 5.3\% fuel burn benefit
over the geared reference engine.
Experimental validation of the intercooler design and the CFD design tool is also presented
in this thesis. With the help of particle image velocimetry (PIV) and pressure measurements,
flow topology inside the intercooler was visualized. Generally, by comparing the CFD results
and the experimental data, the computational capability of porous media modeling predicting the flow
distribution within the tubular heat transfer units was confirmed. The flow topology within
the associated ducts was considered well-described by CFD.
variable flow path