Modern axial compressor demands high performance and increased operating range.
High performance is generally obtained by employing 3D design features, such as leaned
and swept blades. To improve operating range use of circumferential casing grooves is
quite common. A research involving numerical study is carried out to assess the impact
of lean and sweep in an axial compressor performance and stall margin, in presence of
circumferential casing grooves. The numerical methodology used in this study is
validated with performance as well as hub to shroud profile data from NASA Rotor37
test results. NASA Rotor37 is chosen for validation of numerical methodology as this
rotor is a good representative rotor of modern day gas turbine engine compressor axial
rotors. This rotor has a good pressure ratio (2+) and it operates in transonic reason with
shock at the higher span of the rotor. Grid sensitivity as well as turbulence model
validation is carried out to build confidence in the numerical methodology. A no lean
and no sweep blade is generated by radially stacking blade profiles through center of
gravity of hub and shroud profiles of NASA Rotor37. After taking out intermediate
profiles and lean and sweep from NASA Rotor37 the resulting rotor had a lower mass
flow rate than original NASA Rotor37. To get the flow in the similar range as NASA
Rotor37, tip profile is re-staggered. This geometry is used as a baseline geometry.
Leaned and swept geometries are generated by changing the stacking axis in the
circumferential direction and in the direction of chord. Lean and sweep considered in
this study are employed only at part span of the blade. Different amount of lean and
sweep is considered in this study and total eleven leaned rotors and nineteen swept rotors
are compared with baseline rotor. The two top leaned rotors and two top swept rotors,
in terms of stall margin improvements, are combined to create four combined leaned and
swept rotors, to find out the impact on performance. Best stall margin cases are also
investigated without casing grooves. In case of grooved rotors there is a small drop in
choke mass flow observed due to reduction in meridional velocity near tip. It is observed
that lean in the opposite direction of rotation results in reduced tip loading and decreases
separation bubble size. This in turn results in thinner trailing edge wake. Also shock
strength of leaned blade is lower in the suction side near tip region. These factors have
contributed towards increased stall margin for leaned rotors in the opposite direction of rotation. It is observed that there exists an optimum combination of span where lean or
sweep starts from and amount of lean, for the geometry considered here. Effect of
circumferential grooves on leaned blade is found to be more pronounced than on swept
blades in terms of increased operating range of the compressor. Introduction of sweep
has resulted in flow migration and corresponding blade loading redistribution, which
helps in increased stall margin. Impact of sweep is higher on stall margin improvement
than circumferential casing grooves whereas impact of lean in stall margin improvement
is lesser than circumferential casing grooves. It is also observed that in case of swept
rotors low momentum zone near blade tip region is found to be lesser than the baseline
as well as leaned rotors. A nominal decrease in efficiency is observed for all casing
groove cases. The stall margin of the four rotors created by combining top two leaned
and swept rotors are found to be lesser than corresponding leaned only or swept only
rotors. It is noticed that one of the combined leaned and swept rotor has a drastically
reduced stall margin which is due to high losses near the forward part of the rotor blade.
This indicates that these two design features are not additive in terms of stall margin
improvements and they need to be considered together for optimizing stall margin of a
rotor. The swept rotor with best stall margin improvement is also analyzed at part speed
(90% corrected speed). Impact of sweep on stall margin improvement is found to be
more significant than casing groove, when rotor is operating at part speed. Another
observation made is that the efficiency is higher for part speed rotors, which is due to
lesser total pressure loss inside the rotor passages at 90% corrected speed. A detailed
flow field investigation in terms total pressure, total temperature, adiabatic efficiency,
flow angle, Mach number, flow turning, is presented to understand the underlying
physics.