Abstract: The contra-rotating axial machine is a promising solution for several applications, where high pressure and efficiencies are needed. Also, they allow reducing the speed of rotation, the radial spacing and a better flexibility of use. However, this requires a better understanding of their operation, including the influence of second rotor on the overall aerodynamic performances. This work consisted of both experimental and numerical studies to characterize this counter-rotating fan, especially the analysis of the effects of the blades stagger angle and the inter-distance between the rotors. The experimental study served to validate the computational fluid dynamics model (CFD) used in the simulations. The numerical study permitted to cover a wider range of parameter and deeper investigation on flow structures details, including the effects of blade stagger angle and inter-distance, associated with the interaction between the rotors. As a result, there is a clear improvement in aerodynamic performance compared with a conventional machine.
Abstract: This article presents a study of the effect of
a contra-rotating component on the efficiency of centrifugal
compressors. A contra-rotating centrifugal compressor (CRCC) is
constructed using two independent rotors, rotating in the opposite
direction and replacing the single rotor of a conventional centrifugal
compressor (REF). To respect the geometrical parameters of the REF
one, two rotors of the CRCC are designed, based on a single rotor
geometry, using the hub and shroud length ratio parameter of the
meridional contour. Firstly, the first rotor is designed by choosing
a value of length ratio. Then, the second rotor is calculated to be
adapted to the fluid flow of the first rotor according aerodynamics
principles. In this study, four values of length ratios 0.3, 0.4, 0.5, and
0.6 are used to create four configurations CF1, CF2, CF3, and CF4
respectively. For comparison purpose, the circumferential velocity at
the outlet of the REF and the CRCC are preserved, which means that
the single rotor of the REF and the second rotor of the CRCC rotate
with the same speed of 16000rpm. The speed of the first rotor in this
case is chosen to be equal to the speed of the second rotor. The CFD
simulation is conducted to compare the performance of the CRCC
and the REF with the same boundary conditions. The results show
that the configuration with a higher length ratio gives higher pressure
rise. However, its efficiency is lower. An investigation over the entire
operating range shows that the CF1 is the best configuration in this
case. In addition, the CRCC can improve the pressure rise as well
as the efficiency by changing the speed of each rotor independently.
The results of changing the first rotor speed show with a 130% speed
increase, the pressure ratio rises of 8.7% while the efficiency remains
stable at the flow rate of the design operating point.
Abstract: The parametrical study of Shrouded Contra-rotating
Rotor was done in this paper based on 2D axisymmetric simulations.
The calculations were made with an actuator disk as double rotor
model. It objects to explore and quantify the effects of different shroud
geometry parameters mainly using the performance of power loading
(PL), which could evaluate the whole propulsion system capability as
5 Newtontotal thrust generationfor hover demand. The numerical
results show that:The increase of nozzle radius is desired but limited
by the flow separation, its optimal design is around 1.15 times rotor
radius, the viscosity effects greatly constraint the influence of nozzle
shape, the divergent angle around 10.5° performs best for chosen
nozzle length;The parameters of inlet such as leading edge curvature,
radius and internal shape do not affect thrust great but play an
important role in pressure distribution which could produce most part
of shroud thrust, they should be chosen according to the reduction of
adverse pressure gradients to reduce the risk of boundary separation.