A computational investigation of aerodynamic characteristics of model counter-rotating fan with BPR=20, developed in CIAM in the framework of European Project COBRA (Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine), is presented in the work. Unsteady nature of the flow in counter-rotating fan has been studied including analysis of rotor-rotor interaction intensity and unsteady viscous wakes propagation through the axial gap and second rotor blade passages.The results of numerical investigation of the fan tone noise in approach operational conditions are also presented. The acoustic calculations were performed using in-house CIAM aeroacoustic code 3DAS. Directivity diagrams for the first 16 harmonics of tone noise in the forward hemisphere, obtained in the calculation, are shown. Comparison between these results and analogous results for model HBR counter-rotating fan with BPR=10 (designed in VITAL project) is performed. Additionally results were compared with experimental results for HBR fan.

One of the vital tasks related to the improvement of the efficiency of turbomachines is an increase in their operating altitude by reducing the influence of Reynolds numbers, Re, on the turbomachine parameters. Therefore, the results presented in this work on the effect of Re on parameters of an axial compressor composed of two high-loaded stages are attractive both from scientific and practical points of view. This work presents the results of experimental investigations of Re effect on gas-dynamic characteristics of a highly-loaded two-stage compressor (HPC-2), simulating the first two stages of the High Pressure Compressor, (HPC), for an advanced engine. The compressor has the following key gasdynamic parameters: – corrected mass flow rate: 31.8 kg/s – total pressure ratio: 3.7 – coefficient of aerodynamic load: 0.421 The experimental study of HPC-2 is carried out at the Central Institute of Aviation Motors, (CIAM), C-3 test facility. Reynolds number is changed by decreasing pressure at the inlet from 1 bar to 0.2 bar and changing the clocking position of stator rows at optimal points of performance for two rotational speeds, 0.7 and 0.88. Tests of HPC-2 compressor show that a stepwise decrease of the inlet pressure from 1.0 0.7, 0.4 down to 0.2 bar (a decrease in Re from 1785000 to 294000) leads to a smooth decrease in maximum compressor efficiency by 1% and a shift of compressor characteristics towards lower air flow rates (by 2%). The experimental studies of compressors for present-day engines show that unsteady processes play a key role in compressor efficiency and stability. One way to control unsteady flow in compressors is clocking effect. Recently clocking of stators and rotors has been investigated in details using the HPC-2 two-stage compressor (total pressure ratio 3.7) in H = 0; M = 0 conditions. The effect of Reynolds number on compressor characteristics is studied in this work for the HPC-2 compressor while also investigating stator clocking effect. The rotor clocking effect is not studied. Tests of HPC-2 compressor show that a decrease in the inlet pressure and changes in Re results in a stronger clocking effect, which is 0.5% in terms of efficiency under atmospheric conditions at the inlet and reaches 1% with a decrease in the inlet pressure from atmospheric pressure down to 0.2 bar.

One of the perspective schemes of air breathing engine is a scheme with Ultra High Bypass Ratio (BPR 16...25) Counter Rotating Fan. This solution potentially allows significant increase of fuel efficiency compared to modern conventional turbofans. The model UHBR counter rotating fan named COBRA-1 was developed by CIAM within the framework of European Project COBRA (Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine). The fan was designed using up-to-date 1D, 2D and 3D methods. COBRA-1 is a 0.7 m diameter model of counter rotating fan driven by a planetary reduction gearbox. The bypass ratio of COBRA-1 is 20. The R2/R1 torque ratio was chosen to obtain 1.42-muliple prevalence in power for 2nd row. The blade numbers are 8/12 for R1/R2 correspondingly. Final geometry of airfoils was defined by 3D profiling process to achieve required aerodynamics and acoustic parameters. Application of control-diffusion airfoils allows reaching high integral performances: specific mass flow equals 211 kg/(s*m^2) and isentropic efficiency at design point is higher than 0.93. The paper presents results of computational simulation of the flow in UHBR fan COBRA-1 based on 3D steady RANS method, 3D URANS and Non-Linear Harmonic method for different operation conditions in comparison with experimental data. Numerical simulation was carried out using Numeca FINE TURBO software package. Steady RANS approach was used during design process to make quick estimation of performances at different rpm. 3D URANS simulation was conducted to analyze unsteady wake-blade and shock-wave interaction and to make a decision about sufficient value of axial gap between rotors. The COBRA-1 fan was tested in CIAM at C3-A test facility which allows conducting a wide range of measurements of local and integral parameters including acoustics of ducted counter rotating fan at different operating conditions. Experimental results demonstrate a high level of integral performances and good agreement with computed values. Significant part of numerical and experimental investigation is devoted to effect of gear-box requirements on aerodynamics. C3-A rig allows to set rotational speed of rotors independently and measure torques at each shaft to achieve required torque ratio and study the influence of small (3–5%) deviation in rpm on aerodynamic characteristics.

The results of the high bypass ratio turbofan fan tone noise simulation performed in CIAM (Central Institute of Aviation Motors) are presented. The feature of a design of the fan is that in it support struts are integrated to the stator. This investigation is a continuation of a series of papers devoted to numerical calculation of fan tone noise done in CIAM using the 3DAS (3 Dimensional Acoustics Solver) CIAM in-house solver. The calculation was performed at the approach operational conditions of the fan. As a result of the calculation the fields of the flow pulsations in the near field and the distribution of sound pressure levels in the far field on the surface surrounding the fan was obtained. It was shown that the distribution is strongly nonuniform both in the polar and in the azimuth directions. The results of the computation are compared with the experimental data from the CIAM C-3A acoustic test facility. In general, satisfactory correspondence between the calculation and the experiment for the directivity of sound in the horizontal plane is obtained.

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