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.

This paper presents experimental investigations of aerodynamic and acoustic characteristics for the C179-2 bypass fan model with different versions of a slot-type casing treatment (CT). This work aims at optimization the CT configuration for a simultaneously improvement of aerodynamic parameters (efficiency and stall margin), as well as the use of this CT as a reactive type silencer to reduce fan noise. All versions of the slot-type CTs under study are designed on the basis of a semi-empirical procedure developed by CIAM. Three versions of a slot-type CT are designed and tested as applied to the C179-2 fan model. Based on the analysis of experimental data found by aerodynamic tests to study the effect of the number of CT rows, the geometry of CT slots, their relative positions and the height of its annular cavity on key aerodynamic characteristics of the C179-2 fan model, it is found that: - all CTs under study considerably increase stall margins (by 8%–16%) of the fan in moderate and high modes determined by n-corrected rotational speed (n = 75–100 %). The stall margin at n = 54 % increases by approx. 30 %. - relative position of slots in the three CTs with identical number of slots in both rows has a noticeable effect on the CT gas-dynamic efficiency. A half-step shift of axes of the slots relative to each other leads to a slight increase (by max. 1.6%) in stall margins in moderate and high modes and a considerable increase in efficiency (by avg. 2 %) in the same modes, except for n = 100 %. The beneficial effect of the CT on an increase in stall margins ASM and efficiency (along the operating line) is found for the C179-2 single-row bypass fan model stage with total pressure ratio 1.56 in the bypass duct and corrected tip speed 404 m/s. A series of experimental studies of acoustic characteristics of the C179-2 fan model stage with three versions of the slot-type casing treatment is completed in conditions of the C-3A acoustic test facility with an anechoic chamber. The acoustic tests of the fan model are carried out within n = 40–100 % corrected rotational speeds (as compared with the nominal speed). The specified speed range covers takeoff (n = 90.7 %), climb (n = 85.2 %), cruise (n = 100 %), and approach (n = 58.2 %) modes. For all fan operating modes, narrow-band noise spectra and radiation patterns are compared for the C179-2 model configurations with a smooth flow passage and with the CT. In addition to a substantial improvement in gas-dynamic characteristics, the use of the slot-type CT for the C179-2 bypass fan model stage results in a considerable improvement in its acoustic characteristics. In total, the sound power of the C179-2 single-row by-pass fan model decreases by 3 dB for three certification modes.

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A computational investigation of acoustic characteristics of model ducted counter-rotating fan COBRA-1 with ultra-high bypass ratio 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 paper. Calculations of acoustic characteristics of the fan were performed at five operational conditions. For three of them the sums of rotation frequencies of rotors corresponded to those expected for approach conditions, and they differed from each other by relations between frequencies of rotors, and for other two the sums of rotation frequencies corresponded to cutback and sideline operational conditions. Numerical investigations were conducted using the method of 3D numerical calculation of interaction between fan rows implemented in 3DAS (3 Dimensional Acoustics Solver) CIAM in-house solver. The data were compared with the results of the experiments conducted in the CIAM test rig C-3A. The results of comparison show satisfactory qualitative and, in some positions of microphones, quantitative agreement between the results of the simulation and the experiment. Both results demonstrate strong influence of relation between rotation frequencies of rotors on acoustic characteristics and significant dominance of noise radiated from the nozzle over the noise radiated from the inlet.