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An advanced model of active control of fan noise for ultra high bypass turbofan engines has been developed. This model is based on a boundary integral equation method and simulates the propagation, radiation and control of the noise generated by an engine fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow. Con...
Citations
... Active Noise Control (ANC) is one of the solutions developed since the early 1990s to reduce tonal turbofan noise. Currently, most of published results rely on experimental data [1,4,9,13,22] but some analytical and numerical models were also developed [7,10,14,15]. Sound Pressure Level (SPL) reductions from 3 to 20 dB at the Blade Passing Frequency (BPF) were obtained, most of them by using modal decomposition with feedforward control for low radial mode orders. ...
Active Noise Control (ANC) of a turbofan engine is introduced using active stator vanes and rings of loudspeakers as control actuators. It involves a unique coupling of two original analytical and numerical models for the primary and secondary sources respectively, and two different control strategies that attempt to independently control the propagative acoustic modes upstream and downstream for the first time. This is done using Singular Values Decomposition (SVD) and Generalized Singular Values Decomposition (GSVD) without any knowledge on the physical form of the acoustic field. Simulation results are shown and it is demonstrated that the GSVD is a great avenue to separate inlet and outlet radiation.
... In this situation, the boundary integral methods [2,3] become one of the fast, useful and reliable tools. In addition, this method has also been extended to study the optimization design of acoustic treatments [10] and the active control technique [11]. Therefore, any further development for this kind of method may still be required for the practical application point of view. ...
... According to superposition principle of linear waves and Eqs. (11), (17), (22) and (23), the scattering field can be expressed as ...
... It is noted that p d À has the same expression as defined in Eq. (11). As Fig. 3 shows, the acoustic properties of a perforated screen can be described as the compliance related to the Rayleigh conductivity c of a single aperture in a rigid baffle [13][14][15]. ...
This paper presents a unified model to study the effect of both locally and non-locally reacting liners on the sound radiation generated by fan blade rotating sources. This model is set up by the following steps. First, the spinning mode eigenfunction expansions are used to obtain the solution of sound field inside the duct, while the effect of duct liner is modeled by distributed monopole sources, thus effectively avoiding the solution of a difficult complex eigenvalue problem. Secondly, in order to avoid the estimation of the generalized impedances at the inlet and exhaust planes, a boundary element method is used to give the solution outside the duct. With the suitable boundary conditions imposed on the inlet and exhaust planes, a matrix equation is obtained, and the relevant numerical calculation shows this model can not only give a good agreement with existing results for locally reacting liner but also has a capability to predict the sound radiation from fan rotating blade sources with an arbitrary combination of locally and non-locally reacting liners.
... The sound radiation emitted by aeroengines has been studied for along time. From the first studies [1,2,3,4] on the acoustic transmission in ap ipe with flow, to those dealing with more complexc omplexs uch as those focusing on more realistic aeronautical engines (see for example [5,6,7,8,9,10]), this topic has attracted considerable attention. Schematically,the studies published so farhave been of twokinds. ...
... TBIEM3D has been applied to both passive and active noise control research [22][23][24][25]. For given liner length and location, optimal liner impedances were calculated for a host of operating situations in which circumferential mode number, inflow Mach number, and excitation frequency were varied [22]. ...
... For example, in reference [22] liner impedance was chosen so that the maximum sound pressure level along an arc of farfield observers in the direction of the principal radial mode was minimized. Active noise control research based on TBIEM3D has focused on using simple point control sources and a feedforward algorithm to minimize the sound along a particular farfield direction produced by a given source configuration [23]. ...
... Code versatility, ease-of-use, and rapid prediction capability are necessary features for conducting cost-efficient parametric noise reduction analyses. In this regard, the effectiveness of TBIEM3D as an engineering analysis tool has been amply demonstrated both here and in the literature[21][22][23][24][25].Two-Dimensional Scarf Inlet Using the Noise Prediction Code TBIEM2D. 25. ...
The prediction of ducted fan engine noise using a boundary integral equation method (BIEM) is considered. Governing equations for the BIEM are based on linearized acoustics and describe the scattering of incident sound by a thin, finite-length cylindrical duct in the presence of a uniform axial inflow. A classical boundary value problem (BVP) is derived that includes an axisymmetric, locally reacting liner on the duct interior. Using potential theory, the BVP is recast as a system of hypersingular boundary integral equations with subsidiary conditions. We describe the integral equation derivation and solution procedure in detail. The development of the computationally efficient ducted fan noise prediction program TBIEM3D, which implements the BIEM, and its utility in conducting parametric noise reduction studies are discussed. Unlike prediction methods based on spinning mode eigenfunction expansions, the BIEM does not require the decomposition of the interior acoustic field into its radial and axial components which, for the liner case, avoids the solution of a difficult complex eigenvalue problem. Numerical spectral studies are presented to illustrate the nexus between the eigenfunction expansion representation and BIEM results. We demonstrate BIEM liner capability by examining radiation patterns for several cases of practical interest.
... Burdisso and others [30] presented a model with more realistic representation of fan noise. Hutcheson [31] studied the turbofan engine active noise control problem using a comprehensive analytical model of a finite duct and a fan including the duct open end reflections, the effect of air mean flow, and the interactions of inlet and outlet sounds. ...
... All investigations described above, except for one by Hutcheson [31], used simplified models for the duct open-ends in a finite-length duct, neglecting the cross modal coupling effect. In the present thesis, the cross modal coupling effect is naturally included into the matrix-based duct model. ...
The structure of the salts MBr(3), where M(3+) denotes Dy(3+), Y(3+), Ho(3+) or Er(3+), was investigated by using neutron diffraction. On heating DyBr(3), YBr(3) and HoBr(3), a phase transition from the FeCl(3)-type crystal structure to possibly the YCl(3)-type crystal structure was observed. The liquids were studied at the total-structure-factor level and difference function methods were also applied to DyBr(3) and YBr(3) by assuming isomorphous structures. The melts are found to comprise distorted MBr(6)(3-) octahedra with M-Br distances comparable to the sum of the ionic radii and there is evidence for a substantial number of edge-sharing configurations. The octahedra pack to give intermediate-range ionic ordering as manifested by the appearance of a first sharp diffraction peak at 0.79(2)-0.87(2) Angstrom (-1) which is associated with cation correlations.
