Multidomain Spectral Computations of Sound Radiation from Ducted Fans

Stănescu, Dan; Ait‐Ali‐Yahia, D.; Habashi, Wagdi G.; Robichaud, M.

doi:10.2514/2.727

Cited by 33 publications

(12 citation statements)

References 17 publications

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“…Data used in the evaluation off mn can be computed by interpolating from the corresponding data at the GCL points, at the price of a matrix-vector multiplication. 1,16 …”

Section: Spectral Element Discretizationmentioning

confidence: 98%

“…For the second fan setting, corresponding to 10,460 rpm, the radial mode (13,1) can also propagate through the inlet and to the far field. In this the relative amplitude and phase of the propagating modes is not known, and so mode (13, 1) was arbitrarily considered to have a very small amplitude compared to the first mode.…”

Section: Jt15d Inletmentioning

confidence: 98%

“…This approach has already been used successfully in time-domain acoustic computations. 1,12 Its advantages stem from the fact that it is independent of grid topology, is simple to implement, and requires negligible computational overhead. It also allows the exit boundaries to be placed much closer to the noise sources where the flowfield would be highly nonuniform.…”

Section: B Weak Form Of the Acoustic Problemmentioning

confidence: 99%

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Spectral Element Method for LInear Fan Tone Noise Radiation

et al. 2004

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A numerical method for prediction of acoustic spinning mode radiation from turbofan inlets is presented. Sound propagation is modeled by the linearized mass conservation equation for irrotational flows and solved inthe frequency domain. The mean flow through the inlet is obtained as a solution of the full potential equation. Both the mean-flow and the acoustic problem are approximated by Galerkin projection in spectral element spaces of continuous piecewise polynomials defined on the same grid. The Gauss-Chebyshev-Lobatto points within the elements are generated via transfinite interpolation and CAD projection procedures embedded within the code. The linear algebraic systems obtained are then solved using either direct or sparse iterative solvers based on the message passing interface standard for interprocessor communication. The singularity appearing in the acoustic integrals on the symmetry axis is treated by the use of a collocation operator based on the Gauss-Chebyshev, instead of the Gauss-Chebyshev-Lobatto, points. To eliminate reflections from the radiation boundaries, a novel frequencydomain formulation of the matched-layer technique, wherein waves entering the layer are exponentially damped, is proposed. The overall computing procedure is first validated on a tone radiation problem from a semi-infinite cylinder and then applied to an experimental JT15D turbofan inlet setup. Nomenclature c = speed of sound ds = arclength along ∂ h j = Lagrange interpolant at node j i = √ −1 J = Jacobian matrix k = wave number M = Mach number M = mapping tensor m = azimuthal mode order N = order of Lagrange interpolant n = unit normal vector p = pressure T p = pth-order Chebyshev polynomial t = time variable V = velocity vector (x, r, θ) = cylindrical coordinate system β = damping exponent γ = ratio of specific heats (ξ, η) = local coordinate system ρ = density σ M = damping factor = velocity potential = weighting function = computational domain ω = reduced frequency Subscripts c = hard-wall boundary f = inlet boundary i = grid node indices 0 = mean-flow component ∞ = far-field boundary = acoustic component

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“…Data used in the evaluation off mn can be computed by interpolating from the corresponding data at the GCL points, at the price of a matrix-vector multiplication. 1,16 …”

Section: Spectral Element Discretizationmentioning

confidence: 98%

Section: Jt15d Inletmentioning

confidence: 98%

Section: B Weak Form Of the Acoustic Problemmentioning

confidence: 99%

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Spectral Element Method for LInear Fan Tone Noise Radiation

et al. 2004

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“…Coupled with the characteristicboundary conditions implicit in the use of the Riemann solver at the exterior boundary,the damping-layerapproachis effective;compare Ref. 19. Our damping-layer approach sets the source term on the right of Eq.…”

Section: Boundary Conditionsmentioning

confidence: 99%

Discontinuous Spectral Element Solution of Acoustic Radiation from Thin Airfoils

2001

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A time-domain spectral element method is used to compute the acoustic radiation from thin airfoils generated in response to upstream, small amplitude plane vorticity waves. The method is a spectral element (collocation) form of the discontinuous Galerkin method for the solution of the Euler gasdynamics equations. Solutions are presented for at plate and symmetric and nonsymmetric Joukowski airfoils. Comparisons are made to semi-analytic and nite difference computations. Nomenclature a = vortical gust amplitude vector, (a 1 ; a 2 ) c = chord length e = speci c total energy F; G = inviscid Euler uxes J = Jacobian k = wave number vector normalized by 2=c, (k 1 ; k 2 ) = Lagrange interpolating polynomial M = Mach number p = pressure normalized by ½ 1 U 2 1 p ss = steady-state pressure normalized by ½ 1 U 2 1 p 0 = perturbation pressure normalized by ½ 1 U 2 1 Q = vector of dependent variables S = source term t = time normalized by c=.2U 1 / U 1 = upstream mean velocity u; v = Cartesian velocity components normalized by U 1 x = Cartesian coordinates normalized by c=2, (x; y)°= speci c heat ratio 1 x ; 1 y = mesh size in the x and y directions µ = angle with respect to x axis »;´= local coordinates in the unit square ½ = density normalized by ½ 1 Subscript 1 = freestream quantity

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“…Recent advances both in computer architecture and computing methods have already prompted researchers to address the fan tone noise problem using Computational Aeroacoustics (CAA) time-domain techniques [10,14,15]. Stanescu et al [15] used for this purpose a multidomain spectral method and showed that accurate results can be obtained for noise propagation with only a relatively small (between four and five, depending on the highest polynomial degree) number of points per wavelength (PPW).…”

Section: Introductionmentioning

confidence: 99%

Aircraft engine noise scattering - A discontinuous spectral element approach

Stănescu

Hussaini

Farassat

2002

40th AIAA Aerospace Sciences Meeting &Amp; Exhibit

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The paper presents a time-domain method for computation of sound radiation from aircraft engine sources to the far-field. The effects of nonuniform flow around the aircraft and scattering of sound by fuselage and wings are accounted for in the formulation. Our approach is based on the discretization of the inviscid flow equations through a collocation form of the Discontinuous Galerkin spectral element method. An isoparametric representation of the underlying geometry is used in order to take full advantage of the spectral accuracy of the method. Largescale computations are made possible by a parallel implementation based on message passing. Results obtained for radiation from an axisymmetric nacelle alone are compared with those obtained when the same nacelle is installed in a generic configuration, with and without a wing.

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Multidomain Spectral Computations of Sound Radiation from Ducted Fans

Cited by 33 publications

References 17 publications

Spectral Element Method for LInear Fan Tone Noise Radiation

Spectral Element Method for LInear Fan Tone Noise Radiation

Discontinuous Spectral Element Solution of Acoustic Radiation from Thin Airfoils

Aircraft engine noise scattering - A discontinuous spectral element approach

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