An efficient finite element technique for sound propagation in axisymmetric hard wall ducts carrying high subsonic Mach number flows

Tag, I.A.; Lumsdaine, E.

doi:10.2514/6.1978-1154

Cited by 11 publications

(4 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The degree to which Eqs. (7) and (8) approximate the true entrance conditions can be improved by adding both straight entrance and exit sections. In these sections, the higher order modes will decay such that Eqs.…”

Section: Transient Finite Difference Theorymentioning

confidence: 98%

See 1 more Smart Citation

Acoustics in variable area duct - Finite element and finite difference comparisons to experiment

et al. 1983

View full text Add to dashboard Cite

Plane wave sound propagation without flow in a rectangular duct with a converging-diverging area variation is studied experimentally and theoretically. The area variation was of sufficient magnitude to produce large reflections and induce modal scattering. The rms pressure and phase angle on both the flat and curved surface were measured and tabulated. The "steady"-state finite element theory of Astley and Eversman and the transient finite difference theory of White are in good agreement with the data. It is concluded that numerical finite difference and finite element theories appear ideally suited for handling duct propagation problems which encounter large area variations.

show abstract

Section: Transient Finite Difference Theorymentioning

confidence: 98%

“…White's analysis, which uses Eqs. (7) and (8) for the entrance and exit conditions, is typical of these theories. Direct prediction of the transmitted and reflected energy is not generally possible in these theories.…”

mentioning

confidence: 98%

Acoustics in variable area duct - Finite element and finite difference comparisons to experiment

et al. 1983

View full text Add to dashboard Cite

show abstract

“…This approach follows one used successfully by Tag and Lumsdaine, 3 among others. The external flow is assumed to be uniform, steady, of low subsonic Mach number, and parallel to the axis of symmetry.…”

Section: Introductionmentioning

confidence: 94%

“…1 " 3 The radiation problem poses some severe difficulties because of the effectively infinite domain involved and the presence of flow. The use of finite element (FE) methods was precluded because of storage limitations until the infinite domain could be modeled.…”

Section: Introductionmentioning

confidence: 99%

Wave envelope and finite element approximations for turbofan noise radiation in flight

Parrett¹,

Eversman

1986

AIAA Journal

View full text Add to dashboard Cite

The problem of acoustic radiation from turbofan engine inlets in flow has not lent itself fully to analysis by numerical means because of the large domains and high frequencies involved. The current work has extended the use of finite elements and wave envelope elements, elements that simulate decay and wavelike behavior in their interpolation functions, from the no-flow case in which they have proven, to cases incorporating mean flow. By employing an irrotational mean flow assumption, the acoustics problem has been posed in an axisymmetric formulation in terms of acoustic velocity potential, thus minimizing computer solution storage requirements. The results obtained from the numerical procedures agree well with known analytical solutions, static experimental jet engine inflow data, and flight test results. Nomenclaturea£aj~ = incident and reflected modal amplitudes, respectively c = nondimensional speed of sound in flow e£ef = positive and negative uniform duct eigenfunctions, respectively m = spinning mode number TV,-= interpolation function p = pressure t = time u = axial component of local Mach number U = Mach number v = radial component of local Mach number v = acoustic velocity V -velocity x = axial coordinate 7= ratio of specific heats e = penalty parameter TJ, £ = local finite element coordinates K,A = local and axial wave numbers, respectively IJL = uniform duct eigenvalue p = density = velocity potential, trial function $(Q) = trial function space $ = full nondimensional velocity potential \l/ =test function ¥ (fi) = test function space co = harmonic frequency Superscripts ( )' = nondimensional quantity, derivative (see text) e = quantity defined inside a finite element

show abstract

Improved Finite Element Modeling of the Turbofan Engine Inlet Radiation Problem

Roy

Eversman

1995

Journal of Vibration and Acoustics

View full text Add to dashboard Cite

Improvements have been made in the finite element model of the acoustic radiated field from a turbofan engine inlet in the presence of a mean flow. The problem of acoustic radiation from a turbofan engine inlet is difficult to model numerically because of the large domain and high frequencies involved. A numerical model with conventional finite elements in the near field and wave envelope elements in the far field has been constructed. By employing an irrotational mean flow assumption, both the mean flow and the acoustic perturbation problem have been posed in an axisymmetric formulation in terms of the velocity potential, thereby minimizing computer storage and time requirements. The finite element mesh has been altered in search of an improved solution. The mean flow problem has been reformulated with new boundary conditions to make it theoretically rigorous. The sound source at the fan face has been modeled as a combination of positive and negative propagating duct eigenfunctions. Therefore, a finite element duct eigenvalue problem has been solved on the fan face and the resulting modal matrix has been used to implement a source boundary condition on the fan face in the acoustic radiation problem. In the post processing of the solution, the acoustic pressure has been evaluated at Gauss points inside the elements and the nodal pressure values have been interpolated from them. This has significantly improved the results. The effect of the geometric position of the transition circle between conventional finite elements and wave envelope elements has been studied and it has been found that the transition can be made nearer to the inlet than previously assumed.

show abstract

An efficient finite element technique for sound propagation in axisymmetric hard wall ducts carrying high subsonic Mach number flows

Cited by 11 publications

References 3 publications

Acoustics in variable area duct - Finite element and finite difference comparisons to experiment

Acoustics in variable area duct - Finite element and finite difference comparisons to experiment

Wave envelope and finite element approximations for turbofan noise radiation in flight

Improved Finite Element Modeling of the Turbofan Engine Inlet Radiation Problem

Contact Info

Product

Resources

About