scholarly journals ADAM - An axisymmetric duct aeroacoustic modeling system

1983 ◽  
Author(s):  
A. ABRAHAMSON
Keyword(s):  
Axisymmetric Duct

The generation of sound by vorticity waves in swirling duct flows

1977 ◽  
Vol 81 (2) ◽  
pp. 369-383 ◽  
Author(s):  
M. S. Howe ◽  
J. T. C. Liu
Keyword(s):  
Acoustic Pressure ◽  
Swirling Flow ◽  
Sound Waves ◽  
Cross Sectional ◽  
Aerodynamic Sound ◽  
Swirl Velocity ◽  
Perturbation Velocity ◽  
Linearized Model ◽  
Axisymmetric Duct ◽  
Turbine Blading

Swirling flow in an axisymmetric duct can support vorticity waves propagating parallel to the axis of the duct. When the cross-sectional area of the duct changes a portion of the wave energy is scattered into secondary vorticity and sound waves. Thus the swirling flow in the jet pipe of an aeroengine provides a mechanism whereby disturbances produced by unsteady combustion or turbine blading can be propagated along the pipe and subsequently scattered into aerodynamic sound. In this paper a linearized model of this process is examined for low Mach number swirling flow in a duct of infinite extent. It is shown that the amplitude of the scattered acoustic pressure waves is proportional to the product of the characteristic swirl velocity and the perturbation velocity of the vorticity wave. The sound produced in this way may therefore be of more significance than that generated by vorticity fluctuations in the absence of swirl, for which the acoustic pressure is proportional to the square of the perturbation velocity. The results of the analysis are discussed in relation to the problem of excess jet noise.

Angles of peak sound radiation from axisymmetric duct inlets

1980 ◽  
Vol 68 (S1) ◽  
pp. S92-S92
Author(s):  
Joe W. Posey ◽  
Lorenzo R. Clark ◽  
Richard J. Silcox
Keyword(s):  
Sound Radiation ◽  
Axisymmetric Duct

scholarly journals Bound states in the continuum in open acoustic resonators

2015 ◽  
Vol 780 ◽  
pp. 370-387 ◽  
Author(s):  
A. A. Lyapina ◽  
D. N. Maksimov ◽  
A. S. Pilipchuk ◽  
A. F. Sadreev
Keyword(s):  
Bound States ◽  
Three Dimensional ◽  
Life Time ◽  
Three Dimensions ◽  
Destructive Interference ◽  
Acoustic Resonators ◽  
Coupled Mode ◽  
Resonant Modes ◽  
Axisymmetric Duct ◽  
The Continuum

We consider bound states in the continuum (BSCs) or embedded trapped modes in two- and three-dimensional acoustic axisymmetric duct–cavity structures. We demonstrate numerically that, under variation of the length of the cavity, multiple BSCs occur due to the Friedrich–Wintgen two-mode full destructive interference mechanism. The BSCs are detected by tracing the resonant widths to the points of the collapse of Fano resonances where one of the two resonant modes acquires infinite life-time. It is shown that the approach of the acoustic coupled mode theory cast in the truncated form of a two-mode approximation allows us to analytically predict the BSC frequencies and shape functions to a good accuracy in both two and three dimensions.

The Effect of an Upstream Compressor on a Non-Axisymmetric S-Duct

2010 ◽  
Author(s):  
Marios K. Karakasis ◽  
Edward M. J. Naylor ◽  
Robert J. Miller ◽  
Howard P. Hodson
Keyword(s):  
Boundary Layer ◽  
Streamwise Vortex ◽  
Low Loss ◽  
Vortex Pairs ◽  
Engine Design ◽  
Current Design ◽  
Duct Geometry ◽  
Physical Insight ◽  
Inlet Conditions ◽  
Axisymmetric Duct

This paper considers the effect of an upstream compressor stage on a compressor inter-spool duct. The duct geometry must be fixed early in the engine design process, well before the design of the upstream stages. It is therefore important that the designer has a good physical insight into how engine representative inlet conditions affect the limits of the duct design space. An experimental and computational investigation of two strutted inter-spool S-ducts was undertaken. Both were tested with and without an upstream stage present. The first duct is of a conventional axisymmetric design with a radius change to length ratio ΔR/L = 0.50. This duct is characteristic of the most extreme ducts considered in modern engine design. The second duct is of a non-axisymmetric design and is 20% shorter, ΔR/L = 0.625. This is well beyond the design limit of axi-symmetric strutted ducts. The paper shows that the presence of the upstream stage increases the duct loss by 54%. The rise in loss occurs on the hub wall and is the result of the incoming stator wakes pooling onto the hub wall, forming a row of contra-rotating streamwise vortex pairs adjacent to the hub wall. These vortices pump boundary layer fluid into the free stream, thus raising the mixing loss. In the non-axisymmetric duct an extra mechanism was observed. The streamwise vortex pairs act to ‘re-energise’ the boundary layer. This reduces strut secondary losses caused by the endwall contouring. The net result is that on the non-axisymmetric duct the presence of an upstream stage only increases the duct loss by 28%. Comparing the two ducts, it is shown that with engine representative inlet conditions, the conventional symmetric duct and 20% shorter non-axisymmetric duct have identical performance. This shows that low loss ducts can be designed which are significantly more extreme than current design limits.

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