Flow-resonant sound interaction in a duct containing a plate, II: Square leading edge
TL;DR: In this article, the interaction between flow and flow-induced acoustic resonances near rigid plates with square leading edges located in a hard-walled duct is described, and a potential flow model for a plate with a square leading edge is developed and the acoustic power generated by vortices, which grow and shed from the leading edge, is calculated as they move through the resonant acoustic field.
About: This article is published in Journal of Sound and Vibration.The article was published on 1986-01-08. It has received 94 citations till now. The article focuses on the topics: Leading edge & Trailing edge.
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TL;DR: In this paper, a theoretical model for the aero-acoustic sources responsible for low-frequency self-sustained pulsations in pipes with closed side branches is proposed.
225 citations
TL;DR: In this paper, the Strouhal number is shown to be approximately constant and equal to 0.6 for flat plates with square leading and trailing edges having chord-to-thickness ratios 3-16 at Reynolds numbers (1-3) × 103.
Abstract: Vortex shedding from flat plates with square leading and trailing edges having chord-to-thickness ratios 3–16 at Reynolds numbers (1–3) × 103 is investigated experimentally in low-speed wind tunnels. It is shown that vortex shedding from flat plates with square leading and trailing edges is characterized by the impinging-shear-layer instability where the separated shear layer becomes unstable in the presence of a sharp trailing edge corner. The Strouhal number which is based on the plate's chord is approximately constant and equal to 0.6 for chord-to-thickness ratios 3–5. With further increase in the ratio it increases stepwise to values that are approximately equal to integral multiples of 0.6.
167 citations
TL;DR: In this article, the results of about 70 realizations of the BARC flow configuration obtained under a nominally common set-up in both wind tunnel experiments and numerical simulations are compared among themselves and with the data available in the literature prior to BARC, in terms of bulk parameters, flow and aerodynamic load statistics, pressure and force spanwise correlations.
134 citations
Cites result from "Flow-resonant sound interaction in ..."
...[2011] in DES simulations than in URANS, while Wei and Kareem [2011] generally find lower values in LES than in IDDES....
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...[2011] in DES simulations than in URANS, while Wei and Kareem [2011] generally find lower values in LES than in IDDES. Note, however, that the IDDES predictions of t− std(CL) of Wei and Kareem [2011] are significantly larger than those of the DES in Mannini et al....
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TL;DR: In this article, the authors reviewed the wakes of different cross-sectional bluff bodies, including circular, square, triangular and rectangular cylinders, and the dependence on the two parameters of Strouhal number, vorticity, circulation, and efflux angle of vortices in the wake of bluff bodies.
128 citations
TL;DR: In this article, the authors used the finite element method and a discrete-vortex model to predict the observed separated flow and the amount of acoustic energy generated is a function of the phase of the acoustic cycle at which the vortex passes the baffle.
109 citations
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TL;DR: In this article, a reformulation of the Lighthill (1952) theory of aerodynamic sound is described, and the form of the acoustic propagation operator is established for a non-uniform mean flow in the absence of vortical or entropy gradient source terms.
Abstract: This paper describes a reformulation of the Lighthill (1952) theory of aerodynamic sound. A revised approach to the subject is necessary in order to unify the various ad hoc procedures which have been developed for dealing with aerodynamic noise problems since the original appearance of Lighthill's work. First, Powell's (1961 a) concept of vortex sound is difficult to justify convincingly on the basis of Lighthill's acoustic analogy, although it is consistent with model problems which have been treated by the method of matched asymptotic expansions. Second, Candel (1972), Marble (1973) and Morfey (1973) have demonstrated the importance of entropy inhomogeneities, which generate sound when accelerated in a mean flow pressure gradient. This is arguably a more significant source of acoustic radiation in hot subsonic jets than pure jet noise. Third, the analysis of Ffowcs Williams & Howe (1975) of model problems involving the convection of an entropy ‘slug’ in an engine nozzle indicates that the whole question of excess jet noise may be intimately related to the convection of flow inhomogeneities through mean flow pressure gradients. Such problems are difficult to formulate precisely in terms of Lighthill's theory because of the presence of an extensive, non-acoustic, non-uniform mean flow. The convected-entropy source mechanism is actually absent from the alternative Phillips (1960) formulation of the aerodynamic sound problem.In this paper the form of the acoustic propagation operator is established for a non-uniform mean flow in the absence of vortical or entropy-gradient source terms. The natural thermodynamic variable for dealing with such problems is the stagnation enthalpy. This provides a basis for a new acoustic analogy, and it is deduced that the corresponding acoustic source terms are associated solely with regions of the flow where the vorticity vector and entropy-gradient vector are non-vanishing. The theory is illustrated by detailed applications to problems which, in the appropriate limit, justify Powell's theory of vortex sound, and to the important question of noise generation during the unsteady convection of flow inhomogeneities in ducts and past rigid bodies in free space. At low Mach numbers wave propagation is described by a convected wave equation, for which powerful analytical techniques, discussed in the appendix, are available and are exploited.Fluctuating heat sources are examined: a model problem is considered and provides a positive comparison with an alternative analysis undertaken elsewhere. The difficult question of the scattering of a plane sound wave by a cylindrical vortex filament is also discussed, the effect of dissipation at the vortex core being taken into account.Finally an approximate aerodynamic theory of the operation of musical instruments characterized by the flute is described. This involves an investigation of the properties of a vortex shedding mechanism which is coupled in a nonlinear manner to the acoustic oscillations within the instrument. The theory furnishes results which are consistent with the playing technique of the flautist and with simple acoustic measurements undertaken by the author.
775 citations
TL;DR: In this paper, the cross-correlations between surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the separation bubble formed along the sides of a blunt flat plate with right-angled corners.
Abstract: Flow in the separation bubble formed along the sides of a blunt flat plate with right-angled corners has been studied in terms of extensive single- and two-point measurements of velocity and surface-pressure fluctuations. The cross-correlations between the surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the bubble. Large-scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xR, where U∞ is the approaching velocity and xR is the time-mean length of the bubble. On top of this regular vortex shedding, there exists a large-scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large-scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross-correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7–0.8) xR and their convection velocity is about 0.5U∞ near the reattachment line. The cross-correlations also suggest the existence of a longitudinal counter-rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.
454 citations
Journal Article•
TL;DR: In this article, the cross-correlations between surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the separation bubble formed along the sides of a blunt flat plate with right-angled corners.
Abstract: Flow in the separation bubble formed along the sides of a blunt flat plate with right-angled corners has been studied in terms of extensive single- and two-point measurements of velocity and surface-pressure fluctuations. The cross-correlations between the surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the bubble. Large-scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xR, where U∞ is the approaching velocity and xR is the time-mean length of the bubble. On top of this regular vortex shedding, there exists a large-scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large-scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross-correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7–0.8) xR and their convection velocity is about 0.5U∞ near the reattachment line. The cross-correlations also suggest the existence of a longitudinal counter-rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.
445 citations
TL;DR: In this article, a method of calculating the resonant frequencies and the corresponding pressure amplitude distributions is presented, where a critical value of the plate chord/pitch ratio is defined for each mode and below this value the mode does not exist.
207 citations
TL;DR: In this article, the authors examined the physics and detailed fluid dynamics of a flow excited resonance and showed that the imbalance between the source and sink is responsible for both the radiated acoustic power and the power carried away by the vortices as they convect downstream.
193 citations