Download or read book Flow Acoustic Interaction in Duct Inflow written by M. C. Quinn and published by . This book was released on 1987 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sound generation in the convection of turbulence into a flow intake duct is discussed by examination of an idealised problem. Ideal fluid is in motion with uniform low, subsonic velocity above and parallel to a plane, rigid wall. A thin, rigid, semi-infinite plate is parallel to the wall and the fluid flows past its leading edge. The radiated sound is calculated for a turbulent eddy modelled by a weak line vortex which is allowed to convect passively past the leading edge of the plate. Account is taken of the contribution to the radiated sound from the disturbance produced by the convecting vortex in the boundary layers on each side of the plate by means of Howe's (1981) theory of displacement thickness fluctuations, the strength of the disturbance being fixed by a leading edge Kutta condition. It is concluded that the predicted level of the radiated sound is substantially reduced due to the boundary layer disturbances relative to when they are neglected. The case of the convection of a frozen two-dimensional gust is also considered. Examination of the analogous problem of plane wave radiation from the duct shows that the presence of displacement waves enhanced both the far-field intensity in the ambient fluid and the reflected field within the duct.
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct written by Fridolin P. Mechel and published by . This book was released on 1965 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several studies of the interaction between air flow and airborne sound in a duct were made. Three projects were investigated: (1) The excitation of boundary layer distortions in a laminar boundary layer by simulated oscillatory flexural waves was investigated. Results show boundary layer waves are excited whenever the phase velocity of the flexure wave is in the instability range of the phase velocity of boundary layer waves. (2) The propagation of a pressure pulse wave front and the acoustic impedance of porous absorbers are examined in ducts with air flow. Measurements prove the sound energy of the wave front is directed towards the walls and the absorber impedance becomes nonlinear when the absorber is penetrated by the flow. (3) the effect on the acoustic radiation impedance of an orifice with flow discharge restricted by fences and diaphragms was investigated. The acoustic resistance was shown to increase at low frequencies due to the restrictions.
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct written by and published by . This book was released on 1967 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct Propagation of shock fronts and nonlinearity of porus absorbers written by Fridolin P. Mechel and published by . This book was released on 1967 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Interaction Between Air Flow and Air borne Sound in a Duct written by F. P. MECHEL and published by . This book was released on 1962 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: The interaction of a surface bending wave with the flow boundary layer is of practical interest. Several types of surfaces conducting bending waves suitable for boundary layer interaction are tested. For the investigation of the influence of the flow velocity profile in a ducton the sound attenuation the sound pressure profiles in a wide duct with flow were measured. The acoustic impedance of an absorber with flow along its surface was measured. The sound radiation from an orifice with flow discharge depends on the flow velocity. The reflection coefficient of the orifice increases with flow velocity. It depends strongly on the turbulence level of the jet behind the orifice. (Author).
Download or read book Prediction of Flow acoustic Interactions Using Vortex Models written by Kerry Hourigan and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper investigates numerically the flow and acoustic interaction in a duct with baffles, representing an idealized version of a rocket combustion chamber. The numerical techniques include the generation of a compressed mesh, the finite element and the boundary element solution of the sound field, and vortex models of the separated flow. Two vortex models are used: one focuses on the passage of a single point vortex past a baffle and predicts the generation of acoustic energy as a function of the phase of the acoustic cycle at which the vortex passes; the other simulates the growth of vortex clouds from elemental vortices shed from an upstream baffle, tracks the passage of these vortex clouds past a second baffle, predicts the generation of acoustic energy, and accounts for the feedback of sound on the vortex shedding. The two models are used to predict conditions under which acoustic resonance can be sustained and the results are compared with observation.
Download or read book The Shock and Vibration Digest written by and published by . This book was released on 1976 with total page 688 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct Volume I Propagation of Shock Fronts and Nonlinearity of Porous Absorbers written by P. A. Mertens and published by . This book was released on 1967 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The sound propagation in moving air with locally varying flow velocity is investigated by means of shock waves from a spark discharge. To accomplish this, the wave fronts were photographed with a schlieren optics in a flow duct with a large flow boundary layer thickness. Results of these experiments agree with the theories of geometrical acoustics and can be incorporated into the design of ducts having air flow and airborne sound. Also investigated were properties of porous absorbers in the presence of an air flow. Results show a penetration of the absorber by the air flow yields a change of the flow resistance compared with still air. The acoustic flow resistance and the differential static flow resistance are experimentally found to have the same value. Moreover, it is proved that turbulent motions along the surface of the absorber do not affect the flow resistance appreciably. (Author).
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct Volume Ii Acoustic Excitation of Boundary Layer and Radiation Impedance of Orifices written by F. P. Mechel and published by . This book was released on 1967 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report presents the results of three experimental studies on the interaction between air flow and airborne sound in a duct. The first experiment concerns the excitation and suppression of boundary-layer distortions (created by flexural wave-like wall oscillations). Mathematical approximations show and experimental results confirm that the stability of the boundary layer is shifted to higher Reynolds numbers by the flexural wave. The second experiment relates the boundary-layer (produced by static suction) stabilization to the sound field influencing it. Results show that the particle velocity of sound penetrating a porous section of the wall leads to an increase of boundary-layer distortions and that this effect could be suppressed when the flow velocity of the static suction exceeded a threshold value. The final experiment shows the influence of a superimposed air flow on the acoustic impedance of orifices terminating a tube and of constriction, enlargements, and nozzles within a tube. Results show that if the frequency is scaled according to the Mach number, then the ratio between the reflection coefficient gamma pm at Mach number M and the reflection coefficient at zero flow velocity gamma po is independent from the frequency. (Author).
Download or read book Flow resonant Sound Interaction in a Duct Containing a Plate II written by A. N. Stokes and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The interaction between flow and flow-induced acoustic resonances near rigid plates with square leading edges located in a hard-walled duct is described. These plates generate, B-mode acoustic resonances over several discrete ranges of flow velocity. 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. Vortices grow rapidly during the first half cycle and the vortex growth rate is quantified by using a Kutta condition. This model indicates that a major phase-dependent sound source occurs when a vortex passes the trailing edge of the plate. It is the remoteness of this source from the site at the leading edge where the sound affects the flow which makes possible the discrete resonance ranges.
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct Volume Iii Summry Report written by F. P. Mechel and published by . This book was released on 1967 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report briefly summarizes experiments during 1963-64 on the interaction between subsonic airflow and airborne sound in a duct. Also summarized are the results of the following four experiments conducted in 1965. The first experiment investigates the effect of the wall impedance on the stability and phase velocity of boundary layer waves. Measurements revealed a step in the dispersion curve of the flow velocity; this agrees with the dispersion curve of the sound velocity for a transition from capactive to inductive wall impedance. The second experiment investigates a flow boundary layer modified by sinusoidal suction (as opposed to stationary suction) through a porous plate imbedded in the wall of a duct. The alternating motions present in the suction elements excite boundary layer disturbances which may lead to a quicker transition into turbulence as compared to stationary suction. The third experiment was performed to improve the stability of a flow boundary layer by the application of an appropriate wall impedance. It was concluded that the real part of the impedance must be below 0.2 rho c. The final and most detailed experiment investigates the reflection coefficient of cross-sectional area changes and apertures in a tube with sound superimposed on an air flow. Smooth cross-sectional transitions show no acoustical or flow losses, whereas abrupt area changes cause flow separation, turbulence, and flow losses, all of which are associated with acoustic losses. These losses are described as an ohmic resistance which is added to the impedance of the transition. (Author).
Download or read book Interaction Between Air Flow and Airborne Sound in a Duct written by Fridolin P. Mechel and published by . This book was released on 1967 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Notes on Acoustics written by K. Uno Ingard and published by Jones & Bartlett Publishers. This book was released on 2008 with total page 455 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduction -- Oscillations -- Sound waves -- Sound reflection, absorption, and transmission -- The wave equation -- Room and duct acoustics -- Flow-induced sound and instabilities -- Sound generation by fans -- Atmospheric acoustics -- Mean-flow effects and nonlinear acoustics -- Examples.
Download or read book Catalogue of British Official Publications Not Published by HMSO written by and published by . This book was released on 1989 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Technical Memorandum written by and published by . This book was released on 1994 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Technical Reports Awareness Circular TRAC written by and published by . This book was released on 1988-04 with total page 556 pages. Available in PDF, EPUB and Kindle. Book excerpt:
