Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session D24: Acoustics II |
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Chair: Woutijn Baars, University of Melbourne Room: 319 |
Sunday, November 24, 2013 2:15PM - 2:28PM |
D24.00001: Acoustophoretic contactless transport and handling of matter Daniele Foresti, Majid Nabavi, Mirko Klingauf, Aldo Ferrari, Dimos Poulikakos Levitation and controlled motion of matter in air, has a wealth of potential applications ranging from materials processing to biochemistry and pharmaceuticals. We present a novel acoustophoretic concept, for the contactless transport and handling of matter in air. Spatiotemporal modulation of the levitation acoustic field allows continuous planar transport and processing of multiple objects (volume 0.1-10 $\mu l)$. The independence of the handling principle from special material properties (magnetic, optical or electrical) is illustrated with a wide palette of application experiments, such as contactless droplet coalescence and mixing, solid-liquid encapsulation, absorption, dissolution, and DNA transfection. The dynamics of droplets and particles collision is studied numerically and experimentally. The findings show that the secondary acoustic force gives a significant contribution to the samples impact velocity. [Preview Abstract] |
Sunday, November 24, 2013 2:28PM - 2:41PM |
D24.00002: Aeroacoustic sound radiated from a flow past an oscillating and a fixed cylinder in tandem Yuji Hattori, Ryu Komatsu The aeroacoustic sound generated in a two-dimensional flow past two circular cylinders in tandem is studied. The upstream cylinder is forced to oscillate transversely, while the downstream cylinder is fixed. This flow is a simplified model of the sound generation due to the interaction of rotating wings and a strut. The sound is captured by direct numerical simulation of the compressible Navier-Stokes equations using the volume penalization method. The amplitude of the sound increases in general with the amplitude and the frequency of the oscillation of the upstream cylinder. However, large reduction of the sound occurs for particular choices of parameter values as the forces acting on the two cylinders are in anti-phase. [Preview Abstract] |
Sunday, November 24, 2013 2:41PM - 2:54PM |
D24.00003: Adjoint-field errors in high fidelity compressible turbulence simulations for sound control Ramanathan Vishnampet, Daniel Bodony, Jonathan Freund A consistent discrete adjoint for high-fidelity discretization of the three-dimensional Navier-Stokes equations is used to quantify the error in the sensitivity gradient predicted by the continuous adjoint method, and examine the aeroacoustic flow-control problem for free-shear-flow turbulence. A particular quadrature scheme for approximating the cost functional makes our discrete adjoint formulation for a fourth-order Runge-Kutta scheme with high-order finite differences practical and efficient. The continuous adjoint-based sensitivity gradient is shown to to be inconsistent due to discretization truncation errors, grid stretching and filtering near boundaries. These errors cannot be eliminated by increasing the spatial or temporal resolution since chaotic interactions lead them to become $O(1)$ at the time of control actuation. Although this is a known behavior for chaotic systems, its effect on noise control is much harder to anticipate, especially given the different resolution needs of different parts of the turbulence and acoustic spectra. A comparison of energy spectra of the adjoint pressure fields shows significant error in the continuous adjoint at all wavenumbers, even though they are well-resolved. The effect of this error on the noise control mechanism is analyzed. [Preview Abstract] |
Sunday, November 24, 2013 2:54PM - 3:07PM |
D24.00004: Dynamic Mode Decomposition of a Supersonic Jet Exhausting a Convergent-Divergent Nozzle Bernhard Semlitsch, Mihai Mihaescu, Laszlo Fuchs Non-ideal expanded supersonic jets provoke further noise sources additional to the turbulent mixing noise source, which is present in subsonic jets. In particular, the screech tones are a undesired shock associated noise source in the supersonic jet exhaust, since high amplitude acoustic waves are radiated upstream, where the pressure fluctuations could cause damage to the airplane structure. Satisfying suppression of acoustic noise in a supersonic jets requires further investigation of the acoustic noise generation mechanisms. Dynamic Mode Decomposition (DMD) is a flow decomposition method, which is suited to extract the spectral features of the flow-field. Thus, DMD is conceivably capable to extract the spectral flow features, which can lead to the formation of the screech tones. DMD is performed on Large Eddy Simulation data of a Mach $1.56$ over-expanded supersonic jet expanding from a convergent-divergent nozzle. [Preview Abstract] |
Sunday, November 24, 2013 3:07PM - 3:20PM |
D24.00005: Comparison and Properties of Near-Field and Far-Field Events of High Speed Jet Pinqing Kan, Jacques Lewalle Two independent algorithms are applied to different signals to extract events that are potentially responsible for jet noise production. The data consist of 10 kHz TRPIV measurement and pressure sampling in both near- and far-field. One method uses near-field diagnostics (representatives of 2D velocity sections, e.g. velocity, vorticity, Q criterion, etc.) and near-field and far-field pressure. Applying cross-correlation and continuous wavelet to pairs of these signals, we look for the more dominant events in the time, frequency and lag domain. These are regarded as the main contributors of communication between the selected signals and are recorded as Near-Field Events. The other method only uses far-field microphones. The short time excerpts are identified as Far-Field Events that are common to three FF signals and responsible for peak energy spectrum. To compare these events, we map out their property distribution, including frequency, magnitude and time of occurrence. The individual events are also compared and a high portion is found to be common to both lists. We regard this as a verification of both algorithms. [Preview Abstract] |
Sunday, November 24, 2013 3:20PM - 3:33PM |
D24.00006: Supersonic Jet Noise Reduction Using Microjets Ephraim Gutmark, Dan Cuppoletti, Bhupatindra Malla Fluidic injection for jet noise reduction involves injecting secondary jets into a primary jet to alter the noise characteristics of the primary jet. A major challenge has been determining what mechanisms are responsible for noise reduction due to varying injector designs, injection parameters, and primary jets. The current study provides conclusive results on the effect of injector angle and momentum ux ratio on the acoustics and shock structure of a supersonic Md$=$1.56 jet. It is shown that the turbulent mixing noise scales primarily with the injector momentum flux ratio. Increasing the injector momentum flux ratio increases streamwise vorticity generation and reduces peak turbulence levels. It is found that the shock-related noise components are most affected by the interaction of the shocks from the injectors with the primary shock structure of the jet. Increasing momentum flux ratio causes shock noise reduction until a limit where shock noise increases again. It is shown that the shock noise components and mixing noise components are reduced through fundamentally different mechanisms and maximum overall noise reduction is achieved by balancing the reduction of both components. [Preview Abstract] |
Sunday, November 24, 2013 3:33PM - 3:46PM |
D24.00007: High fidelity measurements in the far-field of a Mach 3 jet Romain Fi\'evet, Woutijn J. Baars, David Silva, Charles E. Tinney Recent studies by Baars \& Tinney (2012) [APS DFD12-2012-002085] used 1/4inch pressure-field microphones to produce spatial mappings of the far field spectra, OASPL, skewness and kurtosis of the pressure and pressure derivative, as well as other indicators of local and cumulative nonlinear waveform distortion (quadrature spectral density) of the sound field produced by a laboratory-scale Mach 3 jet flow. It was shown that, despite the presence of crackle, cumulative nonlinear distortions were absent along the peak noise path, where such effects have been shown to reside in full-scale studies. The findings were supported by estimates of the Gol'dberg number using relevant jet operating conditions. The experiment of Baars \& Tinney is revisited here using higher fidelity instruments (1/8th inch pressure field microphones resolving up to 140kHz +/-1dB) to identify the effects imposed by the larger microphones used by Baars \& Tinney (2012). [Preview Abstract] |
Sunday, November 24, 2013 3:46PM - 3:59PM |
D24.00008: Acoustic far-field of shroud-lip-scattered instability modes of supersonic co-flowing jets Arnab Samanta, Jonathan B. Freund We consider the acoustic radiation of instability modes in dual-stream jets, with the inner nozzle buried within the outer shroud, particularly the upstream scattering into acoustic modes that occurs at the shroud lip. For supersonic core jets, several families of instability waves are possible, beyond the regular Kelvin-Helmholtz (K-H) mode, with very different modal shapes and propagation characteristics, which are candidates for changing the sound character of very high-speed jets. The co-axial shear layers are modeled as vortex sheets, with the Wiener-Hopf method used to compute these modes coupled with an asymptotic solution for the far-field radiation. A broadband mode spectra as well as single propagating modes are considered as incident and scattered waves. The resulting far-field directivity patterns are quantified, to show the efficiency of some of these radiation mechanisms, particularly in the upstream direction, which is not directly affected by the Mach-wave-like sound that is radiated from these modes irrespective of any scattering surface. A full Kutta condition, which provides the usual boundary condition at the shroud lip, is altered to examine how vortex shedding, perhaps controllable at the lip, affects the radiated sound. [Preview Abstract] |
Sunday, November 24, 2013 3:59PM - 4:12PM |
D24.00009: Jet Crackle:~Near-field Nonlinear Acoustic Interactions Due to High-Speed Turbulent Sources David Buchta, Jonathan Freund It is thought that supersonically advecting eddies in high-speed turbulent jets can radiate Mach-wave-like sound, which corresponds with the perception of a rasping or crackling character in their radiated sound. This perception is thought to be in part due to weak shocks in the sound field, but there is another feature of the sound which suggests that more than simple one-dimensional wave steepening occurs: the pressure signals at a point are skewed, with $S_k \ge 0.4$ also correlating to the perception of crackle. This is peculiar because simple nonlinear steepening will not of itself generate skewed pressure signals. We use direct numerical simulations of temporally developing turbulent free shear flows ($Re\!=\!1530$ up to $Re\!=\!2810$ based on momentum thickness) of crackling and non-crackling temporal planar shear layers to study their near-field acoustics and turbulent sound source. Space--time correlations of the turbulence, statistical measures of near-field wave density and propagation directions, and observations of wave-wave interactions suggest that very near-field nonlinear acoustics are potentially important for the generation of these observed peculiar sound-field characteristics. [Preview Abstract] |
Sunday, November 24, 2013 4:12PM - 4:25PM |
D24.00010: Time Reversal Acoustic in a flowing medium Trung Dung Luong, Manish Arora, Thomas Hies, Claus-Dieter Ohl We explore the effect of flow on time reversal acoustics (TRA). Traditionally, TRA has been studied in static conditions, while a motion of the medium is expected to degrade the spatio-temporal focussing of the sound pulse. Here, we study the effect of the flow with a TRA system at 1MHz. A controlled flow is added between the emitter and receiver. Additional, a metallic plate is utilized to increases the numerical aperture of the emitting transducer. The impulse response of the non-flowing system, is recorded and time reversed. Then, the response of the hydrophone is recorded in presence and absence of the flow. It is found that the time reversed signal focuses on at the hydrophone in both the cases. In the absence of flow, the focus signal is observed to be shifted in the time domain. Furthermore, there is a drop in the peak-to-peak value of the focus signal in the presence of flow. For a flow rate of 3 cm/s (Re $\sim$ 1000), a distinct shift in the time domain and a reduction of the peak is obtained. The results will be discussed and compared with numerical simulation of TRA under flow conditions. [Preview Abstract] |
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