シュリーレン法による可聴音場可視化のための時空間フィルタリング

早大学位記番号:新7470早稲田大

2D and 3D visualization of acoustic waves by optical feedback interferometry

The visualization of physical phenomena is one of the challenges that researchers are trying to overcome by designing and implementing different sensors that provide information close to realitythrough changes in one of the parameters they measure. Historically, the visualization of variations in physical phenomena has allowed for a better understanding of the problem being studied and has changed our perception of the world and ourselves forever. Over the last 300 years, in particular, many methods have been developed to visualize sound through a visual representation. In the field of acoustics, scientists have attempted to develop a visual representation of sound waves using transducers detecting two fundamental components of sound: sound pressure and particle velocity. In other words, the measurement of kinetic energy and potential, whose quantities provide information on the physical phenomenon of acoustic propagation. In this summary, we briefly present the work of the thesis entitled "2D and 3D Visualizations of Acoustic Waves by Optical Feedback Interferometry" in which a new visualization tool for acoustic phenomena was developed. This system is based on an optical sensor said reinjection in a laser diode and allows to reconstruct in 2D and 3D the image of a propagating acoustic wave. The manuscript is divided into 3 chapters: • a first chapter presents the known methods for the visualization of the acoustic phenomena and presents the context of the research carried out, • a second chapter, allows to detail the principle of measurement and its application to the realization of a two-dimensional image of the acoustic wave • finally, in the last chapter, we demonstrate how a tomographic method can be used to create a three-dimensional image

POD-Galerkin advection model for convective flow Application to a flapping rectangular supersonic jet

International audienceThis article describes a model obtained by applying Proper Orthogonal Decomposition to the ad-vection equation. The resulting set of equations links the POD modes, their temporal and spatial derivatives and the flow convection velocity. It provides a technique to calculate the convection velocity of coherent structures. It follows, from the model, that a priori knowledge of the convection velocity suffices to construct a dynamical model of the flow. This is demonstrated using experimental data

Visualization of ultrasonic wave field by stroboscopic polarization selective imaging

A stroboscopic method based on polarization selective imaging is proposed for dynamic visualization of ultrasonic waves propagating in a transparent medium. Multiple independent polarization parametric images were obtained, which enabled quantitative evaluation of the distribution of the ultrasonic pressure in quartz. In addition to the detection of optical phase differences δ in conventional photo-elastic techniques, the azimuthal angle φ and the Stokes parameter S2 of the polarized light are found to be highly sensitive to the wave-induced refraction index distribution, opening a new window on ultrasonic field visualization

Summary of Supersonic Jet and Rocket Noise

This paper summarizes a two-part special session, “Supersonic Jet and Rocket Noise,” which was held during the 174th Meeting of the Acoustical Society of America in New Orleans, Louisiana. The sessions were cosponsored by the Noise and Physical Acoustics Technical Committees and consisted of talks by government, academic, and industry researchers from institutions in the United States, Japan, France, and India. The sessions described analytical, computational, and experimental approaches to both fundamental and applied problems on model and full-scale jets and rocket exhaust plumes

Measurement of combustion response to transverse modes at high pressure

A two dimensional transverse combustor capable of producing and modulating an unstable flowfield was tested at Purdue. The combustor used an array of coaxial ox-centered shear injector elements. The oxidizer posts were able to be discretely changed in length between tests to investigate different post resonance conditions. A single Study element was placed in the middle of the driven unsteady flowfield so its response could be measured using pressure measurement and high speed imagery. This approach was supported by past testing of the longitudinal Continuously Variable Resonance Combustor and past transverse chambers. Mean flow rates and pressures were fixed across the series of tests. ^ Phase lag data between pressure measurement locations support a simple linear post-to-chamber interaction mechanism. Phase lags between chamber measurements were unaffected by the change in oxidizer post length. Scaling was established between amplitude levels and post lengths between the longitudinal and transverse combustors, which further supported the proposed post-to-chamber response mechanism. ^ High speed imaging of OH* chemiluminesence was used as a marker of heat release. Mean flame behavior showed broad distribution and flame shortening at high forcing amplitude and compact, elongated flame shape at low forcing amplitude. Multiple image analysis techniques were utilized to process these data. Proper orthogonal decomposition and dynamic mode decomposition showed spatial and temporal character of image time slices sorted by descriptive content and frequency, respectively. These analyses both identified significant behavior at the same frequencies as chamber pressure perturbations. ^ A systematic code was developed to select relevant time slices to generate flame describing functions of image magnitude and phase lag as a function of pressure amplitude. The magnitude flame describing functions showed low amplitude linear behavior with a divergence at high amplitude. For phase lag flame describing functions, a convergence towards phase locked behavior was noted as amplitude increased

Triadic Resonance Instability in finite-width internal gravity wave beams

Through the use of both experiments and theoretical modelling, this thesis examines the weakly non-linear dynamics of an internal wave beam becoming unstable to Triadic Resonance Instability (TRI). To date, most theoretical work examines the instability in the context of monochromatic plane waves. In the ocean, however, waves seldom take this form, rather they manifest as beams that span the wavenumber spectra. With an aim of developing our understanding of the role of TRI in oceanic settings, this thesis focuses on how the instability evolves in finite-width internal wave beams. Experiments have been conducted using a new generation of wave maker, featuring a flexible horizontal bottom boundary driven by an array of independently controlled actuators. Using this wavemaker, finite-width internal wave beams of varying amplitude were generated in a linear stratification. Novel experimental results show that when one of these beams becomes unstable via TRI, the approach to a saturated equilibrium state for the triadic waves is not monotonic, rather their amplitudes continue to oscillate without reaching a steady equilibrium. Further diagnostics reveal how the frequencies of the two secondary waves involved in the resonant triad also modulate over time. This behaviour is shown to be a result of the finite spatial extent of the primary beam, which causes cyclic growth and decay of different triadic perturbations. As previously published literature does not consider the triadic energy exchange to be a function of space, it is unable to predict this oscillatory behaviour. Theoretical modelling is developed to capture the essence of the experimental setup. The model uses numerical solutions of a weakly non-linear system in a two-dimensional framework. A detailed study looks at how different wavenumbers and frequencies of the secondary waves affect the development of TRI in a finite-width beam. The results show how the orientation of the secondary waves has a strong influence on the evolution of the instability, as this determines the duration over which the triadic energy exchange can occur. By including multiple possible resonant waves in the system, the results also capture both the amplitude and frequency oscillations exhibited experimentally. This model not only recapitulates the experimental findings, but provides a tool for the community to dissect the underlying dynamics of the instability. Both the experimental and theoretical findings presented in this thesis reveal novel insights into how TRI evolves in finite-width internal wave beams. This work thus provides a key to understanding how this instability mechanism may manifest in oceanic scenarios and its potential role in global ocean circulation.National Environmental Research Council (NERC) grant no. NE/L002507/

Variational fluid flow measurements from image sequences: synopsis and perspectives

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEEVariational approaches to image motion segmentation has been an active field of study in image processing and computer vision for two decades. We present a short overview over basic estimation schemes and report in more detail recent modifications and applications to fluid flow estimation. Key properties of these approaches are illustrated by numerical examples. We outline promising research directions and point out the potential of variational techniques in combination with correlation-based PIV methods, for improving the consistency of fluid flow estimation and simulation

Exploring Passive Flow Control Techniques Applied to a Supersonic Multistream Rectangular Nozzle

Passive control techniques are applied experimentally to examine different aspects of a supersonic multistream rectangular nozzle representing a modern airframe-integrated variable cycle engine. The flow is comprised of a core stream (M = 1.6) and bypass (M = 1.0) that merge behind a splitter plate and exit through a Single Expansion Ramp Nozzle (SERN) onto an aft-deck. Previous efforts for the nominal nozzle configuration have shown that an instability initiated at the splitter plate trailing edge (SPTE) influences the effectiveness of the third stream as a barrier for the aft-deck and persists through the entire do- main due to its reaction with the shock train. To address this, passive flow con- trol was implemented by introducing sinusoidal spanwise modifications along the splitter plate edge. The SPTE was identified as the highest region of sensitivity via LES. Results on different spanwise wavenumbers indicate reduction of the dominating tone with increasing wavenumber. Additionally, the sinusoidal trailing edge induces streamwise vorticity, which enhances mixing between the two streams and breaks up the shed structures seen previously. A wavenumber corresponding to one simulated was tested experimentally via the use of simultaneous nearfield pressure and velocity in conjunction with farfield acoustics. Farfield acoustic measurements have confirmed the diminishment of the tone for the wavy SPTE. PIV and velocity profiles for mean fields revealed higher plume vectoring for the nominal aft-deck. The shear layers and the region along the aft-deck surface displayed significant enhancement of velocity variability through low order statistics. As a result of this increase, the POD modes werereordered for the wavy SPTE. Wavy modes had smaller spatial structures presented in lower modes, with increased energy content when compared to the same modes in the nominal flow