Cumulative nonlinear distortion of an acoustic wave propagating through non-uniform flow

1977 ◽  
Vol 83 (4) ◽  
pp. 751-773 ◽  
Author(s):  
M. Kurosaka
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Near Field ◽  
Direct Consequence ◽  
Confluent Hypergeometric Function ◽  
Uniform Flow ◽  
The Body ◽  
Form Representation ◽  
Physical Features ◽  
Special Case

In this paper we examine how the unsteady flow field radiated from an oscillating body is altered from the result of acoustic theory as the direct consequence of disturbances propagating through the non-uniform flow produced by the presence of the body. Taking the specific example of an oscillating airfoil placed in supersonic flow and having the contour of a parabolic arc, we derive a closed-form representation for the unsteady flow field in terms of the confluent hypergeometric function. The analytical expression reveals explicitly that, though the body shape has a negligible effect in the near field, it inextricably affects the unsteady flow at a large distance, both in its amplitude and phase, and substantially modifies the results of acoustic theory. In addition, we display the relation of this solution to the ‘fundamental solution’ and the other salient physical features connected with disturbances propagating through non-uniform flow. The present results recover Whitham's rule in the limit of zero frequency of oscillation and also include, as another special case, the unsteady solution for a wedge obtained by Carrier and Van Dyke.

Generalized Kirchhoff equations for a deformable body moving in a weakly non-uniform flow field

1994 ◽  
Vol 446 (1926) ◽  
pp. 169-193 ◽  
Keyword(s):  
Flow Field ◽  
Rigid Body ◽  
Degrees Of Freedom ◽  
Surface Deformation ◽  
Nonlinear Differential Equations ◽  
Deformable Body ◽  
Equations Of Motion ◽  
First Integral ◽  
Uniform Flow ◽  
The Body

The classical Kirchhoff’s method provides an efficient way of calculating the hydrodynamical loads (forces and moments) acting on a rigid body moving with six-degrees of freedom in an otherwise quiescent ideal fluid in terms of the body’s added-mass tensor. In this paper we provide a versatile extension of such a formulation to account for both the presence of an imposed ambient non-uniform flow field and the effect of surface deformation of a non-rigid body. The flow inhomogeneity is assumed to be weak when compared against the size of the body. The corresponding expressions for the force and moment are given in a moving body-fixed coordinate system and are obtained using the Lagally theorem. The newly derived system of nonlinear differential equations of motion is shown to possess a first integral. This can be interpreted as an energy-type conservation law and is a consequence of an anti-symmetry property of the coefficient matrix reported here for the first time. A few applications of the proposed formulation are presented including comparison with some existing limiting cases.

Near-Field Noise Prediction for Landing Gear Based on Detached Eddy Simulations

2014 ◽  
Vol 472 ◽  
pp. 105-110
Author(s):  
Ning Hu ◽  
Xuan Hao ◽  
Cheng Su ◽  
Wei Min Zhang ◽  
Han Dong Ma
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Sound Pressure ◽  
Near Field ◽  
Separated Flow ◽  
Landing Gear ◽  
Aerodynamic Noise ◽  
Noise Prediction ◽  
Detached Eddy Simulation ◽  
Eddy Simulation

A four-wheel rudimentary landing gear is studied numerically by detached eddy simulation (DES) based on the Spalart-Allmaras turbulence model. The surface sound pressure level and sound pressure spectra are calculated using the obtained unsteady flow field. The investigation shows that DES can describe the steady and unsteady properties in the flow around rudimentary landing gear. It can give reasonable results since the flow around the landing gear is a massive separated flow. The results prove the feasibility of DES type methods in massive separated unsteady flow field and aerodynamic noise prediction for landing gear, and can be used in the study of landing gear noise reduction.

PIV Measurements of Flow-Field Downstream of a Cylinder in Uniform Flow and Comparisons With CFD

2013 ◽  
Author(s):  
Peter B. Stetson ◽  
Spyros A. Kinnas
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Uniform Flow ◽  
Hydrodynamic Coefficients ◽  
Two Dimensional ◽  
General Sense ◽  
Piv Measurements ◽  
Functional Approximation ◽  
Cfd Models ◽  
Stream Direction

This paper examines the ability of two-dimensional CFD models to predict flow downstream of a cylinder in uniform flow. PIV measurements of the flow-field downstream of the cylinder in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Hydrodynamic coefficients and velocities are compared. In a general sense, two-dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder.

scholarly journals Severe infection including disseminated herpes zoster triggered by subclinical Cushing’s disease: a case report

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Yuki Yamauchi ◽  
Hiraku Kameda ◽  
Kazuno Omori ◽  
Michio Tani ◽  
Kyu Yong Cho ◽  
...  
Keyword(s):  
Herpes Zoster ◽  
Cushing’S Disease ◽  
Cardiopulmonary Arrest ◽  
Severe Infection ◽  
Japanese Woman ◽  
The Body ◽  
Cushing's Disease ◽  
Old Japanese ◽  
Subclinical Cushing’S Disease ◽  
Physical Features

Abstract Background Subclinical Cushing’s disease (SCD) is defined by corticotroph adenoma-induced mild hypercortisolism without typical physical features of Cushing’s disease. Infection is an important complication associated with mortality in Cushing’s disease, while no reports on infection in SCD are available. To make clinicians aware of the risk of infection in SCD, we report a case of SCD with disseminated herpes zoster (DHZ) with the mortal outcome. Case presentation An 83-year-old Japanese woman was diagnosed with SCD, treated with cabergoline in the outpatient. She was hospitalized for acute pyelonephritis, and her fever gradually resolved with antibiotics. However, herpes zoster appeared on her chest, and the eruptions rapidly spread over the body. She suddenly went into cardiopulmonary arrest and died. Autopsy demonstrated adrenocorticotropic hormone-positive pituitary adenoma, renal abscess, and DHZ. Conclusions As immunosuppression caused by SCD may be one of the triggers of severe infection, the patients with SCD should be assessed not only for the metabolic but also for the immunodeficient status.

Modal characteristics and fluid–structure interaction vibration response of submerged impeller

2021 ◽  
pp. 107754632110036
Author(s):  
Shihui Huo ◽  
Hong Huang ◽  
Daoqiong Huang ◽  
Zhanyi Liu ◽  
Hui Chen
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Damping Ratio ◽  
Pure Water ◽  
Vibration Response ◽  
Modal Identification ◽  
Liquid Oxygen ◽  
Modal Characteristics ◽  
Oxygen Pump ◽  
Turbo Pump

Turbo pump is one of the elements with the most complex flow of liquid rocket engine, and as an important component of turbo pump, an impeller is the weak point affecting its reliability. In this study, a noncontact modal characteristic identification technique was proposed for the liquid oxygen pump impeller. Modal characteristics of the impeller under three different submerged media, air, pure water, and brine with same density as liquid oxygen, were tested based on the noncontact modal identification technology. Submersion state directly affects the modal frequencies and damping ratio. The transient vibration response characteristics of the impeller excited by the unsteady flow field was achieved combining with unsteady flow field analysis and transient dynamic analysis in the whole flow passage of the liquid oxygen pump. Vibration responses at different positions of the impeller show 10X and 20X frequencies, and the amplitude at the root of short blade is significant, which needs to be paid more attention in structural design and fatigue evaluation.

scholarly journals Investigation on Wireless Link for Medical Telemetry Including Impedance Matching of Implanted Antennas

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1431
Author(s):  
Ilkyu Kim ◽  
Sun-Gyu Lee ◽  
Yong-Hyun Nam ◽  
Jeong-Hae Lee
Keyword(s):  
Real Time ◽  
Human Body ◽  
Near Field ◽  
Impedance Matching ◽  
The Body ◽  
Field Pattern ◽  
Communication Link ◽  
Far Field ◽  
Antenna Coupling ◽  
Medical Telemetry

The development of biomedical devices benefits patients by offering real-time healthcare. In particular, pacemakers have gained a great deal of attention because they offer opportunities for monitoring the patient’s vitals and biological statics in real time. One of the important factors in realizing real-time body-centric sensing is to establish a robust wireless communication link among the medical devices. In this paper, radio transmission and the optimal characteristics for impedance matching the medical telemetry of an implant are investigated. For radio transmission, an integral coupling formula based on 3D vector far-field patterns was firstly applied to compute the antenna coupling between two antennas placed inside and outside of the body. The formula provides the capability for computing the antenna coupling in the near-field and far-field region. In order to include the effects of human implantation, the far-field pattern was characterized taking into account a sphere enclosing an antenna made of human tissue. Furthermore, the characteristics of impedance matching inside the human body were studied by means of inherent wave impedances of electrical and magnetic dipoles. Here, we demonstrate that the implantation of a magnetic dipole is advantageous because it provides similar impedance characteristics to those of the human body.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

Survey on the Indirect Methods of Potential Flow Used for the Optimization of Airships Profile

2014 ◽  
Vol 554 ◽  
pp. 717-723
Author(s):  
Reza Abbasabadi Hassanzadeh ◽  
Shahab Shariatmadari ◽  
Ali Chegeni ◽  
Seyed Alireza Ghazanfari ◽  
Mahdi Nakisa
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Drag Coefficient ◽  
Body Surface ◽  
Potential Flow ◽  
The Body ◽  
Indirect Methods ◽  
Singularity Method ◽  
Singularity Distribution

The present study aims to investigate the optimized profile of the body through minimizing the Drag coefficient in certain Reynolds regime. For this purpose, effective aerodynamic computations are required to find the Drag coefficient. Then, the computations should be coupled thorough an optimization process to obtain the optimized profile. The aerodynamic computations include calculating the surrounding potential flow field of an object, calculating the laminar and turbulent boundary layer close to the object, and calculating the Drag coefficient of the object’s body surface. To optimize the profile, indirect methods are used to calculate the potential flow since the object profile is initially amorphous. In addition to the indirect methods, the present study has also used axial singularity method which is more precise and efficient compared to other methods. In this method, the body profile is not optimized directly. Instead, a sink-and-source singularity distribution is used on the axis to model the body profile and calculate the relevant viscose flow field.

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