scholarly journals Assessment of Optimization Methods for Aeroacoustic Prediction of Trailing-Edge Interaction Noise in Axisymmetric Jets

Mathematics ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 998
Author(s):  
Sarah Stirrat ◽  
Mohammed Z. Afsar ◽  
Edmondo Minisci
Keyword(s):  
Differential Evolution Algorithm ◽  
Computation Time ◽  
Optimization Methods ◽  
Turnover Time ◽  
Fine Tuning ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Trailing Edge ◽  
Acoustic Spectrum ◽  
Trailing Edge Noise

Our concern in this paper is in the fine-tuning of the arbitrary parameters within the upstream turbulence structure for the acoustic spectrum of a rapid-distortion theory (RDT)-based model of trailing-edge noise. RDT models are based on an appropriate asymptotic limit of the Linearized Euler Equations and apply when the interaction time of the turbulence with the surface edge discontinuity is small compared to the eddy turnover time. When an arbitrary transversely sheared jet mean flow convects a finite region of nonhomogeneous turbulence, the acoustic spectrum of the pressure field scattered by the trailing-edge depends on (among other things) the upstream turbulence via the Fourier transform of the correlation function, R22 (where subscript 2 refers to a co-ordinate surface normal to the plate). We show that the length and time scale parameters that govern the spatial and temporal de-correlation of R22 can be found using formal optimization methods to avoid any uncertainty in their selection by hand-tuning. We assess various optimization methods that are broadly categorized into an ‘evolutionary’ and ‘non-evolutionary’ paradigm. That is, we optimize the acoustic spectrum using the Multi-Start algorithm, Particle Swarm Optimization and the Multi-Population Adaptive Inflationary Differential Evolution Algorithm. The optimization is based upon different objective functions for the acoustic spectrum and/or turbulence structure. We show that this approach, while resulting in the total modest increase in computation time (on average 2 h), gives excellent prediction over most frequencies (within 2–4 dB) where the trailing-edge noise associated amplification in sound exists.

The Simulation of Airframe Noise Applying Euler-Perturbation and Acoustic Analogy Approaches

2005 ◽  
Vol 4 (1-2) ◽  
pp. 69-91 ◽  
Author(s):  
R. Ewert ◽  
J.W. Delfs ◽  
M. Lummer
Keyword(s):  
Mach Number ◽  
Scaling Laws ◽  
Perturbation Approach ◽  
Far Field ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Trailing Edge ◽  
Airframe Noise ◽  
Trailing Edge Noise ◽  
The Mean

The capability of three different perturbation approaches to tackle airframe noise problems is studied. The three approaches represent different levels of complexity and are applied to trailing edge noise problems. In the Euler-perturbation approach the linearized Euler equations without sources are used as governing acoustic equations. The sound generation and propagation is studied for several trailing edge shapes (blunt, sharp, and round trailing edges) by injecting upstream of the trailing edge test vortices into the mean-flow field. The efficiency to generate noise is determined for the trailing edge shapes by comparing the different generated sound intensities due to an initial standard vortex. Mach number scaling laws are determined varying the mean-flow Mach number. In the second simulation approach an extended acoustic analogy based on acoustic perturbation equations (APEs) is applied to simulate trailing edge noise of a flat plate. The acoustic source terms are computed from a synthetic turbulent velocity model. Furthermore, the far field is computed via additional Kirchhoff extrapolation. In the third approach the sources of the extended acoustic analogy are computed from a Large Eddy Simulation (LES) of the compressible flow problem. The directivities due to a modeled and a LES based source, respectively, compare qualitatively well in the near field. In the far field the asymptotic directivities from the Kirchhoff extrapolation agree very well with the analytical solution of Howe. Furthermore, the sound pressure spectra can be shown to have similar shape and magnitude for the last two approaches.

scholarly journals Global optimization of default phases for parallel transmit coils for ultra-high-field cardiac MRI

PLoS ONE ◽  
2021 ◽  
Vol 16 (8) ◽  
pp. e0255341
Author(s):  
Maxim Terekhov ◽  
Ibrahim A. Elabyad ◽  
Laura M. Schreiber
Keyword(s):  
Cardiac Mri ◽  
Computation Time ◽  
Optimization Methods ◽  
Fine Tuning ◽  
Optimization Approach ◽  
Brute Force ◽  
Global Extremum ◽  
High Magnetic Field Strength ◽  
Brute Force Method ◽  
Key Steps

The development of novel multiple-element transmit-receive arrays is an essential factor for improving B1+ field homogeneity in cardiac MRI at ultra-high magnetic field strength (B0 > = 7.0T). One of the key steps in the design and fine-tuning of such arrays during the development process is finding the default driving phases for individual coil elements providing the best possible homogeneity of the combined B1+-field that is achievable without (or before) subject-specific B1+-adjustment in the scanner. This task is often solved by time-consuming (brute-force) or by limited efficiency optimization methods. In this work, we propose a robust technique to find phase vectors providing optimization of the B1-homogeneity in the default setup of multiple-element transceiver arrays. The key point of the described method is the pre-selection of starting vectors for the iterative solver-based search to maximize the probability of finding a global extremum for a cost function optimizing the homogeneity of a shaped B1+-field. This strategy allows for (i) drastic reduction of the computation time in comparison to a brute-force method and (ii) finding phase vectors providing a combined B1+-field with homogeneity characteristics superior to the one provided by the random-multi-start optimization approach. The method was efficiently used for optimizing the default phase settings in the in-house-built 8Tx/16Rx arrays designed for cMRI in pigs at 7T.

Reduction of Wall Jet Trailing Edge Noise by Mean Flow Modification

1980 ◽  
Vol 17 (9) ◽  
pp. 633-640
Author(s):  
M.C. Joshi ◽  
J.C. Yu
Keyword(s):  
Wall Jet ◽  
Mean Flow ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Flow Modification

Experimental Investigation of Turbulent Flow With Separation Over a NACA 4412 Airfoil at Angle of Attack 20 Degree

2002 ◽  
Author(s):  
Omar O. Badran ◽  
Hans H. Bruun
Keyword(s):  
Separation Bubble ◽  
Angle Of Attack ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Separation Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Airfoil Surface

This paper presents the measured mean flow and Reynolds stresses results, obtained on the center-line plane of the airfoil, covering the boundary layers over the upper surface, the potential flow region and the wake downstream of the trailing edge, at αa = 20°. The flying X-hot-wire probe was used to measure mean velocity and turbulence structure over the airfoil. An improved understanding of the physical characteristics of separation on the airfoil sections and in the region of the trailing edge is of direct value for the improvement of high lift wings for aircraft. From the study of the separation flow at angle of attack αa = 20°, the following can be concluded: A stable separation bubble has developed near the trailing edge of the airfoil, covering around 0.6c of the airfoil surface. Also it is found that values of the Reynolds normal and shear stresses move away from the surface with downstream distance, showing turbulence diffusion to be more evident in this flow. In the wake region, relatively large values of Reynolds stresses occurred, which were related to the vertical oscillations in the upper wake.

scholarly journals Trailing edge noise theory for rotating blades in uniform flow

2013 ◽  
Vol 469 (2157) ◽  
pp. 20130065 ◽  
Author(s):  
S. Sinayoko ◽  
M. Kingan ◽  
A. Agarwal
Keyword(s):  
Angular Frequency ◽  
Rotational Frequency ◽  
Mean Flow ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Rotating Blades ◽  
Noise Radiation ◽  
Cooling Fan ◽  
New Formulation

This paper presents a new formulation for trailing edge noise radiation from rotating blades based on an analytical solution of the convective wave equation. It accounts for distributed loading and the effect of mean flow and spanwise wavenumber. A commonly used theory due to Schlinker and Amiet predicts trailing edge noise radiation from rotating blades. However, different versions of the theory exist; it is not known which version is the correct one, and what the range of validity of the theory is. This paper addresses both questions by deriving Schlinker and Amiet's theory in a simple way and by comparing it with the new formulation, using model blade elements representative of a wind turbine, a cooling fan and an aircraft propeller. The correct form of Schlinker and Amiet's theory is identified. It is valid at high enough frequency, i.e. for a Helmholtz number relative to chord greater than one and a rotational frequency much smaller than the angular frequency of the noise sources.

Computation of trailing-edge noise due to turbulent flow over an airfoil

AIAA Journal ◽  
2002 ◽  
Vol 40 ◽  
pp. 2206-2216 ◽  
Author(s):  
A. Oberai ◽  
F. Roknaldin ◽  
T. J. R. Hughes
Keyword(s):  
Turbulent Flow ◽  
Trailing Edge ◽  
Trailing Edge Noise

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

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