scholarly journals On the Application of Wavelet Transform in Jet Aeroacoustics

Fluids ◽  
2021 ◽  
Vol 6 (8) ◽  
pp. 299
Author(s):  
Roberto Camussi ◽  
Stefano Meloni
Keyword(s):  
Wavelet Transform ◽  
Near Field ◽  
Hydrodynamic Pressure ◽  
Turbulent Jet ◽  
Experimental Database ◽  
Future Developments ◽  
Pressure Time ◽  
Propeller Noise ◽  
Stationary Signals ◽  
Conditional Statistics

Wavelet transform has become a common tool for processing non-stationary signals in many different fields. The present paper reports a review of some applications of wavelet in aeroacoustics with a special emphasis on the analysis of experimental data taken in compressible jets. The focus is on three classes of wavelet-based signal processing procedures: (i) conditional statistics; (ii) acoustic and hydrodynamic pressure separation; (iii) stochastic modeling. The three approaches are applied to an experimental database consisting of pressure time series measured in the near field of a turbulent jet. Future developments and possible generalization to other applications, e.g., airframe or propeller noise, are also discussed.

Extrapolation and inversion of near-field propeller noise measurements

2022 ◽  
Vol 185 ◽  
pp. 108395
Author(s):  
Yan Wu ◽  
Michael J. Kingan ◽  
Ryan S. McKay ◽  
Sung Tyaek Go ◽  
Young-min Shim
Keyword(s):  
Near Field ◽  
Propeller Noise ◽  
Noise Measurements ◽  
And Inversion

scholarly journals Improving the validation of turbulent jet breakup models

2019 ◽  
Author(s):  
Ben Trettel
Keyword(s):  
Fire Suppression ◽  
Experimental Studies ◽  
Droplet Size Distribution ◽  
Turbulent Jet ◽  
Liquid Jets ◽  
Experimental Database ◽  
Quality Guidelines ◽  
Water Jet Cutting ◽  
Jet Breakup ◽  
Quantities Of Interest

Understanding the physics of the breakup of turbulent liquid jets is important for a variety of applications including engine sprays, fire suppression systems, and water jet cutting. Models of turbulent jet breakup allow predictions of quantities of interest like the droplet size distribution and breakup length of the jet. These models are compared against experimental data in a process called validation. If the model predictions are within the experimental uncertainty, then the model is "validated" and believed to be accurate, and possibly can explain the physics. Uncertainty quantification is necessary for model validation. While unfortunately relatively few experimental studies quantify uncertainty, that is not the most pressing validation issue in turbulent jet breakup. I detail 3 additional problems that can make the apparent validation of a model actually an illusion, regardless of how well the model appears to match the data. These problems include: 1. important variables being omitted or guessed in experiments and models, 2. confounding between independent variables, that is, two variables changing simultaneously, making determining cause and effect impossible, and 3. testing only combinations of submodels and not each submodel in isolation. To avoid these problems and others, I developed validation guidelines that are detailed in this work. Following these guidelines, I compiled a large experimental database. Only 28 out of 47 experimental studies considered met my data quality guidelines. Only 18 studies had quantified uncertainty, and only 3 studies had substantial variation in the turbulence intensity.

A study of Mach wave radiation using active control

2011 ◽  
Vol 681 ◽  
pp. 261-292 ◽  
Author(s):  
M. KEARNEY-FISCHER ◽  
J.-H. KIM ◽  
M. SAMIMY
Keyword(s):  
Large Scale ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Hydrodynamic Pressure ◽  
Detailed Examination ◽  
Operating Conditions ◽  
Wave Radiation ◽  
Stagnation Temperature ◽  
Azimuthal Mode ◽  
Mach Wave

Mach wave radiation is one of the better understood sources of jet noise. However, the exact conditions of its onset are difficult to determine and the literature to date typically explores Mach wave radiation well above its onset conditions. In order to determine the conditions for the onset of Mach wave radiation and to explore its behaviour during onset and beyond, three ideally expanded jets with Mach numbers Mj = 0.9, 1.3 and 1.65 and stagnation temperature ratios ranging over To/T∞ = 1.0–2.5 (acoustic Mach number 0.83–2.10) were used. Data are collected using a far-field microphone array, schlieren imaging and streamwise two-component particle image velocimetry. Using arc filament plasma actuators to force the jet provides an unprecedented tool for detailed examination of Mach wave radiation. The response of the jet to various forcing parameters (combinations of one azimuthal mode m = 0, 1 and 3 and one Strouhal number StDF = 0.09–3.0) is explored. Phase-averaged schlieren images clearly show the onset and evolution of Mach wave radiation in response to both changes in the jet operating conditions and forcing parameters. It is observed that Mach wave radiation is initiated as a coalescing of the near-field hydrodynamic pressure fluctuations in the immediate vicinity of the large-scale structures. As the jet exit velocity increases, the hydrodynamic pressure fluctuations coalesce, first into a curved wavefront, then flatten into the conical wavefronts commonly associated with Mach wave radiation. The results show that the largest and most coherent structures (e.g. forcing with m = 0 and StDF ~ 0.3) produce the strongest Mach wave radiation. Conversely, Mach wave radiation is weakest when the structures are the least coherent (e.g. forcing with m = 3 and StDF > 1.5).

Near-Field Characteristics of a Turbulent Jet With Ring Injectors

2009 ◽  
Author(s):  
Hamid R. Rahai ◽  
Shahab Moayedian
Keyword(s):  
Cross Section ◽  
Near Field ◽  
Turbulent Jet ◽  
Hole Injection ◽  
Mean Velocity ◽  
Blowing Ratio ◽  
Velocity Decay ◽  
Axial Variation ◽  
Inner Diameter ◽  
Axis Switching

Mixing effectiveness of a heated turbulent jet with two-hole and three-hole ring injectors was experimentally investigated. The injectors were rings with square cross section with side dimensions of approximately 5 mm. The ratio of the ring thickness to the jet inner diameter was 4.7%. For the two-hole injector, the injecting holes were at 180 degrees from each other and for the three-hole injectors, the holes were spaced at 120 degrees. The maximum mean velocity of the jet was at approximately 4 m/s which corresponds to an approximate Reynolds number based on the jet inner diameter of 14,676. The total blowing ratio as compared to the axial momentum for each configuration was at 2%. Results indicate significant increases in RMS fluctuation and mean velocity decay with the ring injectors with these effects being more pronounced for the three-hole injection. Axial variation of momentum thicknesses indicates a possibility of axis switching in the near field for the three-hole ring injector.

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