Wavelet decomposition of hydrodynamic and acoustic pressures in the near field of the jet

2017 ◽  
Vol 813 ◽  
pp. 716-749 ◽  
Author(s):  
Matteo Mancinelli ◽  
Tiziano Pagliaroli ◽  
Alessandro Di Marco ◽  
Roberto Camussi ◽  
Thomas Castelain
Keyword(s):  
Near Field ◽  
Pressure Fluctuations ◽  
Hydrodynamic Pressure ◽  
Far Field ◽  
Simple Arrangement ◽  
Number Variation ◽  
Distinctive Property ◽  
Processing Techniques ◽  
Measured Pressure ◽  
Higher Sensitivity

An experimental investigation of pressure fluctuations generated by a single-stream compressible jet is carried out in an anechoic wind tunnel. Measurements are performed using a linear array of microphones installed in the near region of the jet and a polar arc of microphones in the far field. The main focus of the paper is on the analysis of the pressure fluctuations in the near field. Three novel signal processing techniques are presented to provide the decomposition of the near-field pressure into hydrodynamic and acoustic components. The procedures are all based on the application of the wavelet transform to the measured pressure data and possess the distinctive property of requiring a very simple arrangement to obtain the desired results (one or two microphones at most). The hydrodynamic and acoustic pressures are characterized separately in terms of their spectral and statistical quantities and a direct link between the acoustic pressure extracted from the near field and the actual noise in the far field is established. The analysis of the separated pressure components sheds light on the nearly Gaussian nature/intermittent behaviour of the acoustic/hydrodynamic pressure. The higher sensitivity of the acoustic component to the Mach number variation has been highlighted as well as the different propagation velocities of the two pressure components. The achieved outcomes are validated through the application to the same data of existing separation procedures evidencing the advantages and limitations of the new methods.

On the hydrodynamic and acoustic nature of pressure proper orthogonal decomposition modes in the near field of a compressible jet

2017 ◽  
Vol 836 ◽  
pp. 998-1008 ◽  
Author(s):  
Matteo Mancinelli ◽  
Tiziano Pagliaroli ◽  
Roberto Camussi ◽  
Thomas Castelain
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Time Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Orthogonal Decomposition ◽  
Spectral Energy ◽  
Far Field ◽  
Turbulent Structures ◽  
Proper Orthogonal ◽  
Compressible Jet

In this work an experimental investigation of the near-field pressure of a compressible jet is presented. The proper orthogonal decomposition (POD) of the pressure fluctuations measured by a linear array of microphones is performed in order to provide the streamwise evolution of the jet structure. The wavenumber–frequency spectrum of the space–time pressure fields re-constructed using each POD mode is computed in order to provide the physical interpretation of the mode in terms of hydrodynamic/acoustic nature. Specifically, non-radiating hydrodynamic, radiating acoustic and ‘hybrid’ hydro-acoustic modes are found based on the phase velocity associated with the spectral energy bumps in the wavenumber–frequency domain. Furthermore, the propagation direction in the far field of the radiating POD modes is detected through the cross-correlation with the measured far-field noise. Modes associated with noise emissions from large/fine scale turbulent structures radiating in the downstream/sideline direction in the far field are thus identified.

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).

Surface pressure fluctuations on aircraft flaps and their correlation with far-field noise

2000 ◽  
Vol 415 ◽  
pp. 175-202 ◽  
Author(s):  
Y. P. GUO ◽  
M. C. JOSHI ◽  
P. H. BENT ◽  
K. J. YAMAMOTO
Keyword(s):  
Surface Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Vortex Structures ◽  
Far Field ◽  
Mean Flow ◽  
Noise Sources ◽  
Side Edge ◽  
Field Noise

This paper discusses unsteady surface pressures on aircraft flaps and their correlation with far-field noise. Analyses are made of data from a 4.7% DC-10 aircraft model test, conducted in the 40 × 80 feet wind tunnel at NASA Ames Research Center. Results for various slat/wing/flap configurations and various flow conditions are discussed in detail to reveal major trends in surface pressure fluctuations. Spectral analysis, including cross-correlation/coherence, both among unsteady surface pressures and between far-field noise and near-field fluctuations, is used to reveal the most coherent motions in the near field and identify potential sources of noise related to flap flows. Dependencies of surface pressure fluctuations on mean flow Mach numbers, flap settings and slat angles are discussed. Dominant flow features in flap side edge regions, such as the formation of double-vortex structures, are shown to manifest themselves in the unsteady surface pressures as a series of spectral humps. The spectral humps are shown to correlate well with the radiated noise, indicating the existence of major noise sources in flap side edge regions. Strouhal number scaling is used to collapse the data with satisfactory results. The effects of flap side edge fences on surface pressures are also discussed. It is shown that the application of fences effectively increases the thickness of the flaps so that the double-vortex structures have more time to evolve. As a result, the characteristic timescale of the unsteady sources increases, which in turn leads to a decrease in the dominant frequency of the source process. Based on this, an explanation is proposed for the noise reduction mechanism of flap side edge fences.

scholarly journals Parabolized stability analysis of jets from serrated nozzles

2016 ◽  
Vol 789 ◽  
pp. 36-63 ◽  
Author(s):  
Aniruddha Sinha ◽  
Kristján Gudmundsson ◽  
Hao Xia ◽  
Tim Colonius
Keyword(s):  
Linear Stability ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Hydrodynamic Pressure ◽  
Linear Instability ◽  
Base Flow ◽  
Linear Stability Theory ◽  
Instability Wave ◽  
Mean Flow

We study the viscous spatial linear stability characteristics of the time-averaged flow in turbulent subsonic jets issuing from serrated (chevroned) nozzles, and compare them to analogous round jet results. Linear parabolized stability equations (PSE) are used in the calculations to account for the non-parallel base flow. By exploiting the symmetries of the mean flow due to the regular arrangement of serrations, we obtain a series of coupled two-dimensional PSE problems from the original three-dimensional problem. This reduces the solution cost and manifests the symmetries of the stability modes. In the parallel-flow linear stability theory (LST) calculations that are performed near the nozzle to initiate the PSE, we find that the serrated nozzle reduces the growth rates of the most unstable eigenmodes of the jet, but their phase speeds are approximately similar. We obtain encouraging validation of our linear PSE instability wave results vis-à-vis near-field hydrodynamic pressure data acquired on a phased microphone array in experiments, after filtering the latter with proper orthogonal decomposition (POD) to extract the energetically dominant coherent part. Additionally, a large-eddy simulation database of the same serrated jet is investigated, and its POD-filtered pressure field is found to compare favourably with the corresponding PSE solution within the jet plume. We conclude that the coherent hydrodynamic pressure fluctuations of jets from both round and serrated nozzles are reasonably consistent with the linear instability modes of the turbulent mean flow.

Dynamics of an impinging jet. Part 2. The noise generation

1982 ◽  
Vol 116 ◽  
pp. 379-391 ◽  
Author(s):  
Nagy S. Nosseir ◽  
Chih-Ming Ho
Keyword(s):  
Coherent Structures ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Aerodynamic Noise ◽  
Far Field ◽  
Noise Generation ◽  
Physical Mechanisms ◽  
Field Noise ◽  
Subsonic Jet ◽  
Jet Axis

The aerodynamic noise generated by a subsonic jet impinging on a flat plate is studied from measurements of near-field and surface-pressure fluctuations. The far-field noise measured at 90° to the jet axis is found to be generated by two different physical mechanisms. One mechanism is the impinging of the large coherent structures on the plate, and the other is associated with the initial instability of the shear layer. These two sources of noise radiate to the far field via different acoustical paths.

Experimental investigation of the fluctuating static pressure in a subsonic axisymmetric jet

2021 ◽  
pp. 1475472X2110048
Author(s):  
Songqi Li ◽  
Lawrence S Ukeiley
Keyword(s):  
Static Pressure ◽  
Near Field ◽  
Scaling Law ◽  
Pressure Fluctuations ◽  
Power Spectra ◽  
Hydrodynamic Pressure ◽  
Turbulent Velocity ◽  
Fluctuating Pressure ◽  
Jet Mixing ◽  
Axisymmetric Jet

Measuring the fluctuating static pressure within a jet has the potential to depict in-flow sources of the jet noise. In this work, the fluctuating static pressure of a subsonic axisymmetric jet was experimentally investigated using a 1/8” microphone with an aerodynamically shaped nose cone. The power spectra of the fluctuating pressure are found to follow the -7/3 scaling law at the jet centerline with the decay rate varying as the probe approaches the acoustic near field. Profiles of skewness and kurtosis reveal strong intermittency inside the jet shear layer. By applying a continuous wavelet transform (CWT), time-localized footprints of the acoustic sources were detected from the pressure fluctuations. To decompose the fluctuating pressure into the hydrodynamic component and its acoustic counterpart, two techniques based on the CWT are adopted. In the first method the hydrodynamic pressure is isolated by maximizing the correlation with the synchronously measured turbulent velocity, while the second method originates from the Gaussian nature of the acoustic pressure where the separation threshold is determined empirically. Similar results are obtained from both separation techniques, and each pressure component dominates a certain frequency band compared to the global spectrum. Furthermore, cross-spectra between the fluctuating pressure and the turbulent velocity were calculated, and spectral peaks appearing around Strouhal number of 0.4 are indicative of the footprint of the convecting coherent structures inside the jet mixing layer.

Air‐gun bubble damping by a screen

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1765-1772 ◽  
Author(s):  
Jan Langhammer ◽  
Martin Landrø ◽  
James Martin ◽  
Eivind Berg
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Far Field ◽  
Pressure Amplitude ◽  
Air Bubble ◽  
Air Gun ◽  
Pressure Peak ◽  
Bubble Oscillations ◽  
Measured Pressure ◽  
Optimal Radius

A method for damping unwanted bubble oscillations from a seismic air gun is presented. The method exploits the fact that the primary pressure peak generated by an air gun is produced during the first 5–10 ms after firing. The air bubble is destroyed by mounting a perforated screen with an optimal radius about the gun. Once the primary pressure peak has been generated by the bubble, the bubble is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the secondary bubble oscillations. Controlled near‐field measurements of 40‐cubic inch and 120‐cubic inch air guns with and without damping screens are used. The primary to bubble ratio improves from 1.4 without a screen to 4.4 with a screen in the near‐field. The corresponding values for estimated far‐field signatures are 1.8 to 9.0 when the signatures are filtered with an out‐128 Hz (72 dB/Oct) DFS V filter.

Near-field pressure waveform analysis of an excited Mach 0.9 jet

2018 ◽  
Vol 17 (1-2) ◽  
pp. 114-134 ◽  
Author(s):  
C-W Kuo ◽  
M Crawley ◽  
J Cluts ◽  
M Samimy
Keyword(s):  
Strouhal Number ◽  
Large Scale ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Hydrodynamic Pressure ◽  
Dynamic Mode Decomposition ◽  
Waveform Analysis ◽  
Dynamic Mode ◽  
Azimuthal Mode ◽  
Radial Profiles

This work explores the effects of axisymmetric, helical, and flapping mode perturbations over a range of Strouhal numbers on the near-field pressure of an axisymmetric Mach 0.9 jet with a Reynolds number of 6.2 × 105. Excitation is generated by eight localized arc filament plasma actuators uniformly distributed around the nozzle exit. The excitation of jet shear layer instabilities resulted in large-scale structures. The signature of these structures in the irrotational near field appears as high-amplitude hydrodynamic pressure fluctuations with wavepacket-like growth, saturation, and decay. The excitation Strouhal number and, perhaps more importantly, the azimuthal mode, are seen to strongly affect the spatial evolution of the wavepacket in both axial and radial directions. The dominant excitation Strouhal number is around 0.3, and the most significant effect on the jet statistical properties (such as distributions of velocity and pressure) occurs further downstream for the flapping mode in comparison to the axisymmetric mode. Dynamic mode decomposition is performed to further describe the modal behavior and evolution of hydrodynamic pressure fluctuations. The pressure response in the near field of jet plumes in flapping mode excitation is shown to exhibit two azimuthal mode behaviors: axisymmetric and flapping. An empirical model of hydrodynamic pressure distribution is established with normalized axial and radial profiles. The amplitude and distribution of the hydrodynamic pressure component are well depicted by the empirical reconstruction.

Wavelet analysis of near-field pressure fluctuations generated by a subsonic jet

2012 ◽  
Vol 698 ◽  
pp. 93-124 ◽  
Author(s):  
S. Grizzi ◽  
R. Camussi
Keyword(s):  
Wavelet Transforms ◽  
Acoustic Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Hydrodynamic Pressure ◽  
Processing Technique ◽  
Main Task ◽  
Potential Core ◽  
Fourier Filtering ◽  
The Time Domain

AbstractAn experimental study of the pressure field generated by a subsonic, single stream, round jet is presented. The investigation is conducted in the near-field region at subsonic Mach numbers (up to 0.9) and Reynolds numbers $\mathit{Re}\gt 1{0}^{5} $. The main task of the present work is the analysis of the near-field acoustic pressure and the characterization of its spectral properties. To this aim, a novel post-processing technique based on the application of wavelet transforms is presented. The method accomplishes the separation of nearly Gaussian background fluctuations, interpreted as acoustic pressure, from intermittent pressure peaks induced by the hydrodynamic components. With respect to more standard approaches based on Fourier filtering, the new technique permits one to recover the whole frequency content of both the acoustic and the hydrodynamic contributions and to reconstruct them as independent signals in the time domain. The near-field acoustic pressure is characterized in terms of spectral content, sound pressure level and directivity. The effects of both the Mach number and the distance from the jet axis are analysed and the results are compared with published far-field observations and theoretical predictions. Simultaneous velocity/pressure measurements have been also performed using a hot-wire probe and a microphone pair in the near field. It is shown that the cross-correlation between the near-field acoustic pressure and the axial velocity is large (of the order of 0.2) in the potential core region whereas large velocity/hydrodynamic pressure correlations are located at the nozzle exit and downstream of the potential core.

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