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.

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).

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.

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.

Pressure fluctuations and their effect on cavitation inception within water jets

1994 ◽  
Vol 262 ◽  
pp. 223-263 ◽  
Author(s):  
Bing Ran ◽  
Joseph Katz
Keyword(s):  
Near Field ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Acoustic Excitation ◽  
Potential Core ◽  
Cavitation Inception ◽  
Vortex Pairing ◽  
Pressure Distributions ◽  
Entire Flow ◽  
Onset Of Cavitation

Instantaneous and phase averaged pressure distributions in the near field of a jet, and their effects on the conditions for the onset of cavitation are studied in detail. The measurements are performed by using microscopic bubbles as pressure sensors, and holography as a means of detecting them. Experiments are performed at Red exceeding 4 × 105, with and without acoustic excitation. The results show that the highest negative pressure peaks (–0.97) and the resulting cavitation inception occur because of vortex pairing. Prior to pairing the negative peaks are between –0.8 and –0.9. Weak acoustic excitation changes the entire flow structure and the spatial distributions of bubbles, but has little effect on the onset of cavitation. Downstream of the potential core the highest pressure peaks (∼ –0.6) are considerably smaller, in agreement with the occurrence of cavitation there. It is also shown that although the r.m.s. values of pressure fluctuations do not vary with the jet speed, the probability distribution changes significantly, causing a reduction in the inception index with increasing velocity. The probability of cavitation inception is estimated from the distributions of bubbles and pressure peaks. It is shown that the actual, non-uniform bubble distribution increases the probability of inception owning to migration of the bubbles to the low pressure regions.

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.

Spatial Velocity Correlations and Near Field Pressure Measurements From a Heated Transonic Axisymmetric Jet

2006 ◽  
Author(s):  
Richa Mann ◽  
Lawrence Ukeiley ◽  
John Seiner
Keyword(s):  
Near Field ◽  
Pressure Fluctuations ◽  
Light Sheet ◽  
Potential Core ◽  
Piv Measurements ◽  
Pressure Transducers ◽  
Spatial Velocity ◽  
Convection Speed ◽  
Highly Correlated ◽  
Heated Jet

Turbulence properties and the near field pressure of a Mach 0.85 jet at two different static temperature ratios (0.87 and 2.4) are studied. The turbulence properties were studied using PIV measurements which were performed with the light sheet aligned in the radial and the streamwise directions at locations between 3.3 and 8.2 jet diameters downstream from the nozzle exit. Measurements of the near field pressure fluctuations were acquired using a linear array of 6 pressure transducers evenly spaced from 3.45 to 8.45 jet exit diameters. From the PIV measurements it was observed that the heated jet is narrower than the unheated jet and has a higher peak normalized TKE. The highly correlated area of the 2 point spatial velocity correlations is larger for the unheated jet than the heated jet. The measurements from the pressure transducers reveals that the relative amplitude of the mean fluctuating pressure is slightly higher for the heated jet after the end of the potential core. The convection speed of the waves propagating along the pressure sensor array was calculated to be larger for the heated jet.

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.

A Selective Fast Fourier Filtering Approach Applied to High Frequency Thermoacoustic Instability Analysis

2017 ◽  
Author(s):  
Felix Grimm ◽  
Jean-Michel Lourier ◽  
Oliver Lammel ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Heat Release ◽  
High Frequency ◽  
Compressible Flows ◽  
Acoustic Pressure ◽  
Inverse Transformation ◽  
Turbulent Heat ◽  
Thermoacoustic Instability ◽  
Acoustic Feedback ◽  
Fourier Filtering ◽  
Filtering Approach

A method for selective, frequency-resolved analysis of spatially distributed, time-coherent data is introduced. It relies on filtering of Fourier-processed signals with periodic structures in frequency-domain. Therefrom extracted information can be analyzed in both, frequency- and time-domain using an inverse transformation ansatz. In the presented paper, the approach is applied to a laboratory scale, twelve nozzle FLOX®-GT-burner for the investigation of high-frequency thermoacoustic pressure oscillations and limit-cycle mechanisms. The burner is operated at elevated pressure for partially premixed combustion of a hydrogen and natural gas mixture with air. At a certain amount of hydrogen addition to fuel injection, the burner exhibits self-sustained high-frequency thermoacoustic oscillation. This unstable operation is simulated with the fractional step approach SICS (Semi Implicit Characteristic Splitting), a pressure based solver extension of the Finite Volume based research code THETA (Turbulent Heat Release Extension for the TAU Code) for the treatment of weakly compressible flows with combustion. A hybrid LES/URANS simulation delivers time-resolved simulation data of the thermoacoustically unstable operation condition, which is analyzed with the presented SFFFA (Selective Fast Fourier Filtering Approach). Acoustic pressure distribution in the combustion chamber is explicitly resolved and assigned to different characteristic modes by signal decomposition. Furthermore, the SFFFA is used for the analysis of acoustic feedback mechanism by investigating filtered transient heat release, acoustic pressure, velocity and mixture fraction. Coherent structures in flow field and combustion as well as periodic convective processes are resolved and linked to transient acoustic pressure, extensively describing the acoustic feedback of the examined burner configuration.

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