The separation of radiating and non-radiating near-field pressure fluctuations in supersonic jets

2015 ◽  
Vol 355 ◽  
pp. 172-187 ◽  
Author(s):  
Yongle Du ◽  
Philip J. Morris
Keyword(s):  
Near Field ◽  
Pressure Fluctuations ◽  
Supersonic Jets

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).

The Buzz-Saw Noise Generated by a High Duty Transonic Compressor

1971 ◽  
Vol 93 (1) ◽  
pp. 63-68 ◽  
Author(s):  
M. G. Philpot
Keyword(s):  
Pressure Field ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Field Measurements ◽  
Rotor Blades ◽  
Transonic Compressor ◽  
Harmonic Content ◽  
Circumferential Pressure ◽  
Good Agreement

The buzz-saw noise made by a two-stage transonic research compressor has been investigated experimentally over a range of tip relative Mach numbers up to 1.56. The results show that the phenomenon is due to the propagation at supersonic relative tip speeds of the steady rotating pressure field associated with the first-stage rotor blades. The flow entering the tip section of the rotor has been analyzed theoretically and the circumferential pressure fluctuations computed, with good agreement with near-field measurements. The analysis leads to a clearer understanding of the dependence of the noise on inlet Mach number and three-dimensional effects and indicates the types of rotor irregularity which will most influence the harmonic content.

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.

Flow and Near-field Pressure Fluctuations of Twin Square Jets

2021 ◽  
Author(s):  
Myeonghwan Ahn ◽  
Aatresh Karnam ◽  
Ephraim Gutmark ◽  
Mihai Mihaescu
Keyword(s):  
Near Field ◽  
Pressure Fluctuations ◽  
Square Jets
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