scholarly journals Experimental Characterisation of the Far-Field Noise in Axial Fans Fitted with Shaped Tip End-Plates

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
S. Bianchi ◽  
A. Corsini ◽  
A. G. Sheard
Keyword(s):  
Vortex Breakdown ◽  
Vortex Formation ◽  
Broadband Noise ◽  
Sound Power ◽  
Far Field ◽  
Tip Leakage Flow ◽  
Noise Sources ◽  
End Plate ◽  
Field Noise ◽  
Flow Vortex

The authors investigate the far-field noise emissions of a datum fan blade fitted with tip end-plate geometries, originally designed to control the leakage vortex swirl level. The end-plate geometries influence the tip-leakage flow, vortex formation, and swirl level. In doing so, the end-plate geometries influence the sound-power levels. After an evaluation of fan rotors' aerodynamic performance, the study compares the rotors' far-field noise signature characterised in terms of sound-power and pressure-level spectra to enable and assess the end-plate acoustic pay-off. The investigation attempts to establish a cause-and-effect relationship between the tip-flow dynamics and the radiated sound fields, exploring the diverse directivity patterns. The authors found a tonal reduction, due to the enhanced blade-tip end-plates and clarified the relevance of the tip features influencing the radial distribution of the noise sources using coherence analysis. The modified multiple-vortex breakdown end-plate design was effective in reducing the broadband noise, giving an improvement in the frequency range of the turbulent noise.

Acoustic and flow fields of an excited high Reynolds number axisymmetric supersonic jet

2010 ◽  
Vol 656 ◽  
pp. 507-529 ◽  
Author(s):  
M. SAMIMY ◽  
J.-H. KIM ◽  
M. KEARNEY-FISCHER ◽  
A. SINHA
Keyword(s):  
Reynolds Number ◽  
Nozzle Exit ◽  
Noise Suppression ◽  
Polar Angle ◽  
Broadband Noise ◽  
Far Field ◽  
Initial Growth ◽  
Wide Range ◽  
Field Noise ◽  
Noise Amplification

An axisymmetric perfectly expanded Mach 1.3 jet, with a Reynolds number based on the nozzle exit diameter (ReD) of 1.1 × 106 and turbulent boundary layer at the nozzle exit, was excited using localized arc filament plasma actuators over a wide range of forcing Strouhal numbers (StDF). Eight actuators distributed azimuthally were used to excite azimuthal modes m = 0–3. Far-field acoustic, flow velocity and irrotational near-field pressure were probed with a three-fold objective: (i) to investigate the broadband far-field noise amplification reported in the literature at lower speeds and ReD using excitation of m = 0 at low StDF; (ii) to explore broadband far-field noise suppression using excitation of m = 3 at higher StDF; and (iii) to shed some light on the connection between the flow field and the far-field noise. The broadband far-field noise amplification observed is not as extensive in amplitude or frequency range, but still sufficiently large to be of concern in practical applications. Broadband far-field noise suppression of 4–5 dB at 30° polar angle peak frequency, resulting in approximately 2 dB attenuation in the overall sound pressure level, is achieved with excitation of m = 3 at StDF ~ 0.9. Some of the noteworthy observations and inferences are (a) there is a strong correlation between the far-field broadband noise amplification and the turbulence amplification; (b) far-field noise suppression is achieved when the jet is forced with the maximum jet initial growth rate frequency thus limiting significant dynamics of structures to a shorter region close to the nozzle exit; (c) structure breakdown and dynamic interaction seem to be the dominant source of noise; and (d) coherent structures dominate the forced jet over a wide range of StDF (up to ~ 1.31) with the largest and most organized structures observed around the jet preferred mode StDF.

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 Similarity scaling of jet noise sources for low-order jet noise modelling based on the Goldstein generalised acoustic analogy

2017 ◽  
Vol 16 (6) ◽  
pp. 476-490 ◽  
Author(s):  
Vasily A Semiletov ◽  
Sergey A Karabasov
Keyword(s):  
Jet Noise ◽  
Field Measurements ◽  
Noise Prediction ◽  
Far Field ◽  
Acoustic Analogy ◽  
Noise Sources ◽  
Modelling Framework ◽  
Noise Data ◽  
Field Noise ◽  
Low Order

As a first step towards a robust low-order modelling framework that is free from either calibration parameters based on the far-field noise data or any assumptions about the noise source structure, a new low-order noise prediction scheme is implemented. The scheme is based on the Goldstein generalised acoustic analogy and uses the Large Eddy Simulation database of fluctuating Reynolds stress fields from the CABARET MILES solution of Semiletov et al. corresponding to a static isothermal jet from the SILOET experiment for reconstruction of effective noise sources. The sources are scaled in accordance with the physics-based arguments and the corresponding sound meanflow propagation problem is solved using a frequency domain Green’s function method for each jet case. Results of the far-field noise predictions of the new method are validated for the two NASA SHJAR jet cases, sp07 and sp03 from and compared with the reference predictions, which are obtained by applying the Lighthill acoustic analogy scaling for the SILOET far-field measurements and using an empirical jet-noise prediction code, sJet.

Near and Far Field Noise Decay From a Quadcopter Propeller With and Without a Leading Edge Notch

2018 ◽  
Author(s):  
Kenneth Van Treuren ◽  
Charles Wisniewski ◽  
Emily Cinnamon
Keyword(s):  
Decay Rate ◽  
Electric Propulsion ◽  
Near Field ◽  
Vortex Formation ◽  
Leading Edge ◽  
Tip Vortex ◽  
Test Facility ◽  
Far Field ◽  
Sound Generation ◽  
Field Noise

Electric propulsion is being considered for a wide range of airframes from large commercial transports to the small Unmanned Aerial Systems (UASs). These electric systems, especially for small fixed wing UASs and quadcopters, need to be both efficient and quiet if they are to operate in an urban/populated environment or used in an Intelligence, Surveillance, and Reconnaissance (ISR) scenario. A propeller test facility was developed to record propeller performance and sound generation in the near field behind UAS propellers. The question of defining near and far field noise was studied by characterizing sound decay with distance from a UAS propeller. Defining near and far field noise is a subject that is not addressed well in the literature. Far field noise generally follows the 1/r decay rate and near field does not. Behind the propeller there are other flow field interactions that also change the decay rate, which this study illustrates. The data presented in this paper shows the difficulty in measuring sound around a UAS propeller and begins to resolve this topic. Previous UAS propeller design work by the authors resulted in propellers that were quieter in the near field and at the same time more efficient. Their studies showed RPM and tip vortex formation both contribute significantly to propeller sound generation. Disrupting the tip vortex formation should decrease the noise being generated. The current work extends these initial findings and examines the noise generation of a stock quadcopter propeller from a DJI Phantom 2 platform. One inch aft of the plane of rotation, this propeller, a 9.4 × 5.0, has a peak sound pressure level (SPL) of approximately 118 dBA under normal static operation producing 0.7 lbf of thrust at approximately 5900 RPM. Modifications were made to four stock propellers by cutting a notch perpendicular to the leading edge of the propeller at the 0.75 r/R and 0.87 r/R locations. The notches were of different depths and widths. Of the modifications, three of the configurations did not noticeably decrease the sound. However; the final configuration reduced the peak near field SPL to 111 dBA, a 6% reduction in dBA over the stock configuration corresponding to a greater than 50% reduction in sound generation. Smoke visualization confirms that a notch located at 0.87 r/R effectively disrupts the tip vortex formation, causing the tip vortices to dissipate much earlier than the stock propeller without the notch. Examining the noise frequency spectrums associated with both the stock and the modified propeller also confirm that the notch changes the magnitude and frequency distribution of the sound being generated.

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2012 ◽  
Author(s):  
Clifford Brown
Keyword(s):  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Noise Sources ◽  
Trailing Edge ◽  
Wide Range ◽  
Field Noise ◽  
Interaction Test

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet/Surface Interaction Test was intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. During phase one, the goal was to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet/surface interaction is creating additional noise, and (2) determine regions of interest for more detailed tests in phase two. To meet these phase one objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer (microphone array) and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface was moved through axial positions 2 ≤ xTE/Dj ≤ 20 (measured at the surface trailing edge, xTE, and normalized by the jet diameter, Dj) and radial positions 1 ≤ h/Dj ≤ 20. Far-field and phased array noise data were acquired at each combination of axial and radial surface location using two nozzles and at 8 different jet exit conditions across several flow regimes (subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic cold). The far-field noise results, discussed here, show where the surface shields some of the jet noise and, depending on the location of the surface and the observer, where scrubbing and trailing edge noise sources are created as a surface extends downstream and approaches the jet plume.

The Tip Leakage Vortex Breakdown and its Possible Relationship With Rotating Instability in a Subsonic Compressor Rotor

2021 ◽  
Author(s):  
Fan Yang ◽  
Yanhui Wu
Keyword(s):  
Unsteady Flow ◽  
Vortex Breakdown ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Back Flow ◽  
Tip Leakage ◽  
Rotating Instability ◽  
Flow Vortex

Abstract The unsteady flow in the compressor at small mass flow rate has an important impact on the safety and efficiency of the compressor. Rotating instability was found in the experiment at near stall condition. Through URANS simulation, the origin of unsteady flow in an isolated subsonic rotor is studied. And the relationship between unsteadiness of tip leakage flow and rotating instability is revealed. With the deepening of the throttle, the flow field in the rotor changes from steady to unsteady. The intermittent spiral type breakdown of tip leakage vortex is considered to be the origin of the unsteady flow. Quantitative analysis of the tip leakage vortex shows the breakdown cycle caused by the interaction of the tip leaked vortex with the adjacent blade. When the tangential velocity and axial velocity of the leakage vortex reach a critical value, the tip leakage vortex will break. A radial vortex called back flow vortex will appear periodically after breakdown happens, which plays an important in rotating instability. The back flow vortex at upstream causes an overflow at adjacent blade leading edge, which results the next breakdown happens at downstream. Due to such feedback, the tip leakage vortex breakdown at two location alternately. A possible cause of RI was proposed: The spiral breakdown of the tip leakage vortex at different positions resulted in a cross-passage structure, which propagates into circumferential direction.

Towards a Universal Scaling for Broadband Turbulent Noise in Internal Flow Devices

2013 ◽  
Author(s):  
Arjen de Jong ◽  
Joachim Golliard
Keyword(s):  
High Speed ◽  
Scaling Laws ◽  
Scaling Law ◽  
Power Spectra ◽  
Internal Flow ◽  
Acoustic Power ◽  
Broadband Noise ◽  
Current Work ◽  
Sound Power ◽  
Noise Sources

An investigation is performed on the scalability of broadband noise sources from separated flows in internal pipe systems. Broadband sources from for example wellhead chokes, bends and valves can potentially excite subsea manifolds through fluid acoustic coupling and fluid structural coupling. The focus of the current work is evaluation and improvement of scaling laws for collapse of sound power spectra. The approach proposed here is to use steady-state Computational Fluid Dynamics [CFD] to better estimate the properties of the flow in order to improve the scaling law and obtain a universal broadband spectrum. Steady Reynolds Averaged Navier-Stokes [RANS] simulations of several bend and orifice geometries have been performed. A surface acoustic power model based on modeled turbulent quantities is implemented. Based on the RANS data, more advanced models for scaling have been developed. Experimental sound power spectra from literature of the simulated geometries are scaled using different methodologies in both amplitude and frequency. When a new scaling based on CFD modeled surface acoustic power was used, a universal collapse among geometries occurred. Using CFD, the velocity in the high-speed sound-producing region is obtained, as well as a more accurate length scaling in order to improve the frequency scaling. A vast improvement in collapse over different geometries is achieved. The current work indicates that a universal collapse might indeed be present. The methodology does not require high fidelity calculations and is thus easy to implement. By comparing original and new scaling laws, it turns out that the ratio of fluctuating drag over steady drag can vary among geometries.

Computation of Turbulent Flows and Aero-Acoustics From an Axial Fan

2002 ◽  
Author(s):  
Il-Sung Bae ◽  
Hooi-Joong Kim ◽  
Seungbae Lee
Keyword(s):  
Turbulent Flows ◽  
Dipole Source ◽  
Spanwise Direction ◽  
Far Field ◽  
Axial Fan ◽  
Noise Sources ◽  
Lift Forces ◽  
Fan Blade ◽  
Drag And Lift ◽  
Field Noise

LES formulation was applied to simulate the flow fields around rotating fan blades tested by DLR. The turbulent flows around fan blade rotating with 500 RPM were simulated and the far-field noise was exactly computed by using the Ffowcs Williams and Hawkings equation with an inclusion of quadrupole source formulation. Variations of lift forces and deviation angles in the spanwise direction were analyzed to correlate flow parameters with acoustics parameters and identify noise sources. The dipole noise computed at the far-field by computed drag and lift forces was in good agreement with experimental data and the dipole source was also found to be the major contributor to overall far-field noise from unsteady calculation.

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