Noise generation mechanisms for a supersonic jet impinging on an inclined plate

2016 ◽  
Vol 797 ◽  
pp. 802-850 ◽  
Author(s):  
Christoph Brehm ◽  
Jeffrey A. Housman ◽  
Cetin C. Kiris
Keyword(s):  
Sound Pressure ◽  
Acoustic Noise ◽  
Vortical Flow ◽  
Flow Structures ◽  
Wall Jet ◽  
Far Field ◽  
Noise Generation ◽  
Inclined Plate ◽  
Coherent Flow Structures ◽  
Generation Mechanisms

Noise generation mechanisms for a perfectly expanded supersonic Mach number $M=1.8$ turbulent jet impinging on a $45^{\circ }$ inclined plate are investigated for a Reynolds number of $1.6\times 10^{6}$ employing a large-eddy simulation. Excellent comparisons with experimental acoustic far-field measurements and pressure measurements on the impingement plate are obtained. Two local maxima are identified in the far-field overall sound pressure levels in the $75^{\circ }$ and $120^{\circ }$ observer directions, which are associated with different noise generation mechanisms. The peak frequencies in the spectra with Strouhal numbers of $St=0.2$ for $75^{\circ }$ and $St=0.5$ for $120^{\circ }$ match the experimental measurements. The jet-impingement region generates pressure waves that propagate predominantly in the $120^{\circ }$ observer direction. The noise generation in this region is attributed to vortex stretching and tearing during shear-layer impingement, and shock oscillations that are induced by the motion of downstream convected vortical flow structures. The second peak in the overall sound pressure distribution at $75^{\circ }$ is associated with noise sources located in the wall jet. The noise generation in the wall jet is associated with supersonically convecting large-scale coherent flow structures that also interact with tail shocks in the wall jet causing large localized pressure fluctuations. Strongly coherent flow structures are identified by applying proper orthogonal decomposition (POD) to the unsteady flow field. The frequency characteristics of the most energetic POD modes are distinctly different based on which energy norm is chosen. The most energetic entropy-based POD modes contain a peak frequency of approximately $St=0.4{-}0.6$, while the most energetic turbulent kinetic-energy-based POD modes appear to be dominated by lower-frequency content. The causality method, based on Lighthill’s acoustic analogy, is used to link the acoustic noise signature to the relevant physical mechanisms in the source region. A differentiation is made between the application of normalized and non-normalized cross-correlation functions for noise source identification and characterization.

Low-Order Velocity Estimation and Acoustic Noise Generation by a Turbulent Wall Jet

AIAA Journal ◽  
2018 ◽  
Vol 56 (11) ◽  
pp. 4331-4347 ◽  
Author(s):  
Adam Nickels ◽  
Lawrence Ukeiley ◽  
Robert Reger ◽  
Louis Cattafesta
Keyword(s):  
Acoustic Noise ◽  
Velocity Estimation ◽  
Wall Jet ◽  
Noise Generation ◽  
Turbulent Wall ◽  
Low Order

Far-Field Noise Control in Supersonic Jets From Conical and Contoured Nozzles

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Jin-Hwa Kim ◽  
Martin Kearney-Fischer ◽  
Mo Samimy ◽  
Sivaram Gogineni
Keyword(s):  
Sound Pressure ◽  
Acoustic Noise ◽  
Microphone Array ◽  
Plasma Actuators ◽  
Far Field ◽  
Free Jet ◽  
Naturally Occurring ◽  
Mixing Noise ◽  
Field Noise ◽  
Jet Axis

Plasma actuators are used to control far-field noise in Mach 1.65 jets from contoured and conical supersonic axisymmetric nozzles (henceforth, contoured and conical jets, respectively). The contoured nozzle is designed using the method of characteristics for a shock-free jet. The conical nozzle has converging and diverging conical sections with a sharp throat. Eight plasma actuators, distributed uniformly around the nozzle exit, are used and the jet is forced with azimuthal modes (m) 0–3 and ±4 and forcing Strouhal numbers ranging from 0.09 to 4.0. The far-field acoustic noise is measured by a linear microphone array covering polar angles from 25 deg to 80 deg relative to the jet axis. In both jets, the lower forcing azimuthal modes (m=0 and 1) are less effective than the higher modes (m=2, 3, and ±4), which have similar levels of overall sound pressure level (OASPL) reduction. At shallow angles relative to the jet axis, the reduction in OASPL is about 1.6–1.8 dB at low forcing Strouhal numbers in both jets at the most effective forcing mode of m=3. However, the OASPL in the sideline direction is only slightly increased (about 1 dB) for both the contoured and conical jets at m=3. The reduction at shallow polar angles is related to the decrease in the peak mixing noise level in both jets. The range of forcing Strouhal numbers providing significant noise reduction and the range of polar angles over which the noise is reduced are both much larger in the conical jet compared with the contoured jet. The screech tones are also reduced or suppressed – most likely due to weakening of naturally occurring structures by forcing.

Testing Propeller Tip Modifications to Reduce Acoustic Noise Generation on a Quadcopter Propeller

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Charles F. Wisniewski
Keyword(s):  
Sound Pressure ◽  
Acoustic Noise ◽  
Near Field ◽  
Tip Vortex ◽  
Noise Generation ◽  
Radial Location ◽  
Power Increase ◽  
Vertical Lift ◽  
Near Field Sound ◽  
Field Sound

Abstract If vertical lift vehicles are to operate near population centers, they must be both quiet and efficient. The goal of this research is to develop a propeller that is more efficient and generates less noise than a stock DJI Phantom 2 quadcopter propeller. Reducing the generated tip vortex was the main objective. After studying the literature, seven promising tip treatments were selected and applied to a stock DJI Phantom 2 propeller to reduce the tip vortex. Several different configurations were tested for each tip treatment to determine the rpm and required power to hold 0.7 lbf thrust, the static hover condition. For each test, operating at the hover condition, a radial traverse 1 in. behind the propeller permitted the measurement of the near field sound pressure level (SPL) to find the maximum SPL and its radial location. Several configurations tested resulted in 8–10 dBA reductions in SPL when compared to the stock propeller; however, these configurations also resulted in an unacceptable increase in the power required to achieve the desired thrust. The most promising tip treatment tested was the trailing edge (TE) notch at a radial location of 0.95 r/R with a double slot width and a double depth (DSDD). The DSDD configuration as tested reduced the SPL 7.2 dBA with an increase in power required of only 3.96% over the stock propeller. This tradeoff, while not the largest reduction in noise generation measured, had an acceptable power increase for the decrease in SPL achieved.

Far-Field Noise Control in Supersonic Jets From Conical and Contoured Nozzles

2010 ◽  
Author(s):  
Jin-Hwa Kim ◽  
Martin Kearney-Fischer ◽  
Mo Samimy ◽  
Sivaram Gogineni
Keyword(s):  
Sound Pressure ◽  
Acoustic Noise ◽  
Microphone Array ◽  
Plasma Actuators ◽  
Far Field ◽  
Free Jet ◽  
Naturally Occurring ◽  
Mixing Noise ◽  
Field Noise ◽  
Jet Axis

Plasma actuators are used to control far-field noise in Mach 1.65 jets from contoured and conical supersonic axisymmetric nozzles (henceforth contoured and conical jets, respectively). The contoured nozzle is designed using the method of characteristics for shock-free jet. The conical nozzle has converging and diverging conical sections with a sharp throat. Eight plasma actuators, distributed uniformly around the nozzle exit, are used and the jet is forced with azimuthal modes (m) 0–3, and ±4 and forcing Strouhal numbers ranging from 0.09 to 4.0. The far-field acoustic noise is measured by a linear microphone array covering polar angles from 25 to 80° relative to the jet axis. In both jets, the lower forcing azimuthal modes (m = 0 and 1) are less effective than the higher modes (m = 2, 3, and ±4), which have similar levels of overall sound pressure level (OASPL) reduction. At shallow angles relative to the jet axis, the reduction in OASPL is about 1.6–1.8 dB at low forcing Strouhal numbers in both jets at the most effective forcing mode of m = 3. However, the OASPL in the sideline direction is only slightly increased (about 1 dB) for both the contoured and conical jets at m = 3. The reduction at shallow polar angles is related to the decrease in the peak mixing noise level in both jets. The range of forcing Strouhal numbers providing significant noise reduction and the range of polar angles over which the noise is reduced, are both much larger in the conical jet compared to the contoured jet. The screech tones are also reduced or suppressed most likely due to weakening of naturally occurring structures by forcing.

Numerical investigation of the generation and growth of coherent flow structures in a triggered turbulent spot

2014 ◽  
Vol 759 ◽  
pp. 257-294 ◽  
Author(s):  
Joshua R. Brinkerhoff ◽  
Metin I. Yaras
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Quantitative Description ◽  
Shear Layers ◽  
Vortical Flow ◽  
Flow Structures ◽  
Test Surface ◽  
Turbulent Spot ◽  
Hairpin Vortices ◽  
Coherent Flow Structures

AbstractMultiple mechanisms for the regeneration of hairpin-like coherent flow structures in transitional and turbulent boundary layers have been proposed in the published literature, but a complete understanding of the typical topologies of coherent structures observed in the literature has not yet been achieved. To contribute to this understanding, a numerical study is performed of a turbulent spot triggered in a zero-pressure-gradient laminar boundary layer by a pulsed, transverse jet. Two direct numerical simulations (DNS) capture the growth of the spot into a mature turbulent region containing a large number of coherent vortical flow structures. The boundary-layer Reynolds number based on the test-surface streamwise length is $\mathit{Re}_{L}=309\,200$. The internal structure of the spot is characterized by densely spaced packets of hairpin vortices. Lateral growth of the spot occurs as new hairpin vortices form along the spanwise edges of the spot. The formation of these hairpin vortices is attributed to unstable shear layers that develop in the streamwise–spanwise plane due to the wall-normal motions induced by the streamwise oriented legs of hairpin vortices within the spot. Results are presented that highlight the mechanism by which the instability of such shear layers forms wavepackets of hairpin vortices; how the formation of these vortices produces a flow environment that promotes the creation of new hairpin vortices; and how the newly created hairpin vortices impact the production of turbulence kinetic energy in the flow region surrounding the spot. A quantitative description of the hairpin-vortex regeneration mechanism based on the transport of the instantaneous vorticity vector is presented to illustrate how the velocity and vorticity fields interact with the local strain rates to promote the growth of coherent vortical structures. The simulation results also shed light on a mechanism that seems to have a dominant influence on the formation of the calmed region in the wake of the turbulent spot.

Characterization of Coherent Flow Structures in a Swirl-Stabilized Spray Combustor

2021 ◽  
Author(s):  
Nicholas Rock ◽  
Scott D. Stouffer ◽  
Tyler H. Hendershott ◽  
Edwin Corporan ◽  
Paul Wrzesinski
Keyword(s):  
Flow Structures ◽  
Coherent Flow Structures

scholarly journals Vortical Flow Structures Induced by Red Blood Cells in Capillaries

2021 ◽  
Author(s):  
François Yaya ◽  
Johannes Römer ◽  
Achim Guckenberger ◽  
Thomas John ◽  
Stephan Gekle ◽  
...  
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Vortical Flow ◽  
Flow Structures

scholarly journals Design-Assisted of Pitching Aerofoils through Enhanced Identification of Coherent Flow Structures

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 11 ◽  
Author(s):  
Filippo Avanzi ◽  
Francesco De Vanna ◽  
Yin Ruan ◽  
Ernesto Benini
Keyword(s):  
Pressure Field ◽  
Navier Stokes ◽  
Flow Structures ◽  
Coupled Modes ◽  
Spectral Reconstruction ◽  
Sst Turbulence Model ◽  
Coherent Flow Structures ◽  
Highly Correlated ◽  
Naca 0012 ◽  
Proper Orthogonal

This study discusses a general framework to identify the unsteady features of a flow past an oscillating aerofoil in deep dynamic stall conditions. In particular, the work aims at demonstrating the advantages for the design process of the Spectral Proper Orthogonal Decomposition in accurately producing reliable reduced models of CFD systems and comparing this technique with standard snapshot-based models. Reynolds-Averaged Navier-Stokes system of equations, coupled with k−ω SST turbulence model, is used to produce the dataset, the latter consisting of a two-dimensional NACA 0012 aerofoil in the pitching motion. Modal analysis is performed on both velocity and pressure fields showing that, for vectored values, a proper tuning of the filtering process allows for better results compared to snapshot formulations and extract highly correlated coherent flow structures otherwise undetected. Wider filters, in particular, produce enhanced coherence without affecting the typical frequency response of the coupled modes. Conversely, the pressure field decomposition is drastically affected by the windowing properties. In conclusion, the low-order spectral reconstruction of the pressure field allows for an excellent prediction of aerodynamic loads. Moreover, the analysis shows that snapshot-based models better perform on the CFD values during the pitching cycle, while spectral-based methods better fit the loads’ fluctuations.

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