scholarly journals Study of the Position of Sound Sources in a Turbulent Jet Using Nozzles of Different Configurations

2020 ◽  
Vol 320 ◽  
pp. 00027
Author(s):  
Victor Ershov ◽  
Igor Khramtsov
Keyword(s):  
Initial Conditions ◽  
Turbulent Jets ◽  
Turbulent Jet ◽  
Small Scale ◽  
Equivalent Diameter ◽  
Frequency Noise ◽  
Noise Sources ◽  
Sound Sources ◽  
Nozzle Edge ◽  
Chevron Nozzles

The aim of this work is to study the position of dominant sound sources in a small-scale turbulent jet using the beamforming method. Two nozzles of equivalent diameter and different geometric configurations (conical and chevron) were used to create different initial conditions for the outflow. Based on the analysis of the results obtained, it can be concluded that they are in good agreement with the well-known concepts of the physics of noise generation processes by turbulent jets: higher-frequency sources are generated by smaller-scale turbulent structures located closer to the nozzle edge, which is confirmed by the localization of high-frequency noise sources also closer to the nozzle edge. The chevron nozzles loosen the initial section of the jet, making it less short and thereby facilitating a faster displacement of noise sources to the nozzle edge, as seen when comparing localization maps for conical and chevron nozzles at the same frequencies. The results of localization were compared with the data obtained by other researchers. The results obtained were found to provide confidence in the use of acoustic beamforming to measure the location of the jet noise source with accuracy similar to other methods that have been used in the past.

WAVELET-BASED POSTPROCESSING OF JET LES DATA FOR ACOUSTIC FAR-FIELD EXTRAPOLATIONS

2013 ◽  
Vol 21 (04) ◽  
pp. 1350017
Author(s):  
RAMIN KAVIANI ◽  
VAHID ESFAHANIAN ◽  
MOHAMMAD EBRAHIMI
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Near Field ◽  
Flow Simulation ◽  
Computational Time ◽  
Jet Flows ◽  
Small Scale ◽  
Frequency Noise ◽  
Far Field ◽  
Noise Sources

The affordable grid resolutions in conventional large-eddy simulations (LESs) of high Reynolds jet flows are unable to capture the sound generated by fluid motions near and beyond the grid cut-off scale. As a result, the frequency spectrum of the extrapolated sound field is artificially truncated at high frequencies. In this paper, a new method is proposed to account for the high frequency noise sources beyond the resolution of a compressible flow simulation. The large-scale turbulent structures as dominant radiators of sound are captured in LES, satisfying filtered Navier–Stokes equations, while for small-scale turbulence, a Kolmogorov's turbulence spectrum is imposed. The latter is performed via a wavelet-based extrapolation to add randomly generated small-scale noise sources to the LES near-field data. Further, the vorticity and instability waves are filtered out via a passive wavelet-based masking and the whole spectrum of filtered data are captured on a Ffowcs-Williams/Hawkings (FW-H) surface surrounding the near-field region and are projected to acoustic far-field. The algorithm can be implemented as a separate postprocessing stage and it is observed that the computational time is considerably reduced utilizing a hybrid of many-core and multi-core framework, i.e. MPI-CUDA programming. The comparison of the results obtained from this procedure and those from experiments for high subsonic and transonic jets, shows that the far-field noise spectrum agree well up to 2 times of the grid cut-off frequency.

Large Scale Geometrical Aspects of Turbulent Jet Scalar Regions and Interfaces: Measurement and Modeling

2007 ◽  
Author(s):  
Jennifer Shockro ◽  
Haris J. Catrakis
Keyword(s):  
Large Scale ◽  
Turbulent Jets ◽  
Turbulent Jet ◽  
Small Scale ◽  
Geometric Framework ◽  
Fractal Approach ◽  
Geometrical Properties ◽  
Box Counting ◽  
Fractal Properties ◽  
Fractal Functions

This study focuses on the measurement and modeling of large scale geometrical aspects of turbulent jet scalar regions and interfaces. While several previous studies have focused on the small scale geometrical properties using fractal ideas, examination of the large scale geometrical aspects requires the development of what we call generalized fractals, i.e. the scale-dependent generalization of the original self-similar geometric framework. Our work involves the purely meshless approach to the determination of the generalized fractal properties, pioneered by Catrakis, that eliminates the need for grid-based box counting. We investigate the purely meshless generalized fractal approach using experimental databases generated in our laboratories on fully-developed turbulent jets with a Reynolds number of Re ∼ 20,000 and a Schmidt number of Sc ∼ 2,000. In our approach, we examine the dependence of the generalized fractal aspects of the turbulent interfaces at various spatial resolution scales. Our results indicate that the large scale geometrical aspects are strongly scale dependent and amenable to modeling using generalized fractal functions.

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

Micro Fluidic Jets for Thermal Management of Electronics

Volume 4 ◽  
2004 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heated Surface ◽  
Turbulent Jets ◽  
Harmonic Signal ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Air Cooling ◽  
Infrared Thermal Imaging

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.

scholarly journals Saturation of Zeldovich stretch–twist–fold map dynamos

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
Amit Seta ◽  
Pallavi Bhat ◽  
Kandaswamy Subramanian
Keyword(s):  
Initial Conditions ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Saturation Properties ◽  
Field Amplification ◽  
Saturated State ◽  
Shape Invariant ◽  
Fold Map ◽  
Scale Fluctuation ◽  
The Magnetic Field

Zeldovich’s stretch–twist–fold (STF) dynamo provided a breakthrough in conceptual understanding of fast dynamos, including the small-scale fluctuation dynamos. We study the evolution and saturation behaviour of two types of generalized Baker’s map dynamos, which have been used to model Zeldovich’s STF dynamo process. Using such maps allows one to analyse dynamos at much higher magnetic Reynolds numbers $\mathit{Re}_{M}$ as compared to direct numerical simulations. In the two-strip map dynamo there is constant constructive folding, while the four-strip map dynamo also allows the possibility of a destructive reversal of the field. Incorporating a diffusive step parametrized by $\mathit{Re}_{M}$ into the map, we find that the magnetic field $B(x)$ is amplified only above a critical $\mathit{Re}_{M}=R_{\mathit{crit}}\sim 4$ for both types of dynamos. The growing $B(x)$ approaches a shape-invariant eigenfunction independent of initial conditions, whose fine structure increases with increasing $\mathit{Re}_{M}$. Its power spectrum $M(k)$ displays sharp peaks reflecting the fractal nature of $B(x)$ above the diffusive scale. We explore the saturation of these dynamos in three ways: via a renormalized reduced effective $\mathit{Re}_{M}$ (case I) or due to a decrease in the efficiency of the field amplification by stretching, without changing the map (case IIa), or changing the map (case IIb), and a combination of both effects (case III). For case I, we show that $B(x)$ in the saturated state, for both types of maps, approaches the marginal eigenfunction, which is obtained for $\mathit{Re}_{M}=R_{\mathit{crit}}$ independent of the initial $\mathit{Re}_{M}=R_{M0}$. On the other hand, in case II, for the two-strip map, we show that $B(x)$ saturates, preserving the structure of the kinematic eigenfunction. Thus the energy is transferred to larger scales in case I but remains at the smallest resistive scales in case II, as can be seen from both $B(x)$ and $M(k)$. For the four-strip map, $B(x)$ oscillates with time, although with a structure similar to the kinematic eigenfunction. Interestingly, the saturated state in case III shows an intermediate behaviour, with $B(x)$ similar to the kinematic eigenfunction at an intermediate $\mathit{Re}_{M}=R_{\mathit{sat}}$, with $R_{M0}>R_{\mathit{sat}}>R_{\mathit{crit}}$. The $R_{\mathit{sat}}$ value is determined by the relative importance of the increased diffusion versus the reduced stretching. These saturation properties are akin to the range of possibilities that have been discussed in the context of fluctuation dynamos.

Trailing-edge noise reduction of a wing by a surface modification

2021 ◽  
Vol 263 (3) ◽  
pp. 3194-3201
Author(s):  
Varun Bharadwaj Ananthan ◽  
R.A.D. Akkermans ◽  
Dragan Kozulovic
Keyword(s):  
Noise Reduction ◽  
Stochastic Approach ◽  
Slight Reduction ◽  
Noise Sources ◽  
Trailing Edge ◽  
Sound Sources ◽  
Airframe Noise ◽  
Trailing Edge Noise ◽  
Random Particle ◽  
Noise Production

There is an increased emphasis on reducing airframe noise in the last decades. Airframe noise is sound generated by the interaction of a turbulent flow with the aircraft geometry, and significantly contributes to the overall noise production during the landing phase. One examples of airframe noise is the noise generated at a wing's trailing edge, i.e., trailing-edge noise. In this contribution, we numerically explore the local application of riblets for the purpose of trailing-edge noise reduction. Two configurations are studied: i) a clean NACA0012 wing section as a reference, and ii) the same configuration with riblets installed at the wing's aft part. The numerical investigation follows a hybrid computational aeroacoustics approach, where the time-average flow is studied by means of RANS. Noise sources are generated by means of a stochastic approach called Fast Random Particle Mesh method. The results show a deceleration of the flow behind the riblets. Furthermore, the turbulent kinetic energy indicates increased unsteadiness behind the riblets which is shifted away from the wall due to the presence of the riblets. Lastly, the sound sources are investigated by means of the 3D Lamb-vector, which indicates a slight reduction in magnitude near the trailing edge.

Low frequency noise sources in AlGaN/GaN HEMTs

1999 ◽  
Author(s):  
J. A. Garrido ◽  
F. Calle ◽  
E. Muñoz ◽  
I. Izpura ◽  
J. L. Sánchez-Rojas ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Noise Sources ◽  
Gan Hemts

Barotropic theory for the velocity profile of Jupiter’s turbulent jets: an example for an exact turbulent closure

2018 ◽  
Vol 860 ◽  
pp. 577-607
Author(s):  
E. Woillez ◽  
F. Bouchet
Keyword(s):  
Velocity Profile ◽  
Turbulent Jets ◽  
Equilibrium Structure ◽  
Injection Rate ◽  
Velocity Shear ◽  
Small Scale ◽  
Reynolds Stresses ◽  
Zonal Jets ◽  
Time Scale Separation ◽  
Turbulent Closure

We model the dynamics of Jupiter’s jets by the stochastic barotropic $\unicode[STIX]{x1D6FD}$-plane model. In this simple framework, by analytic computation of the averaged effect of eddies, we obtain three new explicit results about the equilibrium structure of jets. First we obtain a very simple explicit relation between the Reynolds stresses, the energy injection rate and the averaged velocity shear. This predicts the averaged velocity profile far from the jet edges (extrema of zonal velocity). Our approach takes advantage of a time-scale separation between the inertial dynamics on one hand, and the spin-up (or spin-down) time on the other. Second, a specific asymptotic expansion close to the eastward jet extremum explains the formation of a cusp at the scale of energy injection, characterized by a curvature that is independent of the forcing spectrum. Finally, we derive equations that describe the evolution of the westward tip of the jets. The analysis of these equations is consistent with the previously discussed picture of barotropic adjustment, explaining the relation between the westward jet curvature and the $\unicode[STIX]{x1D6FD}$-effect. Our results give a consistent overall theory of the stationary velocity profile of inertial barotropic zonal jets, in the limit of small-scale forcing.

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