Control of the self-sustained shear layer oscillations over rectangular cavities using high-frequency vortex generators

2021 ◽  
Vol 33 (4) ◽  
pp. 045115
Author(s):  
Moamenbellah Abdelmwgoud ◽  
Atef Mohany
Keyword(s):  
Shear Layer ◽  
High Frequency ◽  
The Self ◽  
Vortex Generators

Hearing Loss and Hearing Handicap in Users of Recreational Firearms

2002 ◽  
Vol 13 (03) ◽  
pp. 160-168 ◽  
Author(s):  
Michael Stewart ◽  
Rebecca Pankiw ◽  
Mark E. Lehman ◽  
Thomas H. Simpson
Keyword(s):  
Hearing Loss ◽  
American Academy ◽  
High Frequency ◽  
Pure Tone ◽  
Occupational Safety ◽  
Occupational Safety And Health ◽  
Gender Effects ◽  
The Self ◽  
Safety And Health ◽  
Hearing Handicap

This investigation sought to establish the prevalence of hearing loss and hearing handicap in a population of 232 recreational firearm users. Hearing handicap was calculated based on four methods using pure-tone threshold data from the American Academy of Ophthalmology and Otolaryngology, American Academy of Otolaryngology-Head and Neck Surgery, National Institute of Occupational Safety and Health, and American Speech-Language and Hearing Association in addition to the self-report Hearing Handicap Inventory for Adults-Screener (HHIA-S). Subjects (45 female and 187 male) ranging in age from 13 to 77 years (mean = 40 years, SD = 15.1) completed a short questionnaire regarding demographics and shooting practices followed by pure-tone air audiometry at Occupational Safety and Health Administration test frequencies of 500 to 6000 Hz. A total of 177 who exhibited varying degrees of hearing loss also received a face-to-face administration of the HHIA-S. Audiometric and HHIA-S results revealed that both high-frequency hearing loss and hearing handicap varied significantly as functions of age and occupation. Significant gender effects were observed audiometrically but not as a function of hearing handicap. HHIA-S scores varied significantly as a function of high-frequency (1000–4000 Hz) hearing loss. Correlation coefficients between the four different pure-tone methods of calculating hearing handicap and the self-reported HHIA-S were highest for pure-tone methods that do not employ 500 Hz in the calculation.

scholarly journals On the structure of the self-sustaining cycle in separating and reattaching flows

2018 ◽  
Vol 857 ◽  
pp. 907-936 ◽  
Author(s):  
A. Cimarelli ◽  
A. Leonforte ◽  
D. Angeli
Keyword(s):  
Shear Layer ◽  
Rectangular Plate ◽  
Large Scale ◽  
Reverse Flow ◽  
Leading Edge ◽  
Streamwise Velocity ◽  
The Self ◽  
Small Scale ◽  
Spectral Evolution ◽  
Mean Velocity

The separating and reattaching flows and the wake of a finite rectangular plate are studied by means of direct numerical simulation data. The large amount of information provided by the numerical approach is exploited here to address the multi-scale features of the flow and to assess the self-sustaining mechanisms that form the basis of the main unsteadinesses of the flows. We first analyse the statistically dominant flow structures by means of three-dimensional spatial correlation functions. The developed flow is found to be statistically dominated by quasi-streamwise vortices and streamwise velocity streaks as a result of flow motions induced by hairpin-like structures. On the other hand, the reverse flow within the separated region is found to be characterized by spanwise vortices. We then study the spectral properties of the flow. Given the strongly inhomogeneous nature of the flow, the spectral analysis has been conducted along two selected streamtraces of the mean velocity field. This approach allows us to study the spectral evolution of the flow along its paths. Two well-separated characteristic scales are identified in the near-wall reverse flow and in the leading-edge shear layer. The first is recognized to represent trains of small-scale structures triggering the leading-edge shear layer, whereas the second is found to be related to a very large-scale phenomenon that embraces the entire flow field. A picture of the self-sustaining mechanisms of the flow is then derived. It is shown that very-large-scale fluctuations of the pressure field alternate between promoting and suppressing the reverse flow within the separation region. Driven by these large-scale dynamics, packages of small-scale motions trigger the leading-edge shear layers, which in turn created them, alternating in the top and bottom sides of the rectangular plate with a relatively long period of inversion, thus closing the self-sustaining cycle.

scholarly journals Nominal and Actual Values of Inductor and Capacitor Parameters at High Frequencies

2019 ◽  
Vol 7 (4) ◽  
pp. 44-53 ◽  
Author(s):  
E. V. Gurov ◽  
S. S. Uvaysov ◽  
A. S. Uvaysova ◽  
S. S. Uvaysova
Keyword(s):  
Resonant Frequency ◽  
High Frequency ◽  
The Self ◽  
Impedance Match ◽  
Analog Filters ◽  
Reactive Component ◽  
High Frequencies ◽  
Coil Inductance ◽  
Parasitic Parameters ◽  
Capacitor Capacitance

Coil inductance and capacitor capacitance depend on overall dimensions, structure, and ambient factors. They do not vary with frequency. Reactive component impedance is determined by inductance or capacitance respectively, if active resistance is not considered. This is true for the frequencies which are significantly lower than the self-resonant frequency of the component. Parasitic parameters contribution increases on approaching the self-resonant frequency. Therefore, the componentʼs actual inductance and actual capacitance on operating frequency are defined. They are provided by manufacturers and differ from the nominal values. The actual values provide more accurate impedance of components near the considered frequency. Significant deviation from the considered frequency can cause impedance mismatch even more than the nominal values can provide. Frequency response of the high-frequency circuits such as analog filters and impedance match networks are determined by components impedance, not the nominal values. Thus, calculated values must be close to the actual values. The purpose of this article is to justify actual values application instead of nominal values.

Wall-Pressure Fluctuations Inside Attached Cavitation

2021 ◽  
Author(s):  
Changchang Wang ◽  
Guoyu Wang ◽  
Mindi Zhang ◽  
Qin Wu
Keyword(s):  
Shock Wave ◽  
Shear Layer ◽  
High Frequency ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Cloud Cavitation ◽  
Unsteady Pressure ◽  
Wall Pressure Fluctuations ◽  
Kurtosis Factor ◽  
Skewness And Kurtosis

Abstract This study experimentally investigates the statistics of wall-pressure fluctuations and their source inside attached cavitation under different cavity regimes. Experiments were conducted in the divergent section of a convergent-divergent channel at a constant Reynolds number of Re = 7.8 × 105 based on throat height, and different cavitation numbers σ = 1.18, 0.92, 0.82 and 0.78. Four high-frequency unsteady pressure transducers were flushed-mounted in the divergent section downstream the throat where cavitation develops to sample the unsteady pressure signals induced by cavity behaviors. Flow visualization and wall-pressure measurement in high frequency on the order of MHz were employed using a synchronizing sampling technique. Results are presented for sheet/cloud cavitating flows. Specifically, sheet cavitation with both inception shear layer and fully cavitated shear layer and cloud cavitation under re-entrant jet dominated shedding and shock wave dominated shedding are studied. Compared with re-entrant jet, the interactions between shock wave and cavity could induce pressure peaks with high magnitude within cavity, which will collapse the local vapor along its propagating path and reduce local void fraction. Furthermore, statistics analysis shows that within the cavity, wall-pressure fluctuations increase with the distance to cavity leading edge increase in the first half of cavity length, and the moments of the probability density distribution skewness and kurtosis factor decrease, indicating the asymmetry and intermittency of wall-pressure fluctuation signals decrease. In shock wave dominated cavity shedding condition, the skewness and kurtosis factor increase. These results can provide data to improve the accuracy of turbulence modeling in numerical simulation of turbulent cavitating flow.

Secondary instability of cross-flow vortices in Falkner–Skan–Cooke boundary layers

1998 ◽  
Vol 368 ◽  
pp. 339-357 ◽  
Author(s):  
MARKUS HÖGBERG ◽  
DAN HENNINGSON
Keyword(s):  
Growth Rate ◽  
Shear Layer ◽  
Boundary Layers ◽  
Growth Rates ◽  
High Frequency ◽  
Cross Flow ◽  
Low Frequency ◽  
Secondary Instability ◽  
The Cross ◽  
Flow Vortex

Linear eigenvalue calculations and spatial direct numerical simulations (DNS) of disturbance growth in Falkner–Skan–Cooke (FSC) boundary layers have been performed. The growth rates of the small-amplitude disturbances obtained from the DNS calculations show differences compared to linear local theory, i.e. non-parallel effects are present. With higher amplitude initial disturbances in the DNS calculations, saturated cross-flow vortices are obtained. In these vortices strong shear layers appear. When a small random disturbance is added to a saturated cross-flow vortex, a low-frequency mode is found located at the bottom shear layer of the cross-flow vortex and a high-frequency secondary instability is found at the upper shear layer of the cross-flow vortex. The growth rates of the secondary instabilities are found from detailed analysis of simulations of single-frequency disturbances. The low-frequency disturbance is amplified throughout the domain, but with a lower growth rate than the high-frequency disturbance, which is amplified only once the cross-flow vortices have started to saturate. The high-frequency disturbance has a growth rate that is considerably higher than the growth rates for the primary instabilities, and it is conjectured that the onset of the high-frequency instability is well correlated with the start of transition.

Survival rate of self-tapping implants for bone-anchored hearing aids

2006 ◽  
Vol 121 (2) ◽  
pp. 101-104 ◽  
Author(s):  
A Tjellström ◽  
G Granström ◽  
M Odersjö
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Operating Time ◽  
The Self ◽  
Heavy Smoker ◽  
Exact Test ◽  
Time Period ◽  
Significant Difference ◽  
Bone Anchored Hearing Aid

Objective: The purpose of this study was to investigate whether a new self-tapping implant for a bone-anchored hearing aid (BAHA) had the same high frequency of osseointegration as previous implants requiring pre-tapping.Method: Over a three-year period, 144 consecutive implants were placed in the mastoid for BAHA and evaluated.Results: Two implants were lost; both were of the self-tapping type. One was in an 11-year-old boy, who lost his implant six weeks after surgery when the BAHA was fitted. The other was in an elderly man, a heavy smoker with diabetes. Using Fisher's exact test, there was no significant difference between the two groups (p>0.30).Conclusion: Self-tapping implants facilitate surgery and shorten operating time. Over a short follow up, we did not find any significant difference; however, it is important to follow these implants over a longer time period.

Research on High Bandwidth Rogowski Coil for Measuring Lightning Traveling Wave Current on Double Circuit Transmission Line

2014 ◽  
Vol 986-987 ◽  
pp. 1558-1564
Author(s):  
Cheng Ju Yang ◽  
Cheng Wei Zhang ◽  
Geng Bin Zhang ◽  
Pei Ling Chen ◽  
Shi Jun Xie
Keyword(s):  
Transmission Line ◽  
Traveling Wave ◽  
High Frequency ◽  
Power Grid ◽  
Low Frequency ◽  
Rogowski Coil ◽  
The Self ◽  
Equivalent Model ◽  
High Bandwidth ◽  
Frequency Components

Double circuit transmission line is an important part of the power grid, which is vulnerable to lightning and may endanger the security and stability of the power grid. In order to design a sensor which can monitor the lightning traveling wave current on double circuit transmission line, simulations of lightning on the double circuit transmission line were conducted. The simulation result shows that besides high frequency components, the traveling wave contains a lot of low frequency components. Based on the equivalent model and the frequency response of the self-integrated Rogowski coil, it turns out that the widely used self-integrated Rogowski coil is not suitable for this application as the problem of low frequency distortion. In this paper, through theoretical analysis and simulations in Matlab, an improved Rogowski coil with analog integrator is proposed which can correct the low frequency distortion of the self-integrated Rogowski coil. All the simulations, experiments and operating data installed to a double circuit transmission line in China verify the validity of the high bandwidth Rogowski coil.

Effects of vortex generators on the growth of a compressible shear layer

1992 ◽  
Vol 8 (5) ◽  
pp. 1049-1056 ◽  
Author(s):  
D. S. Dolling ◽  
E. Fournier ◽  
Y. R. Shau
Keyword(s):  
Shear Layer ◽  
Vortex Generators

Control of High-Frequency Thermoacoustic Pulsations by Distributed Vortex Generators

AIAA Journal ◽  
2006 ◽  
Vol 44 (3) ◽  
pp. 550-557 ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim J. Gutmark
Keyword(s):  
High Frequency ◽  
Vortex Generators
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