A Formula for Prediction of Frequency of Tonal Sound in Cavity Flows With Acoustic Resonance

2011 ◽  
Author(s):  
Hiroshi Yokoyama ◽  
Keitaro Terao ◽  
Tatsuya Suzuki ◽  
Akiyoshi Iida
Keyword(s):  
Sound Pressure ◽  
Cavity Length ◽  
Time Lag ◽  
Acoustic Resonance ◽  
Cavity Flow ◽  
Expansion Wave ◽  
Cavity Flows ◽  
Computational Results ◽  
Sustained Oscillations ◽  
New Formula

Self-sustained oscillations with tonal sound in flows over a cavity are investigated by experiments using a wind tunnel and direct numerical simulation of flow and acoustic fields. The effects of the length-to-depth ratio of the cavity and the ratio of the cavity length L to the momentum thickness of the incoming boundary layer on the mode of the oscillations are clarified. The simultaneous measurements of flow pattern and sound pressure are also performed. The results show that a time lag between the generation of an expansion wave due to the collision of a vortex with the downstream edge and the radiation of the expansion wave from the cavity becomes larger for the cavity flow with the acoustic resonance. The computational results explain why the delay becomes larger. Moreover, considering this delay, a new formula for the frequency of the tonal sound in cavity flows with the acoustic resonance is proposed. The frequencies predicted by this formula agree well with those measured.

scholarly journals Effects of Freestream Turbulence on Cavity Tone and Sound Source

2016 ◽  
Vol 2016 ◽  
pp. 1-16 ◽  
Author(s):  
Hiroshi Yokoyama ◽  
Hiroshi Odawara ◽  
Akiyoshi Iida
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Sound Source ◽  
Cavity Length ◽  
Acoustic Resonance ◽  
Cavity Flow ◽  
Cavity Flows ◽  
Freestream Turbulence ◽  
Acoustic Analogy ◽  
Cavity Tone

To clarify the effects of freestream turbulence on cavity tones, flow and acoustic fields were directly predicted for cavity flows with various intensities of freestream turbulence. The freestream Mach number was 0.09 and the Reynolds number based on the cavity length was 4.0 × 104. The depth-to-length ratio of the cavity,D/L, was 0.5 and 2.5, where the acoustic resonance of a depth-mode occurs forD/L= 2.5. The incoming boundary layer was laminar. The results for the intensity of freestream turbulence of Tu = 2.3% revealed that the reduced level of cavity tones in a cavity flow with acoustic resonance(D/L=2.5)was greater than that without acoustic resonance(D/L=0.5). To clarify the reason for this, the sound source based on Lighthill’s acoustic analogy was computed, and the contributions of the intensity and spanwise coherence of the sound source to the reduction of the cavity tone were estimated. As a result, the effects of the reduction of spanwise coherence on the cavity tone were greater in the cavity flow with acoustic resonance than in that without resonance, while the effects of the intensity were comparable for both flows.

Experimental and computational study of unsteady hypersonic cavity flows

2007 ◽  
Vol 111 (1125) ◽  
pp. 673-688 ◽  
Author(s):  
S. Creighton ◽  
R. Hillier
Keyword(s):  
Blunt Body ◽  
Cavity Length ◽  
Computational Study ◽  
Cavity Flow ◽  
Flow Behaviour ◽  
Cavity Flows ◽  
Flow State ◽  
Cfd Simulations

AbstractThis paper presents a combined experimental and computational study of annular cavities on a semi-angle cone in a Mach 8·9 flow. A range of cavity length-to-depth ratios has been considered, and a parameter has been determined that distinguishes between ‘weak oscillations’ and ‘strong oscillations’ of the cavity flow. Essentially the work identifies the transition from the case where the flow can be regarded as ‘pure cavity flow’ to that where the flow behaviour is tending towards that of a ‘spiked blunt body’. The CFD simulations also suggest that, for a certain range of cavity scale, the limiting cavity flow state depends upon the flow initialisation process; it may be weak or strongly oscillating.

Analysis of the Noise Level Generated by Axial Flow Fan Composed of Radial-Bladed Centrifugal Rotor

2014 ◽  
Author(s):  
S. S. Borges ◽  
R. Barbieri ◽  
P. S. B. Zdanski
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Axial Flow ◽  
Acoustic Resonance ◽  
Pressure Level ◽  
Resonance Mode ◽  
Numerical Techniques ◽  
Cooling Systems ◽  
Centrifugal Fans ◽  
Motor Cooling

The objective of this work is to present, by means of experimental, analytical and numerical techniques that sound pressure level generated by radial-bladed centrifugal fans of electric motor cooling systems may be expressed by a logarithmical ratio of the peripheral velocity of rotor, volumetric flow and efficiency of the fan. The proposed methodology proved to be efficient and simple in the prediction of generated noise by radial-bladed centrifugal fans of TEFC motors with accuracy of ± 3 dB. In addition, the acoustic resonance mode of the fan cavity were determined by means of numerical simulations, which its results were validated through experiments using waterfall spectrum.

scholarly journals Exhaust Noise Reduction by Application of Expanded Collecting System in Pneumatic Tools and Machines

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1592
Author(s):  
Dominik Gryboś ◽  
Jacek S. Leszczyński ◽  
Dorota Czopek ◽  
Jerzy Wiciak
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Noise Reduction ◽  
Sound Pressure ◽  
Acoustic Pressure ◽  
Pressure Level ◽  
Computational Results ◽  
Noise Measurements ◽  
Exhaust Noise ◽  
Collecting System

In this paper, we demonstrate how to reduce the noise level of expanded air from pneumatic tools. Instead of a muffler, we propose the expanded collecting system, where the air expands through the pneumatic tube and expansion collector. We have elaborated a mathematical model which illustrates the dynamics of the air flow, as well as the acoustic pressure at the end of the tube. The computational results were compared with experimental data to check the air dynamics and sound pressure. Moreover, the study presents the methodology of noise measurement generated in a pneumatic screwdriver in a quiet back room and on a window-fitting stand in a production hall. In addition, we have performed noise measurements for the pneumatic screwdriver and the pneumatic screwdriver on an industrial scale. These measurements prove the noise reduction of the pneumatic tools when the expanded collecting system is used. When the expanded collecting system was applied to the screwdriver, the measured Sound Pressure Level (SPL) decreased from 87 to 80 dB(A).

Aeroacoustic computation of cavity flow in self-sustained oscillations

2003 ◽  
Vol 17 (4) ◽  
pp. 590-598
Author(s):  
Sung-Ryong Koh ◽  
Yong Cho ◽  
Young J. Moon
Keyword(s):  
Cavity Flow ◽  
Sustained Oscillations

Steady Performance of a Flexible Hydrofoil Near a Free Surface

1990 ◽  
Vol 34 (04) ◽  
pp. 302-310
Author(s):  
Salwa M. Rashad ◽  
Theodore Green
Keyword(s):  
Mathematical Model ◽  
Free Surface ◽  
Cavity Length ◽  
Leading Edge ◽  
Cavity Flow ◽  
Cavitation Number ◽  
Deformation Characteristics ◽  
Flow Depth ◽  
Lift And Drag ◽  
The Galerkin Method

A linearized cavity-flow theory is used to develop a mathematical model to study the steady characteristics of a flexible hydrofoil near a free surface. The Galerkin method is employed to account for the mutual interaction between the fluid and structure forces. Cheng and Rott's method [1]2 is used to derive general expressions for the deformation characteristics in steady flow of an arbitrarily shaped hydrofoil, with a clamped trailing edge and free leading edge. From the analysis it is possible to determine the lift and drag coefficients, cavity length, and the foil steady deformation for any given specific foil shape, cavitation number, angle of attack, flow depth/chord ratio and rigidity. Sample numerical results are given, and the effects of flexibility and the proximity of the free surface are discussed. Chordwise flexibility tends to increase drag and decrease lift coefficients. This effect is more serious near the free surface. A slight increase of the thickness near the leading edge diminishes the flexibility effects.

Combustion Oscillation Analysis of Premixed Flames at Elevated Pressures

1998 ◽  
Author(s):  
Masaya Ohtsuka ◽  
Shohei Yoshida ◽  
Shin’ichi Inage ◽  
Nariyoshi Kobayashi
Keyword(s):  
Dynamic Pressure ◽  
Time Lag ◽  
Premixed Flames ◽  
Acoustic Resonance ◽  
Flame Length ◽  
Elevated Pressures ◽  
Oscillation Analysis ◽  
Analytical Formulas ◽  
Combustion Oscillation ◽  
Analytical Time

A new analytical time lag flame model based on Bloxidge’s flame model was introduced for calculating combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed which was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures between 0.6–0.9MPa. Fluctuating pressure had the maximum peak at the specific value of fτf. Here f is the frequency of resonance and τf is the passing time of premixed gas through flame length. The analysis could simulate the dependency of fuel-to-air ratio and static pressure for dynamic pressure local peak.

Experimental Investigation of Forced Convection Enhancement by Acoustic Resonance Excitations in Turbulated Heat Exchangers

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Samuel Gendebien ◽  
Alex Kleiman ◽  
Boris Leizeronok ◽  
Beni Cukurel
Keyword(s):  
Heat Exchanger ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Minimal Form ◽  
Resonance Frequencies ◽  
Double Pipe ◽  
The Impact

Abstract The present research deals with enhancing the thermal performance of turbulated heat exchangers through the application of sound pressure waves at acoustic resonance frequencies. Extending the findings of prior wind tunnel studies, where a standing wave greatly improved the forced convection in reattaching flows, this paper exploits such a phenomenon in a practical heat exchanger setting. The current experiments are conducted in representative turbulated plate and double-pipe heat exchanger geometries, mounted in a dedicated facility. After identifying the inherent acoustic resonance frequencies of the passageways, the impact of excitation is studied in various sound pressure levels, blockage ratios, as well as Strouhal and Reynolds numbers. The acoustic resonance excitation resulted in heat transfer enhancement of 20% and 10% in the plate and double-pipe designs, respectively, absence of additional pressure penalties. To the best knowledge of the authors, this is the first demonstration of acoustic forced convection enhancement in turbulated heat exchanger geometries. Such a technology can pave the way toward future designs that require low-pressure losses, minimal form factor, and/or process controllability.

Experimental Investigation of Forced Convection Enhancement by Acoustic Resonance Excitations in Turbulated Heat Exchangers

2019 ◽  
Author(s):  
S. Gendebien ◽  
A. Kleiman ◽  
B. Leizeronok ◽  
B. Cukurel
Keyword(s):  
Heat Exchanger ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Minimal Form ◽  
Resonance Frequencies ◽  
Double Pipe ◽  
The Impact

Abstract The present research deals with enhancing thermal performance of turbulated heat exchangers through application of sound pressure waves at acoustic resonance frequencies. Extending the findings of prior wind tunnel studies, where a standing wave greatly improved the forced convection in reattaching flows, this paper exploits such a phenomenon in a practical heat exchanger setting. The current experiments are conducted in representative turbulated plate and double pipe heat exchanger geometries, mounted in a dedicated facility. After identifying the inherent acoustic resonance frequencies of the passageways, the impact of excitation is studied in various sound pressure levels, blockage ratios, as well as Strouhal and Reynolds numbers. The acoustic resonance excitation resulted in heat transfer enhancement of 20% and 10% in the plate and double pipe designs respectively, absent of additional pressure penalties. To the best knowledge of the authors, this is the first demonstration of acoustic forced convection enhancement in turbulated heat exchanger geometries. Such a technology can pave the way towards future designs that require low pressure losses, minimal form factor and/or process controllability.

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