Aeroacoustic Characteristics of Cavity and Effect Study of Mesh on Noise Suppression

2013 ◽  
Vol 421 ◽  
pp. 104-109
Author(s):  
Jing Sun ◽  
Guang Jun Yang ◽  
Jian Jun Liu
Keyword(s):  
Noise Reduction ◽  
Noise Suppression ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Cavity Flow ◽  
Noise Spectrum ◽  
Effect Study ◽  
Suppression Effect ◽  
Reduction Effect ◽  
Suppression Effects

To explore the noise suppression effect of mesh on cavity, the wind tunnel experiment is carried out based on the analysis of clean cavity flow characteristics. The meshes are arranged both in the cavity and at the leading edge of the cavity. Through the analysis of pressure distribution on the cavity bottom and the noise spectrum monitored at front and rear walls respectively, noise suppression effects of mesh programs relative to the clean cavity and changes in the flow field are studied, the results show that the mesh inside the cavity has a better noise reduction effect. The work in this paper provides an effective way for cavity noise reduction.

Research on the Noise Reduction and Efficiency Increase for Axial Fan with Wave Leading Edge Blades

2020 ◽  
Author(s):  
Bo Li ◽  
Yujing Wu ◽  
Dange Guo ◽  
Dan Luo ◽  
Diangui HUANG
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Wave Amplitude ◽  
Sound Pressure ◽  
Noise Analysis ◽  
Leading Edge ◽  
Pressure Level ◽  
Wave Number ◽  
Monitoring Point ◽  
Reduction Effect

Abstract This paper imitates the raised structure of the leading edge of the humpback whale fin limbs, designed six bionic blades. The aerodynamic analysis show that: the wave leading edge blade can improve the total pressure efficiency of the axial flow fan, and under off-design conditions, the aerodynamic performance of bionic fan is better than that of prototype fan. The noise analysis shows that: under the condition of constant wave number, increasing wave amplitude can reduce the overall sound pressure level at the monitoring point, in the middle and high frequency range, the sound pressure level of the bionic fan at the monitoring point is significantly lower than that of the prototype fan, and the noise reduction effect increases with the increase of wave amplitude; under the condition of constant wave amplitude, increasing the wave number can reduce the fan noise. At a certain wave number and amplitude, the overall sound pressure level of the bionic fan at the monitoring point is at most 2.91 dB lower than that of the prototype fan. In this paper, the noise reduction effect of increasing wave number is more obvious than that of increasing wave amplitude.

ANALYSIS OF THE EFFECTS OF MASS-INJECTION AT THE LEADING EDGE ON CAVITY FLOW CHARACTERISTICS

2009 ◽  
Vol 23 (03) ◽  
pp. 413-416 ◽  
Author(s):  
JI FEI WU ◽  
ZHAO LIN FAN ◽  
XIN FU LUO
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Cavity Flow ◽  
Fluctuating Pressure ◽  
Pressure Distributions ◽  
Mass Injection ◽  
Varying Mass ◽  
Hole Number

An experimental investigation was conducted in a high speed wind tunnel to explore the effects of mass-injection on cavity flow characteristics. Detailed static-pressure and fluctuating pressure measurements were obtained at the cavity floor to enable the effects of the mass-injection at the leading edge to be determined. Results indicate that varying mass-injection hole number and the flux rate of mass-injection has no significant effect on cavity flow characteristics. However, mass-injection can reduce the cavity static pressure gradient when the cavity flow type is transitional-cavity flow. The study also indicates that Mach number can influence the effect of mass-injection on cavity fluctuating pressure distributions, and at supersonic speeds, mass-injection can suppress the cavity tones effectively.

Prediction of Aeroacoustic and Control over a Cavity by Delayed Detached Eddy Simulation

2014 ◽  
Vol 598 ◽  
pp. 505-509 ◽  
Author(s):  
Yu Liu ◽  
Ming Bo Tong
Keyword(s):  
Sound Pressure ◽  
Noise Suppression ◽  
Cfd Simulation ◽  
Leading Edge ◽  
Pressure Level ◽  
Detached Eddy Simulation ◽  
Suppression Effect ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
And Control

In the present study CFD simulation with delayed detached eddy simulation (DDES) are performed to investigate an open cavity at Mach 0.85. Two cavity configurations, clean cavity and cavity with a leading-edge saw tooth spoiler, are modeled. The results obtained from clean cavity prediction are compared with experimental sound pressure level (SPL) data from QinetiQ, UK. Furthermore, comparisons are made with the predicted SPL between the two configurations. The main focuses of this investigation are to obtain a further understanding of the cavity aeroacoustics and test the noise suppression effect by a saw tooth spoiler.

scholarly journals Analysis of Composite Scrubber with Built-In Silencer for Marine Engines

2021 ◽  
Vol 9 (9) ◽  
pp. 962
Author(s):  
Myeong-rok Ryu ◽  
Kweonha Park
Keyword(s):  
Noise Reduction ◽  
Transmission Loss ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Frequency Region ◽  
Reverse Direction ◽  
Sulfur Oxide ◽  
Noise Characteristics ◽  
Average Transmission ◽  
Reduction Effect

The International Maritime Organization (IMO) is strengthening regulations on reducing sulfur oxide emissions, and the demand for reducing exhaust noise affecting the environment of ships is also increasing. Various technologies have been developed to satisfy these needs. In this paper, a composite scrubber for ships that can simultaneously reduce sulfur oxide and noise was proposed, and the flow characteristics and noise characteristics were analyzed. For the silencer, vane type and resonate type were applied. In the case of the vane type, the effects of the direction, size, and location of the vane were analyzed, and in the case of the resonate type, the effects of the hole location and the number of holes were analyzed. The result shows that the length increase of the vane increased the average transmission loss and had a great effect, especially in the low frequency region. The transmission loss increased when the vane was installed outside, and the noise reduction effect was excellent when the vane was in the reverse direction. In the resonate type, increasing the number of holes is advantageous for noise reduction. The condition for maximally reducing noise in the range not exceeding 840 Pa, which is 70% of the allowable back pressure, is a vane length of 225 mm in the outer vane reverse type. The pressure drop under this condition was 777 Pa, and the average transmission losses in the low frequency region and the entire frequency region were 43.5 and 54.5 dB, respectively.

scholarly journals Noise reduction effect of leading-edge serrations on axial fan

2019 ◽  
Vol 2019 (0) ◽  
pp. IS-18
Author(s):  
Kenji YOSHIDA ◽  
Yohei KAMIYA ◽  
Masato KOMURA ◽  
Hideki OYA ◽  
Etsuro YOSHINO
Keyword(s):  
Noise Reduction ◽  
Leading Edge ◽  
Axial Fan ◽  
Reduction Effect

scholarly journals Flow characteristics and noise reduction effects of air cleaners of automobile intake systems with built-in resonators with space efficiency

2021 ◽  
Vol 9 (3A) ◽  
Author(s):  
Hoseop Song ◽  
◽  
Haengmuk Cho ◽  
Keyword(s):  
Pressure Drop ◽  
Noise Reduction ◽  
Transmission Loss ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Helmholtz Resonator ◽  
Space Efficiency ◽  
Engine Room ◽  
Air Cleaner ◽  
Reduction Effect

In an automobile intake system, Helmholtz resonator is often used to reduce intake noise. But there is a disadvantage in the engine room. Resonator brings low engine room space efficiency, because resonator needs some. In this paper, we propose air cleaner with built-in resonator for a limited space of air cleaner and analyze the pressure drop effect and the transmission loss performance of the resonator through flow analysis. The air cleaner with a built-in resonator had almost no difference in pressure drop with the conventional air cleaner. Some vortex in conventional air cleaner is removed, and also, the built-in resonator has noise reduction effect at 160Hz at 61dB such as same resonator.

scholarly journals The Hydrodynamic Noise Suppression of a Scaled Submarine Model by Leading-Edge Serrations

2019 ◽  
Vol 7 (3) ◽  
pp. 68 ◽  
Author(s):  
Yongwei Liu ◽  
Yalin Li ◽  
Dejiang Shang
Keyword(s):  
Noise Reduction ◽  
Experimental Test ◽  
Noise Suppression ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Underwater Vehicles ◽  
Counter Rotation ◽  
Hydrodynamic Noise ◽  
High Reynolds

High hydrodynamic noise is a threat to the survival of underwater vehicles. We investigated a noise suppression mechanism by putting leading-edge serrations on the sail hull of a scaled SUBOFF model, through numerical calculation and an experimental test. We found that the cone shape of leading-edge serrations can decrease the intensity of the adverse pressure gradient and produce counter-rotation vortices, which destroy the formation of the horseshoe vortex and delay the tail vortex. To achieve the optimum hydrodynamic noise reduction, we summarized the parameters of leading-edge serrations. Then, two steel models were built, according to the simulation. We measured the hydrodynamic noise based on the reverberation method in a gravity water tunnel. The numerically calculated results were validated by the experimental test. The results show that leading-edge serrations with amplitudes of 0.025c and wavelengths of 0.05h can obtain hydrodynamic noise reduction of at least 6 dB, from 10 Hz to 2 kHz, where c is the chord length and h is the height of the sail hull. The results in our study suggest a new way to design underwater vehicles with low hydrodynamic noise at a high Reynolds number.

scholarly journals Suppression of the Hydrodynamic Noise Induced by the Horseshoe Vortex through Mechanical Vortex Generators

2019 ◽  
Vol 9 (4) ◽  
pp. 737 ◽  
Author(s):  
Yongwei Liu ◽  
Hongxu Jiang ◽  
Yalin Li ◽  
Dejiang Shang
Keyword(s):  
Noise Reduction ◽  
Noise Suppression ◽  
Flow Direction ◽  
Low Frequency ◽  
Sound Field ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Vortex Generators ◽  
Counter Rotation ◽  
Hydrodynamic Noise

The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the flow field and the sound field of the three shapes of mechanical VGs: triangular, semi-circular, and trapezoidal. The triangular VGs with an angle of 30° to the flow direction achieved a better noise reduction. The optimum noise suppression is 8.93 dB, when the distance from the triangular VGs to the sail hull’s leading edge is 0.1c, where c is the chord length. The noise reduction mechanism is such that the mechanical VGs can destroy the formation of the horseshoe vortex at the origin and produce counter-rotation vortices to weaken its intensity. We created two steel models according to the simulation, and the experimental measurement was carried out in a gravity water tunnel. The measured results showed that the formation of the horseshoe vortex could be effectively inhibited by the triangular VGs. The results in our study can provide a new method for hydrodynamic noise suppression by flow control.

Passive Control of Transonic Cavity Flow

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
David G. MacManus ◽  
Diane S. Doran
Keyword(s):  
High Speed ◽  
Passive Control ◽  
Noise Suppression ◽  
Flow Behavior ◽  
Leading Edge ◽  
Cavity Flow ◽  
Step Length ◽  
Geometric Feature ◽  
Sufficient Intensity ◽  
Grazing Flow

Open cavities at transonic speeds can result in acoustic resonant flow behavior with fluctuating pressure levels of sufficient intensity to cause significant damage to internal stores and surrounding structures. Extensive research in this field has produced numerous cavity flow control techniques, the more effective of which may require costly feedback control systems or entail other drawbacks such as drag penalties or rapid performance degradation at off-design condition. The current study focuses on the use of simple geometric modifications of a rectangular planform cavity with the aim of attenuating the aeroacoustic signature. Experiments were performed in an intermittent suck-down transonic wind tunnel by using a typical open flow rectangular planform cavity, which was modularly designed such that the leading and trailing edge geometries could be modified by using a family of inserts. The current work focused on a variety of recessed leading edge step arrangements. Configurations were tested at transonic Mach numbers spanning the range Mach 0.7–0.9, and unsteady pressure measurements were recorded at various stations within the cavity in order to obtain acoustic spectra. The most effective configuration at Mach 0.9 was the leading edge step employing a step height to step length ratio of 0.4. This configuration achieved a tonal attenuation of up to 18.6dB and an overall sound pressure level (OASPL) reduction of approximately 7.5dB. This is a significant level of noise suppression in comparison with other passive control methods. In addition, it offers the additional benefits of being a simple geometric feature, which does not rely on placing flow effectors into the high-speed grazing flow.

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