Numerical study on the contribution of surface and volume components of flow-induced noise in baffle silencers

2021 ◽  
Vol 263 (1) ◽  
pp. 5283-5290
Author(s):  
Bartosz Chmielewski ◽  
Iván Herrero-Durá ◽  
Paweł Nieradka
Keyword(s):  
Laminar Flow ◽  
High Speed ◽  
Numerical Study ◽  
Power Level ◽  
Calibration Method ◽  
Industrial Applications ◽  
Large Reynolds Number ◽  
Sound Power ◽  
Noise Mitigation ◽  
Cfd Simulations

Baffle silencers are a well-known solution for noise mitigation in industrial applications. One of the issues concerning these devices is the flow-inducted noise produced when a non-laminar flow of the medium in the duct occurs. These situations occur, for example, in dedusting installations or exhaust systems with the high-speed flow (large Reynolds number of the turbulence and small Mach number). This kind of installation has a complex shape that causes a turbulent flow in the medium. Installing a baffle silencer in these conditions causes additional noise. This noise cannot be predicted by using a standard approach with equations for laminar flow conditions. This paper presents the first step of the research in this field. The first step is to find a relation between CFD simulations' results and self-noise of the baffle silencer. In this work, we use the formulation proposed by Proudman in 1952 to calculate the sound power generated by the flow. The formulation is based on the turbulent kinetic energy k and dissipation rate ε of the flow, which is calculated by CFD simulations. The resulting sound power level needs to be calibrated. The calibration method is developed and presented. The aim of this research is to design an experimental setup.

A Numerical Study of Forest Fire Progression and Fire Suppression by Aerial Fire Fighting

2004 ◽  
Author(s):  
Kohyu Satoh ◽  
Kunio Kuwahara ◽  
K. T. Yang
Keyword(s):  
Forest Fire ◽  
Forest Fires ◽  
High Speed ◽  
Laboratory Experiments ◽  
Numerical Study ◽  
Water Drop ◽  
Fire Suppression ◽  
Critical Issue ◽  
Fire Fighting ◽  
Cfd Simulations

Forest fires are of common occurrence all over the world, which cause severe damages to valuable natural resources and human lives. In the recent California Fire, which burned 300,000 hectors of land, the disaster danger could reasonably be predicted, but early control of fires by means of aerial fire fighting might have been failed in that situation. Also in Japan, there are similar problems in the aerial fire fighting. Most forest fires occur in the daytime and the fires are freely in progress without any control during the nighttime. Therefore, it is important to attack the fires when there is daylight. The water dropped by helicopters is not always sufficient to control fires, since the quantity of water that can be carried aloft is a critical issue. Large amount of water can be dropped from aircrafts, but the high-speed flight of aircrafts may be dangerous in the mountain, where tall trees and steel towers with electric wires may exist. Therefore, those aircrafts have to fly at much higher altitudes than helicopters, while the water drop at high altitudes changes water into mist in the air. The objective of this study is to examine the methods to prevent the ignition by firebrands in the downwind area by applying water through the aerial fire fighting. However, tests by real aircrafts to obtain such information would be too costly. Therefore, the patterns of water drop from aircrafts were examined in CFD simulations, together with the investigation of needed water drop rate based on the forest fire statistics, the previous real aircraft tests and laboratory experiments. It has been found in the simulations that the water supply with the water density of 2 L/m2 is effective to control fires and the patterns of dropping water are reasonable.

Optimized Perforation Schemes in Railway Wheels Toward Acoustic Radiation Mitigation

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
J. Gutiérrez-Gil ◽  
X. Garcia-Andrés ◽  
J. Martínez-Casas ◽  
E. Nadal ◽  
F. D. Denia
Keyword(s):  
Power Level ◽  
Sound Power ◽  
Noise Mitigation ◽  
Railway Network ◽  
Potential Shape ◽  
Radiated Sound ◽  
Railway Wheels ◽  
Wheel Vibration ◽  
The Web ◽  
Radiated Sound Power

Abstract Rolling noise emitted by railway wheels is a problem that affects human health and limits the expansion of the railway network. It is caused by the wheel vibration due to the wheel-rail contact force, and it is important in almost all the vehicle velocity range. The minimization of noise radiation associated with changes on the wheel web is discussed in this work, focusing on potential shape modifications in existing wheels in the form of a perforation distribution over the web. Such a post-manufacturing technique is a cost-effective solution that can be performed in a relatively short term. The implemented objective function is directly related to the overall radiated sound power, which is minimized using a genetic algorithm-based optimizer. In the acoustic model, radiation efficiencies are approximated to unity, the accuracy of this assumption being also studied in the work. The results reflect that an optimized distribution of perforations on the web of a railway wheel can reduce the total sound power level, by about 5 dB(A) and 2 dB(A) for curved and straight web, respectively. The mitigation of the radiated sound power is due to the fact that certain wheel vibration modes are modified and shifted to other frequencies where they are less excited. Finally, the relevance of the cross-sectional curvature of the web is explored by studying two different web geometries, suggesting that it can strongly influence the noise mitigation effects of the perforation pattern.

scholarly journals Numerical Simulation of Oil Jet Lubrication for High Speed Gears

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Tommaso Fondelli ◽  
Antonio Andreini ◽  
Riccardo Da Soghe ◽  
Bruno Facchini ◽  
Lorenzo Cipolla
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Low Pressure ◽  
Adaptive Meshing ◽  
Viscous Effects ◽  
Cfd Simulations ◽  
Oil Jet ◽  
Oil Injection ◽  
Bypass Ratio

The Geared Turbofan technology is one of the most promising engine configurations to significantly reduce the specific fuel consumption. In this architecture, a power epicyclical gearbox is interposed between the fan and the low pressure spool. Thanks to the gearbox, fan and low pressure spool can turn at different speed, leading to higher engine bypass ratio. Therefore the gearbox efficiency becomes a key parameter for such technology. Further improvement of efficiency can be achieved developing a physical understanding of fluid dynamic losses within the transmission system. These losses are mainly related to viscous effects and they are directly connected to the lubrication method. In this work, the oil injection losses have been studied by means of CFD simulations. A numerical study of a single oil jet impinging on a single high speed gear has been carried out using the VOF method. The aim of this analysis is to evaluate the resistant torque due to the oil jet lubrication, correlating the torque data with the oil-gear interaction phases. URANS calculations have been performed using an adaptive meshing approach, as a way of significantly reducing the simulation costs. A global sensitivity analysis of adopted models has been carried out and a numerical setup has been defined.

scholarly journals Numerical simulation of the process of gas outflow into an open pipe with an obstacle filled with a liquid (water, lead)

2021 ◽  
Vol 2057 (1) ◽  
pp. 012073
Author(s):  
I S Vozhakov ◽  
S I Lezhnin
Keyword(s):  
Numerical Simulation ◽  
Turbulence Model ◽  
Liquid Water ◽  
High Speed ◽  
Numerical Study ◽  
Industrial Applications ◽  
Vof Method ◽  
Gas Jet ◽  
Gas Jets ◽  
Open Pipe

Abstract Submerged gas jets find a wide variety of industrial applications, and their behavior is characterized by the ratio of inertia to buoyancy and can vary from the emergence of individual bubbles to stable jets. A numerical study of the high-speed outflow of gas under a pressure of 18 MPa into a cavity with an obstacle filled with a liquid under a pressure of 2 MPa is carried out. The simulation is performed using the VOF method in conjunction with the k-ε turbulence model. The calculations are realized for three distances between the outflow hole and the obstacle: 100, 200, and 300 mm. Principal scenarios of gas jet evolution and characteristic expiration times are obtained.

scholarly journals Potential noise annoyance from ambient air quality measurement using high volume air sampler (HVAS)

2021 ◽  
Vol 909 (1) ◽  
pp. 012003
Author(s):  
B Purwanto ◽  
Zulfachmi
Keyword(s):  
Flow Control ◽  
Power Level ◽  
High Volume ◽  
Ambient Air ◽  
Sound Power ◽  
Noise Mitigation ◽  
High Frequencies ◽  
Air Sampler ◽  
Noise Annoyance ◽  
Sound Power Level

Abstract One of the benchmarks in air pollution is the quality of ambient air consisting of gas and particulate matter. Measurement of particulates in ambient air can be done using a High-Volume Air Sampler (HVAS). However, in the measurement process it sometimes causes noise annoyance to the community where the measuring instrument is operated, considering that the operating time of the instrument is 24 consecutive hours. This research identifies the value of the sound power level emitted from the several types of HVAS to the surrounding environment. There are two types of HVAS measured in this study consisting of one unit of HVAS with analogue flow control made by Indonesian manufacturer and two units of HVAS with digital flow control made by Japan and United States of America manufacturers. Sound power level is determined using ISO 9614 method with a sound intensity analyzer as the main instrument. The sound power level data for each HVAS were than compared and frequency spectrum distributions are evaluated. Based on the research results, it was found that some sample units emitted sound power levels of more than 90 dBA with dominant noise being at high frequencies starting from 4000 Hz. The results of the research can be used as an early information in the development of the HVAS regarding noise mitigation, because there is different approach for controlling noise specifics in low, mid and high frequencies noise source.

Experimental and Numerical Study of Real-Gas Flow in a Supersonic ORC Turbine Nozzle

2006 ◽  
Author(s):  
Teemu Turunen-Saaresti ◽  
Jin Tang ◽  
Jos van Buijtenen ◽  
Jaakko Larjola
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Power Plants ◽  
Gas Flow ◽  
Numerical Study ◽  
Rankine Cycle ◽  
Nozzle Geometry ◽  
Working Fluid ◽  
Cfd Simulations ◽  
Real Gas

Using organic matter as the working fluid in small Rankine cycle power plants is beneficial. However, high molecular weight of the fluid and the single-stage design of the turbine lead to a supersonic flow in the turbine. An Organic Rankine Cycle (ORC) plant was designed and tested. Toluene was used as the working fluid and as lubricant. The turbine and the feed pump were placed on the same shaft as the high-speed generator in the designed 175 kW unit. CFD simulations were used in the design process. Toluene is behaving as a real gas in the nozzle. To ensure an accurate simulation, a real gas model of toluene was implemented in an existing Navier-Stokes flow solver. Polynomial and rational regression were used to achieve the functions for the gas properties. The pressure and temperature were measured at the nozzle inlet and outlet. In the CFD simulations the nozzle ring was modelled with and without a temperature probe in order to model the effect of the probe to the flow field and compare the simulated pressure and temperature values against the measurements. The nozzle geometry was also modelled in 2D and 3D in order to see the effect of the 3D in the flow field. There was quite a good agreement between the measured and simulated data. The agreement in the temperature was better than in the pressure. The effect of 3D on the simulation results was minor, which was expected. The simulated flow field revealed that the shock waves developing in the trailing edge of the nozzle were seen in the turbine rotor inlet.

scholarly journals Influence of Vertical Fastener Stiffness on Rail Sound Power Characteristics: Numerical Study and Field Measurement

2020 ◽  
Vol 10 (5) ◽  
pp. 1682
Author(s):  
Xi Sheng ◽  
Ying Zhang ◽  
Xiaozhou Liu
Keyword(s):  
Decay Rate ◽  
Numerical Study ◽  
Power Level ◽  
Field Measurements ◽  
Spectral Element ◽  
Center Frequency ◽  
Sound Power ◽  
Power Characteristics ◽  
Sound Power Level ◽  
Rolling Noise

The aim of this paper is to investigate the influence of vertical fastener stiffness on the sound power characteristics of rail rolling noise. The rail mobility is obtained by using the Timoshenko-beam track model and the spectral element method. The decay rate is obtained by using the periodic track model and the spectral transfer matrix method. Then, the simulation results of the rail mobility and the decay rate are used to calculate the sound power level of the rail subjected to a harmonic point excitation. Furthermore, the influence of vertical fastener stiffness on the rail sound power level is investigated. Finally, field measurements of the rail accelerance and the decay rate are performed to verify the accuracy of models and calculation methods. The results show that the sound power level of the rail subjected to a harmonic point excitation increases with the increase of the frequency and peaks at the center frequency of 800 Hz. When the vertical fastener stiffness decreases from 50 kN/mm, the rail sound power level below the center frequency of 200 Hz gets increased. The increase of the sound power level is most significant at the center frequency which is close to the decreased vertical rail resonance frequency, because in the corresponding one-third octave band the rail mobility amplitude increases significantly while the decay rate decreases considerably. The simulations of the rail accelerance and the decay rate both coincide well with the measurements.

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