Flow Noise Level Research Articles

Improving flow and noise performances of centrifugal pump in dishwasher through impeller design optimization

Noise and performance are critical factors in the customer's selection of dishwashers. The centrifugal pump, which circulates water for washing dishes, dominantly influences the performance and noise of a dishwasher. This study aims to improve the performance and reduce the noise of a centrifugal pump by modifying its impeller design. Priorly, the flow and noise characteristics of the target pump were experimentally characterized. Then, the flow performance of the pump was predicted using a virtual pump performance tester based on the computational fluid dynamics techniques to solve the three-dimensional unsteady incompressible Reynolds Averaged Navier-Stokes equations. The noise radiation generated by the impeller was predicted using the Ffowcs Williams-Hawkings equation. The results were validated by comparing the predicted with the measured. The Response Surface Method, where the blade inlet and outlet angles at the hub and shroud locations were used as design variables, was applied to improve the flow and noise performance of the pump. The optimized impeller design increased the pump flow rate by 17.5% and reduced the flow noise level by 3.5 dB at the same flow rate, as per the fan law predictions.

Effect of the Gravel Zone Thickness Created in the Deep Well Test Simulation on the Operating Characteristics of the Pump and Head Loss

This study was conducted in a deep well simulator used for typical irrigation studies. In this work, the changes in the pump flow rate, drawdown, noise level, and pump pressures were analyzed for three different gravel zone thicknesses used in the well. From the study, it was found that a high gravel zone thickness increased the well’s drawdown levels during pumping. For drawdown values of 40, 45, 50 and 55 m3 h–1, an increase in the gravel thickness by 10 cm increased these values by 2.92, 2.41, 2.38 and 2.37 times, respectively. When the gravel thickness was doubled (from 5 cm to 10 cm), the hydraulic conductivity decreased by about half and head loss doubled. As a result, gravel thickness directly affected the drawdown rate of the pump. It was shown that different drawdown values resulting due to different gravel thicknesses should be taken into consideration when placing the pump in a deep well.

Effect of solidity on aeroacoustic performance of a vertical axis wind turbine using improved delayed detached eddy simulation

Vertical axis wind turbines (VAWTs) can be suitably installed in urban regions. Although the power performance is essential, the noise generated by a VAWT may influence the living environment. An accurate prediction of power and noise performance is therefore necessary. In the present study, a precise aerodynamic and aeroacoustic performance assessment of a Darrieus VAWT is accomplished with the aim of exploring the effect of solidity parameter using a high-fidelity method. The improved delayed detached eddy simulation (IDDES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy approaches have been utilized for predicting flow field and noise level. The simulations were performed in three different solidities at a specific tip speed ratio (TSR). It is shown that changing the solidity parameter affects both power and noise level remarkably. Change in the aerodynamic performance mostly occurs due to variation in instantaneous effective angle of attack which comprises many detailed discussions. The lower the solidity the higher the value of effective angle of attack. The noise level also affects by changing solidity as consequence of flow field variation. It is discussed here how the noise level would alter in terms of solidity, TSR, distance and azimuth angle. As the solidity increases, the sound pressure level (SPL) at blade pass frequency increases. Since design of quieter VAWT with application in urban regions recently is of the most interest and importance therefore such deep studies could appropriately address hybrid criteria and be helpful in future investigations.

Acoustic and Flow Aspects of Novel Synthetic Jet Actuator

The acoustic and flow aspects of the novel synthetic jet actuator (SJA) with fins inside the cavity were experimentally investigated for three types of enclosure design and two models of loudspeaker. The aim of the study is to find the parameter which connects the flow and acoustic properties of the SJA and allows us to choose the optimal solution in those regards. The hot wire anemometry was used for the velocity measurements and the sound pressure level was measured with a sound level meter. The model of the loudspeaker turned out to have a significantly stronger impact on the flow parameters and noise level than the shape of the fins in the cavity. The parameter that showed a dependence on the shape of the fins was the actuator’s efficiency. A ratio of the root-mean-square velocity at the orifice axis to the sound pressure level (U0.c/SPL) was used to connect the acoustic and flow properties of the tested actuators. This parameter was subsequently applied to determine the best configuration among the tested actuators.

Various flow channel constructive elements effect on vibroacoustic characteristics of electrohydraulic control devices

In this article author discuss investigation of control valve flow channel with regulating element equipped with meshed screens set on it. The issue provides engineers and scientist with the results of a series of experiments without using of flow noise muffler at the control system scheme.The main idea is to obtain technical information on how to exclude the flow noise muffler from the control system's scheme. Such kind of knowledge is considered to be necessary for the following application in the feed water flow control systems meeting modern and next generation requirements of regulatory documents on vibration and flow noise characteristics.It is discussed the research of the feed water control valve at the test bench mostly. There were designed a several types of scheme for flow channel construction with different meshed screens and they arrangements into it, flow restriction circuits, cartridge constructions etc. It was chosen the two-step pressure reducing scheme of flow channel after the theoretical analysis, which then was produced and fitted with meshed screens at both steps.It is said in the article that the results of discovery bring out the useless of perforated rubber elements implementation into the flow channel construction. They do not make any effect on the acoustic field of control valve. Besides, application of elastic elements makes difficulties for the manufacturing of flow channel and considered as low reliable.The issue provides reader with the information on flow noise level and its excess over the established level by the control valve under study. It is shown how to refine the flow channel construction with regulating element up to the modern and next generation requirements. Also, the proposal of how to exclude flow noise muffler from the schemes of control systems are listed.

Analysing mass flow rate and noise level of blowers through Ansys CFX solver

In general, the blowers mounted on the wind mills are designed to supply cooling effect to the power generator for the extraction of heat, but it is noticed that the axial blowers currently deployed in the windmills tend to produce insufficient cooling effect and generate high level of noise. Thus, sufficient cooling and low noise level are key parameters in the design of blowers. This study of forward-curved centrifugal blower focuses on improving the performance of an industrial blower and implementing the performance characteristics of the system derived from high-fidelity three-dimensional CFX analyses. The objective of the present study is to estimate the aerodynamic and aero acoustic parameters like mass flow rate and noise level of axial blower and centrifugal blower. The blowers are modelled and analysed using Ansys CFX solver based on industry requirements. It is observed from the analysis that centrifugal blower is more preferable to achieve sufficient cooling effect with low noise level.

Tracking marine mammals in 3D using electronic tag data

Summary Information about at‐depth behaviour of marine mammals is fundamental yet very hard to obtain from direct visual observation. Animal‐borne multisensor electronic tags provide a unique window of observation into such behaviours. Electronic tag sensors allow the estimation of the animal's 3‐dimensional (3D) orientation, depth and speed. Using tag flow noise level to provide an estimate of animal speed, we extend existing approaches of 3D track reconstruction by allowing the direction of movement to differ from that of the animal's longitudinal axis. Data are processed by a hierarchical Bayesian model that allows processing of multisource data, accounting for measurement errors and testing hypotheses about animal movement by comparing models. We illustrate the approach by reconstructing the 3D track of a 52‐min deep dive of a Blainville's beaked whale Mesoplodon densirostris adult male fit with a digital tag (DTAG) in the Bahamas. At depth, the whale alternated regular movements at large speed (>1·5 m s ‐1) and more complex movements at lower speed (<1·5m s‐1) with differences between movement and longitudinal axis directions of up to 28. The reconstructed 3D track agrees closely with independent acoustic‐based localizations. The approach is potentially applicable to study the underwater behaviour (e.g. response to anthropogenic disturbances) of a wide variety of species of marine mammals fitted with triaxial magnetometer and accelerometer tags.

Influence of surrounding structures upon the aerodynamic and acoustic performance of the outdoor unit of a split air-conditioner

DC-inverter split air-conditioner is widely used in Chinese homes as a result of its high-efficiency and energy-saving. Recently, the researches on its outdoor unit have focused on the influence of surrounding structures upon the aerodynamic and acoustic performance, however they are only limited to the influence of a few parameters on the performance, and practical design of the unit requires more detailed parametric analysis. Three-dimensional computational fluid dynamics(CFD) and computational aerodynamic acoustics(CAA) simulation based on FLUENT solver is used to study the influence of surrounding structures upon the aforementioned properties of the unit. The flow rate and sound pressure level are predicted for different rotating speed, and agree well with the experimental results. The parametric influence of three main surrounding structures(i.e. the heat sink, the bell-mouth type shroud and the outlet grille) upon the aerodynamic performance of the unit is analyzed thoroughly. The results demonstrate that the tip vortex plays a major role in the flow fields near the blade tip and has a great effect on the flow field of the unit. The inlet ring’s size and throat’s depth of the bell-mouth type shroud, and the through-flow area and configuration of upwind and downwind sections of the outlet grille are the most important factors that affect the aerodynamic performance of the unit. Furthermore, two improved schemes against the existing prototype of the unit are developed, which both can significantly increase the flow rate more than 6 %(i.e. 100 m3·h−1) at given rotating speeds. The inevitable increase of flow noise level when flow rate is increased and the advantage of keeping a lower rotating speed are also discussed. The presented work could be a useful guideline in designing the aerodynamic and acoustic performance of the split air-conditioner in engineering practice.

LES-Based Numerical Simulation of Flow Noise for UUV with Full Appendages

Numerical simulation of flow field and flow noise was carried out on SUBOFF with Lighthill acoustical analogy and large eddy simulation method. The results agreed well with the numerical and experimental results obtained from published literature. The validation of the computational method of flow noise used in this paper was carried out. The geometric model was established for the unmanned underwater vehicle with full appendages and the flow field’s computational region discretization was carried out by using structural grid. Numerical simulation of flow noise for unmanned underwater vehicle with full appendages was taken. The numerical results show that the angle of attack has little effect on the flow noise level of the vehicle while the angle ranged from 0° to 4°. Compared with the “＋”-type rudders, the flow noise level of the underwater vehicle with “X”-type rudders is about 3dB lower.

Flow noise reduction from superhydrophobic surfaces

This work investigates how a highly (super)hydrophobic surface can be used to reduce turbulence-generated drag and noise on a towed streamer cable. The work is done by analyzing full-scale drag and flow noise measurements taken on a commercial seismic streamer in combination with direct numerical simulations of turbulence-generated flow noise. The main findings are that viscous drag and flow noise can be significantly reduced on a seismic streamer that is coated to make the surface highly hydrophobic. In an ocean towing test, a 4% reduction of drag on a streamer section was measured. In a separate test on a commercial seismic vessel, a reduction in the flow noise level of nearly 50% (6 dB) for frequencies below 10 Hz was found. Based upon an analysis of numerical simulation data, it is suggested that the reduction in drag and noise can be attributed to a reduced level of shear stress and change in the kinematic structure of the turbulence, both of which occur in the immediate vicinity of the highly hydrophobic surface.

Reducing high Reynolds number hydroacoustic noise using superhydrophobic coating

The objective of this study is to assess and quantify the effect of a superhydrophobic surface coating on turbulence-generated flow noise. The study utilizes results obtained from high Reynolds-number full-scale flow noise measurements taken on a commercial seismic streamer and results from low Reynolds-number direct numerical simulations. It is shown that it is possible to significantly reduce both the frictional drag and the levels of the turbulence generated flow noise even at very high Reynolds-numbers. For instance, frequencies below 10 Hz a reduction in the flow noise level of nearly 50% was measured. These results can be attributed to a reduced level of shear stress and change in the kinematic structure of the turbulence, both of which occur in the immediate vicinity of the superhydrophobic surface.

Influence of Blade Shape on Flow Performance and Noise Generation of Multi-Blade Blower

The influence of different parameters in the design of multi-blade fan , such as the ratio inner diameter of outer diameter, D1/D2 , number of blades, Z, inclination angle,α, outlet angle,βd2 , and inlet angle,βd1 , were examined in order to study relation between the flow pattern and noise level. In the present report, we investigated the fan performance and the noise characteristic experimentally and compared with simplified two-dimensional CFD analysis. The flow pattern passing the blades under the different geometrical conditions was examined and discussed in terms of fan performance and noise level. The results shows that high efficiency and low noise were attained in range of D1/D2=0.8-0.84 , Z=35-45 , α=30°-40°, and βd2=155°-165°. For these conditions, it was found that the pressure loss and noise generation in the flow between blades were attributed to the separation of the flow which was induced by the circulated vortex at the suction side, reattachment of the separated flow, and shear flow at the trailing edge. It was also confirmed that a large inner to outer diameter ratio gives a defected performance and big noise generation because of no reattachment of the separated flow. Also, the increasing of blade number resulted in the increasing of high frequency noise due to the vortices generation in shear layer in spite of rectification of passing flow.

Wind noise in hearing aids with directional and omnidirectional microphones: Polar characteristics of behind-the-ear hearing aids

Wind noise can be a significant problem for hearing instrument users. This study examined the polar characteristics of flow noise at outputs of two behind-the-ear digital hearing aids, and a microphone mounted on the surface of a cylinder at flow velocities ranging from a gentle breeze (4.5 m/s) to a strong gale (22.5 m/s) . The hearing aids were programed in an anechoic chamber, and tested in a quiet wind tunnel for flow noise recordings. Flow noise levels were estimated by normalizing the overall gain of the hearing aids to 0 dB. The results indicated that the two hearing aids had similar flow noise characteristics: The noise level was generally the lowest when the microphone faced upstream, higher when the microphone faced downstream, and the highest for frontal and rearward incidence angles. Directional microphones often generated higher flow noise level than omnidirectional microphones but they could reduce far-field background noise, resulting in a lower ambient noise level than omnidirectional microphones. Data for the academic microphone- on-cylinder configuration suggested that both turbulence and flow impingement might have contributed to the generation of flow noise in the hearing aids. Clinical and engineering design applications are discussed.

SLITA: A new slim towed array for AUV applications

The typical 70 mm diameter towed array was developed for blue-water detection at long range and low frequencies in the 1960s. Since then, there has been a need for towed arrays that are lighter and less expensive, especially since the maturing field of autonomous vehicles has expanded the potential of such arrays. The marriage of AUVs and lightweight towed arrays is a natural progression in the development of littoral autonomous sensing networks for applications such Anti-Submarine Warfare, marine mammals, or ambient noise measurements. In August 2007, NURC began to design and build a new thin diameter (31 mm) high-frequency (up to 20 kHz) nested towed array for ASW purposes. An engineering at-sea trial of the array towed by OEX AUV was performed beginning of November 2007. The flow noise level of the array while towed and the potential influence of the AUV self-noise on the acoustic array were also measured. This paper will first describe the array design, its acquisition system and its integration on the OEX AUV. Then, the results obtained from the data analysis are presented. It is shown that the SLITA array has performance that will make it easily fit requirements of the applications previously mentioned.

Experimental and computational studies on flow behavior around counter rotating blades in a double-spindle deck

Experimental and computational studies were performed to determine the effects of different blade designs on a flow pattern inside a double-spindle counter rotating mower deck. In the experimental study, two different blade models were tested by measuring air velocities using a forward-scatter LDV system. The velocity measurements were taken at several different azimuth and axial sections inside the deck. The measured velocity distributions clarified the air flow pattern caused by the rotating blades and demonstrated the effects of deck and blade designs. A high-speed video camera and a sound level meter were used for flow visualization and noise level measurement. In the computational works, two-dimensional blade shapes at several arbitrary radial sections have been selected for flow computations around the blade model. For three-dimensional computation applied a non-inertia coordinate system, a flow field around the entire three-dimensional blade shape is used to evaluate flow patterns in order to take radial flow interactions into account. The computational results were compared with the experimental results.

고 흡입저항을 가진 원심 송풍기

Comprehensive study on a centrifugal blower for air-purifier involving a few physical filters for percolation process has been accomplished for an optimal design of the air handling system. The filtering media causes a flow resistance for induced flows by a rotating impeller. The present methodology is to adopt PIV system for velocity measurements and wind tunnel connected with an anechoic chamber for total performance test of the blower. Trial prototypes for the blades of a rotor and casing are presented for satisfaction of both flow rate and noise level set by design objectives. Tapered blades with a special casing for a fan show good performance data. The results of velocity fields also explain the reason of improvements of the blower performance.

Flow-induced noise on a bluff body

Flow noise measurements were made on inertial type pressure gradient hydrophones, configured as three-dimensional cylinders in cross flow, over a diameter-based Reynolds number range of 4×103 to 1.8×104. The measurements were made at frequencies from 4.2 to 50 Hz as the bodies were towed in a quiescent body of water. Systematic changes were made in the cylinder geometry as to affect the flow noise level and to aid in the identification of dominant flow noise sources. The cylinder aspect ratio was varied from 0.5 to 2.5, and the endcap geometry was altered by relieving the 90° edge with radii that ranged from 0.0315D to 0.5D, where D is the diameter of the cylinder. The data from these (and other flow visualization) experiments shows that the presence of a radius at the corner between the endcap and the cylinder results in a significant reduction of the separated flow over the endcap, and that the flow noise levels decrease accordingly. The flow noise levels are also observed to decrease as the body aspect ratio increases which suggests that when three-dimensional effects (endcap flow) are suppressed, unsteady forces will be reduced and the cylinder self-noise will decrease. Thus the dominant source of flow noise on short cylinders in cross flow is attributed to the unsteady separation and turbulent flow over the cylinder endcaps.

Effect of various array structures on flow noise reduction

Turbulent boundary layer pressure fluctuations can be reduced by filtering of its wave-number response with either a finite hydrophone or a hydrophone array, or by filtering the wave-number response through a layer of elastomer. In general practice, hydrophone arrays are embedded within a layer of elastomer to reduce the turbulent boundary layer pressure fluctuations and then mounted to an elastic structure. To understand the role of the mounting structure, this work will examine the performance of idealized and realistic array mounting configurations. Three configurations are modeled in this paper. The first one is a plane elastomer layer backed by a rigid surface. The second one is backed by an elastic plate with a finite thickness. Finally, the third one is backed by a layer of water. The front side of the elastomer layer is exposed to turbulent flow. The transfer functions for the three different configurations will be discussed. The results presented here are the numerically calculated noise reductions relative to the calculated noise level for a flush-mounted point hydrophone. In addition, an equivalent-plane-wave flow noise level is derived and compared among the three configurations to directly show any array performance similarities or differences.

Effect of valve shape on characteristics of oil hydraulic poppet valve. (2nd report Case of a poppet with a plane on the top)

The effect of a difference in the form of a poppet top on the performance of an oil hydraulic poppet valve is investigated experimentally. The flow characteristics, thrust performance, noise level and cavitation limit are researched on the three different shaped poppet valves: type (A) the conical poppet, type (B) the conical with a flat part on the top, and type (C) the cylindrical form. It is made clear that the flatness on the top of a poppet in type (B) has a great effect on the valve performance in the case of converging flow, and a difference in a seat angle in type (C) makes a great change in cavitation condition, flow characteristics and noise level in the case of diverging flow.

The flow noise level at microphones in flow ducts

When sound measurements are made in flow ducts one has to insure that the signal-to-noise ratio of the sound signal to the flow noise, which is produced by the turbulent flow at the microphone, is sufficiently high. To accomplish this, knowledge of the flow noise level under the specific given flow conditions is required. In this paper two procedures for determining the flow noise level are described. For the first method, the mean flow velocity and the turbulence level have to be known to estimate the flow noise level as a function of duct diameter and frequency. For the second method knowledge of only the mean flow velocity is required. The procedure involves two measurements: one with a microphone fitted with a conventional nose cone and one with a microphone fitted with a slit-tube. The slit-tube is a special device for reducing the flow noise level. Finally, guidelines are given for sound measurements in the presence of flow and for the use of a microphone with a slit-tube under unusual temperature conditions or in gases other than air.