scholarly journals Prediction of Aerodynamic Noise Level of Cross-Flow Fans for Air Conditioner (1st Report, Study of Dependence of Aerodynamic Noise on Relative Velocity)

2003 ◽  
Vol 69 (687) ◽  
pp. 2472-2478 ◽  
Author(s):  
Shigehisa FUNABASHI ◽  
Yasushi SHIGENAGA ◽  
Masatoshi WATANABE ◽  
Yoshihiro TAKADA
Keyword(s):  
Noise Level ◽  
Relative Velocity ◽  
Cross Flow ◽  
Aerodynamic Noise ◽  
Air Conditioner

The Influence of Non-Uniform Impeller on the Cross Flow Fan Noise

2016 ◽  
Vol 693 ◽  
pp. 251-256
Author(s):  
Zhi Qiang Yang ◽  
C.J. Wu
Keyword(s):  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Internal Flow ◽  
Broadband Noise ◽  
Aerodynamic Noise ◽  
Air Conditioner ◽  
Fan Noise ◽  
Power Spectral ◽  
Cross Flow Fan

The aerodynamic noise of a cross flow fan with uneven blade spacing in room air-conditioner was simulated by computational aerodynamic acoustics (CAA) method. It is detailed to analyze the vorticity distribution of the flow field and the power spectral density of measured points’ pressure fluctuations, and the results demonstrate the non-uniform impeller used in this paper can significantly improve internal flow characteristics. Thus the broadband noise got reduced.

Development of High-Efficiency Half-Ducted Propeller Fan for Packaged Air Conditioners

2014 ◽  
Author(s):  
Taku Iwase ◽  
Tetsushi Kishitani
Keyword(s):  
Noise Level ◽  
High Efficiency ◽  
Static Pressure ◽  
Suction Side ◽  
Design Tool ◽  
Optimization Techniques ◽  
Aerodynamic Noise ◽  
Air Conditioner ◽  
Fan Noise ◽  
Ducted Propeller

We developed a high-efficiency half-ducted propeller fan to reduce the electric power consumption of the outdoor unit of a packaged air conditioner by using a design tool combining computational fluid dynamics (CFD) with multi-objective optimization techniques based on a genetic algorithm (GA). The baseline fan was a half-ducted propeller fan with three blades of a currently available product. Blade shape was defined using 16 design variables including inlet and outlet blade angles, setting angles, blade length, sweep angles, dihedral angles, and so on. An in-house program was used to automatically generate the grids for CFD calculation. The objective functions were static pressure efficiency and fan noise level for optimization. The fan noise was calculated with an aerodynamic noise prediction model that used the relative inlet and outlet velocities of the fan blades from the CFD results. We found there was a trade-off relationship between the static pressure efficiency and the fan noise. We then selected the optimized fan that had the same noise level as the baseline fan but with an improved static pressure efficiency. The blade tip of the optimized fan was curled toward the suction side direction. Finally, we confirmed through experiments that the static pressure efficiency of the optimized fan was increased by 1.6% compared to the baseline fan.

Quantitative Evaluation of Flow-Induced Fan Casing Structural Vibration and Noise Radiation of Air-Conditioner Outdoor Unit

2014 ◽  
Author(s):  
Xifeng Zhao ◽  
Jinju Sun ◽  
Renheng Gao ◽  
Zhi Zhang ◽  
Weifei Xue
Keyword(s):  
Quantitative Evaluation ◽  
Noise Level ◽  
Sound Radiation ◽  
Numerical Approach ◽  
Structural Vibration ◽  
Aerodynamic Noise ◽  
Response Analysis ◽  
Air Conditioner ◽  
Radiation Boundary Conditions ◽  
Noise Radiation

Noise level of AC (Air-Conditioner) outdoor unit fan system has always been receiving much concern. It involves both aerodynamic noise and vibroacoustic noise. But most previous studies have been focused on aeroacoustics, and less attention is paid to the latter. The objective of present study is to identify the influential factors of vibroacoustic noise and quantify its contribution to the overall noise level of the fan system. A numerical approach has been developed for predicting the flow-induced fan casing vibration and noise radiation. A fluid-solid-sound unidirectional coupling technique is used to transfer the unsteady loading to the structure, and the results arising from structural vibration analysis are used as sound radiation boundary conditions. Unsteady fan flow is solved by Large Eddy Simulation (LES) method. Then, the fluid force produced by the fluctuating pressure component acting on the inner casing surfaces is obtained, and it is used as external excitation in the Finite Element Analysis (FEA) model of the casing structure. Further, harmonic response analysis is conducted and the obtained results are used to calculate sound radiation through Indirect Boundary Element Method (IBEM), while the displacement amplitude obtained in structural analysis is used as boundary condition. Experimental tests are conducted respectively on fan aerodynamic and aeroacoustic performance, and casing vibration. The numerical approach is partially validated by the experimental data. The validated models are used to predict the vibroacoustic noise, based on which, a quantitative evaluation of its contribution to overall sound level is conducted.

Development of High Efficiency and Low Noise Cross-Flow Fans for Room Air Conditioner Indoor Unit

2014 ◽  
Author(s):  
Hironobu Yamakawa
Keyword(s):  
High Efficiency ◽  
Length Distribution ◽  
Cross Flow ◽  
Low Noise ◽  
Navier Stokes ◽  
Outer Diameter ◽  
Air Conditioner ◽  
Blade Edge ◽  
Sinusoidal Shape ◽  
Cross Flow Fan

Cross flow fans are used for fan systems in a household room air conditioner indoor unit. In recently, in the view of environmental problem and cost saving, energy saving performance is important specification for users. Reducing fan motor electric power consumption is effective for this purpose. And also low noise fans are needed for comfortable circumferences. To meet these user needs, we developed a high efficiency and silent cross flow fan using CFD (Computational Fluid Dynamics) and experiments. In CFD, numerical model is calculated by commercial software using steady state, Reynolds-averaged Navier-Stokes (RANS) and k-ε turbulent flow model. The developed cross flow fan is geometrically characterized by the solidity (the ratio of the blade pitch and blade cord length) distribution, and the blade edge shape. The solidity average of developed fan was larger than the conventional fan and the solidity distribution was smooth. And the developed fan has the sinusoidal shape of the outer diameter edge. This sinusoidal shape edge makes pressure distribution on the tongue to be more dispersed compare to that of conventional straight edge so that tonal noise was restrained.

The Influence of the Exit Velocity Profile on the Noise of a Jet

1954 ◽  
Vol 4 (4) ◽  
pp. 341-360 ◽  
Author(s):  
Alan Powell
Keyword(s):  
Velocity Profile ◽  
Noise Level ◽  
Turbulent Pipe Flow ◽  
Aerodynamic Noise ◽  
Noise Levels ◽  
Flow Forming ◽  
Flow Velocity Profile ◽  
Jet Velocity ◽  
Initial Turbulence ◽  
Moving Fluid

SummaryThe noise levels of a jet issuing from a long pipe are compared with those of a jet having a square velocity profile at the exit. A subsonic noise reduction of between 2 and 5 decibels for various conditions is found for the case of the flow emerging with an approximately “turbulent pipe-flow” velocity profile for the same maximum jet velocity, but this is at the expense of a loss in thrust of a quarter. On comparison with a jet of smaller diameter which has an equal thrust for the same maximum jet velocity, it is found that the changes in noise level are rather smaller. For jets of equal diameters, the effects on the subsonic aerodynamic noise generated of a reduction of velocity gradient near the boundary are more than offset by the increased velocities necessary near the centre of the jet to obtain equal thrust. It is concluded that if the effect of differences in initial turbulence can be neglected the use of an auxiliary flow forming a comparatively thin sheath of slower moving fluid at the exit is not likely to result in large decreases in the subsonic noise level, and that a general reduction in jet velocity is more effective.Above the critical pressure larger reductions of up to 10 decibels are found. These are consistent with a delay of the onset of the self-maintained shock-produced noise.

scholarly journals Investigating the In-Flow Characteristics of Multi-Operation Conditions of Cross-Flow Fan in Air Conditioning Systems

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 959
Author(s):  
Weijie Zhang ◽  
Jianping Yuan ◽  
Qiaorui Si ◽  
Yanxia Fu
Keyword(s):  
Pressure Distribution ◽  
Flow Rate ◽  
Total Pressure ◽  
Air Conditioning ◽  
Pressure Pulsation ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Operating Conditions ◽  
Aerodynamic Noise ◽  
Cross Flow Fan

Cross-flow fans are widely used in numerous applications such as low-pressure ventilation, household appliances, laser instruments, and air-conditioning equipment. Cross-flow fans have superior characteristics, including simple structure, small size, stable airflow, high dynamic pressure coefficient, and low noise. In the present study, numerical simulation and experimental research were carried out to study the unique secondary flow and eccentric vortex flow characteristics of the internal flow field in multi-operating conditions. To this end the vorticity and the circumferential pressure distribution in the air duct are obtained based on the performed experiments and the correlation between spectral characteristics of multiple operating conditions and the inflow state is established. The obtained results show that when the area of the airflow passage decreases while the area of the eccentric vortex area gradually increases, then the airflow of the cross-flow fan decreases, the outlet expands, and the flow pattern uniformity reduces. It was found that wakes form in the vicinity of the blade and the tail of the volute tongue, which generate pressure pulsation, and aerodynamic noise. The pressure distribution along the inner circumference shows that the total minimum pressure appears in the eccentric vortex near the volute tongue and the volute returns near the zone. Moreover, it was found that the total pressure near the eccentric vortex is significantly smaller than that of the main flow zone. As the flow rate decreases, the pressure pulsation amplitude of the eccentric vortex region significantly increases, while the static and total pressure pulsation amplitudes are gradually increased. Close to the eccentric vortex on the inner side of the blade in the volute tongue area, total pressure is low, total pressure on the outside of the blade is not affected, and pressure difference between the inner and outer sides is large. When the flow rate of the cross-flow fan is 0.4 Qd, there is no obvious peak at the harmonic frequency of the blade passage frequency. This shows that the aerodynamic noise is caused by the main unstable flow.

Calculation of Aerodynamic Noise for Centrifugal Fan of Air-Conditioner

2013 ◽  
Author(s):  
Taku Iwase ◽  
Hideshi Obara ◽  
Hiroyasu Yoneyama ◽  
Yoshinobu Yamade ◽  
Chisachi Kato
Keyword(s):  
Sound Pressure ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Coarse Grid ◽  
Aerodynamic Noise ◽  
Absolute Velocity ◽  
Centrifugal Fan ◽  
Air Conditioner ◽  
Simulation Code ◽  
Fine Grid

Flow fields in a centrifugal fan for an indoor unit of an air-conditioner were calculated with finite element method-based large eddy simulation (LES) with the aim of predicting fan performance and aerodynamic noise in this study. The numerical simulation code employed throughout the LES was called FrontFlow/blue (FFB). We compared 10M grid [coarse grid] and 60M grid [fine grid] calculation results for investigation of influence of grid resolution. In the fine grid, the number of grid elements in blade-to-blade direction, and of region between the shroud and the bell mouth increased in particular. By calculating with the fine grid, calculated distributions of absolute velocities at blade exit reasonably agreed with experimental results. Because of this, maximum absolute velocity by fine grid near hub decreased as compared to those by coarse grid. Calculated sound pressure level by fine grid was therefore smaller than that by coarse grid, and the overestimation of sound pressure was suppressed by calculating with fine grid. This decrease of the absolute velocity was a first factor for the improvement of calculation accuracy. Moreover, number of captured streaks on the blade, hub, and shroud surfaces by fine grid increased as compared to those by coarse grid. As a result, size of streak by fine grid became smaller than that by coarse grid. Static pressure fluctuations by fine grid on the blade, hub, and shroud surfaces therefore reduced as compared to those by coarse grid. Aerodynamic noise was related to static pressure fluctuations according to Curle’s equation. This reduction of static pressure fluctuations was therefore a second factor for improvement of calculation accuracy.

Simulation of Flow and Heat Transfer in a Moving Bed Reactor With Cross Flow

2008 ◽  
Author(s):  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Relative Velocity ◽  
Solid Phase ◽  
Cross Flow ◽  
Vertical Direction ◽  
Momentum Equation ◽  
Solid Matrix ◽  
Flow And Heat Transfer ◽  
Temperature Distributions ◽  
Solid Phases

Heat transfer in a porous reactor under cross flow is investigated. The reactor is modeled as a porous bed in which the solid phase is moving horizontally and the flow is forced into the bed in a vertical direction. Equations are time-and-volume averaged and the solid phase is considered to have a constant imposed velocity. Additional drag terms appearing the momentum equation are a function of the relative velocity between the fluid and solid phases. Turbulence equations are also affected by the speed of the solid matrix. Results show temperature distributions for several ratios of the solid to fluid speed.

scholarly journals Thermal Decomposition of a Single AdBlue® Droplet Including Wall–Film Formation in Turbulent Cross-Flow in an SCR System

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2600
Author(s):  
Kaushal Nishad ◽  
Marcus Stein ◽  
Florian Ries ◽  
Viatcheslav Bykov ◽  
Ulrich Maas ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Relative Velocity ◽  
Pipe Wall ◽  
Film Formation ◽  
Droplet Diameter ◽  
Cross Flow ◽  
Operating Conditions ◽  
Wall Film ◽  
Wall Interaction ◽  
Scr System

The selective catalytic reduction (SCR) methodology is notably recognized as the widely applied strategy for NOX control in exhaust after-treatment technologies. In real SCR systems, complex unsteady turbulent multi-phase flow phenomena including poly-dispersed AdBlue® spray evolve with a wide ranging relative velocity between the droplet phase and carrier gas phase. This results from an AdBlue® spray that is injected into a mixing pipe which is cross-flowing by a hot exhaust gas. To reduce the complexity while gaining early information on the injected droplet size and velocity needed for a minimum deposition and optimal conversion, a single droplet with a specified diameter is addressed to mimic a spray featuring the same Sauter Mean Diameter. For that purpose, effects of turbulent hot cross-flow on thermal decomposition processes of a single AdBlue® droplet are numerically investigated. Thereby, a single AdBlue® droplet is injected into a hot cross-flowing stream within a mixing pipe in which it may experience phase change processes including interaction with the pipe wall along with liquid wall–film and possible solid deposit formation. First of all, the prediction capability of the multi-component evaporation model and thermal decomposition is evaluated against the detailed simulation results for standing droplet case for which experimental data is not available. Next, exploiting Large Eddy Simulation features the effect of hot turbulent co- and cross-flowing streams on the dynamic droplet characteristics and on the droplet/wall interaction is analyzed for various droplet diameters and operating conditions. This impact is highlighted in terms of droplet evaporation time, decomposition efficiency, droplet trajectories and wall–film formation. It turns out that smaller AdBlue® droplet diameter, higher gas temperature and relative velocity lead to shorter droplet life time as the droplet evaporates faster. Under such conditions, possible droplet/wall interaction processes on the pipe wall or at the entrance front of the monolith may be avoided. Since the ammonia (NH3) gas generated by urea decomposition is intended to reduce NOX emission in the SCR system, it is apparent for the prediction of high NOX removal performance that UWS injector system which allows to realize such operating conditions is favorable to support high conversion efficiency of urea into NH3.

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