Influence of diffuser on aerodynamic noise of a forward curved fan

In order to clarify the influence of a diffuser on the characteristics of a forward curved fan,the influence of the bare ratio and the outlet angle on the characteristics of the fan were measured through an experiment performed with an actual fan as well as through a numerical simulation,respectively.The mechanism of the discrete frequency noise generated by the separated flow of the diffuser was analyzed.The optimized bare ratio was approximately 17%.The flow separated inside of the diffuser generated discrete frequency noise owing to the interaction between the reversed flow from the diffuser and the impeller rotating at the blade passing frequency.The diffuser outlet angle influenced the pressure ratio more than that by the bare ratio.Furthermore,it was confirmed that restraining the separation in the diffuser effectively decreases the fan noise.     

Influence of separated vortex on aerodynamic noise of an airfoil blade

In order to clarify the mechanism by which aerodynamic noise is generated from separated flow around an airfoil blade, the relation between the attack angle and the aerodynamic noise of the blade was analyzed using a wind tunnel experiment and a CFD code. In the case of rear surface separation, the separated vortex which has a large-scale structure in the direction of the blade chord is transformed into a structure that concentrates at the trailing edge with an increase in the attack angle. The aerodynamic noise level then becomes small according to the vortex scale in the blade chord. When the flow is separated at the leading edge, a separated vortex of low pressure is formed at the vicinity of the trailing edge. The pressure fluctuations on the blade surface at the vicinity of the trailing edge become large due to the vortex in the wake. It is considered that the aerodynamic noise level increases when the flow is separated at the leading edge because the separated vortex is causing the fluctuations due to wake vortex shedding.     

Prediction of dynamic and aerodynamic characteristics of the centrifugal fan with forward curved blades

The main aim of this paper is determine the centrifugal fan with forward curved blades aerodynamic characteris- tics based on numerical modeling. Three variants of geometry were investigated. The first, basic ＂A＂ variant con- tains 12 blades. The geometry of second ＂B＂ variant contains 12 blades and 12 semi-blades with optimal length [1]. The third, control variant ＂C＂ contains 24 blades without semi-blades. Numerical calculations were per- formed by CFD Ansys. Another aim of this paper is to compare results of the numerical simulation with results of approximate numerical procedure. Applied approximate numerical procedure [2] is designated to determine char- acteristics of the turbulent flow in the bladed space of a centrifugal-flow fan impeller. This numerical method is an extension of the hydro-dynamical cascade theory for incompressible and inviscid fluid flow. Paper also par- tially compares results from the numerical simulation and results from the experimental investigation. Acoustic phenomena observed during experiment, during numerical simulation manifested as deterioration of the calcula- tion stability, residuals oscillation and thus also as a flow field oscillation. Pressure pulsations are evaluated by using frequency analysis for each variant and working condition.     

Mechanism of tonal noise generation from circular cylinder with spiral fin

The pitch of the spiral finned tube influences seriously to the acoustic resonance in the heat exchanger.In this research,the flow characteristics in relating to the aeolian tone from the finned cylinder are studied by the numerical simulation.It is observed that the tonal noise generated from the finned tube at two pitch spaces.The ratio of the fin pitch to the cylinder diameter is changed at 0.11 and 0.27.The tone level increases and the frequency decreases with the pitch shorter.The separation flow from the cylinder generates the span-wise vortices,Karman vortices,and the separation flow from the fin generates the stream-wise vortices.When the fin pitch ratio is small,the stream-wise vortices line up to span-wise and become weak rapidly.Only the Karman vortices are remained and integrate in span.So the Karman vortex became large.This causes the low frequency and the large aeolian tone.     

Influence of wake dynamics on the performance and aeroelasticity of wind turbines

Wind turbines are currently a rapidly expanding form of renewable energy. However, there are numerous technological challenges that must be overcome before wind energy provides a significant amount of power in the United States. One of the primary challenges in wind turbine design and analysis is accurately accounting for the aerodynamic environment. This study is focused on a comprehensive verification and validation of the NREL FAST code, which is enhanced to include a free vortex wake model. The verification and validation is carried out through a comparison of blade lift distribution, wind turbine power and force and moment coefficients using a combination of CFD and experimental data. The results are also compared against Blade Element Momentum theory, and results from a 2001 double-blind NREL study on the prediction capabilities of wind turbine modeling tools. Results indicate that the enhanced aeroelastic code generally provides improved predictions. However, in several notable cases the predictions are only marginally improved, or even worse, than those generated using Blade Element Momentum theory aerodynamics. It is concluded that modeling of the aerodynamic environment remains incomplete, even after inclusion of wake effects. One important aspect identified is modeling of the unsteady aerodynamic lift characteristics of the rotor. Finally, the aeroelastic response in the combined presence of wake effects and inflow turbulence is examined. Significant differences are observed in loads, power, and structural response between results computed using the free wake model or simpler models, such as Blade Element Momentum theory.     

The unsteady pressure field and the aerodynamic performances of a Savonius rotor based on the discrete vortex method

The aim of this paper is to numerically explore the non-linear two-dimensional unsteady potential flow over a Savonius rotor and to develop a code for predicting its aerodynamics performances. In the model developed, the rotor is represented in a median plane by two semicircles, displaced along their common diameter. The two semicircles can be considered to produce lifting effects. As a result, they are modelled by a collection of discrete vortices on their contours. The flow field is then governed by the Laplace equation. The versatile Neumann boundary condition, applied over the contour of the semicircles and the Kutta Joukowsky condition applied at the four extremities of the semicircles have been used in the modelling. The torque distribution of the stationary rotor and the unsteady pressure field on the blades of the rotating rotor, predicted by the code developed, have been compared and validated by some experimental data.     

Performances and acoustic noise of micro multi-blade fan

In this paper, the performances and the acoustic noise of the traditional type micro multi-blade fan were investi- gated experimentally and numerically, to optimize the specifications of the fan for the resident circumstances. The acoustic noise level decreases but the efficiency deteriorates slightly with the increase of the blade number of the impeller. Besides, the acoustic noise decreases with the increase of the distance between the impeller outlet and the volute tongue, in accompanying with the increase of the input and the deterioration of the fan efficiency.     

Near wake flow analysis of a vertical axis wind turbine by stereoscopic particle image velocimetry

The development of the near wake of a vertical axis wind turbine is investigated by stereoscopic particle image velocimetry. The experiments are conducted in an open-jet wind tunnel on an H-shaped rotor, operated at a tip speed ratio of 4.5 and at an average chord-based Reynolds number of 1.7 × 10⁵. Phase-locked measurements are acquired at the turbine mid span in order to study the horizontal wake dynamics at the symmetry plane. Results show the evolution of the vorticity shed by the blade, how it organizes in large scale vortical structures at the edges of the wake and the resulting asymmetric induction field in the wake. The evolution of the blade tip vortices and the 3D wake geometry are detailed by a second set of measurements acquired at several vertical planes aligned with the free stream. The dynamics of the system of tip vortices, their vertical motion and interactions are discussed and related to the geometry and the recovery of the wind turbine wake. The experimental data are made publicly available for research purposes.     

基于FLUENT的可变；呙流节气门流场仿真

节气门开度是影响发动机进气的一个关键因素。可变涡流节气门利用进气涡流来组织气流运动,对传统节气门起到了进气加强的作用。本文建立了可变涡流节气门的数学模型,并在FLUENT软件里面进行了流场计算。结果表明,由于阀片的斜向打开设计,可变涡流节气门在进气过程中产生了涡旋运动,进气流速增加,流量进一步增强,在一定程度上可以起到进气增压的目的,从而可以多喷入燃油,使燃料燃烧更彻底,提高发动机的动力性和经济性。     

Two improvements to the dynamic wake meandering model: including the effects of atmospheric shear on wake turbulence and incorporating turbulence build‐up in a row of wind turbines

The dynamic wake meandering (DWM) model is an engineering wake model designed to physically model the wake deficit evolution and the unsteady meandering that occurs in wind turbine wakes. The present study aims at improving two features of the model:

相似文献   

Empirical and numerical analysis of small wind turbine aerodynamic performance at a plateau terrain in Kenya

Kenya's energy depends on fossil fuels and the country is yet to embrace alternative sources that are environmentally friendly. In this paper, empirical and computational approaches are presented to investigate aerodynamic performance of Small Wind Turbine (SWT) operation at arid rural Mwingi-Kitui plateau region, Kenya. We used empirical statistics to represent wind resource, and Computational Fluid Dynamics (CFD) to address SWT aerodynamic performance at the site. The numerical simulations, employing Transition Shear Stress Transport (SST) model and fully mesh resolved rotor, were performed and results obtained compared with empirical methods. From the Wind Power Density (WPD) values, 44.50–85.48 W/m² between turbine hub heights 20 and 60 m, the site corresponds to wind class ≈1; hence unsuitable for grid-connected power generation. In addition, the numerical findings give useful insights to SWT aerodynamic performance with respect to empirical approach at a plateau terrain wind regime.     

Prediction of hub corner stall characteristics of a highly loaded low speed single stage fan

In this paper a numerical investigation has been presented on the stall mechanism of a highly loaded Single Stage Low Speed Fan designed for the research test facility to be installed at North Western Polytechnic University (NWPU) Xi’an, China. The results presented are for the design point, near stall and just stall operating conditions at design speed. Design point studies have been found to be an indicative of stall area. Unsteady method of domain scaling has been used to compute the results at near stall and just stall conditions. It has been found that unlike the conventional tip leakage flow of the rotor, stator hub section is mainly responsible for the stall of the fan. The flow mechanism has been discussed with correlation to the design variables and previous investigations. Commercial CFD code NUMECA FINE/Turbo has been used for computations; results have been compared with results obtained from commercial CFD code ANSYS-CFX. The loss prediction of latter code is conservative than the former. The stall mechanism predicted by both codes is analogous.     

Study on noise of rapeseed oil blends in a single-cylinder diesel engine

This study was undertaken to obtain the knowledge necessary for reducing noise of mixed oil composed of rapeseed oil and conventional diesel oil and for improving the performance of engine fuelled by the mixture. A S195 (8.8 kW) type single-cylinder diesel engine was used to determine the effect of four adjustable working parameters, i.e. intake-valve-closing angle (α), exhaust-valve-opening angle (β), fuel delivery angle (θ) and injection pressure (P, in 10⁴ Pa) on noise when an oil mixture of 30% rapeseed oil and 70% diesel oil was used. Single-factor and multi-factor quadratic regressive orthogonal design test method were adopted in the experiments to find the relationship between noise and four adjustable working parameters. Relationship between these parameters and noise was analysed under two typical operating conditions and mathematical equations characterizing the relationship were formulated. The equation of noise from the regressive test under each operating condition was set as the objective function and the ranges for the four adjustable working parameters were the given constraint condition. Models of nonlinear programming were then constructed. Computer-aided optimization of the working parameters for 30:70 rapeseed oil/diesel oil mixed fuel was achieved. Field test verified that the engine (in use) working condition was found to be bad at maladjustment. The optimum working parameters for two working conditions of the engine were used to adjust the four working parameters. Test results showed that optimum adjustment could achieve noise reduction between 2 and 4 dB and that the power could be increased by 0.6–1.8 kW. The experimental results also provided useful reference material for selection of the most preferable combination of working parameters.     

The wake structure in a 2D grid installation of the horizontal axis micro wind turbines

In order to develop applications for micro-wind turbines, an experimental analysis of the flow field around integrated micro-wind turbines was performed. The wake flows of a single turbine and 5×5 array unit were measured by using hot-wire and ultrasonic anemometers and particle image velocimetry (PIV). The present array of turbines follows a fundamental lattice layout; however, it has the flexibility to optimize its layout according to the environmental conditions. hot-wire and ultrasonic anemometers and PIV measurements were used for stand-alone turbines and their integrated systems. Comparisons between the mean velocity field and turbulent intensity were described for stand-alone full-scale and 1/10-scale wind turbine models. Thereafter, a typical array of the 1/10-scale model was assumed and its wake flow was investigated in a wind tunnel. The velocity profile and turbulence behind the array were measured and studied at different streamwise locations. The scale effect and model similarities were discussed. The experimental results show that a zone exists with constant and linear wake deficit ratios in the downstream regions.     

基于深度学习的翼型气动弹片流场参数预测

弹片是解决翼型流动分离的重要技术手段,合理的弹片参数对翼型表面压力分布尤为重要。基于数据驱动的深度学习方法与计算流体力学(Computational Fluid Dynamics, CFD)相结合,可快速有效地完成对复杂流场特征的识别与提取。本文提出一种基于卷积神经网络(Convolutional Neural Network, CNN)的翼型表面压力分布预测方法,通过提取流场的尾流速度、压力等流动特征构建翼型表面压力分布的预测模型。首先,通过数值模拟计算了8种不同抬起角度的NACA 0012弹片翼型的流场;其次,采用提取的流场数据建立CNN预测模型;最后,将预测值和CFD计算值进行对比。结果表明：基于CNN的预测模型对翼型表面压力系数分布有较高的预测精度,其中尾流速度模型在弹片抬起角度为15°时的预测均方根误差仅为0.1,说明尾流速度中包含丰富的流场信息。     

大容量锅炉尾部烟道空气动力场研究

阐述了北方农村秸秆高效利用技术研究的重要意义;对各种秸秆高效利用技术进行了分析,指出了它们推广应用的技术关键。秸秆固化成型技术在近期已经具备一定推广应用条件。秸秆成型燃料燃烧特性艮好,且便于储存和运输。秸秆成型加工可以作为秸秆燃料的预处理技术,为各种秸秆的高效利用技术特别是直接燃烧技术准备原料。秸秆成型机技术已有较大进步,进一步研究需要在降低能耗和提高成产率方面开展。     

Prediction of ash flow temperature based on liquid phase mass fraction by FactSage

To investigate the relationship between flow temperature (FT) and the temperature that corresponds to different liquid phase mass fractions, the FTs of 10 coal ashes and 45 synthetic ashes were tested by an ash-fusion-temperature analyzer. The linear correlation between the FT and the temperature that corresponded to a 90% liquid phase (T₉₀) calculated by FactSage was: FT = 245.837 + 0.765T₉₀, and its correlation coefficients was 0.91. This model may be more accurate for low Si/Al coal. The differences between measured and predicted FT based on the model were in the measuring error range.     

Influence of the karman vortex street on the broadband noise generated from a multiblade fan

Introduction Multiblade fans are widelyused in domestic airconditioners, commercial sanitary apparatuses, etc. In the case of these fans, decreasing the fan noise is one of the important technical issues for its comfortable operation. The spectra of the fan noise showed that the noise is composed of a few types of aerodynamic noise. This noise comprises not only a discrete frequency noise due to the interference with the wake and the tongue of the scroll casing but also a broadband noise dist…     

Numerical simulations of wake characteristics of a wind turbine in uniform inflow

The wake of a wind turbine operating in a uniform inflow at various tip speed ratios is simulated using a numerical method, which combines large eddy simulations with an actuator line technique. The computations are carried out in a numerical mesh with about 8.4·10⁶ grid points distributed to facilitate detailed studies of basic features of both the near and far wake, including distributions of interference factors, vortex structures and formation of instabilities. Copyright © 2009 John Wiley & Sons, Ltd.     

An experimental study on aerodynamic sound generated from wake interference of circular cylinder and airfoil vane in tandem

The purpose of this study is to investigate the characteristics of aerodynamic sound generated from wake inter-ference of circular cylinder and airfoil vane located in tandem and to clarify the generation mechanism of thesound source with discrete frequency.The effects of the interval between the cylinder and the airfoil on the char-acteristics of aerodynamic sound are investigated by acoustic measurement,flow visualization and explorationtest of sound source.The relation between the flow field and the sound field with discrete frequency noise(DFN)is shown,and then it is found that the downstream airfoil works as the sound source of DFN,which has the fre-quency of vortex shedding from the upstream cylinder,when the interval of two bodies is longer than a criticaldistance.