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Appropriate changes to the blade tip pattern can effectively improve fan performance. In this research, the effect of two blade tip patterns and speed variation on aerodynamic performance of a ducted axial-flow fan was numerically investigated. In order to ensure the accuracy of the solving method, numerical results were compared with the experimental data from wind tunnel of the NACA Propeller-Research Center. Numerical results show that both the coefficients of pressure and torque increases with the appropriate groove at the tip of the blade. But due to the higher rate of increase in the coefficient of pressure than that of the torque, aerodynamic efficiency has also increased significantly. This increase has been observed in both patterns and in all operational speed of the fan. But, the increase in aerodynamic coefficients had rising trend up to 3000 rpm and, then, declined. The results determine the best pattern for the tip of the blade. In fact, the structure of the groove is such that it traps a rotating airflow with high kinetic energy at the tip, and this vortex, like a barrier, prevents air leakage. This causes reduction in losses due to mixing of the leakage flow and passage flow. With increasing fan rpm, the generated vortexes in tip groov are amplified, which, in addition to a further decrease in the leakage flow rate from the tip region, increases the viscosity and turbulence losses in the area. [ABSTRACT FROM AUTHOR]

Axial flow fans play key roles in the thermo-flow performance of direct dry cooling system under windy conditions, so the energy efficiency of a power generating unit can be improved by optimizing the operation strategies of the axial flow fans. In this work, various measures based on the partition adjustment of axial flow fans with constant power consumption of a 2 × 660 MW power plant are studied by computational fluid dynamics (CFD) methods. The results show that increasing the rotational speed of the windward fans is beneficial to reduce the inlet air temperature and increase the mass flow rates of the fans, which enhance the heat rejections of the air-cooled condensers, especially at high wind speeds. Moreover, the turbine back pressures for the optimal and original cases are achieved by iterative methods, with the largest drop of 2.77 kPa at the wind speed of 12 m/s for 110-case 3 in the wind direction of −90°. It is recommended to adopt 110-case 1 and 110-case 3 at low and high wind speeds, respectively, in the wind directions of 90° and −90°, while 110-case 2 is always the best choice in the 0° wind direction.

Abstract In the present paper, the fuzzy c-means method is extended, and an algorithm is proposed for fuzzy clustering of data lying in a feature space of arbitrary dimensions, with one of them being periodic. To aid in determining the optimal number of clusters, the Xie-Beni validity index is extended, to account for the periodicity. Furthermore, the relative weights of the dimensions in the calculation of distances are investigated. The method is incorporated into a procedure for processing turbomachinery beamforming maps. Thus, an objective, robust way of identifying the sound sources being present in such machines is obtained. These properties are ensured by selecting the required parameters through parameter studies. Presented through a case study, the method is used to determine the most significant sound source mechanisms in an axial fan. [ABSTRACT FROM AUTHOR]

Highlights • Winglets increase the efficiency of the partially shroud-covered axial fan. • Winglets decrease the efficiency of the 100% shroud-covered axial fan. • The fan efficiency is not the highest with 0 tip clearance in partial shroud. • The fan efficiency is the highest with certain tip clearance in partial shroud. Abstract This study is concerned with the improvement in efficiency of axial flow fans that are being used in numerous fields including outdoor units of air conditioners. The tip leakage flow occurring between a blade tip and shroud is one of the major losses in the axial flow fan. A well-known method used to control such tip leakage flow is locating winglet on the suction side of blade tips. Only a few articles have studied the impact of tip clearance on the flow structure of tip leakage flow of axial flow fans with winglet. In this study, the flow structure occurring on the blade tip due to the location of a winglet was analyzed. We confirm the existence of an optimal tip clearance which results in the maximum efficiency for an axial flow fan with a shroud height measuring 30% of the axial chord length. [ABSTRACT FROM AUTHOR]

In this study, some of the optimal parameters for a new-style marine axial flow fan are defined by using numerical simulation and experimental tests with a large marine axial flow fan, based on the analysis of the blade perforation’s influences on its internal flow field and aerodynamic noise characteristics. Test result shows that the noise reduction for the axial flow fan with perforated blade is about 3 dB when the blade perforation diameter D is 10 mm and its deflection angle α is 45°. The results of the study show that there is an inhibitory effect on the discrete noise of axial flow fan with perforated blade on the tip area, and its total noise level emerged as the fluctuated distribution characteristics with the increase in the perforation diameter D and reduced along with the increase in the deflection of perforation angle α, at the same time varied as a linear characteristics, which can be reasonably explained by the acoustic interference theory. The results of the study have also further confirmed that the improvement of the flow of axial flow fan with perforated blade helps to reduce the pressure pulsation amplitude caused by the turbulence of the blade surface boundary layer, thereby suppressing the back-flow and vortex from the pressure surface to the suction surface efficiently. It is indicated that the improved vortex shedding phenomenon at the blade trailing edge after perforation on the area of blade tip is the main reason for the aerodynamic noise reduction of axial flow fan. [ABSTRACT FROM AUTHOR]

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The effect of tip clearance in an axial fan on its aerodynamic and aeroacoustic performance is investigated experimentally as well as via a Lattice–Boltzmann flow simulation method. An increase in tip clearance degrades fan pressure rise and efficiency, but also increases significantly the overall sound power emitted by the fan. A large tip clearance causes a clear structure of well distinguishable unsteady vortices which interact with neighboring blades and hence produce an increase in broadband sound. Moreover, if, compared to the design flow rate, there is a moderate flow rate reduction, the local tip vortex systems of all individual blade tips form a circumferentially coherent flow structure, resulting in distinct humps of sound pressure in the acoustic far field. By means of a rigid ring-type protrusion fixed to the inner casing wall, the generation of the tip clearance vortices and slowly rotating coherent flow structures could be suppressed. As a consequence, the sound emitted by the fan is substantially reduced. [ABSTRACT FROM AUTHOR]

This paper proposes the use of microplates as a new flow control device to suppress boundary layer separation on blades and thus improve the aerodynamic performance of a low-speed axial flow fan. A computational study is performed by means of computational fluid dynamics (CFD) simulations. Numerical investigations are carried out based on Reynolds-averaged Navier-Stokes (RANS) method. The shear stress transport (SST) turbulence model and high-quality computational grids are adopted for CFD simulations. An exhaustive comparison of the fans with and without control has been conducted in terms of characteristic curves, streamlines and pressure distributions. The purpose of this work is to better understand the underlying flow control mechanisms of microplates. It is found that the total efficiency is slightly lowered when the controlled fan operates at the design flow rate. However, as the flow rate changes, the total efficiency of the controlled fan varies more gently than the original fan without control. Traced streamlines show that flow separation on blade surfaces is effectively controlled and radial flow migration on the suction surface is evidently diminished. Numerical results indicate that microplates significantly alleviate fan stall and have considerable beneficial effects on fan performance. [ABSTRACT FROM AUTHOR]

Purpose: This study focuses on one of the key design aspects of mine ventilation fans, i.e. the selection of an appropriate aerofoil blade profile for the fan blades in order to enhance the energy efficiency of axial flow mine ventilation fans, using CFD simulations. Methods: Computational simulations were performed on six selected typical aerofoil sections using CFD code ANSYS Fluent 6.3.26 at angles of attack varying from 0° to 21° at an interval of 3° and at Reynolds number Re=3×106 , and various aerodynamic parameters, viz. coefficients of lift (Cl) and drag (Cd) as a function of angle of attack (α) were determined to assess the efficiency of the aerofoils. Results: The study revealed that the angle of attack has a significant effect on the lift and drag coefficients and stall condition occurred at α values of 12° and 15° in most of the aerofoils. Based on the criterion of higher lift to drag ratio (Cl/Cd), a blade profile was chosen as the most efficient one for mine ventilation fans. Practical implications: This study forms a basis for selecting appropriate blade profiles for the axial flow fans used for ventilation in mining industry. Originality/value: The application of an appropriate aerofoil blade profile will impart energy efficiency to the mine ventilation fans and thereby result in energy saving in mine ventilation.

In this study, different designs of the opening pattern of computer fan grills were investigated. The objective of this study was to propose a simulation analysis and compare it to the experimental results for a set of optimized fan designs. The FLUENT computational fluid dynamics (CFD) simulation software was used to analyze the fan blade flow. The experimental results obtained by the simulation analysis of the optimized fan designs were analyzed and compared. The effect of different opening pattern designs on the resulting airflow rate was investigated. Six types of fans with different grills were analyzed. The airflow velocity distribution in the simulated flow channel indicated that the wind speed efficiency of the fan and its influence were comparable with the experimental model. The air was forced by the fan into the air duct. The flow path was separately measured by analog instruments. The three-dimensional flow field was determined by performing a wind speed comparison on nine planes containing the mainstream velocity vector. Moreover, the three-dimensional curved surface flow field at the outlet position and the highest fan rotation speed were investigated. The air velocity distribution at the inlet and the outlet of the fan indicated that among the air outlet opening designs, the honeycomb shaped air outlet displayed the optimal performance by investigating the fan characteristics and the estimated wind speed efficiency. These optimized designs were the most ideal configurations to compare these results. The air flow rate was evenly distributed at the fan inlet.

We report on the low noise optimization of an axial fan specifically designed for the cooling of CSP power plants. The duty point presents an uncommon combination of a load coefficient of 0.11, a flow coefficient of 0.23 and a static efficiency ηstat > 0.6. Calculated fan Reynolds number is equal to Re = 2.85 × 107. Here we present a process used to optimize and numerically verify the fan performance. The optimization of the blade was carried out with a Python code through a brute-force-search algorithm. Using this approach the chord and pitch distributions of the original blade are varied under geometrical constraints, generating a population of over 200000 different possible individuals. Each individual was then tested using an axisymmetric Python code. The software is based on a blade element axisymmetric principle whereby the rotor blade is divided into a number of streamlines. For each of these streamlines, relationships for velocity and pressure are derived from conservation laws for mass, tangential momentum and energy of incompressible flows. The final geometry was eventually chosen among the individuals with the maximum efficiency. The final design performance was then validated through with a CFD simulation. The simulation was carried out using a RANS approach, with the cubic k-ε low Reynolds turbulence closure of Lien et al. The numerical simulation was able to verify the air performance of the fan and was used to derive blade-to-blade distributions of design parameters such as flow deviation, velocity components, specific work and diffusion factor of the optimized blade. All the computations were performed in OpenFOAM, an open source C++- based CFD library. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations on the effect of deflecting rings featuring different axial lengths on aerodynamic performance of the small axial flow fan were conducted under the condition of maximum flow rate. Two deflecting rings, the semi-open type and closed type, were investigated. Aerodynamic and aeroacoustic performances have been measured in experiment, and key analysis of flow was based on computational fluid dynamics results. The numerical and experimental results show that the deflecting ring has great influence on the performance of an axial flow fan. For the semi-open-type deflecting ring, the fan has better P-Q performance and higher efficiency; pressure, vorticity, and vorticity gradient distributions on the blade surface are more uniform; and noise level of the fan is lower at wider frequency bands. For the closed-type deflecting ring, the performance curve has a convex feature; blade pressure difference between the pressure surface and the suction surface is much bigger. The result shows that better aerodynamic and aeroacoustic performances of the axial flow fan can be acquired when the semi-open-type deflecting ring is adopted. [ABSTRACT FROM AUTHOR]

The effect of five blade tip patterns on performance and acoustics of a twin-stage variable-pitch axial fan is investigated numerically. The best tip pattern is determined by comparing the overall performance under the condition of those patterns carving in stage I impeller, and the performance promotion is then examined under the selected tip grooving in stage I impeller, stage II impeller and both two stage impellers. Finally, flow dynamics and acoustic noise are explored. The results show that all proposed tip patterns can improve fan performance effectively, and the best scenario is the direct groove tip implementing in stage I impeller. After blade tip grooving, the internal dynamics in the tip clearance tends to be more complex, the static pressure reduces notably in the suction side and the sound power level in the tip increases significantly, while the leakage losses decline distinctly. Blade tip pattern changes the profile and amplitude of the sound pressure in time domain; the base frequency and first five−order harmonics are clearly observed in two stage impellers, but only the second−order harmonics are emerged in the other regions. The noise is generated largely by low and medium frequency sound with an obvious broadband feature. [ABSTRACT FROM AUTHOR]

An objective and algorithmised methodology is proposed to analyse beamform data obtained for axial fans. Its application is demonstrated in a case study regarding the tip region of a low-speed cooling fan. First, beamforming is carried out in a co-rotating frame of reference. Then, a distribution of source strength is extracted along the circumference of the rotor at the blade tip radius in each analysed third-octave band. The circumferential distributions are expanded into Fourier series, which allows for filtering out the effects of perturbations, on the basis of an objective criterion. The remaining Fourier components are then considered as base sources to determine the blade-passage-periodic flow mechanisms responsible for the broadband noise. Based on their frequency and angular location, the base sources are grouped together. This is done using the fuzzy c-means clustering method to allow the overlap of the source mechanisms. The number of clusters is determined in a validity analysis. Finally, the obtained clusters are assigned to source mechanisms based on the literature. Thus, turbulent boundary layer – trailing edge interaction noise, tip leakage flow noise, and double leakage flow noise are identified. [ABSTRACT FROM AUTHOR]

In order to investigate the impact of blade tip winglet position on the internal flow and noise characteristics of axial flow fans,three different blade tip winglets,namely the TSW blade, the SSW blade, and the PSW blade,were hereby proposed. The accuracy of the simulation model was verified through experiments, and the circumferential internal flow characteristics and noise characteristics of these different blades were studied by numerical simulation using the blade tip partition method. The calculation results indicated the high-level efficiency of TSW, SSW and PSW blades in reducing the blade tip leakage flow in Z1 and Z2 regions and suppressing its circumferential propagation in the Z3 region. Besides, it was found that SSW blade and PSW blade had larger total pressure loss relative to Ori blade, and that TSW had higher total pressure difference at low blade height. Additionally TSW blades performed the best in improving the blade tip blockage,while TSW, SSW and PSW blades effectively reduced the leakage flow against the main stream, and blade tip winglet blades could effectively improve the fan discrete noise, SSW had the most significant noise reduction effect in the total sound pressure level, and in the overall blade,Z1, Z2 and Z3 were reduced by 2.16 dB,1.68 dB,2.24 dB and 3.74 dB., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors. Published by Elsevier Ltd.)

Radial-vaned air separators produce strong stall improvement effect in axial flow fans. Changes in the fan internal flow patterns achieved by the device are confirmed by Pitot traverse measurements. For the air separator condition, with a decrease in the fan flow rate the meridional streamline inclinations through the rotor blades have become increasingly steep and the circumferential velocities increase toward the tip region, in contrast to relatively little changes in the behaviors of the streamlines and flow patterns in the solid wall condition. It is suggested that the stall suppression is achieved by a combination of the following effects of the air separator; (1) suction of casing boundary layers and elimination of embryos of stall, (2) separation of reversed flow from the main flow, (3) induction of the flow toward the casing wall and strengthening of meridional streamline inclination, thus keeping the Euler head increasing, and (4) reinforcement of axi-symmetric flow structure. Appearance of these effects in the descending order is considered to achieve the great stall suppression effect that would be difficult by other types of stall prevention devices.

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depend on the distance between hub-cap and blade leading edge. Three-dimensional Reynolds-averaged Navier-Stokes equations are introduced to analyze the flow characteristics inside the blade passage. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces separated flow on the blade surfaces near the hub region, and thus deteriorates the performance of fan rotor. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

The recent development of small and lightweight rack mount servers and computers has resulted in the decrease of the size of cooling fans. However, internal fans still need to achieve a high performance to release the heat generated from interior parts, and they should emit low noise. On the contrary, measurement data, such as flow properties and flow visualizations, cannot be obtained easily when cooling fans are small. Thus, a numerical analysis approach is necessary for the performance evaluation and noise reduction of small cooling fans. In this study, the noise of a small cooling fan used for computers or servers was measured and then compared with the aeroacoustic noise result based on a numerical analysis. Three-dimensional Navier-Stokes equations were solved to predict the unsteady flow field and surface pressure fluctuation according to the blades and casing surface used. The simplified Ffowcs Williams and Hawkings equation was used to predict aeroacoustic noise by assuming that a dipole is the major cause of fan noise. Results of the aeroacoustic noise analysis agreed well with that of the experiment, and a tonal noise whose frequency was lower than the first blade passing frequency could be identified in the noise spectrum. This phenomenon is caused by the shape of the bell mouth. A coherence analysis was performed to examine the correlation between the shape of the cooling fan and the noise. [ABSTRACT FROM AUTHOR]

The cooling effectiveness of air-cooled steam condenser units is impacted by the performance of the large diameter axial flow cooling fans, which ultimately affects the overall efficiency of the power plant. Because of the large diameters of these fans, performance tests are carried out at test facilities with smaller, standardized diameters and measuring equipment. The performance of the large scale fans can be predicted based on the small scale test results using the similarity laws and scale-up formulae. This article details the results of small scale experimental tests and numerical simulations that were performed on a pair of 1.25 m diameter axial flow fans. Full scale, 10.360 m, diameter simulations of the same axial flow fans were subsequently performed and compared with the experimental results that were scaled up using the fan scaling laws. [ABSTRACT FROM AUTHOR]

The effect of the deviation angle of an abnormal blade Δ β on the performance of an axial fan is investigated using 3D steady simulation. The sound pressure distribution in the time and frequency domains is examined using LES (large eddy simulation) and FW–H (Ffowcs Williams–Hawkings) noise model. The energy features of the sound pressure are extracted using WPD (wavelet packet decomposition) and EMD (empirical mode decomposition). The results show that under the abnormal condition, fan performance is lower than normal value and the noise rises. The main noise sources are concentrated on the leading edge and tip of the suction surface. The aerodynamic noise is generated mainly by low-frequency sound, and the impeller exhibits an obvious broadband sound feature. In the regions outside of the impeller, the wavelet packet energy in the fundamental frequency band under abnormal conditions is much lower than that under the normal condition, and the difference becomes significant with increasing Δ β . The EMD energy features appear as obvious changes in the relative percentages of the intrinsic mode function energies; the energy entropy is closely related to the deviation angle. The characteristics obtained by WPD and EMD provide significant references for detecting the deviation angle in axial flow fans. [ABSTRACT FROM AUTHOR]

Modelling air-cooled condensers (ACCs) incorporating hundreds of fans, necessitates the use of simplified fan models when performing a computational fluid dynamics (CFD) analysis of the condenser. The perimeter fans in these ACCs are subjected to distorted inlet flow conditions. This paper compares the accuracy of three different simplified fan models and proposes an improved model, based on numerical and experimental results from representative fan configurations. Three different fan configurations are tested as perimeter fans in a three-fan test facility, and their results compared to CFD results. The experimental evaluation by particle image velocimetry (PIV) reveals the shape of the velocity profiles immediately upstream of the perimeter fan. The accuracy of the CFD-predicted flow field directly upstream of the perimeter fan varies according to the model used to represent the fan as well as the configuration of the specific perimeter fan. The paper indicates a discrepancy of as much as 30% between experimental and simulated volumetric effectiveness values for a specific simulation model and fan configuration. The standard and extended actuator disc fan models perform better than the pressure jump model in predicting the volumetric effectiveness of the perimeter fans, and the extended actuator disc model performs best at predicting fan inlet velocity profiles. [ABSTRACT FROM AUTHOR]

We describe a mechanical/acoustic study of a short-ducted axial flow fan. The purpose is to compare mechanical noise to that caused by flow phenomena. The eigenfrequencies of the fan are identified through measurement and finite element computations. The fan acoustics is evaluated by beamforming studies using the Phased Array Microphone technique. The acoustic measurement data is processed by the Rotating Source Identifier method. The modal analysis of the fan model and the acoustic experiments reveal that the fan noise is dominated by mechanical noise in the few hundred Hz range and rotating sources of broadband noise above. [ABSTRACT FROM AUTHOR]

Appropriate changes to the blade tip structure can effectively improve fan performance. The performance of the OB-84 axial fan with different grooved blade tips is simulated using Fluent. The effects of various tip structures on the flow field, losses distribution, and noise characteristics are investigated. Analysis of static structure and vibration characteristics is performed with the Ansys finite element analysis module. Simulated results show that for the grooved blade tips, both the total pressure rise and shaft power of the fan decrease, but the efficiency improves distinctly; the grooved blade tip structure perturbs the flow and vortex fields and impedes the development of the leakage flow; this eventually results in the reduction of mixing losses between the leakage flow and mainstream. Blade tip case 4 produces the maximum efficiency with an increase of 1.07% at design volume flow rate, and case 7 obtains the lowest shaft power compared with the original tip. Grooved blade tips amplify the fan noise, so measures should be taken to control the noise. Analysis of dynamic characteristics reveals that the distortion and fracture failure of the blade as well as resonance of the impeller would not occur by adopting grooved blade tips. [ABSTRACT FROM AUTHOR]

The paper aims at discovering the relationship between the spanwise gradient of blade circulation and the total efficiency gain due to forward sweep, in the case of low-speed axial flow fans, at the design point. For this purpose, an extensive set of literature data have been processed and evaluated by statistical means. A trend function has been established for quantifying the aforementioned relationship. By such means, it has been pointed out that the efficiency gain due to forward sweep tends to increase with the spanwise gradient of blade circulation. This means that the purposeful incorporation of forward sweep in the design process offers an increased potential for efficiency improvement in the case of rotors of controlled vortex design. The maximum efficiency gain has been observed to be 2% to 3%, due to an in-house developed design method. It has been noted that the efficiency improvement due to forward sweep tends to be minor for free-vortex rotors. Furthermore, the efficiency tends to deteriorate if spanwise decreasing blade circulation occurs in forward-swept rotors. Remarks have been made on the means of simultaneous reduction of loss and noise related to low-speed axial fans, for a prescribed aerodynamic performance. [ABSTRACT FROM AUTHOR]

Off-statistics input data sets are common in axial-flow fans design and may easily result in some violation of the requirements of a good aerodynamic blade design. In order to circumvent this problem, in the present paper, a solution to the radial equilibrium equation is found which minimizes the outlet kinetic energy and fulfills the aerodynamic constraints, thus ensuring that the resulting blade has acceptable aerodynamic performance. The presented method is based on the optimization of a three-parameters vortex law and of the meridional channel size. The aerodynamic quantities to be employed as constraints are individuated and their suitable ranges of variation are proposed. The method is validated by means of a design with critical input data values and CFD analysis. Then, by means of systematic computations with different input data sets, some correlations and charts are obtained which are analogous to classic correlations based on statistical investigations on existing machines. Such new correlations help size a fan of given characteristics as well as study the feasibility of a given design. [ABSTRACT FROM AUTHOR]

Three dimensional steady and unsteady velocity distributions in the axial flow fan were measured using a hot wire probe for various operational conditions, various rotational speeds and various measuring positions. For measuring the velocity distributions in the blade passage, a specially designed and manufactured hot wire traversing apparatus was used. Steady velocity distributions, turning angles, effects of incident to the cascade, flow leakage through the tip clearance and effects of the flow separation show the flow phenomena through the blade passages. Unsteady velocity distributions show time dependent procedures of the wake flowing through the moving blade passage. Considering these results of measurements, the effects of the upstream stationary blade and the effects of Reynolds number on the flow were considered.

Highlights: [•] It is of use to propose anti-freezing measures for air-cooled condenser. [•] Heat load capacity matching principle for the anti-freezing is suggested. [•] Anti-freezing steam flow rate increases with decreasing ambient temperature. [•] Anti-freezing fan flow rate increases with increasing exhaust steam flow rate. [•] Back pressure can be much more reduced at secure steam flow rates. [ABSTRACT FROM AUTHOR]

A radial flow rotor with radially aligned straight blades, used in electric motor cooling, has been considered as datum fan. The aerodynamic performance and acoustic behaviour of the datum fan have been measured, in order to establish a basis for redesign. As replacement for the datum fan, an axial flow shrouded rotor with skewed blades has iteratively been designed, involving computational fluid dynamics and computational aero-acoustics tools. The aim of redesign was reducing fan noise and moderating motor shaft power absorbed by the fan, while retaining the original cooling performance. Special flow features have been taken into consideration in three-dimensional axial rotor design, such as leakage flow in the axial clearance between the rotor shroud inlet and the perforated cover, and strong radial flow as well as deviation due to the motor shield located close downstream. The axial rotor has been manufactured via rapid prototyping. Measurements on the prototype confirmed the achievement of the redesign goal. The effect of axial clearance size on the operation of the axial rotor has been investigated by computational fluid dynamics, computational aero-acoustics and experimental means. It has been pointed out that the axial clearance size is a sensitive parameter in influencing fan aerodynamics and aero-acoustics, for which the major mechanisms, associated with the leakage flow, were qualitatively identified. Both the computational and experimental studies revealed the existence of an acoustically unfavourable clearance size, for which maximum noise emission can be expected. A semi-empirical model was outlined as starting point in prediction of cooling flow rate as a function of axial clearance size as well as other parameters. [ABSTRACT FROM PUBLISHER]

Highlights: [•] The visualisation of a flow field was performed within the rotor blades passage. [•] Phase-locked averaging on the blade passing and rotating stall event was performed. [•] 1020 PIV images were sorted and phase-locked averaged to replicate rotating stall. [•] A sequence of images was composed presenting a flow field changing over 10° angular steps. [•] The initiation and development of flow distortion and flow normalisation were clearly shown. [ABSTRACT FROM AUTHOR]

Abstract: The study has focused on outdoor unit noise reduction by fan geometry modification with the refined numerical and experimental approaches. The outlet louver, electric motor and its support are included to refine the flow and acoustic model and a hybrid method incorporating CFD and CAA is used to predict the noise behavior. The fan performance curve is well-predicted; the moderate acoustic power is obtained on the outlet louver, motor support and motor exhibiting a significant contribution to overall noise behavior. The aeroacoustic test is conducted in an anechoic chamber and the obtained results are compared with the semi-anechoic chamber ones, and the unremarkable differences are produced, which indicate the ground floor being of some influence. Both modified fan geometries are effective to reduce the noise but the flanging outer-edge blade is more effective. The noise directivities of three geometry fans are investigated both numerically and experimentally and the produced asymmetric characteristics are analyzed. [Copyright &y& Elsevier]

In this paper, the unsteady characteristics of tip leakage flow in axial fans with circumferential skewed blades were investigated at off-design conditions using wall pressure test. The static pressure fluctuations near blade tip were captured at off-design conditions by using pressure sensors mounted on casing wall. From the measured results, instantaneous characteristics of tip leakage flow in circumferential skewed fans were analyzed. Based on the measurement results, as the flow rate decreases, the broadband frequency components of tip leakage flow tend to increase in the low frequency domain. The forward-skewed blade is found to be effective in controlling tip leakage flow to expand from blade leading edge to tail edge, the TLF component of the BSK rotor propagates more fast than that of FSK rotor. The instability of tip leakage flow under off-design conditions is controlled by circumferential skewed blades. [ABSTRACT FROM AUTHOR]

The flow field of an axial fan in a direct air-cooled condenser for a large power plant is modeled numerically. In order to improve the efficiency of heat exchange of the air-cooled condenser, methods of increasing the rotational velocity of the fan and laying out the guide blade at the outlet of the fan are adopted. Results show that increasing the rotational velocity of the fan can effectively increase the flux of the fan, and can improve the efficiency of an air-cooled condenser; laying out the guide blade at the fan outlet can ameliorate the flow field in an A-flame. This causes the rotational kinetic energy to change into static pressure at the fan outlet, so the ability of the heat exchange of the air-cooled condenser is improved. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21027 [ABSTRACT FROM AUTHOR]

Flexible printed circuit boards (FPCBs) are going to replace rigid boards (PCBs) in numerous electronic devices due to their reduced thickness and ability to bend and adapt to various shapes. Deflection and stress are key factors affecting the reliability of FPCBs. In this paper, the fluid flow solver FLUENT and structural solver ABAQUS, are used to study the deflection and stress induced by axial flow fan on FPCBs, in the fan sucking mode. The flow is assumed to be 3-D, laminar, compressible, and steady. The effect of air flow rate on the force acting on the components mounted on the FPCB is analyzed. In the structural simulation using ABAQUS, the deflection and stress are observed for nine cases of different mounting options of the FPCB, at a fixed air flow rate. The proper selections of air flow rate and mounting option are found to be crucial in minimizing the flow induced deflection and stress in FPCBs. [ABSTRACT FROM PUBLISHER]

Abstract: The topic treated in these experimental investigations is the wall pressure fluctuations in axial flow fans. Steady and unsteady wall pressure measurements of an automotive cooling fan have been achieved. In fact, in order to predict the flow induced noise, a predictive tool which can model wall pressure fluctuations in complex geometries is required. Computational Fluid Dynamics (CFD) coupled with semi-empirical aeroacoustic models is used. The models using Reynolds Averaged Navier–Stokes (RANS) equations are chosen as they are able to predict flow characteristics well for configurations of practical interest. Then semi-empirical models that predict the surface pressure power spectra are used with the RANS boundary layer data. Since these models were developed for flows over a flat plate, a test rig allowing the acquisition of wall pressure on the blade of an axial flow fan is designed and manufactured. Flush mounted compact pressure sensors and a slip ring enable the measurement of wall pressure in rotation. Mean surface pressure data from numerical simulation are compared with experimental ones. The wall pressure spectra levels computed with semi-empirical models are underestimated in the low frequency range (100–2000Hz) but match quite well in the high frequency range (2–10kHz). [Copyright &y& Elsevier]

Abstract: CFD method could replace experiment for development of a fan, but it cannot be applicable to some of real design stage because of limitation that rotating speed must be set as boundary condition. That is, most experiments without a Dynamo set only voltage of a motor as input condition. The remarkable difference between the above mentioned experiment and the current CFD is that the rotating speed varies with flow rate. Therefore, the numerical results calculated by the boundary condition of constant rotating speed have limitation of real application, and especially, when predicting efficiency, there exists a striking difference from the real situation. In this article, we developed a new algorithm in which we are able to determine both static pressure and rotating speed through setting up the only voltage as a boundary condition with motor performance test results. The new developed algorithm on the basis of experiment and CFD showed good qualitative and accurate results with a significant difference of less than 5%. [Copyright &y& Elsevier]

Abstract: Ambient wind plays important roles in the thermo-flow performances of air-cooled condensers, but the wind effect mainly imposes on the upwind and bilateral condenser cells and will decay immediately. It is of benefit to the design and operation optimization of air-cooled condensers in a power plant to investigate the wind effect and its decay characteristics. On the basis of a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flows for the air-cooled condensers at various ambient wind speeds and directions are set up. The velocity and temperature fields are presented and the volumetric flow rate, inlet air temperature and heat rejection for different condenser cells are obtained by using CFD simulation. The results show that the reversed flows happened in the upwind condenser cells lead to the high inlet air temperature, worsening the cooling capability of air at high wind speeds. Due to the combined behavior of hot plume discharge and ambient wind, the wind effect decays rapidly along the wind direction. At the wind direction of 90°, the deficiencies of the thermo-flow performances of air-cooled condensers are mainly resulted from the flow rate decrease of the upwind condenser cells, not the hot plume recirculation. The hot plume recirculation flows play adverse roles in deteriorating the performances of air-cooled condensers at the wind direction of 0°. [Copyright &y& Elsevier]

Special A-frame geometry of the air-cooled condenser cell and the complicated flow field at the exit of the axial flow fan bring on the air mal-distribution on the surface of the finned tube bundles and the deteriorated thermo-flow performances of a condenser cell. It is of benefit to the design and operation optimization of the direct dry cooling system in a power plant to investigate the thermo-flow characteristics of the condenser cell and propose the flow leading measures of cooling air. On the basis of the representative configuration of the air-cooled condenser cell in a 600 MW direct dry cooling power plant, the computational models of the air side fluid and heat flows are built, in which the actual fan blade geometric details are considered. Various flow field leading ways of cooling air are presented and the thermo-flow characteristics in the A-frame condenser cell and through the finned tube bundles are compared. Results show that the flow field leading measures can result in the increased volumetric flow rate and heat rejection, thus bringing on the improved performance of the condenser cell. The improvement of thermo-flow performances depends upon the geometric details of the flow guiding device. [ABSTRACT FROM AUTHOR]

Small size axial flow fans are used as a cooling component for computers, electronic equipment and other electronic components. With the increasing power of electrical equipment, the demand for lower noise and higher ventilation of cooling fan is also increasing. Traditional methods of improving ventilation by raising the fan's rotation speed causes a decrease in efficiency and an increase in noise. In this paper, different structures of fans were simulated, and as a result, the counter-rotating fan can achieve higher pressure, efficiency and facilitate ventilation in a smaller space. Furthermore, some other conclusions are as follows: The simulation results are of important significance to the quantitative analysis and optimization design of the counter-rotating fan. [ABSTRACT FROM AUTHOR]

The aerodynamic behavior of tens of axial flow fans incorporated with air-cooled condensers in a power plant is different from that of an individual fan. Investigation of the aerodynamic characteristics of axial flow fan array benefits its design optimization and running regulation. Based on a representative 2×600 MW direct-dry cooling power plant, the flow rate of each fan and the overall flow rate of the fan array are obtained in the absence of ambient wind and at various wind speeds and directions, using CFD simulation. The cluster factor of each fan and the average cluster factor of the fan array are calculated and analyzed. Results show that the cluster factors are different from each other and that the cluster effect with ambient wind is significantly different from the cluster effect with no wind. The fan at the periphery of the array or upwind of the ambient wind generally has a small cluster factor. The average cluster factor of the array decreases with the increasing wind speeds and also varies widely with wind direction. The cluster effect of the axial flow fan array can be applied to optimize the design and operation of air-cooled condensers in a power plant. [ABSTRACT FROM AUTHOR]

A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter, including calculation of aerodynamic parameters and performance parameters. When calculating inlet shock loss, the shock loss coefficient is obtained by comparing results of theoretical calculation, experimental and numerical calculation. The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition. Tip leakage vortex moves downstream as flow rate increases. When flow rate decreases, Re decreases, and boundary layer thickness from hub to shroud area all increases gradually. Tip leakage vortex moves upstream, and secondary loss increases. Low speed area in the passage is widened along with high speed area moving to hub area, influenced by boundary layer separation. Consequently wake area and jet area at fan outlet are both larger than rated condition. Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss. A reliable method is supplied for estimating altitude performance of lubricating system in helicopter. [ABSTRACT FROM AUTHOR]

Abstract: A newly developed computational approach different from the conventional methods which are popularly adopted by the fan designers is employed to study the flow field and performance characteristics of an axial flow fan by using the commercial code (STAR-CD) of computational fluid dynamics. The new approach, which is termed the “downstream flow resistance” (DFR) method, engages the flow resistance of the fan test bench in the downstream area of the computational domain. Both the static and moving grids are employed in the computation. The results show at least three emphases. Firstly, the deviations of the calculated fan performance curves from the experimental results can attain levels less than 3% and 1.5% by using the DFR method with static-grid and moving-grid schemes, respectively. These results present dramatic improvement over the maximum deviation of about 26% obtained by using the conventional method with the static-grid scheme. Secondly, usage of the static or moving grids for the purpose of fan performance prediction is no longer an important issue when the DFR method is employed because both the static and moving grids show almost identical results. Thirdly, the stall occurs when the aerodynamic contour of the fan blade is inappropriately designed for the mid and high back-pressure operations. Under this situation, recirculation bubble would appear around the trailing edge of the suction surface of the fan blade, and therefore obstructs the development of the flow. At deep-stall, large recirculation flow structures may even appear around the pressure surface and block the passage between the neighboring fan blades to cause the reduction of flow rate. [Copyright &y& Elsevier]

Abstract: The purpose of this work is to study the influence of the axial flow fan sweep on the downstream turbulent flow. The fans studied are three low-pressure and low-Mach-number axial flow fans, with respectively a radial, a forward and a backward sweep. Experimental and computational fluid dynamics (CFD) investigations are carried out on three fans, and the results are compared. The CFD method is a three-dimensional (3D) Reynolds average Navier–Stokes (RANS) numerical simulation with the Reynolds stress model (RSM) as the turbulence model. It allows us to compute the Reynolds stress tensor components. Unsteady velocity measurements are carried out downstream of the fans with hot-wire anemometry. The values of the three velocity components of the flow and the six components of the Reynolds stress tensor obtained from experiments and simulations are compared. Overall performances are also measured to validate the design and fan simulation. It appears that a forward sweep decreases the radial component of the velocity whereas a backward sweep increases this component. Moreover, the sweep has a significant influence on the turbulent kinetic energy downstream of the fan. [Copyright &y& Elsevier]