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With the increased usage of air filtration and deodorization devices in livestock houses, the demand of agricultural axial flow fans with higher pressure has been raised. To improve the aerodynamic performance of an agricultural axial fan and expand its operating range, a new axial fan was developed using the theory of variable circulation method design via wind tunnel experiments and numerical simulations. The purpose is to change the structural form at the hub of the existing blade to improve the internal flow pattern of the agricultural axial fan, so as to achieve the purpose of improving the aerodynamic performance of the agricultural axial fan and expanding the range of stable operation. In this paper, a new agricultural axial flow fan is designed using the variable circulation method with 0.91m agricultural axial flow fan size and target airflow as design parameters. Secondly, the structural parameters at the hub of the axial fan are optimized by combining the simulation results of the flow field of the designed fan. Factors such as hub diameter d, the placement angle α and the number of moving blades n are analyzed individually, revealing the basic law of the influence of the changes of these factors on the performance of the fan, and the influence of the changes of each factor on the internal flow field of the fan is observed in combination with post-processing. using the better intervals for each factor derived from the one-factor optimisation results, the ventilation volume Q and the energy efficiency ratio N were selected as response values, and a response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface functional equations were obtained and the better parameter combinations were determined. The correctness of the functional model is further verified by observing the flow field characteristics and external characteristics through post-processing. Finally, the optimised impeller was fabricated by 3D printing technology and wind tunnel tests were conducted, and the results of the actual tests further confirmed the accuracy of the optimisation results. The numerical simulation results of the study show that the optimum combination of these parameters is d=260 mm, α=-0.369°, and n=4 pieces. Experimental test results show that the optimized axial fan performance is better than initial axial fans. On the high-pressure level (120 Pa), the ventilation volume Q of agricultural axial fan increased by 163%, and the energy efficiency ratio N increased by 18.9%. This study proves the feasibility of the variable circulation method in the design of high-pressure agricultural axial flow fan, and the optimization of structural parameters can further reduce the internal vorticity of the fan. The optimized axial fan reduced the secondary flow in the internal flow field, increased the work capacity of the blades, and improved the aerodynamic performance of the fan, ensuring that the axial fan can achieve air circulation and regulation more efficiently in agricultural applications. [ABSTRACT FROM AUTHOR]

In the context of controlling axial fan aerodynamic noise, one effective approach involves the redesign of the blade. In the present study, a novel blade design was formulated for a specific model of axial flow fan, targeting the mitigation of the tip leakage vortex (TLV) and subsequent reduction of noise levels. The assessed noise-reduction blades have perforations drilled from the leading edge (LE) to the pressure surface (PS) of the blades. By impeding the tip leakage flow (TLF), these perforations effectively weaken the TLV. The three-dimensional non-constant flow field within the channel is computed employing the shear stress transport (SST) turbulence model. The aerodynamic noise prediction, which is based on the Lighthill's acoustic analogy theory, shows that the designed blades can effectively reduce the aerodynamic noise of the axial fan. Specifically, enhancing the ratio of inlet area to outlet area of the ventilation holes leads to an improved noise reduction effect. Notably, for ratios of 0.44 and 1.06, the designed blades exhibit noise reductions of up to 3.3 dB(A) and 3.9 dB(A), respectively. Meanwhile, the static efficiency of these two fans is reduced by 0.50% and 0.26%, respectively. The study thus provides good theoretical support for the design of axial flow fans in the context of noise reduction. [ABSTRACT FROM AUTHOR]

ObjectivesAs the main equipment of the dry cooling system, the aerodynamic performances of axial flow fans play an important role in the flow and heat transfer performances of the direct dry cooling system. Because the flow and heat transfer problems of the air-cooled island spans multiple scales in geometric dimensions, the experimental method is hard to realize while the numerical simulation method is usually used. Therefore, it is necessary to discuss and analyze the accuracy of simplified lumped parameter fan model (i. e., the simplified model) used in the previous simulation work.MethodsBased on the numerical simulation method, the real model containing the fan blade fan model (real model) model and the simplified model were both built. Under different weather conditions, the transport properties of the direct dry cooling system were studied. The comparison and analysis of the air-side pressure field and flow field distributions were conducted. Furthermore, the pressure drops and flow rate of the cooling air through the axial flow fan in each air-cooled condenser cell of the direct dry cooling system with different fan models were analyzed and compared.ResultsThe difference between the real model and the simplified model is mainly reflected for the axial flow fans with low flow rates, and the difference becomes more obvious with the increase of wind speed.ConclusionsThe results of this paper can provide reference for improving the accuracy of numerical simulation of the direct dry cooling system.

An axial flow fan is designed for dry cooling of a sCO2 Brayton cycle for a CSP plant, and a scaled model of the fan is manufactured and tested experimentally in an ISO 5801:2017 Type A fan test facility. While the design procedure's estimate of the total-to-static efficiency at the design flow rate is relatively high, at 74.4%, the experimental fan efficiency was found to be only 50.6%. This paper details an investigation into the causes of fan performance degradation, using both experimental and numerical methods. The investigation finds that the hub configuration, tip clearance size, and scale of the test fan is responsible for the reduced performance. Two alternative hub and casing configurations are identified which improve the fan's performance significantly. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Axial flow fan is a mechanical fan that generates airflow in the same direction as its rotational axis. These fans find widespread use in various applications, including ventilation, cooling, and air circulation across industrial, commercial, and residential settings. However, designing these fans can be challenging in the fan manufacturing industry due to the need to accommodate diverse operating conditions. This complexity arises from the fact that multiple design parameters significantly influence fan performance, requiring careful consideration and optimization to ensure efficient operation across various scenarios. In this paper, we present a technique for monitoring and maintenance of axial flow fans using hybrid optimal deep learning with IoT system. Our method leverages the pre-trained U-Net architecture to extract hidden features effectively from the dataset. Furthermore, we introduce an improved triple tree-seed optimization (IT2SO) algorithm for feature optimization, which identifies the most optimal features among the extracted ones. To make informed decisions about axial flow fan process monitoring, we propose the deep boosted hybrid learning (DBHL) technique as the decision model to maintain the proper operation. To validate the effectiveness of proposed IT2SO+DBHL technique, we have conducted experiments using the air movement and control association international (AMCA) dataset. The results demonstrate the superior performance of our monitoring approach compared to existing techniques across various evaluation measures. [ABSTRACT FROM AUTHOR]

It is essential to maintain the aerodynamic performance of the air-conditioning system meanwhile reducing the noises (including aerodynamic, broadband, and discrete noises), determining the consumer's comfort level. In this work, depending on the coupling of the wavy leading-edge and the seagull airfoil, the aeroacoustics noise and aerodynamic performance of the impellers with the coupling bionic blade were investigated in detail. The results indicate the aerodynamic performance was improved by the coupling bionic optimization. Moreover, the total pressure efficiency (η) of the coupling bionic blade increases by 2.28% in comparison to the original blade. Furthermore, A smaller static differential pressure is observed between the suction and pressure sides, and vortices and backflows from the pressure side to the suction side are hampered, causing a reduction in turbulence noise. Additionally, the broadband noise of the coupling bionic blade decreases by 3.59 dB. Besides, the coupling bionic blade improves the directivity of the sound pressure level, especially in the middle-frequency and low-frequency region, resulting in a decrease of 7.9 dB for the aeroacoustics noise of the coupling bionic blade. What's more, the modal analysis demonstrates the security of the designed coupling bionic blade. In generally, this work provides some inspiration to design axial flow fans with excellent aerodynamic performance and low-noise characteristics.

Higher capacity of negative pressure suction has been required in the traditional agricultural axial fan, particularly with the increase of filtration and deodorization devices in livestock and poultry farming. This study aims to improve the aerodynamic performance of agricultural axial fans, and then to expand their working range. A common type-550 axial fan was taken as the research object. The inlet guide vanes were added under the experiments and numerical simulations. The single factor and response surface analysis were selected to investigate the effects of guide vane installation angle (α), axial distance (L), and number of guide vane (n) on the fan performance and flow field. The influence of each factor on the performance of the fan was then obtained, according to the response surface analysis. The best combination of installation parameters was achieved for the better performance of the axial fan. A series of 3D-printed fan and tunnel experiments were carried out to verify the best combination of installation parameters of inlet guide vanes. Numerical simulation results showed the improved performance was represented by four perspectives after the addition of the inlet guide vane. Firstly, the inlet guide vane was adjusted to a suitable installation angle. After that, the meridian plane axial velocity increased significantly to black the leakage vortex extension to the inlet. As such, the static pressure efficiency was improved, due to the weak internal vortex, and the reduced flow loss. Secondly, the inlet guide vane was adjusted to a suitable installation distance. The fully pre-rotating was found in the inlet flow of the high span, leading to a more uniform flow in the axial flow fan. Thirdly, a suitable number of blades was set in the inlet guide vane. There was a decrease in the intensity of flow change in the inner channel of the axial flow fan, indicating a more stable flow field. Finally, there was an increase in the static pressure difference at the limit position of the blade pressure surface and suction surface, particularly with the higher working capacity of the fan blade. The better performance was achieved with an guide vane mounting angle of −25° to −15°, axial distance of 57 to 81mm, and a number of guide vane of 4 to 6. Specifically, the installation parameters were obtained with the guide vane mounting angle α=−21°, the axial distance L=57 mm, and the number of guide vane n=4. These optimal parameters were used for the installation of the 3Dprinted inlet guide vane on the fan. Tunnel experiments showed that the ventilation volume and energy efficiency ratio of the modified fan were significantly improved after adding the inlet guide vane, where the ventilation volume increased from 5.7% to 10.39%, and the energy efficiency ratio increased from 6.62% to 10.89% in the fan performance test. Furthermore, the ventilation volume and energy efficiency ratio increased by 6.76% and 7.75%, respectively, under the working condition of 50 Pa. Consequently, the addition of inlet guide vanes can be expected to enhance the negative pressure suction capacity of agricultural axial flow fans. [ABSTRACT FROM AUTHOR]

It is essential to maintain the aerodynamic performance of the air-conditioning system meanwhile reducing the noises (including aerodynamic, broadband, and discrete noises), determining the consumer's comfort level. In this work, depending on the coupling of the wavy leading-edge and the seagull airfoil, the aeroacoustics noise and aerodynamic performance of the impellers with the coupling bionic blade were investigated in detail. The results indicate the aerodynamic performance was improved by the coupling bionic optimization. Moreover, the total pressure efficiency (1) of the coupling bionic blade increases by 2.28% in comparison to the original blade. Furthermore, A smaller static differential pressure is observed between the suction and pressure sides, and vortices and backflows from the pressure side to the suction side are hampered, causing a reduction in turbulence noise. Additionally, the broadband noise of the coupling bionic blade decreases by 3.59 dB. Besides, the coupling bionic blade improves the directivity of the sound pressure level, especially in the middle-frequency and low-frequency region, resulting in a decrease of 7.9 dB for the aeroacoustics noise of the coupling bionic blade. What's more, the modal analysis demonstrates the security of the designed coupling bionic blade. In generally, this work provides some inspiration to design axial flow fans with excellent aerodynamic performance and low-noise characteristics. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented by modifying the trailing edge of the prototype fan. The effect of the bionic forked trailing edge on the aerodynamic and aeroacoustic performance was investigated experimentally, and detailed analyses of the blade load and internal vortex structures were performed based on large-eddy simulations (LES). It is shown that the bionic forked trailing edge could effectively adjust the blade load distribution, reduce the pressure difference between the pressure side and suction side near the trailing edge of the blade tip region, and weaken the intensity and influence range of the inlet vortex (IV) and the tip leakage vortex (TLV). The discrete noise caused by the vortices in the rotor tip area was also reduced, particularly at the blade passing frequency (BPF) and its harmonic frequency. The experimental results confirmed the existence of an optimal bionic forked trailing-edge structure, resulting in the maximum power-saving rate γ of 7.5% and the reduction of 0.3 ~ 0.8 dB of aerodynamic noise, with an included angle θt of 13.5°. The detailed analysis of the internal vortex structures provides a good reference for the efficiency improvement and noise reduction of axial flow fans. [ABSTRACT FROM AUTHOR]

In order to ensure the safe and reliable operation of the circulating water system of the cooling tower, the fan speed and blade installation angle of the cooling tower were set according to the maximum heat exchange. However, due to the influence of production process, ambient temperature and other related factors, the heat exchange of the cooling tower fan changes from time to time. Therefore, the cooling capacity of the cooling tower fan does not match the actual demand, resulting in a large amount of energy waste, therefore a new energy saving scheme based on the self-adjustment of the cooling tower fan blade based on the hydraulic system was proposed. Firstly, the working principle of the self-adjusting angle system was analyzed, and the structure of the self-adjusting angle mechanism was designed by using Solidworks software, and the working principle of the hydraulic drive system was analyzed. Then, the curve of the driving force provided by the hydraulic system with the change of installation angle was obtained by the method of calculating the aerodynamic load of the wind turbine. Finally, AMES im was used to explore the working characteristics of self-adjusting angle of various hydraulic circuits, and the influence of throttle valve opening on the stability of hydraulic circuits was analyzed. The research results show that the device can adjust the blade installation angle of the fan without stopping the machine. The PID speed regulating valve hydraulic circuit improves the accuracy and stability of the system. When the speed regulating valve internal throttle opening K equals 0.08, it can effectively reduce the shock time, and reduce the shock peak. [ABSTRACT FROM AUTHOR]

Axial flow fans are commonly used for a system or machinery cooling process. It also used for ventilating warehouses, factories, and garages. In the fan manufacturing industry, the demand for varying fan operating points makes design parameters complicated because many design parameters affect the fan performance. This study combines the deep neural network (DNN) with a genetic algorithm (GA) for axial flow design and development. The characteristic fan curve (P-Q Curve) can be generated when the relevant fan parameters are imported into this system. The system parameters can be adjusted to achieve the required characteristic curve. After the wind tunnel test is performed for verification, the data are integrated and corrected to reduce manufacturing costs and design time. This study discusses a small axial flow fan NACA and analyzes fan features, such as the blade root chord length, blade tip chord length, pitch angle, twist angle, fan diameter, and blade number. Afterwards, the wind tunnel performance test was performed and the fan performance curve obtained. The feature and performance test data were discussed using deep learning. The Python programming language was used for programming and the data were trained repeatedly. The greater the number of parameter data, the more accurate the prediction. Whether the performance condition is met could be learnt from the training result. All parameters were calculated using a genetic algorithm. The optimized fan features and performance were screened out to implement the intelligent fan design. This method can solve many fan suppliers' fan design problems. [ABSTRACT FROM AUTHOR]

The sound generated by axial flow fans has become increasingly important in several industrial areas. These devices represent considerable noise sources that must be considered from the design stage. The scope of this research work is to present an axial fan design methodology based on the theory of the wing lift and to compare the aerodynamic and aeroacoustics behavior with the free vortex and the non-free vortex conditions. The effect of forward circumferential sweep on the rotor blades is analyzed in both conditions, which consists of a displacement in the tangential direction in the direction of rotor rotation. A cubic polynomial function is proposed for the construction of the blade geometry with circumferential sweep. It defines the center line of the blade and it is taken at 50% of the leading edge of each blade profile. The methodology for analyzing aeroacoustics behavior in fans is based on the integration of Computational Aeroacoustics and Computational Fluid Dynamics in order to analyze aerodynamic behavior, sound power level and sound pressure level at the preliminary design stage. It was verified that although both rotors present a similar aerodynamic behavior (the NFV rotor has a slightly lower performance), according to the analysis of local sound sources, the NFV rotor presents a slight decrease in the sound sources. It was also verified that the NFV rotor presents 2.2 dB less in sound pressure level than the FV rotor.

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The axial flow fan, as a key part of the outdoor unit of air conditioner, has an important impact on the performance of air conditioner. In order to reduce the power consumption and aerodynamic noise of the outdoor unit, the outer edge profile with a depression structure, inspired by the effective control of butterfly wings for airflow, is reconstructed and adopted in the design of bionic blades. The effects of bionic blades with four different depression depths on the aerodynamic performance of the outdoor unit are investigated numerically. It is found that when the depression depth is 1.9 mm, the aerodynamic performance of the outdoor unit is the best. For the axial flow fan with the optimal design blade, the numerical simulation and experimental test on the noise of the outdoor unit are carried out. Based on the experimental results, the shaft power of the outdoor unit is reduced by 1% and the noise is reduced by 1.3 dB when the bionic blade with the depression depth of 1.9 mm is adopted. Based on the numerical results, the flow characteristics of the axial flow fan with the bionic blades is analyzed and the noise reduction mechanism of the depression structure is revealed. The studied results show that the depression structure with proper depth at the outer edge of the blades effectively changed the development and trajectory of the tip leakage vortex, which has a positive influence on the aerodynamic performance improvement and noise reduction of the axial flow fan. [ABSTRACT FROM AUTHOR]

The sound generated by axial flow fans has become increasingly important in several industrial areas. These devices represent considerable noise sources that must be considered from the design stage. The scope of this research work is to present an axial fan design methodology based on the theory of the wing lift and to compare the aerodynamic and aeroacoustics behavior with the free vortex and the non-free vortex conditions. The effect of forward circumferential sweep on the rotor blades is analyzed in both conditions, which consists of a displacement in the tangential direction in the direction of rotor rotation. A cubic polynomial function is proposed for the construction of the blade geometry with circumferential sweep. It defines the center line of the blade and it is taken at 50% of the leading edge of each blade profile. The methodology for analyzing aeroacoustics behavior in fans is based on the integration of Computational Aeroacoustics and Computational Fluid Dynamics in order to analyze aerodynamic behavior, sound power level and sound pressure level at the preliminary design stage. It was verified that although both rotors present a similar aerodynamic behavior (the NFV rotor has a slightly lower performance), according to the analysis of local sound sources, the NFV rotor presents a slight decrease in the sound sources. It was also verified that the NFV rotor presents 2.2 dB less in sound pressure level than the FV rotor. [ABSTRACT FROM AUTHOR]

Copyright of Food Science & Technology & Economy is the property of Grain Science & Technology & Economy Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise. [ABSTRACT FROM AUTHOR]

Low-speed axial flow fans are widely used especially in air conditioning and ventilation systems. The performance of axial flow fans is negatively affected by the blockage and loss resulted from the tip leakage vortex (TLV) and the reverse flow. This paper investigates the development of TLV in a partially shrouded fan used in the outdoor unit of an air-conditioning system. It was found that the TLV follows the blade tip chord, due to the radial inflow in the initial unshrouded part of the blade, unlike the fully covered fan. Thus, the TLV trajectory can be manipulated by modifying the blade tip chord shape. It was also found that the reverse flow from the outlet near the shroud is driven by the negative component of TLV. The blade tip chord was modified to be in the axial direction before reaching the shrouded part to reduce the blockage and negative component of TLV. Comparing the results for the modified blade shows that the reverse flow and TLV blockage are effectively reduced by adjusting the TLV trajectory to be along the fan's rotational axis. The maximum flow rate increased up to 12% accompanied by a noticeable reduction in the loss by the tip modification. [ABSTRACT FROM AUTHOR]

This study investigates the potential gains in operating volume flow rate and static efficiency of an induced draught axial flow fan system. These gains are achieved through pressure recovery, i.e. the conversion of dynamic pressure at the fan exit into static pressure. Pressure recovery is achieved using downstream diffusers, stator blade rows, and combinations of these. Three different diffuser lengths are considered. Of the shortest diffusers, a conical diffuser increases the operating volume flow rate by 3.2 % and the fan static efficiency by 9.8 % (absolute). A longer conical diffuser increases it by 3.9 % and 11.9 %, respectively. Of the longest diffusers, an annular diffuser increases the flow rate by 5.5 % and the fan static efficiency by 16.8 %. [ABSTRACT FROM AUTHOR]

The present study introduces an innovative aerodynamic redesign of an axial flow fan based on constant diffusion factor and radial equilibrium. All input design parameters such as mass flow rate, hub to tip ratio, aspect ratio, tip diameter and angular velocity are taken from NASA Rotor 67 as a conventional axial flow fan. A computer program is developed to extract the three-dimensional geometry of a fan and to estimate the span-wise distribution of parameters. The new designed fan flow field is investigated in detail by CFD tool at both design and off design conditions. Finally, a turbofan cycle analysis is conducted based on thermodynamic and gas dynamic principles to evaluate the fan performance in a turbofan engine in comparison to NASA Rotor 67. Achieving a higher total pressure ratio, meeting the target pressure ratio in lower rotational speed with higher efficiency, delivering more bypass air in a constant diameter and less fuel consumption for the same specific thrust force are the main advantages for the new design strategy in comparison to the conventional designed fans such as Rotor 67. However, efficiency reduction in fan over speed is the main disadvantage.

To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented by modifying the trailing edge of the prototype fan. The effect of the bionic forked trailing edge on the aerodynamic and aeroacoustic performance was investigated experimentally, and detailed analyses of the blade load and internal vortex structures were performed based on large-eddy simulations (LES). It is shown that the bionic forked trailing edge could effectively adjust the blade load distribution, reduce the pressure difference between the pressure side and suction side near the trailing edge of the blade tip region, and weaken the intensity and influence range of the inlet vortex (IV) and the tip leakage vortex (TLV). The discrete noise caused by the vortices in the rotor tip area was also reduced, particularly at the blade passing frequency (BPF) and its harmonic frequency. The experimental results confirmed the existence of an optimal bionic forked trailing-edge structure, resulting in the maximum power-saving rate γ of 7.5% and the reduction of 0.3 ~ 0.8 dB of aerodynamic noise, with an included angle θt of 13.5°. The detailed analysis of the internal vortex structures provides a good reference for the efficiency improvement and noise reduction of axial flow fans.

The fan installed in the outdoor unit of air-conditioning (AC) systems is often partially shrouded to increase the inlet area and allow the installation of a larger upstream heat exchanger. However, the effect of radial inflow from the unshrouded part on the aerodynamic performance of the fan is seldom studied. The current paper studies the flow structure in a partially shrouded fan to understand the effects of radial inlet flow on the main flow and the flow in the tip region. The results showed that the flow from the unshrouded region has the same scale as the axial inflow in a partially shrouded fan. The flow field and tip leakage vortex development in the partially shrouded fan are substantially different and the loss corresponding to the TLV is intensified compared to the fully shrouded one. In a partially shrouded fan, the TLV rolls up adjacent to the tip section due to the interaction with radial inflow and follows the tip chord in the unshrouded part. The TLV then moves away from the suction surface in the shrouded part inducing a large blockage and loss at the fan outlet. A vortex street is created outside the fan by the exiting TLV which restricts the main flow from radial expansion and increases the fan backpressure. The reverse flow near the shroud is mainly driven by the TLV and can be controlled by changing the TLV trajectory. [ABSTRACT FROM AUTHOR]

A single-stage axial fan having a pressure ratio of 1.01 is designed in the current study. The design pressure ratio is chosen based on the power available from the existing motor (2.2 kW). The design space for the axial flow fan was generated by varying specific flow and geometrical parameters in suitable steps, using a program written in MATLAB. The varied flow parameters are mass flow rate, inlet Mach number, inlet flow angle, and rotor speed. The geometrical parameters that were varied are hub to tip ratio, aspect ratio, and blade solidity. Using these as the input variables and applying free vortex theory for 3-dimensional blade design, the aerodynamic design of the axial flow fan was carried out. Performance parameters like flow coefficient, stage loading coefficient, degree of reaction, diffusion factor, De Haller's number, and blade angles were calculated at the blade's hub, mean, and tip. Total design space of 92160 data points was obtained from the combination of input parameters. Several constraints were applied to optimise the design space based on the available power from the existing motor and in-house manufacturing limitations. The initial design space was reduced to 82 data points using these constraints. To further reduce the number of points in the design space, off-design performance was evaluated for each of these data points. Following this, one design point was selected based on the optimum performance range in off-design operation, while considering manufacturing limitations. Using Mellor charts, a suitable blade profile was chosen based on the inlet and exit blade angles. NACA 65-410 airfoil was selected with a stagger of 55 degrees and an incidence of 6 degrees for optimum performance. [ABSTRACT FROM AUTHOR]

For a direct dry cooling system, the turbine back pressure fluctuates with the meteorological conditions. Moreover, the operation of axial flow fans plays an important role in the cooling performance of air‐cooled condensers (ACC). It is of significant use to study the operation strategies of axial flow fans under various ambient conditions. Based on typical 2 × 660MWdirect dry cooling power generating units, the ACC model coupled with the turbine thermodynamic characteristics is developed, by which the thermo‐flow performances of the ACC are predicted in the dominant wind direction, and then the standard coal consumption is calculated. The results show that the increased ambient temperature and wind speed, or the reduced fan rotational speed leads to the high turbine back pressure. At the low ambient temperature and wind speed, the standard coal consumption rate of the unit can be reduced by reducing the speed of axial flow fans appropriately, with the maximum drop in coal consumption rate reached 0.734 g/(kWh) when the ambient temperature is 10°C without wind. If the wind speed exceeds 12 m/s or the ambient temperature reaches 25°C, 110% of the rated fan rotational speed is recommended. [ABSTRACT FROM AUTHOR]

This study illustrates that downstream diffusers can significantly aid the performance of an induced draught axial flow fan. Two conical diffusers of length 0.2 and 0.4 times the fan diameter and an annular diffuser with a length equal to the fan diameter are tested. At the design flow rate of the fan, the short conical diffuser increases the available static pressure by 17.6% and the static efficiency by 8.9 %. The medium-length conical diffuser increases it by 21.9 % and 11.7 %, respectively. The long annular diffuser produces a 28.2 % pressure increase and a 14.2% efficiency increase. The paper also compares the obtained pressure recovery coefficients of the different discharge diffusers using two-dimensional axisymmetric and threedimensional computations. It shows that the pressure at the outlet of the fan cannot be assumed to be equal to atmospheric pressure, as is prescribed by the fan testing standards. A new method of measuring pressure recovery from two-dimensional computations is proposed. [ABSTRACT FROM AUTHOR]

This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise.

Direct dry cooling system adopts large-scale axial flow fan group to cool exhaust steam of turbine. So the noise of direct dry cooling system becomes one of the hazards of power plants. By using computational fluid dynamics software Fluent, the simulation of flow field and noise forecast of direct dry cooling cell and system were performed in this paper. The changes of flow field and noise of ACCs (air-cooled steam condensers) were simulated after increasing the noise reduction wall. The large eddy simulation was applied to analyze the flow field. Noise forecast was proceeded by means of the unsteady and implicit solver. The results show that the porous sound-absorbing materials decorated inside the wind wall have no effect on the flow field of ACCs. But they could effectively reduce the noise level of ACCs, especially reducing the low frequency noise.

For poor diagnosis effect of existing fault diagnosis methods for axial flow fan based on spectrum analysis which correlated fault type with spectrum characteristic value simply, a fault diagnosis method for axial flow fan based on vector ellipsoid spectrum and hidden Markov model (HMM) was proposed. Firstly, two orthogonal vibration signals of axial flow fan in the same section are fused into a complex signal in time domain, and full-spectrum amplitudes of the vibration signals under multi characteristic frequencies are obtained by fast Fourier transform of the complex signal. Secondly, the full-spectrum amplitudes under different fault conditions are used to train HMM. Finally, full-spectrum amplitudes of real-time vibration signals are as input of HMM, and Viterbi algorithm is used to calculate likelihood probability outputted by HMM. Fault type is judged according to the maximum logarithm value of the likelihood probability, which avoids simple association between the vibration amplitude and fault type. The experimental result shows that correct rate of fault diagnosis of the method is above 90%.

Axial flow fans of outdoor units are equipped with specially shaped winglets and shroud for reduction of the flow-induced noise. In this study, the unsteady state flow field and the characteristics of the flow-induced noise according to the application of the sweptback tip winglets and 30 % covered shroud in an axial flow fan of an outdoor unit of air conditioner were experimentally and numerically analyzed. To analyze the unsteady flow field, large eddy simulation (LES) reflecting the geometry of complicated outdoor unit was performed; and the LES results were used by simplified Ffowcs Williams and Hawkings (FW-H) equation in order to calculate the noise numerically. As a result, asymmetric flow characteristics inside the outdoor unit by the mount and the shape of blade tip and shroud were found to cause inconsistent movement of the tip leakage vortex, which was revealed to change the characteristics of the flow-induced noise. [ABSTRACT FROM AUTHOR]

This study developed a computational fluid dynamics (CFD) model to assess the impact of the site of location of a commercial device (HEPA filter/ultraviolet light) on its capacity for microbial decontamination of indoor air. The three locations of the air decontamination device (ADD) in the aerobiology chamber were at the center, the middle of one of the lateral sides, and at the middle of the side in front of the axial air circulating fan. The findings were then compared to the experimental data generated in an earlier study on the same device using aerosolized Staphylococcus aureus as the challenge. The findings of the CFD model were strongly correlated to the experimental results, and the best site for the ADD was found to be at the middle of one of the lateral sides of the chamber. In this state, the microbial decontamination efficiency of the ADD was 99.46%. Additionally, this modeling study identified (a) the device's optimal location in the chamber for microbial decontamination and the device's effectiveness, (b) the axial fan's location and its ability to uniformly distribute the airborne bacteria inside the chamber, and (c) suitability of the air samples collecting from the chamber's center. The incorporation of this model could boost the design and construction of the chamber, reduce the need for laboratory experimentation, and also help to simulate and investigate an ADD's efficacy for maximum reduction of airborne pathogens. [ABSTRACT FROM AUTHOR]

The power consumption of axial flow fans may account for more than 1% of the rated power output of the power generating unit, so it is of benefit to the energy efficiency of the power generating unit to propose an operation adjustment approach to axial flow fans. On the basis of representative 2 × 600 MW direct dry cooling generating units, a computational model of air‐side flow and heat transfer of an air‐cooled condenser (ACC) combined with exhaust steam condensation is developed, by which the airflow rate, inlet air temperature of ACCs, the power consumption of axial flow fans, turbine backpressure, and net power output of power generating units at various wind speeds and in various wind directions are obtained. The results show that the net power output in the presence of winds always decreases when the rational speeds of the first upwind row axial flow fans increase from the rated speed of 79 rpm by 10% to 86.9 rpm. However, the net power output will increase in various wind directions if the rational speeds of all the fans except the upwind first row fans increase to 86.9 rpm. This can contribute to the optimal operation of the ACC by rotational speed adjustment of axial flow fans. [ABSTRACT FROM AUTHOR]

This study investigates the potential gain in operating volume flow rate and static efficiency for an induced draught fan arrangement by reducing the outlet kinetic energy loss. The reduction is achieved through pressure recovery, which is the conversion of dynamic pressure into static pressure. Downstream diffusers, stator blade rows, or a combination of these can recover pressure. Six different discharge configurations are tested for a fan. An annular diffuser with equiangular walls at an angle of 22° from the axial direction and a length equal to the fan diameter recovers the most pressure over a range of volume flow rates. The diffuser causes the operating volume flow rate and static efficiency to increase by 6.3 % (relative) and 20 % (absolute), respectively, compared to the initial design point of the particular fan. [ABSTRACT FROM AUTHOR]

Axial flow fans are used in many fields in order to ensure the mass and heat transfer from air, chiefly in the heating, ventilation and air conditioning industry (HVAC). A more proper understanding of the airflow behavior through the systems is necessary to manage and optimize the fan operation. Computational fluid dynamics (CFD) represents a real tool providing the ability to access flow structures in areas that measuring equipment cannot reach. Reducing the leakage flow rate, inherent in operation, by synthetic-jet techniques improves performance. This paper presents the CFD results performed on a hollow blade fan developed by our team. The leakage flow is controlled by blowing air from 16 designated circular holes and arranged on the fan shroud. We discuss the results for two rotational speeds (1000 and 2000 rpm) and two injection rates (400 and 800 L/min). The numerical results consistent with the experimental show, for the low rotation speed and high injection ratio, significant gains in power (53%), torque (80%) and leakage flow rate (80%).

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.

The operating conditions of axial flow fans are closely related to the thermo-flow characteristics of the mechanical draft direct dry cooling system. Moreover, the uneven distribution of cooling air driven by axial flow fans may lead to the deterioration of the heat transfer capacity of air-cooled condensers (ACCs). Therefore, developing energy-saving operating methods for axial flow fans is very meaningful. In this work, two kinds of adjustment strategies to make the flow field more uniform are proposed for a 2 × 300 MW direct dry cooling power-generating unit. The performance of ACCs in the prevailing wind direction is predicted with the help of the macro heat exchanger model. It is found that the inlet air temperatures of fans are significantly reduced by proposed strategies, especially at high wind speeds. Moreover, the minimum cooling air can meet the cooling demand of ACCs for the strategy which made the air flow rates of all fans consistent. Compared with the case without adjustment of fans, the total power consumption of the fan array was cut down effectively, up to 13.94% at the wind speed of 12 m/s. In conclusion, the energy efficiency of ACCs can be improved by the uniform flow field.

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• We investigated the effect of a casing fence on the aerodynamic performances and tip-leakage flow of an axial flow fan. • At the design condition, the fan efficiency was increased by the casing fence located near the trailing edge of the blade. • The casing fence blocked backward leakage flows and suppressed the azimuthal development of the tip-leakage vortex, thus preventing the interaction between the tip-leakage vortex and following blade. The effect of a casing fence on the tip-leakage flow of an axial flow fan is investigated using large eddy simulation. A fence is attached on the shroud near the trailing edge of an axial flow fan used in an outdoor unit of air conditioner. The Reynolds number is 547,000 based on the blade tip radius and tip velocity. At the design condition, the fan efficiency is increased by the casing fence. The roles of the fence are to block backward leakage flows near the shroud and to weaken the movement of the tip-leakage vortex (TLV) in the azimuthal direction. Also, the fence reduces the double-leakage tip-clearance flow generated at the aft part of the blade tip due to the TLV-blade interaction, reducing the strength of the tip-separation vortex. Consequently, the tip leakage and total pressure losses are reduced, and the efficiency is increased. The pressure fluctuations on the aft part of the blade tip of the pressure surface caused by the TLV-blade interaction are also significantly reduced by the fence, indicating reduction of the noise source. According to the interaction between the fence and backward leakage flow induced by the TLV, the fence significantly and slightly increases the aerodynamic performances at the design and peak efficiency conditions, respectively, but reduces them at an overflow condition. [ABSTRACT FROM AUTHOR]

• The loss of the axial fan in an outdoor unit occurs mainly in the end-wall region. • The interaction between hub entrance vortex and a blade affects the fan efficiency. • The certain condition of cleaved hub vortex by a blade increases the fan efficiency. The improvement in efficiency of axial flow fans is major concern in turbomachinery industries including outdoor units of air conditioners. The end wall region is responsible for losses in axial flow fan. Researches on the relationship between the efficiency and the vortex occurring on the hub with a short length have been little found in the literature. Variations of the vortical flow field and the effects on the efficiency have been investigated with the entrance hub length and corner shape of the axial flow fan. The losses and the efficiency were evaluated by the stagnation pressure loss coefficient distribution calculated using commercial CFD solver SC/Tetra v12. The results show the efficiency was improved at specific entrance hub length due to the interaction between the hub vortex and the blade. [ABSTRACT FROM AUTHOR]

In this paper, the performance deterioration for the fan due to geometry changes by erosion is investigated and discussed. Furthermore, the fan life time is predicted. The fan in concern is installed in General Electric CF6-50 high bypass turbofan engine. It is large in diameter and has highly twisted blades. Moreover, the overall engine performance degradation due to fan performance deterioration is predicted. The studied aircraft mission lasts on the average for 3.5 hours. 7.5% of the mission time is near the ground and the remaining 92.5% is for the cruising condition. The life time of the fan is divided into 2000 cycles intervals. After each interval the fan geometry is updated and the flow field is solved to predict the fan performance. The fan performance is predicted after 2000, 4000, 6000, and 8000 cycles. Finally the fan performance characteristics are used to determine the performance deterioration in the CF6 turbofan engine. It is found that, fan erosion causes a remarkable degradation on both the fan and the engine performances. After 8000 operating cycles it was found that, the surge margin is reduced from 10.5% and 9.77% to 2.5% and 1.5% at cruise and takeoff, respectively. Furthermore, there is a decrease of 2.35% and 3.55% in the fan pressure ratio and fan efficiency for both cruise and takeoff, respectively. The fan life time based on the blend limits provided by the engine manufacturer is found to be after nearly 5000 operating cycles. [ABSTRACT FROM AUTHOR]

We investigate the evolution of tip-leakage vortex (TLV) in a low-pressure axial flow fan using digital particle image velocimetry. The blade rotational speed is fixed at 1000 rpm, and the Reynolds number is 547000 based on the blade tip radius and tip velocity. The evolution of TLV in downstream is highly influenced by the incoming flow rate. The TLV breakup occurs for the peak efficiency and stall conditions and sometimes for a higher flow rate, but does not occur for the highest flow rate considered. Thus, the migration speed of the TLV for the peak efficiency condition is faster due to the TLV breakup than those for higher flow rates. The scatter plot of the TLV center location indicates that the TLV wanders around its mean location and the region swept by the wandering motion increases as the TLV migrates downstream. High turbulent kinetic energy exists at the phase-averaged TLV center and its upstream location, respectively, owing to the wandering motion and the interaction between the TLV and main axial flow. [ABSTRACT FROM AUTHOR]

Abstract The A-frame configuration of finned tube bundles and complex aerodynamics of axial flow fan result in the increased pressure loss of cooling air and unfavorable thermo-flow performances of air-cooled condenser cell. In this work, an air-cooled condenser cell with oblique finned tube bundles is proposed to weaken the adverse effects due to the geometric flaws of conventional condenser cell. By means of CFD simulation and experimental validation, the pressure drop and heat transfer for the oblique finned tube bundles with the inclined angles of 0°, 15°, 30°, 45° and 60° are obtained. Using a lumped parameter radiator approach, the air-cooled condenser cell model is developed, by which the velocity and temperature fields as well as the total mass flow rate and heat transfer rate are computed and compared. The results show that the thermo-flow performances of the proposed condenser cell are greatly improved at the lower regions, especially for the inclined angle of 45° with the mass flow and heat transfer growth rates reaching up to 12.81% and 8.96% respectively, so the angle of 45° is preferred in the practical application of oblique finned tube bundles to air-cooled condenser. Highlights • An air-cooled condenser cell with oblique finned tube bundles is proposed. • Dead velocity and high temperature zones at lower parts vanish for proposed cell. • The performance gets improved for proposed cell as fan rotational speed increases. • 45° is an optimal inclined angle with best thermo-flow performances of proposed cell. [ABSTRACT FROM AUTHOR]