Axial Fan Research Articles

An airflow velocity field reconstruction method with sparse or incomplete data using physics-informed neural network

Velocity field is critical for creating a healthy and comfortable indoor environment but it is difficult to be measured experimentally. Due to the limitations of measurement instruments and site conditions, the captured data are usually sparse, incomplete, and low-dimensional, which limits further research on indoor velocity field. This study proposes a practical reconstruction and super-resolution method based on physics-informed learning that seamlessly integrates imperfect measured data and physical laws. The ability to reconstruct the airflow velocity field with imperfect data as the training dataset was validated using a three-dimensional and three-component airflow field generated with an axial fan. This method successfully recovered the airflow field from sparse or insufficient data (even when the amount of data was only 5 % of the original vector fields) and incomplete data. This indicates that the proposed method can reconstruct and super-resolve the airflow velocity vector fields from sparse, incomplete, and low-dimensional data.

Enhancing Axial Flow Fan Performance in Air-Cooled Condensers: Tip Vortex Manipulators and Comparative Analysis of Numerical Simulation and Experimental Testing

Abstract Direct dry-cooled power plants typically operate numerous large-diameter axial flow fans in air-cooled condensers (ACCs) to facilitate the condensation of steam in the plant's thermodynamic cycle. Enhanced fan efficiency may, at scale, lead to significant parasitic power reductions and subsequent increases in plant power output. The performance of these fans may be increased by adding blade-tip modifications, which act to control blade-tip leakage flow. Previous studies have shown that manipulating the tip leakage vortex (TLV) increases the blade-to-air momentum transfer and stabilizes the air flow structures as it traverses the fan blade. This paper takes a step toward the development of improved tip vortex manipulators for an ACC fan. Three-dimensional computational fluid dynamics (CFD) simulations, and experimental testing of the modified and unmodified fan within an ISO test facility are performed. The results are then utilized to assess the accuracy of the simulation model, visualize the manipulated flow structures at the blade tip, and ultimately quantify the effect of the endplate designs on fan performance. Excellent correlation between numerical and test results for the unmodified fan is observed, and the benefit of blade-tip modification on fan performance is again confirmed experimentally. The simulation model, however, fails to predict improvements in fan performance under modification, and simulated tip leakage flows are investigated for clarification. It is hypothesized that deflection of tip endplates under operation account for differences between simulation and experiment, and that fluid–structure interaction analyses could potentially resolve discrepancies.

Experimental investigation of the effect of droplet size on the vaporization of butanol in turbulent environments at elevated pressure

This paper presents an experimental study of the effect of droplet size on the vaporization rate of butanol fuel under turbulent flow conditions at elevated pressure and room temperature. The butanol droplet is suspended at the intersection of two micro-fibers in the center of a spherical vessel. The initial size of the butanol droplet is varied in the range between 300 and 700 μm. A controlled turbulent flow field, characterized by quasi-zero mean velocity and turbulence intensity of up to 1.5 m/s, was generated by eight axial fans. The findings reveal an improvement in the vaporization rate of butanol droplet as the droplet size increases. This improvement is more pronounced under conditions of elevated pressure and turbulence intensity. The results show that turbulence begins to influence the vaporization process when the droplet diameter exceeds the Kolmogorov length scale. Butanol droplet vaporization rate is found to lie between heptane and decane, leaning towards decane under all explored test conditions. The results reveal that the vaporization rate of hydrocarbon fuels is more sensitive to the droplet size variations than butanol. Turbulence is found to exert greater impact on the vaporization of fuels that have lower gas-phase mass diffusivity and higher thermal diffusivity. Finally, the previously proposed correlations, expressed in terms of Damköhler and turbulent Reynolds numbers, are assessed and found capable of predicting the vaporization of butanol droplet over a wide range size.

An innovative double-jet design as an air flow barrier to isolate temperature and humidity in a low-temperature storage room

This study used an innovative double-jet design to isolate the temperature and humidity of a lower temperature storage room (-15 °C) from an adjoining higher temperature room (5 °C). This device can reduce the chance of forming a hazardous area in the working environment. Several axial fans are installed on the top of the flow isolation device (FID) to provide an air flow barrier. Those fans blow the air that can induce the Coanda effects outside of the FID. A blockage body is designed and installed in the downstream area on a perforated plate that can divide the flow into two symmetric separated jets. Computational Fluid Dynamics (CFD) is used to simulate the flow pattern with two different practical air velocities, 5 and 5.6 m/s. The results show that the case where the FID is installed in both rooms exhibits the highest isolation efficiency, up to approximately 94% for RH and 93% for temperature. The findings of flow analysis demonstrate that significant amounts of energy can potentially be saved. The practical implications of these findings could be in food and pharmaceuticals industries.

Investigating the effect of axial fan shrinkage obtained by centrifugal casting technology on aerodynamic characteristics

Centrifugal casting technology was developed for the application of manufacturing axial fans. In the literature, these fans were usually manufactured by injection molding, mechanical processing or heat pressing. The main characteristic of this molding technology allows the creation of thick and hollow blades. This characteristic of the blades gives useful advantages of the fan that cannot be achieved by conventional methods. The centrifugal casting technology has been applied to fabricate axial fans in recent research. However, the issue of quality control and especially the shrinkage of the resulting fan compared to the molding has not yet been considered. Therefore, more in-depth studies and approaches are required. In this study, 3D scanning method is used to evaluate the shrinkage of the blades. The used 3D scanner is the Comet L3D 5M type based on structured light (blue LED) with a 5-megapixel sensor. This device achieves high accuracy and reliability (resolution 18 μm). The theoretical basis for determining fan shrinkage compared to CAD molds is based on the following main parameters: Chord line L (mm), relative thickness Emax (%), and stagger angle ( (degrees). In addition, the aerodynamic characteristics of the proposed fan are compared to those of a fan made of aluminum (blades are identical, but different in fabricating technology). Characteristics of this aluminum rigid-fan are assumed as reference. The results showed that the difference was not large between the blades. Besides, the results of aerodynamic testing on the test bench of the two fans are almost similar. This indicates the good adaptability of the axial fan received by the centrifugal casting technology.

Full-scale experimental, numerical, and theoretical research on the spatio-temporal evolution of the flow structure in longitudinal and semi-transversal ventilated tunnels

This paper presents full-scale experimental, numerical, and theoretical research on the spatial and temporal structure of airflow for different modes of ventilation system operation in a road tunnel. The tunnel under investigation is equipped with a semi-transverse ventilation system. There are 19 pairs of axial jet fans in each tunnel tube and 164 air supply vents on both sides of a tube located just above the road surface. A set of seven stand poles with mounted vane anemometers were arranged along the tunnel tube axis. Different configurations of axial jet fans and air supply vents were employed, and changes in airflow velocity were recorded. Since the main objective of the study is to achieve a deeper understanding of the examined phenomena, a numerical model of the flows in the tunnel was built, and the acquired data was used to validate it. Some theoretical considerations are provided and also validated. All of this together reveals a very uneven distribution of longitudinal air velocity along the tunnel axis. Then, time constants when switching the fans on and off are determined. It is shown that the time needed to achieve a stable flow after the fans are turned on is in the order of five minutes, and the decay time after the fans are turned off is much longer; it takes about 15 min to calm down the flow. Next, it is determined that the transverse air supply significantly changes the airflow structure: the average longitudinal air velocity at the inlet portal was up to 25% lower than without it, while values at the outlet portal were similar. Finally, it is indicated that axial fans that operate in the suction mode are similarly efficient to those in the pumping mode.

Experimental and numerical comparisons among various skewed blades of low speed axial fan rotors

Literature indicates that there is lack of study related to the effects of axially skewed blades on the aerodynamic performance of axial flow fans. In this study rotors of various blade skews, namely, axial, circumferential and axial-circumferential types, are studied and their aerodynamic performances are compared to those of the baseline radial rotors of two types, namely, constant chord and varying chord. The skew in a blade can be considered as combination of sweep and dihedral. The skew change from the circumferential to axial type causes reversal of dihedral induced radial blade force and hence a reversal of meridional streamline curvature which in turn reverses the modulation of the end-wall loads. The inherent forward sweep in the forward skewed blades also modulates hub and tip loads. Thus, in a forward axial skew blade the forward sweep and positive dihedral combine favorably to unload the tip and to upload the hub. In the forward circumferentially skewed blades, forward sweep and the negative dihedral have mutually countering effects on end-wall load modulation. The highlight of this study is that it has demonstrated experimentally the unloading of the tip in the forward axially skewed blades which resulted in reduced losses and better performance including increased stall margin. Reduced tip loading was also verified from the casing pressure sensor measurements which showed weakening of tip vortex. The relative influence of sweep and dihedral on performance was additionally demonstrated in the axially-circumferentially skewed rotor of the constant chord type, with improvements attributable to higher sweep.

Numerical Study on the Effects of Re on the Unsteady Behaviors in a Transonic Axial-Fan Under Inlet Distortion

Abstract The dynamic response of a compression system is the complex dynamic behaviors reacted by the compressor subject to non-uniform inflow excitation. However, in a real operating condition, the compressor would work at a wide range of altitudes within the flight envelope, which forces us to consider how Re additionally affects the compressor performance loss and dynamic response characteristic due to inlet distortion. To explore this issue, a full-annulus unsteady 3D simulation has been used to calculate the performance of a transonic axial fan with a 180-deg distortion at different Re. The results show that Re has additional detrimental effects on the fan aerodynamic performance with non-uniform inflow. To further explore the mechanisms of Re effects on fan–distortion interaction, the spatial and temporal distribution of the rotor blade response is discussed. The temporal distribution of the fan–distortion interaction is not changed with Re by analyzing the dynamic response orbit of the fan rotor. However, the spatial distribution of Re effects is highly related to the blade profile loaded mode at different spanwise locations. The results indicate that the time constant of fan dynamic response decreases by 17% at the mid-loaded region in the middle of the blade and increases by 40% at the aft-loaded region near the blade tip. Further analysis reveals that due to the low Re and flow separation of the suction surface, the thickness variation of blade boundary layer is the main cause for varying the blade time constant.

Fault diagnosis of mine main ventilator based on multi-eigenvalue selection and data fusion

As a strong nonlinear complex system, the mine main ventilator is difficult to select eigenvalues of the ventilator fault. This study proposed a multiple eigenvalue selection method based on ensemble empirical modal decomposition (EEMD). Firstly, an experimental platform of axial flow fan was built to simulate the bearing fault and fan blade fault. Secondly, the vibration and wind pressure data of the above three faults and the normal state were collected, and the vibration signals were decomposed by EEMD. The normalized Root Mean Square Error was used to evaluate the signal separation degree of different faults under the same eigenvalue and to select the eigenvalue. Then, combined with wind pressure information, multi-data information fusion was used to construct the failure indicator vector table. Finally, the BP neural network was trained and tested with a vector table, and the fault diagnosis of the mine main ventilator was achieved. The experiment results showed that the diagnostic accuracy of test results was 98.87% after eigenvalue selection and data fusion. The method has high accuracy and adaptability, and is very suitable for mechanical equipment such as mine ventilator.

Investigation into the predicted performance of a cooling fan for an sCO2 concentrated solar power plant

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.

Design, Study, and Comparison of a New Axial Fan Using the Fibonacci Spiral and a Classic Axial Fan

Design, Study, and Comparison of a New Axial Fan Using the Fibonacci Spiral and a Classic Axial Fan

대규모 와 모사를 통한 운전부하가 튜브 축류홴의 난류유동장 분포양상에 미치는 영향 분석

대규모 와 모사를 통한 운전부하가 튜브 축류홴의 난류유동장 분포양상에 미치는 영향 분석

Design of Sinusoidal Leading Edge for Low-Speed Axial Fans Operating under Inflow Distortion

Axial fans may be equipped with passive flow control devices to enhance rotor efficiency or minimize noise emissions. In this regard, blade designs influenced by biomimicry, such as rotors with sinusoidal leading edges (LEs), have gained popularity in recent years. However, their design is predominantly driven by a trial-and-error approach, with limited systematic studies on the influence of rotor performance. Furthermore, their effectiveness is typically evaluated under controlled conditions that may significantly differ from operations in real installation layouts. In this work, a systematic review of the design process for sinusoidal LE axial fan rotors is provided, aiming to summarize previous design experiences. Then, a modified sinusoidal LE is designed and fitted to a 7.3 m low-speed axial fan for air-cooled condensers (ACCs). These fans operate at environmental conditions, providing a quasi-zero static pressure rise, often with inflow non-uniformities. A series of RANS computations were run to simulate the performance of the baseline fan and that of the sinusoidal leading edge, considering a real installation setup at Stellenbosh University, where the ACC is constrained between buildings and has a channel running on the ground below the fan inlet. The aim is to explore the nonbalanced inflow condition effects in both rotor geometries and to test the effect of the installation layout on fan performance. The results show that the modification to the rotor allows for a more even distribution of flow in the blade-to-blade passages with respect to the baseline geometry.

A multi-source subdomain adaptation fault diagnosis method based on unidirectional movement of the target domain

The traditional domain adaptation method for fault diagnosis of axial fans faces two main problems: (1) source domain moves to target domain makes the source feature distribution changed; (2) the narrow decision boundary of source domain features leads to misclassification of target samples. Therefore, a multi-source subdomain adaption fault diagnosis method based on unidirectional movement of the target domain is proposed. The method uses triplet-center loss to improve the discrimination of target domain samples, which reducing intra-class distance and increasing inter-class distance of source domain features; extracting the domain invariant feature of the target samples by asymmetric adversarial and improved subdomain feature distance measurement; the cosine similarity is used to align the classifiers’ outputs of different source domains; the mean value of all classifiers’ outputs are used as pseudo labels, and the pseudo labels are optimized by maximum entropy to improve their reliability. A large number of experiments show that this method has a significant effect on solving the problem of cross conditions fault diagnosis.

Design and Fabrication of Low-Speed Wind Tunnel (LSWT)

The design and fabrication of a low-speed wind tunnel (LSWT), which is a critical component for testing and comprehending aircraft aerodynamics, is presented in this study. Despite the increasing prominence of computational fluid dynamics (CFDs) in manufacturing engineering, wind tunnels remain essential for the intricate development of aircraft and automobile designs with complex flow interactions. Using SolidWorks, we focused on controlling flow turbulence approaching the test section, emphasizing performance and quality parameters. The construction of the wind tunnel used plywood with an axial fan regulating the airspeed, and Arduino facilitated data acquisition. The drag and lift on the Y Clerk Airfoil were quantified by two load cells along the XY-axis, complemented by a Pitot Static Tube and a multitube inclined plane manometer for pressure and velocity calculation. Fusion 360 simulation software was used to analyze pressure and velocity profiles at speeds ranging from 10 to 20 m/s, providing a comprehensive quantitative evaluation of the wind tunnel’s capabilities. By emphasizing both design innovation and quantitative performance metrics, this study underscores the continuing significance of wind tunnels in engineering.

Impact of geometric modifications of small axial fans on psychoacoustic metrics

This paper presents a comprehensive experimental investigation of a basic axial fan and its various modifications. The fan blades were designed according to recommendations from the literature. The prototypes were 3D printed and tested under different operating conditions in accordance with the ISO 5136 and ISO 5801 standards. The aim of the study was to investigate the effects of the axial fan design on the characteristic curve and on the acoustic and psychoacoustic properties of the emitted sound.The characteristic curves were influenced by geometrical features that can lead to obstruction of the flow. The A-weighted sound power level spectra showed that low-frequency (subharmonic) noise humps can be effectively reduced by modifications near the fan hub, while tonal noise in the mid-frequency range can be mitigated by blade root enlargement, small wing tips and low-amplitude edge serrations. The tonal noise was greatly affected by the addition of tip flanges and rotating shrouds, but these modifications reduced the high frequency noise. The psychoacoustic evaluation showed a higher sensitivity to the characteristics of the emitted noise compared to conventional A-weighted one-third octave spectra. While all modifications led to changes in psychoacoustic metrics, loudness, roughness and tonality showed the greatest variability and influence on psychoacoustic annoyance, while sharpness and fluctuation strength were less affected by the different modifications.The results presented emphasize the complex interplay between geometry, aerodynamics, acoustics and psychoacoustics in small axial fans and highlight the need for holistic approaches to fan design in order to solve noise-related problems. The 3D printed machines had similar energy and acoustic characteristics as traditionally manufactured fans, so the use of additive manufacturing techniques proved to be a cost-effective and practical step in the fan design process that could be easily implemented.

Analysis of aerodynamic and aeroacoustic performances of axial flow fans with variable winglet curvature in chordwise direction

This study introduces a novel concept for axial-flow fans with winglets featuring gradually decreasing curvature along the chordwise direction. The objective is to mitigate the formation of leakage vortices in the gap flow region between the fan blade tip and the shroud. Two types of axial-flow fans, denoted as VR-A and VR-B, are designed, each incorporating variable winglets with differing rates of curvature reduction compared to the baseline CR fan with constant winglet curvature. The research encompasses a comprehensive approach involving computational fluid dynamics (CFD) simulations and experimental analyses. Numerical simulations employ incompressible Unsteady Reynolds-averaged Navier-Stokes (URANS) equations to capture intricate flow behaviors, while a virtual fan performance tester is used for flow performance predictions. Furthermore, the Ffowcs Williams & Hawking (FW–H) integral equation is utilized to estimate the radiated aerodynamic noise. Experimental measurements include flow performance assessments and noise evaluations, yielding data on flow rate, efficiency, and sound pressure spectrum. Comparisons between numerical and experimental results validate the numerical methods. Subsequent evaluations highlight the advantages of the VR fans over the CR fan, showing increased flow rates and reduced noise levels. These enhancements are attributed to the weakened leakage vortex in the gap flow region. The findings provide valuable insights for optimizing axial-flow fans partially covered by shrouds, offering improved flow performance and decreased noise radiation.

Further Development of Rotating Beamforming Techniques Using Asynchronous Measurements

When rotating noise sources, such as turbomachinery, are investigated using phased microphone array measurements and beamforming, sidelobes appear on the resulting beamforming maps. Sidelobes can be decreased by increasing the number of microphones. However, if the investigated phenomenon is steady, then there is a cost-effective alternative: performing asynchronous measurements using phased arrays having a limited number of microphones. The single beamforming maps can be combined in order to arrive at results that are superior in resolution and sidelobe levels. This technique has been investigated in the literature, but according to the authors’ best knowledge, has not yet been applied to turbomachinery. This article introduces a means for applying the asynchronous measurement technique and the combination methods for rotating noise sources. The combination methods are demonstrated on two rotating point sources (both in simulations and measurements), and then on an axial flow fan test case. In the case of the two rotating point sources, the achievable improvement in resolution, average-, and maximum sidelobe levels are shown as compared to the single results. In the case of the axial flow fan, it is demonstrated that the combination methods provide more reliable noise source locations and reveal further noise sources.

The Effects of Rotation and Solidity on the Aerodynamic Behavior of Low-Pressure Axial Flow Fans

Abstract Implicit axial flow fan models are commonly used for the numerical analysis of industrial heat exchanger systems. However, these fan models perform poorly within the often complex off-design flow environments characteristic of these systems, as their low-order formulations lose applicability under highly 3D flow conditions. At off-design flow conditions, rotation and blade solidity effects cause physical fan blade behavior to deviate from the anticipated 2D behavior characterized by the implicit models. Physical fan blade behavior at off-design flow conditions, however, remains uncertain and the specific effects of rotation and solidity are not yet widely understood. This study investigates off-design fan blade behavior by presenting explicit 3D computations of two low-pressure axial flow fans. The effects of rotation and blade solidity are then identified through a side-by-side comparison of the computed 3D fan blade data against isolated 2D airfoil data. The rotating fan blade lift characteristics are shown to be distinct from the comparative 2D airfoil trends. At low-flow (off-design) operating conditions, rotation establishes large radial flow movements, and the high blade solidities cause standing vortices to develop within the rotating blade passages. The radial outflow energizes the blades' boundary layers, and the vortices inhibit the flow from separating from the blades' surfaces. Consequently, blade stall is avoided and high lift coefficient values are realized. The presented fan blade lift characteristics are unique relative to literature on other turbomachines of lower blade solidity, highlighting the importance of considering solidity effects in implicit rotor model developments.

Optimization and experimental validation of the air intake holes of the lithium-ion battery pack

Energy storage systems enable the storage of energy and provide access to carbon-neutral, environmentally friendly energy whenever or wherever it is needed. Lithium-ion batteries are currently the most preferred type among various battery technologies and are widely used in energy storage systems. Some of the features that make lithium-ion batteries advantageous include high energy density, long life, low maintenance requirements, and high operating voltage. The growing demand for energy throughout the day increases the need for batteries with high storage capacity. However, the increased capacity also leads to heating issues in lithium-ion batteries. The heating problem in lithium-ion batteries can result in nonhomogeneous temperature distribution, shortened lifespan, thermal runaway, increased internal resistance, and performance loss. Therefore, an effective thermal management system is essential for cooling lithium-ion batteries. This study aims to provide insight into the forced air cooling of prismatic 280 Ah LiFePo4 batteries, which have limited information in the literature and are more prone to overheating compared to lower-capacity batteries. In this study, five different battery pack case designs, each with different sizes and numbers of air intake holes, were determined and modelled using the SolidWorks program. Within the battery pack cases, 16 280 Ah lithium-ion batteries are placed, and an axial fan is used to cool these batteries. Initially, computational fluid dynamics analyses of the five different designs were performed in the SolidWorks Flow Simulation program. An experiment was then conducted on the design that provided the most efficient thermal management to validate the numerical results. The selected design, fulfilling the purpose of homogeneous temperature distribution and having the minimum temperature difference between batteries, was designated as Design 5. It exhibited a 62 % improvement in cooling performance with a 0.25 °C temperature difference, indicating successful temperature homogeneity between batteries. During a two-hour experiment with a 140 A discharge current, temperature measurements were taken from the surfaces of the batteries using thermocouples. Finally, the maximum error rate between experimental and numerical studies was determined to be 1.47 %, indicating successful validation of the numerical study. The air intake hole optimization, a novel design approach, prevents temperature distribution inhomogeneity caused by the distance of the batteries to the fan and offers an effective way to cool down high-capacity 280 Ah batteries.