Axial Flow Fan Blades Research Articles

Development of a Performance-Based Design Technique for an Axial-Flow Fan Unit Using Airfoil Cascades Based on the Blade Strip Theory

Axial-flow fans are widely used as cooling fans in the outdoor units of split-type air conditioners. The design of an axial-flow fan blade involves stacking several airfoils that can be differently designed for each spanwise section. However, the complex flow field around the fan blade, including circumferential and axial flows, presents challenges when applying the single airfoil theory. This study proposed a systematic performance-based design method for axial-flow fans using a cascade of airfoils based on the blade strip theory. The theory characterized the complex three-dimensional flow field driven by an axial-flow fan in terms of a two-dimensional cascade of airfoil flows. Computational fluid dynamics based on finite volume methods were used to predict the flow field and aerodynamic sound sources of an existing low-pressure axial-flow fan partially covered by a fan shroud, and the results were validated against experimental measurements. Three radial locations in the spanwise region from the hub to the blade tip that have a significant impact on aerodynamic performance were selected, and the two-dimensional flow field on a cylindrical surface with a constant radius was extracted from the three-dimensional flow field to characterize the performance of an axial fan. Then, the airfoils at the targeted span locations were optimized for a higher flow rate and greater efficiency via two-dimensional simulations using the cascades of the airfoil, and the selected optimized airfoils were applied to existing fan blades. The effectiveness of the proposed performance-based design method for low-pressure axial-flow fans was validated by the results, which showed that the redesigned fan blades with cascades of airfoils performed as predicted, increasing the intended higher flow rate by about 1%, improving power consumption by 8%, and lowering the overall sound pressure level by 1.5 dBA.

Fracture parameters of woven jute fibre reinforced axial flow fan blade material: an experimental investigation and FEA analysis

Airflow required for the heat and mass transfer in industrial applications is often provided by axial flow fans. Glass fibre reinforced polymers (GFRP) are most often used to make these fan blades. The usage of glass fibres in composite materials is growing. By 2025, the global market for glass fibres will be worth 16.5 billion pounds. However, non-biodegradable composite reinforcement has major ecological and human health concerns, especially when reaching the end of its operational lifespan. Until now, industries have shown a strong inclination to use GFRP without adequately contemplating the potential consequences associated with their disposal. The economic viability of glass fibre recycling is questionable. However, natural fibres like jute and fibres extracted from vegetable plants are of much popular among academics and researchers due to their sustainability and ease of use. So, they’re suitable for making polymer composites. The amount of natural fibres that may be added to GFRP composites without materially altering their mechanical characteristics is a crucial factor in improving their decreased embodied emissions and biodegradability after service life. In this work the material represents an 18-ft axial flow fan blade material made of GFRP. This study used the term denotes the specific material utilised in the fabrication of 18-feet axial flow fan blades for industrial purposes. By substituting one layer of with woven jute and changing its position in it, the materials through are produced. All the materials are tested for fracture parameters like plane strain fracture toughness and Critical strain energy release rate as per ASTM D-5045. The results were validated by using finite element models implemented in a commercially available software ANSYS R19.2. The optimal layup sequence for fan blade material with single-layer woven jute reinforcement was found, which preserves fracture properties, also improves biodegradability after service life.

Investigation of shear properties of axial flow fan blade material with partial woven jute reinforcements

Axial flow fan blades are often made from glass-fibre reinforced polymers (GFRP), which are increasingly used in making composites. These non-biodegradable composite reinforcements, on the other hand, pose significant environmental and human health risks, especially at the end of its service life. Until now, companies have hustled to use GFRP without regard to disposal. Glass fibres recycling is expensive and unjustifiable. On the other hand, natural fibres are gaining popularity due to their sustainability. So, they're suitable for polymer composites. To improve the biodegradability of GFRP composites after service life, it must be determined to what extent natural fibres can be reinforced in them without significantly affecting mechanical properties. In this work, the material C1 is an 18-ft axial flow fan blade material made of GFRP. The materials C2 to C6 were made by substituting one layer of C1 with woven jute and changing the location of the jute in C1. All the materials are tested for shear strength as per IS 1998-62. The shear strength results were validated by using the finite element software ANSYS R19.2. The woven jute fibre composite has higher shear properties when jute is placed in the second position (C2). C2 preserves the shear strength of the blade material and also improves biodegradability after service life.

Effects of Outer Edge Bending on the Aerodynamic and Noise Characters of Axial Fan for Air Conditioners

Outer edge bending is already used on the axial fan blades of air conditioners, reducing the leakage flow loss at the blade tip and suppressing the tip vortex development, thereby improving fan aerodynamic and acoustic performance. However, there are few studies on the multi-parameter design and optimization of this complicated structure, and most studies only focus on the overall sound pressure level rather than the sound quality when evaluating the fan noise. This study investigated the effects of outer edge bending structure on the aerodynamic performance and sound quality of air conditioners’ axial fans by experiments and numerical methods. Based on the orthogonal design method, the effects of three bending parameters, the circumferential starting angle, radial relative position, and the bending degree effects on the performance of the axial flow fan blade were analyzed, and the best efficiency scheme was selected. A comparative analysis of the preferred and the original bending schemes shows that the bending towards the blade suction surface successfully inhibits the development of tip leakage vortex at the blade tip, thereby achieving efficiency enhancement and noise reduction. The experimental results show that the preferred bending scheme with a 10° circumferential starting angle, 90% radial relative position, and 8% bending degree can effectively reduce the fan’s broadband noise within 200~1000 Hz by 0.54~2.68 dB (A) at different operating conditions. Additionally, the preferred bending blade with reasonably designed bending effectively reduced the loudness and roughness of the fan noise in the rated conditions, and the sound quality of the studied fan was correspondingly improved.

The effect of stacking sequence on the tensile properties of jute fibre reinforced hybrid composite material for axial flow fan blades: An experimental and finite element investigation

Axial flow fans are used extensively in industrial applications to provide the airflow needed for heat and mass transfer requirements. Glass Fibre Reinforced Polymers are often used in axial flow fan blades. These glass fibres are synthetic and have a very high stiffness and strength to weight ratio. However, composite reinforcement including such fibres, particularly towards the end of their service life, has negative environmental and human health effects since they are not biodegradable. On the other hand, certain natural fibres, such as jute, are becoming more popular with academicians and researchers because of their environmental friendliness and sustainability, making them attractive for use in polymer composites. As biofuels are only able to be blended with conventional diesel to save fuel when no engine replacement is required, likewise, it must be determined to what extent natural fibres can be used in conventional components without significantly affecting mechanical properties and improving biodegradability after service life. In this study, an 18-ft axial flow fan blade material (GFRP) with 14 layers of glass fibres in various forms was considered as C1 and tested for tensile characteristics according to ASTM D-638. Cases C2 to C6 were examined and tested by substituting one layer of GFRP with woven jute and keeping it in different positions within the GFRP. Using finite element software ANSYS R19.2, by changing the number of woven jute layers, and their position the effect of the layup sequence was also investigated. Based on experimental and numerical results, the best layup sequence with partial woven jute reinforcements for GFRP blades was recommended,which does not substantially influence tensile characteristics but enhances biodegradability after service life.

Characterization of Glass/Jute Hybrid Fibre Reinforced Epoxy Composite for Axial Flow Fan Blade

Traditionally axial flow fan blades were manufactured by using metal alloys, but with the increase in blade size the blades grew heavier resulting in more vibrations during its working. It is impossible to manufacture the metallic blades to close tolerances making it uneconomical. Due to this dimensional instability, the metallic impeller fan blades are instead fabricated with glass fiber reinforced plastics (GFRP). To reduce the after effects of GFRP blades on the environment necessitates the partial reinforcement of natural fibre. This paper deals with the characterization of GFRP blade material with partial Jute reinforcements i.e., glass to jute (95:5) weight percentage and estimating the properties like tensile strength, bending strength, shear strength, fracture toughness. The conventional GFRP blade material has 14 layers of glass fibers in various forms. By placing jute layer at various positions in GFRP blade material the mechanical strengths were estimated and compared with conventional one.

Air-structure coupling features analysis of mining contra-rotating axial flow fan cascade

The interaction between contra-rotating axial flow fan blade and working gas has been studied by means of establishing air-structure coupling control equation and combining Computational Fluid Dynamics (CFD) and Computational solid mechanics (CSM). Based on the single flow channel model, the Finite Volume Method was used to make the field discrete. Additionally, the SIMPLE algorithm, the Standard k-ε model and the Arbitrary Lagrangian-Eulerian dynamic grids technology were utilized to get the airflow motion by solving the discrete governing equations. At the same time, the Finite Element Method was used to make the field discrete to solve dynamic response characteristics of blade. Based on weak coupling method, data exchange from the fluid solver and the solid solver was processed on the coupling interface. Then interpolation was used to obtain the coupling characteristics. The results showed that the blade's maximum amplitude was on the tip of the last-stage blade and aerodynamic force signal could reflect the blade working conditions to some extent. By analyzing the flow regime in contra-rotating axial flow fan, it could be found that the vortex core region was mainly in the blade surface, the hub and the blade clearance. In those regions, the turbulence intensity was very high. The last-stage blade's operating life is shorter than that of the pre-stage blade due to the fatigue fracture occurs much more easily on the last-stage blade which bears more stress.

Numerical study on air-structure coupling dynamic characteristics of the axial fan blade

In order to understand the dynamic characteristics of the axial-flow fan blade due to the effect of rotating stress and the action of unsteady aerodynamic forces caused by the airflow, a numerical simulation method for air-structure coupling in an axial-flow fan with fixed rear guide blades was performed. The dynamic characteristics of an axial-flow fan rotating blade were studied by using the two-way air-structure coupling method. Based on the standard k-ε turbulence model, and using weak coupling method, the preceding six orders modal parameters of the rotating blade were obtained, and the distributions of stress and strain on the rotating blade were presented. The results show that the modal frequency from the first to the sixth order is 3Hz higher than the modal frequency without considering air-structure coupling interaction; the maximum stress and the maximum strain are all occurred in the vicinity of root area of the blade no matter the air-structure coupling is considered or not, thus, the blade root is the dangerous location subjected to fatigue break; the position of maximum deformation is at the blade tip, so the vibration of the blade tip is significant. This study can provide theoretical references for the further study on the strength analysis and mechanical optimal design.

Numerical Analysis of Erosion Caused by Biomimetic Axial Fan Blade

Damage caused by erosion has been reported in several industries for a wide range of situations. In the present work, a new method is presented to improve the erosion resistance of machine components by biomimetic method. A numerical investigation of solid particle erosion in the standard and biomimetic configuration blade of axial fan is presented. The analysis consists in the application of the discrete phase model, for modeling the solid particles flow, and the Eulerian conservation equations to the continuous phase. The numerical study employs computational fluid dynamics (CFD) software, based on a finite volume method. User-defined function was used to define wear equation. Gas/solid flow axial fan was simulated to calculate the erosion rate of the particles on the fan blades and comparatively analyzed the erosive wear of the smooth surface, the groove-shaped, and convex hull-shaped biomimetic surface axial flow fan blade. The results show that the groove-shaped biomimetic blade antierosion ability is better than that of the other two fan blades. Thoroughly analyze of antierosion mechanism of the biomimetic blade from many factors including the flow velocity contours and flow path lines, impact velocity, impact angle, particle trajectories, and the number of collisions.

Effect of Different Operating Points on Flow around Small Axial Flow Fan Blade

Effect of Different Operating Points on Flow around Small Axial Flow Fan Blade

An optimal design for axial-flow fan blade: theoretical and experimental studies

The technique of inverse design problem (IDP) for optimizing the three-dimensional shape of an axial-flow fan blade based on the desired airflow rate is presented in this work. The desired volume flow rate of air can be obtained from the airflow rate of the existing axialflow fan by multiplying it with a constant which is greater than unity. The geometry of the redesigned fan blade is generated using numerous design variables, which enables the shape of the fan blade to be constructed completely; thus the technique of parameter estimation for the inverse design problem can be used in this study. Results show that with the redesigned optimal fan blade, the airflow rate of fan can be increased, thereby improving the performance of the axial-flow fan. Finally, to verify the validity of this work, the prototypes of the original and optimal axial-flow fan blades are fabricated and fan performance tests are conducted with these blades on the basis of the AMCA-210-99 standard. The algorithm used in the present study can be applied to the blade design problem in any propulsion and power systems.

Numeric Analysis of Pneumatic Elasticity of Large Axial-flow Fan Blade

Numeric Analysis of Pneumatic Elasticity of Large Axial-flow Fan Blade

Design optimization of low-speed axial flow fan blade with three-dimensional RANS analysis

This work presents a numerical optimization procedure for a low-speed axial flow fan blade with polynomial response surface approximation model. Reynolds-averaged Navier-Stokes equations with SST turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. The blade profile as well as stacking line is modified to enhance blade total efficiency, i.e., the objective function. The design variables of blade lean, maximum thickness and location of maximum thickness are selected, and a design of experiments technique produces design points where flow analyses are performed to obtain values of the objective function. A gradient-based search algorithm is used to find the optimal design in the design space from the constructed response surface model for the objective function. As a main result, the efficiency is increased effectively by the present optimization procedure. And, it is also shown that the modification of blade lean is more effective to improve the efficiency rather than modifying blade profile.

익형의 형상최적화를 통한 고효율 축류송풍기 설계

This study presents a numerical optimization to optimize an axial flow fan blade to increase the efficiency. The radial basis neural network is used as an optimization method with the numerical analysis by Reynolds-averaged Navier-Stokes equations using SST model as turbulence closure. Four design variables related to airfoil maximum camber, maximum camber location, leading edge radius and trailing edge radius, respectively, are selected, and efficiency is considered as objective function which is to be maximized. Thirty designs are evaluated to get the objective function values of each design used to train the neural network. Optimum shape shows the efficiency increased by 1.0%.

On-line fan blade damage detection using neural networks

This paper presents a methodology for monitoring the on-line condition of axial-flow fan blades with the use of neural networks. In developing this methodology, the first stage was to utilise neural networks trained on features extracted from on-line blade vibration signals measured on an experimental test structure. Results from a stationary experimental modal analysis of the structure were used for identifying global blade mode shapes and their corresponding frequencies. These in turn were used to assist in identifying vibration-related features suitable for neural network training. The features were extracted from on-line blade vibration and strain signals which were measured using a number of sensors.The second stage in the development of the methodology entails utilising neural networks trained on numerical Frequency Response Function (FRF) features obtained from a Finite Element Model (FEM) of the test structure. Frequency domain features obtained from on-line experimental measurements were used to normalise the numerical FRF features prior to neural network training. Following training, the networks were tested using experimental frequency domain features. This approach makes it unnecessary to damage the structure in order to train the neural networks.The paper shows that it is possible to classify damage for several fan blades by using neural networks with on-line vibration measurements from sensors not necessarily installed on the damaged blades themselves. The significance of this is that it proves the possibility to perform on-line fan blade damage classification using less than one sensor per blade. Even more significant is the demonstration that an on-line damage detection system for a fan can be developed without having to damage the actual structure.

An optimal design of axial-flow fan blades by the machining method and an artificial neural network

The geometry design and machining of blades for axial-flow fans are important issues because the twisted profile and flowfield of blades are complicated. The rapid design of a blade that performs well and satisfies machining requirements is one of the goals in designing fluid machinery blades. In this study, an integrated approach combining computational fluid dynamics (CFD), an artificial neural network, an optimization method and a machining method is proposed to design a three-dimensional blade for an axial-flow fan. From the machining point of view, the three-dimensional surface geometry of a fan blade can be defined as the swept surface of the tool path created by using the generated machining method. By taking advantage of its powerful learning capability, a back-propagation artificial neural network is used to set up the flowfield models and to forecast the flow performance of the axial-flow fan. The desired optimal blade geometry is obtained by using a complex optimization method.

A Prediction Model for the Vortex Shedding Noise from the Wake of an Airfoil or Axial Flow Fan Blades

An analytical model is presented for predicting the vortex shedding noise generated from the wake of axial flow fan blades. The downstream wake of a fan blade is assumed to be dominated by the von Kármán vortex street, and the strength and the shedding frequency of the wake vortex are determined from the wake structure model. The fluctuating pressure and lift on the blade surface, which are induced from the vortices in the wake, are analyzed by incorporating the wake model for the von Kármán vortex street with thin airfoil theory. The predicted vortex shedding frequency and the overall sound pressure level compare favorably with the measured results for the vortex shedding noise from axial flow fans.

Flutter of a Fan Blade in Supersonic Axial Flow

An application of a simple aeroelastic model to an advanced supersonic axial flow fan is presented. Lane’s cascade theory is used to determine the unsteady aerodynamic loads. Parametric studies are performed to determine the effects of mode coupling, Mach number, damping, pitching axis location, solidity, stagger angle, and mistuning. The results show that supersonic axial flow fan and compressor blades are susceptible to a strong torsional mode flutter having critical reduced velocities that can be less than one.

Flow Visualization around Axial Flow Fan Blades

In this paper, we established a method of flow visualization around the wing of an axial fiow fan by use of a drum camera, which could measure the velocity distribution around the wing by overlapping the measurement results of the time-line and the stream-line obtained from the spark trace and the smoke wire respectively. In addition, we applied this method to two types of fans, which have different performances, in order to correlate the flow around the wing with the wing element efficiency. We also quantified the effect of tip vortex on the total fan noise.