Axial Fan Blade Research Articles

Numerical and experimental investigation of axial fan with trailing edge self-induced blowing

Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. In the present paper, a modification of conventional axial fan blades with numerical and experimental investigation is presented. Hollow blades were manufactured from the hub to the trailing edge at the tip of the blades. They enable the formation of self-induced internal flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the openings near the fan hub and exits through the trailing edge slots at the tip of the blade. The study of the influence of internal flow on the flow field of axial fan and the modifications of aerodynamic characteristics of the axial fan have been made. The numerical and experimental results show a comparison of integral and local characteristics of the axial fan with the internal flow, compared to characteristics of a geometrically equivalent fan without internal flow. The experimental results of local characteristics were performed with a five-hole probe and computer-aided visualization. A reduction of adverse flow conditions near the trailing edge at the tip of the blade was achieved, as well as boundary layer reduction on the blade suction side and the reduction of flow separation. The introduction of self-induced blowing led to the preservation of the direction of external flow, defined by blade geometry, and enabled maximal local energy conversion. The integral characteristic reached higher degree of efficiency.

Patented Hollow Blades of the Axial Fan with Trailing Edge Self-Induced Blowing

Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. In the present paper, a modification of conventional axial fan blades with experimental investigation is presented. Patented hollow blades were manufactured from the hub to the trailing edge at the tip of the blades. They enable the formation of self-induced internal flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the openings near the fan hub and exits through the trailing edge slots at the tip of the blade. The influence of internal flow on the flow field of axial fan and the modifications of aerodynamic characteristics of the axial fan have been studied along with recent patents. An experimental investigation of the interaction of two flows with the flow around hollow airfoil NACA series in a low-speed wind tunnel was studied. The determination of flow structure on the hollow airfoil was performed with computer-aided visualization. With the introduction of the internal flow and interaction with the external flow, a reduction of circulation effects on the fan hollow blade was achieved. The introduction of self-induced blowing led to the preservation of the direction of external flow, defined by blade geometry, and enabled maximal local energy conversion. Aerodynamic characteristic of the axial fan reached higher degree of pressure difference and efficiency through the entire fan working conditions. Keywords: Axial fan, hollow blade, aerodynamic characteristic, wind tunnel and computer-aided visualization

Analytical and numerical investigation of the optimum pressure distribution along a low-pressure axial fan blade

In the field of axial flow turbomachines, the two-dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined aerofoil profiles. While most design strategies based on the aerofoil theory assume constant total pressure at all streamlines, i.e. free-vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at a specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted (i.e. sufficient lift and controlled deceleration of the flow on the contour) so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20 per cent absolute increase in the static efficiency of the optimized impeller.

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%.

최적화기법을 이용한 축류형 송풍기개발에 관한 연구

An axial-type fan which operates at the relative total pressure of 671 ㎩ and static pressure of 560 ㎩ with the flow rate of 416.6 ㎥/min is developed with an optimization technique based on the gradient method. Prior to the optimization of fan blade, a three-dimensional axial-type fan blade is designed based on the free-vortex method along the radial direction. Twelve design variables are applied to the optimization of the rotor blade, and one design variable is selected for optimizing a stator which is located behind of the rotor and is used to support a fan driving motor. The total and static pressure are applied to the restriction condition with the operating flow rate on the design point, and the efficiency is chosen as the response variable to be maximized. Through these procedures, an initial axial-fan blade designed by the free vortex method is modified to increase the efficiency with the satisfaction of the operating condition. The optimized fan is tested to compare the aerodynamic performance with an imported same class fan. The test result shows that the optimized fan operates with the satisfaction of restriction conditions, but the imported fan cannot. From the experimental and numerical test, they show that this optimization method improves the fan efficiency and operating pressures of a fan designed by the classical fan design method.

An investigation of bending fatigue behavior for glass-fiber reinforced polyester composite materials

To investigate bending fatigue behaviors for glass-fiber reinforced polyester composite material, 800 g/m 2, 500 g/m 2, 300 g/m 2, and 200 g/m 2 glass-fiber woven and 225 g/m 2, 450 g/m 2, and 600 g/m 2 randomly distributed glass-fiber mat samples with polyester resin have been used. The samples have been produced by the RTM (Resin Transfer Molding) method and the samples have been cut down with directions of 0/90°, ±45°. As results of the combinations from the samples, nine different structures has been obtained. Furthermore, a new mold have been designed for the RTM method. To provide a full infiltration (wetting) of fibers, a simple method has been applied in this new mold system. A new computer aided and multiple-specimen test apparatus have been designed and constructed to simulate load and stress behavior of axial fan blades on the wind tribunes. This multiple specimen apparatus has a big advantage to shorten test time and to test 16 specimens at the same time. Firstly, composite specimens have been applied to the three-point bending test. Later, fatigue tests have been carried out. For the bending fatigue test, “fixed stress” fatigue type has been used. To determine the fatigue limit of all the specimens, S–N diagrams (Wöhler plots) have been derived from experimental results. According to the test results, the highest fatigue life has been obtained from 800 g/m 2 fiber glass woven specimens with 0/90° (group E). The property of anisotropy of the GFRP (Glass Fiber Reinforced Plastic) material is dominant on the fatigue strength which has been clearly observed from the experiments. In the test results, the effective parameters are density of fiber distribution on the area, fiber angle, resin permeability of woven fiber, full infiltration (wetting) or without infiltration of fibers.

Development of a new free wake model considering a blade–vane interaction for a low noise axial fan planform optimization

Multidisciplinary Design Optimization (MDO) is an essential part for low noise axial fan design since various parameters, such as flow rate, efficiency, noise etc., should be considered. For this reason, Response Surface Method (RSM) design technique is adopted as an axial fan design method. RSM has an advantage of choosing objective functions and constraint conditions unrestrictedly on a design space. However, RSM needs a lot of independent variables to construct a proper response surface. Thus an efficient and accurate flow analysis tool is indispensable for optimization. In an axial fan, the discrete (commonly called Blade-Passage-Frequency) components are usually dominant in the noise spectrum. Especially the blade–guide vane interaction is one of most important noise sources. In order to predict this noise component efficiently at the design stage, a new free wake model named Finite Vortex Element (FVE) is devised to simulate this blade–guide vane interaction, which is very difficult to analyze numerically in a conventional free wake model. In this new free wake model, the blade–wake–guide vane interaction is described by cutting a vortex filament when the filament collides with a guide vane. This FVE model is compared with a conventional curved vortex methodology and verified by a comparison with measured data to show its effectiveness and validity. Then FVE model is coupled with RSM to implement a low noise axial fan blade optimization. Using this method, a reduction of 8 dB(A) at 2 m from fan hub in the overall noise level is achieved while the flow rate and the efficiency are maintained as the values of the baseline blade, which implies that FVE wake model coupled with RSM is very effective methodology for MDO problems such as a low noise axial fan design.

Stereoscopic PIV 기법의 개발과 이를 이용한 축류 홴 후류의 유동해석

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. 등록된 정보가 없습니다.

Unsteady Pressure Field Investigation of an Axial Fan—Blade Unsteady Pressure Field Measurement

This article has no abstract.

1102 軸流ファンの翼先端近傍の速度変動による騒音発生

1102 軸流ファンの翼先端近傍の速度変動による騒音発生

An Improved Fan Blade Impact Test

Impact testing may be performed on an axial fan blade using a strain gage as a reference and a dead blow hammer instead of an instrumented impact hammer. The strain gage is mounted between the blade base and airfoil and is sensitive to all bending modes. This method is useful when the mass of a hammer or exciter armature would affect the blade response adversely. A small accelerometer is moved around a grid in the normal fashion. Some of the improvements are a better defined response in both bending and twisting modes and higher coherence frequency response functions.

Problems of fatigue strength definition for shell structures

Stresses caused by oscillations of shell structures may vary significantly even for the same oscillation form. Therefore, during fatigue tests it is very important to solve the loading problem for these structures and further evaluate their fatigue strength statistical parameters. A new method for solution of these difficult problems is proposed in this paper. The basic idea is to take into account relative load values of fatigue tests instead of often used absolute load values. The fatigue loads are reproduced on a test bed by the same means by which the dynamic loads were determined. Levels of fatigue loads used in the tests are based on the individual dynamic loads for each of the structures investigated. The basic principles are described for axial fans used in railway transport. Axial fan blades are a characteristic example of shell structures.

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.

A Simple Method for the Selection of Axial Fan Blade Profiles

Existing data on aerofoil sections suitable for axial flow fans are replotted on axes of angle of incidence against camber angle. The carpet plots so obtained permit the best operating conditions for each type of aerofoil to be immediately identified and thus the most suitable section can be easily selected for a given specification. A design method based on the use of these carpet plots is proposed and illustrated with a numerical example.

A Simple Method for the Selection of Axial Fan Blade Profiles

A Simple Method for the Selection of Axial Fan Blade Profiles

Influence of design factors on amplitude-frequency characteristics of axial fan blades

Influence of design factors on amplitude-frequency characteristics of axial fan blades