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Low-pressure axial fan impellers designed according to the principle of equal specific work of all elementary stages have blades whose profile near the fan hub is under a significantly larger inclination angle than at the impeller periphery. In order to minimize the spatial curvature of the fan blades and the fan hub length, impeller blades of low-pressure axial fans can be designed with different specific work of elementary stages, so that the specific work of elementary stages is smaller at the hub than at the periphery. This paper presents the operating characteristics of a low-pressure reversible axial fan with straight blade profiles, de-signed with different specific work of elementary stages. The fan was tested on a standard test rig, with air intake loading on the suction side of the fan. [ABSTRACT FROM AUTHOR]

This paper describes research involving an in-service failure of a "variable pitch in motion" fan's blade bearing. Variable pitch in motion fans rotate at a constant speed, with the changing blade angle varying the load. A pitch-change mechanism facilitates the change in blade angle. A blade bearing supports each blade enabling it to rotate. The author observed that as the fan aerodynamic stage loading progressively increased, so did the rate of blade-bearing wear. The reported research addressed two separate, but linked, needs. First, the ongoing need to increase fan pressure development capability required an increase in fan loading. This increase was within the context of an erosive operating regime which systematically reduced fan pressure development capability. The second need was to identify the root cause of blade-bearing failures. The author addressed the linked needs using a computational analysis, improving the rotor inflow aerodynamic characteristics through an analysis of the inlet box and design of inlet guide vanes to control flow nonuniformities at the fan inlet. The results of the improvement facilitated both an increase in fan-pressure-developing capability and identification of the root cause of the blade-bearing failures. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue failure of holding U-bolt of a cooling fan blade is analyzed. Fractography of the fracture surface reveals the characteristics of a fatigue fracture. Finite element modeling is used for stress analyzing. Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue. Effective alternating and mean stresses are obtained based on the multiaxial fatigue criteria. By using the modified Goodman approach and considering the notch effect, effective stress amplitude, is obtained for all nodes. The highest stress amplitude is obtained at six critical nodes. Fatigue life for the most critical node is determined as 3.63 million cycles. [Copyright &y& Elsevier]

Abstract: The present work was carried out to investigate the failure mechanism of a power plant forced draft fan (FDF) blade made of 2014-T6 Al alloy, using visual examination, microstructural characterizations, study of the fracture surface and hardness testing. Based on the obtained results, surface defects including corrosion pits due to the existence of Cl ion and also erosion pits due to mechanical action of particles in the air entering from the filtration system and abrading on the fan blades surfaces, increased the probability of surface crack initiation. Cyclic loading and stress concentration on these surface defects influenced the fatigue life of the blade due to elevating the mean stress and resulted in fatigue failure of the investigated FDF component. [Copyright &y& Elsevier]

Abstract: The purpose of this work is to study the effects of blade thickness on the performances of an axial-flow fan. Two fans that differ only in the thickness of their blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin blades. The second fan has much thicker blades compatible with the rotomoulding conception process. The overall performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus flow-rate) is slightly steeper for the fan with thick blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick blades fan is lower than the efficiency of the fan with thin blades but remains high on a wider flow-rate range. The mean velocity fields downstream of the rotors are very similar at nominal points with less centrifugation for the thick blades fan. Moreover, the thick blades fan maintains an axial exit-flow on a wider range of flow-rates. The main differences concern local properties of the flow: phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick blades fan that for the thin blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range. [Copyright &y& Elsevier]

This paper studies the effects of blades' forward-swept amount in the rotation direction and forward-inclined amount in the intake direction on the flow around the fan blades of a large open-type motor. The authors have previously clarified this flow separation on the blade surface under high ventilation resistance from flow analysis and visualization experiments. To prevent flow separation, they proposed forward-swept and inclined blades, together with reduction of the air path's ventilation resistance. In this study, numerical fluid analyses were performed on the flow around forward-swept and inclined blades of axial fans for large open-type motors. Several combinations of forward-swept and inclined amounts were studied. The relationship between forward-swept and inclined amounts and flow was evaluated quantitatively, and an ideal combination was obtained. The study revealed that an axial fan with this combination showed much higher flow rate than a conventional fan without forward-swept and inclined blades. Furthermore, it significantly decreased fluid noise and axis power. [ABSTRACT FROM AUTHOR]

The effect of the pitch of the blades in an axial fan with an UK-2M impeller 2.8 m in diameter on the characteristics of a horizontal three-section air cooler (AC), the six-tier heat-exchange sections of which consist of bimetallic finned tubes with rolled aluminum fins (tube-finning factor of 20.4; medium cooled – gasoline) is analytically investigated. It is found that for the same power consumed by the fan drive, the pitch of the fan blades in the interval from 15 to 25° will not affect the thermal flux of the AC. Recommendations are given for selection of energy-expedient pitches of the blades during AC operation, and also for thermal analyses of units under design. [ABSTRACT FROM AUTHOR]

Abstract: This study presents an experimental work concerning the thermal performance of piezoelectric fans. A total of six piezoelectric fans with various blade geometries are made and tested. The influence of geometric parameters, including the horizontal/vertical arrangement, and location of the piezofan, on the performance of piezofans is examined. It is found that the heat transfer augmentation of the piezofan comes from the entrained airflow during each oscillation cycle and the jet-like air stream at the fan tip, yet these two modes are of the same order of magnitude. The heat transfer performance for vertical arrangement shows a symmetrical distribution and peaks at the center region whereas the horizontal arrangement possesses an asymmetrical distribution and shows an early peak at x/L =0.25. It is also found that the heat transfer performance for horizontal arrangement is not necessarily lower than that of vertical one. Based on the dimensionless analysis to the test results for the all six fans, a correlation applicable for x/L =0 is proposed. The mean deviation is 4.8% that can well describe the influence of geometrical parameters. [Copyright &y& Elsevier]

Abstract: The failure analysis of a generator rotor fan blade was investigated by mechanical analysis and metallurgical examination of fracture surface. Fracture took place at the airfoil root, surface examination showed that the blade had cracked by a high cycle fatigue mechanism. However, there was no evidence of material defect. A series of analytical, finite element and experimental analysis was utilized to determine the steady-state stresses and dynamic characteristic of the blade. Possibly the failure was due to aerodynamical disturbances that resulted in a state of resonant condition of vibration. The simulation of blade with final crack showed the stress intensity factor (SIF) under these condition exceed the critical SIF and final fracture could be occurred under analyzed stresses. [Copyright &y& Elsevier]

Initially in this research, effects of blade inlet and outlet angles on the performance were considered by measuring performances. Twelve impellers with various blade angles were used for the measurements. The most suitable inlet and outlet angles and the inclination angle were acquired. Then, measurements on the inlet and outlet flows and their axial and circumferential distributions were taken for various operating conditions at the various measuring positions. The turning angles through the blade were calculated from these measured results. The inlet and outlet flows of the sirocco fan are not uniform around the circumference. The distributions of the flow have some relations with the development of flow in the inlet part and in the casing. Discussions were made on the flow to have a improved performance. [ABSTRACT FROM AUTHOR]