Performance Of Axial Flow Fan Research Articles

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.

Effect of tip geometry on the performance of low-speed axial flow fan

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.

Effect of meridional shape on performance of axial-flow fan

In this study, the effect of impeller meridional shape on the performance of axial-flow fan is investigated by CFD method. Three axialflow fan impellers with different meridional shapes are designed. The blade angle, blade stacking condition and other structure factors of the impellers are all remained consistent. The performance curves of the three impellers are calculated and compared. In almost all the interested flowrate range, the impeller W3 with an inverted-isosceles-trapezoid meridional shape and the longer blade camber achieves both the higher pressure rise and the higher efficiency than the other two impellers. A two-stage axial-flow fan designed on basis of W3 is manufactured and tested. Test results show good agreement with the calculated performance curves. Further, analyses of the CFD results are conducted to reveal the reasons for the different performance. A newly-defined Local Euler head (LEH) is introduced to represent the distribution of the major Euler work in the axial-flow fan. And the LEH distributions in the three impellers are obtained. W3 achieves the highest LEH at blade Trailing edge (TE), because it could perform the most Euler work to the fluid with the longest blade camber. Then losses in the impellers are analyzed by means of the entropy generation. Among the losses in impeller, the tip leakage loss and endwall friction loss are dominated at design flowrate. The generation condition of the tip leakage loss shows significant differences among the three impellers. And the whole power loss in impeller of W3 is slightly higher than those of the other two models. However, the power loss difference among the three impellers is negligible. And due to the highest shaft power, the efficiency loss of W3 is the lowest of all.

Investigation of aerodynamic performance of small axial flow fan coupled with deflecting ring

Experimental and numerical investigations on the effect of deflecting rings featuring different axial lengths on aerodynamic performance of the small axial flow fan were conducted under the condition of maximum flow rate. Two deflecting rings, the semi-open type and closed type, were investigated. Aerodynamic and aeroacoustic performances have been measured in experiment, and key analysis of flow was based on computational fluid dynamics results. The numerical and experimental results show that the deflecting ring has great influence on the performance of an axial flow fan. For the semi-open-type deflecting ring, the fan has better P-Q performance and higher efficiency; pressure, vorticity, and vorticity gradient distributions on the blade surface are more uniform; and noise level of the fan is lower at wider frequency bands. For the closed-type deflecting ring, the performance curve has a convex feature; blade pressure difference between the pressure surface and the suction surface is much bigger. The result shows that better aerodynamic and aeroacoustic performances of the axial flow fan can be acquired when the semi-open-type deflecting ring is adopted.

Simulating the Effect of Wind on the Performance of Axial Flow Fans in Air-Cooled Steam Condenser Systems

The use of air-cooled steam condensers (ACSCs) is preferred in the chemical and power industry due to their ability to adhere to stringent environmental and water use regulations. ACSC performance is, however, highly dependent on the prevailing wind conditions. Research has shown that the presence of wind reduces the performance of ACSCs. It has been found that cross-winds (wind perpendicular to the longest side of the ACSC) cause distorted inlet flow conditions, particularly at the upstream peripheral fans near the symmetry plane of the ACSC. These fans are subjected to what is referred to as “two-dimensional” wind conditions, which are characterized by flow separation on the upstream edge of the fan inlets. Experimental investigations into inlet flow distortion have simulated these conditions by varying the fan platform height. Low platform heights resulted in higher levels of inlet flow distortion, as also found to exist with high cross-wind velocities. The similarity between platform height and cross-wind velocity is investigated in this study by conducting experimental and numerical investigations into the effect of distorted inlet flow conditions on the performance of various fan configurations (representative of configurations used in the South-African power industry). A correlation between system volumetric effectiveness, platform height, and cross-wind velocity is derived which provides a means to compare platform height and cross-wind velocity effects.

Numerical Investigation of Blade Trimming Effect on Performance of Axial Flow Fan

Blade trimming is a simple and effective mean to solve the excessive margin of axial fans. For a variable-pitch axial fan of OB-84 type, the variation of performance curves with relative blade trimming quantity of 5%, 10% and 15%, respectively, are simulated when the tip clearance is changed and unchanged. The effects of blade trimming quantity and tip clearance on internal dynamics and operating performance are investigated, and the formulas of operating points before and after blade trimming are presented. The results show that both of full pressure and efficiency curves for the fan with blade trimming tend to decrease compared with the original one, and it is confirmed that the performance of the fan with tip clearance unchanged, near the design condition, is superior to that when tip clearance changed, which is contrary to the large flow rate. The margin of parameters provided by original design is so large that the fan usually operates at the left side of rated load; therefore, the blade trimming of axial fan should keep tip clearance unchanged in order to maintain better performance. The tip clearance has a significant effect on the formulas of operating points before and after blade trimming. The formulas given effective to predict the actual trimming amount of blades, which provide an important reference for blade trimming in practical applications of axial fans.

Numerical Simulation on Axial Flow Fan Performance with Changing Tip Clearance

Taking the relative tip clearance as the variable, we numerically simulated the effect of tip clearance size on the performance of a straight-blade axial flow fan using the 3-D viscous flow solver. The tip clearance is referenced in the relative value. By comparing the flow field corresponding to five different values of the tip clearance 0, 0.5%, 1.0%, 1.5% and 2.0% with other parameters kept constant, we concluded that the changing of the tip clearance has a great influence on the performance of the axial flow fan. Both the efficiency and the total pressure decrease with the increase of the tip clearance.

CFD Optimization Analysis of a Cooling Fan for Mining Dump Truck

Axial flow fans are widely used in our daily lives such as automotive cooling systems, electronic appliances and air conditioning. The factors that affect the aerodynamic performance of axial flow fans include blade number, fan diameter, hub ratio, blade angle, rotating speed, etc. This paper investigates effects of hub ratio and bladenumber on the aerodynamic performance of the axial flow fan of the radiator of a dump truck we previously designed for mining. With the computational fluid dynamics (CFD) method, the fans operation condition, such as entry static pressure, effective power and flow rate, are numerically simulated with various hub ratios and blade numbers. The results of the numerical simulations are quantitatively analyzed and curves of fans performance changing with hub ratio and blade number are given. An optimization design for the cooling fan is conducted. The results of numerical simulation give conclusion that an increase of 5.6% of the vacuum static pressure and an increase of 3% of flow rate can be obtained when the hub ratio is between 500-600mm, with the same or even less power consumption. The flow rate increment reaches its peak at 8%, while power consumption efficiency is almost linearly increased, when the blade number increases to be in the range of 8 to 10. That is to say when the blade number is between 8 to 10, the fan is apparently making better use of energy. Compared with experimental method, computational fluid dynamics (CFD) method can reduce design circle and lower cost. The CFD results provide guidance to improvement of design efficiency and energy utilization.

CFD Simulation of Installation Angle for Axial Flow Fan of a Motor

To analyze the effect of the installation angle on the performance of axial flow fan, single blade model and whole model was established, steady flow in the axial flow fan of the 7500KW air-cooled motor was simulated by software FLUENT. Volume flow rate and hydraulic efficiency of the fan with different installation angle under specific outlet pressures were analyzed, the effect of different turbulence model on the numerical simulation results was discussed, and the effect of the single blade model, the whole model and lengthened flow passage model on the numerical calculation results was compared. The results show that the fan volume flow rate and hydraulic efficiency is higher with the installation angle of 30°, the results simulated by standard k-ε model are close to the results simulated by k-ω-SST model, calculation results of these three methods have a good agreement with each other, and the result coincides well with experimental measured values.

The Effects of Radially Distorted Incident Flow on Performance of Axial-Flow Fans With Forward-Skewed Blades

In this study, experiments and numerical simulations were carried out to evaluate the effects of radially distorted incident flow on the performance of axial-flow fans, which were equipped with three kinds of forward-skewed blades. Loss coefficient and velocity components at exit section as well as overall performance are discussed, both at the design point and the lower mass flow rate point. Furthermore, rotating stall was also observed by use of three dynamic pressure sensors. All results reveal that there are beneficial effects of forward-skewed blades on the fan performance, but the fan performance and its unsteady aerodynamic characteristics are quite affected by the radially distorted incident flow.

에어컨 실외기용 축류홴의 성능에 관한 연구: 유동 특성

The aerodynamic performance of axial flow fans for outdoor unit of air-conditioner is investigated by numerical and experimental approaches in this study. The pressure drop and volumetric flow rate are compared each other in several different conditions and fan speeds. It is shown that the predicted fan performances are quite well matched with the experimental results. It is also shown that the curvature of the fan arc and hub height have significant influences on the flow distribution after hub. By the results of this study, it can be suggested that several ways to improve the aerodynamic performance of the axial flow fan can be found using the numerical analysis.

에어컨 실외기용 축류홴의 성능에 관한 연구: 소음 특성

The aerodynamic performance of axial flow fans for outdoor unit of air-conditioner is investigated by numerical and experimental approaches in this study. The pressure drop and volumetric flow rate are compared each other in several different conditions and fan speeds. It is shown that the predicted fan performances are quite well matched with the experimental results. It is also shown that the curvature of the fan arc and hub height have significant influences on the flow distribution after hub. By the results of this study, it can be suggested that several ways to improve the aerodynamic performance of the axial flow fan can be found using the numerical analysis.

Effect of inlet box on performance of axial flow fans

Numerical investigations on 3D flow fields in an axial flow fan with and without an inlet box have been extensively conducted, focusing on the variation of fan performance caused by the internal flow fields and the velocity evenness at the exit of the inlet box. It is interesting to find that although the inlet box is well designed in accordance with basic design principles, there is a flow separation region in it. Furthermore, this flow separation and the resulting uneven velocity distribution at the exit lead to some decrease in the efficiency and an increase in the total pressure rise of the fan. This research shows that the inlet box needs further improvement and such a check on the flow fields is of value for the design of inlet boxes.

Effects of Inflow Distortion due to Hub Cap's Shape on the Performance of Axial Flow Fan

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depend on the distance between hub-cap and blade leading edge. Three-dimensional Reynolds-averaged Navier-Stokes equations are introduced to analyze the flow characteristics inside the blade passage. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces separated flow on the blade surfaces near the hub region, and thus deteriorates the performance of fan rotor. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

Exit Flow Field and Performance of Axial Flow Fans

Flow fields near the exit and the global performance parameters of the various types of axial flow fans are studied with Particle Image Velocimetry and a standard AMCA 210 flow bench. The fans used in this study included the shrouded, shroudless, and winglet-blade types. The velocity vectors, streamlines, vorticity contours, velocity distributions, and performances are presented and discussed. The flow patterns on the radial and axial planes show that a vortex always exists near the exit of the fans at various impeller angles. The experimental results demonstrate that the shrouded fan with winglets has the most stable flow field and the best fan performance.

Numerical investigation into the effect of cross-flow on the performance of axial flow fans in forced draught air-cooled heat exchangers

Air-cooled heat exchangers (ACHEs) which utilise large arrays of axial fans, commonly suffer from inlet flow losses related to off-axis flow into the fans. This investigation aims to extend current knowledge on the effect of off-axis inflow on the performance of axial fans in this type of installation. An actuator disk fan-model was developed for the Computational Fluid Dynamics (CFD) code, FLUENT TM, and validated against experimental data for off-axis inflow angles up to 45°. Agreement between numerical and experimental pressure rise was good, although fan power consumption and fan static efficiency were under and over-predicted respectively. Experimentally observed trends were confirmed numerically: fan static pressure rise and efficiency were adversely affected, while fan power consumption was not significantly affected by the presence of cross-flow into the fan. The investigation revealed that while the torque characteristics over the outer portion of the fan blades are fundamental in determining the global fan power requirements, the net effect of cross-flow in this region is very small. Local variations of blade torque at diametrically opposed orientations more or less cancel each other out, explaining the independence of fan power consumption to cross-flow conditions. The adverse effect of off-axis inflow on fan static pressure rise was attributed to two factors: increased kinetic energy per unit volume at the fan exit, and greater dissipation through the fan itself. Off-axis inflow was found to affect fan-blade loading characteristics, with implications for blade fatigue.