Effect of Pre-Swirling Flow on Performance and Flow Fields in Semi-Opened Axial Fan

In this study, we tried to improve the performance by giving a pre-swirling flow to the radial inflow that occurred in the semi-opened axial fan. In addition, the flow fields of rotor outlet were clarified experimentally, and the effect of pre-swirling flow was considered. The experiment was carried out using a performance test wind tunnel with a square cross section of 880 mm. Three types of casings were prepared, in which the blade tip protruded 0%, 20%, and 40% of the meridional chord length. They were called R25, R15, and R05, respectively, in the casing bellmouth model code. Guide blades for generating a pre-swirling flow were installed on the vertical wall surface of the casing. In addition, a vertical wall was installed 60% upstream of the meridional chord length as an obstacle to prevent axial inflow. The velocity fields of the rotor outlet were measured using a hot-wire anemometer. From the results, the pre-swirling flow did not significantly affect the fan performance. When there was no obstacles wall upstream, there was a partial increase in efficiency, but the difference was not so large. When there was an obstacle wall upstream, the efficiency increased overall in the case of R15, but in the case of R05, the efficiency increased only in the low flow rate region, and conversely decreased in the high flow rate region. By observing the blade outlet flow fields when the performance was improved, it was confirmed that the influence of the tip leakage vortex was weakened.

INFLUENCE OF GEOMETRIC PARAMETERS ON CENTRIFUGAL FAN PERFORMANCE AND ITS SIGNIFICANCE IN AUTOMOTIVE APPLICATIONS

In this paper,the effect of geometrical parameters of centrifugal fan on performance has been presented with a system approach.Often,the operators or the design engineers focus on the immediate requirements of the engine/equipment and they neglect the broader question of how the fan parameters are affecting the equipment.For instance,change in fan angles will change the performance e.g.,airflow rates and efficiency.However,it also affects the contaminants build-up on the blades.Blade angle with higher angle of attack will promote contaminants build-up on blade surfaces,which in turn causes performance degradation and unstable operation.The system approach in fan parameter selection will result in a more reliable system.Significance of other fan parameters is also discussed.We present an experimental setup and validated computational fluid dynamic(CFD)model.Fan power consumption is determined experimentally and compared with the CFD model.Further parametric simulations were carried out to investigate the effect on fan performance.Effect of system resistance,inlet and outlet angle,blade thickness,and no-uniform spaced blades has been described with discussions on industrial relevance.A fan with higher flow rates is desirable to reduce engine temperatures and enhance the durability.However,higher flow rates result in more fan power consumption at a given fan speed.The test results suggest that a fan with higher power coefficient does not affect the vehicle’s mileage significantly.This paper will help design engineers in making informed decision about the interaction between the fans and system,and its effect during the operation.

PERFORMANCE IMPROVEMENT OF CENTRIFUGAL FAN BY MEANS OF NUMERICAL SIMULATION

Numerical simulation is used to investigate the flow field in a model centrifugal fan for steam power stations in order to improve the performance. During testing the model fan, it is found that the efficiency is only 62.5% with inlet box, without it the efficiency is 83%. In addition, the strong vibration of test rig is observed with inlet box. It would be highly desirable if the aerodynamics of the fan could be studied. Therefore, numerical simulation is carried out to investigate the internal flow characteristics of a model fan with inlet box. The results from CFD analysis show that the whole region of the inlet box is occupied by a spiral vortex rotating inversely as the rotor＇s direction, which significantly affect the most flow＇region inside the fan. For this reason, a dummy plate is arranged in the inlet box to impede the generation of the spiral vortex, the results from CFD after the reform demonstrate that the modification is quiet effective, the former large spiral vertex has been destroyed effectively, the large one is superseded in favor of two small vortexes. However, two small vortexes have little effect on the inner flow of the rotor and the following parts. Finally, the efficiency of the model fan is improved by the test and the strong vibration of the test rig disappears. This type of modification has been used in steam power stations, the fan efficiency raises to 84% successfully.

INTERNAL FLOW IN CROSS-FLOW FAN FOR AIR CONDITIONER

A numerical analytic process is suggested combining direct boundary element methodwith discrete vortex method and internal flow in cross-flow fan calculated. The process considersnot only function of impeller, but also effect of volute casing. Internal flow field of cross-flow fan ispractically measured, and results compared with that from calculation. It shows that the process isexpected to be used in predicting performances of fluid machinery.

EXPERIMENTAL INVESTIGATION OF PASSIVE CONTROL ON UNSTABLE CHARACTERISTICS IN AXIAL FLOW FAN

Experimental investigation of the passive control on improving the unstable characteristics in axial flow fans is performed. It is confirmed that the air-separator is an excellent equipment for rotating stall suppression. The air-separator can effectively remove low energy fluid near the fan casing. Further, it can improve the low flow rate range performance and increase stall margin of the axial flow fan.

Evaluation of ventilation performance and energy efficiency of greenhouse fans

In order to investigate fan performance in fan-ventilated greenhouses(Urbana,USA),the effects of guard screen and loose belts on fan ventilation airflow and power consumption in greenhouse operations were examined with four belt-driven fans as trial subjects.The Fans Assessment Numeration System was used to measure the airflow rate.Temperature,relative humidity and power consumption were also monitored.Results show there were significant differences in the airflow rate between the fans with a cleaned and uncleaned guard screen(P<0.05).Power consumption also differed significantly even with the same cooling effect in greenhouse.When fan belts were adjusted to the proper tension,the fan speed and airflow rate were 13.1% and 30.1% higher than those of original belts,respectively.The daily average power consumption for the fan with the original loose belts was 20.4% higher than that with the adjusted belts when the pad was not working and 24.2% higher with pad working.The ventilation performance of fans with identical specifications showed a variation by up to 13.0% in terms of the ventilating efficiency ratio.These results demonstrated that fans should be cleaned routinely,and belt tension should be checked to ensure that fan performance meets specifications.This can reduce the power consumption in greenhouses for environmental control.Moreover,reordering fan staging,so that the most efficient fans are used in areas of greatest demand,can also reduce ventilation energy costs.