EFFECT OF TIP CLEARANCE ON PERFORMANCE AND FLOW FIELD OF SMALL SIZED HIGH SPEED CENTRIFUGAL FAN

A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to the fixed outer casing. Computational models with/without the tip clearance are built and the κ-ω shear stress transport （SST） turbulence model and the unstructured mesh are applied to the numerical simulation for unsteady solutions. The overall performance is measured on a standard experimental bench and the major flow feature of each component inside the centrifugal fan is numerically investigated. In the presence of the tip clearance due to the difference of static pressure between leading and trailing edges of the clearance, i. e. , leading and trailing edges of the impeller, a strong return flow exists inside the clearance passage and re-circulates the main stream inside the impeller passage, and produces the strong flow interaction, thus changing the flow field and influencing the overall performance.

Prediction and optimization of aerodynamic noise in an automotive air conditioning centrifugal fan

The high aerodynamic noise induced by automotive air conditioning systems has important effects on the ride comfort, and the centrifugal fan is the largest noise source in these systems. It is very important to reduce the aerodynamic noise generated by the centrifugal fan. The flow field and the sound field on the whole centrifugal fan configuration have been carried out using the computational fluid dynamics. Simulation results show that the sound pressure level near the outlet of the centrifugal fan is too high. Based on the relationship between flow characteristics and the aerodynamic noise, four parameters of the centrifugal fan, i.e., impeller blade＇s outlet angle 0, volute tongue＇s gap t, collector inclination angle fl, and rotating speed n, were selected as design variables and optimized using response surface methodology. While keeping the function of flow rate unchanged, the peak noise level is reduced by 8 dB or 10.8%. The noise level is satisfactorily reduced.

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.

Fluent-based numerical simulation of flow centrifugal fan

Testing centrifugal fan flow field by physical laboratory is difficult because the testing system is complex and the workload is heavy, and the results observed by naked-eye deviates far from the actual value. To address this problem, the computational fluid dynamics software FLUENT was applied to establish three-dimensional model of the centrifugal fan. The numeral model was verified by comparing simulation data to experimental data. The pressure centrifugal fan and the speed changes in distribution in centrifugal fan was simulated by computational fluid dynamics soft-ware FLUENT. The simulation results show that the gas flow velocity in the impeller increases with impeller radius increase. Static pressure gradually increases when gas from the fan access is imported through fan impeller leaving fans.

Multi-objective Optimization Design and Experimental Investigation of Centrifugal Fan Performance

Current studies of fan performance optimization mainly focus on two aspects： one is to improve the blade profile, and another is only to consider the influence of single impeller structural parameter on fan performance. However, there are few studies on the comprehensive effect of the key parameters such as blade number, exit stagger angle of blade and the impeller outlet width on the fan performance. The G4-73 backward centrifugal fan widely used in power plants is selected as the research object. Based on orthogonal design and BP neural network, a model for predicting the centrifugal fan performance parameters is established, and the maximum relative errors of the total pressure and efficiency are 0.974% and 0.333%, respectively. Multi-objective optimization of total pressure and efficiency of the fan is conducted with genetic algorithm, and the optimum combination of impeller structural parameters is proposed. The optimized parameters of blade number, exit stagger angle of blade and the impeller outlet width are seperately 14, 43.9~, and 21 cm. The experiments on centrifugal fan performance and noise are conducted before and after the installation of the new impeller The experimental results show that with the new impeller, the total pressure of fan increases significantly in total range of the flow rate, and the fan efficiency is improved when the relative flow is above 75%, also the high efficiency area is broadened. Additionally, in 65% -100% relative flow, the fan noise is reduced. Under the design operating condition, total pressure and efficiency of the fan are improved by 6.91% and 0.5%, respectively. This research sheds light on the considering of comprehensive effect of impeller structrual parameters on fan performance, and a new impeller can be designed to satisfy the engineering demand such as energy-saving, noise reduction or solving air pressure insufficiency for power plants.

Application of a Cleaning System Made up of a Centrifugal Fan with Double Channel and One Sieve to Combine

In this paper the application of a cleaning system which was made up of a centrifugal fan with double channel and one sieve to 4LZ-3.5 combine was introduced. This cleaning system with double channel compared with the traditional air-sieve cleaning system of combines may omit one two sieves and simplify the transmission mechanism. It is also compared with the present cleaning system with double channel applied to some combines, such as the Commandor 112CS/ 228CS combines of Claas Corporation in Germany and the MAXIMIZERTMombincs of John Deerc company in U.S.A. It may omit one sieve and the preclcaner and simlify the transmission mechanism. The measuring results indicated that the cleaning ratio of wheat grain is 99.1% and the cleaning loss ratio of wheat is 0.17% when the feed rate is 4.01 kg/ s.

Bionic Volute Tongue Optimization Design of Multi-blade Centrifugal Fan Inspired by the Wave Leading-edge of Humpback Whale Flippers

The volute tongue can split the gas in the multi-blade centrifugal fan to make the gas flow to the volute outlet as much as possible.However,the unsteady axial deflection of the gas in the impeller results in different air flow angles at the outlet of the impeller at different blade heights.This seriously affects the flow near the volute tongue.The wave leading-edge structure of humpback whale flippers has a very high flow control effect under complex flow conditions.Therefore,the wave leading-edge structure is studied in this paper and applied to the optimization design of multi-blade centrifugal fan volute tongue.First,based on the wave leading-edge structure of humpback whale flippers,three-dimensional wave leading-edge airfoils with different wave direction angles are established to judge the adaptability of the new wave leading-edge structure under different attack angles.Then,aiming at the internal flow field and noise characteristics of multi-blade centrifugal fan,a bionic volute tongue optimization design method is proposed,and studied its influence on the internal flow field and noise characteristics of the fan.The results show that when the wave direction angle is 45°,the wave leading-edge structure can effectively suppress the generation of the leading-edge separation vortex and the shedding of the wake vortex,which is also helpful to reduce the noise.The bionic volute tongue with the wave leading-edge structure can adapt to the situation that the impeller outlet air flow angle is small.At the maximum volume flow rate operating point,the static pressure recovery coefficient of the bionic volute tongue fan is increased by about 5%compared to the original fan,the air volume is increased by 5.16%,and the noise is reduced by 0.6 dB.

Effects of Bionic Volute Tongue on Aerodynamic Performance and Noise Characteristics of Centrifugal Fan Used in the Air-conditioner

The aerodynamic noise generated by the centrifugal fan used in the air conditioner is related to the comfort of human living and working,which can be controlled by using the bionic design and optimization of key components of centrifugal fan.Inspired by the non-smooth leading edge of long-eared owl wing,eight kinds of volute tongues are proposed to reduce the aerodynamic noise of a centrifugal fan.The flow and sound characteristics are numerically investigated by incorporating computational fluid dynamics and computational aero-acoustics.The optimal result exhibits a noise reduction of up to 1.5 dB with a slight increase in mass flow rate.The acoustic characteristics,with respect to the sound pressure level,power spectral density,and sound directivity are discussed.The time-domain,frequency-domain,and root mean square values of pressure fluctuation are monitored and analyzed to assess the unsteady flow interaction between the volute tongue and impeller.The intensity and scale of vortices in the centrifugal fan are suppressed in the upstream and downstream of the bionic volute tongue,and the turbulence effect on the surface of the volute tongue becomes even and weak.

Numerical Experiment of the Solid Particle Erosion of Bionic Configuration Blade of Centrifugal Fan

In this paper, a bionic method was presented to improve the erosion resistance of blade of the centrifugal fan. A numerical investigation of the solid particle erosion on the standard and bionic configuration blade of 4-72N_o10C centrifugal fan was presented. The numerical study employs computational fluid dynamics （CFD） software, based on a finite volume method, in which the discrete phase model was used to modele the solid particles flow, and the Eulerian conservation equation was adopt to simulate the continuous phase. Moreover, user-defined function was used to define wear equation. The various diameters of the particles were taken into account. The positions of collision of standard and bionic fan blades were discussed, and two kinds of centrifugal fan blade wear were compared. The results show that the particles from the incident source with different positions have different processes of turning and movement when enter into the impeller. The trajectories of flow in the fan channel are significantly different for the particles with different diameters. Bionic fan blade have lower erosion rate than the standard fan blade when the particle size is 20 μm. The anti-erosion mechanism of the bionic fan blade was discussed.

Application of Numerical Simulation of the Flow Field of Centrifugal Impellers for Fan Design

An impeller is the most important component affecting the performance of centrifugal fans. The flow in the impeller is very complicated, and the 3\|D viscous flow is difficult to simulate numerically. This paper presents a numerical method for simulating the flow in practical commercial impellers. The predictions are compared with experimentally measured fan performance results. The predicted total pressure and efficiency for two fan models, whose optimum designs were determined by this method, agree well with the measured data for the design flow rate. The results show that the aerodynamic and noise levels for these two models are excellent. The paper also presents several new ideas about the shape of the front plate and the blade flow pattern to improve the flow in an impeller channel. The practical simulation methodology and results developed here will be very useful to the fan industry in the future.

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.

Erosion-Resistant Surfaces Inspired by Tamarisk

Tamarisk, a plant that thrives in arid and semi-arid regions, has adapted to blustery conditions by evolving extremely ef- fective and robust anti-erosion surface patterns. However, the details of these unique properties and their structural basis are still unexplored. In this paper, we demonstrate that the tamarisk surface only suffers minor scratches under wind-sand mixture erosion. The results show that the anti-erosion property of bionic sample, inspired by tamarisk surface with different surface morphologies, can be attributed to the flow rotating in the grooves that reduces the particle impact speed. Furthermore, the simulation and experiment on the erosion wear behavior of the bionic samples and bionic centrifugal fan blades show that the bionic surface with V-type groove exhibits the best erosion resistance. The bionic surface on centrifugal fan blades with opti- mum parameters can effectively improve anti-erosion property by 28.97%. This paper show more opportunities for bionic application in improving the anti-erosion performance of moving parts that work under dirt and sand particle environment, such as helicopter rotor blades, airplane propellers, rocket motor nozzles, and pipes that regularly wear out from erosion.

Study of Unsteady Flow Simulation of Backward Impeller with Non-uniform Casing

The flow characteristics of the centrifugal fans with different blade outlet angles are basically discussed on steady and unsteady simulations for a rectangular casing fan. The blade outlet angles of the impellers are 35° and 25° respectively. The unsteady flow behavior in the passage of the impeller 35° is quite different from that in the steady flow behavior. The large flow separation occurs in the steady flow field and unsteady flow field of the impeller 35°, the flow distribution in the circumferential direction varies remarkably and the flow separation on the blade occurs only at the back region of the fan; but the steady flow behavior in the impeller 25° is almost consistent with the unsteady flow behavior, the flow distribution of the circumferential direction doesn't vary much and the flow separation on the blade hardly occurs. When the circumferential variation of the flow in the impeller is large, the steady flow simulation is not coincident to the unsteady flow simulation.