Simulation of Broadband Noise Sources of an Axial Fan under Rotating Stall Conditions
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Study on the influence of rotating stall on the aerodynamic noise of axial fan has important value to warn of the occurrence of stall through monitoring the noise variations. The present work is to analyze the aerodynamic noise before and after the phenomenon of rotating stall by solving Navier-Stokes equations, coupled with the throttle condition and the broadband noise sources model. The impeller exit rotational Mach number and rotational Reynolds number are separately 0.407 and 8.332 × 10 6 . The results show that the aerodynamic noise source of the fan is mainly the rotation noise under the design condition. The vortex noise accounts for the major part of fan noise after the occurrence of stall, and the maximum acoustic power level of the fan appears in the rotor domains. In the evolution process from the stall inception to the stall cell, the high noise regions of the rotor develop along the radial, circumferential, and axial directions, and the area occupied by high noise regions increases from 33% to 46% impeller channels area. On rotating stall condition, the high noise regions occupying about 46% impeller channels area propagate with the stall cell along the circumferential direction at a half of rotor speed.Keywords:
Stall (fluid mechanics)
Mechanical fan
Axial Compressor
Stall (fluid mechanics)
Axial Compressor
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The stall-prevention effect of air separators incorporating radial vanes in place of the existing axial vanes was investigated on a low-speed, single-stage, lightly loaded axial-flow fan for effective and compact air separators of a simplified structure. From the survey, paying attention to several geometrical dimensions of the device, the following conclusions are obtained: (1) Simplified radial vanes made of flat plates could show strong stall-prevention effect comparable to those of the curved-vane type one. The most favorable ones showed no stall up to the fan shut-off conditions. (2) Radial heights of the recirculation passage within the air separator showed significant influences on the stall improvement. It should be larger than some critical size experimentally given in the study. (3) The axial length of the device should be larger than some critical size given experimentally in the study. Too much reduced axial length could give rise to an abrupt loss in the effect. (4) The optimum axial locations of the rotor-tip blade leading edge within the device inlet opening were found to lie near the center of the width of the inlet opening from both aspects of stall improvement and fan efficiency.
Stall (fluid mechanics)
Axial Compressor
Mechanical fan
Separator (oil production)
Leading edge
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Rotating stall is a primary constraint for the performance of axial flow compressors. This paper establishes a necessary and sufficient condition for a quadratic feedback controller to locally stabilize the critical equilibrium of the uniform flow at the inception of rotating stall. The explicit condition obtained in this paper provides an effective synthesis tool for rotating stall control.
Stall (fluid mechanics)
Axial Compressor
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Small-sized axial fan is used as air cooler for electric equipments. But there is demand for higher power of fan according to the increase of quantity of heat from electric device. Therefore, higher rotational speed design is necessary but it causes the deterioration of efficiency and increases the noise. Contra-rotating axial fan is smaller than single axial fan under the same rotational speed, and is effective against lower rotational speed design under the same diameter. In addition, contra-rotating small-sized axial fan is higher efficiency compared with single small-sized axial fan. Then the adoption of contra-rotating rotor for small-sized fan was proposed for the improvement of performance. In the present paper, experiment was conducted to investigate the effect on performance by changing the axial distance between front and rear rotors of contra-rotating small-sized axial fan. And the relationship between the performance and axial distance between front and rear rotors was clarified with the experimental results.
Mechanical fan
Axial Compressor
Fan-in
Axial-flow pump
Centrifugal fan
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Axial flow fan is extensively applied in automation control systems for cooling. Improving the rotational speed is undoubtedly an effective method to achieve higher total pressure and larger flow rate. In this paper, the performance of axial flow fan under high rotational speed is investigated by using Computational Fluid Dynamics (CFD). Ffowcs Williams and Hawkings (FW-H) model is used to capture the noise propagation. The results show that with the increase of rotational speed, the input power of the axial flow fan tremendously increases refer to the increase of total pressure. With increasing rotational speed the noise gradually rises. Besides the noise on the pressure side is higher. The characteristics of the axial flow fan provide important reference for designing and applying the axial flow fan under high rotational speed condition.
Axial Compressor
Mechanical fan
Overall pressure ratio
Electronic speed control
Static pressure
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This paper reports on an experiment in a centrifugal pump at low flowrates. A variety of measurement techniques was used: laser Doppler anemometry (LDA), impeller vane surface static pressure, a three-hole pneumatic probe and time-resolved static pressure. Some light is shed on the flow mechanisms present in the impeller off design. Evidence is found of a recirculation vortex, at 49 per cent of design flow-rate, in the impeller flow passages. From design flowrate down to 46 per cent of design flowrate there is no evidence of rotating stall, which first appears at 43 per cent. The most likely interpretation of this result is that there is a three-cell rotating stall system with the cells rotating at approximately 43 per cent of the impeller rotational speed. At 20 per cent of the design flowrate, the fluid in the inlet pipe ‘prerotates’ with no time mean flow reversal, interpreted as a developed stall cell system.
Stall (fluid mechanics)
Specific speed
Axial Compressor
Slip factor
Static pressure
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Experimental studies are carried out at a low speed axial compressor with five different rotor/stator gaps. Analysis of the effect of axial spacing of two successive blade rows on the measured mean flow coefficient at stall inception and on the flow range of compressor under multi-cell rotating stall operating conditions proves that the stator can suppress the flow disturbance in the compressor and strengthen the stability of the compressor. Experimental data show that the stall flow coefficient decreases by reducing the axial spacing of successive blade rows. Moreover, by reducing the axial spacing, the stall pattern transition pace from multi-cell stall to single-cell stall can be shifted. And the compressor directly slips into single-cell stall at 21.0% C(subscript R) axial spacing. By analyzing the pressure fluctuation closed to the surge line, it can be known that there exists an eigenfrequency where the amplitude of the oscillating pressure suddenly and dramatically increases as the compressor runs close to the surge line and this pressure disturbance is relevant to the compressor instability.
Stall (fluid mechanics)
Axial Compressor
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In vacuum cleaners radial impellers with high rotational speed are very often used. A high rotational speed is connected with a best efficiency point of the radial impeller at a high flow rate. This is contrary to the working point of the whole system. Thus there is need for a radial impeller designs having a high efficiency at low flow rates under the restriction of a high rotational speed. One important parameter connected to the hydraulic efficiency characteristics of the radial impeller is the blade inflow angle β1. In order to shift the best efficiency point towards lower flow rates radial impellers with double curved blades and a linear β1 distribution were designed and CFD simulations were done in order to investigate the effect of this approach. A linear variation of the inflow angle β1 enables the designer to shift the efficiency characteristics of the impeller towards lower flow rates with a gain in hydraulic efficiency and pressure increase.
Inflow
Slip factor
Specific speed
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The flow field and the distribution of the flow parameters in the rotating stall regime in a three stage axial flow compressor were obtained in detail using three-hole cylindrical probes containing fast response transducers in association with a digital data acquisition system and an ensemble averaging technique. An appreciable amount of experimental data are presented in this paper with a critical discussion on those.
Stall (fluid mechanics)
Axial Compressor
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Based on Realizable k-eturbulent model,the flow field in an axial flow fan was numerically simulated under rotating stall conditions,while the static characteristics of its impeller was studied using finite element method and fluid-structure interaction theory with software Ansys.Results show that under rotating stall conditions of fan,a stall cell exists in the impeller with its propagation direction same as the rotation direction of the impeller.The equivalent stress distribution is greatly influenced by the centrifugal force,but slightly influenced by the rotating stall.The maximum equivalent stress of impeller is found to be lower than the material yield limit,proving the impeller to be safe.The aerodynamic force has important influence on the impeller total deformation.Under stall conditions,maximum total deformation appears in the area of stall cell center,which is 72.2%larger than the design condition.
Stall (fluid mechanics)
Slip factor
Axial Compressor
Mechanical fan
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Citations (1)