风扇噪音分析曾群Analysis of motor-driven thin blade fan noiseZeng QunAbstract: For a long time, there is not a method to predicting the noise level of motor-driven blade. In order to satisfy, we developed a method for calculating the sound generated when a rotating blade is excited by the torque pulsation of a motor. The sound pressure values calculated by the new method for a rotating blade were found to correspond well with experimentally measured ones.(0001 7.S5e)l 7 20e01 67A0 63131 5.8601973.6401 3.19e*012.7 iO1 2 30eU)1 185#*01 1.4101 .62e00 X 5.16.00 7.05010i Phase of velocity at ith node (rad);q Mass density (kg/mIntroduction A method for predicting the electromagnetic noise of a thin blade fan driven by an electric motor has been developed.Electric motors are used as actuators in various kinds of machinery. Vibrating motions and noise in the machinery arise when the excitation forces of electric motors act on elastic parts of machinery. For instance, an air conditioner has a fan structure attached to the motor shaft. The thin blade fan vibrates and radiates electromagnetic noise when the torque pulsation acts on the rotating blades.A number of investigators have studied vibration and noise caused by motors. Here we propose a new noise calculation method fbr rotating blades that are excited by the torque pulsation of a capacitor motor. The calculation method is composed of two main modules, one for analyzing the vibration response of the blades, and one for calculating the electromagnetic noise of a rotating blade. In the analyzing module, the vibration response of a rotating thin blade is analyzed using both torque pulsation and the mesh model of the blade. To calculate the motors torque pulsation, we employed an equivalent electric circuit corresponding to the motor. The calculated torque pulsation was used to obtain the vibration response. In measuring the vibration response at various);xAngular frequency (rad/s);xrAngular velocity of rotating radiator (rad/s);List of symbolsds Reference small area (nV);ri Instantaneous distance from ith node to P (m);j Imaginaiy unit;S Area of sound radiator (m2);k Free field wave number of plane wave (l/m);V Velocity distribution of sound radiator (m/s);P Field point (m);Vi Amplitude of velocity at ith node (m/s);p Sound pressure level (Pa);q Angle of sound radiator (rad);R Observed radius (m);r Distance from reference small area ds (m);points along the length of the rotating blade, we found that the calculation and experimental results agreed well for each point.This calculation module for electromagnetic noise calculates the sound field caused by sound radiated from the rotating blade excited by the torque pulsation of the motor. It was found that the sound pressure values calculated by the new calculation method for a rotating blade corresponded well with experimentally measured ones.2 Experimental device2.1 Specifications of experimental device. The motor referred to in this paper is a capacitor motor with the specifications shown in Table 1. The main part of the testing system, shown schematically in Fig. 1, primarily consists of a motor, a four-bladed fan, and a high-stiffness block. The high-stiffness block is a steel block 220x220x220 mm in size and 83 kg in mass; its natural frequency is 6.7 kHz. A foam rubber was inserted under the block to prevent vibration from the floor from being transmitted to the motor and blades. The four-bladed fan was attached to the motor shaft. Each blade is an aluminum plate 300x80x3 mm in size. The motor rotates at a slow speed of 210 rpm because of the air resistance of this large fan. An accelerometer and slip ring were used to measure the vibration response of a rotating blade.2.2 Measurement device for radiated noiseThe system for measuring the sound pressure, shown schematically in Fig. 2, was set up in a semi-anechoic chamber. The blade rotates at a distance of 645 mm.Table 1 Motor specificationsMotor typeRated powerPower supply frequencyPower supply voltageCapacitorPoleStator slotRotor slotRotation speedCapacitor motor140W50 HzAC 150V81F62434210 rpm( four-bladed fan)Fig. 1 Experimental deviceAbove the floor to prevent noise from the floor from influencing the results. The points evaluated lie at a distance of 210 mm above the blade.2.3 Characteristics of radiated noise.Figure 3 shows the frequency response of the sound pressure produced by the testing system. In this figure, the microphone is set up at a radius of 200 mm from the rotating center. Many frequency components are shown in this figure, with the blade passage frequency causing a peak frequency component at 14 Hz. The peak frequency components at 100 Hz and 200 Hz are the result of electromagnetic noise caused by torque pulsation.3 Calculation method for radiated noise3.1 Basic formulajcop V(x.y) L 057：Where