Study On Characteristics Analysis And Control Of Aeroacoustics Of Automotive Alternator

An automobile alternator converts the mechanical rotational energy of the engine into electrical energy by connecting to the engine with a belt. With the increase of the rotational speed, aerodynamic noise has become an increasingly important part of the alternator noise. The studies on characteristics of alternator aerodynamic noise and noise reduction have important significance. Aiming at alternator aerodynamic noise problem, not only establish the method for calculating the aerodynamic noise, but also study the characteristics of far-field radiation of the main aerodynamic noise source in this paper. Analyze different turbulence model of alternator aerodynamic noise. Predict aerodynamic noise frequency characteristics under different working conditions. By using the method of experimental study to analyze the alternator aerodynamic noise characteristics. Based on the method, establish the models of multi-objective optimizations of alternator aerodynamic noise, and optimize the design for alternator noise’s reduction.By using the incompressible Navier-Stokes equation, RNG k-ε turbulence model and the LES turbulence model to study the three dimensional unsteady numerical simulation about characteristics of the vehicle alternator aerodynamics. The sliding mesh technology and FW-H aerodynamic noise model are applied to study the aerodynamic noise of alternator by numerical simulation. Use numerical simulation to tell us that the geometric model, numerical model and the analysis method of CFD of alternator aerodynamic noise are reasonable, feasible and correct. The front and rear blades are the aerodynamic noise sources for this type of alternator. The main components of aerodynamic noise are the6th,8th,10th,12th and18th orders.Through the prediction of the alternator aerodynamic noise to analyse the characteristics of alternator aerodynamic noise flow field and sound field when working condition is12000r/min. Therefore, RNG k-ε turbulent model in terms of alternator aerodynamic noise prediction, compares the main order time and amplitude with experiment to show that is in good agreement under1400Hz. LES is in good consistency with experimental results at below5000Hz.For the numerical predictions of aerodynamic noise characteristics of the problem, the method called "removing components Law" for the relevant experiments is used in the paper. The main components of aerodynamic noise are the6th,8th,10th,12th and18th orders; The main components of aerodynamic order noise are from the alternator cooling fan noise; The noise contribution of front fan to the12th and18th orders is clearly higher than rear fan, while the latter contribution is more strong than the6th,8th and10th orders, the main impact of the order of36th is not the aerodynamic order noise. By changing the way of the stator coil’s noise propagation to get alternator B stator coil which is better than the A stator, the total sound pressure level and12th,18th order of noise are reduced. By changing the stator windings pore state which is on the way to obtain12th order of the sound pressure level that raise1.2dBA,18th order of the sound pressure level is reduced approximately1.6dBA, the other order are not obvious.On this basis, what’s more four factors about considering alternator direction of rotation, the height of rear fan block slice, the angle of front end cover to radial grid and the distribution of blade angle. Regarding lowering the rotation noise of single frequency as the alternator optimization design by low noise, high flow, and the structure of spectrum optimizing to study the aerodynamic noise and noise reduction. Anti-rotation alternator aerodynamic noise is large and flow is small; the alternator rear-fan without brackets of the total noise value and the mass flow are reduced; After changing the angle of the front to grid and using vector synthesis method to optimize the front-blade, not only the total noise level is reduced but also the mass flow rate is improved.The aerodynamic noise characteristics and the method of noise reduction that studied in this paper can provide practical reference for the improvement of aerodynamic performance and high speed noise for vehicle alternator.