The Investigation On Aerodynamic Performance Optimization And Noise Reduction Of Low-pressure Axial-flow Fan Blade Shape

As an important type of ventilation equipment,the low-pressure axial-flow fan is widely used in HVAC,transportation,power industry,electronic cooling and other fields.The low-pressure axial flow fan has a large amount,low operating efficiency,and prominent problems of high energy consumption and noise pollution.With the increasing demands of low-pressure axial-flow fan’s aerodynamic performance and noise quality,the existing design methods and cognition of fan internal flow are more difficult to meet the requirements of multi-parameter and multi-objective refinement.Therefore,it is very important to study the blade shape optimization and noise reduction for improving the product quality and design level of low-pressure axial-flow fan.In this paper,a typical single-rotor low-pressure axial-flow fan is selected as the research object.The flow and aerodynamic noise characteristics,blade shape optimization and tip noise reduction of low pressure axial fan are studied by numerical simulation method.The main contents of the paper are as follows:(1)Based on RANS equation and k-ωsst turbulence model,a flow simulation model of lowpressure axial-flow fan is established.The accuracy of the numerical model is verified by comparing with the test data.Combined with the numerical simulation results,the internal flow field of the fan is analyzed.It is found that the leakage vortex induced by tip leakage flow is the most important flow field characteristic in low pressure axial flow fan due to tip clearance(2)In order to realize the optimal design of the stacking line shape of low pressure axial flow fan,the flow simulation method,parameterization method,proxy model technology and genetic algorithm were combined to construct the optimal design flow for the stacking line shape of blade.The optimization design of aerodynamic performance of stacking line shape is realized.The optimization process uses Bézier curve to parameterize the shape of a three-dimensional stacking-line.The objective function of optimization is the static efficiency under design condition.The surrogate model between design variables and objective functions is constructed by design of experiment and radial basis function.Finally,the genetic algorithm is used to optimize the shape of the stacking-line.The static efficiency and static pressure of the optimized fan are increased by 3.76%and 5.82% respectively.Through the analysis of the flow field before and after optimization,it is found that the change of the stacking line shape at the blade tip increases the control ability of the blade to the tip flow,reduces the blade load at the blade tip,and reduces the intensity of the tip leakage vortex.Therefore,the leakage loss of the fan can be reduced and the static efficiency of the fan can be improved.The optimization results are helpful to expand the distribution of the stacking lines and improve the optimization design level of the stacking lines(3)In order to solve the problem of large number of design parameters in multi-objective shape optimization of low-pressure axial-flow fan blades,the MOAT sensitivity analysis method is introduced based on the stacking line shape optimization process.The design parameter selection and multi-objective optimization of blade shape for low-pressure axial-flow fan are realized.Using sensitivity analysis method,16 design parameters were selected from 33 shape parameters such as fan blade stacking line,installation angle and airfoil section.The number of parameters and the amount of simulation calculation are effectively reduced,and the optimization efficiency is improved.The optimized Pareto front shows that the static pressure efficiency of the fan increases by 1.26% at low flow rate and by 5.47% at high flow rate,which shows the effectiveness of the improved optimization process.By comparing the three typical optimal models on the Pareto front,it can be found that the optimal models redistribute the low pressure area of the meridional hydrostatic pressure and reduce the tip leakage vortex intensity as compared with the baseline.The results show that the flow control ability of the blade can be effectively improved by changing the local characteristics of the blade stacking-line and the airfoil profile.The research results can provide useful reference for multi-objective optimization of blade shape of low-pressure axial fan.(4)The aerodynamic noise simulation model of low-pressure axial-flow fan is established using the hybrid CAA method,and the validity of the numerical simulation method is verified based on the experimental results.The influence of tip clearance size,tip groove parameters and tip groove type on the fan’s aerodynamic noise performance is discussed in the light of the characteristics of the fan’s noise source and the radiation noise.The results show that the overall sound pressure level of radiated noise decreases with the decrease of tip clearance.When the tip clearance decreases,the tip leakage flow intensity decreases,which reduces the pressure fluctuation in tip area,especially in suction side of tip,and then reduces the sound source intensity on the blade surface,thus achieving the effect of noise reduction in discrete and broadband noise.In the research of noise reduction of tip-groove,the three mechanisms of tip-groove acting on tip fluid,consuming kinetic energy and blocking leakage passage are analyzed.The noise reduction effects of different blade tip-groove sizes are compared,and the recommended groove depth is h/s=0.67 and the recommended groove wall thickness is w/t=0.16.At the same time,the recommended number of multi-groove in blade thickness direction and chordwise direction are both two.The research results can provide useful guidance for the design of blade tip-groove noise reduction of low-pressure axial flow fan.