Noise Reduction Inside Launch Vehicle Fairing Using Melamine Foam And Helmholtz Resonator

With the increase of demand in Aerospace and Astronautics,heavy-lift launch vehicles are started to be used to launch LEO spacecrafts and large communications satellites,which leads to more serious vibration and noise problems.A lot of studies has been done to mitigation noise level inside payload farings and improve security of payload during lift-off and flying.Because porous materials have good sound absorption performance in high frequency range and Helmholtz resonators have significant low frequency sound attenuation ability,these two materials(or devices)are used to reduce sound pressure level inside launch vehicle fairings individually or co-operatively.In this paper,the melamine foam and Helmholtz resonator with horn-shaped neck are applied to reduct noise inside launch vehicle fairings.The acoustical properties,coupling with enclosure cavity,noise attenuation performance and optimal design of these two materials(or devices)are investigated theoretically,numerically and experimentally.The main research efforts of this paper are summarized as following.(1)The noise test bench of reduced scale model of launch vehicle fairing's cylindrical section is established.The reduced scale model of payload faring's cylindrical section is processed using aluminum alloy,and its cavity's acoustic characteristic is investigated theoretically.The noise test bench and its corresponding FE model are established which are used to test or simulate the noise attenuation performance of melamine foam and Helmholtz resonators.(2)The noise attenuation technology inside launch vehicle fairings using melamine foam is constructed.By comparing sound absorb coefficient of common porous materials,the high frequency noise attenuation performance of melamine foam is better than the others.The optimum selection range of acoustical parameters of melamine foam is given to achieve best sound absorb performance.The calculation formulas of natural frequence of cylindrical cavity with melamine foam lining is deduced,which indicate that the reduction of natural frequence is proportional to lining thickness.The real acoustical parameters of melamine foam is given by series acoustical test,and the simulation results using these parameters show that melamine foam also can be used to reduct low-mid frequency noise,which is consistant with experimental results.The low-mid frequency range noise reduction optimum is studied numerically and experimentally under same lining rate condition or same lining mass condition,the results shows that the optimum could increase noise reduction in low-mid frequency range,but would lead to decrease of noise reduction in high frequency range.(3)The low frequenye noise attenuation technology inside launch vehicle fairings using Helmholtz resonator with horn-shaped neck is constructed.The resonance frequency canculation formulas of Helmholtz resonator with horn-shaped neck under rigid wall assumption are deduced using lumped parameter model and Webster's function,and the formulas under elastic wall assumption are deduced using electroacoustic analogies;these two series formulas could be used to design Helmholtz resonator inside fairings.The relationship between resonate frequency and neck type,neck geometric parameters or wall thickness is analyzed,which denotes that exponential neck is the best choice and wall elasticity should be considered when equivalent acoustic reactance of wall is close to the value of cavity.The analysis of different sound dissipation mechanism shows that viscous damping at neck is the major facto.Numerical and experimental efforts are used to find out the optimal installation location,number and resonator frequency distribution,results shows that using series Helmholtz resonators with different resonance frequency would obtain best noise reduction results.(4)The low frequency noise reduction inside launch vehicle fairing using Helmhotlz resonators separately or with melamine form together is evaluated.The FE model of a launch vehicle fairing is built,and the response characteristic of faring cavity is provided by constrast with experiment result of noise test in a reverberation chamber.Numerical study and experimental study of acoustical response inside Launch vehicle fairing lining with Helmholtz resonator are carried out to confirm its low frequency noise reduction performance at optimized installation position and amounts.The low frequency noise reduction inside launch vehicle fairing using Helmhotlz resonators and melamine is evaluated,and results show that the effect of melamine lining on natural frequency of fairing cavity should be considered if we want to use the two materials(or devices)together.The rearch of this paper would improve noise reduction designusing melamine foam and Helmholtz resonator,promote noise mitigation technology of launch vehicle fairing,and provide theoretic and applied reference for dealing with noise problem of heavy-lift launch vehicle fairings.