谐振管形状对热声发动机内非线性声场的影响

研究了谐振管一端受活塞声源激励,另一端刚性封闭条件下,管道形状对热声发动机谐振管内部非线性声场的影响。基于流体力学基本方程建立了渐变截面谐振管内一维非线性声场的模型,考虑了黏性耗散及非线性效应的影响。利用伽辽金法数值求解了该模型的速度势方程,分析了谐振管形状、活塞振动速度及激励频率对管内声场的影响。将双曲形、指数形、锥形、正弦形等四种变截面谐振管内的非线性声场与圆柱形直管的情况进行了比较。结果反映了谐振管内声场的压力波动受活塞振动速度及谐振管形状的影响;显示了当活塞振动幅度较大时,谐振管内出现的波形畸变、频率曲线偏移、共振频率滞后等非线性现象;揭示了变截面谐振管在抑制管内的高阶谐波及提高压比等方面的优越性。      

活塞驱动的指数形谐振管内的非线性振荡

本文通过理论分析和推导得到了活塞驱动的指数形谐振管内气体的压力和压比的近似表达式。对指数形谐振管的各种驱动幅值,计算了管端压比随形状参数m的变化曲线,获得最大压比时的谐振管形状参数。本文的研究结果可用于活塞驱动的指数形谐振管内非线性振荡的分析和大声幅谐振管的设计。     

谐振管谐振频率计算方法的研究

为了准确地计算声谐振管的谐振频率,提出了基于对管内声压分布进行理论模拟的声压模拟法,以及基于驻波最小点位置与管两端声阻抗关系的驻波最小点法。结果表明这两种方法因为考虑了声谐振管两端的声阻对谐振频率的影响,所得谐振频率更加精确、严格,所以特别适用于要求谐振管的谐振频率严格控制的声学领域。同时表明:声压模拟法与驻波最小点法虽然出发点不同,但谐振频率的计算结果完全相同。驻波最小点法计算比较方便,而声压模拟法在计算出谐振频率的同时,还可以给出管中的声压随位置的分布情况。     

指数型热声谐振管的固有频率

采用计算流体力学软件Fluent模拟研究了11种不同形状参数的指数型热声谐振管内二维非线性声场特性,分析了驱动频率和驱动强度对管内声压演化过程及固有频率的影响,并探索了指数管的固有频率与理论计算谐频之间的关系.研究发现:当驱动频率偏离谐振管固有频率时,管内将出现明显的"拍"现象;指数管的固有频率随驱动强度的增加而增加,呈现硬弹簧效应,但驱动强度对固有频率的影响较小并且在任何驱动下指数管的固有频率均小于理论计算谐频.针对所研究的指数型管,获得了其固有频率与理论计算谐频之间的关系式.结果表明,相同驱动下,形状参数m值约等于2.8的指数管所能获得的压力幅值及压比最大,且m=2.8指数管的固有频率与理论计算谐频之间的关系式与其他管型略有不同.      

基于LabVIEW的声波谐振管实验研究

为了更高效地测量声波谐振管的谐振频率,本文基于LabVIEW设计了测量声波谐振管谐振频率的扫频程序,分别得到了两端闭管条件下不同管长的谐振频率,以及首端闭管与尾端闭管条件下的谐振频率.此外,还通过绘制管内驻波波形图对声压波腹发生偏离的假设进行了验证.最后,对谐振管管身小孔开闭对谐振频率的影响进行了探究,发现小孔位置越接近驻波的声压波腹,谐振频率的偏离量越大.     

气体火焰驻波在低频段熄火的研究

用驻波函数和伯努利方程推导出火焰驻波管内任意位置的声压方程,并分析了低频时熄火的原因.引入压节(波幅)、压腹(波节)解释了驻波管两端出现高火焰的原因.用全封闭的驻波管完整地呈现了低频段共振点的驻波.     

管内气体声振荡特性的气-动格式模拟

本文对活塞驱动的谐振管中气体的非线性振荡,给出了考虑热、黏作用的气-动格式模型,并数值分析了气体振荡的演化过程和谐振时的激波特性.研究了频率对谐振荡行为、模式及压力波形的影响.并分析了压比随频率的变化关系.计算结果与早期文献研究的实验及计算结果具有好的一致性.模拟结果显示了气-动格式在谐振管内非线性气体振荡模拟中的数值...     

有限长号筒中非线性声传播的数值模拟研究

研究了大振幅活塞声源经有限长号筒向外辐射声波的非线性声学问题。采用具有频散保持特性的高精度计算格式求解了适用于变截面管道的一维非线性声场模型,并考虑到声波的非线性畸变及管口处的声反射,加入了宽频时域声阻抗边界条件。宽频阻抗模型的共轭复数系数采用优化拟合方法近似求解,并采用递推卷积算法快速求解出时域声阻抗。在弱非线性条件下模拟指数形号筒中的声传播取得了与已有实验相一致的结果,表明模型能够描述声波非线性畸变带来的宽频特性。进而采用本模型数值模拟了大振幅活塞声源在双曲形、锥形、指数形和正弦形号筒中的非线性声传播问题,结果表明号筒出口声压级受活塞振动速度、频率以及号筒形状的影响,并分析讨论了波形畸变与号筒几何形状之间的关系。     

有限长号筒中非线性声传播的数值模拟研究

研究了大振幅活塞声源经有限长号筒向外辐射声波的非线性声学问题。采用具有频散保持特性的高精度计算格式求解了适用于变截面管道的一维非线性声场模型,并考虑到声波的非线性畸变及管口处的声反射,加入了宽频时域声阻抗边界条件。宽频阻抗模型的共轭复数系数采用优化拟合方法近似求解,并采用递推卷积算法快速求解出时域声阻抗。在弱非线性条件下模拟指数形号筒中的声传播取得了与已有实验相一致的结果,表明模型能够描述声波非线性畸变带来的宽频特性。进而采用本模型数值模拟了大振幅活塞声源在双曲形、锥形、指数形和正弦形号筒中的非线性声传播问题,结果表明号筒出口声压级受活塞振动速度、频率以及号筒形状的影响,并分析讨论了波形畸变与号筒几何形状之间的关系。      

指数型谐振管内非线性声场的模拟研究

采用气体动理学方法模拟研究五种不同驱动强度下,=0的圆直热声谐振管和=2 2的指数型热声谐振管内的非线性声场特征。研究发现:指数型管能抑制激波及声饱和现象,但管内会出现尖峰现象。尖峰处的压力波形发生了畸变;它们是非线性的能量传递与各种耗散的竞争过程中产生的不同形态的波特征;当活塞驱动位移幅值400μm时,指数型管内压力振幅增长速度明显下降。     

Numerical simulation of nonlinear propagation of sound waves in a finite horn

Nonlinear acoustic propagation generated by a piston in a finite horn is numerically studied.A quasi-one-dimensional nonlinear model with varying cross-section uses high-order low-dispersion numerical schemes to solve the governing equation.Because of the nonlinear wave distortion and reflected sound waves at the mouth,broadband time-domain impedance boundary conditions are employed.The impedance approximation can be optimized to identify the complex-conjugate pole-residue pairs of the impedance functions,which can be calculated by fast and efficient recursive convolution.The numerical results agree very well with experimental data in the situations of weak nonlinear wave propagation in an exponential horn,it is shown that the model can describe the broadband characteristics caused by nonlinear distortion.Moreover,finite-amplitude acoustic propagation in types of horns is simulated,including hyperbolic,conical,exponential and sinusoidal horns.It is found that sound pressure levels at the horn mouth are strongly affected by the horn profiles,the driving velocity and frequency of the piston.The paper also discusses the influence of the horn geometry on nonlinear waveform distortion.     

Numerical model for nonlinear standing waves and weak shocks in thermoviscous fluids.

Nonlinear standing waves in a one-dimensional tube are studied numerically by using a finite-difference algorithm. The numerical code models the acoustic field in resonators for homogeneous, thermoviscous fluids. Calculations are performed exclusively in the time domain, and all harmonic components are obtained by one resolution. The fully nonlinear differential equation is written in Lagrangian coordinates. It is solved without truncation. Effects of absorption are included. Displacement and pressure wave forms are calculated at different locations and results are shown for different excitation levels and tube lengths. Amplitude distributions along the resonator axis for every harmonic component are also evaluated. Simulations are performed for amplitudes ranging from linear to strongly nonlinear and weak shock. A very good concordance with classic experimental and analytical results is obtained.     

腔壁弹性对水下小型圆柱形亥姆霍兹共振器共振频率的影响

理论和实验研究了腔壁弹性对水下小型圆柱形亥姆霍兹共振器共振频率的影响.基于电-声类比理论,建立了小型共振器的简化模型,利用电路分析方法得到了便于计算的共振频率一般表达式.分别仿真分析了共振器壁面厚度和材料对共振频率的影响,得到了不同尺寸的小型共振器的近似刚性条件.在充水驻波罐中对不同壁厚、不同材料的小型圆柱形亥姆霍兹共振器的共振频率进行了测量,实验结果较好地验证了理论分析和近似刚性条件的正确性.所得结果对小型圆柱形亥姆霍兹共振器的设计和水下应用具有较好的参考价值. 关键词： 亥姆霍兹共振器 共振频率 传递函数 辐射阻抗     

Numerical and experimental analysis of strongly nonlinear standing acoustic waves in axisymmetric cavities

In this paper the behaviour of strongly nonlinear waves in axisymmetric resonators is experimentally and numerically studied. Experiments are carried out in a cylindrical cavity, which transversal dimension is bigger than the longitudinal one, excited by a narrow band transducer. The quality factor and displacement amplitudes are experimentally quantified. A finite difference numerical model is developed to solve, in the time domain, a proposed set of full nonlinear differential equations written in Lagrangian coordinates. Pressure field is obtained for complicated modes. Good agreement between numerical and experimental results is found. New nonlinear properties of quasi-standing waves in axisymmetric resonators are described. Results are compared to linear approximation and show the importance of three-dimensional analysis.     

Influence of resonator shape on nonlinear acoustic field in a thermoacoustic engine

The influence of the resonator shape on nonlinear acoustic field in a thermoacoustic engine is studied.The resonator of themoacoustic engine is boundary driving by a piston at one end,and the other end of it is rigid closed.A one-dimensional wave equation that accounts for gas dynamic nonlinearities and viscous dissipation in the resonator is established based on the governing equations of viscous hydromechanics.The nonlinear wave equation is solved using approximate Galerkin method.The nonlinear acoustic field in four different types of shaped resonators including hyperbolical,exponential,conical and sinusoidal are obtained and compared with that of a cylindrical resonator.It is found that the amplitude and waveform of the pressure are strongly affected by the resonator shape,the driving amplitude and the oscillation frequency of the piston.Waveform distortion,resonance frequency shift and hysteresis are observed,when the piston oscillation amplitude is large enough.The advantages of shaped resonator for thermoacoustic engine lie in inhibition of higher order harmonics and improvement of pressure ratio,etc.     

Description of Finite-amplitude Standing Acoustic Waves Using Convection-diffusion Equations

This paper deals with problems of finite-amplitude standing waves in acoustical resonators of variable cross-section. Set of two one-dimensional partial differential equations in the third approximation, formulated in conservative form, is derived from the fundamental equations of gas dynamics. The model equations which takes into account external driving force, gas dynamic nonlinearities and thermoviscous dissipation are solved numerically in time domain using a central scheme developed for convection-diffusion equations integration. In this paper numerical results for closed air-filled acoustic resonators are presented.