喷射流场及其辐射声场数值模拟

为研究喷管结构对射流噪声的影响,采用大涡模拟对不同截面形状喷口形成的非定常湍射流场进行了数值模拟.在流场计算的基础上,结合Ffowcs Williams-Hawkings积分方程对远场声场进行了计算,得到不同喷管结构对应的湍射流场的流动结构及其辐射噪声的频谱特性.计算结果表明,椭圆形截面喷管的出口附近存在大量的旋涡结构,增大了射流边界层处的气流掺混,从而降低了射流核心区的长度,有效抑制了喷射噪声,在5种不同结构的喷管中,椭圆形截面的喷管对应的辐射声压最低,而矩形喷管对应的辐射声压最高;在射流方向的30°～75°扇形区域内,辐射声信号最强且存在明显的指向性.

Numerical simulation of jet flow field and its radiated sound field

In order to study the effect of nuzzle structure on aeroacoustic noise,the unsteady turbulent jet flow generated by nozzles with different cross-section shapes was numerically simulated by large-eddy simulation.Based on the simulation results of jet flow,the far-field sound field was calculated by the Ffowcs Williams-Hawkings integral equation.The structures of unsteady turbulent flow of different nozzles and the spectrum characteristics of the radiated noise were obtained.Results show that a large number of vortex structures were found at the exit of the nozzle with an elliptical cross section.The vortices enhanced the gas entraining at the jet boundary layer.As a result,the radiated noise was reduced by shortening the potential core.Among five kinds of nozzles,the radiated sound pressure level of the elliptical nozzle was the minimun,while the radiated sound pressure level of the rectangular nozzle was found to be the maximum.In the fan-shaped region of 30° to 75° along the jet direction,the radiated acoustic signal was the strongest and displayed significant directivity.