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中文核心期刊

空腔流动的动量分解及能量输运特性

MOMENTUM DECOMPOSITION AND ENERGY TRANSFER CHARACTERISTICS OF OPEN CAVITY FLOW

  • 摘要: 空腔结构广泛应用于航空航天飞行器部件及地面交通工具中, 其复杂的流声特性是相关工程设计中必须考虑的关键问题. 空腔流动中的流声相互作用是空腔自持振荡的重要过程, 准确识别并解耦空腔内的流体动力学模态和声模态, 是深入理解空腔流声相互作用和能量转化机制的关键. 通过直接求解二维Navier-Stokes方程数值模拟来流马赫数Ma=0.8的亚声速空腔流动, 获得高精度流场数据; 采用动量势理论, 对动量进行流声组分分解, 获得了动量的涡熵动力学组分和声组分, 并分析各组分的空间分布特征、时间演化特性以及能量输运特性. 结果表明: 空腔流动中动量的涡熵动力学组分仅存在于近场, 集中于剪切层内呈层状分布特性, 且二者分布相似, 随主流以对流速度向下游运动; 其中涡组分携带的能量从剪切层内不断输运至剪切层外侧及空腔后缘点处, 熵组分携带的能量则不断向剪切层内输运, 并在剪切层内耗散; 声组分同时存在于近场和远场, 呈现出典型的压缩膨胀特征, 其携带的能量以声能形式由后缘点处不断以声速向上游和远场传播.

     

    Abstract: Cavity structure is extensively employed in the aerospace vehicle components and ground vehicles. The complex characteristics of the flow and acoustic fields is one of the key problems that must be considered in the design of the associated practical engineering. In the cavity flow, the hydro-acoustic interaction plays an important role in the self-sustained oscillation. Accurate identification and decomposition of the hydrodynamic and acoustic mode is the key to improving the understanding of the hydro-acoustic interaction and the associated energy transfer mechanism. In this paper, the two-dimensional Navier-Stokes equation is directly solved to conduct numerical simulation of open cavity flow with inflow Mach number of 0.8 to obtain the high-order accuracy unsteady flow field. Adopting Doak’s momentum potential theory, the momentum of the flow is decomposed into three parts of the hydrodynamic vortical component, the hydrodynamic entropic component and the acoustic component. The physical properties and the associated energy transfer characteristics of each component are analyzed. The results show that the hydrodynamic vortical and entropic components exist only in the near field, which are convected downstream with the main flow at the speed of shear layer convection. The spatial distribution of the vortical and entropic components are concentrated in the shear layer and resembles each other. The hydrodynamic energy carried by the vortical component is transported from the inside of the shear layer to the outside of the shear layer and to the rear-end of the cavity while the energy carried by the entropic component is continuously transported to the shear layer and then dissipated there. The acoustic component exists in both the near and far field, and the spatial distribution of the acoustic component exhibits a classical compression-divergence pattern. The acoustic energy is radiated from the rear-end of the cavity and propagates to the upstream and the far field at the speed of sound.

     

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