动态舱门对空腔复杂流动和噪声特性影响分析

Investigations of complex cavity flows and noise induced by moving cavity doors

  • 摘要: 为研究运动舱门对内埋弹舱(空腔)非定常流场和舱内噪声特性的影响,开发了应用于运动问题的动态嵌套重叠网格组装方法,采用改进的脱体涡模拟方法对亚声速流场(Ma = 0.6)进行了高精度数值模拟。首先采用空腔标准模型(M219)验证所用的高精度数值格式的有效性,然后应用发展的方法对干净空腔(C201)、带静态舱门(30°、60°、90°和120°)的空腔以及运动舱门的空腔进行模拟,并分析静、动态舱门对空腔湍流流场和腔内气动噪声的影响。针对运动舱门的非稳态非定常流动问题,采用经验模态分解方法分析空腔中的湍流脉动特征和声压级。通过分析研究结果发现,与干净空腔相比,舱门小开度(30°)时,舱门会限制法向和展向的流动,从而降低腔内流场与外部流场的流动掺混和交换,腔内壁面总声压级比干净空腔低5~8 dB,但是两者变化趋势一致,且二阶Rossiter模态频率偏高;在打开角度较大(60°以后)时,舱门对腔内流动的影响主要表现在展向,此时空腔上方的剪切层涡结构运动的高度更高,舱门阻碍噪声的展向传播,使得腔内的总声压级升高(3~10 dB不等),二阶Rossiter模态的强度增大。然而舱门开启过程中,腔内总声压级介于小开度与大开度之间,与干净空腔水平相当;在舱门打开角度为90°时,腔内总声压级呈现与准定常模拟结果类似的分布,该研究对真实弹舱的流动分析与设计有指导价值。

     

    Abstract: Turbulent flows in cavities play an important role in the generation of cavity noise and are inevitably modulated by moving doors. This paper proposes a dynamic hierarchical overset method and integrates it into Improved Delayed Detached-Eddy Simulations to characterize the impact of non-stationary doors on cavity flows. The numerical methods, validated using a canonical cavity (M219), are applied to simulate subsonic (Ma = 0.6) flow fileds in cavities (C201) without doors, with stationary doors (with opening angles of 30°, 60°, 90°, and 120°), and with moving doors. Turbulence statistics and cavity noise in a statistically unsteady flow induced by moving doors are analyzed using the Empirical Mode Decomposition. For stationary doors with an opening angle of 30°, cavity flow is constrained in the cross-flow directions, suppressing the mixture between flows inside and outside the cavity. This results in a lower Overall Sound Pressure Level (OASPL) by 5~8 dB compared to the one in a cavity without doors and the frequency of the second Rossiter mode becomes higher, while the trend exhibits similar changes. In contrast, when the opening angles of stationary doors are larger (≥60°), shear layers over cavities are further away from the cavity floor than those in cases with smaller opening angles. The noise propagation is restricted in the spanwise direction, yielding higher OASPL (by 3~10 dB) at the cavity floor and amplified second Rossiter mode. OASPL for cavities with the opening of doors is comparable to those in a clean cavity. However, when the opening angle of moving doors is around 90°, the distribution of OASPL is similar to that in a cavity with stationary vertical doors.

     

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