Study on the Breakdown of Compressible Jet and the Mechanism of its Aeroacoustic Emission

可压缩射流击穿及其气动声发射机理研究

基本信息

批准号：
10450373
负责人：
NAKAMURA Yoshiaki
金额：
$ 7.94万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

In this study both numerical simulation and experiments regarding high-speed jets were performed. In the experiments mini-jets were used as an actuator to enhance jet mixing, the results of which are summarized as follows : (1) The flapping mode of actuation was most effective in mixing, where the axial length of the potential core was reduced by 35%, compared with that of the baseline. (2) As the frequency of actuation becomes higher, the jet breaks down more upstream. (3) As under-expanded jets are intrinsically stable, it does not change so easily by external disturbances, compared with the case of optimum jet. (4) As for noise, only steady actuation can decrease the noise level. On the other hand, regarding numerical simulations, the following results were obtained. (1) In axisymmetric calculation of jet, periodical roll-up of the jet shear layer was observed. These vortices merge with each other, and show the motion of acceleration, which leads to sound emission. (2) In 3D simulation, some instability produced upstream cannot maintain the state of being axisymmetric in the downstream, and three-dimensional unstable modes appear. As a result, the degree of jet breakdown is weakened, which reduces Mach wave-like sound emissions. (3) The velocity distribution along the jet axis shows good agreement between 3D numerical simulation and experimental data. However, there is a slight difference between them in the downstream. (4) In under-expanded jets, vortices in the jet shear layer interact with the shock cell, which makes a kind of noise.

在这项研究中，进行了有关高速射流的数值模拟和实验。在实验中，使用微型射流作为促动器来增强射流混合，其结果总结如下：（1）扑动促动模式在混合中最有效，其中势芯的轴向长度减少了与基线相比，降低了 35%。 (2) 随着驱动频率变高，射流在上游破裂得更多。 (3) 由于欠膨胀射流本质上是稳定的，因此与最佳射流的情况相比，它不容易受到外部干扰而改变。 (4)对于噪音，只有平稳驱动才能降低噪音水平。另一方面，关于数值模拟，获得了以下结果。 (1)在射流轴对称计算中，观察到射流剪切层的周期性卷起。这些漩涡相互融合，并表现出加速运动，从而导致声音发射。 (2)在3D模拟中，上游产生的一些不稳定性无法维持下游的轴对称状态，出现三维不稳定模态。结果，射流击穿程度减弱，从而减少了马赫波状声音的发射。 (3)沿射流轴的速度分布显示3D数值模拟与实验数据具有良好的一致性。但在下游，两者略有不同。 (4) 在欠膨胀射流中，射流剪切层中的涡流与激波单元相互作用，从而产生一种噪声。