Experimental characterisation of the screech feedback loop in underexpanded round jets
Experimental characterisation of the screech feedback loop in underexpanded round jets
复制标题
欠膨胀圆形射流中尖叫反馈回路的实验表征
DOI：
--
复制
发表时间：
2017
影响因子：
3.7
通讯作者：
C. Bailly
中科院分区：
文献类型：
--
作者：
B. Mercier;T. Castelain;C. Bailly
在10个圆形喷流上进行了近场声学测量和时间分辨纹影可视化，目的是系统地分析与尖叫现象有关的反馈回路的不同部分。所研究的喷流的理想展开马赫数范围从$M_{j}=1.07$到$M_{j}=1.50$。根据马赫数的不同，在A1和A2模式的第四激波尖端和B模式的第三或第四激波尖端存在单一的尖叫声波源。在从喷嘴到震源的剪切层中，通过纹影可视化来测量尖叫声周期的相位。给出了各种情况下对流速度的估计值，并指出了对流速度随轴向距离增大的趋势。这些结果与从双麦克风调查得出的震源定位一起使用，以确定尖叫声循环中包含的尖叫声周期的数量。对于A1和B模式，对于辐射激波是第四个的情况，在环路中包含四个周期，并且当辐射激波尖端是第三个时，在环路中包含三个周期，而A2模式的环路包含五个周期。
Near-field acoustic measurements and time-resolved schlieren visualisations are performed on 10 round jets with the aim of analysing the different parts of the feedback loop related to the screech phenomenon in a systematic fashion. The ideally expanded Mach number of the studied jets ranges from $M_{j}=1.07$ to $M_{j}=1.50$ . The single source of screech acoustic waves is found at the fourth shock tip for A1 and A2 modes, and at either the third or the fourth shock tip for the B mode, depending on the Mach number. The phase of the screech cycle is measured throughout schlieren visualisations in the shear layer from the nozzle to the source. Estimates of the convective velocities are deduced for each case, and a trend for the convective velocity to grow with the axial distance is pointed out. These results are used together with source localisation deduced from a two-microphone survey to determine the number of screech periods contained in a screech loop. For the A1 and B modes, four periods are contained in a loop for cases in which the radiating shock is the fourth, and three periods when the radiating shock tip is the third, whereas the loop of the A2 mode contains five periods.