Digital signal process of low turbulence intensity based on EMD
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摘要: 采用热线风速仪在3座典型低速风洞中进行了流场湍流度测量，这3座低速风洞包括1个低湍流风洞、1个常规闭口风洞和1个开口射流风洞。针对湍流信号通常受噪声干扰的问题，在湍流度值处理中引入了经验模式分解（EMD)自适应滤波和HHT时频谱分析方法。将EMD方法与其他几种湍流度值处理方法进行了比较，包括带通滤波方法（BP)、电磁噪声解耦方法（ENC)和高通惯性衰滤波方法（HPIA)。采用EMD方法测得低湍流风洞的湍流度值，在流场速度30~100 m/s的范围内小于0.05%。采用HHT方法完成了脉动速度信号的时频分析，分析发现开口风洞试验段的脉动速度HHT时频谱有突出的低频信号。所构建的EMD自适应滤波器可以有效控制噪声对热线输出信号的影响，是一种有效的低湍流度信号处理方法。Abstract: Hot wire anemometer is used in three typical low speed wind tunnels to measure the flow field turbulence intensity, including a low turbulence wind tunnel, a general closed wind tunnel and an open jet wind tunnel. To deal with the disturbance to the turbulence signal caused by noise, an EMD(Empirical Mode Decomposition) self-adaptive filter and HHT(Hilbert-Huang Transform) time-frequency analysis methodology are introduced in turbulence intensity data processing. The EMD method is compared with several other turbulence intensity processing methods, including BPF(Band Pass Filter), ENC(Electronic Noise Correction) and HPIA(High Pass Inertia Attenuation Filter). Using the EMD filter, the turbulence intensity in the low turbulence wind tunnel test section is measured and found to be less than 0.05% in the flow speed range of 30~100m/s. Using HHT method, we complete the time-frequency analysis of the flow fluctuation signal, and the low frequency flow flucturation signal is found predominatnt in the open jet wind tunnel. The designed EMD self-adaptive filter is effective at controlling the influence of the noise on the hot wire output signal, and therefore it is a practical method for low turbulence intensity signal processing.
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图 1 低湍流风洞试验段脉动速度幅值谱比较
Figure 1. Comparition of flow velocity fluctuation amplitude spectrum in the low turbulence WT
图 3 开口风洞试验段湍流度不同信号处理结果的比较
Figure 3. Comparison of results obtained by different kinds of data processing methods in the open jet WT
图 5 常规低速风洞闭口试验段湍流度信号处理结果
Figure 5. Turbulence intensity results in the general low speed WT
图 6 低湍流风洞试验段脉动速度0～200Hz信号HHT时频谱
Figure 6. HHT spectrum of 0～200Hz flow velocity fluctuation in the low turbulence WT
图 7 常规低速风洞试验段脉动速度0～200Hz信号HHT时频谱
Figure 7. HHT spectrum of 0～200Hz flow velocity fluctuation in the general low speed WT
图 8 开口风洞试验段脉动速度0～200Hz信号HHT时频谱
Figure 8. HHT spectrum of 0～200Hz flow velocity fluctuation in the open jet WT
图 9 常规低速风洞试验段脉动速度200～1000Hz信号HHT时频谱
Figure 9. HHT spectrum of 200～1000Hz flow velocity fluctuation in the general low speed WT
图 10 开口风洞试验段脉动速度200～1000Hz信号HHT时频谱
Figure 10. HHT spectrum of 200～1000Hz flow velocity fluctuation in the open jet WT
表 1 3种低速风洞中的能量密度与其平均周期的乘积
Table 1. A list of Em×Tm in the 3 kinds of low speed wind tunnel
风洞类型 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 低湍流 0.44 0.05 0.10 0.04 0.22 0.21 0.03 0.01 1.05 33.79 37.20 47.05 27.88 27.62 7.76 3.96 常规低速 0.34 0.21 0.03 0.17 0.07 0.01 0.53 0.20 0.50 1.99 16.60 25.63 36.38 11.32 20.11 4.31 开口风洞 0.65 0.25 0.03 0.01 0.02 0.11 0.03 0.20 0.09 0.79 9.01 8.68 451.32 18.75 13.57 19.57 
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