仿生覆羽控制分离剪切流动相干结构试验

doi:10.7527/S1000-6893.2024.30284

Abstract

Abstract:

The flexible serrated coverts on the upper wing of the owl play an effective role in controlling flow separation and reducing acoustic noise. In this paper， wind tunnel experiments were conducted to study the flow control effectiveness of the flexible serrated coverts structures on the large-scale coherent structures in the parallel shear flow downstream of backward-facing step. In the experiment， the bionic coverts of different thicknesses were installed on the step edge， and were driven to adaptively flutter by the air flow. The turbulent velocity in the downstream were measured by the hot wire anemometer， and the coherent features were analyzed in both the time and frequency domains. The results show that the coverts of different thicknesses were capable of controlling flow separation， reducing turbulent fluctuation intensity， and suppressing the generation of the large-scale coherent structures within the shear layer. Among them， the coverts of 0.2 mm show the most effective results， which reduced the separation length by approximately 20% and decreased the turbulent intensity peaks by approximately 30%. Furthermore， wavelet analysis shows that adaptive fluttering motions had the effect of “fluttering-combing” the separated shear layer downstream of backward-facing step， suppressing the spanwise generation of high- and low-speed streaks， and reducing the proportion of low-frequency large-scale coherent structures. The experimental study shows the flow control effect of flexible serrated coverts of birds， and reveals the underlying mechanism of flow separation control and acoustic noise reduction.

Key words: bionics, covert, flow control, separated shear layer, coherent structure

CLC Number:

V211.7

Yihong LIU, Xingyu MA, Jiateng PAN, Nan JIANG. Test on controlling coherent structure of separated shear flow by bionic coverts[J]. Acta Aeronautica et Astronautica Sinica, 2024, 45(23): 630284.

Figures/Tables 14

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工况名称	A1	A2	A3	A4
厚度/mm	0.1	0.2	0.3	0.4
齿尖长度/mm	17	17	17	17
齿尖间距/mm	10	10	10	10
连接段长度/mm	20	20	20	20
覆羽总长度/mm	200	200	200	200
硅胶类型	常规	常规	常规	常规
面密度/（g·cm^-2）	0.012 5	0.025	0.037 5	0.05

x/h	下降率/%
x/h	A1	A2	A3	A4
1	-11.4	6.0	11.6	25.4
2	20.1	25.8	20.7	26.0
3	17.5	24.7	16.9	23.0
4	19.6	29.2	22.2	23.3
5	25.0	34.0	26.6	24.9
6	28.6	37.7	32.2	27.3

x/h	高度/mm
x/h	A1	A2	A3	A4
1	2	4	2	0
2	4	6	2	2
3	4	6	4	2
4	2	6	2	2
5	2	4	4	0
6	2	4	4	0

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Test on controlling coherent structure of separated shear flow by bionic coverts

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References 24

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x/h	剪切层中心位置/mm
x/h	A0	A1	A2	A3	A4
1	19	17	15	17	19
2	17	15	11	15	15
3	15	11	9	11	13
4	13	11	7	11	11
5	13	11	9	9	11
6	13	11	11	11	13

x/h	剪切层中心位置/mm
x/h	A0	A1	A2	A3	A4
1	19	17	15	17	19
2	17	15	11	15	15
3	15	11	9	11	13
4	13	11	7	11	11
5	13	11	9	9	11
6	13	11	11	11	13

x/h	剪切层中心位置/mm
x/h	A0	A1	A2	A3	A4
1	19	17	15	17	19
2	17	15	11	15	15
3	15	11	9	11	13
4	13	11	7	11	11
5	13	11	9	9	11
6	13	11	11	11	13