Schlieren visualization of hypersonic boundary layer transition on a circular cone
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摘要: 为发展高超声速边界层转捩的试验研究手段，在中国空气动力研究与发展中心（CARDC）超高速空气动力研究所的FD-14激波风洞上开展了基于纹影显示技术的边界层转捩特性研究。试验模型为半锥角为7°的钝锥，头部钝度Rn有2.0和0.5mm两种。试验的名义马赫数为8和10，单位雷诺数变化范围为1.6×107~4.4×107m-1，高速相机的拍摄帧频20kHz。纹影显示捕捉到了第二模态不稳定波和湍流斑的空间结构。对纹影图像的灰度分布进行了功率谱密度（PSD）分析，结果表明第二模态波长约为边界层厚度的2倍。对纹影图像序列的分析表明，湍流斑波前传播速度大于波尾，并且略大于边界层外缘速度。Abstract: To develop the experimental technique for investigating the hypersonic boundary layer transition, schlieren visualization is used to study the characteristics of the boundary layer transition in the FD-14 shock tunnel at the Hypervelocity Aerodynamics Institute of China Aerodynamics Research and Development Center(CARDC). The test model is a 7° half-angle blunt cone with two different nosetip radiuses, 2.0 and 0.5mm, respectively. The nominal Mach numbers are 8 and 10 and the unit Renolds number varies from 1.6×107 to 4.4×107 m-1. The high-speed camera's frame frequency is 20kHz. Structures of the second mode instability waves and turbulent spots are obtained by schlieren visualization and the power spectral density is analyzed based on the gray scale distribution of schlieren images. Results indicate that the wavelength of the second mode wave is nearly twice as large as the boundary layer thickness. Analysis results of the schlieren image sequence show that the propagation speed of the turbulent spot front is higher than that of the turbulent spot tail, and is slightly higher than the velocity of the boundary layer outer edge.
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Key words:
- boundary layer transition /
- schlieren visualization /
- second mode /
- turbulent spot
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图 2 子午线热流测量结果(流场1，头部钝度2.0mm)
Figure 2. Heat flux results of meridian under the freestream condition 1 with Rn=2.0mm
图 3 子午线热流测量结果(流场3，头部钝度2.0mm)
Figure 3. Heat flux results of meridian under the freestream condition 3 with Rn=2.0mm
图 4 纹影图像、灰度分布及功率谱密度分析结果(流场3，头部钝度2.0mm)
Figure 4. Schlieren images, gray scale density distribution and PSD results under the freestream condition 3 with Rn=2.0mm
图 5 纹影图像、灰度分布及功率谱密度分析结果(流场1，头部钝度2.0mm)
Figure 5. Schlieren images, gray scale density distribution and PSD results under the freestream condition 1 with Rn=2.0mm
图 6 t0+50μs时刻边界层4个位置的法向灰度分布
Figure 6. Vertical gray scale density distribution of four locations of boundary layer at t0+50μs
图 7 纹影图像、灰度分布及功率谱密度分析结果(流场2，头部钝度0.5mm)
Figure 7. Schlieren images, gray scale density distribution and PSD results under the freestream condition 2 with Rn=0.5mm
图 8 流场1~3的纹影图像功率谱密度曲线
Figure 8. PSD curves of grey denstiy of schlieren images under the freestream conditions 1~3
表 1 流场条件
Table 1. Freestream conditions
流场 Ma∞ Re∞/m-1 U∞/(m·s-1) 1 8.2 2.7×107 1329 2 8.1 4.4×107 1228 3 10.2 1.6×107 1376 
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表 2 湍流斑传播速度
Table 2. Propagation speed of turbulent spot
区间 t0~t0+50μs t0+50μs~t0+100μ Uf/(m·s-1) 1400 — Ut/(m·s-1) 740 760 Ut/U∞ 0.56 0.57
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