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Open AccessArticle

Measurement of the Convection Velocities in a Hypersonic Turbulent Boundary Layer Using Two-Point Cylindrical-Focused Laser Differential Interferometer

by Ranran Huang, Tao Xue and Jie Wu

Aerospace 2024, 11(1), 100; https://doi.org/10.3390/aerospace11010100 - 22 Jan 2024

Cited by 2 | Viewed by 1835

Abstract

A two-point cylindrical-focused laser differential interferometer (2P-CFLDI) system and a conventional Z-type Schlieren were used to measure the hypersonic turbulent boundary layer on a flat plate at Mach number Ma = 6 and Reynolds number Re = 1.08 × 10⁶ m⁻¹. The boundary layer thickness at the measurement location and the noise radiation angle were obtained by post-processing the Schlieren image. The 2P-CFLDI data underwent cross-correlation analysis to calculate the mean convective velocities at different heights and compared with previous experimental and numerical results. The experimentally measured mean convective velocities agree with the trend of available DNS and experimental results. The mean convective velocity near the wall is significantly larger than the local mean velocity and is the main noise source region. Further filtering treatment shows that the convective velocity of the disturbed structure decreases gradually with the increase in the disturbance scale. The differences between convective velocities at different scales are significantly larger outside the boundary layer than inside the boundary layer, which is in agreement with the findings of the previous hot wire experiments. Near the wall, large-scale disturbances mainly determine the localized mean convective velocity, which are the main source of noise radiation for the hypersonic turbulent boundary layer. Full article

(This article belongs to the Special Issue Selected Papers from 10th International Conference on Vortex Flow Mechanics)

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31 pages, 8327 KB

Open AccessArticle

Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

by Giannino Ponchio Camillo, Alexander Wagner, Takahiko Toki and Carlo Scalo

Aerospace 2023, 10(6), 570; https://doi.org/10.3390/aerospace10060570 - 20 Jun 2023

Cited by 13 | Viewed by 3006

Abstract

This work investigates a hypersonic turbulent boundary layer over a

7^{°}

half angle cone at a wall-to-total temperature ratio of 0.1,

M_{\infty} = 7.4

and

R e_{\infty m} = 4.2 \times 10^{6}

^{- 1}

, in terms of [...] Read more.

This work investigates a hypersonic turbulent boundary layer over a

7^{°}

half angle cone at a wall-to-total temperature ratio of 0.1,

M_{\infty} = 7.4

and

R e_{\infty m} = 4.2 \times 10^{6}

^{- 1}

, in terms of density fluctuations and the convection velocity of density disturbances. Experimental shock tunnel data are collected using a multi-foci Focused Laser Differential Interferometer (FLDI) to probe the boundary layer at several heights. In addition, a high-fidelity, time-resolved Large-Eddy Simulation (LES) of the conical flowfield under the experimentally observed free stream conditions is conducted. The experimentally measured convection velocity of density disturbances is found to follow literature data of pressure disturbances. The spectral distributions evidence the presence of regions with well-defined power laws that are present in pressure spectra. A framework to combine numerical and experimental observations without requiring complex FLDI post-processing strategies is explored using a computational FLDI (cFLDI) on the numerical solution for direct comparisons. Frequency bounds of 160 kHz

< f < 1

MHz are evaluated in consideration of the constraining conditions of both experimental and numerical data. Within these limits, the direct comparisons yield good agreement. Furthermore, it is verified that in the present case, the cFLDI algorithm may be replaced with a simple line integral on the numerical solution. Full article

(This article belongs to the Section Aeronautics)

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8 pages, 1635 KB

Open AccessCommunication

Tunable Spatial Resolution Focused Laser Differential Interferometer for Density Fluctuation Measurement

by Hongxun Li, Yudong Li, Li Chen and Xianghong Yao

Appl. Sci. 2023, 13(5), 3253; https://doi.org/10.3390/app13053253 - 3 Mar 2023

Cited by 2 | Viewed by 1887

Abstract

We first propose and demonstrate a novel approach for achieving a focused laser differential interferometer (FLDI) system with tunable spatial resolution. The spatial resolution of the FLDI can be adjusted continuously between 83 μm and 382 μm. The density fluctuation of a supersonic shear flow is measured using the FLDI system with a spatial resolution of 182 μm, and the density fluctuations at different locations of the supersonic shear flow are measured and analyzed. The ability to adjust the spatial resolution in this work is of great significance for enhancing the spatial resolution and flexibility of the FLDI system. Full article

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15 pages, 6186 KB

Open AccessArticle

Numerical and Experimental Validation of a Supersonic Mixing Layer Facility

by Yudong Li, Li Chen, Hongxun Li, Yungang Wu and Shuang Chen

Appl. Sci. 2022, 12(11), 5489; https://doi.org/10.3390/app12115489 - 28 May 2022

Cited by 2 | Viewed by 2613

Abstract

The design of a supersonic-supersonic mixing layer facility was motivated by the need for a benchmark experimental platform to study the physical phenomena underlying supersonic mixing layers. The facility is an intermittent blowdown wind tunnel characterized by a two-stream design separated by a splitter plate in the middle of the nozzle. The splitter plate ends exactly at the start of the mixing layer test section. The Mach number of the primary stream is M₁ = 3 for all nozzles and the secondary streams are M₂ = 2, 2.5, and 2.9 to generate different convective Mach numbers of Mc = 0.25, 0.10, and 0.01, respectively. The facility was calibrated by pressure measurements to verify the Mach number and the pressure distribution in the streamwise direction. Large-eddy simulation (LES) was performed to illustrate a full view of the turbulent compressible mixing layer flow field and to compare this against the experimental data. Optical diagnosis measurements, i.e., femtosecond laser-induced electronic excitation tagging velocimetry (FLEET) for velocity measurement and focused laser differential interferometer (FLDI) for the density fluctuation, were also performed on the facility. Full article

(This article belongs to the Special Issue Theory and Applications of High-Order Methods in Computational Fluid Dynamics)

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