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Simultaneous temperature and velocity measurements based on novel fluid density-matched phosphorescent microspheres
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-28 DOI: 10.1007/s00348-025-03965-7
Tao Cai, Di Luan, Ruiyu Fu, Yingzheng Liu, Di Peng, Weiwei Cai, Hong Liu

Using temperature-sensitive phosphorescent materials, particle tracing technology presents a promising avenue to simultaneously obtain temperature and velocity fields in thermal fluids. However, the application of the technique is limited by the poor particle tracking ability of inorganic phosphorescent materials, particularly in low-speed flows due to their high density. To address this problem, this study developed fluid density-matched phosphorescent microspheres. Phosphorescent microspheres with hollow structures were synthesized via emulsion polymerization, which enables them to maintain the temperature measurement functionality while exhibiting favorable fluid density-matching properties and enhanced flow field tracking capabilities. The microsphere size and average density were meticulously controlled by adjusting the stirring time and temperature. The microsphere diameters were 57–120 μm, the theoretical average densities were 0.58–3.2 g/cm3, and the operational temperatures were 0–200 °C. The result of the numerical simulation indicates that the temperature response time of the microsphere was within 1.41 ms. Based on the developed microspheres, a temperature–velocity simultaneous measurement method was developed for low-speed thermal fluids. An application demonstration simultaneously measured the temperature and velocity fields in low-speed hot–cold mixed flows. Comparison with thermocouple measurements reveals that the current method can achieve a fluid temperature measurement with an error of 1.575%. The results underscore the efficacy of fluid density-matched phosphorescent microspheres in simultaneously acquiring temperature and velocity fields in low-speed thermal flows.

Graphic abstract

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引用次数: 0
A contribution to 3D tracking of deformable bubbles in swarms using temporal information
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-27 DOI: 10.1007/s00348-025-03963-9
Lantian Wang, Tian Ma, Dirk Lucas, Kerstin Eckert, Hendrik Hessenkemper

Reliable Lagrangian 3D tracking of individual bubble swarm members allows a deeper understanding of hydrodynamic bubble–bubble interactions and their collective rise. For multi-view measurements, we have recently developed such a tracking method (Hessenkemper in Int J Multiph Flow 179:104932, 2024), which is able to track deformable bubbles with low to moderate view obstruction through the bubbles to each other. In the present work, we aim to further enhance the 3D tracking performance by additionally incorporating 2D temporal information in the form of previously established 2D tracks in each camera view. The new 3D tracking method is able to disambiguate cross-view object associations at each time step by using the 2D track information accumulated over time. In addition, the temporal information from multiple 2D domains is used in two post-processing steps to improve the completeness of established 3D trajectories. Compared to the previous 3D tracking method, the extended 3D tracking framework shows noticeable improvements in tracking ability, accuracy, and completeness of trajectories.

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引用次数: 0
A large test section low-speed water tunnel in a small package
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-27 DOI: 10.1007/s00348-025-03959-5
Sean Devey, Morteza Gharib

A novel type of low-speed water tunnel has been designed which uses an array of submersible electric thrusters to propel water through a test section centered within a large rectangular tank. This design can operate as a suction or blowdown tunnel to alternately create uniform, low-turbulence flow or spatially and temporally varying flows such as shear layers, wakes, and gusts. The thruster array architecture also enables an order of magnitude improvement in tunnel footprint for a given test section size, eschewing the need for bulky traditional elements such as the contraction, turning, and settling chambers. Planar digital particle image velocimetry (DPIV) and single-component constant temperature anemometry (CTA) measurements of flow uniformity and turbulence intensity indicate comparable flow quality to larger traditional tunnels when operated in suction mode. Dye visualizations of low Reynolds number cylinder wake flows are also presented to demonstrate tunnel capabilities.

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引用次数: 0
The aerodynamics of sharp- and filet-edged cylinders in high supersonic flow
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-25 DOI: 10.1007/s00348-025-03968-4
Travis A. Duchene, Stuart J. Laurence

To develop a physical understanding and accurate trajectory models for atmospheric re-entry objects like space debris, the influence of the flight attitude on the aerodynamic coefficients of cylindrical bodies in high-speed flow is of interest. Experiments were conducted in a Mach-4 Ludwieg tube at The University of Maryland to study the aerodynamics of cylinders with varying aspect ratios and edge sharpness. A free-flight technique with a high-speed object tracking apparatus was used that allows unconstrained model motion, free of any sting interference, over a full range of angle of attack. A piece-wise analytic function for the model outline combined with a subpixel edge-detection routine allowed measurements of the aerodynamic coefficients based on the 4-degrees-of-freedom model motion. Experimental results were compared to modified Newtonian flow solutions, with generally good agreement. The influence of the angle of attack on the aerodynamic loading was determined to vary strongly according to the aspect ratio and edge radius. In the case of sharp-edged cylinders, increasing the aspect ratio led to an increase in both the flight region for positive lift and larger regions of static stability. By adding curvature to the cylinder base edges, the location of the statically stable trim points occurs at the fully base-exposed and fully body-exposed orientations. It was also found that the flight attitude region for which the cylinder was statically stable was expanded due to the addition of edge curvature. Further, as the aspect ratio was increased for these filet-edged cylinders, the magnitude of the moment coefficient increased noticeably.

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引用次数: 0
Dynamic wall shear stress measurement using event-based 3d particle tracking
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-24 DOI: 10.1007/s00348-024-03946-2
Christian E. Willert, Joachim Klinner

We describe the implementation of a 3d Lagrangian particle tracking (LPT) system based on event-based vision (EBV) and demonstrate its application for the near-wall characterization of a turbulent boundary layer (TBL) in air. The viscous sublayer of the TBL is illuminated by a thin light sheet that grazes the surface of a thin glass window inserted into the wind tunnel wall. The data simultaneously captured by three synchronized event cameras are used to reconstruct the 3d particle tracks within (400,upmu text{m}) of the wall on a field of view of (12.0,text{mm} times 7.5,text{mm}). The velocity and position of particles within the viscous sublayer permit the estimation of the local vector of the unsteady wall shear stress (WSS) under the assumption of linearity between particle velocity and WSS. Thereby, time-evolving maps of the unsteady WSS and higher-order statistics are obtained that are in agreement with DNS data at matching Reynolds number. Near-wall particle acceleration provides the rate of change of the WSS which exhibits fully symmetric log-normal superstatistics. Two-point correlations of the randomly spaced WSS data are obtained by a bin-averaging approach and reveal information on the spacing of near-wall streaks. The employed compact EBV hardware coupled with suited LPT tracking algorithms provides data quality on par with currently used, considerably more expensive, high-speed framing cameras.

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引用次数: 0
Study on the movement behavior of ping-pong ball on water surface under microgravity
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-24 DOI: 10.1007/s00348-024-03952-4
Yi fan Zhao, Shu yang Chen, Di Wu, Liang Hu, Li Duan, Qi Kang

In a microgravity environment, where gravity is almost absent, surface tension plays a dominant role in the behavior of fluid motion. The motion of fluids within storage tanks can lead to significant oscillations of the tank itself or even the entire vehicle, posing substantial safety risks. Solid foam particle anti-sloshing technology represents a novel research topic in addressing this issue. The anti-sloshing technology using solid foam particles is a novel research topic. In this experiment, ping-pong balls were used to simulate individual foam particles, and a transparent liquid tank was designed to observe their motion. Two different hydrophobic materials were applied to the surface of the balls to alter their surface tension in water. A drop tower was used to create a microgravity environment, and the motion of the balls in water under microgravity was recorded with a camera. Both static and dynamic analyses were conducted on the balls under normal gravity and microgravity conditions, considering water resistance, surface tension, and added mass forces. The control equations for the position and velocity of the ball’s center of mass were derived. The experimental results showed that under microgravity, hydrophilic balls tend to submerge into the water, while hydrophobic balls move upwards, away from the water surface. The equilibrium adsorption position of the hydrophilic balls differed significantly between microgravity and normal gravity conditions, with noticeable oscillatory movement in the vertical direction. The experimental results showed good agreement with the dynamic model.

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引用次数: 0
Heat transfer visualization of transitional growth of turbulent spot on a wedge in Mach 5.2 hypersonic flow using fast-response TSP
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-24 DOI: 10.1007/s00348-025-03964-8
Kosuke Yoshikawa, Hiroshi Ozawa

In the present study, the propagation velocity and lateral spreading angle of turbulent spots on a wedge in transient hypersonic boundary layer flows were investigated and characterized by measuring the heat flux distribution using a fast-response temperature-sensitive paint (TSP) in a shock tunnel facility. The shock tunnel was operated under the over-tailored condition and provided with the low- to high-unit Reynolds number during a test duration, which was realized by the contact surface arrival in the shock tube that changed the temperature and density of the reservoir gas. Power spectral density estimated from the pressure recordings may indicate that the boundary layer flow was transitional. In TSP measurements, the global heat flux distribution on the wedge was accurately obtained qualitatively. Surprisingly, turbulent spots were visualized using TSP for each unit Reynolds number condition. The propagation velocities at the head, peak heat flux point, and tail of turbulent spots for low- and high-unit Reynolds number conditions were approximated from the TSP images to be 87 ~ 96%, 69 ~ 73%, and 52 ~ 57% of the boundary layer edge velocities at each condition, respectively. These results were in good agreement with the available data in previous investigations. The lateral spreading angle of turbulent spots was also measured to be 5° ~ 10° from the TSP images. This study showed that the fast-response TSP had the ability to visualize the temporally resolved turbulent spots by measuring the heat flux on the wedge.

Graphical abstract

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引用次数: 0
Ghost particle suppression multiplicative algebraic reconstruction technique for tomographic PIV
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-23 DOI: 10.1007/s00348-024-03935-5
Peng Lei, Hua Yang, Zhouping Yin, Feng Shan

The exponential distribution law of the intensity of tomographic particle image velocimetry (Tomo-PIV) reconstructed particles is validated through a probabilistic approach. Moreover, a new Tomo-PIV particle reconstruction method is proposed based on the intensity distribution law of ghost particles and the self-similarity of true particles. In this method, ghost particles are treated as reconstruction noise. Furthermore, a combination of the variational denoising method and the inverse diffusion equation with a regularization constraint is used to suppress ghost particles. This method is called the ghost particle suppression multiplicative algebraic reconstruction technique (GS-MART). The proposed algorithm was evaluated numerically on cylindrical wake simulation data, and the reconstruction quality, intensity distribution of true particles and ghost particles, and velocity calculation accuracy were analyzed under different particle densities. To validate the effectiveness of GS-MART in real flow field measurement applications, we conducted an experiment on jet flow. The findings demonstrated that the high-precision 3D particle reconstruction achieved by GS-MART significantly enhanced the accuracy of the velocity field estimation.

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引用次数: 0
Comparison of displacement estimation techniques for background-oriented schlieren of high-speed compressible turbulent flows 高速可压缩湍流背景纹线位移估计技术比较
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-22 DOI: 10.1007/s00348-024-03944-4
Tanbo Zhou, Jonathan Gaskins, Jonathan Poggie, Sally P. M. Bane

Background-oriented schlieren (BOS) is a non-intrusive optical method for measuring density gradients in a fluid flow based on changes of local refractive index. The density gradients can be obtained by observing the displacement between two images of a background pattern, with and without the presence of the flow. Existing methods to estimate displacements include block matching and optical flow. Image registration in computer vision seeks reasonable transformations between two images such that one matches the other and has been under-utilized in determining the displacement for BOS image processing. Deformable image registration (DIR) methods allow non-global transformations and are proposed as displacement estimation methods for processing BOS images. Numerical ray tracing simulations are performed to generate synthetic BOS images of various flows. The estimated density gradient results of block matching, optical flow, and DIR methods are compared to the ground truth (the path-averaged density gradient of the schlieren object used in ray tracing) to assess and compare their performances. The performances of these methods are also validated on experimental BOS images to determine the displacement estimation method that is most suitable for high-speed, turbulent flows.

背景取向纹影(BOS)是一种基于局部折射率变化测量流体密度梯度的非侵入式光学方法。密度梯度可以通过观察背景图案的两幅图像之间的位移来获得,有和没有流的存在。现有的位移估计方法包括块匹配和光流。计算机视觉中的图像配准寻求两幅图像之间的合理转换,使一幅图像匹配另一幅图像,并且在确定BOS图像处理的位移方面尚未得到充分利用。可变形图像配准(DIR)方法允许非全局变换,并被提出作为处理BOS图像的位移估计方法。通过数值射线追踪模拟,生成了不同流场的合成BOS图像。将块匹配、光流和DIR方法的估计密度梯度结果与地面真值(光线追踪中使用的纹影物体的路径平均密度梯度)进行比较,以评估和比较它们的性能。在实验BOS图像上验证了这些方法的性能,以确定最适合高速湍流的位移估计方法。
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引用次数: 0
Plasma-based anti-/de-icing: an experimental study utilizing supercooled water droplet image velocimetry 等离子体防冰/除冰:利用过冷水滴成像测速的实验研究
IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL Pub Date : 2025-01-22 DOI: 10.1007/s00348-025-03960-y
Weiwei Hui, Zhipeng Chen, Jianjun Ma, Xuanshi Meng

This paper presents an image velocimetry technique that employs supercooled water droplets as seeding particles in an icing wind tunnel. The innovative work involves reconstructing the pressure distribution using the velocity field measured by the water droplets and providing the water collection efficiency at the leading edge of the airfoil using pathlines. The study compares the relative errors of the velocity fields obtained through traditional particle image velocimetry (PIV) and the supercooled water droplet image velocimetry (SWDIV) methods. Results indicate that the velocity root mean square error of SWDIV is (17.4 %) of the incoming flow velocity, and the average angle error was 5.36°. The streamlines derived from the SWDIV method align well with the water droplet trajectories calculated using the Lagrangian approach, providing a more accurate representation of the flow dynamics involving supercooled water droplets of varying sizes. Using this technique, the study quantitatively analyzes the changing characteristics of the airfoil flow field during the anti-icing and de-icing processes under plasma actuation. Key observations include identifying changes in ice configuration, evaluating water droplet collection efficiency at the leading edge, and analyzing the velocity and pressure fields. In the icing wind tunnel experiments, the incoming flow velocity was 15 (text {m/s}), resulting in a Reynolds number of (1.8 times 10^5). The liquid water content was 1.0 (text {g/m}^3), with a median volume diameter of water droplets at 20 (upmu text {m}) and an average diameter of 6.4 (upmu text {m}) The static temperature of the incoming flow was − 10 °C. The anti-icing research revealed that plasma actuation prevents icing on the leading edge while maintaining the suction peak. However, runback ice formed downstream of the actuator at low incoming flow velocities, significantly reducing local negative pressure and leading to lift loss. Moreover, the aerodynamic effects generated by plasma reduced the peak water droplet collection coefficient at the leading edge by approximately 0.05. When the airfoil’s leading edge was covered with a 5 mm thick layer of mixed ice, its geometric shape became irregular, and the pressure peak was notably diminished. Upon activation of the plasma actuator, the resulting aerodynamic and thermal coupling melted the surface ice, disrupting the adhesion between the ice and the airfoil surface. This caused the ice to detach and be carried downstream by the airflow, effectively achieving de-icing within approximately 203 s. After ice removal, the negative pressure peak on the upper surface of the airfoil’s leading edge returned to baseline levels, restoring lift to a great degree.

提出了一种利用过冷水滴作为结冰风洞种子粒子的图像测速技术。创新工作包括利用水滴测量的速度场重建压力分布,并利用路径提供翼型前缘的集水效率。比较了传统粒子图像测速(PIV)和过冷水滴图像测速(SWDIV)方法得到的速度场的相对误差。结果表明,SWDIV的速度均方根误差为来流速度(17.4 %),平均角度误差为5.36°。SWDIV方法得出的流线与使用拉格朗日方法计算的水滴轨迹很好地吻合,可以更准确地表示不同大小的过冷水滴的流动动力学。利用该技术,定量分析了等离子体驱动下翼型防冰和除冰过程中流场的变化特征。主要观测内容包括识别冰态变化、评估前缘水滴收集效率、分析速度场和压力场。在结冰风洞实验中,来流速度为15 (text {m/s}),得到雷诺数为(1.8 times 10^5)。液态水含量为1.0 (text {g/m}^3),水滴体积直径中位数为20 (upmu text {m}),平均直径为6.4 (upmu text {m}),来流静态温度为−10℃。反结冰研究表明,等离子体驱动可以在保持吸力峰值的同时防止前缘结冰。然而,在低流速下,执行器下游形成回流冰,显著降低了局部负压,导致升力损失。此外,等离子体产生的气动效应使前缘的峰值水滴收集系数降低了约0.05。当翼型前缘被5毫米厚的混合冰覆盖时,其几何形状变得不规则,压力峰值明显减弱。激活等离子体致动器后,由此产生的气动和热耦合融化了表面冰,破坏了冰和翼型表面之间的粘附。这导致冰分离并被气流带到下游,在大约203秒内有效地实现了除冰。除冰后,机翼前缘上表面的负压峰值恢复到基线水平,在很大程度上恢复了升力。
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引用次数: 0
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Experiments in Fluids
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