{"title":"Physical meaning of advection velocity estimated from phase delay of heat transfer coefficients","authors":"Hiroki Nakajima, Kazuhito Dejima, Kiyoshi Kawasaki","doi":"10.1016/j.expthermflusci.2025.111597","DOIUrl":"10.1016/j.expthermflusci.2025.111597","url":null,"abstract":"<div><div>Clarifying the relationship between heat transfer and flow in energy devices is crucial. However, directly measuring heat transfer and flow is challenging. To address this issue, we apply a method for estimating the flow velocity near the wall based on wall thermal data, and we verify the physical meaning of the estimated velocity. Focusing on the channel turbulence at Reynolds numbers of 2,700, 3,300 and 3,800, the heat transfer coefficient was calculated from the wall temperature data experimentally obtained via infrared thermography. The advection velocity of the fluid was estimated based on the phase difference of the time-series fluctuations of the heat transfer coefficients at the upstream and downstream locations. The estimated advection velocity was compared with that obtained via particle image velocimetry (PIV). The time-averaged advection velocity reflects the increase in the mean flow velocity for each Reynolds number. Furthermore, the time-averaged advection velocity corresponded to the PIV results at <em>y</em><sup>+</sup>= 14.5 ± 1.9, which was within the buffer layer (5 < <em>y</em><sup>+</sup> < 30). In addition, we confirm that the proposed method can capture instantaneous velocity to some extent.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111597"},"PeriodicalIF":3.3,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144893748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hydrophobic wettability effects on low-Weber-number droplets morphology evolution","authors":"Xiangjun Zhou, Nian Xu, Xinyu Zhang, Huaqiang Chu","doi":"10.1016/j.expthermflusci.2025.111596","DOIUrl":"10.1016/j.expthermflusci.2025.111596","url":null,"abstract":"<div><div>The impact behavior of the droplets was significantly influenced by the substrate temperature, surface hydrophobicity, and tilt angle. To elucidate the underlying interaction mechanisms between the droplet and the surface, this paper presents an experimental investigation of the interaction between droplets impacting various heated metallic surfaces. The study utilized three distinct hydrophobic aluminum substrates and employed 4 wt% glycerol aqueous solution as the test liquid. The temperature of the metallic substrates was maintained between 80 °C to 260 °C, while the droplet impact velocity was kept constant at 0.884 m/s. Under low-temperature conditions, droplets exhibit a sequence of spreading, receding, and oscillation. In contrast, elevated temperatures induce atomization and the Leidenfrost effect; these elevated temperatures promote spreading, accelerate receding, and enhance droplet rebound. Hydrophobic surfaces inhibit maximum spreading diameter while simultaneously increasing receding velocity and rebound amplitude; stronger hydrophobicity results in a more regular rebound morphology. As the tilt angle increases, droplet spreading and rebound tend to occur in the direction of the tilt, causing changes in the trajectory, displacement, and shape of the droplets. Furthermore, the synergistic effect of high temperature and strong hydrophobicity intensifies the coupling between receding and rebound. Adjustment of the tilt angle can amplify or qualitatively alter the interdependencies among other factors. Ultimately, the macroscopic spreading characteristics are determined by the dynamic balance between the intrinsic contact angle properties and the extrinsic tilt angle.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111596"},"PeriodicalIF":3.3,"publicationDate":"2025-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144878250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Investigation of flow field structures induced by cavity geometry in supersonic Mach 2 conditions","authors":"Zhong-Xuan He, Zhi-Jun Liao, Ho-Tse Huang, Szu-I Yeh","doi":"10.1016/j.expthermflusci.2025.111594","DOIUrl":"10.1016/j.expthermflusci.2025.111594","url":null,"abstract":"<div><div>This study utilizes particle image velocimetry (PIV) to analyze the flow field dynamics in cavity flame holders with varying geometries, emphasizing the quantitative effects of shear layer impingement location and cavity geometry on recirculation zone behavior. Experimental findings reveal that reducing the aft ramp angle weakens high-speed reverse flow near the bottom of the cavity, promoting increased circulation values and a more stable flow structure through the suppression of small-scale vortices. Moreover, as the cavity length-to-depth ratio (L/D) increases, the shear layer impingement location shifts further toward the cavity bottom, causing the primary recirculation zone to diminish or vanish. Concurrently, the secondary recirculation zone expands, leading to a decrease in both average vorticity and circulation values. Enhanced positive axial flow is also observed within the cavity, attributed to the interaction between the shear layer and three-dimensional flow dynamics. This study offers new insights into the transient flow behavior within cavities under supersonic conditions, emphasizing the role of shear layer impingement and recirculation characteristics. The findings provide valuable guidance for the design of cavity-based flameholders, bridging the gap between fundamental flow understanding and practical scramjet combustor applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111594"},"PeriodicalIF":3.3,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zichen Zhang , Xueqin Bu , Guiping Lin , Liang Wang , Jiayi Bao
{"title":"An experimental study on the oscillation dynamics of wind-driven droplets at the verge of shedding","authors":"Zichen Zhang , Xueqin Bu , Guiping Lin , Liang Wang , Jiayi Bao","doi":"10.1016/j.expthermflusci.2025.111593","DOIUrl":"10.1016/j.expthermflusci.2025.111593","url":null,"abstract":"<div><div>An experimental investigation was conducted to explore the dynamics of droplet oscillation for wind-driven droplets. Droplet profiles and velocity fields in the symmetry plane of the droplets were measured using time-resolved particle image velocimetry (PIV) and high-speed imaging techniques. These measurements enabled analysis of the droplet oscillation dynamics. The eigenfrequencies of the droplet oscillation, velocity fluctuations in droplet wake, and the natural oscillation were measured. It was found that droplet oscillation is a self-excited oscillation rather than a vortex-induced oscillation. Due to the self-excited oscillation, the eigenfrequency of wind-driven droplets coincides with the eigenfrequency of the natural oscillation. Furthermore, the self-excited oscillation leads to periodic velocity fluctuations in the shear layer, resulting in a frequency that closely matches that of the droplet oscillation. Velocity fluctuations diminish with the cessation of droplet oscillation for high-viscosity droplets. Based on the oscillation characteristics, a dynamic model of droplet oscillation was developed to address the research gap. The oscillation characteristics of the droplet centroid predicted by the developed model are consistent with the experimental results.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111593"},"PeriodicalIF":3.3,"publicationDate":"2025-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144861098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Study on the spreading and splashing characteristics of droplets impacting a high-speed rotating surface","authors":"Zhengnan Yang , Yulong Li","doi":"10.1016/j.expthermflusci.2025.111591","DOIUrl":"10.1016/j.expthermflusci.2025.111591","url":null,"abstract":"<div><div>In the field of aero engines, droplet impact on compressor blades is a common phenomenon that holds significant importance for research. During the mass injection of pre-compressor cooling, a large number of droplets are injected into the intake duct. The droplets that do not evaporate inevitably collide with the compressor blades, affecting their performance and influencing the wet compression process. Therefore, it is essential to study the impact of droplets on rotating surfaces. This paper experimentally investigated the droplet impact process on a rotating surface, considering the effects of impact velocity, rotational speed, and the radius of the impact location. The condition with high rotational speed was investigated especially. Key observations included asymmetric spreading, splashing, and the generation of secondary droplets. The results indicated that varying rotational speeds led to different outcomes following droplet impact. At lower rotational speeds, droplets deposited on the surface and undergo asymmetric spreading. In contrast, at higher rotational speeds, droplets splashed and broke up, producing secondary droplets. Through statistical analysis, the average diameter of the secondary droplets generated by impact on the rotating surface was in the range between 0.08 and 0.25 times the diameter of initial droplet. The correlations for the diameter distribution parameters and the average diameter of the secondary droplets have been proposed.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111591"},"PeriodicalIF":3.3,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144892140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J.M. Foucaut , C. Arrive , C. Cuvier , J.C. Monnier , C.E. Willert , J. Soria
{"title":"Scaling mean velocity and Reynolds stress of a turbulent boundary layer submitted to an adverse pressure gradient","authors":"J.M. Foucaut , C. Arrive , C. Cuvier , J.C. Monnier , C.E. Willert , J. Soria","doi":"10.1016/j.expthermflusci.2025.111578","DOIUrl":"10.1016/j.expthermflusci.2025.111578","url":null,"abstract":"<div><div>Despite considerable progress in understanding zero pressure gradient boundary layers, turbulence in adverse pressure gradient (APG) boundary layers remains less well understood, particularly in high Reynolds number flows. Unfavorable pressure gradient regions are commonly encountered in industrial applications, but turbulence models often lack the physical basis necessary for reliable predictions in these flows. This study focuses on analyzing the effects of adverse pressure gradient on boundary layer scaling, essential for predicting flow characteristics and validating turbulence models. Building on recent advances in experimental methods and using large-scale particle image velocimetry (PIV), the research aims to provide an analysis of turbulent boundary layer flows in APG. Experiments have been carried out in a wind tunnel using inclined plates to induce pressure gradients at an angle of <span><math><mrow><mo>−</mo><msup><mrow><mn>8</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow></math></span>, complementing an existing database obtained at <span><math><mrow><mo>−</mo><msup><mrow><mn>5</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow></math></span> (see Cuvier et al., 2017) and offering new insights into flow behavior. An analysis of the literature has enabled the authors to compare various scaling approaches and to propose a scaling that is suitable for both mean velocity and Reynolds stress.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111578"},"PeriodicalIF":3.3,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144904308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Senthil Kumar Parimalanathan , Pierre Colinet , Alexey Rednikov , Adam Chafai , Yannis Tsoumpas , Hosein Sadafi , Loucine Mekhitarian , Christophe Wylock , Benjamin Sobac , Sam Dehaeck
{"title":"Mach–Zehnder interferometry for fluid physics experiments involving contact lines and phase change","authors":"Senthil Kumar Parimalanathan , Pierre Colinet , Alexey Rednikov , Adam Chafai , Yannis Tsoumpas , Hosein Sadafi , Loucine Mekhitarian , Christophe Wylock , Benjamin Sobac , Sam Dehaeck","doi":"10.1016/j.expthermflusci.2025.111579","DOIUrl":"10.1016/j.expthermflusci.2025.111579","url":null,"abstract":"<div><div>Mach–Zehnder interferometry is a powerful optical technique for investigating thermo-fluidic phenomena, particularly in experiments involving contact line and phase change measurements. This study presents a comprehensive experimental framework leveraging Mach–Zehnder interferometry to analyze liquid film thickness profiles, vapor concentration fields (vapor clouds), and concentration fields in a Hele-Shaw cell. The technique is applied to sessile droplet profilometry on transparent substrates, revealing wetting dynamics, contact angle evolution, and Marangoni-driven flows and instabilities in spreading and evaporating droplets. Apart from volatile pure droplets, where the thermal Marangoni effect may be essential on account of evaporative cooling, the study also explores the role of solutal Marangoni stresses in hygroscopic binary mixtures. Additionally, vapor interferometry is employed to quantify the concentration field above evaporating droplets and liquid pools, demonstrating the method’s capability for non-invasive measurement of evaporation rates. We also showcase the application of interferometry in <span><math><msub><mrow><mi>CO</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> dissolution studies within Hele-Shaw cells. The results highlight the versatility of Mach–Zehnder interferometry in capturing all those complex phenomena, offering valuable insights for the study of evaporation, wetting, and mass transport in confined geometries.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111579"},"PeriodicalIF":3.3,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144885777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiao Liu , Xiaolei Zhang , Xiaoxin Yao , Zuohua Huang , Chenglong Tang
{"title":"Experimental analysis of liquid ammonia spray with different orifice diameter under marine engine conditions","authors":"Xiao Liu , Xiaolei Zhang , Xiaoxin Yao , Zuohua Huang , Chenglong Tang","doi":"10.1016/j.expthermflusci.2025.111580","DOIUrl":"10.1016/j.expthermflusci.2025.111580","url":null,"abstract":"<div><div>The application of ammonia in high-power marine engines has been receiving more attention on achieving zero-carbon emission goals. Due to the unique flashing boiling characteristics of ammonia, the influence of orifice diameter on its spray characteristics needs further research. Present study presents a comprehensive experimental analysis of liquid ammonia spray macroscopic characteristics using three injector orifice diameters (0.15 mm, 0.3 mm, and 0.45 mm) under high-pressure conditions (injection pressure up to 100 MPa, ambient pressure up to 6 MPa). The results show that ambient pressure exerts a more pronounced influence on spray characteristics than injection pressure. Notably, flash boiling significantly enhances radial spray expansion, particularly causing substantial axial momentum loss in sprays from larger orifice diameter. In non-flash boiling region, although the spray from small orifice diameter develops rapidly at the initial stage, the spray from large orifice diameter exhibits superior performance in penetration distance, velocity and area during later stages. Based on these experimental results, a developed prediction model on spray tip penetration is proposed and verified to be well applicable to different orifice diameters, which provides a reference for orifice diameter optimization. According to the predicted fuel–air mixing degree of spray analyzed through equivalent ratio calculation, present results indicate 0.3 mm orifice diameter is optimal for flash boiling conditions, whereas a 0.45 mm diameter proves more effective for non-flash boiling and high-pressure marine engine operations. These findings offer significant contributions to the design and optimization of ammonia-fueled marine propulsion systems, advancing the development of sustainable maritime technologies.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111580"},"PeriodicalIF":3.3,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144827548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A.W. Mauro, A.F. Passarelli, F. Pelella, L. Viscito
{"title":"A mechanistic predictive model for pressure drop and void fraction calculation in two-phase flows and annular flow regime","authors":"A.W. Mauro, A.F. Passarelli, F. Pelella, L. Viscito","doi":"10.1016/j.expthermflusci.2025.111590","DOIUrl":"10.1016/j.expthermflusci.2025.111590","url":null,"abstract":"<div><div>This paper presents a mechanistic model for predicting the pressure gradient and other relevant flow characteristics during annular two-phase flow, by introducing a novel physical interpretation of the enhancement of the friction factor at the vapor–liquid interface, as a function of the liquid to vapor core inertia forces ratio. This interpretation is demonstrated to be consistent with literature relating the interfacial friction factor to the equivalent sand roughness. An experimental database, consisting of 6377 annular flow data points, has been used to enlarge the range of operating conditions with mass velocities from 99 to 2000 kg m<sup>-2</sup>s<sup>−1</sup>, tube diameters from 0.5 to 14.0 mm, reduced pressures from 0.0363 to 0.6896 and frictional pressure drop values from 0.3 to 1332 kPa/m. The proposed method is able to predict pressure gradients with a mean absolute percentage error of 18 % and 83 % of data points falling within a ± 30 % error range. The method allows also the calculation of the void fraction with a good agreement with the Rouhani-Axelsson correlation.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111590"},"PeriodicalIF":3.3,"publicationDate":"2025-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144805817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yan Pan , Zhuoliang Yu , Leonardo P. Chamorro , Fei Ma , Tengfei Cai
{"title":"Outlet tube effects on cavitation cloud dynamics and erosion in self-excited waterjets","authors":"Yan Pan , Zhuoliang Yu , Leonardo P. Chamorro , Fei Ma , Tengfei Cai","doi":"10.1016/j.expthermflusci.2025.111573","DOIUrl":"10.1016/j.expthermflusci.2025.111573","url":null,"abstract":"<div><div>Using high-speed imaging and three-dimensional surface morphology analysis, we examined the cavitation cloud dynamics and erosion characteristics of self-excited pulsating cavitating waterjets. Erosion experiments on aluminum specimens were conducted to evaluate the influence of varying outlet tube diameters and lengths on the waterjet’s performance. Mass loss measurements revealed that the erosion capability increased approximately threefold under the optimal outlet tube configuration. Proper Orthogonal Decomposition (POD) of high-speed snapshots identified distinct primary and secondary shedding modes driven by passive acoustic excitation. The presence of an outlet tube was found to enhance the volume and development of the primary cavitation cloud while facilitating the merging of secondary and primary modes. This mode-specific structural evolution leads to a synergistic amplification of cavitation cloud intensity, which governs the enhancement of erosion capacity.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"170 ","pages":"Article 111573"},"PeriodicalIF":3.3,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144771243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}