Pub Date : 2025-09-22DOI: 10.1016/j.expthermflusci.2025.111622
Yushuai Liu , Chuanyu Fang , Shaolin Wang , Cunxi Liu , Yong Mu , Gang Xu
Swirl cup airblast fuel injectors are critical components in modern low-emission gas turbine combustors. Understanding the underlying physics of the interaction between fuel spray and complex swirling airflow is crucial for optimizing injector performance. This study investigates the influence of Venturi outlet angles (15°, 25°, and 35°) on airflow field and spray atomization dynamics. Advanced optical diagnostics, including high-speed shadowgraph, Phase Doppler Particle Analyzer (PDPA), Particle Imaging Velocimetry (PIV), and Planar Mie scattering (PMie), were employed to quantify flow-spray interactions under controlled fuel flow rates (2.0–4.0 kg/h) and 3 % relative air pressure drop. Results demonstrate that the Venturi outlet angle significantly modulates primary atomization. Increasing the angle from 15° to 35° reduces liquid film length by 69.2 % due to enhanced gas–liquid shear stress. Moreover, larger angles amplify central toroidal recirculation zone (CTRZ) reverse velocity (−1.2 to −6.8 m/s), intensifying droplet entrainment and reducing Sauter Mean Diameter (SMD) by 30.9 %. These findings highlight that Venturi angles > 25° optimize atomization by balancing shear-driven breakup and recirculation-enhanced mixing, providing critical insights for designing fuel injectors with improved combustion stability and emission performance.
{"title":"Swirling flow and spray atomization interactions in a swirl cup airblast fuel injector: Venturi outlet angle","authors":"Yushuai Liu , Chuanyu Fang , Shaolin Wang , Cunxi Liu , Yong Mu , Gang Xu","doi":"10.1016/j.expthermflusci.2025.111622","DOIUrl":"10.1016/j.expthermflusci.2025.111622","url":null,"abstract":"<div><div>Swirl cup airblast fuel injectors are critical components in modern low-emission gas turbine combustors. Understanding the underlying physics of the interaction between fuel spray and complex swirling airflow is crucial for optimizing injector performance. This study investigates the influence of Venturi outlet angles (15°, 25°, and 35°) on airflow field and spray atomization dynamics. Advanced optical diagnostics, including high-speed shadowgraph, Phase Doppler Particle Analyzer (PDPA), Particle Imaging Velocimetry (PIV), and Planar Mie scattering (PMie), were employed to quantify flow-spray interactions under controlled fuel flow rates (2.0–4.0 kg/h) and 3 % relative air pressure drop. Results demonstrate that the Venturi outlet angle significantly modulates primary atomization. Increasing the angle from 15° to 35° reduces liquid film length by 69.2 % due to enhanced gas–liquid shear stress. Moreover, larger angles amplify central toroidal recirculation zone (CTRZ) reverse velocity (−1.2 to −6.8 m/s), intensifying droplet entrainment and reducing Sauter Mean Diameter (SMD) by 30.9 %. These findings highlight that Venturi angles > 25° optimize atomization by balancing shear-driven breakup and recirculation-enhanced mixing, providing critical insights for designing fuel injectors with improved combustion stability and emission performance.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111622"},"PeriodicalIF":3.3,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155945","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}
Pub Date : 2025-09-17DOI: 10.1016/j.expthermflusci.2025.111619
Feixiang Chang , Mang Yan , Hongliang Luo , Wuli Hong , Yewen Feng , Fei Liu , Chang Zhai , Kang Yang , Bo Song , Jian Zhang , Samir Chandra Ray
In Direct Injection Spark Ignition (DISI) internal combustion engines, fuel droplets inevitably impact the cylinder walls, resulting in droplet adhesion and incomplete combustion, thereby increasing pollutant emissions. The injection strategy has been proven to significantly improve the droplet-wall interaction. Initially, the Refractive Index Matching (RIM) method was used to measure fuel adhesion under both single and double injection conditions, with results confirming that the double injection strategy significantly reduced the fuel adhesion mass. To investigate the mechanisms underlying the reduction in fuel adhesion with double injection, Particle image analysis (PIA) and a multiple droplets producer were employed to examine the micro-behavior of successive droplet clusters near the wall surface. Statistical analyses were conducted on droplet size and velocity. Results showed that, when the two successive droplet clusters impact the wall, the Sauter Mean Diameter (SMD) of the second cluster is greater than that of the first cluster. There are two reasons for this. First, this difference is attributed to the coalescence between the leading droplets of the second droplet cluster and the trailing droplets of the first droplet cluster. Second, when the second droplet cluster impacts the wall, the breakup of fuel adhesion can also lead to the formation of larger droplets. Moreover, the second droplet cluster exhibits a significantly higher penetration velocity than that of the first, which can be attributed to the interaction of the velocity fields between the trailing droplets of the first cluster and the leading droplets of the second cluster. Furthermore, analysis of the average minimum droplet distance shows that droplet number density near the wall is relatively high and decreases with increasing distance from the wall. Lastly, the Bai model was used to predict the probabilities of stick, rebound, spread, and splash of successive droplet clusters at various observation points.
在直喷式火花点火（Direct Injection Spark Ignition， DISI）内燃机中，燃油液滴不可避免地会撞击汽缸壁面，造成液滴粘附，燃烧不完全，从而增加污染物排放。该注入策略已被证明可以显著改善液滴-壁面相互作用。首先，使用折射率匹配（RIM）方法测量了单次和双次喷射条件下的燃油粘附质量，结果证实双次喷射策略显著降低了燃油粘附质量。为了研究双重喷射降低燃油粘附的机制，采用粒子图像分析（PIA）和多液滴产生器对壁面附近连续液滴团的微观行为进行了研究。对液滴大小和速度进行了统计分析。结果表明，当连续两个液滴团撞击壁面时，第二个液滴团的Sauter Mean Diameter （SMD）大于第一个液滴团。这有两个原因。首先，这种差异归因于第二个液滴团的先导液滴和第一个液滴团的尾随液滴之间的聚并。其次，当第二液滴簇撞击壁面时，燃料黏附的破裂也会导致更大液滴的形成。第二液滴团的穿透速度明显高于第一液滴团，这可能是由于第一液滴团尾部液滴与第二液滴团前导液滴之间的速度场相互作用所致。此外，对平均最小液滴距离的分析表明，液滴数密度在壁面附近较高，且随着离壁面距离的增加而减小。最后，利用Bai模型预测了不同观测点连续液滴团的粘附、反弹、扩散和飞溅概率。
{"title":"Study on the microscopic characteristics of successive droplet clusters impacting on the wall","authors":"Feixiang Chang , Mang Yan , Hongliang Luo , Wuli Hong , Yewen Feng , Fei Liu , Chang Zhai , Kang Yang , Bo Song , Jian Zhang , Samir Chandra Ray","doi":"10.1016/j.expthermflusci.2025.111619","DOIUrl":"10.1016/j.expthermflusci.2025.111619","url":null,"abstract":"<div><div>In Direct Injection Spark Ignition (DISI) internal combustion engines, fuel droplets inevitably impact the cylinder walls, resulting in droplet adhesion and incomplete combustion, thereby increasing pollutant emissions. The injection strategy has been proven to significantly improve the droplet-wall interaction. Initially, the Refractive Index Matching (RIM) method was used to measure fuel adhesion under both single and double injection conditions, with results confirming that the double injection strategy significantly reduced the fuel adhesion mass. To investigate the mechanisms underlying the reduction in fuel adhesion with double injection, Particle image analysis (PIA) and a multiple droplets producer were employed to examine the micro-behavior of successive droplet clusters near the wall surface. Statistical analyses were conducted on droplet size and velocity. Results showed that, when the two successive droplet clusters impact the wall, the Sauter Mean Diameter (SMD) of the second cluster is greater than that of the first cluster. There are two reasons for this. First, this difference is attributed to the coalescence between the leading droplets of the second droplet cluster and the trailing droplets of the first droplet cluster. Second, when the second droplet cluster impacts the wall, the breakup of fuel adhesion can also lead to the formation of larger droplets. Moreover, the second droplet cluster exhibits a significantly higher penetration velocity than that of the first, which can be attributed to the interaction of the velocity fields between the trailing droplets of the first cluster and the leading droplets of the second cluster. Furthermore, analysis of the average minimum droplet distance shows that droplet number density near the wall is relatively high and decreases with increasing distance from the wall. Lastly, the Bai model was used to predict the probabilities of stick, rebound, spread, and splash of successive droplet clusters at various observation points.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111619"},"PeriodicalIF":3.3,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106734","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}
Pub Date : 2025-09-16DOI: 10.1016/j.expthermflusci.2025.111620
Qazi Talal , Zubairu Abubakar , Ahmed Gaber H. Saif , ELSaeed Saad ELSihy , M. Raghib Shakeel , Esmail M.A. Mokheimer
Stratified flames have attracted significant attention due to their superior resilience to turbulence and enhanced flame stability, enabling reduced NOx and CO emissions. In this study, an innovative dual annular stratified burner was designed and experimentally investigated to characterize thermoacoustic instability, emissions and flame macrostructure in swirling and non-swirling (jet) methane-air flames. Experiments were systematically conducted across stratification ratios (SR = 1–3) and global equivalence ratios (Φg) ranging from lean blowoff to rich conditions (Φg = 1.2). Swirling flames exhibited consistently acceptable emissions (NOx and CO < 20 ppm) under stable lean operating conditions (Φg = 0.55–0.8) for all SRs tested. Jet flames showed no thermoacoustic instabilities irrespective of SR or Φg variations. Similarly, swirling flames remained stable for Φg < 0.8; however, at Φg = 0.8, thermoacoustic instability initiated, characterized by coupled oscillations of acoustic pressure and heat release fluctuations. These oscillations were sustained until Φg = 1.1, beyond which decoupling occurred. Limit cycle oscillations with heightened sound pressure amplitudes were observed at lower stratification ratios (SR = 1–1.5), whereas no limit cycles were detected at higher SR values (>1.5). Increasing SR significantly suppressed instability amplitudes, notably resulting in a 70 % reduction of oscillation amplitudes at Φg = 0.9 when SR increased from 1 to 3. Flame macrostructure analysis confirmed improved anchoring and mixing characteristics of swirling flames compared to jet flames, particularly at higher SR conditions. This work highlights that controlled stratification effectively enhances operational stability and produces more compact flames in swirling combustors, offering valuable insights for developing low-emission and high-efficiency combustion systems.
{"title":"Effect of stratification on thermoacoustic instability, emissions, and flame macrostructure in a swirl-stabilized dual annular burner: An experimental study","authors":"Qazi Talal , Zubairu Abubakar , Ahmed Gaber H. Saif , ELSaeed Saad ELSihy , M. Raghib Shakeel , Esmail M.A. Mokheimer","doi":"10.1016/j.expthermflusci.2025.111620","DOIUrl":"10.1016/j.expthermflusci.2025.111620","url":null,"abstract":"<div><div>Stratified flames have attracted significant attention due to their superior resilience to turbulence and enhanced flame stability, enabling reduced NO<sub>x</sub> and CO emissions. In this study, an innovative dual annular stratified burner was designed and experimentally investigated to characterize thermoacoustic instability, emissions and flame macrostructure in swirling and non-swirling (jet) methane-air flames. Experiments were systematically conducted across stratification ratios (SR = 1–3) and global equivalence ratios (Φ<sub>g</sub>) ranging from lean blowoff to rich conditions (Φ<sub>g</sub> = 1.2). Swirling flames exhibited consistently acceptable emissions (NO<sub>x</sub> and CO < 20 ppm) under stable lean operating conditions (Φ<sub>g</sub> = 0.55–0.8) for all SRs tested. Jet flames showed no thermoacoustic instabilities irrespective of SR or Φ<sub>g</sub> variations. Similarly, swirling flames remained stable for Φ<sub>g</sub> < 0.8; however, at Φ<sub>g</sub> = 0.8, thermoacoustic instability initiated, characterized by coupled oscillations of acoustic pressure and heat release fluctuations. These oscillations were sustained until Φ<sub>g</sub> = 1.1, beyond which decoupling occurred. Limit cycle oscillations with heightened sound pressure amplitudes were observed at lower stratification ratios (SR = 1–1.5), whereas no limit cycles were detected at higher SR values (>1.5). Increasing SR significantly suppressed instability amplitudes, notably resulting in a 70 % reduction of oscillation amplitudes at Φ<sub>g</sub> = 0.9 when SR increased from 1 to 3. Flame macrostructure analysis confirmed improved anchoring and mixing characteristics of swirling flames compared to jet flames, particularly at higher SR conditions. This work highlights that controlled stratification effectively enhances operational stability and produces more compact flames in swirling combustors, offering valuable insights for developing low-emission and high-efficiency combustion systems.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111620"},"PeriodicalIF":3.3,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106732","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}
Pub Date : 2025-09-13DOI: 10.1016/j.expthermflusci.2025.111612
Manaf Muhammed , Anvesh Dhulipalla , Harsha Sista , Hassan A. Khawaja , Muhammad S. Virk , Hui Hu
An experimental study is performed to investigate the transient ice accretion process along the surface of a high-lift, S1223 airfoil model, and the icing-induced aerodynamic performance degradation. The UAV airfoil model was exposed to typically glaze and rime icing conditions encountered by UAVs flying in low-altitude airspace. While the rime ice accretion was found to conform with the original profile of the UAV airfoil model well in general, substantial “feather-like” ice roughness elements were observed to grow rapidly over both the suction-side and pressure-side surfaces near the airfoil leading edge. The glaze ice accretion process was featured by obvious wind-driven water runback to transport the unfrozen water mass from the airfoil frontal surface to further downstream locations, causing the formation of complex rivulet-shaped ice structures and growth of ice “horns” along the leading edge and “finger-liked icicles” near the trailing edge. The aerodynamic performance of the UAV airfoil was found to degrade continuously with the increasing ice accretion time. The ice accretion over a period of 463 s was found to reduce UAV endurance from 18% to 46 % and diminish the UAV flying range by 13 % to 40 %, depending on the nature of ice accreted. The acquired ice accretion images were coordinated with the aerodynamic force measurements to gain further insight into the underlying physics for a better understanding of the UAV inflight icing phenomena.
{"title":"An experimental investigation of transient ice accretion process on a high-lift airfoil model for UAV applications","authors":"Manaf Muhammed , Anvesh Dhulipalla , Harsha Sista , Hassan A. Khawaja , Muhammad S. Virk , Hui Hu","doi":"10.1016/j.expthermflusci.2025.111612","DOIUrl":"10.1016/j.expthermflusci.2025.111612","url":null,"abstract":"<div><div>An experimental study is performed to investigate the transient ice accretion process along the surface of a high-lift, S1223 airfoil model, and the icing-induced aerodynamic performance degradation. The UAV airfoil model was exposed to typically glaze and rime icing conditions encountered by UAVs flying in low-altitude airspace. While the rime ice accretion was found to conform with the original profile of the UAV airfoil model well in general, substantial “feather-like” ice roughness elements were observed to grow rapidly over both the suction-side and pressure-side surfaces near the airfoil leading edge. The glaze ice accretion process was featured by obvious wind-driven water runback to transport the unfrozen water mass from the airfoil frontal surface to further downstream locations, causing the formation of complex rivulet-shaped ice structures and growth of ice “horns” along the leading edge and “finger-liked icicles” near the trailing edge. The aerodynamic performance of the UAV airfoil was found to degrade continuously with the increasing ice accretion time. The ice accretion over a period of 463 s was found to reduce UAV endurance from 18% to 46 % and diminish the UAV flying range by 13 % to 40 %, depending on the nature of ice accreted. The acquired ice accretion images were coordinated with the aerodynamic force measurements to gain further insight into the underlying physics for a better understanding of the UAV inflight icing phenomena.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111612"},"PeriodicalIF":3.3,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106790","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}
Pub Date : 2025-09-13DOI: 10.1016/j.expthermflusci.2025.111617
Letian Chen , Zhanqi Tang , Zhenqing Li , Nan Jiang
This study investigates the far-field wake behavior and entrainment motions of the over-tripped boundary layer (OT-BL) turbulence induced by a family of wall-mounted tripwires with different wall blockage rate . Friction Reynolds number is more than twice that of the unperturbed canonical turbulent boundary layer. Far-field streamwise development of the OT-BL is referred to as a cooperative action of wall-driven and wake-driven mechanisms. Spatial two-point correlation and intermittency factor are employed to quantify the wall-driven and wake-driven ranges. The wall driver shows a weak dependence on the tripwire configuration, whereas the wake driver is clearly related to the tripwire configuration. Along with downstream development, the wake-driven region exhibits an upward and spreading trend, which correlates positively with of tripwires. The wake dynamics in turbulent region and near-interface region are revealed from the turbulent/non-turbulent interface perspective. In the upstream stage, the wake is controlled by the tripwire-excited disturbed eddies, and then, in the downstream stage, the near-interface wake dynamics are gradually similar to canonical pattern. Further, entrainment is considered based on nibbling and engulfing motions. For OT-BL, tripwire-excited disturbed eddies enhance nibbling and engulfing entrainment. Nibbling entrainment is the main entrainment mode, although engulfing process is also a significant component. Finally, the study assesses the far-field recovery trend of the OT-BLs’ wake dynamics and entrainment motion. This research provides a reference for tripwire design to simulate higher- OT-BL in a finite test section. Meanwhile, we discuss the evaluation scheme on the wake turbulence characteristics of OT-BL from multiple perspectives.
{"title":"Wake behavior and entrainment motion in the far-field stage of over-tripped boundary layer turbulence","authors":"Letian Chen , Zhanqi Tang , Zhenqing Li , Nan Jiang","doi":"10.1016/j.expthermflusci.2025.111617","DOIUrl":"10.1016/j.expthermflusci.2025.111617","url":null,"abstract":"<div><div>This study investigates the far-field wake behavior and entrainment motions of the over-tripped boundary layer (OT-BL) turbulence induced by a family of wall-mounted tripwires with different wall blockage rate <span><math><mrow><msub><mi>σ</mi><mi>w</mi></msub></mrow></math></span>. Friction Reynolds number <span><math><mrow><msub><mrow><mi>Re</mi></mrow><mi>τ</mi></msub></mrow></math></span> is more than twice that of the unperturbed canonical turbulent boundary layer. Far-field streamwise development of the OT-BL is referred to as a cooperative action of wall-driven and wake-driven mechanisms. Spatial two-point correlation and intermittency factor are employed to quantify the wall-driven and wake-driven ranges. The wall driver shows a weak dependence on the tripwire configuration, whereas the wake driver is clearly related to the tripwire configuration. Along with downstream development, the wake-driven region exhibits an upward and spreading trend, which correlates positively with <span><math><mrow><msub><mi>σ</mi><mi>w</mi></msub></mrow></math></span> of tripwires. The wake dynamics in turbulent region and near-interface region are revealed from the turbulent/non-turbulent interface perspective. In the upstream stage, the wake is controlled by the tripwire-excited disturbed eddies, and then, in the downstream stage, the near-interface wake dynamics are gradually similar to canonical pattern. Further, entrainment is considered based on nibbling and engulfing motions. For OT-BL, tripwire-excited disturbed eddies enhance nibbling and engulfing entrainment. Nibbling entrainment is the main entrainment mode, although engulfing process is also a significant component. Finally, the study assesses the far-field recovery trend of the OT-BLs’ wake dynamics and entrainment motion. This research provides a reference for tripwire design to simulate higher-<span><math><mrow><msub><mrow><mi>Re</mi></mrow><mi>τ</mi></msub></mrow></math></span> OT-BL in a finite test section. Meanwhile, we discuss the evaluation scheme on the wake turbulence characteristics of OT-BL from multiple perspectives.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111617"},"PeriodicalIF":3.3,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106733","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 study of the high-speed impact of water droplets on smooth and microtextured fluoropolymer-coated titanium surfaces is presented. The experimental samples had an average roughness Ra from 0.04 μm to 15.4 μm and a static contact angle θ from 74° to 164°. The 0.5–1.3-mm droplets were impacted on the surfaces at velocities U0 = 5–20 m/s (the Weber number We = 450–2,800). Using a high-speed video camera with a sample rate of 60,000 frames per second, the values of the opening angle α, the maximum diameter Dcor, and the lifetime of the corona were measured and analyzed. In addition, the mean splashing velocities of both large and small secondary fragments were captured. A dimensionless ratio, α/θ, which characterizes the predominance of inertial or adhesive forces, was proposed for the development of an empirical model for predicting Dcor. This model was validated using data from other authors, which proved its applicability in the ranges of We = 450–2,800, Ra = 1.05–38 µm, θ = 69–164° (water) and θ 0° (ethanol). The research elucidated that superhydrophobic microtextured surfaces provide greater symmetry in corona splash and a larger opening angle. However, these surfaces also delayed liquid removal during splashing, which has the potential to impact the effectiveness of their water-repellent properties.
{"title":"High-speed impact of water droplets on microtextured surfaces: Effect of roughness and wettability on corona splashing","authors":"Danila Verkhodanov , Nikita Khomutov , Maxim Piskunov , Ivan Vozhakov , Sergey Starinskiy , Alexey Safonov , Nikita Smirnov","doi":"10.1016/j.expthermflusci.2025.111618","DOIUrl":"10.1016/j.expthermflusci.2025.111618","url":null,"abstract":"<div><div>A study of the high-speed impact of water droplets on smooth and microtextured fluoropolymer-coated titanium surfaces is presented. The experimental samples had an average roughness <em>R<sub>a</sub></em> from 0.04 μm to 15.4 μm and a static contact angle <em>θ</em> from 74° to 164°. The 0.5–1.3-mm droplets were impacted on the surfaces at velocities <em>U<sub>0</sub></em> = 5–20 m/s (the Weber number <em>We</em> = 450–2,800). Using a high-speed video camera with a sample rate of 60,000 frames per second, the values of the opening angle <em>α</em>, the maximum diameter <em>D<sub>cor</sub></em>, and the lifetime of the corona were measured and analyzed. In addition, the mean splashing velocities of both large and small secondary fragments were captured. A dimensionless ratio, <em>α/θ</em>, which characterizes the predominance of inertial or adhesive forces, was proposed for the development of an empirical model for predicting <em>D<sub>cor</sub></em>. This model was validated using data from other authors, which proved its applicability in the ranges of <em>We</em> = 450–2,800, <em>R<sub>a</sub></em> = 1.05–38 µm, <em>θ</em> = 69–164° (water) and <em>θ</em> <span><math><mo>≈</mo></math></span> 0° (ethanol). The research elucidated that superhydrophobic microtextured surfaces provide greater symmetry in corona splash and a larger opening angle. However, these surfaces also delayed liquid removal during splashing, which has the potential to impact the effectiveness of their water-repellent properties.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111618"},"PeriodicalIF":3.3,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106731","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}
Pub Date : 2025-09-10DOI: 10.1016/j.expthermflusci.2025.111616
Qiuxiang Chen, Xinying Wang, Qiang Li, Hongfei Hu, Haijun Wang
The interaction between jet drainage films and crossflow is widespread in engineering systems such as liquid rocket engines and nuclear reactor emergency cooling systems. In these processes, an understanding of the flow behavior and fluctuation characteristics of drainage films under crossflow is essential. In this study, an experimental system was constructed to investigate the behavior of jet drainage films under crossflow. The spatial evolution of film offset, average film thickness, base film thickness, wave height, and fluctuation characteristics was investigated under varying crossflow velocities using high-speed imaging and spectral confocal measurement techniques. The results show that the drainage film is shifted to the crossflow direction, and the offset increases linearly with the flow distance, which is inversely proportional to the jet Weber number and directly proportional to the crossflow Weber number. The spatial distribution characteristics of the average liquid film thickness, base film thickness, and wave height are jointly influenced by the jet Weber number and crossflow velocity. The cross-sectional averages of liquid film thickness, base film thickness, and wave height exhibit an initial decrease followed by a subsequent increase with flow distance. The standard deviation of the liquid film thickness was significantly and linearly correlated with its average value, with a slope of approximately 0.3. As the crossflow velocity increases, the liquid film fluctuations on the leeward side of the drainage film are significantly suppressed at low jet Weber numbers, while the liquid film fluctuations on the windward side are notably weakened at the high jet Weber number.
{"title":"Flow and wave characteristics of jet drainage film under crossflow","authors":"Qiuxiang Chen, Xinying Wang, Qiang Li, Hongfei Hu, Haijun Wang","doi":"10.1016/j.expthermflusci.2025.111616","DOIUrl":"10.1016/j.expthermflusci.2025.111616","url":null,"abstract":"<div><div>The interaction between jet drainage films and crossflow is widespread in engineering systems such as liquid rocket engines and nuclear reactor emergency cooling systems. In these processes, an understanding of the flow behavior and fluctuation characteristics of drainage films under crossflow is essential. In this study, an experimental system was constructed to investigate the behavior of jet drainage films under crossflow. The spatial evolution of film offset, average film thickness, base film thickness, wave height, and fluctuation characteristics was investigated under varying crossflow velocities using high-speed imaging and spectral confocal measurement techniques. The results show that the drainage film is shifted to the crossflow direction, and the offset increases linearly with the flow distance, which is inversely proportional to the jet Weber number and directly proportional to the crossflow Weber number. The spatial distribution characteristics of the average liquid film thickness, base film thickness, and wave height are jointly influenced by the jet Weber number and crossflow velocity. The cross-sectional averages of liquid film thickness, base film thickness, and wave height exhibit an initial decrease followed by a subsequent increase with flow distance. The standard deviation of the liquid film thickness was significantly and linearly correlated with its average value, with a slope of approximately 0.3. As the crossflow velocity increases, the liquid film fluctuations on the leeward side of the drainage film are significantly suppressed at low jet Weber numbers, while the liquid film fluctuations on the windward side are notably weakened at the high jet Weber number.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111616"},"PeriodicalIF":3.3,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047489","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}
The impact-freezing behavior of droplets on cold superhydrophobic cylinders was investigated using silica-based coating and a self-constructed low-temperature droplet impact experimental platform. The effects of surface temperature, droplet impact velocity, and surface curvature on droplet dynamics and freezing behavior were systematically investigated. Experimental results revealed that the surface temperature predominantly inhibited droplet retraction, with limited influence on the spreading stage. The effect of surface curvature was found to be more complicated. Droplets tended to freeze rather than rebound at smaller curvature diameters, highlighting the dominance of heat transfer. As the curvature diameter increased, fluid flow effects became more pronounced, leading to a larger circumferential spreading factor. Then, this factor gradually decreased with further increases in diameter and eventually stabilized. Experiment also showed that the circumferential maximum spreading factor was positively correlated with both the surface supercooling degree and the Weber number, but negatively correlated with the curvature diameters ratio. Notably, the influence of surface temperature on impact-freezing was highly related to surface curvature. These findings provided insights into optimizing structured superhydrophobic surfaces for anti-icing performance.
{"title":"Water droplet impact-freezing behaviors on cold superhydrophobic cylindrical surfaces","authors":"Qi Guo , Jiaxiang Zheng , Zunru Fu , Hui Gao , Dongsheng Wen","doi":"10.1016/j.expthermflusci.2025.111613","DOIUrl":"10.1016/j.expthermflusci.2025.111613","url":null,"abstract":"<div><div>The impact-freezing behavior of droplets on cold superhydrophobic cylinders was investigated using silica-based coating and a self-constructed low-temperature droplet impact experimental platform. The effects of surface temperature, droplet impact velocity, and surface curvature on droplet dynamics and freezing behavior were systematically investigated. Experimental results revealed that the surface temperature predominantly inhibited droplet retraction, with limited influence on the spreading stage. The effect of surface curvature was found to be more complicated. Droplets tended to freeze rather than rebound at smaller curvature diameters, highlighting the dominance of heat transfer. As the curvature diameter increased, fluid flow effects became more pronounced, leading to a larger circumferential spreading factor. Then, this factor gradually decreased with further increases in diameter and eventually stabilized. Experiment also showed that the circumferential maximum spreading factor was positively correlated with both the surface supercooling degree and the Weber number, but negatively correlated with the curvature diameters ratio. Notably, the influence of surface temperature on impact-freezing was highly related to surface curvature. These findings provided insights into optimizing structured superhydrophobic surfaces for anti-icing performance.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111613"},"PeriodicalIF":3.3,"publicationDate":"2025-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047490","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}
Pub Date : 2025-09-04DOI: 10.1016/j.expthermflusci.2025.111603
Tianyi Wang, Yannis Hardalupas
The physical understanding of liquid jet breakup in quiescent air remains incomplete due to the complex interactions among influencing parameters and limitations in current measurement techniques. In this study, a needle pin was positioned at the nozzle exit of a liquid jet pressure atomiser to introduce an artificial perturbation of controlled magnitude, enabling an investigation on the influence of flow disturbances on the breakup process. This perturbation is introduced to model potential flow disturbances that may occur inside the nozzle of an atomiser, such as liquid flow separation or cavitation. The interfacial characteristics of the liquid jet, including surface morphology and interfacial motion, were analysed to assess the impact of the imposed perturbation on the breakup process. Optical Connectivity (OC), which transmits a laser beam through the intact liquid core, was employed to capture detailed interface geometry. The instantaneous interfacial characteristics were tracked in time using Optical Flow Velocimetry (OFV) to measure the interfacial velocity. Proper Orthogonal Decomposition (POD) was applied to extract the dominant interfacial wave structures, which were subsequently correlated with interfacial motion to provide a comprehensive assessment of the perturbation effects. The consistency between the dominant interfacial geometry extracted from POD and the measured interfacial velocity further validates the reliability of the OC-OFV technique. The findings reveal that introducing artificial perturbations and adjusting their amplitude can alter the interfacial motion and geometry of the liquid jet by modifying internal flow patterns, which in turn influence the liquid breakup process and the velocity of the resulting liquid fragments. This highlights the significant impact of nozzle disturbances, such as cavitation or manufacturing defects, on atomisation performance. Moreover, the results suggest that applying controlled artificial perturbations could serve as an effective strategy for controlling the breakup process and optimising the resulting spray droplet velocity.
{"title":"Interfacial characteristics of a perturbed liquid jet in quiescent air","authors":"Tianyi Wang, Yannis Hardalupas","doi":"10.1016/j.expthermflusci.2025.111603","DOIUrl":"10.1016/j.expthermflusci.2025.111603","url":null,"abstract":"<div><div>The physical understanding of liquid jet breakup in quiescent air remains incomplete due to the complex interactions among influencing parameters and limitations in current measurement techniques. In this study, a needle pin was positioned at the nozzle exit of a liquid jet pressure atomiser to introduce an artificial perturbation of controlled magnitude, enabling an investigation on the influence of flow disturbances on the breakup process. This perturbation is introduced to model potential flow disturbances that may occur inside the nozzle of an atomiser, such as liquid flow separation or cavitation. The interfacial characteristics of the liquid jet, including surface morphology and interfacial motion, were analysed to assess the impact of the imposed perturbation on the breakup process. Optical Connectivity (OC), which transmits a laser beam through the intact liquid core, was employed to capture detailed interface geometry. The instantaneous interfacial characteristics were tracked in time using Optical Flow Velocimetry (OFV) to measure the interfacial velocity. Proper Orthogonal Decomposition (POD) was applied to extract the dominant interfacial wave structures, which were subsequently correlated with interfacial motion to provide a comprehensive assessment of the perturbation effects. The consistency between the dominant interfacial geometry extracted from POD and the measured interfacial velocity further validates the reliability of the OC-OFV technique. The findings reveal that introducing artificial perturbations and adjusting their amplitude can alter the interfacial motion and geometry of the liquid jet by modifying internal flow patterns, which in turn influence the liquid breakup process and the velocity of the resulting liquid fragments. This highlights the significant impact of nozzle disturbances, such as cavitation or manufacturing defects, on atomisation performance. Moreover, the results suggest that applying controlled artificial perturbations could serve as an effective strategy for controlling the breakup process and optimising the resulting spray droplet velocity.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111603"},"PeriodicalIF":3.3,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145007649","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}
Pub Date : 2025-09-04DOI: 10.1016/j.expthermflusci.2025.111604
Himmet Erdi Tanürün , Abdussamed Yıldız , Mehmet Seyhan
The present work addresses the aerodynamic penalties caused by laminar separation bubbles in low Reynolds number regimes, which are prevalent in UAVs and small wind turbines. The slot design, which has been subjected to experimental validation, offers a passive, cost-effective solution for enhancing aerodynamic efficiency in such critical applications. Therefore, this study investigates the aerodynamic performance of the NACA 63(4)-421 airfoil equipped with a Trailing Edge Slot (TES) at suction side, evaluated through Force Measurement Experiments (FMEs) and Surface Oil Flow Visualization (SOFV) techniques in suction type wind tunnel. To improve flow reattachment and aerodynamic efficiency, the TES slot geometry was designed taking into account the following parameters: slot width ratio, slot angle, slot inlet location, and Coanda radius (rc), slot outlet suction side radius (rt), and slot inlet pressure side radius (rp). Among the four TES configurations tested in the 0° to 30° range; Model 2 (M2) demonstrated superior performance across the investigated angle of attack (AoA) range. The stall angle of M2 was delayed by 3°, reaching 17° compared to the baseline (B1), and the maximum lift coefficient (CL,max) reached 1.51, corresponding to a 122% increase compared to B1. M2 model significantly reduces the undesired fluctuating lift via jet injection from the slot geometry as compared to the B1 at pre-stall region. At AoAs between 6° and 16°, the high-momentum slot flow effectively interacted with the main flow, re-energizing the boundary layer and enhancing surface attachment. This mechanism directly contributes to delaying the stall. Furthermore, NACA 63(4)-421 airfoil having TES has been demonstrated to re-energise the boundary layer, modify the position of the Laminar Separation Line (LSL), and Turbulent Reattachment Line (TRL) and expand the turbulent flow region. This, in turn, has been shown to enhance surface flow attachment and delay stall by controlling the laminer separation bubble (LSB). The combination of optimized slot geometry and effective flow interaction confirms that TES configurations significantly enhance aerodynamic performance in Re of 9x104.
{"title":"Aerodynamic performance analysis of a NACA 63(4)-421 airfoil equipped with a trailing edge slot at suction side","authors":"Himmet Erdi Tanürün , Abdussamed Yıldız , Mehmet Seyhan","doi":"10.1016/j.expthermflusci.2025.111604","DOIUrl":"10.1016/j.expthermflusci.2025.111604","url":null,"abstract":"<div><div>The present work addresses the aerodynamic penalties caused by laminar separation bubbles in low Reynolds number regimes, which are prevalent in UAVs and small wind turbines. The slot design, which has been subjected to experimental validation, offers a passive, cost-effective solution for enhancing aerodynamic efficiency in such critical applications. Therefore, this study investigates the aerodynamic performance of the NACA 63(4)-421 airfoil equipped with a Trailing Edge Slot (TES) at suction side, evaluated through Force Measurement Experiments (FMEs) and Surface Oil Flow Visualization (SOFV) techniques in suction type wind tunnel. To improve flow reattachment and aerodynamic efficiency, the TES slot geometry was designed taking into account the following parameters: slot width ratio, slot angle, slot inlet location, and Coanda radius (<em>r<sub>c</sub></em>), slot outlet suction side radius (<em>r<sub>t</sub></em>), and slot inlet pressure side radius (<em>r<sub>p</sub></em>). Among the four TES configurations tested in the 0° to 30° range; Model 2 (M2) demonstrated superior performance across the investigated angle of attack (AoA) range. The stall angle of M2 was delayed by 3°, reaching 17° compared to the baseline (B1), and the maximum lift coefficient (C<sub>L,max</sub>) reached 1.51, corresponding to a 122% increase compared to B1. M2 model significantly reduces the undesired fluctuating lift via jet injection from the slot geometry as compared to the B1 at pre-stall region. At AoAs between 6° and 16°, the high-momentum slot flow effectively interacted with the main flow, re-energizing the boundary layer and enhancing surface attachment. This mechanism directly contributes to delaying the stall. Furthermore, NACA 63(4)-421 airfoil having TES has been demonstrated to re-energise the boundary layer, modify the position of the Laminar Separation Line (LSL), and Turbulent Reattachment Line (TRL) and expand the turbulent flow region. This, in turn, has been shown to enhance surface flow attachment and delay stall by controlling the laminer separation bubble (LSB). The combination of optimized slot geometry and effective flow interaction confirms that TES configurations significantly enhance aerodynamic performance in Re of 9x10<sup>4</sup>.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"171 ","pages":"Article 111604"},"PeriodicalIF":3.3,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145019317","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}
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