Pub Date : 2025-11-07DOI: 10.1016/j.expthermflusci.2025.111653
Rajesh Sadanandan, Remesh R. Konat, I.R. Praveen Krishna
The influence of swirl strength on the flame characteristics and the naturally excited thermo-acoustic instabilities in a confined partially premixed flame is experimentally investigated. Variation in the swirl strength is achieved by varying the axial to tangential airflow momentum in an in-house developed swirl and bluffbody stabilized burner. Empirical mode decomposition analysis, along with Hilbert’s transformation of the acoustic and heat release data, is carried out to reveal the underlying oscillatory modes and their time–frequency representation. For a fixed global equivalence ratio (), the burner exhibited self-excited acoustic instability and decreased flame standoff distance under high swirl strengths. Temporal modulation of both acoustic and heat release oscillation has been observed during instability. The self-excited oscillations are found to be vortex-driven, and the thermo-acoustic coupling depends on the location of the heat release zone with respect to the local acoustic pressure of the standing wave inside the combustor. The study shows that modulating the swirl strength also makes it possible to disrupt or mitigate the thermo-acoustic coupling existing in the system.
{"title":"Influence of swirl on the thermo-acoustic characteristics of partially-premixed flames","authors":"Rajesh Sadanandan, Remesh R. Konat, I.R. Praveen Krishna","doi":"10.1016/j.expthermflusci.2025.111653","DOIUrl":"10.1016/j.expthermflusci.2025.111653","url":null,"abstract":"<div><div>The influence of swirl strength on the flame characteristics and the naturally excited thermo-acoustic instabilities in a confined partially premixed flame is experimentally investigated. Variation in the swirl strength is achieved by varying the axial to tangential airflow momentum in an in-house developed swirl and bluffbody stabilized burner. Empirical mode decomposition analysis, along with Hilbert’s transformation of the acoustic and heat release data, is carried out to reveal the underlying oscillatory modes and their time–frequency representation. For a fixed global equivalence ratio (<span><math><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>g</mi></mrow></msub></math></span>), the burner exhibited self-excited acoustic instability and decreased flame standoff distance under high swirl strengths. Temporal modulation of both acoustic and heat release oscillation has been observed during instability. The self-excited oscillations are found to be vortex-driven, and the thermo-acoustic coupling depends on the location of the heat release zone with respect to the local acoustic pressure of the standing wave inside the combustor. The study shows that modulating the swirl strength also makes it possible to disrupt or mitigate the thermo-acoustic coupling existing in the system.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111653"},"PeriodicalIF":3.3,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145464370","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 : 2025-11-07DOI: 10.1016/j.expthermflusci.2025.111638
Xiyuan Liang , Tong Ye , Xinyu Wang , Lin Ye , Cunliang Liu , Xiying Niu
To enhance the film cooling effectiveness of the leading-edge showerhead on turbine vanes, combined compound angle configurations of film holes were incorporated into the cooling structure design. Pressure-sensitive paint (PSP) technology was used to measure the film cooling effectiveness under various momentum flux ratios ranging from 0.09 to 6.04 and the mainstream turbulence intensity ranging from 2.03 %∼23.58 %. The effects of the momentum flux ratio and mainstream turbulence intensity were compared. The results revealed that the effect of the mainstream turbulence intensity on the film cooling effectiveness at the leading-edge was related to the momentum flux ratio. For the vane leading-edge pressure side, the effect of mainstream turbulence intensity on the film cooling effectiveness was related to the momentum flux ratio. Under a low momentum flux ratio, an increase in mainstream turbulence intensity led to a sharp decline in the film cooling effectiveness, resulting in a maximum reduction of 52.5 % in the area-averaged film cooling effectiveness on the pressure side. When the momentum flux ratio was high, the increased mainstream turbulence intensity enhanced the energy dissipation of the cooling jet, thereby improving the film cooling performance in this region, with a maximum increase of 13.8 % in the film cooling effectiveness. As for the vane leading-edge suction side, the film cooling effectiveness decreases with increasing mainstream turbulence intensity, with a maximum reduction of 36.9 %. Moreover, within the varied range of mainstream turbulence intensities and momentum flux ratios studied in this paper, an increase in the film hole compound angle improved the film cooling effectiveness and relieved the degree of reduction in the film cooling effectiveness caused by the film jet blown off. However, for the pressure side, excessively large film hole compound angle did not significantly improve the film cooling effectiveness. In contrast, to ensure good film cooling characteristics, larger compound-angle film holes can be designed on the vane leading-edge suction side, whereas smaller compound-angle film holes can be created on the vane leading-edge pressure side.
{"title":"Experimental investigation of the cooling effectiveness of a leading-edge showerhead configuration with counter-inclined compound holes under the influence of freestream turbulence","authors":"Xiyuan Liang , Tong Ye , Xinyu Wang , Lin Ye , Cunliang Liu , Xiying Niu","doi":"10.1016/j.expthermflusci.2025.111638","DOIUrl":"10.1016/j.expthermflusci.2025.111638","url":null,"abstract":"<div><div>To enhance the film cooling effectiveness of the leading-edge showerhead on turbine vanes, combined compound angle configurations of film holes were incorporated into the cooling structure design. Pressure-sensitive paint (PSP) technology was used to measure the film cooling effectiveness under various momentum flux ratios ranging from 0.09 to 6.04 and the mainstream turbulence intensity ranging from 2.03 %∼23.58 %. The effects of the momentum flux ratio and mainstream turbulence intensity were compared. The results revealed that the effect of the mainstream turbulence intensity on the film cooling effectiveness at the leading-edge was related to the momentum flux ratio. For the vane leading-edge pressure side, the effect of mainstream turbulence intensity on the film cooling effectiveness was related to the momentum flux ratio. Under a low momentum flux ratio, an increase in mainstream turbulence intensity led to a sharp decline in the film cooling effectiveness, resulting in a maximum reduction of 52.5 % in the area-averaged film cooling effectiveness on the pressure side. When the momentum flux ratio was high, the increased mainstream turbulence intensity enhanced the energy dissipation of the cooling jet, thereby improving the film cooling performance in this region, with a maximum increase of 13.8 % in the film cooling effectiveness. As for the vane leading-edge suction side, the film cooling effectiveness decreases with increasing mainstream turbulence intensity, with a maximum reduction of 36.9 %. Moreover, within the varied range of mainstream turbulence intensities and momentum flux ratios studied in this paper, an increase in the film hole compound angle improved the film cooling effectiveness and relieved the degree of reduction in the film cooling effectiveness caused by the film jet blown off. However, for the pressure side, excessively large film hole compound angle did not significantly improve the film cooling effectiveness. In contrast, to ensure good film cooling characteristics, larger compound-angle film holes can be designed on the vane leading-edge suction side, whereas smaller compound-angle film holes can be created on the vane leading-edge pressure side.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111638"},"PeriodicalIF":3.3,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145517746","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 : 2025-11-07DOI: 10.1016/j.expthermflusci.2025.111655
Ž. Lokar, J. Petelin, D. Horvat, V. Agrež, R. Petkovšek
Laser induced breakdown in water generates shockwaves and cavitation bubble, both originating from the breakdown of the plasma. The dynamics of a shockwave propagating from a point source changes significantly with distance. In spherical geometry without energy loss, the energy spreads out in accordance with the inverse square law, the pressure decreases proportionally with distance. Thus, closer to the shockwave source a more pronounced shockwave dynamics is expected. A fast, robust and precisely positioned sensor with a small detection area is needed to accurately measure the shockwave pressure in such conditions. A single mode optic fiber-based hydrophone meets these requirements. In addition to measuring the shockwave induced change in light reflectance from the fiber tip, the fiber optic hydrophone, when positioned very close to the breakdown bubble, picks up some of the light which exits the sensor and is reflected from the bubble wall. Due to bubble growth, this results in an oscillating interference signal. We introduce signal processing to distinguish between the two signals, originating from different phenomena but captured in a single oscilloscope trace. While using only FFT processing to remove the oscillations from the signal does not preserve the shockwave properties properly, the introduced local filtering procedure allows for correct separation of the two overlapping contributions to the waveform. The transient interference signal allowed for extraction of tens of bubble wall velocity data points in the first 100 ns of a single bubble growth event, showing the very early bubble growth behaviour. After this contribution was eliminated from the signal, the shockwave pressure trace was successfully assessed at very small distances, down to the situation where the hydrophone nearly touched the plasma edge. Pressure trace allowed for extraction of various parameters such as maximum pressure, risetime, shockwave energy and pressure impulse. The shockwave energy was measured to decay as 6.5 dB/mm for distances above 50 μm.
{"title":"Laser induced cavitation bubble and shockwave measurements with fiber optical hydrophone very close to origin","authors":"Ž. Lokar, J. Petelin, D. Horvat, V. Agrež, R. Petkovšek","doi":"10.1016/j.expthermflusci.2025.111655","DOIUrl":"10.1016/j.expthermflusci.2025.111655","url":null,"abstract":"<div><div>Laser induced breakdown in water generates shockwaves and cavitation bubble, both originating from the breakdown of the plasma. The dynamics of a shockwave propagating from a point source changes significantly with distance. In spherical geometry without energy loss, the energy spreads out in accordance with the inverse square law, the pressure decreases proportionally with distance. Thus, closer to the shockwave source a more pronounced shockwave dynamics is expected. A fast, robust and precisely positioned sensor with a small detection area is needed to accurately measure the shockwave pressure in such conditions. A single mode optic fiber-based hydrophone meets these requirements. In addition to measuring the shockwave induced change in light reflectance from the fiber tip, the fiber optic hydrophone, when positioned very close to the breakdown bubble, picks up some of the light which exits the sensor and is reflected from the bubble wall. Due to bubble growth, this results in an oscillating interference signal. We introduce signal processing to distinguish between the two signals, originating from different phenomena but captured in a single oscilloscope trace. While using only FFT processing to remove the oscillations from the signal does not preserve the shockwave properties properly, the introduced local filtering procedure allows for correct separation of the two overlapping contributions to the waveform. The transient interference signal allowed for extraction of tens of bubble wall velocity data points in the first 100 ns of a single bubble growth event, showing the very early bubble growth behaviour. After this contribution was eliminated from the signal, the shockwave pressure trace was successfully assessed at very small distances, down to the situation where the hydrophone nearly touched the plasma edge. Pressure trace allowed for extraction of various parameters such as maximum pressure, risetime, shockwave energy and pressure impulse. The shockwave energy was measured to decay as 6.5 dB/mm for distances above 50 μm.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111655"},"PeriodicalIF":3.3,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145517747","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 : 2025-11-03DOI: 10.1016/j.expthermflusci.2025.111640
Baolei Jiao , Lifeng Chen , Xuemin Yan , Xiaoda Wang
Bubble dynamics within contracting microchannels exhibit profound complexity, receiving a long-standing research focus. This study systematically investigated bubble behaviors in elongated constrictions both in the 2D and 3D pore-throat combinations. A high-speed imaging device captured the bubble evolution in structurally diverse constrictions, while the effects of gas–liquid flow rates and fluid properties were quantified to establish transitional boundaries between distinct flow regimes. Bubble breakup—a typical flow pattern—demonstrated notable disparities between 2D and 3D configurations. To elucidate these differences, interfacial dynamics were tracked to analyze breakup mechanisms during the constriction traversal. In both dimensional systems, bubble breakup was primarily driven by the drawing and squeezing forces exerted by the continuous phase. Crucially, in the 3D pore-throat combination, the intensified drawing forces and prolonged squeezing forces, significantly enhanced breakup propensity. Mutual squeezing among the daughter-bubbles induced asynchronous breakup events, yielding non-uniform daughter-bubble size distributions. A power-law relationship characterized the dependence of mean daughter-bubble size on the mother-bubble length and the superficial flow velocity, with the exponent critically governed by microchannel geometric parameters. This work will advance fundamental understanding of bubble breakup mechanics in confined geometries and provide actionable insights for microfluidic device design.
{"title":"Bubble breakup in the microchannels with a long constriction","authors":"Baolei Jiao , Lifeng Chen , Xuemin Yan , Xiaoda Wang","doi":"10.1016/j.expthermflusci.2025.111640","DOIUrl":"10.1016/j.expthermflusci.2025.111640","url":null,"abstract":"<div><div>Bubble dynamics within contracting microchannels exhibit profound complexity, receiving a long-standing research focus. This study systematically investigated bubble behaviors in elongated constrictions both in the 2D and 3D pore-throat combinations. A high-speed imaging device captured the bubble evolution in structurally diverse constrictions, while the effects of gas–liquid flow rates and fluid properties were quantified to establish transitional boundaries between distinct flow regimes. Bubble breakup—a typical flow pattern—demonstrated notable disparities between 2D and 3D configurations. To elucidate these differences, interfacial dynamics were tracked to analyze breakup mechanisms during the constriction traversal. In both dimensional systems, bubble breakup was primarily driven by the drawing and squeezing forces exerted by the continuous phase. Crucially, in the 3D pore-throat combination, the intensified drawing forces and prolonged squeezing forces, significantly enhanced breakup propensity. Mutual squeezing among the daughter-bubbles induced asynchronous breakup events, yielding non-uniform daughter-bubble size distributions. A power-law relationship characterized the dependence of mean daughter-bubble size on the mother-bubble length and the superficial flow velocity, with the exponent critically governed by microchannel geometric parameters. This work will advance fundamental understanding of bubble breakup mechanics in confined geometries and provide actionable insights for microfluidic device design.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111640"},"PeriodicalIF":3.3,"publicationDate":"2025-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145464359","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 : 2025-11-01DOI: 10.1016/j.expthermflusci.2025.111639
Zheng Sun , He Shen , Yiting Wang , Haotian Zheng , Fang Feng , Yan Li
Icing on wind turbine blades severely compromises turbine operation, while existing standalone anti-icing and de-icing methods exhibit inherent limitations. This study experimentally investigates the synergistic de-icing performance of wind turbine blades using the PCMS-C14 phase-change microcapsule coating, developed independently by the Wind Energy Laboratory at Northeast Agricultural University, combined with electrothermal heating. Experiments were conducted in an icing wind tunnel under controlled parameters: water flow rate (60 mL/min), ambient temperatures (−5 °C, −10 °C, −15 °C), incoming wind speeds (3 m/s, 6 m/s, 9 m/s), and energy flux densities (8 kW/m2, 10 kW/m2, 12 kW/m2). Results demonstrate that although higher wind speeds and lower temperatures increase de-icing energy demand, the hybrid coating-electrothermal approach significantly outperforms pure electrothermal de-icing across all tested scenarios: the highest energy-saving efficiency of 19.23 % was achieved at an energy flux density of 10 kW/m2; an energy reduction of 21.5 % was observed at an ambient temperature of −10 °C; and the optimal energy-saving effect was obtained at a wind speed of 6 m/s. This integrated strategy effectively reduces de-icing time by 25–68 s, lowers energy consumption by 12.89 % to 21.5 %, and significantly improves de-icing uniformity and thermal management stability. This study provides a practical solution and experimental basis for enhancing the energy efficiency and operational reliability of wind turbines in cold regions.
{"title":"Study on the de-icing performance of wind turbine blades based on PCMS-C14 coating combined with electrothermal heating","authors":"Zheng Sun , He Shen , Yiting Wang , Haotian Zheng , Fang Feng , Yan Li","doi":"10.1016/j.expthermflusci.2025.111639","DOIUrl":"10.1016/j.expthermflusci.2025.111639","url":null,"abstract":"<div><div>Icing on wind turbine blades severely compromises turbine operation, while existing standalone anti-icing and de-icing methods exhibit inherent limitations. This study experimentally investigates the synergistic de-icing performance of wind turbine blades using the PCMS-C14 phase-change microcapsule coating, developed independently by the Wind Energy Laboratory at Northeast Agricultural University, combined with electrothermal heating. Experiments were conducted in an icing wind tunnel under controlled parameters: water flow rate (60 mL/min), ambient temperatures (−5 °C, −10 °C, −15 °C), incoming wind speeds (3 m/s, 6 m/s, 9 m/s), and energy flux densities (8 kW/m<sup>2</sup>, 10 kW/m<sup>2</sup>, 12 kW/m<sup>2</sup>). Results demonstrate that although higher wind speeds and lower temperatures increase de-icing energy demand, the hybrid coating-electrothermal approach significantly outperforms pure electrothermal de-icing across all tested scenarios: the highest energy-saving efficiency of 19.23 % was achieved at an energy flux density of 10 kW/m<sup>2</sup>; an energy reduction of 21.5 % was observed at an ambient temperature of −10 °C; and the optimal energy-saving effect was obtained at a wind speed of 6 m/s. This integrated strategy effectively reduces de-icing time by 25–68 s, lowers energy consumption by 12.89 % to 21.5 %, and significantly improves de-icing uniformity and thermal management stability. This study provides a practical solution and experimental basis for enhancing the energy efficiency and operational reliability of wind turbines in cold regions.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111639"},"PeriodicalIF":3.3,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145464371","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 : 2025-11-01DOI: 10.1016/j.expthermflusci.2025.111636
Chinmaya Joshi , Clancy Milam , Stephen Pierson , Ying Sun , Jared Berg , Han Hu
In this paper, we have investigated the effect of thermal interface materials (TIMs) on the accuracy and uncertainty of thermal conductivity measurements. A modified ASTM D5470 thermal resistance tester (TRT) has been developed to measure the out-of-plane thermal conductivity of pyrolytic graphite (PG) and titanium grade 2 (TiG2) with and without TIMs. Compared to the ASTM D5470 standard, this modified design uses three thermocouples per side to support regressive analysis of the temperature profile and quantifies the uncertainty of the measurements with and without TIMs. Nine PG samples and four TiG2 samples of varying thickness have been tested to obtain thermal resistance as a function of sample thickness. The steady-state temperature profiles were used for heat flux and thermal resistance calculation. The results reveal that TIMs significantly reduce measurement uncertainty for both samples, i.e., 38.8 % for TiG2 and 27.8 % for PG. The effect of TIMs on the measurement accuracy diverges, with a far more pronounced effect on TiG2 than PG. This can be owed to the higher out-of-plane thermal conductivity of TiG2 (∼16.2 W/m-K) than PG (∼2 W/m-K). Contact resistance is expected to play a more critical role in tests of materials with higher thermal conductivity, and TIMs can effectively mitigate contact resistance. For lower conductivity materials, the weight of contact resistance is lower, and the effect of TIMs is thus less pronounced. This work establishes a robust framework for quantifying and mitigating uncertainties in thermal conductivity measurements, which will lead to more accurate characterization of materials for the design and qualification of advanced thermal management systems in aerospace, electronics, and energy applications.
{"title":"Quantification and mitigation of uncertainties in thermal conductivity measurements using a modified ASTM D5470 thermal resistance tester","authors":"Chinmaya Joshi , Clancy Milam , Stephen Pierson , Ying Sun , Jared Berg , Han Hu","doi":"10.1016/j.expthermflusci.2025.111636","DOIUrl":"10.1016/j.expthermflusci.2025.111636","url":null,"abstract":"<div><div>In this paper, we have investigated the effect of thermal interface materials (TIMs) on the accuracy and uncertainty of thermal conductivity measurements. A modified ASTM D5470 thermal resistance tester (TRT) has been developed to measure the out-of-plane thermal conductivity of pyrolytic graphite (PG) and titanium grade 2 (TiG2) with and without TIMs. Compared to the ASTM D5470 standard, this modified design uses three thermocouples per side to support regressive analysis of the temperature profile and quantifies the uncertainty of the measurements with and without TIMs. Nine PG samples and four TiG2 samples of varying thickness have been tested to obtain thermal resistance as a function of sample thickness. The steady-state temperature profiles were used for heat flux and thermal resistance calculation. The results reveal that TIMs significantly reduce measurement uncertainty for both samples, <em>i.e.</em>, 38.8 % for TiG2 and 27.8 % for PG. The effect of TIMs on the measurement accuracy diverges, with a far more pronounced effect on TiG2 than PG. This can be owed to the higher out-of-plane thermal conductivity of TiG2 (∼16.2 W/m-K) than PG (∼2 W/m-K). Contact resistance is expected to play a more critical role in tests of materials with higher thermal conductivity, and TIMs can effectively mitigate contact resistance. For lower conductivity materials, the weight of contact resistance is lower, and the effect of TIMs is thus less pronounced. This work establishes a robust framework for quantifying and mitigating uncertainties in thermal conductivity measurements, which will lead to more accurate characterization of materials for the design and qualification of advanced thermal management systems in aerospace, electronics, and energy applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111636"},"PeriodicalIF":3.3,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145464358","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 : 2025-10-30DOI: 10.1016/j.expthermflusci.2025.111637
Sandeep Kumar, Prashanth Reddy Hanmaiahgari
This study aims to understand local scour dynamics and turbulence characteristics around the head of repelling spur dikes by analyzing sediment bed morphology, higher-order turbulence statistics, turbulent kinetic energy fluxes, and quadrant-based turbulence events, which remain insufficiently understood in the context of these river training structures. The flow field was measured using Vectrino ADV under two Reynolds numbers () of 48,508 and 42579. The sediment bed topography exhibited distinct patterns, with maximum scour depth ( of 0.48 h () and 0.55 h at the first spur dike in both scenarios, and at the second spur dike, greater erosion occurred at a higher Reynolds number. Higher-order turbulence moments and revealed ejections followed by primarily sweep, outward, and inward events near the bed. The magnitude exhibited greater variation primarily with ejection events; these phenomena were shaped by bed morphology. At both Reynolds numbers, the sweep events dominate ejection events at first and second spur dikes near-bed zone. In contrast, inward and outward events prevailed at the third spur dike. Turbulent kinetic energy flux, and revealed greater magnitudes at the first and second spur dikes with dissimilarity in their sign. A significantly high vorticity is observed immediately u/s and d/s of the first spur dike throughout the depth. Quadrant analysis confirmed energetic activity near the bed zone dominated by sweep and ejection events governed turbulence structures, while the coherent structure near the water surface persisted throughout the test reach but weakened in the downstream.
本研究旨在通过分析沉积物床形态、高阶湍流统计、湍流动能通量和基于象限的湍流事件，了解在这些河流训练结构背景下仍未得到充分了解的排斥性直堤头部周围的局部冲刷动力学和湍流特征。在雷诺数Re为48,508和42579时，采用Vectrino ADV对流场进行了测量。两种情况下，第1支脉的最大冲刷深度（ds）分别为0.48 h （h=流深）和0.55 h，第2支脉的最大冲刷深度在较高雷诺数下发生较大的侵蚀。高阶湍流时刻M12，M21，M30和m03显示出抛射，随后主要是在床附近扫向，向外和向内的事件。m03星等的变化主要与喷发事件有关；这些现象是由床层形态形成的。在两种雷诺数下，在第一和第二直堤近层带处，扫射事件主导喷射事件。相比之下，在第三直堤，内向和外向的事件占主导地位。湍流动能通量、Fku和Fkw在第1和第2直堤处表现出较大的量级，但其标志不同。在整个深度处，第一直脉的u/s和d/s涡度都很高。象限分析证实，床带附近的能量活动主要由横扫和喷射事件控制湍流结构，而靠近水面的相干结构在整个测试河段持续存在，但在下游减弱。
{"title":"Analysis of scour dynamics and turbulence structures at a sequence of repelling spur dikes using higher-order moments, turbulent kinetic energy fluxes, and quadrant analysis","authors":"Sandeep Kumar, Prashanth Reddy Hanmaiahgari","doi":"10.1016/j.expthermflusci.2025.111637","DOIUrl":"10.1016/j.expthermflusci.2025.111637","url":null,"abstract":"<div><div>This study aims to understand local scour dynamics and turbulence characteristics around the head of repelling spur dikes by analyzing sediment bed morphology, higher-order turbulence statistics, turbulent kinetic energy fluxes, and quadrant-based turbulence events, which remain insufficiently understood in the context of these river training structures. The flow field was measured using Vectrino ADV under two Reynolds numbers (<span><math><msub><mtext>R</mtext><mtext>e</mtext></msub></math></span>) of 48,508 and 42579. The sediment bed topography exhibited distinct patterns, with maximum scour depth (<span><math><mrow><msub><mtext>d</mtext><mtext>s</mtext></msub><mrow><mo>)</mo></mrow></mrow></math></span> of 0.48 <em>h</em> (<span><math><mrow><mi>h</mi><mo>=</mo><mtext>flow depth</mtext></mrow></math></span>) and 0.55 <em>h</em> at the first spur dike in both scenarios, and at the second spur dike, greater erosion occurred at a higher Reynolds number. Higher-order turbulence moments <span><math><mrow><msub><mtext>M</mtext><mtext>12</mtext></msub><mtext>,</mtext><mspace></mspace><msub><mtext>M</mtext><mtext>21</mtext></msub><mtext>,</mtext><mspace></mspace><msub><mtext>M</mtext><mtext>30</mtext></msub></mrow></math></span> and <span><math><msub><mtext>M</mtext><mtext>03</mtext></msub></math></span>revealed ejections followed by primarily sweep, outward, and inward events near the bed. The<span><math><msub><mtext>M</mtext><mtext>03</mtext></msub></math></span> magnitude exhibited greater variation primarily with ejection events; these phenomena were shaped by bed morphology. At both Reynolds numbers, the sweep events dominate ejection events at first and second spur dikes near-bed zone. In contrast, inward and outward events prevailed at the third spur dike. Turbulent kinetic energy flux, <span><math><msub><mtext>F</mtext><mtext>ku</mtext></msub></math></span> and <span><math><msub><mtext>F</mtext><mtext>kw</mtext></msub></math></span> revealed greater magnitudes at the first and second spur dikes with dissimilarity in their sign. A significantly high vorticity is observed immediately u/s and d/s of the first spur dike throughout the depth. Quadrant analysis confirmed energetic activity near the bed zone dominated by sweep and ejection events governed turbulence structures, while the coherent structure near the water surface persisted throughout the test reach but weakened in the downstream.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111637"},"PeriodicalIF":3.3,"publicationDate":"2025-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145414504","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 : 2025-10-26DOI: 10.1016/j.expthermflusci.2025.111633
Qinrui Xu, Jiang Li, Kang Li, Shihui Cheng
The rebound/fusion characteristics of high-temperature aluminium droplets impact on aluminium liquid film are crucial for accurately predicting the evolution of solid rocket motor slag deposition. In this study, the rebound and fusion characteristics of aluminium droplet impact on aluminium liquid film were systematically investigated through experimental research and direct numerical simulation (DNS). Electromagnetic induction heating and pneumatic driving technology are used to generate high-temperature aluminium droplets, combined with a high-speed camera to capture the impact transient process. For the numerical simulations, we use the Basilisk software with Volume of Fluid model. This model helps us understand how the gas film evolves and how the interfaces interact during droplet impact. The results show that the droplet impact results are dominated by Weber number (We), and the droplets rebound when We ≤ 5.4, while fusion occurs when We > 5.4. This critical condition applies to the dimensionless liquid film thickness of 20 ≤ H* ≤ 30 and the Ohnesorge number of 0.8 ≤ Oh ≤ 1.0 × 10-3. The numerical simulation results showed that the wall effect was significant in the thin liquid film (H* < 1.5), with an inverted “hump” shape of the gas film and limited liquid film retraction. For thick liquid film (H* ≥ 1.5), the gas film forms an arc-shaped profile. We also establish a formula for the maximum dimensionless penetration depth of the liquid film, based on the Weber and Ohnesorge numbers. Additionally, we propose a prediction model for the rebound and fusion of high-surface-tension droplets on liquid films. This model is based on the liquid film surface arc length and energy analysis. This study reveals the kinetic mechanism of high-surface-tension droplet impact. It provides useful insights for predicting slag deposition in engines and optimizing thermal protection systems.
{"title":"Research on the rebound and fusion characteristics of high temperature aluminium droplets impact on aluminium liquid film","authors":"Qinrui Xu, Jiang Li, Kang Li, Shihui Cheng","doi":"10.1016/j.expthermflusci.2025.111633","DOIUrl":"10.1016/j.expthermflusci.2025.111633","url":null,"abstract":"<div><div>The rebound/fusion characteristics of high-temperature aluminium droplets impact on aluminium liquid film are crucial for accurately predicting the evolution of solid rocket motor slag deposition. In this study, the rebound and fusion characteristics of aluminium droplet impact on aluminium liquid film were systematically investigated through experimental research and direct numerical simulation (DNS). Electromagnetic induction heating and pneumatic driving technology are used to generate high-temperature aluminium droplets, combined with a high-speed camera to capture the impact transient process. For the numerical simulations, we use the Basilisk software with Volume of Fluid model. This model helps us understand how the gas film evolves and how the interfaces interact during droplet impact. The results show that the droplet impact results are dominated by Weber number (<em>We</em>), and the droplets rebound when <em>We</em> ≤ 5.4, while fusion occurs when <em>We</em> > 5.4. This critical condition applies to the dimensionless liquid film thickness of 20 ≤ <em>H</em>* ≤ 30 and the Ohnesorge number of 0.8 ≤ <em>Oh</em> ≤ 1.0 × 10<sup>-3</sup>. The numerical simulation results showed that the wall effect was significant in the thin liquid film (<em>H</em>* < 1.5), with an inverted “hump” shape of the gas film and limited liquid film retraction. For thick liquid film (<em>H</em>* ≥ 1.5), the gas film forms an arc-shaped profile. We also establish a formula for the maximum dimensionless penetration depth of the liquid film, based on the Weber and Ohnesorge numbers. Additionally, we propose a prediction model for the rebound and fusion of high-surface-tension droplets on liquid films. This model is based on the liquid film surface arc length and energy analysis. This study reveals the kinetic mechanism of high-surface-tension droplet impact. It provides useful insights for predicting slag deposition in engines and optimizing thermal protection systems.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111633"},"PeriodicalIF":3.3,"publicationDate":"2025-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145414516","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 : 2025-10-24DOI: 10.1016/j.expthermflusci.2025.111635
P. Senthilkumar , T.N.C. Anand
Injecting Urea-Water sprays at low pressure into the hot exhaust gas flow stream in the presence of catalysts is one of the most effective ways to reduce NO emissions in diesel engines. The effectiveness of NO conversion is greatly impacted by spray parameters such as droplet size, velocity, dispersion, and homogeneity upstream of the catalyst. For estimating droplet size, Particle/Droplet Image Analysis (PDIA) is a reliable technique, and it has numerous benefits, including the ability to visualize the droplet shape and quantify non-spherical droplets. In this present study, the PDIA and Particle Tracking Velocimetry (PTV) techniques with high pixel resolution were used to look at the size and velocity of the droplets of the urea-water solution (UWS) spray in a heated cross-flow. The results indicate that smaller spherical droplets are located at the top of the spray, whereas the majority of the bigger droplets are non-spherical and present at the bottom. Droplet size decreases as injection pressure and air velocity rise due to improved atomization. Droplet velocity in the flow direction increases with air velocity and decreases with size. The PDIA method has the ability to measure both spherical and non-spherical droplets. When non-spherical droplets are excluded from droplet size measurements, there is a significant difference in the SMD measured, highlighting the importance of using a technique which can measure non-spherical droplets in such sprays. However, since the PDIA method is usually used with low repetition rate cameras, droplets must be captured over a range of imaging times, from the time they begin to appear in the field of view to the time they eventually disappear.
{"title":"Examination of urea water solution spray characteristics in hot cross flow","authors":"P. Senthilkumar , T.N.C. Anand","doi":"10.1016/j.expthermflusci.2025.111635","DOIUrl":"10.1016/j.expthermflusci.2025.111635","url":null,"abstract":"<div><div>Injecting Urea-Water sprays at low pressure into the hot exhaust gas flow stream in the presence of catalysts is one of the most effective ways to reduce NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> emissions in diesel engines. The effectiveness of NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> conversion is greatly impacted by spray parameters such as droplet size, velocity, dispersion, and homogeneity upstream of the catalyst. For estimating droplet size, Particle/Droplet Image Analysis (PDIA) is a reliable technique, and it has numerous benefits, including the ability to visualize the droplet shape and quantify non-spherical droplets. In this present study, the PDIA and Particle Tracking Velocimetry (PTV) techniques with high pixel resolution were used to look at the size and velocity of the droplets of the urea-water solution (UWS) spray in a heated cross-flow. The results indicate that smaller spherical droplets are located at the top of the spray, whereas the majority of the bigger droplets are non-spherical and present at the bottom. Droplet size decreases as injection pressure and air velocity rise due to improved atomization. Droplet velocity in the flow direction increases with air velocity and decreases with size. The PDIA method has the ability to measure both spherical and non-spherical droplets. When non-spherical droplets are excluded from droplet size measurements, there is a significant difference in the SMD measured, highlighting the importance of using a technique which can measure non-spherical droplets in such sprays. However, since the PDIA method is usually used with low repetition rate cameras, droplets must be captured over a range of imaging times, from the time they begin to appear in the field of view to the time they eventually disappear.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111635"},"PeriodicalIF":3.3,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145414505","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 : 2025-10-23DOI: 10.1016/j.expthermflusci.2025.111632
Arun Chand , Nishab Ali , Andallib Tariq
Matrix cooling is gaining attention as an advanced internal cooling strategy for gas turbines, offering both enhanced mechanical integrity and superior heat transfer. However, the aerothermal behavior in bend regions, especially downstream of the matrix, remains insufficiently explored. This study presents a detailed experimental investigation of flow dynamics and heat transfer across the bend section that occurs downstream of the matrix channel. Two matrix configurations, i.e., (i) 3-subchannel (3SC) and (ii) 4-subchannel (4SC), are systematically studied at Reynolds numbers (Re) of 5,000, 7,500, and 10,000. High-resolution particle image velocimetry (PIV) and liquid crystal thermography (LCT) techniques have been used for multi-plane aerothermal measurements to elucidate the correlation of complex flow with thermal fields. Results indicate that the matrix emanates the corotating vortices, leading to spatially non-uniform secondary flows, including the emergence of Dean-type vortices at the downstream bend. In particular, the 4SC matrix promotes stronger vortex-driven mixing, yielding significant local and average heat transfer enhancement in the bend region. At Re = 10,000, the 4SC channel achieves a peak heat transfer augmentation of 133 % relative to a smooth baseline, while incurring only a slight increase in friction factor. Across all conditions, the 3SC and 4SC configurations deliver thermal performance factors (TPF) of up to 2.09 and 2.34, respectively. These findings support the potential of matrix cooling to deliver high thermal effectiveness in next-generation internal cooling applications.
{"title":"Experimental investigation of flow and heat transfer characteristics in the bend region of matrix channel","authors":"Arun Chand , Nishab Ali , Andallib Tariq","doi":"10.1016/j.expthermflusci.2025.111632","DOIUrl":"10.1016/j.expthermflusci.2025.111632","url":null,"abstract":"<div><div>Matrix cooling is gaining attention as an advanced internal cooling strategy for gas turbines, offering both enhanced mechanical integrity and superior heat transfer. However, the aerothermal behavior in bend regions, especially downstream of the matrix, remains insufficiently explored. This study presents a detailed experimental investigation of flow dynamics and heat transfer across the bend section that occurs downstream of the matrix channel. Two matrix configurations, i.e., (i) 3-subchannel (3SC) and (ii) 4-subchannel (4SC), are systematically studied at Reynolds numbers (<em>Re</em>) of 5,000, 7,500, and 10,000. High-resolution particle image velocimetry (PIV) and liquid crystal thermography (LCT) techniques have been used for multi-plane aerothermal measurements to elucidate the correlation of complex flow with thermal fields. Results indicate that the matrix emanates the corotating vortices, leading to spatially non-uniform secondary flows, including the emergence of Dean-type vortices at the downstream bend. In particular, the 4SC matrix promotes stronger vortex-driven mixing, yielding significant local and average heat transfer enhancement in the bend region. At <em>Re</em> = 10,000, the 4SC channel achieves a peak heat transfer augmentation of 133 % relative to a smooth baseline, while incurring only a slight increase in friction factor. Across all conditions, the 3SC and 4SC configurations deliver thermal performance factors (TPF) of up to 2.09 and 2.34, respectively. These findings support the potential of matrix cooling to deliver high thermal effectiveness in next-generation internal cooling applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111632"},"PeriodicalIF":3.3,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145414586","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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