Fangfang Zhang , Shuyan Che , Hao Yin , Xiangyu Li , Chuangyao Zhao
{"title":"Falling film flow pattern transition of ionic liquid aqueous solution on horizontal tube bundles","authors":"Fangfang Zhang , Shuyan Che , Hao Yin , Xiangyu Li , Chuangyao Zhao","doi":"10.1016/j.expthermflusci.2025.111490","DOIUrl":"10.1016/j.expthermflusci.2025.111490","url":null,"abstract":"<div><div>The 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) ionic liquid aqueous solution is a promising absorbent used in absorption refrigeration technology. In this paper, the falling film flow pattern transition of the [EMIm]Ac ionic liquid aqueous solution was experimentally studied. The findings reveal that the critical Reynolds number for flow pattern transitions rises with increases in tube spacing, inlet liquid temperature, and circulating liquid temperature. In comparison to deionized water, the ionic liquid aqueous solution exhibits much smaller critical Reynolds numbers, and provides a more stable liquid film, and produces much smoother and clearer interfaces between liquid and gas. Additionally, hysteresis in flow pattern transitions is observed, and it generally increases with increasing tube spacing, inlet liquid temperature, and circulating liquid temperature. Criteria for flow pattern transitions are developed, and flow pattern maps are constructed for conditions with increasing and decreasing film flow rates, respectively.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111490"},"PeriodicalIF":2.8,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143785854","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}
Jaime Gimeno, Pedro Martí-Aldaraví, Marcos Carreres, César Carvallo
{"title":"Gasoline direct injection spray-wall impingement: Macroscopic characterization and optical analysis","authors":"Jaime Gimeno, Pedro Martí-Aldaraví, Marcos Carreres, César Carvallo","doi":"10.1016/j.expthermflusci.2025.111476","DOIUrl":"10.1016/j.expthermflusci.2025.111476","url":null,"abstract":"<div><div>Spray-wall interaction (SWI) plays a crucial role in spray-based processes, influencing atomization, mixing, combustion efficiency, and pollutant formation. This study investigates SWI by analyzing spray morphology and key geometrical parameters, including spray penetration, spray area, spreading behavior on a quartz wall, and post-impingement spray thickness. Three optical visualization techniques were employed to study the effects of varying injection and ambient pressures, fuel and ambient temperatures, and injector tip-to-wall distance. The impact of cold-start and other evaporative engine conditions on spray morphology was analyzed. An increase in the injection pressure, an increase in wall-to-tip distance, and a decrease in ambient back-pressure delay the start of the spray-wall interaction. Higher injection pressure leads to greater spray spreading over the wall. Regarding extinction profiles, a higher injection pressure and ambient temperature result in lower liquid concentration in the spray.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111476"},"PeriodicalIF":2.8,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143767705","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}
Jinji Li, Yingchao Zhang, Ruizhuo Zhou, Zhe Zhang, Guohua Wang
{"title":"Investigation on aerodynamic force behavior and flow structure of Ahmed body under crosswind","authors":"Jinji Li, Yingchao Zhang, Ruizhuo Zhou, Zhe Zhang, Guohua Wang","doi":"10.1016/j.expthermflusci.2025.111488","DOIUrl":"10.1016/j.expthermflusci.2025.111488","url":null,"abstract":"<div><div>This study investigates the aerodynamic performance and the near wake of the Ahmed body under crosswind conditions experimentally at a length-based Reynolds number <span><math><msub><mrow><mi>Re</mi></mrow><mi>l</mi></msub></math></span> <span><math><mo>∈</mo></math></span>[0.11, 0.64] × 10<sup>6</sup>. The slant angle of the Ahmed body is 35°, and the yaw angle (β) ranges from 0° to 30°. Throughout the investigations, force, pressure, particle image velocimetry (PIV) and flow visualization measurements are conducted. The variation of drag coefficient <span><math><msub><mi>C</mi><mi>d</mi></msub></math></span> with yaw angle follows a parabolic curve, with a remarkable increase in <span><math><msub><mi>C</mi><mi>d</mi></msub></math></span> occurring at 6°<β < 16° yaw angle. Non-uniformity and asymmetry in pressure distribution are shown on the base and slant surfaces, which can be attributed to the asymmetry behavior of recirculation structures behind the body. As the yaw angle increases, the shrinking of recirculation structures and the movement of their foci toward the surface contribute to a significant reduction in pressure on the leeward side of rear surface, thereby increasing drag. The shear layer on the windward side is suppressed, while on the leeward side, it separates prematurely, corresponding to an increase in the side force. Based on the findings of the present study and previous literature, a conceptual model of the flow structure is proposed for the 35° slant angle Ahmed body under crosswind, aiming to explain the evolution of the behavior of forces, pressure distribution, and the flow structures.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111488"},"PeriodicalIF":2.8,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143777020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"2C-2D PIV/PTV measurements of high Reynolds number turbulent channel flow with sub-viscous-length wall-normal resolution","authors":"Bihai Sun, Callum Atkinson, Julio Soria","doi":"10.1016/j.expthermflusci.2025.111481","DOIUrl":"10.1016/j.expthermflusci.2025.111481","url":null,"abstract":"<div><div>This study presents a high spatial resolution hybrid particle image velocimetry/particle tracking velocimetry (PIV/PTV) methodology for investigating high Reynolds number turbulent channel flow. Utilising two 103-megapixel cameras, the experiment captures the entire channel height with a spatial resolution finer than the viscous length scale. To ensure accurate mapping of the PIV image pairs to a common coordinate system, a novel holography-based pixel-to-pixel imaging sensor registration technique is developed, which achieves an uncertainty of better than <span><math><mrow><mn>0</mn><mo>.</mo><mn>5</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>. At the same time, an efficient second calibration process accounts for lens distortion. The hybrid PIV/PTV analysis leverages PIV velocity vectors as predictors to identify particle pairs for PTV, with velocity vectors sorted into bins of 0.6 viscous length height in the wall-normal direction for statistical velocity analysis. The resulting first- and second-order velocity statistics and the streamwise velocity spectra agree with the equivalent results obtained from direct numerical simulations (DNS) of turbulent channel flow at similar friction Reynolds number, validating the effectiveness of the proposed methodology in capturing the structure of turbulent channel flow with resolution equivalent to DNS resolution.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111481"},"PeriodicalIF":2.8,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143767889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Morphology and dynamics scaling of water sheet jets generated by microfluidic convergent nozzles","authors":"Alexandros Peteinaris , Priyanka Sinha , Julian Schmid , Alexandros Terzis","doi":"10.1016/j.expthermflusci.2025.111480","DOIUrl":"10.1016/j.expthermflusci.2025.111480","url":null,"abstract":"<div><div>The morphological dynamics of water sheet jets generated by microfluidic convergent nozzles represent a critical area of research with significant implications for advancing controlled spray formation. This study employs anodically bonded Silicon wafer chips with etched converging nozzle geometries to investigate the effects of geometric parameters under varying flow conditions. High-speed shadowgraph imaging is utilized to assess the influence of nozzle thickness, outlet width, converging angle, and flow rate on the size and stability of water sheet jets. Experimental results demonstrate that sheet size is primarily governed by flow rate, while stability is strongly affected by nozzle design. Scaling correlations are developed to quantitatively describe water sheet dimensions and transitions between jet breakup, stable sheets, and unstable sheet spray breakup. These findings advance the understanding of water sheet jet dynamics and provide a robust framework for designing microfluidic systems optimized for planar and controlled spray formation.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111480"},"PeriodicalIF":2.8,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143767704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An experimental study to evaluate the effectiveness of a Rotor-Integrated-Heating system for UAV inflight icing protection","authors":"Abdallah Samad, Anvesh Dhulipalla, Hui Hu","doi":"10.1016/j.expthermflusci.2025.111485","DOIUrl":"10.1016/j.expthermflusci.2025.111485","url":null,"abstract":"<div><div>An experimental investigation was conducted to evaluate the effectiveness of a Rotor-Integrated Heating System (RIHS) for Uncrewed-Aerial-Vehicle (UAV) inflight icing protection. The RIHS is composed of a flexible electric film heater that is wrapped around the blades of a UAV rotor model to heat the blade surfaces for icing mitigation. The experimental study is conducted in the Icing Research Tunnel of Iowa State University (ISU-IRT) with the rotor model exposed to a variety of typical icing conditions experienced by UAVs flying in low-altitude airspace. During the experiments, while a phase-locked technique is employed to record the anti-/de-icing features over the surface of the rotor blade with the activated RIHS, the aerodynamic forces generated by the rotor model and the electric power required by the UAV rotor spinning at a pre-selected angular speed are also measured during the icing experiments to quantify the benefits of employing the RIHS for UAV inflight icing mitigation. While the RIHS is found to be effective in ensuring that the rotor model generates almost the same amount of aerodynamic forces over the entire duration of the icing experiments, the minimum power density required by the RIHS to remove/shed ice accretion from the rotor blade is found to be <em>P<sub>D</sub></em> = 2.0, 6.0 and 10.0 k<em>W/m<sup>2</sup></em> under the glaze, mixed and rime icing conditions, respectively. It is also demonstrated that, in comparison to the scenario without taking any anti-/de-icing measures, the successful anti-/de-icing with the activated RIHS can lead to at least 65 %, 63 % and 57 % saving in the required power consumption for the UAV rotor generating required lifting forces to ensure the UAV stay airborne under the glaze, mixed and rime icing conditions, respectively.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111485"},"PeriodicalIF":2.8,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143734882","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}
Vaishakh Tholan , Sascha Heitkam , Anna-Elisabeth Sommer , Muhammad Ziauddin , Volker Recksiek , Martin Rudolph , Kerstin Eckert
{"title":"Comparison of measured gas flux with Drift Flux Theory in a two-phase counter-current flow channel","authors":"Vaishakh Tholan , Sascha Heitkam , Anna-Elisabeth Sommer , Muhammad Ziauddin , Volker Recksiek , Martin Rudolph , Kerstin Eckert","doi":"10.1016/j.expthermflusci.2025.111479","DOIUrl":"10.1016/j.expthermflusci.2025.111479","url":null,"abstract":"<div><div>This experimental study aims to test the validity of the Drift Flux Theory (DFT) within a lab scale REFLUX<sup>TM</sup> Flotation Cell (RFC<sup>TM</sup>). The DFT, which is an analytical model, studies the transport conditions of rising bubbles in downward liquid flux. The model relates the component volumetric fluxes to the relative velocity between the liquid and gas phases and to their volume fractions. This requires measuring the local gas volume fraction and bubble diameter with high spatial and temporal resolution, which remains a challenge due to the limitations of existing sensors. To tackle this problem, newer sensors were used in the current study to revisit the hydrodynamics of the RFC<sup>TM</sup>. In the current experimental setup, the gas fraction is measured using the Wire-Mesh Sensor, which has a high spatial and temporal resolution of <span><math><mrow><mn>0</mn><mo>.</mo><mn>5</mn><mspace></mspace><mstyle><mi>m</mi><mi>m</mi></mstyle></mrow></math></span> and <span><math><mrow><mn>10</mn><mspace></mspace><mstyle><mi>k</mi><mi>H</mi><mi>z</mi></mstyle></mrow></math></span> respectively. The bubble size distribution is measured in situ with an optical process microscope. The experimental parameters, such as gas flux, liquid flux, and wash-water fluxes, were changed to set different conditions in the model. These parameteric values were compared to predictions from the DFT which revealed significant deviations from the theoretical claims made on the basis of simplified transport conditions. The application of the drift-flux theory to highly turbulent multiphase flows, such as RFC<sup>TM</sup>, must therefore be reviewed and requires further research.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111479"},"PeriodicalIF":2.8,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143737858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Matteo Migliorini, Pavlos K. Zachos, David G. MacManus, Alexandros Giannouloudis
{"title":"Experimental investigation of unsteady fan-intake interactions using time-resolved stereoscopic particle image velocimetry","authors":"Matteo Migliorini, Pavlos K. Zachos, David G. MacManus, Alexandros Giannouloudis","doi":"10.1016/j.expthermflusci.2025.111482","DOIUrl":"10.1016/j.expthermflusci.2025.111482","url":null,"abstract":"<div><div>Understanding engine response to unsteady intake flow distortion is a crucial requirement to de-risk the development of novel aircraft configurations. This is more critical for configurations with highly embedded engines. Recent advances in non-intrusive, laser-based flow diagnostics demonstrated the ability to measure unsteady flows in convoluted intakes with high resolution in time and space. This work presents novel non-intrusive, unsteady flow measurements ahead of a fan rotor coupled to a convoluted diffusive intake. The fan rotor caused a local increase of the maximum levels of swirl intensity at the blade tip region, as well as flow re-distribution at the interface plane between the fan and the inlet duct compared to the baseline configuration with no fan in place. This contributed to the reduction of the overall swirl angle unsteadiness across the main flow distortion frequencies. This research presents a notable advance in unsteady fan-intake interaction characterisation. The work shows that high-resolution optical measurements offer notably better understanding of these complex aerodynamic interactions and have the potential to be part of larger scale, industrial testing programmes for future product development and certification.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111482"},"PeriodicalIF":2.8,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143705864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Phase-locking PIV measurement of vortex–vortex interactions inside dual-slit cavity during high-intensity acoustic modulation","authors":"Yuchao Tang, Peng Wang, Yingzheng Liu","doi":"10.1016/j.expthermflusci.2025.111483","DOIUrl":"10.1016/j.expthermflusci.2025.111483","url":null,"abstract":"<div><div>This study experimentally investigates the vortex–vortex interaction mechanism inside a dual-slit cavity structure under high-intensity external acoustic modulation. Particular attention was paid to the slit distance, which corresponded to different vortex behaviors under the combined acoustic forcing effect and wall-confinement effect. A phase-locking particle image velocimetry measurement was performed using the incident acoustic wave as a phase-determination signal. The dynamically interactive response between acoustics and vortices was accurately phase-resolved through a field-programmable gate array with a precast wave decomposition method and a hard-computation approach. Four types of interaction mechanisms (rapid vortex merging, mutually interfered vortex shedding, isolated vortex evolution, and wall-confined vortex jets, with <span><math><mrow><msup><mrow><mi>S</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo></mrow></math></span> 2, 16, 32 and 49, respectively) were classified. Subsequent analysis on their vortex trajectory, convection velocity and kinetic energy consolidate our findings on the acoustic impedance and absorption characteristics, which are significantly reduced by the wall-confinement effect, whereas the vortex-merging effect can have a positive augmentation effect. Finally, multi-scale analysis by proper orthogonal decomposition (POD) and turbulence-production theory was conducted on the interactive vortex structures. POD identified the dominant energy distribution and demonstrated that vortex merging will disrupt the independent periodic wavepacket distribution and make the energy distribution mixed. Meanwhile, the production and dissipation processes of small-scale turbulence structures were identified, accompanying with the variations of turbulence stresses by the interactive vortex structures.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111483"},"PeriodicalIF":2.8,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143705863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An efficient offline sensor placement method for flow estimation","authors":"Junwei Chen, Marco Raiola, Stefano Discetti","doi":"10.1016/j.expthermflusci.2025.111448","DOIUrl":"10.1016/j.expthermflusci.2025.111448","url":null,"abstract":"<div><div>We present an efficient method to optimize sensor placement for flow estimation using sensors with time-delay embedding in advection-dominated flows. Our solution allows identifying promising candidates for sensor positions using solely preliminary flow field measurements with non-time-resolved Particle Image Velocimetry (PIV), without introducing physical probes in the flow. Data-driven estimation in advection-dominated flows often exploits time-delay embedding to enrich the sensor information for the reconstruction, i.e. it uses the information embedded in probe time series to provide a more accurate estimation. Optimizing the probe position is the key to improving the accuracy of such estimation. Unfortunately, the cost of performing an online combinatorial search to identify the optimal sensor placement in experiments is often prohibitive. We leverage the principle that, in advection-dominated flows, rows of vectors from PIV fields embed similar information to that of probe time series located at the downstream end of the domain. We propose thus to optimize the sensor placement using the row data from non-time-resolved PIV measurements as a surrogate of the data a real probe would actually capture in time. This optimization is run offline and requires only one preliminary experiment with standard PIV. Once the optimal positions are identified, the probes can be installed and operated simultaneously with the PIV to perform the time-resolved field estimation. We show that the proposed method outperforms equidistant positioning or greedy optimization techniques available in the literature.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"167 ","pages":"Article 111448"},"PeriodicalIF":2.8,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143855073","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}