Experimental Thermal and Fluid Science最新文献

{"title":"Aerodynamic flame stabilization at sub-limit global equivalence ratio, exploiting high velocity ratio coaxial jets: An experimental approach","authors":"Stavros-Marios Panou,&nbsp;Michalis Manoudakis,&nbsp;Evangelos-Panagiotis Mitsopoulos,&nbsp;Konstantinos Souflas,&nbsp;Panayiotis Koutmos","doi":"10.1016/j.expthermflusci.2025.111504","DOIUrl":"10.1016/j.expthermflusci.2025.111504","url":null,"abstract":"<div><div>This work investigates the flow and flame stabilization characteristics of a novel partially premixed aerodynamic flame stabilization configuration. Flames are established in the interaction region of high velocity ratio coaxial jets, at the location where the local flame speed and the reacting flow velocity match. The isothermal flow and mixing field characteristics are first experimentally investigated at four velocity ratios, ranging from 5 to 9, to delineate the operating conditions that promote the formation of a centrally located recirculation region. Combined with a suitable and freely adjustable fuel injection methodology, that supplies the reacting region with a locally flammable mixture, an inverted bowl-shaped flame is aerodynamically established, at sub-limit global equivalence ratio values, with ignition. These flames have no fixed edge anchoring point and remain relatively stationary throughout the investigated load variations, suffering no heat losses to the burner. Particle Image Velocimetry, Fourier Transform Infrared Spectroscopy, Mie scattering and OH* Chemiluminescence measurements have been conducted to investigate the flow and mixing characteristics, flame topology and turbulence effects as well as displacement speed correlations with turbulence intensity. Results indicated that the flame brush location and topology are demarcated by the flame induced accelerating region and maximum OH* chemiluminescence intensity with local Damköhler (<span><math><mrow><mi>Da</mi></mrow></math></span>) and Karlovitz (<span><math><mrow><mi>Ka</mi></mrow></math></span>) numbers suggesting that flame stability is primarily governed by reaction kinetics rather than turbulence effects. Finally, the local displacement speeds revealed a lineal correlation with the fluctuating velocities, for the flame configurations studied, highlighting characteristic resemblances with the typical low-swirl burner setup.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"168 ","pages":"Article 111504"},"PeriodicalIF":2.8,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899020","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":"A study for enhancing accuracy of POD analysis for near wake behind circular cylinder","authors":"Keh-Chin Chang,&nbsp;Tzu-Hsun Lin,&nbsp;Chia-Chun Chu","doi":"10.1016/j.expthermflusci.2025.111506","DOIUrl":"10.1016/j.expthermflusci.2025.111506","url":null,"abstract":"<div><div>This study performs a parametrical study of the proper orthogonal decomposition (POD) for the near wake behind a circular cylinder. Two cases with Reynolds numbers (Re, based on the cylinder diameter) of 3840 and 9440 are tested. The study confirms that the field of view (FOV) must not be less than the maximum spacing (<span><math><mrow><mi>λ</mi></mrow></math></span>) between the vortices in the K<span><math><mrow><mover><mi>a</mi><mo>́</mo></mover></mrow></math></span>rm<span><math><mrow><mover><mi>a</mi><mo>́</mo></mover></mrow></math></span>n vortex street and the FOV should be as close to <span><math><mrow><mi>λ</mi></mrow></math></span> as possible to provide better image solution in the measurement using the particle image velocimetry (PIV) for the POD analysis. The accuracy of the PIV measurement determines the minimum number of image pairs (MT) that is required to achieve statistically stationary results for the POD analysis. It shows that 14000 &lt; MT &lt; 260000 at different upstream subregions for the two tested cases. A criterion based on the accuracy of the PIV measurement is proposed to determine the number of leading modes (m) for the low dimensional representation of fluid dynamics. The study shows that the values of MT and m increase as Re increases and m <span><math><mrow><mo>≪</mo><mi>M</mi><mi>T</mi></mrow></math></span>. Moreover, the MT value increases as the subregion of interest moves to more downstream of wake flow due to decay of the K<span><math><mrow><mover><mi>a</mi><mo>́</mo></mover></mrow></math></span>rm<span><math><mrow><mover><mi>a</mi><mo>́</mo></mover></mrow></math></span>n vortex street.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"168 ","pages":"Article 111506"},"PeriodicalIF":2.8,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143886421","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":"Measurements of the vortex structure in the wake of a scale helicopter rotor in forward motion","authors":"Bradley Gibeau,&nbsp;Ed Soltys,&nbsp;Sina Ghaemi","doi":"10.1016/j.expthermflusci.2025.111503","DOIUrl":"10.1016/j.expthermflusci.2025.111503","url":null,"abstract":"<div><div>This paper provides experimental insight into the vortex structures that form in the wake of a scale helicopter rotor in forward motion. Time-resolved stereoscopic particle image velocimetry was used to capture the vortices that form on the advancing and retreating sides of the rotor at an advance ratio of 0.20. The rotor radius was <em>R</em> = 425 mm and its two blades with chord length <em>c</em> = 35 mm spun at 1,500 RPM, resulting in a Reynolds number of <em>U</em>_tip<em>R</em>/<em>ν</em> = 1.7 × 10⁶ (<em>U</em>_tip<em>c</em>/<em>ν</em> = 1.4 × 10⁵) where <em>U</em>_tip is the blade tip speed. The collective, lateral cyclic, and longitudinal cyclic pitch settings were varied one at a time. The structure of vortices measured in the wake was compared to reference paths that we expect the vortices to take if they advect into the wake at a constant velocity without interaction. We find that the vortices on the retreating side of the rotor closely match the reference paths. Conversely, the vortices on the advancing side often exhibited large deviations from the paths. The vortices on both sides of the rotor had opposite directions of rotation when the collective pitch setting was varied. In contrast, varying the lateral and longitudinal cyclic pitch resulted in the formation of vortices with the same direction of rotation on the advancing and retreating sides. Notable vortex formation was observed on both sides of the rotor when the lateral cyclic pitch setting was varied, while vortex formation was dominant on the advancing side when varying the longitudinal cyclic pitch.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"168 ","pages":"Article 111503"},"PeriodicalIF":2.8,"publicationDate":"2025-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143881823","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":"Dynamics and interactions of counter-rotating waves in rotating detonation combustors","authors":"Provence Barnouin ,&nbsp;Christian Oliver Paschereit ,&nbsp;Eric Bach ,&nbsp;Myles D. Bohon","doi":"10.1016/j.expthermflusci.2025.111486","DOIUrl":"10.1016/j.expthermflusci.2025.111486","url":null,"abstract":"<div><div>Better understanding of non-canonical modes such as counter-rotating wave dynamics provides valuable insights for future rotating detonation engine injector design and combustion mode control. The objective of this work is to study the dynamics and interactions of counter-rotating waves in an RDC experimentally. Previous experimental and numerical data suggest that at collision points, the resulting pressure amplitude is not necessarily the result of a linear combination between the waves, but rather a more complex interaction. In this study, we analyze temporally resolved, high-speed pressure and luminosity data for two counter-rotating waves propagating at equal (2CR) and different (2CRT) speeds. This analysis employs a soft-dynamic time warping averaging scheme, which preserves the shape of the data even in the presence of lap-to-lap fluctuations. From this analysis, the non-linear pressure and luminosity interaction at collision is quantified over the wave lap and for different geometries and operating conditions. Notably, it is found that the strength of the non-linearity at collision is mode dependent and increases as one wave becomes stronger relative to the other one. Furthermore, a one-dimensional gas dynamics model is applied to capture wave collisions in an RDC. The model captures the counter-rotating wave interaction in the 2CR mode, indicating that these waves behave like shock waves. However, in the 2CRT mode, the model underestimates the collision pressure, suggesting that additional mechanisms contribute to the nonlinear interaction between the counter-rotating waves.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"168 ","pages":"Article 111486"},"PeriodicalIF":2.8,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143890986","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":"Flow field analysis of submerged oblique and normally impinging twin jets at varying impinging angles","authors":"C. Sandoval ,&nbsp;C. Treviño ,&nbsp;A. Alvarez ,&nbsp;D. Matuz ,&nbsp;J. Lizardi ,&nbsp;L. Martínez-Suástegui","doi":"10.1016/j.expthermflusci.2025.111491","DOIUrl":"10.1016/j.expthermflusci.2025.111491","url":null,"abstract":"<div><div>In this work, two-dimensional time-resolved particle image velocimetry (TR-PIV) measurements are carried out to study the flow structure and impinging interactions of two turbulent submerged isothermal circular impinging water jets. In this configuration, the uphill and downhill jets impinge obliquely and normally onto a flat target surface, respectively. A comprehensive parametric study is carried out for values of the jets’ exit Reynolds number of <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>=</mo><mn>5000</mn></mrow></math></span> and 8000, jets’-to-surface target distances of <span><math><mrow><mi>H</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>3</mn></mrow></math></span> and 5, and inclination angles of the uphill oblique jet-to-impingement surface of (<span><math><mrow><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>=</mo></mrow></math></span>30°, 45°, 60°). For all the experiments, the jet-to-jet spacing distances were varied for each impingement angle of the oblique jet so that the impingement point of both jets coincide at the geometric intersection of the jets’ axes. Flow visualization images showing ensemble-averaged and instantaneous flow distributions and turbulent characteristics for equal and non-equal Reynolds numbers of the jets are presented. Velocity profiles and Reynolds shear stress distributions of the downhill wall jet development and its corresponding dimensionless shedding frequencies are also obtained. A proper orthogonal decomposition (POD) analysis reveals the spatial structure of the dominant fluctuation motions of the turbulent flow as well as their respective contributions to the total kinetic energy. Our results show that the jets’ exit Reynolds numbers, the oblique impingement angle of the uphill jet and the jets’-to-surface distance play a major role on the complex flow structure and dynamics, location of the stagnation point and entrainment characteristics of the turbulent flow field of the twin jets.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"167 ","pages":"Article 111491"},"PeriodicalIF":2.8,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143833432","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":"Measurement of particulates formed during thermal protection system spallation in an arc-jet environment","authors":"K.J. Price,&nbsp;A. Martin,&nbsp;S.C.C. Bailey","doi":"10.1016/j.expthermflusci.2025.111487","DOIUrl":"10.1016/j.expthermflusci.2025.111487","url":null,"abstract":"<div><div>An arc-jet campaign conducted in the Aerodynamic Heating Facility at NASA Ames was conducted to investigate the spallation of thermal protection system materials by estimating the size of particles ejected from these materials, as well as the corresponding mass loss. Particle sizes were determined both from analysis of particle tracking velocimetry, utilizing a force balance on the particulates, and by direct measurement of particles captured through targeted design of the test articles. Analysis of the captured particles revealed that they took on different geometries consisting of fine particulates, individual fibers, and clumps of multiple fibers. Different methods were required for each particle sizing approach to determine particle quantities, and corresponding mass loss. However, similar values for mass loss were determined using both techniques. In addition, it was found that the particle size distributions were independent of surface heat flux, and whether the carbon preform contained additional phenolic resin. It was found, however, that the presence of phenolic resin caused a measurable reduction in the rate of particle production, potentially due to its pyrolysis reducing the diffusion of oxygen from the free stream into the sample.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"167 ","pages":"Article 111487"},"PeriodicalIF":2.8,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821567","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":"Experimental investigation of rotating detonation engine fueled by liquid ethanol and oxygen-enriched air","authors":"Jianghong Li ,&nbsp;Songbai Yao ,&nbsp;Ying Lei ,&nbsp;Jingtian Yu ,&nbsp;Yeqi Zhou ,&nbsp;Wenwu Zhang","doi":"10.1016/j.expthermflusci.2025.111494","DOIUrl":"10.1016/j.expthermflusci.2025.111494","url":null,"abstract":"<div><div>In this short communication, we explore the feasibility of using renewable ethanol fuel for the rotating detonation engine (RDE) and examine the behavior of the two-phase rotating detonation wave under varying working conditions. The liquid ethanol is injected at ambient temperature, while oxygen-enriched air (60 % oxygen by mass) is supplied at mass flow rates ranging from 90 to 200 g/s. The operation of the RDE is examined under fuel-lean conditions with equivalence ratios ranging from 0.4 to 0.9. At lower mass flow rates, the rotating detonation can still be initiated but remains highly unstable. As the mass flow rate increases, the stability of the ethanol-fueled RDE improves, premature extinction becomes less frequent, and the velocity deficit of the rotating detonation wave decreases.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"167 ","pages":"Article 111494"},"PeriodicalIF":2.8,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828237","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":"Mitigating thermoacoustic instabilities in a Rijke tube burner using iron nanopowder additives","authors":"Xiaokang Liu ,&nbsp;Dongbin Wang ,&nbsp;Shen Fang ,&nbsp;Siyi Zhang ,&nbsp;Lijun Yang ,&nbsp;Jingxuan Li","doi":"10.1016/j.expthermflusci.2025.111472","DOIUrl":"10.1016/j.expthermflusci.2025.111472","url":null,"abstract":"<div><div>This study introduces a novel passive control method for mitigating thermoacoustic instabilities by adding iron nanopowder to the flame within a Rijke tube. A comprehensive experimental setup was designed to investigate how varying nanopowder concentrations influence self-excited oscillations at different Rijke tube lengths. Results show that even small amounts of iron nanopowder can suppress certain high-frequency instability modes or induce nonlinear behavior, such as mode switching from higher to lower modes. At higher concentrations, thermoacoustic instabilities can be almost entirely eliminated. Detailed analysis reveals that iron nanopowder mitigates thermoacoustic instabilities by extending the flame length, which reduces the heat release rate gain to the system, and by enhancing particle-induced acoustic damping.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"166 ","pages":"Article 111472"},"PeriodicalIF":2.8,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143785893","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":"Falling film flow pattern transition of ionic liquid aqueous solution on horizontal tube bundles","authors":"Fangfang Zhang ,&nbsp;Shuyan Che ,&nbsp;Hao Yin ,&nbsp;Xiangyu Li ,&nbsp;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}

{"title":"Gasoline direct injection spray-wall impingement: Macroscopic characterization and optical analysis","authors":"Jaime Gimeno,&nbsp;Pedro Martí-Aldaraví,&nbsp;Marcos Carreres,&nbsp;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}