Pub Date : 2025-11-22DOI: 10.1016/j.expthermflusci.2025.111661
Maha El Nahas , Thomas Pottier , Jean-Jacques Letourneau , Yann Landon
In recent years supercritical carbon dioxide (sCO) has emerged as a promising technology for machining assistance. Its contribution to the tool lifetime relies on both tribological and thermal actions on the control of the cutting zone. The present contribution proposes an experimental investigation of the flow features of a sCO jet. It intends to address primary data regarding the influence of the operating parameters on the shock structures and the flow characteristic (laminar–turbulent). It also intends to provide some explanations for the thermal behavior of such flow already observed in other published papers. This work addresses both free and impinged jets and investigates the influence of the impingement on the nature of the flow through Schlieren imaging and flow velocity estimation.
{"title":"Quantitative analysis of supercritical CO2 jet structure from Schlieren imaging in free and impinged configurations","authors":"Maha El Nahas , Thomas Pottier , Jean-Jacques Letourneau , Yann Landon","doi":"10.1016/j.expthermflusci.2025.111661","DOIUrl":"10.1016/j.expthermflusci.2025.111661","url":null,"abstract":"<div><div>In recent years supercritical carbon dioxide (sCO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>) has emerged as a promising technology for machining assistance. Its contribution to the tool lifetime relies on both tribological and thermal actions on the control of the cutting zone. The present contribution proposes an experimental investigation of the flow features of a sCO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <!--> <!-->jet. It intends to address primary data regarding the influence of the operating parameters on the shock structures and the flow characteristic (laminar–turbulent). It also intends to provide some explanations for the thermal behavior of such flow already observed in other published papers. This work addresses both free and impinged jets and investigates the influence of the impingement on the nature of the flow through Schlieren imaging and flow velocity estimation.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111661"},"PeriodicalIF":3.3,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621053","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 : 2025-11-20DOI: 10.1016/j.expthermflusci.2025.111662
Xueqing Zhang, Burak A. Tuna, Serhiy Yarusevych, Sean D. Peterson
This study investigates flow development over three-dimensional droplet-inspired models submerged in a boundary layer using particle image velocimetry (PIV). Aerodynamic drag is estimated from stereoscopic PIV measurements performed in multiple planes in a laminar boundary layer regime for a Reynolds number based on obstacle height of and a relative droplet submergence in the boundary layer of . Three geometries are considered: a sessile droplet, a droplet on the verge of runback (depinning), and a hemisphere for baseline comparison with prior studies. The drag coefficients of the sessile and runback models are and 0.35, respectively. Although the difference in drag coefficients between the two droplet configurations is modest, the runback model demonstrates a reduction in drag force proportional to its reduced frontal area. The effects of relative submergence and boundary layer regime on flow development and wake dynamics are further examined at and 1.4 for laminar boundary layers, and , 2.0, and 3.5 for turbulent boundary layers based on time-resolved PIV measurements in the symmetry plane of the models. The results reveal notable effect of model submergence on the wake topology and dynamics. A turbulent incoming boundary layer delays separation from the protuberance in comparison with laminar flow conditions, thus altering the wake dynamics. Spectral and modal analysis using proper orthogonal decomposition provides further insight into the attendant dominant coherent structures and the associated dynamic loading and response of the droplets close to depinning conditions.
{"title":"Drag estimation for isolated, surface-mounted, droplet-inspired geometries and the effect of boundary layer parameters on flow development","authors":"Xueqing Zhang, Burak A. Tuna, Serhiy Yarusevych, Sean D. Peterson","doi":"10.1016/j.expthermflusci.2025.111662","DOIUrl":"10.1016/j.expthermflusci.2025.111662","url":null,"abstract":"<div><div>This study investigates flow development over three-dimensional droplet-inspired models submerged in a boundary layer using particle image velocimetry (PIV). Aerodynamic drag is estimated from stereoscopic PIV measurements performed in multiple planes in a laminar boundary layer regime for a Reynolds number based on obstacle height of <span><math><mrow><msub><mrow><mi>Re</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>≈</mo><mn>2070</mn></mrow></math></span> and a relative droplet submergence in the boundary layer of <span><math><mrow><mi>δ</mi><mo>/</mo><mi>h</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>0</mn></mrow></math></span>. Three geometries are considered: a sessile droplet, a droplet on the verge of runback (depinning), and a hemisphere for baseline comparison with prior studies. The drag coefficients of the sessile and runback models are <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>≈</mo><mn>0</mn><mo>.</mo><mn>33</mn></mrow></math></span> and 0.35, respectively. Although the difference in drag coefficients between the two droplet configurations is modest, the runback model demonstrates a reduction in drag force proportional to its reduced frontal area. The effects of relative submergence and boundary layer regime on flow development and wake dynamics are further examined at <span><math><mrow><mi>δ</mi><mo>/</mo><mi>h</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>0</mn></mrow></math></span> and 1.4 for laminar boundary layers, and <span><math><mrow><mi>δ</mi><mo>/</mo><mi>h</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>5</mn></mrow></math></span>, 2.0, and 3.5 for turbulent boundary layers based on time-resolved PIV measurements in the symmetry plane of the models. The results reveal notable effect of model submergence on the wake topology and dynamics. A turbulent incoming boundary layer delays separation from the protuberance in comparison with laminar flow conditions, thus altering the wake dynamics. Spectral and modal analysis using proper orthogonal decomposition provides further insight into the attendant dominant coherent structures and the associated dynamic loading and response of the droplets close to depinning conditions.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111662"},"PeriodicalIF":3.3,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A compact, robust and portable prototype laser absorption sensor is presented for temperature and CO concentration measurements in AP–HTPB composite propellant flames using calibration-free wavelength modulation spectroscopy. Open-path monitoring of AP–HTPB composite propellant flames exhibits unprecedented challenges for in situ, quantitative, and real-time combustion sensing, including high luminosity and opacity, strong beam-steering and significant optical transmission losses. We present here detailed design, optimization and demonstration of a compact, robust prototype laser absorption sensor, including laser transmission system, detection system and retroreflection system, to cope with the challenges associated with the harsh AP–HTPB composite propellant combustion behaviors. A mid-infrared interband cascade laser with 1 kHz scan rate and 50 kHz modulation rate is used to access two CO absorption transitions located at 2059.91 cm−1 and 2060.33 cm−1. Time-resolved diagnostics of temperature and CO concentration are accomplished in the open-path measurement of the AP–HTPB composite propellant flames. The whole combustion process consists of three stages, namely, flame propagation stage ( s), flame retreating stage ( s), and flame extinction stage ( s). The average temperature and CO concentration in flame propagation stage are determined to be 1681.3 K and 13.9%, with a standard deviation of LOS-averaged temperature to 561.9 K and absolute CO concentration of 12.6%, respectively. High-fidelity measurement is achieved with a single-scan CO concentration detection limit of 1200 ppm at the measured condition of 1540.6 K, 1 atm, and 6.07% CO at s. The measured uncertainties for temperature and CO concentration are estimated to be 4.89% and 6.02% at s, respectively. The developed compact and portable prototype CO absorption sensor is capable of providing robust and accurate measurements in the open-path test of AP–HTPB composite propellant flames and can be readily generalized to relevant combustion environments with similar challenges.
{"title":"Open-path measurement of temperature and CO concentration in AP–HTPB composite propellant flames using calibration-free wavelength modulation spectroscopy","authors":"Zhenhai Wang , Xiaoliang Chen , Wensheng Qiao , Xing Chao","doi":"10.1016/j.expthermflusci.2025.111660","DOIUrl":"10.1016/j.expthermflusci.2025.111660","url":null,"abstract":"<div><div>A compact, robust and portable prototype laser absorption sensor is presented for temperature and CO concentration measurements in AP–HTPB composite propellant flames using calibration-free wavelength modulation spectroscopy. Open-path monitoring of AP–HTPB composite propellant flames exhibits unprecedented challenges for <em>in situ</em>, quantitative, and real-time combustion sensing, including high luminosity and opacity, strong beam-steering and significant optical transmission losses. We present here detailed design, optimization and demonstration of a compact, robust prototype laser absorption sensor, including laser transmission system, detection system and retroreflection system, to cope with the challenges associated with the harsh AP–HTPB composite propellant combustion behaviors. A mid-infrared interband cascade laser with 1 kHz scan rate and 50 kHz modulation rate is used to access two CO absorption transitions located at 2059.91 cm<sup>−1</sup> and 2060.33 cm<sup>−1</sup>. Time-resolved diagnostics of temperature and CO concentration are accomplished in the open-path measurement of the AP–HTPB composite propellant flames. The whole combustion process consists of three stages, namely, flame propagation stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>14</mn></mrow></math></span> s), flame retreating stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>14</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>30</mn></mrow></math></span> s), and flame extinction stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>30</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>875</mn></mrow></math></span> s). The average temperature and CO concentration in flame propagation stage are determined to be 1681.3 K and 13.9%, with a standard deviation of LOS-averaged temperature to 561.9 K and absolute CO concentration of 12.6%, respectively. High-fidelity measurement is achieved with a single-scan CO concentration detection limit of 1200 ppm at the measured condition of 1540.6 K, 1 atm, and 6.07% CO at <span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>568</mn></mrow></math></span> s. The measured uncertainties for temperature and CO concentration are estimated to be 4.89% and 6.02% at <span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>568</mn></mrow></math></span> s, respectively. The developed compact and portable prototype CO absorption sensor is capable of providing robust and accurate measurements in the open-path test of AP–HTPB composite propellant flames and can be readily generalized to relevant combustion environments with similar challenges.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111660"},"PeriodicalIF":3.3,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145622798","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 : 2025-11-17DOI: 10.1016/j.expthermflusci.2025.111657
Jera Van Nieuwenhuyse , Steven Lecompte , Michel De Paepe
Heat transfer to supercritical refrigerants is applied in systems such as the transcritical organic Rankine cycle. For refrigerants under horizontal flow, research on heat transfer under these conditions is limited. In addition, most of the studies focus on small diameter tubes and on R134a, which has a high Global Warming Potential. However, results on one fluid cannot be directly translated to another one and studies on larger tube diameters are required to study the influence of buoyancy on heat transfer and the occurrence of heat transfer deterioration. In this work, local heat transfer measurements at the top, side and bottom of a heated horizontal tube with a large inner diameter of 22.9 mm were performed on R1234zeE, for various supercritical pressure levels, heat fluxes and mass fluxes. Pressure has no influence on heat transfer or buoyancy, indicating that buoyancy forces on the flow are strong under the considered operating conditions. Increasing mass flux has a positive effect on heat transfer, and this effect is stronger for the top of the tube at lower heat fluxes. A rise in heat flux reduces heat transfer, but this effect is dependent on applied pressure and mass flux. Buoyancy is enlarged with increasing heat flux and at higher heat flux, this effect becomes less strong when the flow is more developed. Finally, the prediction capability of several buoyancy criteria from literature were evaluated, where none of the criteria were directly applicable to the current dataset and an update of the threshold values is required.
{"title":"Experimental determination of the heat transfer characteristics and buoyancy effects of supercritical R1234zeE flowing in a large diameter horizontal tube","authors":"Jera Van Nieuwenhuyse , Steven Lecompte , Michel De Paepe","doi":"10.1016/j.expthermflusci.2025.111657","DOIUrl":"10.1016/j.expthermflusci.2025.111657","url":null,"abstract":"<div><div>Heat transfer to supercritical refrigerants is applied in systems such as the transcritical organic Rankine cycle. For refrigerants under horizontal flow, research on heat transfer under these conditions is limited. In addition, most of the studies focus on small diameter tubes and on R134a, which has a high Global Warming Potential. However, results on one fluid cannot be directly translated to another one and studies on larger tube diameters are required to study the influence of buoyancy on heat transfer and the occurrence of heat transfer deterioration. In this work, local heat transfer measurements at the top, side and bottom of a heated horizontal tube with a large inner diameter of 22.9 mm were performed on R1234zeE, for various supercritical pressure levels, heat fluxes and mass fluxes. Pressure has no influence on heat transfer or buoyancy, indicating that buoyancy forces on the flow are strong under the considered operating conditions. Increasing mass flux has a positive effect on heat transfer, and this effect is stronger for the top of the tube at lower heat fluxes. A rise in heat flux reduces heat transfer, but this effect is dependent on applied pressure and mass flux. Buoyancy is enlarged with increasing heat flux and at higher heat flux, this effect becomes less strong when the flow is more developed. Finally, the prediction capability of several buoyancy criteria from literature were evaluated, where none of the criteria were directly applicable to the current dataset and an update of the threshold values is required.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111657"},"PeriodicalIF":3.3,"publicationDate":"2025-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145577032","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 : 2025-11-16DOI: 10.1016/j.expthermflusci.2025.111659
P.Di Gloria , M.G.De Giorgi , M.A. Signore , L. Francioso
This work presents a multi-domain experimental characterization of combustion instabilities in a liquid-fueled swirling combustor operating with Jet-A1, combining high-speed optical imaging, dynamic pressure measurements, and structural vibration monitoring. Experiments were conducted at two global equivalence ratios (Φ = 0.36 and Φ = 0.18), representative of stable and ultra-lean unstable operating conditions. Flame dynamics were analyzed using Proper Orthogonal Decomposition (POD), Spectral POD (SPOD), and Cross-Fourier Transform (Cross-FFT), while pulsation mechanics were investigated through the Autocorrelation Function (ACF). Pressure fluctuations and structural vibrations were monitored using a commercial pressure sensor and an innovative uniaxial AlN-based piezoelectric MEMS accelerometer, fabricated via CMOS-compatible processes and characterized in terms of sensitivity, linearity, resonance, and hysteresis. Time-domain analysis revealed increased signal dispersion and intermittency at Φ = 0.18, while frequency-domain analysis showed that the MEMS accelerometer effectively captures transient components between 156 and 625 Hz, typical of turbulent combustion. Cross-spectral analysis demonstrated high coherence between accelerometer signals and dominant flame modes, highlighting the sensor’s capability to monitor structural dynamics and localized instabilities in real time. The results confirm that the MEMS accelerometer is a compact, non-intrusive, and reliable tool for real-time diagnostics of thermoacoustic instabilities, which can be integrated with optical and pressure measurements for advanced monitoring and control strategies. This combined approach offers valuable perspectives for developing advanced monitoring strategies and real-time control of gas turbine combustors.
{"title":"Multi-domain investigation of combustion instability in gas turbine engines using a uniaxial MEMS piezoelectric accelerometer","authors":"P.Di Gloria , M.G.De Giorgi , M.A. Signore , L. Francioso","doi":"10.1016/j.expthermflusci.2025.111659","DOIUrl":"10.1016/j.expthermflusci.2025.111659","url":null,"abstract":"<div><div>This work presents a multi-domain experimental characterization of combustion instabilities in a liquid-fueled swirling combustor operating with Jet-A1, combining high-speed optical imaging, dynamic pressure measurements, and structural vibration monitoring. Experiments were conducted at two global equivalence ratios (Φ = 0.36 and Φ = 0.18), representative of stable and ultra-lean unstable operating conditions. Flame dynamics were analyzed using Proper Orthogonal Decomposition (POD), Spectral POD (SPOD), and Cross-Fourier Transform (Cross-FFT), while pulsation mechanics were investigated through the Autocorrelation Function (ACF). Pressure fluctuations and structural vibrations were monitored using a commercial pressure sensor and an innovative uniaxial AlN-based piezoelectric MEMS accelerometer, fabricated via CMOS-compatible processes and characterized in terms of sensitivity, linearity, resonance, and hysteresis. Time-domain analysis revealed increased signal dispersion and intermittency at Φ = 0.18, while frequency-domain analysis showed that the MEMS accelerometer effectively captures transient components between 156 and 625 Hz, typical of turbulent combustion. Cross-spectral analysis demonstrated high coherence between accelerometer signals and dominant flame modes, highlighting the sensor’s capability to monitor structural dynamics and localized instabilities in real time. The results confirm that the MEMS accelerometer is a compact, non-intrusive, and reliable tool for real-time diagnostics of thermoacoustic instabilities, which can be integrated with optical and pressure measurements for advanced monitoring and control strategies. This combined approach offers valuable perspectives for developing advanced monitoring strategies and real-time control of gas turbine combustors.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111659"},"PeriodicalIF":3.3,"publicationDate":"2025-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145577029","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 : 2025-11-15DOI: 10.1016/j.expthermflusci.2025.111654
Ahmed M. Abdulnaim , Ahmed H. Elkholy , Mohamed Elmously , Hany A. Moneib , Ayman M. Elbaz
Environmental concerns, particularly greenhouse gas emissions, have intensified interest in renewable fuels such as biogas. However, the low reactivity of biogas presents challenges for achieving stable and efficient combustion. This study investigates the impact of inner swirl intensity on both the aerodynamic and thermal characteristics of biogas–methane cofiring in a concentric double-swirl burner. First, the influence of swirl intensity on non-reacting and reacting flow fields is analyzed using two-dimensional Particle Image Velocimetry (PIV). The study then extends to examine the effects on flame temperature distribution and exhaust emissions. Slightly rich premixed biogas/air mixtures were introduced through the inner swirl, while lean methane/air mixtures were supplied via the outer swirl. The outer swirl number was fixed at Sout = 0.49, while the inner swirl number Sin was varied (0.41, 0.72, and 1.24). Results show that increasing Sin enhances mixing and strengthens jet-to-jet interactions. A central recirculation zone (CRZ) consistently forms under all conditions, with additional outer recirculation zones appearing in non-reacting flows. In reacting cases, higher Sin reduces CRZ width while accelerating flow within it. Increased shear and vorticity at the inner shear layer enhance turbulence and sustain velocity fluctuations downstream, promoting faster mixing between fresh reactants and recirculated hot gases. Flame heat release induces radial expansion of the swirling flow and elevates turbulence intensity (Vrms), further improving mixing. These effects collectively enhance combustion efficiency, broaden the temperature field, and lead to significant reductions in CO and NO emissions. The findings highlight the effectiveness of double-swirl burners in improving biogas combustion performance and reducing their environmental impact.
{"title":"Analysis of non-reacting and reacting flows in biogas/methane cofiring within a double-swirl burner: role of the inner swirler","authors":"Ahmed M. Abdulnaim , Ahmed H. Elkholy , Mohamed Elmously , Hany A. Moneib , Ayman M. Elbaz","doi":"10.1016/j.expthermflusci.2025.111654","DOIUrl":"10.1016/j.expthermflusci.2025.111654","url":null,"abstract":"<div><div>Environmental concerns, particularly greenhouse gas emissions, have intensified interest in renewable fuels such as biogas. However, the low reactivity of biogas presents challenges for achieving stable and efficient combustion. This study investigates the impact of inner swirl intensity on both the aerodynamic and thermal characteristics of biogas–methane cofiring in a concentric double-swirl burner. First, the influence of swirl intensity on non-reacting and reacting flow fields is analyzed using two-dimensional Particle Image Velocimetry (PIV). The study then extends to examine the effects on flame temperature distribution and exhaust emissions. Slightly rich premixed biogas/air mixtures were introduced through the inner swirl, while lean methane/air mixtures were supplied via the outer swirl. The outer swirl number was fixed at S<sub>out</sub> = 0.49, while the inner swirl number S<sub>in</sub> was varied (0.41, 0.72, and 1.24). Results show that increasing S<sub>in</sub> enhances mixing and strengthens jet-to-jet interactions. A central recirculation zone (CRZ) consistently forms under all conditions, with additional outer recirculation zones appearing in non-reacting flows. In reacting cases, higher S<sub>in</sub> reduces CRZ width while accelerating flow within it. Increased shear and vorticity at the inner shear layer enhance turbulence and sustain velocity fluctuations downstream, promoting faster mixing between fresh reactants and recirculated hot gases. Flame heat release induces radial expansion of the swirling flow and elevates turbulence intensity (V<sub>rms</sub>), further improving mixing. These effects collectively enhance combustion efficiency, broaden the temperature field, and lead to significant reductions in CO and NO emissions. The findings highlight the effectiveness of double-swirl burners in improving biogas combustion performance and reducing their environmental impact.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111654"},"PeriodicalIF":3.3,"publicationDate":"2025-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145577031","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 : 2025-11-12DOI: 10.1016/j.expthermflusci.2025.111656
Nicolas Brossardt , Sebastian Hoelle , Lars Zigan
Although oil spray cooling is a promising cooling concept for electrical engines with high power density, there is a lack of universal measurement data and correlations for design purposes. In this article, an experiment is designed specifically for this application using similarity theory in a generic spray-wall situation. The comprehensive investigation shows a clear dependence of the heat transfer on the oil mass flow density and the droplet energy on impact into the oil film formed on the heated windings. Also, the thermal interaction between the spray droplets and the surrounding air is found to be an essential mechanism in oil spray cooling heat transfer. The experimental results are eventually used to derive a Nusselt number correlation, which is valid for spray Reynolds numbers of , oil Prandtl numbers of and nozzle Weber numbers of .
{"title":"An experimental investigation of oil spray cooling heat transfer for electrical machine cooling","authors":"Nicolas Brossardt , Sebastian Hoelle , Lars Zigan","doi":"10.1016/j.expthermflusci.2025.111656","DOIUrl":"10.1016/j.expthermflusci.2025.111656","url":null,"abstract":"<div><div>Although oil spray cooling is a promising cooling concept for electrical engines with high power density, there is a lack of universal measurement data and correlations for design purposes. In this article, an experiment is designed specifically for this application using similarity theory in a generic spray-wall situation. The comprehensive investigation shows a clear dependence of the heat transfer on the oil mass flow density and the droplet energy on impact into the oil film formed on the heated windings. Also, the thermal interaction between the spray droplets and the surrounding air is found to be an essential mechanism in oil spray cooling heat transfer. The experimental results are eventually used to derive a Nusselt number correlation, which is valid for spray Reynolds numbers <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>D</mi></mrow></msub></mrow></math></span> of <span><math><mrow><mtext>2.1</mtext><mo>−</mo><mtext>17.1</mtext></mrow></math></span>, oil Prandtl numbers <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> of <span><math><mrow><mtext>63</mtext><mo>−</mo><mtext>108</mtext></mrow></math></span> and nozzle Weber numbers <span><math><mrow><mi>W</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>d0</mi></mrow></msub></mrow></math></span> of <span><math><mrow><mtext>5.6</mtext><mo>−</mo><mtext>56.6</mtext></mrow></math></span>.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111656"},"PeriodicalIF":3.3,"publicationDate":"2025-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145577030","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 : 2025-11-12DOI: 10.1016/j.expthermflusci.2025.111658
Burak Özer, Reinhold Kneer, Anna Maßmeyer
Self-sustained pulverized biomass swirl flames are investigated experimentally under oxy-fuel atmosphere concerning the effect of thermal load, and oxygen content of the oxidizer stream on flame characteristics. Experiments are conducted employing a swirl burner in a down-fired cylindrical chamber. Operating conditions are selected in ranges of thermal loads between to and oxidizer oxygen contents between 25 and 30 vol.-% while keeping the flame stoichiometry constant. Particle velocity profiles are obtained employing non-intrusive 2D laser Doppler velocimetry. Spectrally narrow-band imaging of the near burner region enables the identification of reaction zones via OH* radical emission imaging as well as regions of high particle temperature by imaging their thermal radiation. The results show that the occurrence of an fuel particle recirculation is related to the ratio of the momentum flow rate of swirled secondary stream over the momentum flow rate of the fuel with its carrying stream. By either reinforcing the flame thermal power or lowering the oxidizer oxygen content, the momentum ratio increases, progressively leading to the fuel particle recirculation at the central axis of the flame. In the flames with a recirculation of hot fuel particles towards the burner, homogeneous devolatilization and char combustion regions are observed in the radical emission of OH* and thermal radiation images, respectively.
{"title":"Experimental assessment of velocity and narrow-band measurements in oxy-fuel combustion of pulverized walnut shells","authors":"Burak Özer, Reinhold Kneer, Anna Maßmeyer","doi":"10.1016/j.expthermflusci.2025.111658","DOIUrl":"10.1016/j.expthermflusci.2025.111658","url":null,"abstract":"<div><div>Self-sustained pulverized biomass swirl flames are investigated experimentally under oxy-fuel atmosphere concerning the effect of thermal load, and oxygen content of the oxidizer stream on flame characteristics. Experiments are conducted employing a swirl burner in a down-fired cylindrical chamber. Operating conditions are selected in ranges of thermal loads between <span><math><mrow><mn>60</mn><mspace></mspace><msub><mrow><mstyle><mi>k</mi><mi>W</mi></mstyle></mrow><mrow><mi>th</mi></mrow></msub></mrow></math></span> to <span><math><mrow><mn>100</mn><mspace></mspace><msub><mrow><mstyle><mi>k</mi><mi>W</mi></mstyle></mrow><mrow><mi>th</mi></mrow></msub></mrow></math></span> and oxidizer oxygen contents between 25 and 30<!--> <!-->vol.-% while keeping the flame stoichiometry constant. Particle velocity profiles are obtained employing non-intrusive 2D laser Doppler velocimetry. Spectrally narrow-band imaging of the near burner region enables the identification of reaction zones via OH* radical emission imaging as well as regions of high particle temperature by imaging their thermal radiation. The results show that the occurrence of an fuel particle recirculation is related to the ratio of the momentum flow rate of swirled secondary stream over the momentum flow rate of the fuel with its carrying stream. By either reinforcing the flame thermal power or lowering the oxidizer oxygen content, the momentum ratio increases, progressively leading to the fuel particle recirculation at the central axis of the flame. In the flames with a recirculation of hot fuel particles towards the burner, homogeneous devolatilization and char combustion regions are observed in the radical emission of OH* and thermal radiation images, respectively.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111658"},"PeriodicalIF":3.3,"publicationDate":"2025-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145517745","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.2025.111652
Roberto Pio Puttini , Lorenzo Capponi , Massimo Franco , Edward Mansfield , Daniel J. Bodony , Gregory S. Elliott , Gianluca Rossi , Francesco Panerai
High-enthalpy plasma jets exhibit complex, unsteady flow behavior that is critical to the development of thermal protection systems and validation of multiphysics models for non-equilibrium flow and material response. Irradiance-based diagnostics provide high-resolution spatial and temporal characterizations, enabling visualization of flow structures, temperature estimation, and instability detection. This study investigates the dynamics of an inductively coupled plasma jet, focusing on the effects of mass flow rate, torch power, and reactor pressure on jet morphology and radiative energy distribution. Using a multi-view diagnostic system based on two synchronized, orthogonal high-speed cameras, the jet behavior is resolved in space and time. The results show that increasing flow rate produces broader, less organized jet structures, while torch power and pressure strongly influence the spatial distribution of radiative energy.
{"title":"Orthographic high-speed visible emission imaging of plasma jet dynamics","authors":"Roberto Pio Puttini , Lorenzo Capponi , Massimo Franco , Edward Mansfield , Daniel J. Bodony , Gregory S. Elliott , Gianluca Rossi , Francesco Panerai","doi":"10.1016/j.expthermflusci.2025.111652","DOIUrl":"10.1016/j.expthermflusci.2025.111652","url":null,"abstract":"<div><div>High-enthalpy plasma jets exhibit complex, unsteady flow behavior that is critical to the development of thermal protection systems and validation of multiphysics models for non-equilibrium flow and material response. Irradiance-based diagnostics provide high-resolution spatial and temporal characterizations, enabling visualization of flow structures, temperature estimation, and instability detection. This study investigates the dynamics of an inductively coupled plasma jet, focusing on the effects of mass flow rate, torch power, and reactor pressure on jet morphology and radiative energy distribution. Using a multi-view diagnostic system based on two synchronized, orthogonal high-speed cameras, the jet behavior is resolved in space and time. The results show that increasing flow rate produces broader, less organized jet structures, while torch power and pressure strongly influence the spatial distribution of radiative energy.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"172 ","pages":"Article 111652"},"PeriodicalIF":3.3,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145463926","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.2025.111653
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}
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