New directives and increasing competition push automakers to get better performances (engine power increase), along with mass and size reduction (consumption). These evolutions lead to an increase of the thermal solic...New directives and increasing competition push automakers to get better performances (engine power increase), along with mass and size reduction (consumption). These evolutions lead to an increase of the thermal solicitations undergone by the automotive clutches whereas their weight must be decreased, as it is one of the main influent factors on CO2 emissions. Previous studies only focused on the air flow created by the clutches, but none of them have shown the impact of the clutch housing on the cooling of the clutch parts. In order to determine the influence of the clutch housing on the thermal behavior of automotive clutch systems, a numerical study has been performed on a simplified model of a clutch system. A parametric variation has been performed on the clutch housing size in order to evaluate its impact on the flow and the thermal behavior of clutches. The results show that clutch housing has a significant impact on the air flow and the thermal behavior of clutches. Thermal tests on real clutches with and without clutch housing have confirmed these results.展开更多
The mid-infrared spectral region opens up new possibilities for applications such as molecular spectroscopy with high spatial and frequency resolution.For example,the mid-infrared light provided by synchrotron sources...The mid-infrared spectral region opens up new possibilities for applications such as molecular spectroscopy with high spatial and frequency resolution.For example,the mid-infrared light provided by synchrotron sources has helped for early diagnosis of several pathologies.However,alternative light sources at the table-top scale would enable better access to these state-of-the-art characterizations,eventually speeding up research in biology and medicine.Midinfrared supercontinuum generation in highly nonlinear waveguides pumped by compact fiber lasers represents an appealing alternative to synchrotrons.Here,we introduce orientation-patterned gallium arsenide waveguides as a new versatile platform for mid-infrared supercontinuum generation.Waveguides and fiber-based pump lasers are optimized in tandem to allow for the group velocities of the signal and the idler waves to match near the degeneracy point.This configuration exacerbates supercontinuum generation from 4 to 9μm when waveguides are pumped at 2750 nm with few-nanojoule energy pulses.The brightness of the novel mid-infrared source exceeds that of the thirdgeneration synchrotron source by a factor of 20.We also show that the nonlinear dynamics is strongly influenced by the choice of waveguide and laser parameters,thus offering an additional degree of freedom in tailoring the spectral profile of the generated light.Such an approach then opens new paths for high-brightness mid-infrared laser sources development for high-resolution spectroscopy and imaging.Furthermore,thanks to the excellent mechanical and thermal properties of the waveguide material,further power scaling seems feasible,allowing for the generation of watt-level ultra-broad frequency combs in the mid-infrared.展开更多
Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active s...Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields,ranging from pattern formation in physical and chemical systems,to self-assembly problems in biology.Yet,very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions,and the link between model parameters and thermodynamic quantities is not established.Here,we report a modified phase field model that describes the subtlety of the ice vapour phase transition,through anisotropic water molecules attachment and condensation,surface diffusion,and strong anisotropic surface tension,that guarantee the anisotropy,faceting and dendritic growth of snowflakes.We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram.We find that the growth dynamics of snow crystals matches the selection theory,consistently with previous experimental observations.展开更多
Three high order shock-capturing schemes are compared for large eddy simulations(LES)of temporally evolving mixing layers for different convective Mach numbers ranging from the quasi-incompressible regime to highly co...Three high order shock-capturing schemes are compared for large eddy simulations(LES)of temporally evolving mixing layers for different convective Mach numbers ranging from the quasi-incompressible regime to highly compressible supersonic regime.The considered high order schemes are fifth-order WENO(WENO5),seventh-order WENO(WENO7)and the associated eighth-order central spatial base scheme with the dissipative portion of WENO7 as a nonlinear post-processing filter step(WENO7fi).This high order nonlinear filter method of Yee&Sjogreen is designed for accurate and efficient simulations of shock-free compressible turbulence,turbulence with shocklets and turbulence with strong shocks with minimum tuning of scheme parameters.The LES results by WENO7fi using the same scheme parameter agree well with experimental results compiled by Barone et al.,and published direct numerical simulations(DNS)work of Rogers&Moser and Pantano&Sarkar,whereas results by WENO5 andWENO7 compare poorly with experimental data and DNS computations.展开更多
基金The support of the DOE/SciDAC SAP grant DE-AI02-06ER25796 is acknowledgedFinancial support from the NASA Aerosciences/RCA program for the second author is gratefully acknowledgedWork by the fifth author was performed under the auspices of the U.S.Department of Energy at Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
文摘New directives and increasing competition push automakers to get better performances (engine power increase), along with mass and size reduction (consumption). These evolutions lead to an increase of the thermal solicitations undergone by the automotive clutches whereas their weight must be decreased, as it is one of the main influent factors on CO2 emissions. Previous studies only focused on the air flow created by the clutches, but none of them have shown the impact of the clutch housing on the cooling of the clutch parts. In order to determine the influence of the clutch housing on the thermal behavior of automotive clutch systems, a numerical study has been performed on a simplified model of a clutch system. A parametric variation has been performed on the clutch housing size in order to evaluate its impact on the flow and the thermal behavior of clutches. The results show that clutch housing has a significant impact on the air flow and the thermal behavior of clutches. Thermal tests on real clutches with and without clutch housing have confirmed these results.
基金We acknowledge the financial support from Agence Nationale de la Recherche(ANR-16-CE08-0031 BISCOT,ANR-20-CE42-0003 FLEX-UV,ANR-21-CE24-0001 MIRthFUL)H2020 Future and Emerging Technologies(PETACom 829153)Conseil Régional de Nouvelle-Aquitaine(SIP2,Femto-VO2,MIR-X).
文摘The mid-infrared spectral region opens up new possibilities for applications such as molecular spectroscopy with high spatial and frequency resolution.For example,the mid-infrared light provided by synchrotron sources has helped for early diagnosis of several pathologies.However,alternative light sources at the table-top scale would enable better access to these state-of-the-art characterizations,eventually speeding up research in biology and medicine.Midinfrared supercontinuum generation in highly nonlinear waveguides pumped by compact fiber lasers represents an appealing alternative to synchrotrons.Here,we introduce orientation-patterned gallium arsenide waveguides as a new versatile platform for mid-infrared supercontinuum generation.Waveguides and fiber-based pump lasers are optimized in tandem to allow for the group velocities of the signal and the idler waves to match near the degeneracy point.This configuration exacerbates supercontinuum generation from 4 to 9μm when waveguides are pumped at 2750 nm with few-nanojoule energy pulses.The brightness of the novel mid-infrared source exceeds that of the thirdgeneration synchrotron source by a factor of 20.We also show that the nonlinear dynamics is strongly influenced by the choice of waveguide and laser parameters,thus offering an additional degree of freedom in tailoring the spectral profile of the generated light.Such an approach then opens new paths for high-brightness mid-infrared laser sources development for high-resolution spectroscopy and imaging.Furthermore,thanks to the excellent mechanical and thermal properties of the waveguide material,further power scaling seems feasible,allowing for the generation of watt-level ultra-broad frequency combs in the mid-infrared.
基金financial support through the CISTIC project of programme Investissements d’Avenir LabEx EMC3(ANR-10-LABX-09-01).
文摘Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields,ranging from pattern formation in physical and chemical systems,to self-assembly problems in biology.Yet,very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions,and the link between model parameters and thermodynamic quantities is not established.Here,we report a modified phase field model that describes the subtlety of the ice vapour phase transition,through anisotropic water molecules attachment and condensation,surface diffusion,and strong anisotropic surface tension,that guarantee the anisotropy,faceting and dendritic growth of snowflakes.We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram.We find that the growth dynamics of snow crystals matches the selection theory,consistently with previous experimental observations.
基金Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
文摘Three high order shock-capturing schemes are compared for large eddy simulations(LES)of temporally evolving mixing layers for different convective Mach numbers ranging from the quasi-incompressible regime to highly compressible supersonic regime.The considered high order schemes are fifth-order WENO(WENO5),seventh-order WENO(WENO7)and the associated eighth-order central spatial base scheme with the dissipative portion of WENO7 as a nonlinear post-processing filter step(WENO7fi).This high order nonlinear filter method of Yee&Sjogreen is designed for accurate and efficient simulations of shock-free compressible turbulence,turbulence with shocklets and turbulence with strong shocks with minimum tuning of scheme parameters.The LES results by WENO7fi using the same scheme parameter agree well with experimental results compiled by Barone et al.,and published direct numerical simulations(DNS)work of Rogers&Moser and Pantano&Sarkar,whereas results by WENO5 andWENO7 compare poorly with experimental data and DNS computations.
