Insect flight is a complex trait involved in different behaviors,from the search for sexual partners,food,or breeding sites.Many studies have postulated the adaptive advantages of certain morphological traits in relat...Insect flight is a complex trait involved in different behaviors,from the search for sexual partners,food,or breeding sites.Many studies have postulated the adaptive advantages of certain morphological traits in relation to increased flight capacity,such as low values of wing loading or high values of wing:thorax ratio and wing-aspect ratio.However,few studies have evaluated the relationship between variables related to flight and morphological traits in Drosophila.This work aimed to study morphological traits in males and females of two pairs of sibling species:Drosophila buzzati Patterson and Wheeler-Drosophila koeferae Fontdevila and Wasserman,and Drosophila melanogaster Meigen-Drosophila simulans Sturtevant,and to analyze its relationship with flight.We detected the highest proportion of flight time in D.koepferae and D.simulans compared to D.buzzati and D.melanogaster,respectively.Our results also revealed sexual dimorphism,with males exhibiting a higher proportion of flight time than females.Surprisingly,we did not find a general pattern to explain the relationship between morphology and the proportion of flight time because associations varied depending upon the analyses(considering all groups together or each sex-species combination separately).Moreover,these associations explained a low percentage of variation,suggesting that other nonmorphological components related to flight,such as physiological variables,should be taken into account.This work allowed us to show the variability and complexity of an aspect of flight,suggesting that the adaptive role of the morphological traits studied might have been overestimated.展开更多
Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibili...Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibility effect came from the reduced pressure-strain term due to reduced pressure fluctuations. Although better understanding of the compressible turbulence is generally achieved with the increased DNS and experimental research effort, there are still some discrepancies among these recent findings. Analysis of the DNS and experimental data suggests that some of the discrepancies are apparent if the compressible effect is related to the turbulent Mach number, Mt. From the comparison of two classes of compressible flow, homogenous shear flow and inhomogeneous shear flow （mixing layer）, we found that the effect of compressibility on both classes of shear flow can be characterized in three categories corresponding to three regions of turbulent Mach numbers： the low-Mr, the moderate-Mr and high-Mr regions. In these three regions the effect of compressibility on the growth rate of the turbulent mixing layer thickness is rather different. A simple approach to the reduced pressure-strain effect may not necessarily reduce the mixing-layer growth rate, and may even cause an increase in the growth rate. The present work develops a new second-moment model for the compressible turbulence through the introduction of some blending functions of Mt to account for the compressibility effects on the flow. The model has been successfully applied to the compressible mixing layers.展开更多
Turbulent dispersed multiphase flows,including gas-particle,gas-droplet and bubble-liquid flows,are widely encountered in various engineering facilities.Modeling of two-phase turbulence,in particular the dispersed pha...Turbulent dispersed multiphase flows,including gas-particle,gas-droplet and bubble-liquid flows,are widely encountered in various engineering facilities.Modeling of two-phase turbulence,in particular the dispersed phase turbulence,is the key problem in the Eulerian-Eulerian simulation of practical dispersed multiphase flows.Although different models were developed and used,the experimental validation shows that they cannot always give satisfactory prediction results.In this paper the present author give a detailed review of the unified second-order moment (USM),k-k p and nonlinear k-k p two-phase turbulence models,proposed by him.The derivation and closure of these models are described in detail and the experimental validation and application of these models are extensively discussed.展开更多
Turbulent two-phase combustion is widely encountered in spray and pulverized-coal combustors,and large-eddy simulation(LES)becomes a powerful CFD method for its simulation,because LES can give unsteady flame structure...Turbulent two-phase combustion is widely encountered in spray and pulverized-coal combustors,and large-eddy simulation(LES)becomes a powerful CFD method for its simulation,because LES can give unsteady flame structures and more reasonable statistical results than Reynolds-averaged modeling.Present combustion models in LES either lack of generality or are computationally too expensive.A statistical moment model based on the idea of turbulence modeling called“second-order moment(SOM)combustion model”was developed by the present authors for LES of two-phase combustion.In this paper,a review is given on our published research results for SOM-LES of two-phase combustion,including the description of the SOM-LES model,its application,validation of statistical results by experiments,as well as the phenomena obtained by instantaneous results.展开更多
基金supported by funding of Agencia Nacional de Promocion Cientifica y Tecnologica granted to V.PC.(PICT-2018-00753 and PICT-2015-0277)and to JJF(PICT-2016-2256).
文摘Insect flight is a complex trait involved in different behaviors,from the search for sexual partners,food,or breeding sites.Many studies have postulated the adaptive advantages of certain morphological traits in relation to increased flight capacity,such as low values of wing loading or high values of wing:thorax ratio and wing-aspect ratio.However,few studies have evaluated the relationship between variables related to flight and morphological traits in Drosophila.This work aimed to study morphological traits in males and females of two pairs of sibling species:Drosophila buzzati Patterson and Wheeler-Drosophila koeferae Fontdevila and Wasserman,and Drosophila melanogaster Meigen-Drosophila simulans Sturtevant,and to analyze its relationship with flight.We detected the highest proportion of flight time in D.koepferae and D.simulans compared to D.buzzati and D.melanogaster,respectively.Our results also revealed sexual dimorphism,with males exhibiting a higher proportion of flight time than females.Surprisingly,we did not find a general pattern to explain the relationship between morphology and the proportion of flight time because associations varied depending upon the analyses(considering all groups together or each sex-species combination separately).Moreover,these associations explained a low percentage of variation,suggesting that other nonmorphological components related to flight,such as physiological variables,should be taken into account.This work allowed us to show the variability and complexity of an aspect of flight,suggesting that the adaptive role of the morphological traits studied might have been overestimated.
基金the National Natural Science Foundation of China (10232020,90505005)
文摘Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibility effect came from the reduced pressure-strain term due to reduced pressure fluctuations. Although better understanding of the compressible turbulence is generally achieved with the increased DNS and experimental research effort, there are still some discrepancies among these recent findings. Analysis of the DNS and experimental data suggests that some of the discrepancies are apparent if the compressible effect is related to the turbulent Mach number, Mt. From the comparison of two classes of compressible flow, homogenous shear flow and inhomogeneous shear flow （mixing layer）, we found that the effect of compressibility on both classes of shear flow can be characterized in three categories corresponding to three regions of turbulent Mach numbers： the low-Mr, the moderate-Mr and high-Mr regions. In these three regions the effect of compressibility on the growth rate of the turbulent mixing layer thickness is rather different. A simple approach to the reduced pressure-strain effect may not necessarily reduce the mixing-layer growth rate, and may even cause an increase in the growth rate. The present work develops a new second-moment model for the compressible turbulence through the introduction of some blending functions of Mt to account for the compressibility effects on the flow. The model has been successfully applied to the compressible mixing layers.
基金supported by the National Key Project of Fundamental Research of China (Grant No.G1999-0222-07-08)the National Natural Science Foundation of China (Grant Nos.50736006 and 50606026)the Foundation of State Key Laboratory of Engines,Tianjin University (Grant No.K2010-07)
文摘Turbulent dispersed multiphase flows,including gas-particle,gas-droplet and bubble-liquid flows,are widely encountered in various engineering facilities.Modeling of two-phase turbulence,in particular the dispersed phase turbulence,is the key problem in the Eulerian-Eulerian simulation of practical dispersed multiphase flows.Although different models were developed and used,the experimental validation shows that they cannot always give satisfactory prediction results.In this paper the present author give a detailed review of the unified second-order moment (USM),k-k p and nonlinear k-k p two-phase turbulence models,proposed by him.The derivation and closure of these models are described in detail and the experimental validation and application of these models are extensively discussed.
基金sponsored by the Project of National Natural Science Foundation of China under the Grant 51390493.
文摘Turbulent two-phase combustion is widely encountered in spray and pulverized-coal combustors,and large-eddy simulation(LES)becomes a powerful CFD method for its simulation,because LES can give unsteady flame structures and more reasonable statistical results than Reynolds-averaged modeling.Present combustion models in LES either lack of generality or are computationally too expensive.A statistical moment model based on the idea of turbulence modeling called“second-order moment(SOM)combustion model”was developed by the present authors for LES of two-phase combustion.In this paper,a review is given on our published research results for SOM-LES of two-phase combustion,including the description of the SOM-LES model,its application,validation of statistical results by experiments,as well as the phenomena obtained by instantaneous results.
