The migration speed of a typical barchan on the border of Minqin oasis,Gansu Province,northwestern China,was estimated by means of two methods.One is on the basis of a simple physical model and short-term field measur...The migration speed of a typical barchan on the border of Minqin oasis,Gansu Province,northwestern China,was estimated by means of two methods.One is on the basis of a simple physical model and short-term field measurements.The other comes from the combination of the barchan internal structure detected by ground-penetrating radar and optical/radiocarbon dating techniques.The upper limit of migration speed given by conventional C-14 dating is 3.42 m/yr.The optically stimulated luminescence dating indicates that the time-average migration speed of the studied barchan was 1.78 m/yr in 28 years prior to 2007.The physical estimation further suggests that the annual migration speed has increased in recent years.展开更多
Barchan dunes are among the most common accumulative phenomena made by wind erosion,which are usually formed in regions where the prevailing wind direction is almost constant throughout the year and there is not enoug...Barchan dunes are among the most common accumulative phenomena made by wind erosion,which are usually formed in regions where the prevailing wind direction is almost constant throughout the year and there is not enough sand to completely cover the land surface.Barchans are among the most common windy landscapes in Pashoueyeh Erg in the west of Lut Desert,Iran.This study aims to elaborate on morphological properties of barchans in this region using mathematical and statistical models.The results of these methods are very important in investigating barchan shapes and identifying their behavior.Barchan shapes were mathematically modeled by simulating them in the coordinate system through nonlinear parabolic equations,so that two separate equations were calculated for barchan windward and slip-face parabolas.The type and intensity of relationships between barchan morphology and mathematical parameters were determined by the statistical modeling.The results indicated that the existing relationships followed the power correlation with the maximum coefficient of determination and minimum error of estimate.Combining the above two methods is a powerful basis for stimulating barchans in virtual and laboratory environments.The most important result of this study is to convert the mathematical and statistical models of barchan morphology to each other.Focal length is one of the most important parameters of barchan parabolas,suggesting different states of barchans in comparison with each other.As the barchan's focal length decreases,its opening becomes narrower,and the divergence of the barchan's horns reduces.Barchans with longer focal length have greater width,dimensions,and volume.In general,identifying and estimating the morphometric and planar parameters of barchans is effective in how they move,how much they move,and how they behave in the environment.These cases play an important role in the management of desert areas.展开更多
Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and ...Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand.Saline sand samples(mean particle size of 164.50–186.08μm and the total silt,clay and salt content of 0.80%–8.25%)were collected from three saline sand dunes(one barchan dune and two linear dunes)in the Qarhan Desert,Qaidam Basin of China.Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation,respectively.Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment.The motion of sand particles was determined by the observers with a solid laser.The laser sheet(0.80 cm thick),which was emitted by the solid laser,horizontally covered the sand surface and was bound to the sand.Results show that the cohesion of saline sand results from a combination of salt and water.The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes.There is a positive linear correlation between the original moisture content and relative threshold shear velocity.The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content.Our results will provide valuable information about the sand transport of highly saline soil in the desert.展开更多
A new type of microstructure inspired by the cross section of barchan dunes was proposed to reduce windage,which was considered as a passive drag reduction technology in aerospace manufacturing field.Computational flu...A new type of microstructure inspired by the cross section of barchan dunes was proposed to reduce windage,which was considered as a passive drag reduction technology in aerospace manufacturing field.Computational fluid dynamics method was carried out to discuss the effect of the microstructure on the skin friction reduction under high velocity flow condition.Different microstructure heights were employed to survey the reduction of drag.The results illustrated that the appearance of microstructure led to a generation of pressure drag in non-smooth model(with microstructures inspired by cross section of barchan dune)in contrast to smooth model.However,the microstructure significantly increased the thickness of the low-speed fluid by 11.4%in the near-wall flow field,causing the low-speed fluid to rise and decreasing the velocity gradient near the wall,thereby reducing viscous resistance.In addition,high-speed fluid flowed above the microstructure units instead of along the inner side of the units due to the influence of micro-vortex,resulting in a reduction of friction near the surface.Further-more,micro-vortex was considered to be the significant internal factor to achieve turbulent drag reduction since it could not only reduce the viscous resistance by promoting the fluid flow above the microstructure but also pro-vide a reverse thrust force.The understanding of the mechanism of drag reduction provides theoretical guidance for further fabrication of drag reduction coatings using renewable materials.展开更多
In desert areas in Hexi region,11 barchan dunes,6 chains of barchan dunes,6 pyramid dunes,6 parabolic dunes and 6 accumulated sand-belts were chosen to study their movement speed based on images obtained by Google Ear...In desert areas in Hexi region,11 barchan dunes,6 chains of barchan dunes,6 pyramid dunes,6 parabolic dunes and 6 accumulated sand-belts were chosen to study their movement speed based on images obtained by Google Earth in various periods.The results show that among the dunes,the movement of the barchan dunes was the fastest,followed by the chains of barchan dunes,and only the tops of the pyramid dunes swayed,while the parabolic dunes and accumulated sand-belts hardly moved forward.The higher the barchan dunes(or the chains of barchan dunes) were,the slower the movement was.On the contrary,the higher the pyramid dunes were,the faster the swing was.There was a positive correlation between the movement speed of the barchan dunes and the average wind speed of sandstorms.展开更多
[Objective] The paper was to discuss why the top of tall barchan dunes and barchan chains widespread in single prevailing wind area had not been leveled by wind erosion. [Method] Based on the preliminary survey of dis...[Objective] The paper was to discuss why the top of tall barchan dunes and barchan chains widespread in single prevailing wind area had not been leveled by wind erosion. [Method] Based on the preliminary survey of distribution status,the morphological characteristics and environmental conditions of barchan dunes and barchan chains in Hexi desert area of Gansu were investigated in details. The significance of difference between samples and significance of correlation between indicators were examined via variance test. [Result] Barchan dunes and barchan chains in Hexi desert area of Gansu distributed at the leeward direction of desert fringe,generally in patch distribution. The distribution area was gravelly beach or cohesive gravel beach,with broader dune slack; winds in distribution area of barchan dunes and barchan chains blew obviously from one direction,while winds at other directions were light or occasionally strong but with low frequency;the barchan dune in the desert fringe of Hexi desert area of Gansu was relatively tall,while barchan chain was even more taller and larger. Coincidence or separation of the dune peak and the sand ridge might be related to distribution frequency of dominant prevailing wind or wind at opposite direction and the observation seasons.[Conclusion]Studying top stability of barchan dune has an important academic value in revealing blowing sand movement rule at desert fringe,invasion of sand flow,and expansion of desert.展开更多
For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine tra...For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.展开更多
Barchan dune is one of the basic forms of eolian landform, it is usually moulded by highconcentration nonsaturated windsand flow. The formation process of barchan dune begins from “wavegrain duality” of windsand mov...Barchan dune is one of the basic forms of eolian landform, it is usually moulded by highconcentration nonsaturated windsand flow. The formation process of barchan dune begins from “wavegrain duality” of windsand movement, and goes through two developmental stages of sand material accumulating (highconcertration saturated windsand flow) and dune form moulding (highconcentration nonsaturated windsand flow), i.e. the processes of dissipative increase and dispersive decrease. The scattered single barchan dunes on nonsandy bed surface have obvious characteristics of mobility and unstability (not including barchan sand hill). The formation of barchan dune in wind tunnel (its dune scale is one order of magnitude larger than sand ripple scale) is helpful to know the formation mechanism of barchan dunes.展开更多
Barchan dunes are a common type of dune. There are a lot of barchan dunes at accumulated sand-belts of the oasis edge of Hexi desert area of Gansu. What is characteristic of the particle size of barchan dunes? How is ...Barchan dunes are a common type of dune. There are a lot of barchan dunes at accumulated sand-belts of the oasis edge of Hexi desert area of Gansu. What is characteristic of the particle size of barchan dunes? How is this particle size characteristic formed? Characteristics of particle size were analyzed in this paper by comprehensive investigation and sampling in Hexi Corridor desert area, and repeated sampling and determination in Minqin desert area. The results showed that:(1) The particle size of 0.25–0.05 mm and particle size of 0.5–0.25 mm were the main ingredients at the surface 0–5 cm depth of barchan dunes and barchan dune chains in desert area in Hexi Corridor of Gansu. Sand in Gulang desert area was relatively finer and the particle size was quite different from that of Jinchang, Linze, Jinta and Minqin desert area;(2) The particle size was changed from coarse to fine from the bottom to the top of the dunes in the main wind direction(NW) process. i.e. there was the most silt at the top of the dunes, followed by the middle of the leeward slope. The bottom of the windward slope had the most coarse sand, followed by the middle of the windward slope. The barchan dunes were changed from coarse to fine, then from fine to coarse from the bottom to the top of the dunes in the reverse wind direction(SE) process, i.e. there was the most silt in the middle of the windward slope, followed by the top of sand dunes. The bottom of the windward slope had the most coarse sand, followed by the middle of the windward slope. The standard deviation and coefficient of variation of sand dune particle size in the main wind direction process was larger, and the standard deviation and coefficient of variation of sand dune particle size in the reverse wind direction process was smaller;(3) The two processes of the main wind direction(NW) and the reverse wind direction(SE) led to alternating changes in particle size in various parts of the dunes. Two different conclusions on particle size distribution of barchan dunes in windward slope were due to the observation season differences.展开更多
[ Objective ] The paper was to study the particle size characteristics of barchan dune and its formation mechanism in Hexi desert area d Gansu. [ Method] Through particle size measurement and wind speed flow field obs...[ Objective ] The paper was to study the particle size characteristics of barchan dune and its formation mechanism in Hexi desert area d Gansu. [ Method] Through particle size measurement and wind speed flow field observation d dune, the particle size differences of various sampling plots and various parts of dune were analyzed using analysis of variance, and the relationship between particle size and wind speed was analyzed using correlation coefficient method. [ Result] （ 1 ） Barehan dune and barehan chains in Hexi desert area of Gansu were mainly consisted of fine sands and medium sands at the depth of 0 -5 cm： the sand particle in Gulang desert area was fine, which had significant difference with that in Jinchang, Linze, Jinta and Minqin desert areas. （2） Medium sands gradually increased from the bottom of windward slope to the dune peak in both barchan dune and barchan chain. On the windward slope of barehan dune, fine sands gradual- ly increased from the middle to both sides, while coarse sands and medium sands gradually decreased. On the windward slope of barehan chain, fine sands first de- creased then increased from the middle to NE side, but first increased then decreased from the middle to SW side. （3） In terma of particle size, there were great variations between fine sands and coarse sands ; for dune parts, there were great variations between dune peak and leewant slope toe; for dune types, the variation of fine sands in various parts of barchan chain was greater than that of barchan dune, while differentiation degree of medium sands and fine sands was greater than that of barchan dune. The particle size of fine sands was positively correlated with wind speed, and that of medium sands was negatively correlated with wind speed. [ Conclusion] The formation environment of particle size of berehan dune mainly included sand source and dynmnic source, and wind speed was the dynamic source for particle size distribution of barchan dune.展开更多
As continuous of the previous sand-dune-inspired design,the Barchan-Dune-Shaped Injection Compound(BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically....As continuous of the previous sand-dune-inspired design,the Barchan-Dune-Shaped Injection Compound(BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically.While the public 777-shaped hole was served as a baseline,the BDSIC’s endwall effectiveness was assessed at various blowing ratios.Experiments were performed in a single-passage transonic wind tunnel using pressure-sensitive paint(PSP)technique.Carbon dioxide was used as coolant with density ratio of DR=1.53.The purge slot’s blowing ratio was fixed at M=0.3,but the coolant holes were adjusted within M=0.5–2.0.The measured experimental results indicate that the film distribution at the endwall is strongly affected by the passage flow structures.The BDSIC holes demonstrate much higher film effectiveness than the 777-shaped holes for all blowing ratios,~30%enhancement for regionally averaged effectiveness at M=1.0 and~26%at M=2.0.As shown by the numerical results,the existence of BDSIC reduced the coolant penetration effect at a higher blowing ratio.Coolant was deflected and its momentum increased in the streamwise direction,therefore providing more robust film coverage over the endwall region.The anti-counter-rotating vortex pair induced by the BDSIC further stabilized the coolant film and increased the coolant spreading downstream.展开更多
基金supported by 973 project No. 2000048700NSFC projects No. 40601053 and 40872108Ministry of Science and Technology of China project No. 2006FY110800
文摘The migration speed of a typical barchan on the border of Minqin oasis,Gansu Province,northwestern China,was estimated by means of two methods.One is on the basis of a simple physical model and short-term field measurements.The other comes from the combination of the barchan internal structure detected by ground-penetrating radar and optical/radiocarbon dating techniques.The upper limit of migration speed given by conventional C-14 dating is 3.42 m/yr.The optically stimulated luminescence dating indicates that the time-average migration speed of the studied barchan was 1.78 m/yr in 28 years prior to 2007.The physical estimation further suggests that the annual migration speed has increased in recent years.
文摘Barchan dunes are among the most common accumulative phenomena made by wind erosion,which are usually formed in regions where the prevailing wind direction is almost constant throughout the year and there is not enough sand to completely cover the land surface.Barchans are among the most common windy landscapes in Pashoueyeh Erg in the west of Lut Desert,Iran.This study aims to elaborate on morphological properties of barchans in this region using mathematical and statistical models.The results of these methods are very important in investigating barchan shapes and identifying their behavior.Barchan shapes were mathematically modeled by simulating them in the coordinate system through nonlinear parabolic equations,so that two separate equations were calculated for barchan windward and slip-face parabolas.The type and intensity of relationships between barchan morphology and mathematical parameters were determined by the statistical modeling.The results indicated that the existing relationships followed the power correlation with the maximum coefficient of determination and minimum error of estimate.Combining the above two methods is a powerful basis for stimulating barchans in virtual and laboratory environments.The most important result of this study is to convert the mathematical and statistical models of barchan morphology to each other.Focal length is one of the most important parameters of barchan parabolas,suggesting different states of barchans in comparison with each other.As the barchan's focal length decreases,its opening becomes narrower,and the divergence of the barchan's horns reduces.Barchans with longer focal length have greater width,dimensions,and volume.In general,identifying and estimating the morphometric and planar parameters of barchans is effective in how they move,how much they move,and how they behave in the environment.These cases play an important role in the management of desert areas.
基金funded by the National Natural Science Foundation of China(41601002,41871008)
文摘Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand.Saline sand samples(mean particle size of 164.50–186.08μm and the total silt,clay and salt content of 0.80%–8.25%)were collected from three saline sand dunes(one barchan dune and two linear dunes)in the Qarhan Desert,Qaidam Basin of China.Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation,respectively.Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment.The motion of sand particles was determined by the observers with a solid laser.The laser sheet(0.80 cm thick),which was emitted by the solid laser,horizontally covered the sand surface and was bound to the sand.Results show that the cohesion of saline sand results from a combination of salt and water.The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes.There is a positive linear correlation between the original moisture content and relative threshold shear velocity.The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content.Our results will provide valuable information about the sand transport of highly saline soil in the desert.
基金This work was supported by the National Natural Science Foundation of China(Nos.52075246 and U1937206)the Project Funded by China Postdoctoral Science Foundation(No.2019M661826)+1 种基金Open Fund of Key Laboratory of Icing and Anti/De-icing(No.IADL20190202)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(KYCX19_0181).
文摘A new type of microstructure inspired by the cross section of barchan dunes was proposed to reduce windage,which was considered as a passive drag reduction technology in aerospace manufacturing field.Computational fluid dynamics method was carried out to discuss the effect of the microstructure on the skin friction reduction under high velocity flow condition.Different microstructure heights were employed to survey the reduction of drag.The results illustrated that the appearance of microstructure led to a generation of pressure drag in non-smooth model(with microstructures inspired by cross section of barchan dune)in contrast to smooth model.However,the microstructure significantly increased the thickness of the low-speed fluid by 11.4%in the near-wall flow field,causing the low-speed fluid to rise and decreasing the velocity gradient near the wall,thereby reducing viscous resistance.In addition,high-speed fluid flowed above the microstructure units instead of along the inner side of the units due to the influence of micro-vortex,resulting in a reduction of friction near the surface.Further-more,micro-vortex was considered to be the significant internal factor to achieve turbulent drag reduction since it could not only reduce the viscous resistance by promoting the fluid flow above the microstructure but also pro-vide a reverse thrust force.The understanding of the mechanism of drag reduction provides theoretical guidance for further fabrication of drag reduction coatings using renewable materials.
基金Sponsored by Major State Basic Research Development Program(973 Program)(2014CB460611)National Natural Science Foundation of China(41261102)
文摘In desert areas in Hexi region,11 barchan dunes,6 chains of barchan dunes,6 pyramid dunes,6 parabolic dunes and 6 accumulated sand-belts were chosen to study their movement speed based on images obtained by Google Earth in various periods.The results show that among the dunes,the movement of the barchan dunes was the fastest,followed by the chains of barchan dunes,and only the tops of the pyramid dunes swayed,while the parabolic dunes and accumulated sand-belts hardly moved forward.The higher the barchan dunes(or the chains of barchan dunes) were,the slower the movement was.On the contrary,the higher the pyramid dunes were,the faster the swing was.There was a positive correlation between the movement speed of the barchan dunes and the average wind speed of sandstorms.
基金Supported by Special Project for Preceding Study of 973 Program"Stability Research of Tall Barchan Dune at Oasis Fringe(2014CB460611)National Natural Science Foundation of China"Climatic and Environmental Factors for Formation of Sand Sediment Zone and Its Ecological Effects at Minqin Oasis Fringe of Gansu Province(41261102)
文摘[Objective] The paper was to discuss why the top of tall barchan dunes and barchan chains widespread in single prevailing wind area had not been leveled by wind erosion. [Method] Based on the preliminary survey of distribution status,the morphological characteristics and environmental conditions of barchan dunes and barchan chains in Hexi desert area of Gansu were investigated in details. The significance of difference between samples and significance of correlation between indicators were examined via variance test. [Result] Barchan dunes and barchan chains in Hexi desert area of Gansu distributed at the leeward direction of desert fringe,generally in patch distribution. The distribution area was gravelly beach or cohesive gravel beach,with broader dune slack; winds in distribution area of barchan dunes and barchan chains blew obviously from one direction,while winds at other directions were light or occasionally strong but with low frequency;the barchan dune in the desert fringe of Hexi desert area of Gansu was relatively tall,while barchan chain was even more taller and larger. Coincidence or separation of the dune peak and the sand ridge might be related to distribution frequency of dominant prevailing wind or wind at opposite direction and the observation seasons.[Conclusion]Studying top stability of barchan dune has an important academic value in revealing blowing sand movement rule at desert fringe,invasion of sand flow,and expansion of desert.
基金supported by the National Key R&D Program of China (No.2018YFB1105100)the National Natural Science Foundation of China (No.51975246)+2 种基金the Advanced Manufacturing Project of Provincial School Construction of Jilin Province (No. SXGJSF2017-2)the Program for JLU Science and Technology Innovative Research Team (2019TD-34)the China Postdoctoral Science Foundation Funded Project (No. 2016M590256)
文摘For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.
文摘Barchan dune is one of the basic forms of eolian landform, it is usually moulded by highconcentration nonsaturated windsand flow. The formation process of barchan dune begins from “wavegrain duality” of windsand movement, and goes through two developmental stages of sand material accumulating (highconcertration saturated windsand flow) and dune form moulding (highconcentration nonsaturated windsand flow), i.e. the processes of dissipative increase and dispersive decrease. The scattered single barchan dunes on nonsandy bed surface have obvious characteristics of mobility and unstability (not including barchan sand hill). The formation of barchan dune in wind tunnel (its dune scale is one order of magnitude larger than sand ripple scale) is helpful to know the formation mechanism of barchan dunes.
基金Sponsored by National Natural Science Foundation of China(41661064)
文摘Barchan dunes are a common type of dune. There are a lot of barchan dunes at accumulated sand-belts of the oasis edge of Hexi desert area of Gansu. What is characteristic of the particle size of barchan dunes? How is this particle size characteristic formed? Characteristics of particle size were analyzed in this paper by comprehensive investigation and sampling in Hexi Corridor desert area, and repeated sampling and determination in Minqin desert area. The results showed that:(1) The particle size of 0.25–0.05 mm and particle size of 0.5–0.25 mm were the main ingredients at the surface 0–5 cm depth of barchan dunes and barchan dune chains in desert area in Hexi Corridor of Gansu. Sand in Gulang desert area was relatively finer and the particle size was quite different from that of Jinchang, Linze, Jinta and Minqin desert area;(2) The particle size was changed from coarse to fine from the bottom to the top of the dunes in the main wind direction(NW) process. i.e. there was the most silt at the top of the dunes, followed by the middle of the leeward slope. The bottom of the windward slope had the most coarse sand, followed by the middle of the windward slope. The barchan dunes were changed from coarse to fine, then from fine to coarse from the bottom to the top of the dunes in the reverse wind direction(SE) process, i.e. there was the most silt in the middle of the windward slope, followed by the top of sand dunes. The bottom of the windward slope had the most coarse sand, followed by the middle of the windward slope. The standard deviation and coefficient of variation of sand dune particle size in the main wind direction process was larger, and the standard deviation and coefficient of variation of sand dune particle size in the reverse wind direction process was smaller;(3) The two processes of the main wind direction(NW) and the reverse wind direction(SE) led to alternating changes in particle size in various parts of the dunes. Two different conclusions on particle size distribution of barchan dunes in windward slope were due to the observation season differences.
基金Supported by Special Project for Preceding Study of 973 Program "Stability Research of Tall Barchan Dune at Oasis Fringe(2014CB460611)National Natural Science Foundation of China "Climate Factors and Their Ecological Effects on Formation of Accumulation Sand-belt at Oasis Edge of Minqin(41261102)
文摘[ Objective ] The paper was to study the particle size characteristics of barchan dune and its formation mechanism in Hexi desert area d Gansu. [ Method] Through particle size measurement and wind speed flow field observation d dune, the particle size differences of various sampling plots and various parts of dune were analyzed using analysis of variance, and the relationship between particle size and wind speed was analyzed using correlation coefficient method. [ Result] （ 1 ） Barehan dune and barehan chains in Hexi desert area of Gansu were mainly consisted of fine sands and medium sands at the depth of 0 -5 cm： the sand particle in Gulang desert area was fine, which had significant difference with that in Jinchang, Linze, Jinta and Minqin desert areas. （2） Medium sands gradually increased from the bottom of windward slope to the dune peak in both barchan dune and barchan chain. On the windward slope of barehan dune, fine sands gradual- ly increased from the middle to both sides, while coarse sands and medium sands gradually decreased. On the windward slope of barehan chain, fine sands first de- creased then increased from the middle to NE side, but first increased then decreased from the middle to SW side. （3） In terma of particle size, there were great variations between fine sands and coarse sands ; for dune parts, there were great variations between dune peak and leewant slope toe; for dune types, the variation of fine sands in various parts of barchan chain was greater than that of barchan dune, while differentiation degree of medium sands and fine sands was greater than that of barchan dune. The particle size of fine sands was positively correlated with wind speed, and that of medium sands was negatively correlated with wind speed. [ Conclusion] The formation environment of particle size of berehan dune mainly included sand source and dynmnic source, and wind speed was the dynamic source for particle size distribution of barchan dune.
基金funding supports from the NSFC(92052107,51806138)。
文摘As continuous of the previous sand-dune-inspired design,the Barchan-Dune-Shaped Injection Compound(BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically.While the public 777-shaped hole was served as a baseline,the BDSIC’s endwall effectiveness was assessed at various blowing ratios.Experiments were performed in a single-passage transonic wind tunnel using pressure-sensitive paint(PSP)technique.Carbon dioxide was used as coolant with density ratio of DR=1.53.The purge slot’s blowing ratio was fixed at M=0.3,but the coolant holes were adjusted within M=0.5–2.0.The measured experimental results indicate that the film distribution at the endwall is strongly affected by the passage flow structures.The BDSIC holes demonstrate much higher film effectiveness than the 777-shaped holes for all blowing ratios,~30%enhancement for regionally averaged effectiveness at M=1.0 and~26%at M=2.0.As shown by the numerical results,the existence of BDSIC reduced the coolant penetration effect at a higher blowing ratio.Coolant was deflected and its momentum increased in the streamwise direction,therefore providing more robust film coverage over the endwall region.The anti-counter-rotating vortex pair induced by the BDSIC further stabilized the coolant film and increased the coolant spreading downstream.
