This article describes an experimental study on friction and heat transfer performances of a transitional airflow in a rectangular channel with stagger-arrayed short pin fins. Friction factors, average Nusselt numbers...This article describes an experimental study on friction and heat transfer performances of a transitional airflow in a rectangular channel with stagger-arrayed short pin fins. Friction factors, average Nusselt numbers and overall thermal performances of the transitional flow are obtained. The experimental study has showed that the pin fins enhance the heat transfer performance sig- nificantly, however increasing the flow frictional resistance considerably. After comparing the experimental results with the p...展开更多
Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimen...Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.展开更多
It is observed that the feather surface exhibits anisotropic resistances for the streamwise and spanwise flows.To obtain a qualitative understanding about the effect of this anisotropic resistance feature of surface o...It is observed that the feather surface exhibits anisotropic resistances for the streamwise and spanwise flows.To obtain a qualitative understanding about the effect of this anisotropic resistance feature of surface on the boundary-layer transitional flow over a flat plate,a simple phenomenological model for the anisotropic resistance is established in this paper.By means of the large eddy simulation(LES)with high-order accurate finite difference method,the numerical investigations are conducted.The numerical results show that with the spanwise resistance hindering the formation of vortexes,the transition from laminar flow to turbulent flow can be delayed,and turbulence is weakened when the flow becomes fully turbulent,which leads to significant drag reduction for the plate.On the contrary,the streamwise resistance renders the flow less stable,which leads to the earlier transition and enhances turbulence in the turbulent region,causing a drag increase for the plate.Thus,it is indicated that a surface with large resistance for spanwise flow and small resistance for streamwise flow can achieve significant drag reduction.The present results highlight the anisotropic resistance characteristic near the feather surface for drag reduction,and shed a light on the study of bird’s efficient flight.展开更多
The terminal velocity has been widely used in extensive fields, but the complexity of drag coefficient expression leads to the calculation of terminal velocity in transitional flow （1 〈 Re ≤ 1000） with much more d...The terminal velocity has been widely used in extensive fields, but the complexity of drag coefficient expression leads to the calculation of terminal velocity in transitional flow （1 〈 Re ≤ 1000） with much more difficulty than those in laminar flow （Re ≤ 1） and turbulent flow （Re ≥ 1000）. This paper summarized and compared 24 drag coefficient correlations, and developed an expression for calculating the terminal velocity in transitional flow, and also analyzed the effects of particle density and size, fluid density and viscosity on terminal velocity. The results show that 19 of 24 previously published correlations for drag coefficient have good prediction performance and can be used for calculating the terminal velocity in the entire transitional flow with higher accuracy. Adapting two dimensionless parameters （w＊, d＊）, a proposed explicit correlation, w＊=-25.68654 × exp （-d＊/77.02069）＋ 24.89826, is attained in transitional flow with good performance, which is helpful in calculating the terminal velocity.展开更多
A new algebraic transition model is proposed based on a Structural Ensemble Dynamics(SED)theory of wall turbulence,for accurately predicting the hypersonic flow heat transfer on cone.The model defines the eddy viscosi...A new algebraic transition model is proposed based on a Structural Ensemble Dynamics(SED)theory of wall turbulence,for accurately predicting the hypersonic flow heat transfer on cone.The model defines the eddy viscosity in terms of a two-dimensional multi-regime distribution of a Stress Length(SL)function,and hence is named as SED-SL.This paper presents clear evidence of precise predictions of transition onset location and peak heat flux of a wide range of hypersonic Transitional Boundary Layers(TrBL)around straight cone at zero incidence,to an unprecedented accuracy as validated by over 70 measurements for varying five crucial influential factors(Mach number,temperature ratio,cone half angle,nose Reynolds number and noise level).The results demonstrate the universality of the postulated multi-regime similarity structure,in characterizing not only the spatial non-uniform distribution of the eddy viscosity in hypersonic TrBL on cone,but also the dependence of the transition onset location on the five influential factors.The latter yields a novel correlation formula for transition center Reynolds number which takes similar functional form as the SL function within the symmetry approach.It is concluded that the SED-SL model simulates TrBL around cone with uniformly high accuracy,and then points out to an optimistic alternative way to construct hypersonic transition model.展开更多
Hilly terrain pipeline is a common form of pipeline in oil and gas storage and transportation industry.Due to the hilly terrain influence, the liquid at the elbow of the gathering pipeline is easy to flow back and acc...Hilly terrain pipeline is a common form of pipeline in oil and gas storage and transportation industry.Due to the hilly terrain influence, the liquid at the elbow of the gathering pipeline is easy to flow back and accumulate to form slug flow, so it is necessary to remove the accumulated liquid by gas purging. In this paper, experiment is carried out in hilly terrain pipelines. Three flow patterns of stratified flow, slug flow and stratified entrained flow are observed. The process of gas purging accumulated liquid is divided into four stages, namely liquid accumulation, liquid rising, continuous outflow and tail outflow. At the same time, the flow pattern maps of each stage are drawn. The pressure drop signal is analyzed in time domain and frequency domain, and the contour map of pressure drop distribution is drawn. It is found that the ratio of range to average value can well distinguish the occurrence range of each flow pattern.Based on visualization, the transition process of slug flow to stratified flow and stratified entrained flow is studied, and the transition boundary prediction model is established. An image processing method is proposed to convert the image signal into a similarity curve, and PSD analysis is performed to calculate the slug frequency. The normal distribution is used to fit the slug frequency, and the predicted correlation is in good agreement with the experimental data.展开更多
On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junc...On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junction angle, and the discharge ratio was suggestedwhich agrees well with the experimental results. The results calculated by the present formulationfor the depth ratio were compared with the results of earlier one-dimensional formulations andexperiments. It is found that the present results coincide better with experiments than those ofothers.展开更多
The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry （LDV） is used for the study, focusing on the att...The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry （LDV） is used for the study, focusing on the attenuation characteristics of the axial velocity, the variation of the velocity gradient, the effect of the angle between the axis and the resultant velocity vector, and the relationship between the energy coefficient and the flow state. The attenuation characteristics of the axial velocity along the radial direction are obtained. It is shown that with the increase of the Reynolds number, the change rate of the velocity gradient slows down with a similar distribution, and a rapid decrease is seen in the near wall region. The amplitude and the frequency of the angular variation are obviously improved with the increase of the Reynolds number. The instability of the velocity field is enhanced with the increase of the energy coefficient.展开更多
Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat ...Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process(LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2spiral wound heat exchanger.The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.展开更多
The investigation is intended to verify a coupled solver developed for turbines to illustrate how transition exerts effects on the predicted thermal loads. The solver couples the N-S solver named HIT-3D, with a therma...The investigation is intended to verify a coupled solver developed for turbines to illustrate how transition exerts effects on the predicted thermal loads. The solver couples the N-S solver named HIT-3D, with a thermal conduction module using the finite difference method. Three operating conditions of the NASA-MarkII vane are selected to be the cases for tests. The models used in the simulations include Baldwin-Lomax (B-L) algebraic model, q-ω low-Re model and B-L & Abu-Ghannam and Shaw (AGS) model. The pre...展开更多
The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine...The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.展开更多
The predictions of the multiple-regime flows from continuum regime to free molecular regime are crucial for the aerodynamic design in a large number of engineering applications,such as the near-space craft,the ultra-l...The predictions of the multiple-regime flows from continuum regime to free molecular regime are crucial for the aerodynamic design in a large number of engineering applications,such as the near-space craft,the ultra-low orbit spacecraft and the micro-electro-mechanical systems(MEMS).Since the essence of this multiple-regime problem is a complex system composed by different scales and mechanics,the modeling and numerical prediction of these multiple-regime flows are very challenging at both theoretical and practical levels.Moreover,the single flow field with multiple flow regimes will make the problem extremly complicated.Unfortunately,this typical flow field is very common in hypersonic application and important for the development of multiple-regime aerodynamics.On the other hand,both the constructions of the low density wind tunnel with high enthalpy and the high altitude flight experiment are also very challenging at the present stage.Therefore,the researches on the multiple-regime flows and the corresponding complex science hit a worldwide bottleneck.This paper reviews the breakthroughs in the computational methods for multiple-regime flows in the last ten years,which can be used as numerical experimental tools for studying the multiple-scale flow mechanism and providing data for aerodynamic designs and thermal protections.This paper focuses on the progress of the unified wave-particle methods established in recent years,which are proved to be both accurate and efficient for multiple-regime flows with extremly high speed.展开更多
This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined...This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.展开更多
Aqueous foam is broadly applicable to enhanced oil recovery(EOR).The rheology of foam as a function of foam quality,gas and liquid velocities,and surfactant concentration constitute the foundation of its application.T...Aqueous foam is broadly applicable to enhanced oil recovery(EOR).The rheology of foam as a function of foam quality,gas and liquid velocities,and surfactant concentration constitute the foundation of its application.The great variations of the above factors can affect the effectiveness of N2 foam in EOR continuously in complex formations,which is rarely involved in previous relevant studies.This paper presents an experimental study of foam flow in porous media by injecting pre-generated N2 foam into a sand pack under the conditions of considering a wide range of gas and liquid velocities and surfactant concentrations.The results show that in a wide range of gas and liquid velocities,the pressure gradient contours are L-shaped near the coordinate axes,but V-shaped in other regions.And the surfactant concentration is a strong factor influencing the trend of pressure gradient contours.Foam flow resistance is very sensitive to the surfactant concentration in both the high-and low-foam quality regime,especially when the surfactant concentration is less than CMC.The foam quality is an important variable to the flow resistance obtained.There exists a transition point from low-to high-quality regime in a particular flow system,where has the maximum flow resistance,the corresponding foam quality is called transition foam quality,which increases as the surfactant concentration increases.The results can add to our knowledge base of foam rheology in porous media,and can provide a strong basis for the field application of foams.展开更多
In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been conducted.The...In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been conducted.The former were carried out using an open circulating water tank experimental platform and a single cylinder and square column as geometrical models(their characteristic length being D).The latter were based on the well-known SIMPLE algorithm for incompressible flow.The results show that the gap ratio is an important factor affecting the wake characteristics of near-wall bluff bodies.When the gap ratio is small,the influence of the wall on the bluff body wake is large.With an increase in the gap extension,periodic vortex shedding is enabled and heat transfer is strengthened accordingly;in addition,the vortex shedding period is larger for the square column.The square column displays hysteresis compared with the cylinder at the same gap ratio(the critical gap ratio of cylinder is 0.2~0.4,while that of square column is 0.40.6).展开更多
The research on the multiphase flow characteristics of hydrate slurry is the key to implementing the risk prevention and control technology of hydrate slurry in deep-water oil and gas mixed transportation system.This ...The research on the multiphase flow characteristics of hydrate slurry is the key to implementing the risk prevention and control technology of hydrate slurry in deep-water oil and gas mixed transportation system.This paper established a geometric model based on the high-pressure hydrate slurry experimental loop.The model was used to carry out simulation research on the flow characteristics of gas-liquid-solid three-phase flow.The specific research is as follows:Firstly,the effects of factors such as slurry flow velocity,hydrate particle density,hydrate particle size,and hydrate volume fraction on the stratified smooth flow were specifically studied.Orthogonal test obtained particle size has the most influence on the particle concentration distribution.The slurry flow velocity is gradually increased based on stratified smooth flow.Various flow patterns were observed and their characteristics were analyzed.Secondly,increasing the slurry velocity to 2 m/s could achieve the slurry flow pattern of partial hydrate in the pipeline transition from stratified smooth flow to wavy flow.When the flow rate increases to 3 m/s,a violent wave forms throughout the entire loop.Based on wave flow,as the velocity increased to 4 m/s,and the flow pattern changed to slug flow.When the particle concentration was below 10%,the increase of the concentration would aggravate the slug flow trend;if the particle concentration was above 10%,the increase of the concentration would weaken the slug flow trend,the increase of particle density and liquid viscosity would weaken the tendency of slug flow.The relationship between the pressure drop gradients of several different flow patterns is:slug flow>wave flow>stratified smooth flow.展开更多
We investigated the influence of an inserted bar on the hopper flow experimentally.Three geometrical parameters,size of upper outlet D1,size of lower outlet D0,and the height of bar H,are variables here.With varying H...We investigated the influence of an inserted bar on the hopper flow experimentally.Three geometrical parameters,size of upper outlet D1,size of lower outlet D0,and the height of bar H,are variables here.With varying H we found three regimes:one transition from clogging to a surface flow and another transition from a surface flow to a dense flow.For the dense flow,the flow rate follows Beverloo’s law and there is a saturation of inclination of free surfaceθ.We plotted the velocity field and there is a uniform linear relation between the particle velocity and depth from the free surface.We also found that the required value of D_(1) to guarantee the connectivity of flow is little smaller than D_(0).For the transition from a surface flow to a dense flow,there is a jump of flow rate and the minimumθfor flowing is two degrees larger than the repose angle.展开更多
Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the trans...Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.展开更多
An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate v...An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate values of the scaling lengths associated with vortex shedding and shear layer frequencies to predict the power law relationship with Reynolds number. The predicted results are in good agreement with experimental results. The findings will provide a greater insight into the overall phenomenon involved.展开更多
Accurate and real-time passenger flow prediction of rail transit is an important part of intelligent transportation systems(ITS).According to previous studies,it is found that the prediction effect of a single model i...Accurate and real-time passenger flow prediction of rail transit is an important part of intelligent transportation systems(ITS).According to previous studies,it is found that the prediction effect of a single model is not good for datasets with large changes in passenger flow characteristics and the deep learning model with added influencing factors has better prediction accuracy.In order to provide persuasive passenger flow forecast data for ITS,a deep learning model considering the influencing factors is proposed in this paper.In view of the lack of objective analysis on the selection of influencing factors by predecessors,this paper uses analytic hierarchy processes(AHP)and one-way ANOVA analysis to scientifically select the factor of time characteristics,which classifies and gives weight to the hourly passenger flow through Duncan test.Then,combining the time weight,BILSTM based model considering the hourly travel characteristics factors is proposed.The model performance is verified through the inbound passenger flow of Ningbo rail transit.The proposed model is compared with many current mainstream deep learning algorithms,the effectiveness of the BILSTM model considering influencing factors is validated.Through comparison and analysis with various evaluation indicators and other deep learning models,the results show that the R2 score of the BILSTM model considering influencing factors reaches 0.968,and the MAE value of the BILSTM model without adding influencing factors decreases by 45.61%.展开更多
基金National Natural Science Foundation of China (50806045)
文摘This article describes an experimental study on friction and heat transfer performances of a transitional airflow in a rectangular channel with stagger-arrayed short pin fins. Friction factors, average Nusselt numbers and overall thermal performances of the transitional flow are obtained. The experimental study has showed that the pin fins enhance the heat transfer performance sig- nificantly, however increasing the flow frictional resistance considerably. After comparing the experimental results with the p...
文摘Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.
基金Project supported by the National Natural Science Foundation of China (No.12072281)the Foundation of National Key Laboratory of Science and Technology on Aerodynamic Design and Research (No.614220121030224)the Fundamental Research Funds for the Central Universities of China (No.D5000220178)。
文摘It is observed that the feather surface exhibits anisotropic resistances for the streamwise and spanwise flows.To obtain a qualitative understanding about the effect of this anisotropic resistance feature of surface on the boundary-layer transitional flow over a flat plate,a simple phenomenological model for the anisotropic resistance is established in this paper.By means of the large eddy simulation(LES)with high-order accurate finite difference method,the numerical investigations are conducted.The numerical results show that with the spanwise resistance hindering the formation of vortexes,the transition from laminar flow to turbulent flow can be delayed,and turbulence is weakened when the flow becomes fully turbulent,which leads to significant drag reduction for the plate.On the contrary,the streamwise resistance renders the flow less stable,which leads to the earlier transition and enhances turbulence in the turbulent region,causing a drag increase for the plate.Thus,it is indicated that a surface with large resistance for spanwise flow and small resistance for streamwise flow can achieve significant drag reduction.The present results highlight the anisotropic resistance characteristic near the feather surface for drag reduction,and shed a light on the study of bird’s efficient flight.
文摘The terminal velocity has been widely used in extensive fields, but the complexity of drag coefficient expression leads to the calculation of terminal velocity in transitional flow （1 〈 Re ≤ 1000） with much more difficulty than those in laminar flow （Re ≤ 1） and turbulent flow （Re ≥ 1000）. This paper summarized and compared 24 drag coefficient correlations, and developed an expression for calculating the terminal velocity in transitional flow, and also analyzed the effects of particle density and size, fluid density and viscosity on terminal velocity. The results show that 19 of 24 previously published correlations for drag coefficient have good prediction performance and can be used for calculating the terminal velocity in the entire transitional flow with higher accuracy. Adapting two dimensionless parameters （w＊, d＊）, a proposed explicit correlation, w＊=-25.68654 × exp （-d＊/77.02069）＋ 24.89826, is attained in transitional flow with good performance, which is helpful in calculating the terminal velocity.
基金supported by the National Numerical WindTunnel Project,China(No.NNW2019ZT1-A03)the National Natural Science Foundation of China(Nos.91952201,11372008 and 11452002).
文摘A new algebraic transition model is proposed based on a Structural Ensemble Dynamics(SED)theory of wall turbulence,for accurately predicting the hypersonic flow heat transfer on cone.The model defines the eddy viscosity in terms of a two-dimensional multi-regime distribution of a Stress Length(SL)function,and hence is named as SED-SL.This paper presents clear evidence of precise predictions of transition onset location and peak heat flux of a wide range of hypersonic Transitional Boundary Layers(TrBL)around straight cone at zero incidence,to an unprecedented accuracy as validated by over 70 measurements for varying five crucial influential factors(Mach number,temperature ratio,cone half angle,nose Reynolds number and noise level).The results demonstrate the universality of the postulated multi-regime similarity structure,in characterizing not only the spatial non-uniform distribution of the eddy viscosity in hypersonic TrBL on cone,but also the dependence of the transition onset location on the five influential factors.The latter yields a novel correlation formula for transition center Reynolds number which takes similar functional form as the SL function within the symmetry approach.It is concluded that the SED-SL model simulates TrBL around cone with uniformly high accuracy,and then points out to an optimistic alternative way to construct hypersonic transition model.
基金supported by the Basic Science Center Program for Ordered Energy Conversion of the National Natural Science Foundation of China(No.52488201)the National Natural Science Foundation of China(No.52422606).
文摘Hilly terrain pipeline is a common form of pipeline in oil and gas storage and transportation industry.Due to the hilly terrain influence, the liquid at the elbow of the gathering pipeline is easy to flow back and accumulate to form slug flow, so it is necessary to remove the accumulated liquid by gas purging. In this paper, experiment is carried out in hilly terrain pipelines. Three flow patterns of stratified flow, slug flow and stratified entrained flow are observed. The process of gas purging accumulated liquid is divided into four stages, namely liquid accumulation, liquid rising, continuous outflow and tail outflow. At the same time, the flow pattern maps of each stage are drawn. The pressure drop signal is analyzed in time domain and frequency domain, and the contour map of pressure drop distribution is drawn. It is found that the ratio of range to average value can well distinguish the occurrence range of each flow pattern.Based on visualization, the transition process of slug flow to stratified flow and stratified entrained flow is studied, and the transition boundary prediction model is established. An image processing method is proposed to convert the image signal into a similarity curve, and PSD analysis is performed to calculate the slug frequency. The normal distribution is used to fit the slug frequency, and the predicted correlation is in good agreement with the experimental data.
文摘On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junction angle, and the discharge ratio was suggestedwhich agrees well with the experimental results. The results calculated by the present formulationfor the depth ratio were compared with the results of earlier one-dimensional formulations andexperiments. It is found that the present results coincide better with experiments than those ofothers.
基金supported by the National Natural Science Foundation of China(Grant No.10972123)
文摘The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry （LDV） is used for the study, focusing on the attenuation characteristics of the axial velocity, the variation of the velocity gradient, the effect of the angle between the axis and the resultant velocity vector, and the relationship between the energy coefficient and the flow state. The attenuation characteristics of the axial velocity along the radial direction are obtained. It is shown that with the increase of the Reynolds number, the change rate of the velocity gradient slows down with a similar distribution, and a rapid decrease is seen in the near wall region. The amplitude and the frequency of the angular variation are obviously improved with the increase of the Reynolds number. The instability of the velocity field is enhanced with the increase of the energy coefficient.
基金supported by the National Natural Science Foundation of China(52304067,62273213)the Natural Science Foundation of Shandong Province of China(ZR2021QE073)+1 种基金the Natural Science Foundation of Shandong Province for Innovation and Development Joint Funds(ZR2022LZH001)the China Postdoctoral Science Foundation(2023M732111)。
文摘Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process(LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2spiral wound heat exchanger.The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.
基金National Natural Science Foundation of China (50476028, 50576017, 50706009)
文摘The investigation is intended to verify a coupled solver developed for turbines to illustrate how transition exerts effects on the predicted thermal loads. The solver couples the N-S solver named HIT-3D, with a thermal conduction module using the finite difference method. Three operating conditions of the NASA-MarkII vane are selected to be the cases for tests. The models used in the simulations include Baldwin-Lomax (B-L) algebraic model, q-ω low-Re model and B-L & Abu-Ghannam and Shaw (AGS) model. The pre...
基金Supported by the Petrochina Science and Technology Project(2021DJ18).
文摘The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12172301,11902266,12072283,and 11902264)the 111 Project of China(Grant No.B17037).
文摘The predictions of the multiple-regime flows from continuum regime to free molecular regime are crucial for the aerodynamic design in a large number of engineering applications,such as the near-space craft,the ultra-low orbit spacecraft and the micro-electro-mechanical systems(MEMS).Since the essence of this multiple-regime problem is a complex system composed by different scales and mechanics,the modeling and numerical prediction of these multiple-regime flows are very challenging at both theoretical and practical levels.Moreover,the single flow field with multiple flow regimes will make the problem extremly complicated.Unfortunately,this typical flow field is very common in hypersonic application and important for the development of multiple-regime aerodynamics.On the other hand,both the constructions of the low density wind tunnel with high enthalpy and the high altitude flight experiment are also very challenging at the present stage.Therefore,the researches on the multiple-regime flows and the corresponding complex science hit a worldwide bottleneck.This paper reviews the breakthroughs in the computational methods for multiple-regime flows in the last ten years,which can be used as numerical experimental tools for studying the multiple-scale flow mechanism and providing data for aerodynamic designs and thermal protections.This paper focuses on the progress of the unified wave-particle methods established in recent years,which are proved to be both accurate and efficient for multiple-regime flows with extremly high speed.
基金supported by the National Natural Science Foundation of China(Project No.52166004)the National Key Research and Development Program of China(Project No.2022YFC3902000)the Major Science and Technology Special Project of Yunnan Province(Project Nos.202202AG050007,202202AG050002).
文摘This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.
基金financially supported by National Natural Science Foundation of China(No.U20B6003).
文摘Aqueous foam is broadly applicable to enhanced oil recovery(EOR).The rheology of foam as a function of foam quality,gas and liquid velocities,and surfactant concentration constitute the foundation of its application.The great variations of the above factors can affect the effectiveness of N2 foam in EOR continuously in complex formations,which is rarely involved in previous relevant studies.This paper presents an experimental study of foam flow in porous media by injecting pre-generated N2 foam into a sand pack under the conditions of considering a wide range of gas and liquid velocities and surfactant concentrations.The results show that in a wide range of gas and liquid velocities,the pressure gradient contours are L-shaped near the coordinate axes,but V-shaped in other regions.And the surfactant concentration is a strong factor influencing the trend of pressure gradient contours.Foam flow resistance is very sensitive to the surfactant concentration in both the high-and low-foam quality regime,especially when the surfactant concentration is less than CMC.The foam quality is an important variable to the flow resistance obtained.There exists a transition point from low-to high-quality regime in a particular flow system,where has the maximum flow resistance,the corresponding foam quality is called transition foam quality,which increases as the surfactant concentration increases.The results can add to our knowledge base of foam rheology in porous media,and can provide a strong basis for the field application of foams.
基金This work was supported by National Natural Science Foundation of China(Grant No.51476080).
文摘In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been conducted.The former were carried out using an open circulating water tank experimental platform and a single cylinder and square column as geometrical models(their characteristic length being D).The latter were based on the well-known SIMPLE algorithm for incompressible flow.The results show that the gap ratio is an important factor affecting the wake characteristics of near-wall bluff bodies.When the gap ratio is small,the influence of the wall on the bluff body wake is large.With an increase in the gap extension,periodic vortex shedding is enabled and heat transfer is strengthened accordingly;in addition,the vortex shedding period is larger for the square column.The square column displays hysteresis compared with the cylinder at the same gap ratio(the critical gap ratio of cylinder is 0.2~0.4,while that of square column is 0.40.6).
基金supported by the National Natural Science Foundation of China(Grant No.52274061&52004039&51974037)China Postdoctoral Science Foundation(Grant No.2023T160717&2021M693908)+1 种基金The major project of universities affiliated to Jiangsu Province basic science(natural science)research(Grant No.21KJA440001)Jiangsu Qinglan Project,Changzhou Longcheng Talent Plan-Youth Science and Technology Talent Recruitment Project.
文摘The research on the multiphase flow characteristics of hydrate slurry is the key to implementing the risk prevention and control technology of hydrate slurry in deep-water oil and gas mixed transportation system.This paper established a geometric model based on the high-pressure hydrate slurry experimental loop.The model was used to carry out simulation research on the flow characteristics of gas-liquid-solid three-phase flow.The specific research is as follows:Firstly,the effects of factors such as slurry flow velocity,hydrate particle density,hydrate particle size,and hydrate volume fraction on the stratified smooth flow were specifically studied.Orthogonal test obtained particle size has the most influence on the particle concentration distribution.The slurry flow velocity is gradually increased based on stratified smooth flow.Various flow patterns were observed and their characteristics were analyzed.Secondly,increasing the slurry velocity to 2 m/s could achieve the slurry flow pattern of partial hydrate in the pipeline transition from stratified smooth flow to wavy flow.When the flow rate increases to 3 m/s,a violent wave forms throughout the entire loop.Based on wave flow,as the velocity increased to 4 m/s,and the flow pattern changed to slug flow.When the particle concentration was below 10%,the increase of the concentration would aggravate the slug flow trend;if the particle concentration was above 10%,the increase of the concentration would weaken the slug flow trend,the increase of particle density and liquid viscosity would weaken the tendency of slug flow.The relationship between the pressure drop gradients of several different flow patterns is:slug flow>wave flow>stratified smooth flow.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11705256 and 11905272)National Postdoctoral Program for Innovative Talents,China(Grant No.BX201700258)West Light Foundation of the Chinese Academy of Sciences(Grant No.2018-98)。
文摘We investigated the influence of an inserted bar on the hopper flow experimentally.Three geometrical parameters,size of upper outlet D1,size of lower outlet D0,and the height of bar H,are variables here.With varying H we found three regimes:one transition from clogging to a surface flow and another transition from a surface flow to a dense flow.For the dense flow,the flow rate follows Beverloo’s law and there is a saturation of inclination of free surfaceθ.We plotted the velocity field and there is a uniform linear relation between the particle velocity and depth from the free surface.We also found that the required value of D_(1) to guarantee the connectivity of flow is little smaller than D_(0).For the transition from a surface flow to a dense flow,there is a jump of flow rate and the minimumθfor flowing is two degrees larger than the repose angle.
文摘Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.
文摘An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate values of the scaling lengths associated with vortex shedding and shear layer frequencies to predict the power law relationship with Reynolds number. The predicted results are in good agreement with experimental results. The findings will provide a greater insight into the overall phenomenon involved.
基金supported by the Program of Humanities and Social Science of Education Ministry of China(Grant No.20YJA630008)the Ningbo Natural Science Foundation of China(Grant No.202003N4142)+1 种基金the Natural Science Foundation of Zhejiang Province,China(Grant No.LY20G010004)the K.C.Wong Magna Fund in Ningbo University,China.
文摘Accurate and real-time passenger flow prediction of rail transit is an important part of intelligent transportation systems(ITS).According to previous studies,it is found that the prediction effect of a single model is not good for datasets with large changes in passenger flow characteristics and the deep learning model with added influencing factors has better prediction accuracy.In order to provide persuasive passenger flow forecast data for ITS,a deep learning model considering the influencing factors is proposed in this paper.In view of the lack of objective analysis on the selection of influencing factors by predecessors,this paper uses analytic hierarchy processes(AHP)and one-way ANOVA analysis to scientifically select the factor of time characteristics,which classifies and gives weight to the hourly passenger flow through Duncan test.Then,combining the time weight,BILSTM based model considering the hourly travel characteristics factors is proposed.The model performance is verified through the inbound passenger flow of Ningbo rail transit.The proposed model is compared with many current mainstream deep learning algorithms,the effectiveness of the BILSTM model considering influencing factors is validated.Through comparison and analysis with various evaluation indicators and other deep learning models,the results show that the R2 score of the BILSTM model considering influencing factors reaches 0.968,and the MAE value of the BILSTM model without adding influencing factors decreases by 45.61%.
