共查询到20条相似文献，搜索用时 234 毫秒
1.
本文用DLR（近壁低雷诺数）型k-ε紊流模型·BFC（边界拟合曲线坐标变换）法对锥形扩散器内的紊流进行了数值仿真与分析。通过对数值仿真结果和实验结果的比较,分析不同模型常数组、模型函数组和时间步长对时均速度和紊流动能的影响。 相似文献
2.
An analysis of the instability in the Taylor-Couette flow of fiber suspensions with respect to the non-axisymmetric disturbances was performed. The constitutive model proposed by Ericksen was used to represent the role of fiber additives on the stress tensor. The generalized eigenvalue equation governing the hydrodynamic stability of the system was solved using a direct numerical procedure. The results showed that the fiber additives can suppress the instability of the flow. At the same time, the non-axisymmetric disturbance is the preferred mode that makes the fiber suspensions unstable when the ratio of the angular velocity of the outer cylinder to that of the inner cylinder is a large negative number. 相似文献
3.
This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle（RUAV）. The control objective is to let the RUAV track some pre-defined time-varying position and headingtrajectories. The proposed controller employs feedback linearization process to realize the dynamic decoupling controland applies adaptive sliding mode control to compensate for the parametric uncertainties and external disturbances.The global asymptotical stability is proved via stability analysis. Compared with the cascaded controller, the proposedcontroller demonstrates a superior tracking performance and robustness through numerical simulation in the presenceof parametric uncertainties and unknown disturbances. 相似文献
4.
Short path distillation (SPD) is a kind of high vacuum distillation method, which is suitable for the separation of high boiling, heat sensitivity and viscidity products.In this paper,through measuring the phase-averaged velocity distributions with a conditional sampling method of the particle imaging velocimetry (PIV), the liquid flow field that affects the heat and mass transfer of evaporating thin-film in an SPD evaporator is investigated.Measured results show that the flow velocities decrease rapidly apart from the wiper at different wiper velocities, the maximum velocity appears before wipers, and the quicker the wiping, the larger the flow velocity. Meanwhile, the evaluation of numerical calculations is carried out.The measured velocity distributions indicate clearly the effect of the wiper both on the flow field along its moving direction and on the vortices behind the wiper.Simulation data show that the performance of liquid flow field on the heating surface not only agrees with the experimental results well,but also can give further more information, such as the distribution of turbulent kinetic energy.In this study,turbulent kinetic energy mainly distributes before wipers and laminar flow appears far away from the wipers. 相似文献
5.
Short path distillation (SPD) is a kind of high vacuum distillation method, which is suitable for the separation of high boiling, heat sensitivity and viscidity products. In this paper ,through measuring the phase-averaged velocity distributions with a conditional sampling method of the particle imaging velocimetry ( PIV), the liquid flow field that affects the heat and mass transfer of evaporating thin-film in an SPD evaporator is investigated. Measured results show that the flow velocities decrease rapidly apart from the wiper at different wiper velocities, the maximum velocity appears before wipers, and the quicker the wiping, the larger the flow velocity. Meanwhile, the evaluation of numerical calculations is carried out. The measured velocity distributions indicate clearly the effect of the wiper both on the flow field along its moving direction and on the vortices behind the wiper. Simulation data show that the performance of liquid flow field on the heating surface not only agrees with the experimental results well, but also can give further more information, such as the distribution of turbulent kinetic energy. In this study ,turbulent kinetic energy mainly distributes before wipers and laminar flow appears far away from the wipers. 相似文献
6.
INTRODUCTION Turbulent gas-particle flows are frequently found in natural phenomena and industrial processes.Cases of cylinders in cross flows with particles occur in heat exchange equipment,including the convective zone of a fluidized-bed combustor,and in the primary superheaters,reheaters,and economizers of coal-fired boilers.Coherent structures often occur in the above-mentioned gas-particle flow,and have great effect on such different systems,while some features of tur-bulent multiphas… 相似文献
7.
本建立了一维数值模型来模拟顺直冲积渠道的冲刷过程．模型考虑了床沙的非均匀性、床面形态变化，应用该模型预测计算了冲刷过程中的床沙级配变化．模型计算结果表明床沙粗化过程不仅与水流的水力特性有关，还与床沙的颗粒大小及分布有关．模型计算结果与2组非均匀床沙水槽试验结果进行了比较，结果表明模型计算结果与试验结果符合得较好． 相似文献
8.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｔｕｒｂｕｌｅｎｔｈｅａｔｔｒａｎｓｆｅｒｏｃｃｕｒｓｉｎｔｈｅｐｒｅｓｅｎｃｅｏｆｔｈｅｒ ｍａｌｓｔｒａｔｉｆｉｃａｔｉｏｎｉｎｍａｎｙｉｍｐｏｒｔａｎｔｅｎｇｉｎｅｅｒｉｎｇａｎｄｇｅｏｐｈｙｓｉｃａｌｆｌｏｗｓ ,ｗｈｅｒｅ ,ａｓａｎｅｘａｍｐｌｅ ,ａｓｔａｂｌｅｓｔｒａｔ ｉｆｉｃａｔｉｏｎｏｃｃｕｒｓｎｅａｒｔｈｅｃｏａｓｔａｎｄａｎｕｎｓｔａｂｌｅｓｔｒａｔｉｆｉｃａ ｔｉｏｎｏｃｃｕｒｓｉｎａｃｏｎｖｅｃｔｉｖｅｌｙｄｒｉｖｅｎａｔｍｏｓｐｈｅｒｅ .Ｍｅａ… 相似文献
9.
气液两相搅拌槽内气泡直径的数值模拟 总被引：1，自引：0，他引：1
搅拌槽内气泡直径是一个很重要的参数.本文对搅拌槽内气泡直径进行了数值模拟,模拟结果表明,在搅拌槽内排出流区和循环区内模拟值同实验值的吻合情况都比较好.在模拟过程中仅考虑了湍流动能耗散率对气泡大小的影响,没有考虑到气泡本身凝并和循环过程,所以在循环区中模拟值要比实验值稍大. 相似文献
10.
Because of the complexities of fluid dynamics equations and the structure of heat exchangers, few theoretical
solutions have been acquired to specify the shell side characteristics of the rod baffle heat exchanger (RBHE)．Based on the
platform of PHEONICS version 3.5.1, a three-dimensional numerical method for predicting the turbulent fluid flow behavior
in the shell side of the rod baffle heat exchangers is developed in this paper. With this method, modeling of the tube bundle
is carried out based on the porous media concept using volumetric porosities and applicable flow resistance correlations.
Turbulence effects are modeled using a standard κ-ε model. It is shown that the simulation results and experimental results
are in good agreement in the shell side. The maximum absolute deviation value of pressure drops is less than 5%, and that
of the heat transfer coefficients is less than 8%. Furthermore, the numerical model is used to optimize the structure of the
RBHE and improves its performance. 相似文献
solutions have been acquired to specify the shell side characteristics of the rod baffle heat exchanger (RBHE)．Based on the
platform of PHEONICS version 3.5.1, a three-dimensional numerical method for predicting the turbulent fluid flow behavior
in the shell side of the rod baffle heat exchangers is developed in this paper. With this method, modeling of the tube bundle
is carried out based on the porous media concept using volumetric porosities and applicable flow resistance correlations.
Turbulence effects are modeled using a standard κ-ε model. It is shown that the simulation results and experimental results
are in good agreement in the shell side. The maximum absolute deviation value of pressure drops is less than 5%, and that
of the heat transfer coefficients is less than 8%. Furthermore, the numerical model is used to optimize the structure of the
RBHE and improves its performance. 相似文献
11.
1 Introduction The traditional segmental baffle heat exchangers(SHE) can be si mply manufactured and run reliably,but they are mainly suitable for the situation of lowerflow velocity. When fluid velocity becomes higher inthe shell side ,the pressure dropi… 相似文献
12.
The trajectory model of dispersed phase drops and the model of basic flow for drop motion between two inclined parallel plates are derived with the optimized calculation. The analytical results of direct numerical simulation indicate that the basic flow plays an important role in the drop coalescence on liquid-liquid interface. In the stratified two-phase flow field, the smaller droplets are difficult to drain the thin continuous film between the approaching droplets and bulk interfaces and eventually immerse into the trickling film to yield coalescence. They almost attain the velocity of their local surroundings. Moreover, the basic flow exerts a dominant influence on the motion of smaller droplet. The smaller droplets are easily entrained by the basic flow. On the contrary, the larger drop presents advantageous characteristics of coalescence due to its high velocity. The range of 0.3 mm δR≤ 0.75 mm is the advantageous drop coalescence condition since the rapidly varied velocity and its first derivative theoretically cause the forces acting on a drop to become imbalanced. On the other hand, the thin layer of the continuous phase drained from the interval between the drops and trickling film should not be neglected in the calculation of shearing force since it is important for drop rotation. The drop rotation is an indispensable factor in coalescence. 相似文献
13.
SMITH Eiamsa-ard PONGJET Promvonge 《浙江大学学报(A卷英文版)》2006,7(8):1406-1415
INTRODUCTION Vortex tube is a device for producing hot and cold air when compressed air flows tangentially into the vortex chamber through the inlet nozzles. This causes the vortex and swirl flow movement inside the vortex tube. The air in the middle region of the tube has lower velocity and lower temperature than the inlet air. So the air near the tube wall has higher ve-locity and higher temperature than the inlet air. The cold air in the core region of the tube flows out through the o… 相似文献
14.
Three-dimensional transient numerical simulation for gas exchange process in a four-stroke motorcycle engine 总被引：3，自引：0，他引：3
INTRODUCTION In-cylinder flow characteristics during fuel in-jection and subsequent interactions with fuel sprays and combustion are important effect on engine per-formance and exhaust emissions of an engine(Floch et al.,1998;Kim et al.,1999).Four key parameters control the flow field in an engine:the mean flow components,the stability of the mean flow,the tem-poral turbulence evolution during the intake and compression strokes,and the mean velocity near the spark gap at the time of ignit… 相似文献
15.
This paper focuses mainly on the stability analysis of two-lane traffic flow with lateral friction, which may be caused by irregular driving behavior or poorly visible road markings, and also attempts to reveal the formation mechanism of traffic jams. Firstly, a two-lane optimal velocity (OV) model without control signals is proposed and its stability condition is obtained from the viewpoint of control theory. Then delayed-feedback control signals composed of distance headway information from both lanes are added to each vehicle and a vehicular control system is designed to suppress the traffic jams. Lane change behaviors are also incorporated into the two-lane OV model and the corresponding information about distance headway and feedback signals is revised. Finally, the results of numerical experiments are shown to verify that when the stability condition is not met, the position disturbances and resulting lane change behaviors do indeed deteriorate traffic performance and cause serious traffic jams. However, once the proper delayed-feedback control signals are implemented, the traffic jams can be suppressed efficiently. 相似文献
16.
徐涛 《广东轻工职业技术学院学报》2006,5(1):6-8
采用FLUENT6．0软件对整个螺旋隔板花瓣管单管换热器的一段的流场、温度场进行数值模拟，结果显示壳程内的主体流动趋势仍是螺旋状，但在翅片附近速度场的大小和方向变化较大，证明翅片的存在激发了流体的边界层分离和湍动，从而强化了传热。 相似文献
17.
Lagrangian and Eulerian time scales were obtained from the direct numerical simulation of turbulent channel flow at two Reynolds numbers based on the friction velocity and channel half-height, Rer= 80, 100. The Lagrangian integral time scales and time microscales were compared to their Eulerian equivalents. It is found that the ratio of Lagrangian to TL Eulerian integral time scales is given by TE/TiE= 1 ＋ 0.1y＋ for y＋ ≤ 10, and that the ratios between the Lagrangian to theEulerian time microscales are almost the same irrespective of the components. Those increase with y＋ are approximated by ≈ 2.75 - 1.75 exp （-v＋/a） . These results also show that these expressions are independent of the Reynolds number. 相似文献
18.
《天津大学学报(英文版)》2015,(4)
The stability and local bifurcation of the lateral parameter-excited resonance of pipes induced by the pulsating fluid velocity and thermal load are studied. A mathematical model for a simply supported pipe is developed according to Hamilton principle. The Galerkin method is adopted to discretize the partial differential equations to the ordinary differential equations. The method of multiple scales and the singularity theory are utilized to analyze the stability and bifurcation of the trivial and non-trivial solutions. The transition sets and bifurcation diagrams are obtained both in the unfolding parameter space and physical parameter space, which can reveal the relationship between the thermal field parameter and the dynamic behaviors of the pipe. The numerical results demonstrate the accuracy of the single-mode expansion of the solution and verify the stability and local bifurcation analyses. The critical thermal rates are obtained both by the numerical simulation and the local bifurcation analysis. The natural frequency of lateral vibration decreases as the mean fluid velocity or the thermal rate increases according to the numerical results. The present work can provide valuable information for the design of the pipeline and controllers to prevent structural instability. 相似文献
19.
The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result. 相似文献
20.
INTRODUCTIONThecenteringofaparticlewhichsettlesatsmallReynoldsnumbershadbeenstudiedbyseveralresearchers.ChristophersonandDowson(1959)foundthattheoretically,whentheeffectofinertiaisnegligible ,aballachieveseccentricequilibriuninaverticaltubehavingadiameteronlyslightlyexceedingthediameteroftheball.Theyverifiedtheiranalysiswithexperiments.VaseurandCox (1977)didexperimentsonthesedimentationofasmallsphereinaverticalductofarectangularcross section .Theyobservedthatthespherealwaysmigratedtothec… 相似文献