Effects of Crosswise Appendage Plate Flexibility on the Drag Reduction Characteristics of Cylinder

In engineering applications (Like an ocean riser), fluid flow around bluff bodies generates substantial resistance, which can jeopardize structural integrity, lifespan, and escalate resource consumption. Therefore, employing drag reduction measures becomes particularly crucial. This paper employs the immersed boundary method to investigate the impact of transversely oriented appendage plate flexibility on the drag of cylinders under different Reynolds numbers and distances. The results indicate that flexible appendage plate exerts drag reduction effects on the downstream cylinder, with this effect gradually diminishing as Reynolds numbers increase. At identical Reynolds numbers, the drag reduction effect initially increases and then decreases with distance, with the optimal drag reduction distance observed at D = 2.5. Compared to cylinders without appendage plate, the maximum drag reduction achieved is 30.551%. Addressing the drag reduction issue in cylinders holds significant importance for ensuring engineering structural integrity, enhancing engineering efficiency, and developing novel underwater towing systems.

INVESTIG ATIONS OF WAKE FLOWS OF A FLAT PLATE IN STEADY, OSCILLATORY AND COMBINED FLOWS

Numerical study on near wake flows of a flat plate in three kinds of oncoming flows is made by using the discrete vortex model and improved vorticity creation method. For steady oncoming flow, both gross and detailed features of the wake flow are calculated and discussed. Then, in harmonic oscillatory oncoming flow two different wake flow patterns with K_c=2,4 and 10 are obtained respectively. Our results present a new wake flow pattern for low K_c numbers (K_c<5) describing vortex shedding, pairing and moving in a period of the oscillatory flow starting from rest. The calculated drag and inertia force coefficients are closer to experimental data from the U-tube than the previous results of vortex simulation. For in-line combined oncoming flow the vortex lock-in and dynamic characteristics are simulated. The results are shown to be in good agreement with experiments.

Visual Study on Flow and Operational Characteristics of Flat Plate Closed Loop Pulsating Heat Pipes

This paper presents an experimental study including visualization on a flat plate closed loop pulsating heat pipes.It consists of a total of 40 channels with square cross section(2 mm×2 mm,165 mm long) machined directly on an aluminum plate(180 mm×120 mm×3 mm) covered by a transparent plate.The working fluid employed is ethanol.As a result,various flow patterns and their transitions are observed and found to be related to the fluid fill ratio,input heat load and the device orientation.Also the operational characteristics and working mechanism are discussed.

Simulations of the Transient Flow Generated from a Started Flat Plate

Transient operations are commonly founded in fluid machineries such as the starting, stopping, and variations of rotor speeds, etc. Flow generated from a started fiat plate is of fundamental importance. Experiments have been done to observe the flow evolution in current researches. And in order to explore the flow in more detailed scale, some vortex methods with high resolution and other numerical methods were developed to solve various related problems by some researchers. But the promotion of vortex method to engineering application is rare due to its complexity and difficulty in specifying the boundary conditions. In order to build up a method of numerical study for such problems, a simplified model is built up with a flat plate. The development of two-dimensional viscous incompressible flow generated from an impulsively started and uniformly accelerated infinitesimally thin flat plate is simulated numerically. A dynamic mesh（DM） method based on the spring analogue and local remeshing is applied to realize the mesh motion caused by the started plate. Researches show that the mesh quality will decline under large grid shear force during the updating process. To conquer this problem, a region near the plate is separated to guarantee the mesh quality at location of interest which is the innovation of the present paper. All computations at least cover a period during which the plate translates 6 times its length. The simulated instantaneous velocity profiles, flow structures and drag coefficients under several Reynolds numbers （20 ≤ Re ≤ 126） and accelerations （20 m/s2≤ a ≤ 152 m/s2） are presented and compared with existing results in literatures. Comparisons are found to be satisfactory, confirming the validity of the current proposed method（region separated DM）. The proposed DM method is firstly used to study the transient flow generated from a started flat plate and can be used in further study of transient characteristics during transient operations of turbo machineries.

AN APPROXIMATE METHOD FOR DETERMING THE VELOCITY PROFILE IN A LAMINAR BOUNDARY-LAYER ON FLAT PLATE

In this paper, using the integration method, it is sought to solve the problem for the laminar boundary_layer on a flat plate. At first, a trial function of the velocity profile which satisfies the basical boundary conditions is selected. The coefficients in the trial function awaiting decision are decided by using some numerical results of the boundary_layer differential equations. It is similar to the method proposed by Peng Yichuan, but the former is simpler. According to the method proposed by Peng, when the awaiting decision coefficients of the trial function are decided, it is sought to solve a third power algebraic equation. On the other hand, in this paper, there is only need for solving a linear algebraic equation. Moreover, the accuracy of the results of this paper is higher than that of Peng.

Pulsatile electroosmotic flow of a Maxwell fluid in a parallel flat plate microchannel with asymmetric zeta potentials

The pulsatile electroosmotic flow （PEOF） of a Maxwell fluid in a parallel flat plate microchannel with asymmetric wall zeta potentials is theoretically analyzed. By combining the linear Maxwell viscoelastic model, the Cauchy equation, and the electric field solution obtained from the linearized PoissomBoltzmann equation, a hyperbolic par- tial differential equation is obtained to derive the flow field. The PEOF is controlled by the angular Reynolds number, the ratio of the zeta potentials of the microchannel walls, the electrokinetic parameter, and the elasticity number. The main results obtained from this analysis show strong oscillations in the velocity profiles when the values of the elas- ticity number and the angular Reynolds number increase due to the competition among the elastic, viscous, inertial, and electric forces in the flow.

Features of Flow Past Square Cylinder with a Perforated Plate

A numerical investigation was performed on the reduction of the fluid forces acting on the square cylinder in the laminar flow regime with a perforated plate. The effects of geometric parameters such as the distance between the square cylinder and the perforated plate on the wake of the square cylinder were discussed. Furthermore, the flow characteristics such as the drag coefficient, lift coefficient, Strouhal number and flow pattern were obtained. It can be concluded that the drag force of the square cylinder reduces to some extent due to the addition of the perforated plate. The flow structure varies when the perforated plate is located behind the square cylinder. Moreover, the recirculation zone augments with the increase of L/D, and the vortex trace on the upper and lower surface of the square cylinder moves gradually backwards until a stable recirculation zone formed between the square cylinder and the perforated plate.

Experimentation on Optimal Configuration and Size of Thin Cylinders in Natural Convection

In this paper,an experimental study of laminar,steady state natural convection heat transfer from heated thin cylinders in an infinite air medium has been reported.Two electrically heated cylinders having the same slenderness ratio(L/D)i.e.6.1 but different diameters i.e.3.8 cm and 5.08 cm were used.105 experiments were carried out to study the effect of diameter and inclination angle of thin cylinder on natural convection heat transfer.After mandatory corrections of radiation and endcap heat losses,convective heat transfer results were presented in the form of local and average dimensionless numbers.For vertical configuration of thin cylinder,Nusselt number was varied from 52.99 to 95.10 corresponding to 1.28×10^(8)≤Ra*L≤1.08×10^(10).While for horizontal configuration,Nusselt number was varied from 10.74 to 17.78 corresponding to 9.42×10^(4)≤Ra*D≤8.17×10^(6).Results were compared with the published data and found satisfactory as the maximum percentage difference was only 3.09%.The essence of research is that the heat transfer coefficient increases with decrease in diameter and increase in inclination angle.Smoke flow visualization was done to capture patterns of fluid flow.Finally,comparison was made to quantify increase in Nusselt number from slender cylinder as compared to the flat plate.

平板有升力绕流的Lattice Boltzmann模拟

介绍了一种不同于传统流体力学数值方法的 L attice Boltzmann流体动力学的含体积力模型 ,并用此方法模拟了平板有升力粘性绕流 。

Comparison of Rheometric Devices for Measuring the Rheological Parameters of Debris Flow Slurry

Soil samples with clay content ranging from 15% to 31%, were taken from three debris flow gullies in Southwest China. Three debris flow slurry samples were prepared and tested with four measuring systems of an Anton Paar Physica MCR301 rheometer, including the concentric cylinder system,the parallel-plate system, the vane geometry, and the ball measuring system. All systems were smoothwalled. Flow curves were plotted and yield stress was determined using the Herschel-Bulkley model,showing differences among the different systems.Flow curves from the concentric cylinder and parallelplate systems involved two distinct regions, the low shear and the high shear regions. Yield stresses determined by data fitting in the low shear region were significantly lower than the values from the inclined channel test which is a practical method for determining yield stress. Flow curves in the high shear region are close to those from the vane geometry and the ball measuring system. The fitted values of yield stress are comparable to the values from the inclined channel test. The differences are caused by wall-slip effects in the low shear region.Vane geometry can capture the stress overshoot phenomenon caused by the destruction of slurry structure, whereas end effects should be considered in the determination of yield stress. The ball measuring system can give reasonable results, and it is applicable for rheological testing of debris flow slurries.

Application of Hypothesis of Replacement at the Analysis of a Slow Flow of a Body by a Viscous Fluid

On the basis of hypothesis of replacement and the vector formula of Newton’s law for a viscous fluid the way of a finding of resistance a slow flow by an incompressible fluid of bodies of the various form is represented. Application of an offered way to calculation of a flow of various bodies is shown: a sphere, a cylinder, a oblong ellipsoid, a flat plate. Comparison with results of other authors is given.

Calculation of Turbulent Flow with Pseudo-spectral Method

This paper deals with the numerical simulation of incompressible turbulent boundary flow of a flat plate with the pseudo-spectral matrix method. In order to appear more than 10 nodes in the turbulent base-stratum and transition of 43×43 computational grids,a coordinate transformation is put up from physical panel to computational panel. Several zero turbulent models are computed comparatively. The results are credible when comparing with the previous methods.

低速湍流边界层DBD控制机制

介质阻挡放电(DBD)激励器具有重量轻、无运动部件、易用及响应快等优势,在流动控制应用中受到广泛关注。等离子体湍流边界层减阻是DBD流动控制诸多应用之一,但DBD湍流减阻机制还需进一步探究。文章通过试验研究来流速度为10 m/s时DBD激励对平板湍流边界层摩擦阻力的影响。试验使用油膜干涉法测量摩阻的变化,利用热线风速仪和粒子图像测速系统(PIV)得到边界层内速度分布。其结果显示,在等离子体激励的作用下,测得的壁面摩擦因数减小。等离子体激励通过减小边界层缓冲层和对数区的速度,减少雷诺切应力以及湍动能,抑制了相干结构的发展,从而达到减阻的效果。

高寒地区平板热管式太阳能集热系统热性能研究

基于呼和浩特地区高寒气候条件,搭建两组完全一致的平板热管式太阳能集热系统,通过实验对比分析太阳辐射强度、传热工质流量、集热板表面积尘等因素对集热器瞬时集热效率以及系统热性能的影响。结果表明,在同等外界条件下,集热器的集热效率随着工质流量的增加而增大,集热效率与太阳辐射强度变化趋势相近,随积尘密度的增加,集热板表面积尘导致系统的得热量减少,集热性能下降。

平板集热器冬季高流速运行数值模拟研究

针对平板集热器(FPSC)冬季热水收集温度不足等问题提出高流速运行方案,以期提高系统的集热性能以及全年利用率.通过CFD技术数值模拟FPSC系统在不同流速工况下(0.02~0.15 kg/s)各组件温度的变化情况,计算系统的集热效率,结合温度云图对比高流速运行的优势.结果显示,高流速运行能够减少集热损失,具有更佳的集热性能.

宽幅梳棉机的应用和维护保养

为提高梳棉机梳理质量和生产效率,介绍宽幅梳棉机的发展历程及国内外几款新型梳棉机的特点,从宽幅梳棉机喂棉箱结构设计、给棉板结构设计及固有频率计算、盖板骨架优化设计、自动检测与调节等方面阐述宽幅梳棉机的结构特征;分析Autocard SC6型宽幅梳棉机在涡流纺粘胶、赛络集聚纺、气流纺、环锭纺等品种的应用案例,并从系统应用、针布保养、质量页面、日常巡回方面提出维护保养要点。指出:宽幅梳棉机能适用多场景、多型式纺纱,通过工艺调整,可达到高质高产;宽幅梳棉机通过对喂棉箱优化,采用低惯量、高响应的给棉板,应用新型抗弯铝合金盖板骨架,配置智能传感技术等措施,分梳面积增加、分梳能力增强,高效性和稳定性提升,能实现数字化智能控制、按需维护保养。

求细气柱对垂直静止平板吹力的两种方法及与风力比较

给出求细气柱对垂直静止平板吹力的两种方法,即动量定理法与动能定理法,并指出后一种解法中的参考系切换与伽利略速度变换的思想,同时也指出这两种解法的物理前提便是细气柱为流速不太大的理想流体.作为对比,又分析给出风对圆形垂直静止平板吹力的表达式,并将其与细气柱对垂直静止平板的吹力进行对比,指出其中显著差异的原因在于物理机制上的不同——风在与平板相互作用时存在绕流现象,并且已不是理想流体,其内部在绕流后存在着明显的湍流迹象.

Experimental study on hypersonic crossflow instability over a swept flat plate by flow visualization

An experimental study on the traveling crossflow instability over a 60∘swept flat plate was conducted.The Mach number is 6,the angle of attack of the model is 5∘.The traveling crossflow waves and the secondary instability of the traveling crossflow waves were visualized by nano-tracer-based planar laser scattering(NPLS)technique.In the spanwise NPLS images,the traveling crossflow waves appeared as regular strikes,and the secondary instability appeared as small eddies attached to strikes.The wavelet transform was used to study the wavelength contents of the traveling crossflow waves.The most amplified wavelength is stable before the secondary instability happening,which is around 12 mm at Re_(∞)=3.45×10^(6)m^(−1).Besides,the Reynolds number effects on the boundary layer transition and traveling crossflow instability were discussed.

Control of vortex-induced vibrations of the cylinder by using split-ter plates immersed in the cylinder wake at low Reynolds number

The vortex-induced vibrations of a cylinder with two plates symmetrically distributed along the centerline of the wake are studied by using the fluid-structure interaction simulations on the Arbitrary Lagrangian-Eulerian method.In this study,the different geo-metrical distribution parameters of the splitter plates and inflow velocities are taken into account.The physical mechanisms of vortex-induced vibration of the cylinder with symmetrical plates are revealed from the cylinder amplitude,hydrodynamic force characteristics,vortex shedding frequency,and flow pattern modification.The results show that the dynamic interaction between the vortex shed from the oscillation cylinder and plates is responsible for the wake stabilization mechanism,and the stable wake and the dynamic response reduction of the main cylinder can be achieved at a wide range of reduced velocities by placing sym-metrical sheets at suitable locations.

高速液压缸平板节流缓冲过程的研究

探讨了一种可用于高速液压缸的平板节流的缸内缓冲装置的结构和原理 ,建立了其相应的数学模型 ,并在此基础上进行了系统仿真 ,利用仿真结果分析了模型结构参数对缓冲效果的影响 ,仿真结果与试验结果基本一致 。