Mechanism of Thermally Radiative Prandtl Nanofluids and Double-Diffusive Convection in Tapered Channel on Peristaltic Flow with Viscous Dissipation and Induced Magnetic Field

The application of mathematical modeling to biological fluids is of utmost importance, as it has diverse applicationsin medicine. The peristaltic mechanism plays a crucial role in understanding numerous biological flows. In thispaper, we present a theoretical investigation of the double diffusion convection in the peristaltic transport of aPrandtl nanofluid through an asymmetric tapered channel under the combined action of thermal radiation andan induced magnetic field. The equations for the current flow scenario are developed, incorporating relevantassumptions, and considering the effect of viscous dissipation. The impact of thermal radiation and doublediffusion on public health is of particular interest. For instance, infrared radiation techniques have been used totreat various skin-related diseases and can also be employed as a measure of thermotherapy for some bones toenhance blood circulation, with radiation increasing blood flow by approximately 80%. To solve the governingequations, we employ a numerical method with the aid of symbolic software such as Mathematica and MATLAB.The velocity, magnetic force function, pressure rise, temperature, solute (species) concentration, and nanoparticlevolume fraction profiles are analytically derived and graphically displayed. The results outcomes are compared withthe findings of limiting situations for verification.

Numerical Study of Viscous Wave-Making Resistance of Ship Navigation in Still Water

The prediction of a ship＇s resistance especially the viscous wave-making resistance is an important issue in CFD applications. In this paper, the resistances of six ships from hull 1 to hull 6 with different hull forms advancing in still water are numerically studied using the solver naoe-FOAM-SJTU, which was developed based on the open source code package OpenFOAM. Different components of the resistances are computed and compared while considering two speed conditions （12 kn and 16 kn）. The resistance of hull 3 is the smallest while that of hull 5 is the largest at the same speed. The results show hull 3 is a good reference for the design of similar ships, which can provide some valuable guidelines for hull form optimization.

Numerical computation and analysis of unsteady viscous flow around autonomous underwater vehicle with propellers based on sliding mesh

The flexible transmission shaft and wheel propeller are combined as the kinetic source equipment, which realizes the nmlti-motion modes of the autonomous underwater vehicle （AUV） such as vectored thruster and wheeled movement. In order to study the interactional principle between the hull and the wheel propellers while the AUV navigating in water, the computational fluid dynamics （CFD） method is used to simulate numerically the unsteady viscous flow around AUV with propellers by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and pressure with splitting of operators （PISO） algorithm based on sliding mesh. The hydrodynamic parameters of AUV with propellers such as resistance, pressure and velocity are got, which reflect well the real ambient flow field of AUV with propellers. Then, the semi-implicit method for pressure-linked equations （SIMPLE） algorithm is used to compute the steady viscous flow field of AUV hull and propellers, respectively. The computational results agree well with the experimental data, which shows that the numerical method has good accuracy in the prediction of hydrodynamic performance. The interaction between AUV hull and wheel propellers is predicted qualitatively and quantitatively by comparing the hydrodynamic parameters such as resistance, pressure and velocity with those from integral computation and partial computation of the viscous flow around AUV with propellers, which provides an effective reference to the shady on noise and vibration of AUV hull and propellers in real environment. It also provides technical support for the design of new AUVs.

Periodical streaming potential and electro-viscous effects in microchannel flow

This paper presents an analytical solution to periodical streaming potential, flow-induced electric field and velocity of periodical pressure-driven flows in twodimensional uniform microchannel based on the Poisson-Boltzmann equations for electric double layer and Navier-Stokes equation for liquid flow. Dimensional analysis indicates that electric-viscous force depends on three factors： （1） Electric-viscous number representing a ratio between maximum of electric-viscous force and pressure gradient in a steady state, （2） profile function describing the distribution profile of electro-viscous force in channel section, and （3） coupling coefficient reflecting behavior of arnplitude damping and phase offset of electro-viscous force. Analytical results indicate that flow-induced electric field and flow velocity depend on frequency Reynolds number （Re = wh^2/v）. Flow-induced electric field varies very slowly with Re when Re 〈 1, and rapidly decreases when Re 〉 1. Electro-viscous effect on flow-induced electric field and flow velocity are very significant when the rate of the channel width to the thickness of electric double layer is small.

基于STAR-CCM+的全附体潜艇水压场特性及附体影响性研究

潜艇航行引起的流场压强变化称为潜艇水压场,其特性常被应用于水雷,以实现目标探测,攻守兼备。考虑指挥台围壳、尾翼影响,以全附体艇体为研究对象,在验证性研究的基础上,基于粘流理论研究了潜艇水压场特性,揭示了附体对艇体表面、周围流场、水底流场的压强分布影响规律。结果表明:附体对艇体表面的压强分布影响显著,但影响范围局限于附体小区域,而对水底处的水压场影响仅在潜艇近底航行时才略显著,可见非近底航行工况下可忽略附体影响,实现潜艇水压场的快速预报;在研究近水面航行工况时,水面兴波对海底潜艇水压场的分布存在影响,具体影响潜艇水压场的峰值大小和位置等。

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF THE FLOW FIELD AROUND A CIRCULAR CYLINDRICAL ARTIFICIAL ISLAND UNDER THE ACTION OF WAVES AND VISCOUS CURRENT

Experimental study and theoretical research were described in the paper on the characteristics of the flow field around a vertical circular cylindrical artificial island under the . action of waves and viscous current. Flow field and hydrodynamic coefficientS of an artificial island under the action of waves and viscous current were computed and compared with those for the cases of pure viscous current and pure incident waves and those of measured resultS with good agreement.

Non-axisymmetric Homann MHD stagnation point flow of Al2O3-Cu/water hybrid nanofluid with shape factor impact

The heat transfer of Homann flow in the stagnation region of the Al2 O3-Cu/water hybrid nanofluid is investigated by adopting the Tiwari-Das model over a cylindrical disk.The effects of the nanoparticle shape,the viscous dissipation,and the nonlinear radiation are considered.The governing equations are obtained by using similarity transformations,and the numerical outcomes for the flow and the temperature field are noted by bvp4 c on MATLAB.The numerical solutions of the flow field are compared with the asymptotic behaviors of large shear-to-strain-rate ratio.The effects of variations of parameters involved are inspected for both nanofluid and hybrid nanofluid flows,temperature profiles,local Nusselt numbers,and skin frictions.It is concluded that the velocity and temperature fields in the hybrid nanophase function more rapidly than those in the nanofluid phase.

Numerical simulation of the 3D flow field in a ring die pellet mill considering viscous heating

Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow physical model was established.The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW.The distribution laws of pressure,velocity,shear rate,viscosity,viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control.The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center,and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction.There were larger velocity gradients,shear rates and viscous heating levels in the deformation and compaction zone,the negative pressure zone behind the extrusion zone and the die holes.The distribution of viscosity was opposite to that of the shear rate.The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the Z-axis direction,and the temperature increased accordingly.The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation.The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die.Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment,the relative error was less than 5%,which indicated that the numerical simulation method was reliable.

Entropy generation under the influence of radial magnetic field and viscous dissipation of generalized Couette flow in an annulus

This paper investigates the combined effect of radial magnetic field and viscous dissipation on entropy generation in horizontal co-axial cylinders of generalized Couette flow.The analytical solutions for velocity and temperature profiles are obtained and utilized to compute the entropy generation,Bejan number as well as the average entropy generation number.The effect of relevant parameters on temperature field,velocity field,entropy generation,average entropy and Bejan number are portrayed graphically and discussed.We isoflux heating near the inner surface of the fixed outer cylinder with higher dominance in the case of isoflux heating.The reverse is seen on the moving inner cylinder.

Characteristics of Nanofluids over a Non-Linearly Stretched Sheet under the Influence of Thermal Radiation and Magnetic Field

Recent studies carried out in terms of viscous flow and heat transfer of nano-fluids on the non-linear sheets. In this paper, detailed studies to understand the characteristics such as viscous flow and heat transfer of nano-fluids under the influence of thermal radiation and magnetic fields are studied using Keller-Box method. Various governing parameters affecting the viscous flow and heat transfers are drawn based on quantitative results. The raise in temperature affected the velocity to a negative value;however, the same observation was made even for the increasing magnetic field. The impact of radiation parameter is proportional seems to be proportional to temperature and it is observed to be inversely proportional with concentration.

线性液动压抛光加工的流场特性研究

分析了线性液动压抛光加工中液流对工件表面的作用形式,推导了黏性切应力和液动压力数学模型。对线性液动压抛光流场进行了数值模拟,剖析了抛光辊子尺寸以及抛光工艺参数对液动压和黏性切应力的数值及分布均匀性的影响规律。研究结果表明:液动压力和黏性切应力数值随辊子直径和辊子转速的增加而增加,与此同时其分布均匀性反而下降;抛光间隙值越小,液动压力和黏性切应力数值越大,且其分布均匀性越好。最后采用自制的线性液动压抛光实验平台,以K9玻璃为实验对象,探究了抛光加工表面形貌和表面粗糙度的创成过程。

PERIODICAL PRESSURE-DRIVEN FLOWS IN MICROCHANNEL WITH WALL SLIP VELOCITY AND ELECTRO-VISCOUS EFFECTS

In a microfluidic system, the flow slip velocity on a solid wall can be the same order of magnitude as the average velocity in the microchannel. The flow-electricity interaction in a complex microfluidic system subjected to a joint action of wall slip and electro-viscosity is an important topic. An analytical solution for the periodical pressure-driven flow in a two-dimensional uniform microchannel, with consideration of wall slip and electro-viscous effect is obtained based on the Poisson-Boltzmann equation for the Electric Double Layer （EDL） and the Navier-Stokes equations for the liquid flow. The analytic solutions agree well with the numerical solutions. The analytical results indicate that the periodical flow velocity and the Flow-Induced Electric Field （FIEF） strongly depend on the frequency Reynolds number （Re = （wh2/v ）, that is a function of the frequency, the channel size and the kinetic viscosity of fluids. For Re 〈 1, the flow velocity and the FIEF behave similarly to those in a steady flow, whereas they decrease rapidly with Re as Re 〉 1. In addition, the electro-viscous effect greatly influences the periodical flow velocity and the FIEF, particularly, when the electrokinetic radius kH is small. Furthermore, the wall slip velocity amplifies the FIEF and enhances the electro-viscous effect on the flow.

三体船阻力的数值计算研究

采用商业CFD软件FLUENT模拟了三体船周围的粘性流场,并考虑流体粘性及自由表面影响,数值预报了一艘三体船试验船模的阻力.计算中进行了2种不同侧体布置情况下船体周围流场细节的详细模拟,得到了相应情况下的船体总阻力,确定了合理的侧体位置.在此基础上,改变了侧体与主体横向间距进行了3种布置方案的相应计算,并进行比较,选取了最佳的侧体间距.通过计算结果与实验值进行的对比,验证了计算的可靠性,计算达到了船型优化的目的.

固体火箭喷管两相粘性跨音速流场计算

本文进行了固体火箭喷管两相粘性湍流跨音速流场计算.粘性的气相控制方程用隐式近似因子分解法求解,粒子方程采用跟踪粒子轨迹的特征线法求解,粘性湍流选用代数模型,气相和凝相充分地偶合.CFL数可以取500左右,收敛速度快,使粘性两相跨音速喷管流场计算耗费的机时达到工程计算可以接受的程度.通过计算,获得了在粘性和粒子同时作用下的流场参数分布.这对固体火箭发动机流场需要同时考虑粒子和粘性作用的专题研究大有裨益.

多块结构化网格在含附体水面船模粘性流场数值计算中的应用

本文使用RANS方程和剪切应力输运k-棕模型求解含附体的水面船舶粘性流场。整个计算域被分成很多区块,各个区块单独生成结构化网格,在包含不同附体部件的区块之间,网格是不匹配的,交界面处各流场变量由插值计算传递。计算中没有考虑自由液面的影响。从最后计算得到的桨盘面伴流分布结果来看,数值计算较好地反映了桨盘面流场的特征。

潜艇主艇体三维粘性流场数值计算方法研究

采用不同的湍流模型、边界条件对SUBOFF模型主艇体的七种网格模型进行了三维粘性流场数值模拟。将计算所得的艇体表面的压力系数和壁面剪应力系数沿艇长的分布与有关文献的试验结果进行了比较,并以曲线的形式展现出来。分析了湍流模型、边界条件和y+值范围对潜艇主艇体三维粘性流场数值计算结果的影响。

粘性跨音速喷管流场计算

本文继用隐式近似因子分解法成功地计算无粘跨音速喷管流场之后,用同样的方法,结合任意曲线坐标系,通过非定常方程在相当长时间后的定常解,针对矩形截面喷管和轴对称喷管粘性跨音速流场,求解了可压缩层流薄层N-S方程,获得了核心流,特别是边界层中的流动参数.对于矩形截面和轴对称两种喷管进行了计算,其结果和实验数据相当一致.将本文的方法应用到粘性两相流动计算,可望较多的节省机时.

桥区航行船舶水动力计算及分析(英文)

研究桥墩对桥区航行船舶的干扰水动力,对正确地控制船舶航迹以保证船舶安全通过桥区,具有重要的参考意义。文章基于CFD软件Fluent,采用准定常和非定常两种方法,通过数值模拟在桥墩邻域航行船舶的粘性绕流场,计算分析了桥墩对船舶的干扰水动力特性。数值结果表明,桥墩对船舶的干扰水动力与船与桥墩的相对位置紧密相关,船舶在桥墩邻域一定的范围内航行时,桥墩干扰水动力明显。

全附体潜艇粘性流场的RANS模拟及场量和涡量的校验分析

采用相同拓扑结构和相近网格质量的4套网格和5种湍流模型,对全附体Suboff潜艇粘性流场进行RANS模拟,分析了网格密度、节点空间分布规律和湍流模型对计算精度的影响,详细校验了其力积分量、速度场量和涡量特征。结果表明:网格密度最大的G4网格(140万)计算精度最高,总阻力较实验值误差为0.723%,其采用SST湍流模型时最优。计算得到的压力系数和剪切应力系数分布均与实验值吻合很好;桨盘面速度等值线分布计算精度与文献相当,轴向相对速度0.9以上的计算半径稍大于实验值,其余半径与实验吻合较好;桨盘面上0.25倍半径处速度分量沿周向分布计算精度较文献高,轴向分量与实验值吻合较好,径向分量峰值稍小于实验值,但峰值所处周向位置与实验值一致。成功捕捉到了附体端面绕流诱导对旋涡、附体叶根截面下游处项链形涡对、尾翼端面尾缘上方附着涡蹄、附体马蹄涡系、尾翼截面通道流体挤压作用诱导涡以及桨盘面涡量汇集的潜艇涡量场特征,且围壳端面绕流诱导对旋涡沿流动方向持续稳定,不影响桨盘面涡量场,均与文献中由大涡模拟模拟得到的定性结论一致。研究表明,在网格密度较大、节点分布合理、网格质量较高、湍流模型选取适当和壁面函数使用有效的条件下,RANS模拟潜艇粘性流场的场量和涡量特征同样具有很高的计算精度,能够在工程应用中有力支撑新型艇型设计与性能分析。

一种模拟气液两相流的格子波尔兹曼改进模型

基于格子波尔兹曼自由能模型,提出了一种模拟黏性流场中大密度比气液两相流的改进模型.为了提高模型的精度,在原始模型的基础上计入了邻近点间粒子数密度的传递速率控制,考虑了碰撞项的差分松弛;为了避免两相间大密度比造成的数值不稳定问题,分别采用六点和九点差分格式求解和2.同时,与传统格子波尔兹曼方法不同,实现了由单步碰撞操作到两步操作的转化.通过对无重力场中气泡的模拟及与已有模型的计算结果的对比分析,表明该模型具有更高的数值精度.成功模拟了重力作用下,单个上浮气泡的形变和尾涡形成过程,以及水平和竖直方向上两个气泡的相互作用过程,并验证了其质量守恒和体积不可压缩性.