Numerical Study of a Three-Dimensional Laminar Flow in a Rectangular Channel with a 180-Degree Sharp Turn

This study presents a numerical analysis of three-dimensional steady laminar flow in a rectangular channel with a 180-degree sharp turn. The Navier-Stokes equations are solved by using finite difference method for Re = 900. Three-dimensional streamlines and limiting streamlines on wall surface are used to analyze the three-dimensional flow characteristics. Topological theory is applied to limiting streamlines on inner walls of the channel and two-dimensional streamlines at several cross sections. It is also shown that the flow impinges on the end wall of turn and the secondary flow is induced by the curvature in the sharp turn.

MHD three dimensional flow of viscoelastic fluid with thermal radiation and variable thermal conductivity

The objective of the present work is to model the magnetohydrodynamic(MHD) three dimensional flow of viscoelastic fluid passing a stretching surface. Heat transfer analysis is carried out in the presence of variable thermal conductivity and thermal radiation. Arising nonlinear analysis for velocity and temperature is computed. Discussion to importantly involved parameters through plots is presented. Comparison between present and previous limiting solutions is shown. Numerical values of local Nusselt number are computed and analyzed. It can be observed that the effects of viscoelastic parameter and Hartman number on the temperature profile are similar in a qualitative way. The variations in temperature are more pronounced for viscoelastic parameter K in comparison to the Hartman number M. The parameters N and ε give rise to the temperature. It is interesting to note that values of local Nusselt number are smaller for the larger values of ε.

Experimental and Numerical Study of Three-Dimensional Unsteady Incompressible Flow Past Two Identical Circular Cylinders in Tandem Arrangements

The possible states in the flow past two identical cylinders in tandem arrangements are investigated. The effect of the gap （L/D = 1.5, 1.75 and 2） between the two cylinders at Reynolds number （Re = 52,639） is taken into consideration. The presence of three-dimensional flow structures was observed to include notable changes to the response of the flow as result of variation of cylinder separation. A number of planes （z/h = 0.02, 0.25, 0.5 and 0.98） were taken at 20 step times of interval 0.005 s. to cover the details of flow along the cylinders. CFD FLUENT program was used to detect the flow structure. It is observed that the gap between the two cylinders affects the flow regime, i.e., there is no distinct vortex shedding downstream of the first cylinder.

NUMERICAL STUDY OF TOPOLOGICAL STRUCTURE OF 3-D TRANSONIC VISCOUS FLOW FIELD (TVFF) INSIDE TURBINE CASCADE

The major purpose of this paper is to numerically study the complex structure of vortex system occurring within transonic turbine cascade. The transonic viscous flow in turbine cascade is simulated by solving full 3D Reynolds average N S equations, and then detailed analyses of vortex system structure are presented. Under guidance of topology, the wall limiting streamlines are employed to reveal the flow structure near the wall, and an analysis of space streamlines and cross section streamlines is given for the investigation of flow structure in the flow field. Through the analysis, the formation and evolution of the vortex system and the whole process of separation occurring within this turbine cascade are revealed

A NEW NUMERICAL MODEL FOR THREE DIMENSIONAL SURFACE WATER FLOWS

A three dimensional numerical model based on the Reynolds equations is presented that can be used to predict the surface water flow in open channels.The model uses a computational mesh that conforms to the free water sur- face and the bottom of the channel so that the accuracy of boundary condition application,code complexity,and e- conomy could be enhanced.The k-ε turbulence model is used to estimate the eddy viscosity coefficient.Instead of using the“rigid-lid”approximation a 2-D equation derived from integrating the continuity equation over the total depth is adopted to determine the elevation of the free water surface.A new algorithm is presented based on the conventional SIMPLE procedure.The block correction technique is employed to enhance rate of convergence. The model presented is applied to a bottom discharge into a rectangular straight channel for three dimensional phenomena to obtain the free water surface configuration,velocities and pressure.The computed results are in good agreement with the previous experimental values.

航行体水下点火三维流场数值模拟

采用三维网格和VOF(Volume of Fluids)多相流模型,对非轴对称、X型舵的航行体水下点火这一非稳态过程进行了三维流场数值模拟,捕捉了燃气泡的形成、发展及断裂过程,得到了航行体水下点火初期的流场变化和阻力变化,并进行了相关因素探讨和结果对比分析。研究表明,燃气泡的发展变化过程对航行体流场和阻力产生影响。该研究可为航行体水下点火设计及试验提供参考。

The computation of the pitch damping stability derivatives of supersonic blunt cones using unsteady sensitivity equations

The numerical methods for computing the stability derivatives of the aircraft by solving unsteady sensitivity equations which was proposed in our previous papers was extended to solve three-dimensional problems in this paper.Both the static and dynamic derivatives of the hypersonic blunt cone undergoing pitching oscillation around a fixed point were computed using the new methods.The predicted static derivative and dynamic derivative were found to be in reasonable agreement with the experimental data.For the present method,it is possible to distinguish the components of dynamic derivatives caused by different state parameters.It is found that C_(m_α) and C_(mq) are usually of opposite signs and tend to eliminate each other,which makes C_(m_α)+C_(mq) being much smaller than its individual components.Another feature of this method is that the moment of pressure derivatives proposed in the present paper can be used to predict the contribution of each part of the blunt cone to the overall stability quantitatively.It is found that the head region is crucial for the static stability and the body region contributes most to the dynamic stability.