ANSYSIcepak中判断层流或湍流_51CAE_新浪博客
雷诺数
雷诺数（Reynolds number）⼀种可⽤来表征流体流动情况的⽆量纲数，以Re表⽰，Re=ρvr/η，其中v、ρ、η分别为流体的流速、密度与黏性系数，r为⼀特征线度。例如流体流过圆形管道，则r为管道半径。利⽤雷诺数可区分流体的流动是层流或湍流，也可⽤来确定物体在流体中流动所受到的阻⼒。例如，对于⼩球在流体中的流动，当Re⽐“1”⼩得多时，其阻⼒f=6πrηv（称为斯托克斯公式），当Re ⽐“1”⼤得多时，f′=0.2πr2v2⽽与η⽆关。 雷诺数⼩，意味着流体流动时各质点间的粘性⼒占主要地位，流体各质点平⾏于管路内壁有规则地流动，呈层流流动状态。雷诺数⼤，意味着惯性⼒占主要地位，流体呈紊流（也称湍流）流动状态，⼀般管道雷诺数Re＜2000为层流状态，Re＞4000为紊流状态，Re＝2000～4000为过渡状态。在不同的流动状态下，流体的运动规律．流速的分布等都是不同的，因⽽管道内流体的平均流速υ与最⼤流速υmax的⽐值也是不同的。因此雷诺数的⼤⼩决定了粘性流体的流动特性。
Icepak帮助⽂档解释
For problems dominated by forced convection, Icepak computes the Reynolds number (Re) and the Peclet number (Pe), both of which are dimensionless. For flows dominated by natural convection (i.e.,
buoyancy-driven flows), Icepak computes the Rayleigh number (Ra) and the Prandtl number (Pr), which are also dimensionless.The Reynolds number measures the relative importance of inertial forces and viscous forces. When it is large, inertial forces dominate, boundary layers form, and the flow may become turbulent. The Peclet number is similar to the Reynolds number and measures the relative importance of advection to diffusion for the transport of heat. For most flows simulated by Icepak, both the Reynolds and Peclet numbers are large.The Prandtl number measures the relative magnitude of molecular diffusion to thermal diffusion. The Rayleigh number is a measure of the importance of the buoyancy effects.For the flow of air in enclosures of the type simulated with Icepak, typical ranges for the parameters are shown in Table 6.4.1.
Table 6.4.1: Typical Values of Dimensionless Parameters in Forced- and Natural-Convection Problems inIcepak
If the Reynolds number is greater than 2000 or the Rayleigh number is greater than 5x10^7, then lecting the Turbulent option.
在求解之前，Icepak会先判断下问题是属于强制对流还是⾃然对流。强制对流的话计算Re和Pe，⾃然对流的话计算Ra和Pr。关键是最后⼀句话，判断是使⽤层流还是紊流：如果Re>2000或者Ra>5x10^7就选择紊流求解选项。
