CFDa.1.introduction

# CFDa.1.introduction - Fluids Review TRN-1998-004...

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© Fluent Inc. 12/05/10 A1 Fluids Review TRN-1998-004 Introduction to Fluid Mechanics

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© Fluent Inc. 12/05/10 A2 Fluids Review TRN-1998-004 Outline What is a fluid? Fluids as a continuum Fluid properties Fluid kinematics Fluid statics Fluid dynamics Flow classifications Flow configurations Summary
© Fluent Inc. 12/05/10 A3 Fluids Review TRN-1998-004 What is a Fluid? A fluid is a substance which can not resist a shear force without moving Fluids versus Solids A fluid deforms continuously when shear (tangential) forces are exerted on it ( shear stress is proportional to strain rate ) In constrast, a solid deforms by an amount proportional to the applied shear stress which is proportional to strain (Hooke’s Law)

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© Fluent Inc. 12/05/10 A4 Fluids Review TRN-1998-004 Fluids as a Continuum In order to formulate governing equations related to fluid motion, we assume that most fluids behave as a continuous medium . A continuum : the properties at a point represent an average over a tiny volume whose dimension is large compared to the distance between individual molecules, but small enough to be a point in space. Measure of the continuum assumption is the Knudsen Number (Kn) λ = molecular mean free path, l = characteristic length Kn << 1 Continuum assumption is closely obeyed Kn >> 1 Free molecule flow (rarefied gas flow) l Kn λ =
© Fluent Inc. 12/05/10 A5 Fluids Review TRN-1998-004 Fluid Properties Density ( ρ29 - mass per unit volume of fluid Pressure (p) - normal force per unit area exerted on a surface immersed in the fluid Temperature (T) - thermodynamic temperature of the fluid Viscosity (μ29 - relates shear stress ( τ 29 to the rate of angular deformation of the fluid

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