Fluid Mechanics and Mechanical Engineering Sections b Fluid Properties] Fluid Statics Fluid Dynamics Aerodynamics Fundamentals& Summary 1. Fluid Properties A fluid is a substance that deforms continuously under an applied shear stress ☆ Liquids》 water冷Gase The difference between the two is that liquids occupy a definite volume, independent of the volume in which they are contained, whereas gases expand to fill the entire volume of the container in which they are 1.1 Viscosity Viscosity is a fluid property that relates the magnitude of fluid shear stresses to the fluid strain For a Newtonian fluid the shear stress u is a constant called the viscosity(in N-s/m2) 1.2 Newtonian fluids For a large class of fluids, the coefficient of viscosity( u) is independent of the velocity gradient. Such fluids are called Newtonian fluids Most fluids familiar to us, such as water, air, and oil, behave as Newtonian fluids. However, certain other fluids. such as blood, toothpaste, and paint, are non-Newtonian Fluid mechanics is concerned with Newtonian fluids Not The viscosity is a property of the fluid, largely a function of temperature for most Newtonian fluids The fluids that we commonly deal with- water and air- possess relatively low viscosities. Consequently over most of the flow field, the fluid can be treated as nonviscous The magnitude of the coefficient depends on the cohesive force between molecules and the momentum interchange between colliding molecules Temperature Effect The cohesive force is dominant for a liquid, so that as the temperature of a liquid is raised and the cohesive force between molecules decreases, the viscosity also decreases The momentum interchange is dominant for a gas, and as the temperature of the gas is raised, providing for greater momentum interchange, the viscosity of the gas increases Surface Tension Surface tension of a liquid is due to the forces of attraction between like molecules, called cohesion, and those between unlike molecules called adhesion Molecules on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension 2. Fluid statics .8 Fluid statics is the branch of fluid mechanics which deals with situations in which there is no relative motion between fluid elements. The fluid can be either at rest or in uniform motion 2 In a static fluid, there is no motion of one layer of fluid relative to an adjacent layer, so there are no viscous shear forces. Thus, the only forces we shall consider in a study of fluid statics are pressure forcesFluid Mechanics and Mechanical Engineering Sections ❖Fluid Properties❖Fluid Statics❖Fluid Dynamics❖Aerodynamics Fundamentals❖Summary 1. Fluid Properties A fluid is a substance that deforms continuously under an applied shear stress. . ❖ Liquids » water ❖ Gases » air The difference between the two is that liquids occupy a definite volume, independent of the volume in which they are contained, whereas gases expand to fill the entire volume of the container in which they are placed. . 1.1 Viscosity Viscosity is a fluid property that relates the magnitude of fluid shear stresses to the fluid strain rate. . For a Newtonian fluid , τ is the shear stress, μ is a constant called the viscosity (in N·s/m2). 1.2 Newtonian fluids For a large class of fluids, the coefficient of viscosity(μ) is independent of the velocity gradient. Such fluids are called Newtonian fluids. . Most fluids familiar to us, such as water, air, and oil, behave as Newtonian fluids. However, certain other fluids, such as blood, toothpaste, and paint, are non-Newtonian. . Fluid mechanics is concerned with Newtonian fluids. . Notes: The viscosity is a property of the fluid , largely a function of temperature for most Newtonian fluids. The fluids that we commonly deal with — water and air — possess relatively low viscosities. Consequently, over most of the flow field, the fluid can be treated as nonviscous. . The magnitude of the coefficient depends on the cohesive force between molecules and the momentum interchange between colliding molecules. Temperature Effect The cohesive force is dominant for a liquid, so that as the temperature of a liquid is raised and the cohesive force between molecules decreases, the viscosity also decreases. The momentum interchange is dominant for a gas, and as the temperature of the gas is raised, providing for greater momentum interchange, the viscosity of the gas increases. . Surface Tension Surface tension of a liquid is due to the forces of attraction between like molecules, called cohesion, and those between unlike molecules, called adhesion.. Molecules on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension. 2. Fluid Statics ❖ Fluid statics is the branch of fluid mechanics which deals with situations in which there is no relative motion between fluid elements. The fluid can be either at rest or in uniform motion. . ❖ In a static fluid, there is no motion of one layer of fluid relative to an adjacent layer, so there are no viscous shear forces. Thus, the only forces we shall consider in a study of fluid statics are pressure forces and gravity