Lecture – 1 Ms. Thevasha Sathiyakumar MAT 326 1.0 Fluid Dynamics NOTE: To change the image on this slide, select the picture and delete it. Then click the Pictures icon in the placeholder to insert your own image. Lecture – 1 Ms. Thevasha Sathiyakumar

Fluids vs. Solids Fluids flow under the action of a force, and the solids don’t flow but, solids do deform. Therefore it implies that, fluids lack the ability of solids to resist deformation. fluids change shape as long as a force acts. 19 September 2018

What forces cause deformation? Shear Forces (Tangential) Forces acting along edges (faces), such as F, are known as shearing forces 19 September 2018

What is a Fluid? A Fluid is a substance which deforms continuously, or flows, when subjected to shearing forces of any magnitude. (The above definition holds for both gases and liquids ) 19 September 2018

Fluid Dynamics and its Applications Fluid dynamics is a sub-discipline of fluid mechanics that describes the flow of fluids. Vehicles Medicine Industries Weather & Climate 19 September 2018

Fluid Properties For a fluid element moving through at time t, there are four main fluid properties: Fluid density Fluid stress Fluid velocity Viscosity 19 September 2018

Viscosity Viscosity is the fluid property by which a fluid offers resistance to shear stresses. A fluid with high viscosity resists motion, while a fluid with low viscosity flows easily. 19 September 2018

Types of fluid Newtonian Fluid and Non-Newtonian Fluid Compressible and incompressible 19 September 2018

Newtonian Fluid and Non-Newtonian Fluid A Newtonian fluid is any fluid that exhibits a viscosity that remains constant regardless of any external stress that is placed upon it. But, viscosity of Newtonian fluids are affected by temperatures. E.g. Water , Oil Non- Newtonian fluid If the viscosity of some fluids is affected by factors other than temperature then these fluids are termed as non-Newtonian fluids. The viscosity of non- Newtonian fluids may change due to pressure or shear stress. E.g. Honey, Cream, molten polymers 19 September 2018

Compressible and Incompressible Fluids The compressibility of a fluid is the reduction of the volume of the fluid due to external pressures acting on it. A compressible fluid will reduce its volume in the presence of an external pressure. E.g. Air Incompressible fluid An incompressible fluid is a fluid that does not change the volume of the fluid due to external pressure. Most of the basic calculations done in fluid dynamics are done assuming the fluid is incompressible. The approximation of incompressibility is acceptable for most of the liquids as their compressibility is very low. E.g. Water 19 September 2018

Steady and Unsteady Motion If the properties of a fluid (velocity, density, pressure) at a point is independent of time, the fluid is in a steady motion. If at any point in the fluid, the conditions change with time, the flow is described as unsteady. 19 September 2018