1. Lecture – 1 Ms. Thevasha Sathiyakumar
MAT Fluid Dynamics
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Lecture – 1
Ms. Thevasha Sathiyakumar

2. 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.
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3. What forces cause deformation?
Shear Forces (Tangential)
Forces acting along edges (faces), such as F, are known as shearing forces
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4. 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 )
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5. 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
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6. Fluid Properties
For a fluid element moving through at time t, there are four main fluid properties:
Fluid density
Fluid stress
Fluid velocity
Viscosity
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7. 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.
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8. Types of fluid Newtonian Fluid and Non-Newtonian Fluid
Compressible and incompressible
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9. 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
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10. 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
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11. 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.
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