## Polytechnic Notes: Polytechnic 2nd Sem Fluid Mechanics Important Notes

**(a) What is buoyancy?**

When a body is immersed (to put something into a liquid so that it is covered) in a fluid, an upward force is exerted by the fluid on the body. This upward force is equal to the weight of the fluid displaced by the body and is called the force of buoyancy or simply buoyancy.

**(b) What is the Center of Buoyancy:-**

The point at which buoyancy force acts and is equal to the weight of the fluid displaced by the body, the center of buoyancy will be the center of gravity of the fluid displaced.

**(c) What is Archimedes Principle ?**

It states that when a body is immersed in fluid either partial, it is lifted up by a force that is equal to the weight of the fluid displaced by the body.

**(d) What is a metacenter in Fluid Mechanics?**

It is defined as the point at which a body starts oscillating when the body is tilted by a small angle. The meta-center may also be defined as the point at which the line of action of the force of buoyancy will meet the normal axis of the body when the is given a small angular displacement.

### Fluid Kinematics-2nd Semester Polytechnic Notes:-

Polytechnic 2nd Sem Fluid Mechanics Important Notes:

**1. Steady flow and Unsteady flow:**

Steady flow is defined as that type of flow in which the fluid characteristics like velocity pressure, density, etc. at a point do not change with time.

Unsteady flow is that type of flow, in which the velocity, pressure, or density at a point change w.r.t time.

**2. Uniform and Non-Uniform flow:**

Uniform flow is defined as a type of flow in which the velocity at any given time does not change w.r.t space.

Non-Uniform flow is that type of flow in which the velocity at any given time changes w.r.t space.

**3. Laminar and Turbulent flow:**

Laminar flow is defined as that type of flow in which the fluid particles move along well-defined paths or steam lines and all the steam lines are straight and parallel. Thus the particular move in layers gliding smoothly over the adjacent layer. This type of flow is also called streamline flow or viscous flow.

**4. Compressible and Incompressible flow:**

Compressible flow is that type of flow in which the density of the fluid change from point to point in other words the density is not constant for the fluid.

Incompressible flow is that type of flow in which the density is constant for the fluid flow. Liquids are generally incompressible whereas gases are compressible.

**5. Rotational and Inrotational flow :**

Rotational flow is that type of flow in which the fluid particles flow along streamlines, and also rotate about their own axis. And if the fluid particles were flowing along streamlines, and do not rotate about their own axis then that type of flow is called irrotational flow.

**6. One, Two, and Three-dimensional flows:**

**Q. What is One dimensional flow?**

One dimensional flow is that type of flow in which the flow parameter such as velocity is a function of time and one space co-ordinate only, say x. For a steady one-dimensional flow, the velocity is a function of one space coordinate only.

**Q. What is Two-dimensional flow?**

Two-dimensional flow is that type of flow in which the velocity is a function of time and two rectangular space coordinates say x & y. For a steady two-dimensional flow, the velocity is a function of two space coordinates only. The variation of velocity in the third direction is negligible.

**Q. What is Three-dimensional flow?**

Three-dimensional flow is that type of flow in which the velocity is a function of time and three mutually perpendicular directions. But for a steady three-dimensional flow, the fluid parameters are functions of three space coordinates only.