Fluid Mechanics (General Engineering) (SSC JE)

In case of turbulent flow, the loss of pressure head is proportional to th square of velocity

Most efficient section–The section having minimum wetted perimeter in order to obtain maximum possible efficiency is called as most efficient section.

• Theoretically semi-circular section has minimum wetted perimeter but practically semi-circular sections are not maintained during flow so that trapezoidal sections are considered as most economical section on practical basis while semi circular on theoretical basis.

Euler's equation–It is used for steady flow of an ideal fluid along the streamline based on Newton's second law of motion. According to the assumption, there is no force of compressibility, turbulence and velocity are neglected. Therefore, linear momentum will be conserved.

Uniform flow–In a uniform flow, the velocity remains constant all the fluid particles are moving with the same velocity.
• The velocity of fluid particles in uniform flow are equal at all section.

Bernoulli's equation–Bernoulli's equation is based on the principle of consevation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline.

The friction resistance for turbulent flow is–
• Proportional to Vⁿ , where n varies 1.5 to 2.0.
• Proportional to the density of fluid Proportional to the area of surface in contact. So, frictional losses in turbulent flow are proportional to square of fluid velocity.
• Head loss due to friction losses in turbulent flow,

Boundary layer analysis is used for low Reynolds number flow.
• Boundary layer may be either laminar (layered) or turbulent (disordered) depending on the value of the Reynolds number.
For lower Reynolds number, the boundary layer is laminar and the streamwise velocity changes uniformly as one moves away from the wall.

Temperature affects the viscosity. The viscosity of liquids decreases with the increase of temperature while the viscosity of gases increases with the increase of temperature.