Type Of Flow - Practice Questions & MCQ

• Steady flow-

In this type of flow fluid characteristics like  Velocity, Pressure and density etc at a Point do not change with time.

$$
\text { I.e } \frac{d v}{d t}=0, \frac{d p}{d t}=0, \frac{d \rho}{d t}=0
$$

- Unsteady flow-

In this type of flow fluid Characteristics like Velocity, Pressure and density etc At a Point change with respect to time.

$$
\text { 1.e } \frac{d v}{d t} \neq 0, \frac{d p}{d t} \neq 0, \frac{d \rho}{d t} \neq 0
$$
 

• Streamline flow- 

Streamline the flow of a liquid is the type of fluid flow in which each particle of the fluid passing through a point travels along the same path and with the same velocity as the preceding element passes through that point.

Or 

Streamline flow is defined as the path (straight or curved), the tangent to which at any point gives the direction of the flow of liquid.

 

For the above figure path ABC is streamlined.

And All the liquid particles passing through A, B, and C will have velocities as $V_1, V_2$ and $V_3$ respectively.

Property of streamline flow-

1. The direction of velocity at any point on the flow line is along the tangent.

2. Two streamlines cannot cross each other.

 

• Laminar flow -

If a liquid is flowing over a horizontal surface with a steady flow and moves in the form of infinitesimal parallel layers of different velocities which do not mix with each other, then the flow of liquid is called laminar flow.

This type of flow is also referred to as streamline flow.

In this flow, the velocity of liquid flow is always less than the critical

velocity of the liquid.

• Turbulent Flow-
  When the velocity of liquid flow is greater than its critical velocity, then the motion of the particles of the liquid becomes disordered or irregular. Such a flow is called turbulent flow.

           In turbulent flow velocity of the fluid at a point is continuously undergoing changes in both magnitude and direction.

• Critical velocity-

Critical velocity is defined as that velocity of the liquid, flow up to which it's streamlined/laminar and above which it's flow become turbulent.

 

• Reynold's Number-

Reynold's number is a number which determines the nature of the flow of liquid through a pipe.

Reynold's Number is defined as Ratio of inertial force per unit area to the viscous force per unit Area for a flowing fluid.

It is denoted by  R_e which is given by

$$
R_e=\frac{\rho V \cdot d}{\eta}
$$

where $\rho=$ density of fluid
$\eta=$ coefficient of viscocity
$\mathrm{V}=\mathrm{velocity}$ of fluid
$\mathrm{d}=$ diameter of the pipe

 

• Range of Reynold's number

 

1. If it lies Between 0 - 2000 then the flow of liquid is streamlined or laminar

2. If it lies Between 2000 - 3000 then the flow of liquid is unstable

              (means it changing from streamline to turbulent)

3. If it is Above - 3000 then the flow of liquid is turbulent.