INTERVIEW SHORT QUESTION ANSWERS-TURBULENT FLOW

INTERVIEW SHORT QUESTION ANSWERS-TURBULENT FLOW

  1. Define a turbulent flow.
  • A turbulent flow has variable velocity (at every point) both in magnitude and direction. Pressure is also variable at every point. This flow is highly irregular. Fluid flow lines cross each other randomly. Velocity loss, pressure loss and  energy loss is there in a turbulent flow. Flow is complex and difficult to analyze. Thus only empirical correlations have been developed to analyze turbulent flow.
  1. What is turbulence? What are the various types of turbulence?

Turbulence is small-scale, short-term, random fluctuations. In appearance, it  is like a turbulent flow. It causes random variations in pressure and velocity but these short lived. But its intensity can be big or small. A big disturbance can be extremely harmful.

  1. What are the advantages of Venturimeter over orifice meter  in a flow measurement?

The comparison of Venturimeter and an Orifice meter is as flows:

Sr. No. Venturimeter Orifice meter
ADVANTAGES
1. Coefficient of discharge

is Cd =0.98.

Coefficient of discharge

is Cd =0.60 to 0.65

2. Rate of flow will be higher with the same diameter Rate of flow will be lesser with the same diameter
3. It is very accurate. It is less accurate.
DISADVANTAGES
4. It is costly. It is cheap.
5. More space is required Less space is required
6. Energy losses are high. Energy losses are low.

 

  1. What is Vena Contracta?

The Vena Contracta is the reduction in the diameter (or area) of a fluid jet after it comes out from a circular small hole (aperture) in a pressurized reservoir.

Or

When fluid comes out from a tank through a hole, the cross section of the fluid flowing goes on decreasing. It becomes minimum at some distance from the tank. This minimum area of flow of fluid has been named as Vena Contracta. Up to the Vena Contracta flow lines are parallel and straight and are perpendicular to the plane of the orifice. It is only after the Vena Contracta; flow is deflected downwards due to gravity. Example of Vena Contracta is fluid coming out as jet from a nozzle. Concept of Vena Contracta is used in the design of valves to give maximum flow.

  1. State the differences between triangular and rectangular notches.

Triangular notch or V-notch gives more accurate measurement at low flow rates. In this, the height will be more to measure it accurately.  Whereas in case of a rectangular notch, the height would be so small in the measured gap and will give erroneous results.

 

  1. Difference between lower and upper Reynolds critical numbers.

Table: Values of Lower and Upper critical Reynolds Number

Flow in a pipe                                            Flow over a flat plate
Laminar Flow Turbulent Flow Laminar Flow          Turbulent Flow
Lower critical 2100 Upper critical

4000

Lower critical

500000

Upper critical

700000

 

  1. What are limitations and characteristics of a flow net?
  • Limitations of a flow net
  1. Flow net is applicable only for a 2 dimensional flow.
  2. It cannot be applied near the boundary where there are viscous effects are there.
  3. This is also not applicable to a diverging flow.
  4. Flow net analysis is not applicable in case of separation of flow as well as where eddies are formed.
  • Characteristics of a flow net
  1. Flow net is applicable only for a 2 dimensional flow.
  2. This analysis is also applicable for seepage problems in soil and structures like dams and retaining walls.