Test: Reynolds model law - Civil Engineering (CE) MCQ

# Test: Reynolds model law - Civil Engineering (CE) MCQ

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## 5 Questions MCQ Test Irrigation Engineering - Test: Reynolds model law

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Test: Reynolds model law - Question 1

### Reynold's number signifies the ratio of

Detailed Solution for Test: Reynolds model law - Question 1

Reynold's number:

• It is a dimensionless number that determines the nature of the flow of liquid through a pipe.
• It is defined as the ratio of the inertial force to the viscous force for a flowing fluid.
• Reynold's number is written as Re.
• Re = Inertial force/Viscous force

• If  Reynold's number lies between 0 - 2000, then the flow of liquid is streamlined or laminar.
• If Reynold's number lies between 2000 - 3000, the flow of liquid is unstable and changing from streamline to turbulent flow.
• If Reynold's number is above 3000, the flow of liquid is turbulent.
Test: Reynolds model law - Question 2

### A 1:16 scale model of a submarine moving far below the surface of water is tested in a water tunnel. If the speed of prototype is 8 m/s, the corresponding velocity of model in tunnel is ____ [Fluids are same in testing as in actual model]

Detailed Solution for Test: Reynolds model law - Question 2

As submarine is completely submerged in water, thus Reynold’s number need to be same.
∴ (Re)model = (Re)prototype

Vm = 8 (16)
∴ Vm = 128 m/s
Point to remember:

• When body submerged ⇒ Reynold’s numbers are equal
• When body is floating ⇒ Froude’s numbers are equal.
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Test: Reynolds model law - Question 3

### The non-dimensional number related to water hammer phenomenon is:

Detailed Solution for Test: Reynolds model law - Question 3

Concept:
Water hammer is a phenomenon that is linked to the elasticity of the material and the only dimensionless parameter that involves elastic forces is Mach no.
Reynolds no. deals with viscous force, Froude no. with gravity and Weber no with surface tension.

Test: Reynolds model law - Question 4

Water having kinematic viscosity of 0.01 stoke flows at a velocity of 2 m/s in a pipe of 15 cm diameter. For dynamic similarity, the velocity of oil of kinematic viscosity of 0.03 stoke in a pipe of same diameter will be

Detailed Solution for Test: Reynolds model law - Question 4

Concept
For Dynamic similarity the ratio of corresponding forces acting at the corresponding points should be the same in the model and prototype, the ratio of these forces are called dimensionless numbers.
Therefore for the dynamic similarity between the model and prototype the dimensionless should also be the same. The models are designed on the basis of dominating forces.
Reynolds Model law is applicable for pipe flows and submarines airplanes, fully submerged bodies etc.
For dynamic similarity the Reynolds number must be the same.
Reynolds Number Re = VD/v
where V is the velocity, D is the pipe diameter,  ν is the kinematic viscosity
Calculation:
Given:
ν1= 0.01 stoke, V1 = 2 m/s, D1 = D2 = 15 cm, ν2 = 0.03 stoke,
Now  For dynamic similarity, Reynold’s number would be the same.

Test: Reynolds model law - Question 5

A model of a hydraulic turbine is tested at a head of 1/4th of that under which the full scale turbine works. The diameter of the model is half of that of the full scale turbine, if N is the RPM of the full scale turbine, then RPM of the model will be

Detailed Solution for Test: Reynolds model law - Question 5

The relation between rpm (N), diameter (D) and head (H) is,
Calculation:
Given:

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