Fluid Mechanics Questions and Answers – Separation of Boundary Layer

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This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Separation of Boundary Layer”.

1. How can we determine whether the flow is laminar or turbulent?
a) Reynold’s number
b) Mach number
c) Froude number
d) Knudsen number

Explanation: Reynold’s number is used to determine whether the flow is laminar or turbulent. If Reynold’s number is less than 2000, it is a laminar flow. If Reynold’s number is greater than 2000, then it is a turbulent flow.

2. The flow separation occurs when the fluid travels away from the __________
a) Surface
b) Fluid body
d) Inter-molecular spaces

Explanation: Adverse pressure gradient takes place when the static pressure increases. It increases the direction of the flow. Adverse pressure gradient plays an important role in flow separation. Thus, option c is correct.

3. The swirl caused due to eddies are called as ______
a) Vortices
b) Vertices
c) Volume
d) Velocity

Explanation: Vortices are a region in a fluid. It takes place when the flow revolves around an axis line. Vortices can be straight or curved. They form shapes like smoke rings and whirlpools.
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4. Eddy viscosity is a turbulent transfer of_________
a) Fluid
b) Heat
c) Momentum
d) Pressure

Explanation: Eddy viscosity is a turbulent transfer of momentum by eddies. It gives rise to an internal fluid friction. It is in analogous to the action of molecular viscosity in laminar fluid flow. Eddy viscosity takes place on a large scale.

5. Which among the following is a device that converts a laminar flow into a turbulent flow?
b) Vacuum Gauge
c) Turbulator
d) Ionization Gauge

Explanation: Turbulator is a device that converts a laminar flow into a turbulent flow. The turbulent flow can be desired parts of an aircraft or also in industrial applications. Turbulator is derived from the word “turbulent”.

6. Boundary layer separation does not undergo detachment.
a) True
b) False

Explanation: Boundary layer separation undergoes detachment from the surface into a broader wake. It occurs mainly when the portion of the boundary layer is closest to the wall. It leads to reverse in the flow direction.

7. With the boundary layer separation, displacement thickness________
a) Increases
b) Decreases
c) Remains Same
d) Independent

Explanation: With the boundary layer separation, displacement thickness increases sharply. This helps to modify the outside potential flow and its pressure field. Thus, option ‘a’ is the correct choice.

8. What is the instrument used for the automatic control scheme during the fluid flow?
a) Rotameters
b) Pulley plates
c) Rotary Piston
d) Pilot Static Tube

Explanation: Pilot static tube is a system that uses an automatic control scheme to detect pressure. It has several holes connected to one side of the device. These outside holes are called as a pressure transducer, which controls the automatic scheme during fluid flow.

a) Resistance= 0
b) Drag force= 0
c) Temperature = 0

Explanation: D’Alembert’s Paradox states that for an incompressible and inviscid flow potential flow, the drag force is equal to zero. The fluid is moving at a constant velocity with respect to its relative fluid.

10. The steady- state flow must satisfy ___________
a) Kirchhoff’s law
b) Newtons law
c) Rutherford’s experiment
d) Kepler’s law

Explanation: The steady state flow must satisfy Kirchhoff’s first and second law. The first law states that the total flow into the junction equals the total flow away from the junction. Second law is called as the law of conservation of mass. It states that between two junctions, the head loss is independent of the path followed.

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