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Test: Boundary Layer Level - 2 - Mechanical Engineering MCQ


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10 Questions MCQ Test Fluid Mechanics for Mechanical Engineering - Test: Boundary Layer Level - 2

Test: Boundary Layer Level - 2 for Mechanical Engineering 2024 is part of Fluid Mechanics for Mechanical Engineering preparation. The Test: Boundary Layer Level - 2 questions and answers have been prepared according to the Mechanical Engineering exam syllabus.The Test: Boundary Layer Level - 2 MCQs are made for Mechanical Engineering 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Boundary Layer Level - 2 below.
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*Answer can only contain numeric values
Test: Boundary Layer Level - 2 - Question 1

Air is flowing over a thin flat plate which is 1 m long and 0.3 m wide. At the leading edge, the flow is assumed to be uniform and U∞ = 30 m⁄s . The flow condition is independent of z (see Fig.). Using the control volume abcd, calculate the mass flow rate across the surface ab. (in kg/s, upto 3 decimal places). The velocity profile at bc is given by


Detailed Solution for Test: Boundary Layer Level - 2 - Question 1

Due to boundary layer growth mass flow rate through b-c is less than mass through a-d.

ṁ ad = δUw ∙ δ = 1.23 × 30 × 0.3 × 0.004

⇒ ṁ ad = 0.04428 kg/s

ṁ ab = 0.04428 − 0.02952

= 0.01476 kg/s

*Answer can only contain numeric values
Test: Boundary Layer Level - 2 - Question 2

Water flows over a flat plate at a free stream velocity of 0.15 m/s. There is no pressure gradient and the laminar boundary layer is 6 mm thick. Assume a sinusoidal velocity profile

For the flow conditions stated above, calculate the skin friction coefficient. (upto 4 decimal places) [μ = 1.02 × 10−3kg/ms, ρ = 1000 kg/m3]


Detailed Solution for Test: Boundary Layer Level - 2 - Question 2

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Test: Boundary Layer Level - 2 - Question 3

What is the ratio of momentum thickness to the boundary layer thickness δ when the layer velocity profile is given by

Where u is velocity at height y above surface and U is free stream velocity of flow.

Detailed Solution for Test: Boundary Layer Level - 2 - Question 3
Momentum Thickness

*Answer can only contain numeric values
Test: Boundary Layer Level - 2 - Question 4

Water at 15°C flows over a flat plate at a speed of 1.2 m/s. The plate is 0.3 m long and 2 m wide. The boundary layer on each surface of the plane is laminar. Assume the velocity profile is approximated by a linear expression


Detailed Solution for Test: Boundary Layer Level - 2 - Question 4

On a flat plate, the drag is due to skin friction acting on each side of the plate

= 1.745 N

Test: Boundary Layer Level - 2 - Question 5

Consider the following statements pertaining to boundary layer on a flat plate

1. The thickness of laminar boundary layer at a distance x from the leading edge varies as x1⁄2

2. The thickness of turbulent boundary layer at a distance x from the leading edge varies as x4⁄5

3. Boundary layer is laminar when Reynolds number is less than 5 × 105

Which of the above statements are correct?

Detailed Solution for Test: Boundary Layer Level - 2 - Question 5
For laminar boundary layer

For Turbulent boundary layer

Test: Boundary Layer Level - 2 - Question 6

Examine whether or not the following velocity profiles satisfy the essential boundary conditions for velocity distribution in laminar boundary layer on a flat plate

Where u is the velocity at height y above the surface, U0 is the free stream velocity and δ is the nominal boundary layer thickness.

Detailed Solution for Test: Boundary Layer Level - 2 - Question 6
The essential boundary conditions for a laminar boundary layer are,

Test: Boundary Layer Level - 2 - Question 7

A plate 0.5 m × 0.2 m has been placed longitudinally in a stream of crude oil which flows with undisturbed velocity of 6 m⁄s.

Given that oil has a specific gravity 0.9 and kinematic viscosity 1 stroke, calculate the boundary layer thickness and shear stress at the middle of plate.

Detailed Solution for Test: Boundary Layer Level - 2 - Question 7
Kinematic viscosity v = 1 stoke = 1 × 10−4 m2⁄s At the middle of plate,

This is less than the critical Reynolds number for transition to turbulent flow 5 × 105. Thus the boundary layer is of laminar character and the Blasius solution gives:

= 87.8 N ⁄ m2

Test: Boundary Layer Level - 2 - Question 8

What is the commonly used boundary layer control method to prevent separation?

Detailed Solution for Test: Boundary Layer Level - 2 - Question 8
A common method to reduce flow separation is to suck away the fluid which has lost its momentum or blowing in high speed fluid into the boundary layer. Remember, slow fluid is sucked away while high speed fluid is blown in. Flow separation is dependent on the shape of the surface and not on the surface finish whereas a large divergence angle actually encourages separation and hence is avoided.

Test: Boundary Layer Level - 2 - Question 9

Which one of the following is correct? For flow of an ideal fluid over a cylinder, from the front stagnation point.

Detailed Solution for Test: Boundary Layer Level - 2 - Question 9
At the stagnation point, the velocity first decreases and comes to zero as the pressure reaches the value of stagnation pressure. Then further ahead the velocity slowly increases from zero as the pressure begins to reduce.

Test: Boundary Layer Level - 2 - Question 10

Crude oil at 21°C (ν = 9.3 × 10−6 m2 /s, S = 0.86) with a free-stream velocity of 0.3048 m/s flows past a thin, flat plate that is 1.2192 m wide and 1.8288 m long in a direction parallel to the flow. The flow is laminar. Determine the boundary-layer thickness and the wall shear stress at the trailing edge of the plate.

Detailed Solution for Test: Boundary Layer Level - 2 - Question 10
ν = 9.3 × 10−6 m2/s ; v = 0.3048 m/s

Since Rex< />5; flow is laminar

Using Blassius solution

⇒ τ0 = 0.10834 N/m2

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