Elementary ideas of viscous flows - Aerodynamics - Aerospace Engineering Previous Year Questions

1

2007 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2007

The laminar boundary layer over a large flat plate held parallel to the freestream is 5 mm thick at a point 0.2 m downstream of the leading edge. The thickness of the boundary layer at a point 0.8 m downstream of the leading edge will be

A

20 mm

B

10 mm

C

5 mm

D

2.5 mm

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2

2009 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2009

The laminar boundary layer over a large flat plate held parallel to the flow is 7.2 mm thick at a point 0.33 m downstream of the leading edge. If the free stream speed is increased by 50%, then the new boundary layer thickness at this location will be approximately

A

10.8 mm

B

8.8 mm

C

5.9 mm

D

4.8 mm

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3

2010 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2010

Consider an incompressible 2-D Couette flow of water between two walls spaced 1m apart. The lower wall is kept stationary. What is the shear stress acting on the lower wall if the upper wall is moving at a constant speed of 2 m/s? (\(\mu_{water} = 7 \times 10^{-4} N.s/m^2\))

A

\(3.5 \times 10^{-3} N/m^2\)

B

\(7 \times 10^{-3} N/m^2\)

C

\(10.5 \times 10^{-3} N/m^2\)

D

\(14 \times 10^{-3} N/m^2\)

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4

2010 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2010

Consider an incompressible 2-D viscous flow over a curved surface. Let the pressure distribution on the surface be \(p(s) = 2 + \sin\left(\frac{\pi}{2} s\right) N/m^2\), where s is the distance along the curved surface from the leading edge. The flow separates at

A

\(s = (2/3)\pi\) m

B

\(s = (3/2)\pi\) m

C

\(s = (\pi/2)\) m

D

\(s = \pi\) m

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5

2010 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2010

In a 2-D, steady, fully developed, laminar boundary layer over a flat plate, if x is the stream-wise coordinate, y is the wall normal coordinate and u is the stream-wise velocity component, which of the following is true:

A

\(\frac{\partial u}{\partial x} >> \frac{\partial u}{\partial y}\)

B

\(\frac{\partial u}{\partial y} >> \frac{\partial u}{\partial x}\)

C

\(\frac{\partial u}{\partial x} = \frac{\partial u}{\partial y}\)

D

\(\frac{\partial u}{\partial x} = -\frac{\partial u}{\partial y}\)

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6

2011 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2011

Consider a steady two dimensional zero-pressure gradient laminar flow of air over a flat plate as shown below. The free stream conditions are \( U_\infty = 100 \text{ ms}^{-1} \), \( \rho_\infty = 1.2 \text{ kg m}^{-3} \), \( p_\infty = 1 \) atm and \( \mu_\infty = 1.8 \times 10^{-5} \text{ kg m}^{-1} \text{ s}^{-1} \). The ratio of displacement thickness to momentum thickness of the boundary layer at a distance of 2 m from the leading edge is

A

7.53

B

2.59

C

2.91

D

0.39

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7

2012 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2012

Bernoulli’s equation is valid under steady state

A

only along a streamline in inviscid flow, and between any two points in potential flow.

B

between any two points in both inviscid flow and potential flow.

C

between any two points in inviscid flow, and only along a streamline in potential flow.

D

only along a streamline in both inviscid flow and potential flow.

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8

2012 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2012

A vortex flowmeter works on the principle that the Strouhal number of 0.2 is a constant over a wide range of flow rates. If the bluff-body diameter in the flowmeter is 20 mm and the piezo-electric transducer registers the vortex shedding frequency to be 10 Hz, then the velocity of the flow would be measured as

A

0.1 m/s

B

1 m/s

C

10 m/s

D

100 m/s

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9

2012 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2012

What is the radial component of the fluid's velocity at a radial location 0.5 m from the pipe axis?

A

0.01 m/s

B

0.1 m/s

C

1 m/s

D

10 m/s

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10

2012 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2012

What is the tangential component of the fluid's velocity at the same radial location as above?

A

0.01 m/s

B

0.03 m/s

C

0.10 m/s

D

0.31 m/s

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11

2014 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2014

To observe unsteady separated flow in a diverging channel, bubbles are injected at each 10ms interval at point A as shown in figure. These bubbles act as tracer particles and follow the flow faithfully. The curved line AB shown at any instant represents:

A

Streamline, streakline and pathline

B

Streamline and pathline

C

Only a pathline

D

Only a streakline

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12

2014 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2014

Figures (a) - (d) below show four objects. Dimensions and surface conditions of the objects are shown in the respective figures. All four objects are placed independently in a steady, uniform flow of same velocity and the direction of flow is from left to right as shown in (a). The flow field can be considered as 2-D, viscous and incompressible. Following statements are made regarding the drag that these objects experience.
(i) Drag of object (a) is more than the drag of object (d)
(ii) Drag of object (a) is less than the drag of object (d)
(iii) Drag of object (b) is more than the drag of object (c)
(iv) Drag of object (c) is more than the drag of object (b)
(v) Drag of object (a) is more than the drag of object (b)
Choose the correct combination of statements from the options given above.

A

(i), (iii), (v)

B

(ii), (iv), (v)

C

(i), (iv), (v)

D

(i), (iii)

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13

2014 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2014

A student can measure free-stream velocity of a low-speed wind tunnel using
    i. Pitot tube alone aligned with the flow direction.
    ii. Pitot tube aligned with the flow direction with static pressure measurement at an appropriate position on the tunnel wall.
    iii. Pitot tube aligned with the flow direction along with barometer pressure reading of the outside ambient.
    iv. Pitot static tube alone aligned with the flow direction.
Considering the above statements, which of the following options is correct?

A

(i) only

B

(i) & (ii)

C

(iii) & (iv)

D

(i), (iii) & (iv)

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14

2014 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2014

Two overflowing water reservoirs are connected with a 100m long pipe of circular cross-section (of radius, R≅0.02m), such that height difference h remains constant as shown in the figure below. The centerline velocity in the pipe is 10m/s. The velocity profile inside the pipe over the entire length is u = - (R²/(4μ) dp/dx) [1 - r²/R²], where, dp/dx is a constant pressure gradient along the pipe length, x is measured from the left end of the pipe along its central axis and r is radial location inside the pipe with respect to its axis.(Given data: Density and kinematic viscosity of water are 1000kg/m³ and 1x10^-6 m²/s respectively; acceleration due to gravity is 10m/s²).
If all other losses except the frictional losses at the pipe wall are neglected, the value of h in meter is____.

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15

2016 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2016

For a laminar incompressible flow past a flat plate at zero angle of attack, the variation of skin friction drag coefficient (\( C_f \)) with Reynolds number based on the chord length (\( Re_c \)) can be expressed as

A

\(C_f \propto \sqrt{Re_c} \)

B

\(C_f \propto Re_c \)

C

\(C_f \propto \frac{1}{\sqrt{Re_c}} \)

D

\(C_f \propto \frac{1}{Re_c} \)

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16

2016 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2016

Air, with a Prandtl number of 0.7, flows over a flat plate at a high Reynolds number. Which of the following statement is TRUE?

A

Thermal boundary layer is thicker than the velocity boundary layer.

B

Thermal boundary layer is thinner than the velocity boundary layer.

C

Thermal boundary layer is as thick as the velocity boundary layer.

D

There is no relationship between the thicknesses of thermal and velocity boundary layers.

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17

2017 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2017

Which one of the following statements is NOT true

A

Compared to a laminar boundary layer, a turbulent boundary layer is more desirable on a wing operating at large angle of attack

B

The skin friction drag for a turbulent boundary layer is larger than that for a laminar boundary layer

C

The location of transition from laminar to turbulent boundary layer depends only on the operating Reynolds number

D

A separated flow does not necessarily lead to a turbulent boundary layer

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18

2018 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2018

The boundary layer thickness at the location of a sensor on a flat plate in an incompressible, laminar flow of air is required to be restricted to 1 mm for an effective measurement. If the flow velocity is 20 m/s with 1 bar pressure, 300 K temperature, and \( 1.789 \times 10^{-5} \) kg/(m·s) viscosity, the maximum distance (in mm) of the sensor location from the leading edge is ________ (accurate to one decimal place).

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19

2019 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2019

To simulate the aerodynamic forces on a cylinder of 1 m diameter due to a uniform air flow of 1 m/s at standard temperature and pressure (STP), low-speed wind tunnel experiments at STP are conducted on a 0.1 m diameter cylinder. The free stream air speed in the wind tunnel experiments should be ______ m/s (round off to the nearest integer).

A

B

C

D

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20

2019 · Aerospace Engineering · Aerodynamics · Elementary ideas of viscous flows

Aerospace Engineering (AE) 2019

A two-dimensional, incompressible fluid flow is described by the stream function \(\Psi = xy^3\) m²/s on the Cartesian \(x-y\) plane. If the density and dynamic viscosity of the fluid are 1 kg/m³ and 0.1 kg/m-s, respectively, the magnitude of the pressure gradient in the \(x\) direction at \(x=1\) m and \(y=1\) m is __________ N/m³ (round off to 1 decimal place).

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