GATE XE topic:external-flows PYQs & Answers — Page 3

Questions 21–30 of 31. Imported answers require independent review unless marked reviewed.

A spherical metal ball (of density

and diameter

), attached to a string, is exposed to a crossflow (of velocity

) of a viscous fluid (of viscosity

and density

). Due to the crossflow, the string makes an angle of inclination,

, with the top surface as shown in the figure. The acceleration due to gravity is denoted by

. For this flow, Reynolds number,

and buoyancy force in the fluid is negligible compared to viscous force. Assuming the string to be weightless and offering negligible drag, the expression for

Diagram for Engineering Sciences question 11

Your answerChoose one option.

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Figures given below show the velocity and shear stress profiles for the flow in a duct. In each option, ‘1’ represents velocity profile and ‘2’ represents shear stress profile.

Choose the correct option that closely represents the turbulent flow condition.

Your answerChoose one option.

Diagram for Engineering Sciences question 1

Diagram for Engineering Sciences question 1 (figure 2)

Diagram for Engineering Sciences question 1 (figure 3)

Diagram for Engineering Sciences question 1 (figure 4)

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A laminar hydrodynamic boundary layer over a smooth flat plate is shown in the Figure. The shear stress at the wall is denoted by

. Which one of the following conditions is correct.

Diagram for Engineering Sciences question 4

Your answerChoose one option.

Pressure is varying along ‘x’ and

Pressure is constant along ‘x’ and

Pressure is varying along ‘x’ and

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A golf ball is dimpled to make the flow turbulent and consequently to reduce the drag. Turbulent flow reduces the drag on the golf ball because

Your answerChoose one option.

skin friction coefficient is lower in a turbulent flow.

skin friction coefficient is higher in a turbulent flow.

turbulent flow has a lower tendency to separate.

turbulent flow has a higher tendency to separate.

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For a steady laminar incompressible boundary layer flow over a sharp-edged flat plate at zero incidence,

Your answerChoose one option.

the edge of the boundary layer is a streamline.

the edge of the boundary layer is a pathline.

the skin friction coefficient decreases as the distance from the leading edge increases.

the skin friction coefficient remains constant all along the plate.

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For steady laminar flow at zero incidence over a flat plate, the component of velocity parallel to the plate in the boundary layer is given by

, where

is the distance measured normal to the flat plate. If

is the coefficient of dynamic viscosity,

is the velocity parallel to the wall at the edge of the boundary layer and

is the boundary layer thickness, the wall shear stress is given by

Your answerChoose one option.

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A 2.6 gram smooth table-tennis (ping-pong) ball has a diameter of 38 mm. Density (ρ) of air is 1.2 kg/m³. Neglect the effect of gravity. Take coefficient of drag as 0.5. If the ball is struck with an initial velocity of 30 m/s, the initial deceleration, in m/s², is ________.

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On a flat plate, transition from laminar to turbulent boundary layer occurred at a critical Reynolds number (Re_cr). The empirical relations for the laminar and turbulent boundary layer thickness are given by

and

, respectively. The ratio of laminar to turbulent boundary layer thickness, at the location of transition, is 0.3. The value of Re_cr is ________.

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A (150 mm × 150 mm) square pillar is located in a river with water flowing at a velocity of 2 m/s, as shown in figure. The height of the pillar in water is 8 m. Take density of water as 1000 kg/m³ and kinematic viscosity as 1×10⁻⁶ m²/s. The coefficient of drag of the pillar is 2.0. The drag force exerted by water on the pillar in N is ________.

Diagram for Engineering Sciences question 21

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Air flows over a smooth flat plate at a velocity of 4.39 m/s. The density of air is 1.031 kg/m³ and the kinematic viscosity is 1.34×10⁻⁵ m²/s. The plate length is 12.2 m in the direction of the flow. The boundary layer thickness (

) is given as

, where

is the distance from the leading edge and

is the Reynolds number. The boundary layer thickness (in meters, rounded off to the second decimal place) at 12.2 m from the leading edge will be ________

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GATE XE topic:external-flows PYQs

Question 11

Question 1

Question 4

Question 4

Question 5

Question 15

Question 17

Question 18

Question 21

Question 31