Viscous Flow: Master Fluid Dynamics with Friction

Question 1

In a viscous fluid undergoing shear flow, how does shear stress relate to the velocity gradient, du/dy, where u is the velocity in the x-direction and y is the direction perpendicular to the flow?

Accepted Answer

Shear stress is directly proportional to the velocity gradient

Answer

Shear stress is inversely proportional to the velocity gradient

Answer

Shear stress is independent of the velocity gradient

Answer

Shear stress is proportional to the square of the velocity gradient

Question 2

In viscous flow, which of the following statements holds true?

Accepted Answer

Laminar flow exhibits smooth, parallel layers of fluid movement without mixing.

Accepted Answer

Viscosity measures a fluid's resistance to flow, indicating its tendency to deform under shear stress.

Answer

Viscous flow occurs exclusively in liquids due to their higher viscosity compared to gases.

Answer

Turbulent flow, with its unpredictable and chaotic motion, results in higher flow efficiency than laminar flow.

Question 3

In fluid flow, what is a defining characteristic that distinguishes turbulent flow from laminar flow?

Accepted Answer

High mixing and momentum transfer, resulting in irregular flow patterns

Answer

Smooth, predictable flow with minimal mixing

Answer

Low pressure drop along the flow path, enabling efficient fluid transport

Answer

Formation of distinct fluid layers with varying velocities

Question 4

In viscous flow, which dimensionless number quantifies the ratio of inertial forces to viscous forces?

Accepted Answer

Reynolds number

Answer

Mach number

Answer

Froude number

Answer

Prandtl number

Question 5

Which characteristic is unique to turbulent flow compared to laminar flow?

Accepted Answer

Random velocity fluctuations

Answer

Constant velocity profiles

Answer

Absence of boundary layers

Answer

High viscosity

Question 6

In viscous flow, which factors primarily determine the drag force acting on a spherical particle?

Accepted Answer

Particle diameter and fluid viscosity

Answer

Particle density and fluid pressure

Answer

Fluid velocity and particle shape

Answer

Gravitational acceleration and particle roughness

Question 7

For a Newtonian fluid, what is the relationship between shear stress and shear rate?

Accepted Answer

Directly proportional

Answer

Inversely proportional

Answer

Independent

Answer

Nonlinear

Question 8

In viscous flow, laminar flow is characterized by:

Accepted Answer

Fluid layers sliding past each other without any relative motion.

Answer

Fluid particles moving randomly, creating chaotic flow patterns.

Answer

Flow speed being the same at all points in the fluid.

Answer

Fluid viscosity having no effect on the flow behavior.

Question 9

Which characteristic is **not** unique to Newtonian fluids?

Accepted Answer

The relationship between shear stress and shear rate is non-linear.

Answer

Viscosity is independent of shear rate.

Answer

Shear stress is directly proportional to shear rate.

Answer

Density is constant.

Question 10

What is a distinguishing characteristic of viscous flow compared to inviscid flow?

Accepted Answer

Friction between fluid layers

Answer

Always laminar flow

Answer

Incompressible flow

Answer

Isothermal flow

Question 11

In the realm of viscous flow, which of the following accurately describes the behavior of non-Newtonian fluids?

Accepted Answer

Non-Newtonian fluids display a viscosity that varies in response to the applied shear rate.

Answer

Non-Newtonian fluids maintain a consistent viscosity regardless of the shear rate applied.

Answer

Non-Newtonian fluids exhibit a constant viscosity under varying shear rates.

Answer

Non-Newtonian fluids possess a viscosity that is unaffected by temperature changes.

Question 12

In a laminar boundary layer, the velocity gradient at the wall is:

Accepted Answer

Zero at the wall and increases linearly away from the wall

Answer

Zero everywhere

Answer

Constant everywhere

Answer

Increases exponentially away from the wall

Question 13

In laminar flow, which of the following statements is true?

Accepted Answer

The velocity profile is parabolic.

Answer

Fluid particles move randomly.

Answer

The flow is erratic and turbulent.

Answer

The fluid's viscosity is insignificant.

Question 14

Which property is unique to non-Newtonian fluids?

Accepted Answer

A non-zero yield stress exists.

Answer

Viscosity is independent of the shear rate.

Answer

A linear relationship exists between shear stress and shear rate.

Answer

No time-dependent behavior is observed in fluid flow.

Question 15

Which of the following fluids exhibits Non-Newtonian behavior?

Accepted Answer

Honey

Accepted Answer

Glycerol

Answer

Water

Answer

Air

Question 16

Which of the following accurately describes the relationship between shear stress and shear rate in a Newtonian fluid?

Accepted Answer

Shear stress is directly proportional to the shear rate.

Answer

Shear stress is inversely proportional to the shear rate.

Answer

Shear stress is independent of the shear rate.

Answer

Shear stress is directly proportional to the square of the shear rate.

Question 17

In a flow over a flat plate, which statement about the boundary layer thickness is accurate?

Accepted Answer

Thinner for laminar flow than turbulent flow at the same Reynolds number

Answer

Proportional to the square of the Reynolds number

Answer

Independent of the pressure gradient

Answer

Velocity gradient is constant throughout the boundary layer

Question 18

In laminar flow over a flat plate, the velocity profile at a given distance from the plate is:

Accepted Answer

Parabolic

Answer

Linear

Answer

Exponential

Answer

Uniform

Question 19

Which characteristic defines viscous flow?

Accepted Answer

Viscosity measures a fluid's resistance to deformation.

Answer

Fluid particles move in straight lines.

Answer

Laminar flow exhibits chaotic particle movement.

Answer

Turbulent flow features smooth and predictable particle movement.

Question 20

Which property uniquely characterizes Newtonian fluids?

Accepted Answer

Constant viscosity regardless of shear rate

Answer

Unvarying density under all conditions

Answer

Laminar flow at high Reynolds numbers

Answer

Increasing viscosity with decreasing temperature

Question 21

In viscous flow, which of the following is a true statement?

Accepted Answer

Flow can exhibit both laminar and turbulent behavior.

Answer

Viscous stresses are insignificant.

Answer

Velocity gradients are zero throughout the flow.

Answer

Pressure gradient is the only driving force for flow.

Question 22

In laminar flow, how do velocity gradients behave?

Accepted Answer

Zero at the center of the pipe, increasing towards the pipe wall

Answer

Zero everywhere

Answer

Finite everywhere

Answer

Infinite at the pipe wall

Question 23

In laminar flow, which of these is a key characteristic?

Accepted Answer

Smooth, orderly flow with minimal mixing

Answer

High Reynolds number

Answer

Unpredictable and chaotic flow patterns

Question 24

Which of the following is **not** a characteristic of viscous flow?

Accepted Answer

Absence of inertial forces

Answer

Friction between fluid layers

Answer

Non-linear relationship between shear stress and shear rate

Answer

Development of velocity gradients

Question 25

Which fundamental property distinguishes Newtonian fluids from non-Newtonian fluids?

Accepted Answer

Linear relationship between shear stress and shear rate

Answer

Laminar or turbulent flow behavior

Answer

Density

Answer

Transparency

Question 26

Which characteristic uniquely defines a non-Newtonian fluid?

Accepted Answer

Non-linear relationship between shear stress and shear rate

Answer

Constant viscosity under varying shear rates

Answer

Viscosity unaffected by temperature changes

Answer

Exclusive shear thickening behavior

Question 27

Within the boundary layer, where does the velocity gradient reach its highest value?

Accepted Answer

At the solid surface

Answer

At the outer edge of the boundary layer

Answer

At the center of the boundary layer

Answer

At a random point within the boundary layer

Question 28

In fluid mechanics, what is the primary reason for viscous effects, resulting in friction and energy loss?

Accepted Answer

Intermolecular forces between fluid particles

Answer

Density variations within the fluid

Answer

Pressure gradients within the fluid

Answer

Temperature differences within the fluid

Question 29

In viscous flow, how does the velocity profile change depending on the flow type (laminar or turbulent)?

Accepted Answer

Laminar flow has a curved velocity profile, while turbulent flow has a flatter velocity profile.

Answer

Turbulent flow has a curved velocity profile, while laminar flow has a flatter velocity profile.

Answer

The velocity profile is always curved, regardless of the flow type.

Answer

The velocity profile is always flat, regardless of the flow type.

Question 30

In viscous flow, what physical mechanism is responsible for the increase in boundary layer thickness downstream of an object?

Accepted Answer

Viscous shear

Answer

Pressure gradient

Question 31

Which property distinguishes non-Newtonian fluids from Newtonian fluids?

Accepted Answer

Non-Newtonian fluids can have a yield stress.

Answer

Non-Newtonian fluids have a constant viscosity.

Answer

Non-Newtonian fluids are always denser than Newtonian fluids.

Question 32

In a laminar boundary layer, the velocity profile exhibits which of the following characteristics?

Accepted Answer

Parabolic velocity

Answer

Uniform velocity

Question 33

In viscous flow, shear stress within the fluid is directly proportional to:

Accepted Answer

Velocity gradient

Answer

Pressure gradient

Answer

Fluid density

Answer

Fluid temperature

Question 34

In laminar flow through a circular pipe, the velocity profile across the pipe's cross-section is:

Accepted Answer

Symmetric about the pipe's center

Answer

Symmetric about the pipe's upper wall

Answer

Symmetric about the pipe's lower wall

Question 35

In boundary layer theory, which dimensionless parameter represents the ratio of inertial forces to viscous forces?

Accepted Answer

Reynolds number

Answer

Mach number

Answer

Prandtl number

Answer

Stanton number

Question 36

How does the von Kármán constant contribute to understanding the velocity profile in turbulent boundary layers?

Accepted Answer

It relates turbulent shear stress to viscous shear stress near the wall, defining the viscous sublayer and logarithmic region in the velocity profile.

Answer

It calculates the Reynolds number, indicating the balance between inertial and viscous forces.

Answer

It represents the average velocity gradient in the turbulent boundary layer.

Question 37

How does viscosity influence drag reduction techniques? Provide practical examples to illustrate your answer.

Accepted Answer

Viscosity modifiers, like polymers, can effectively reduce drag by altering flow characteristics and boundary layer behavior.

Answer

Viscosity has no significant impact on drag reduction techniques and is not considered in practical applications.

Answer

Increasing viscosity always increases drag, making viscosity modification ineffective for drag reduction.

Answer

Drag reduction techniques focus solely on changing flow velocity, ignoring the influence of viscosity.

Question 38

Define drag coefficient and explain how it varies based on flow conditions and the shape of the object.

Accepted Answer

Drag coefficient is a dimensionless value that quantifies the resistance faced by an object moving through a fluid, influenced by both flow regime and object shape.

Answer

Drag coefficient is only applicable to turbulent flow and is unaffected by object shape.

Answer

Drag coefficient is a fixed value for a specific fluid and flow regime, regardless of object shape.

Answer

Drag coefficient is solely determined by the velocity of the object moving through the fluid.

Question 39

In viscous flow, what are the different types of drag forces that can occur, and what factors influence each type?

Accepted Answer

Pressure Drag: Arises from pressure differences around an object; influenced by its shape, size, and orientation.

Accepted Answer

Shear Drag: Results from viscous forces acting on an object's surface; influenced by fluid viscosity, velocity, and surface roughness.

Accepted Answer

Form Drag: Occurs due to an object's shape and its disruption of the flow; influenced by object geometry and Reynolds number.

Answer

Wave Drag: Not applicable in viscous flow.

Question 40

Which characteristic is indicative of laminar flow?

Accepted Answer

Low velocity gradients

Answer

High Reynolds number

Answer

Turbulence

Answer

High pressure drop

Question 41

What fundamental difference exists between dynamic and kinematic viscosity?

Accepted Answer

Units of measurement

Answer

Physical meaning

Answer

Temperature dependence

Answer

No difference

Question 42

What is the primary role of the Reynolds number in fluid mechanics?

Accepted Answer

Predicts flow regime (laminar or turbulent)

Answer

Determines pressure drop in pipes

Answer

Calculates fluid velocity

Answer

Measures fluid viscosity

Question 43

Which type of flow experiences the highest drag force?

Accepted Answer

Turbulent flow

Answer

Laminar flow

Answer

Plug flow

Answer

Couette flow

Question 44

What is the intended purpose of a boundary layer bleed?

Accepted Answer

To prevent flow separation

Answer

To reduce drag

Answer

To enhance heat transfer

Answer

To increase pressure drop

Question 45

Which primary factor governs whether flow is laminar or turbulent?

Accepted Answer

Reynolds number

Answer

Viscosity

Answer

Density

Answer

Surface roughness

Question 46

How do polymer additives generally affect the flow characteristics of a fluid?

Accepted Answer

Increase viscosity and reduce turbulence

Answer

Decrease viscosity and increase turbulence

Answer

No effect on viscosity or turbulence

Answer

Increase both viscosity and turbulence

Question 47

Why are the Navier-Stokes equations crucial in studying viscous fluid flow?

Accepted Answer

They provide a complete mathematical framework for describing viscous fluid motion.

Answer

They are only applicable to laminar flow and cannot analyze turbulent flow.

Answer

They are only valid for incompressible fluids and cannot be applied to compressible fluids.

Question 48

Define the Reynolds number and explain its significance in determining the transition from laminar to turbulent flow regimes.

Accepted Answer

The Reynolds number is a dimensionless parameter that quantifies the relative dominance of inertial forces over viscous forces in a fluid.

Answer

The Reynolds number is only applicable to characterizing laminar flow.

Answer

The transition from laminar to turbulent flow occurs at a fixed and universal Reynolds number.

Question 49

Define drag coefficient and explain how it varies with flow regime and object shape.

Accepted Answer

Drag coefficient is a dimensionless number that quantifies the resistance encountered by an object moving through a fluid. It depends on the Reynolds number, which characterizes the flow regime, and the shape of the object.

Answer

Drag coefficient is a constant value that remains the same regardless of flow regime and object shape.

Answer

Drag coefficient is only applicable to objects moving in laminar flow.

Answer

Drag coefficient has no practical significance in engineering applications.

Question 50

Which of the following best describes laminar flow?

Accepted Answer

High fluid viscosity and low fluid velocity, resulting in regular and predictable flow patterns

Answer

High fluid velocity and low fluid viscosity, resulting in chaotic and unpredictable flow patterns

Answer

High fluid viscosity and high fluid velocity, resulting in regular and predictable flow patterns

Answer

Low fluid viscosity and low fluid velocity, resulting in chaotic and unpredictable flow patterns

Question 51

What dimensionless number quantifies the balance between inertial and viscous forces in a fluid flow?

Accepted Answer

Reynolds number

Answer

Mach number

Answer

Froude number

Answer

Prandtl number

Question 52

Which type of boundary layer has a velocity profile that gradually increases from zero at the solid surface to the free stream velocity?

Accepted Answer

Laminar boundary layer

Answer

Turbulent boundary layer

Answer

Blasius boundary layer

Answer

Von Kármán boundary layer

Question 53

How does static viscosity differ from dynamic viscosity?

Accepted Answer

Static viscosity is measured at zero shear rate, while dynamic viscosity is measured at some shear rate

Answer

Dynamic viscosity is measured at zero shear rate, while static viscosity is measured at some shear rate

Answer

There is no difference between static and dynamic viscosity

Answer

Static viscosity is a constant property of a fluid, while dynamic viscosity varies with shear rate

Question 54

What is the primary source of drag in viscous flows?

Accepted Answer

Skin friction drag

Answer

Pressure drag

Answer

Induced drag

Answer

Wave drag

Question 55

Which of the following is a key characteristic of laminar flow?

Accepted Answer

Low friction

Answer

High shear stresses

Answer

Fluctuating velocity

Answer

Turbulent mixing

Question 56

How does the boundary layer thickness in turbulent flow typically compare to that in laminar flow?

Accepted Answer

Larger in turbulent flow

Answer

Smaller in turbulent flow

Answer

Independent of flow conditions

Answer

Zero

Question 57

Which dimensionless parameter characterizes the relative significance of viscous forces to inertial forces?

Accepted Answer

Reynolds number

Answer

Prandtl number

Answer

Nusselt number

Answer

Schmidt number

Question 58

The Hagen-Poiseuille equation is primarily used to calculate:

Accepted Answer

Pressure drop in laminar pipe flow

Answer

Heat transfer coefficient in a turbulent boundary layer

Answer

Boundary layer thickness in a developing flow

Answer

Drag coefficient of a sphere

Question 59

What is the von Kármán constant and how does it relate to turbulent boundary layer velocity profiles?

Accepted Answer

A dimensionless constant used to scale the logarithmic velocity profile in turbulent boundary layers.

Answer

A constant that defines the boundary layer thickness.

Answer

An adjustment factor for pressure-gradient effects in boundary layer flows.

Answer

The ratio of viscous forces to inertial forces.

Question 60

Which statement accurately compares the flow characteristics of Newtonian and non-Newtonian fluids?

Accepted Answer

Newtonian fluids have constant viscosity, while non-Newtonian fluids have variable viscosity depending on flow conditions.

Answer

Non-Newtonian fluids always have higher viscosities than Newtonian fluids.

Answer

The flow behavior of non-Newtonian fluids can be described using the same equations as Newtonian fluids.

Answer

Newtonian and non-Newtonian fluids exhibit identical flow characteristics under all conditions.

Question 61

Prandtl's Boundary Layer Equation:

What is the key significance of Prandtl's boundary layer equation in analyzing viscous flow near solid surfaces?

Accepted Answer

Simplifies the governing equations within the boundary layer.

Answer

Ignores viscous forces in the boundary layer.

Answer

Assumes laminar flow in the boundary layer.

Answer

Applies only to flow over flat surfaces.

Question 62

Define the boundary layer displacement thickness, δ*, and explain its importance in airfoil design.

Accepted Answer

δ* is important in airfoil design because it determines the effective shape of the airfoil.

Answer

δ* is the thickness of the boundary layer where the velocity is 99% of the freestream velocity.

Answer

δ* is used to calculate the drag coefficient of an airfoil.

Answer

δ* is a dimensionless parameter that depends only on the Reynolds number.

Question 63

Which of the following is an indicator of laminar flow?

Accepted Answer

Parallel streamlines and low shear stress

Answer

Turbulent velocity fluctuations

Answer

Viscous effects are negligible

Answer

High Reynolds number

Question 64

The boundary layer in viscous flow is characterized by:

Accepted Answer

A region near the solid surface where velocity gradients are significant

Answer

A zone with uniform velocity

Answer

A layer where pressure gradients are negligible