Fluid Flow Questions

---

Very Short Answers Questions [1 Mark Questions]

Ques. Which of the following is true?

1. Flow is turbulent inside the boundary layer and laminar outside
2. Flow is laminar inside the boundary layer and turbulent outside
3. Flow is turbulent both inside and outside of the boundary layer
4. Flow is laminar both inside and outside of the boundary layer

Ans. The correct answer is b. Flow is laminar inside the boundary layer and turbulent outside

Explanation: Flows are classified as laminar or turbulent according to Reynold's number R_e = ρvd / μ, where ρ is the density, d is the diameter of the pipe, and μ is the viscosity. The flow will be laminar for R_e < 2000 and turbulent for R_e > 4000. The viscosity effects must be high (μ should be high) inside the boundary layer for laminar flow. The viscosity effects are insignificant outside of the boundary layer. As a result, the flow will be turbulent.

Ques. Which method is used exclusively in fluid mechanics?

1. Eulerian method
2. Lagrangian method
3. Neither the Lagrangian nor Eulerian method
4. Both Lagrangian and Eulerian methods

Ans. The correct answer is a. Eulerian method

Explanation: The general state of motion at various points in the fluid system (as in the Eulerian method) rather than the motion of each particle (as in the Lagrangian approach) is of interest in Fluid Mechanics. As a result, the Eulerian method is widely utilized in fluid mechanics.

Ques. Which of the following is the basic principle of fluid mechanics?

1. Continuity equation
2. Energy equation
3. Momentum principle
4. All of the above

Ans. The correct answer is d. All of the above

Explanation: The three basic fluid mechanics principles are the continuity equation (i.e. mass conservation), the momentum principle (or momentum conservation), and the energy equation.

Ques. The compressible flow is assumed to be _____________

1. Isentropic only
2. Adiabatic only
3. Polytropic
4. Isentropic and adiabatic

Ans. The correct answer is a. Isentropic only

Explanation: Compressible flow is a branch of fluid mechanics that studies various kinds of flow. Its fundamental importance derives from the change in fluid density. It is concerned with gas dynamics. It is assumed that the flow is isentropic.

Ques. “The velocity of entrance and exit through a nozzle remains the same.” Is this even possible?

1. only if the flow is laminar
2. only if the flow is rotational
3. only if the flow is compressible
4. never possible

Ans. The correct answer is c. only if the flow is compressible

Explanation: According to the continuity equation, ρAV = constant, where ρ = density, A = cross-sectional area of flow, and V = velocity of flow. If v = constant, then A = constant. As a result, a change in A will result in a change in ρ. As a result, the flow is only possible if the fluid is compressible.

Ques. What are the factors that affect fluid flow?

Ans. The factors that affect the flow of fluids are

• Velocity
• Density
• Viscosity

---

Short Answers Questions [2 Marks Questions]

Ques. What are the main types of fluid flow regions?

Ans. There are three types of fluid flow regions: turbulent, transition, and laminar. The components that contribute to each type of flow characteristics vary depending on the system. Fluid flow simulations for various Reynolds numbers are used to clearly define and quantify the transition from laminar to turbulent flow.

Ques. What is an ideal fluid?

Ans. When a fluid cannot be squeezed or compressed, it is said to be an ideal fluid. It doesn't have any viscosity. It is essentially a fictitious fluid that does not exist in the physical world.

Ques. What is an incompressible fluid and compressible fluid?

Ans. An incompressible fluid is one whose density does not change with the application of an external force.

A compressible fluid is one whose density changes in response to the application of an external force.

Ques. What is an ideal plastic fluid?

Ans. An ideal plastic fluid is one in which shear stress is generally proportional to velocity gradient and yield value is smaller than shear stress.

Also Read:

---

Long Answers Questions [3 Marks Questions]

Ques. What are the different properties of fluids?

Ans. The following are the properties of fluids

• Density: The density of a fluid is its mass per unit volume. It is the mathematical ratio of the fluids' mass to volume.
• Specific weight: It is defined as the weight of fluids per unit volume. It is the mathematical ratio of the fluids' weight to volume.
• Specific gravity: Specific gravity is the ratio of fluid-specific weight or mass density to standard fluid-specific weight or mass density. Fluids in the case of liquid standards are water, whereas fluids in the case of gaseous standards are air.
• Specific volume: The volume of fluid per unit weight is known as the specific volume of fluid. It is the inverse of weight density.
• Viscosity: It is the resistance that a layer of fluids experiences when it travels over another layer of fluids.
• Surface tension: It is a tensile force exerted on a liquid's surface in contact with air or between two liquids.

Ques. What are the properties of streamlined flow?

Ans. The following are the properties of streamlined flow

• The tangent at any point of a streamline gives the direction of fluid particles at that point.
• In a steady flow, no two streamlines can cross each other. If they cross each other, then at the point of intersection two tangents can be drawn. It means that the oncoming fluid particles can go either one way or the other. Thus the flow would not be steady.
• Fluid velocity remains constant at any point of a streamline, but it may be different at different points of the same streamline.
• Fluid velocity is greater at the regions where streamlines are closely spaced. This can be proved from the equation of continuity.

Ques. What is the difference between laminar and turbulent flow?

Ans. The differences between laminar and turbulent flow are

---

Very Long Answers Questions [5 Marks Questions]

Ques. It is desired to design an airplane with a lift of 1000 N per square meter of wing area. If the velocity of streamline flow past the lower wing surface is 100 m/s, what will be the required velocity over the upper surface? (The density of air is 1.3 kg/m³)

Ans. The wing of the airplane is designed in such a way that the upper part of the wing is more curved than the lower part. Since the fluid from the upper and lower part of the wing has to reach the other end at the same time, the speed of the fluid flow increases at the upper part. Due to this pressure at the top will be decreased and hence the pressure at the bottom is more as compared to the top. This pressure difference gives a lift to the plane.

Applying Bernoulli’s principle

P₁ + 1/2 ρv₁² + ρgh₁ = P₂ + 1/2 ρv₂² + ρgh₂ 

Where

• P₁ is the pressure at the top
• P₂ is the pressure at the bottom
• ρ is the density of the air
• v₁ is the velocity of the air at the top
• v₂ is the velocity of the air at the bottom
• h₁ and h₂ are the height of the upper and lower part of the wing from a reference point.
• g is the acceleration due to gravity

Since h₁ = h₂ therefore the above equation becomes

P₁ + 1/2 ρv₁² = P₂ + 1/2 ρv₂²

⇒ P₂ – P₁ = 1/2 ρ(v₁² - v₂²)

Given

• P₂ - P₁ = 1000 N/m²
• v₂ = 100 m/s
• ρ = 1.3 kg/m³

On substituting the values in the above equation, we get

1000 = 1/2 x 1.3(v₁² - 100²)

⇒ v₁ = 107.4 m/s

Therefore, the required velocity of the air over the upper surface is 107.4 m/s.

Ques. At what velocity does the water emerge from an orifice in an open tank if the gauge pressure at the orifice is 2 x 10⁵ N/m² before the flow starts?

Ans. For an open tank, the velocity of efflux from an orifice at height h from the surface of the liquid is given by

v = √(2gh) …(i)

Given that the pressure difference (gauge pressure) between the top surface and orifice is, ΔP = 2 x 10⁵ N/m²

Also, ΔP = ρgh

Where

• ρ is the density of the fluid
• g is the acceleration due to gravity
• h is the height of the fluid column

From the above equation, we get

gh = ΔP/ρ

Desnity of water is, ρ = 10³ kg/m³

Therefore, equation (i) becomes

v = √(2ΔP/ρ)

On substituting the values, we get

v = √(2 x 2 x 10⁵ /10³) = 20 m/s

Therefore the velocity with which the water emerges from an orifice in an open tank is 20 m/s.

Ques. What are the different types of fluid flow?

Ans. The different types of fluid flow are

• Steady and Unsteady: A steady fluid flow is one in which conditions such as velocity, pressure, and cross-sectional area remain constant regardless of position or stream. An unsteady fluid flow occurs when the parameters of the fluid, such as velocity, pressure, or cross-sectional area, change with time at any point throughout the flow.
• Viscous and Non-viscous: The parameters of the fluid, such as velocity, pressure, or cross-sectional area, are constant for that period of time or at that point of observation in a viscous fluid flow, which generally occurs at a lower velocity. Non-viscous fluid flow refers to a fluid that has no resistance to internal friction but a higher resistance to fluid flow.
• Laminar and Turbulent: Laminar flow is a form of streamlined flow in which the fluid flow is smooth and constant in velocity, pressure, and cross-sectional area at a particular point of observation and time. The streamlines in this type of flow are all parallel to one another. Turbulent flow is a type of flow in which the fluid's inertial forces dominate, and it is typically observed to flow with a higher velocity and speed at any given position and time.
• Uniform and non-uniform: The velocity at a particular instant of time in uniform fluid flow is the same at any location of the fluid and has the same magnitude in all directions. The velocity of the fluid varies at every instant for every place at any time in non-uniform fluid flow.
• Compressible and incompressible: The density of a fluid in compressible fluid flow may change over time based on the pressure or shear forces acting on the fluid. Most fluids in nature are incompressible at normal room temperature; this is the property of a fluid in which the density does not change when shear forces impact it.
• Rotational and irrotational: The fluid in rotational fluid flow rotates around its own axis while flowing. In irrotational fluid flow, the fluid does not rotate around its own axis.
• One, two, and three-dimensional: When the fluid properties like velocity, density, and pressure are in one, two, and three directions, they are known as One-dimensional, Two-dimensional, and Three-dimensional fluid flow respectively.

---

Previous Year Questions

1. Electric flux at a point in an electric field is..
2. The correct order of acid strength of the following carboxylic acids is..[Jee Advanced 2019]
3. The measurement of voltmeter in the following circuit is...[AIIMS 2017]
4. Angular velocity of minute hand of a clock is...[MP PMT 2004]
5. Highly pure dilute solution of sodium in liquid ammonia...[Jee Advanced 1998]
6. A gas mixture consists of 22 moles of oxygen and 44 moles of Argon at temperature T. Neglecting all vibrational modes, the total internal energy of the system is..[NEET UG 2017]
7. Alkali halides do not show Frenkel defect because​..
8. Let R = {(1,3),(4,2),(2,4),(2,3),(3,1)} be a relation on the set A = {1,2,3,4}. The relation R is...[AIEEE 2004]
9. Degree of freedom for polyatomic gas...[AIIMS 2012]
10. In pyrrole, the electron density is maximum on...[NEET UG 2016]
11. The major product of the following reaction is​...[JEE Main 2019]
12. Major product of the following reaction is..[JEE Main 2023]
13. The percentage of nitrogen in urea is about..
14. The electric field at a point is​
15. Which of the following statements is true?​..[JKCET 2006]

For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates

---

Check-Out: