Short Questions – Fluid Mechanics & Fluid Machines AKTU

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Important Questions For Fluid Mechanics & Fluid Machines : 
*Unit-01     *Unit-02    
*Unit-03    *Unit-04 
*Unit-05    *Short-Q/Ans
*Question-Paper with solution 21-22 

UNIT:1-(Fluid and Bernoulli’s Equation)

1. Define the term fluid.

Ans A substance that constantly deforms in the presence of external shearing force is referred to as a fluid.

2. Define control volume.

Ans The control volume approach, in which a specific volume with a set boundary shape is chosen in space along the fluid flow path, is typically used to apply fundamental fluid flow concepts. The control volume is the name given to this specific volume.

3. Enumerate some important properties of liquid.

Ans. Some important properties of liquid are:

1. Density,
2. Adhesion,
3. Viscosity.
4. Specific gravity,
5. Cohesion,
6. Surface tension

4. Define viscosity.

Ans. The characteristic of a fluid that influences how resistant it is to shearing stresses is known as viscosity. It serves as a gauge for the internal fluid friction that produces flow resistance.

5. What is kinematic viscosity?

Ans. The dynamic viscosity to fluid density ratio is known as kinematic viscosity. Its symbol is v.

6. State the Newton’s law of viscosity.

Ans. According to Newton’s rule of viscosity, the shear stress on a fluid element layer is exactly proportional to The coefficient of viscosity is the name for the proportionality constant.

Mathematically, proportional to the rate of shear strain.

7. Draw the figure of shear stress v/s rate of deformation.

8. Define surface tension. 

Ans Surface tension is the tensile force that acts on a liquid’s surface when it comes into contact with a gas or between two immiscible liquids, causing the surface to behave like a membrane under tension.

9. Define the term cohesion and adhesion.

Ans. Cohesion : It is the attraction between molecules of comparable kinds.

Adhesion: It is the attraction between molecules of different kinds.

10. Describe the assumptions of Bernoulli’s equation.

Ans. Assumptions of Bernoulli’s equation are as follows:

1. Fluid is ideal i.e., viscosity is zero.

2. Flow is incompressible.

3. Flow is steady.

4. Flow is irrotational.

11. State Bernoulli’s theorem.

Ans According to Bernoulli’s theorem, the total energy at any location in an ideal, steady flow of an incompressible fluid is constant.

12. What is a venturimeter ?

Ans. A venturimeter is a tool used to gauge how quickly a fluid is moving through a pipe.

13. Write a short note on the pitot static tube.

Ans. A pitot tube is a tool used to gauge the flow rate in any point or channel. It operates according to Bernoulli’s theorem.

14. What is the stagnation point ?

Ans. The point at which the fluid’s velocity is zero is known as the stagnation point.

15. Write the advantages of triangular notch or weir over rectangular notch or weir.

Ans Advantages of triangular notch or weir over rectangular notch or weir are as follows :

1. A triangular notch or weir does not require ventilation.

2. A triangular notch weir is preferred for low discharge measurements.

16. What is the coefficient of discharge ?

Ans. The ratio of the actual discharge to the theoretical discharge of flow is known as the coefficient of discharge.

UNIT:-02 (Types of Fluid Flow and Continuity Equation)

1. Differentiate between steady and unsteady flow.

Ans Steady Flow: Stable flow is a form of flow in which the fluid parameters at a given site, such as velocity, pressure, density, etc., do not fluctuate over time.

Unsteady Flow : Unsteady flow is the kind of flow when the speed, pressure, or density at a given place varies over time.

2. Define laminar and turbulent flow.

Ans. Laminar Flow: Laminar flow is a flow in which individual particle pathways do not intersect one another and travel along clearly defined paths.

Turbulent Flow: The flow in which fluid particles move zigzag-style is known as a turbulent flow.

3. Explain the rotational and irrotational flow.  OR Define rotational and irrotational flow.

Ans Rotational Flow:If fluid particles are rotating while travelling in the direction of fNow, the flow is said to be rotational.

Irrotational Flow: If the fluid particles do not rotate around their mass centres while travelling in the direction of the flow, the flow is said to be irrotational.

4. Define the continuity equation.

Ans. The continuity equation is the name given to the equation based on the conservation of mass.

5. What do you understand about circulation ?

Ans. The line integral of the tangential velocity about a closed path is what is known as circulation (contour). Integration can be used to obtain the circle’s path around regular curves.

6. Write down the definition of stream function.

Ans. As a function of both space and time, a stream function’s partial derivative with respect to any direction yields the velocity component perpendicular to that direction. It is denoted 

7. The velocity distribution between two parallel plates is given by u = (a² -y²), where u is the velocity at a distance y from the middle of the two plates. Find the expression for stream function. 

8. Discuss velocity potential function.

Ans A scalar function of space and time called a “velocity potential function” is described as having a negative derivative with respect to each direction that corresponds to the fluid velocity in that direction. It is denoted by ɸ.

9. What do you understand about Reynolds number ?

Ans The ratio of a fluid’s viscous force to its inertia force is known as the fluid’s Reynolds number. Thus,

10. What do you understand about dimensional homogeneity ?

Ans Dimensional homogeneity refers to the equality of the dimensions of each term on both sides of an equation.

UNIT:-03 (Flow Through Pipes, Boundary Layer Thickness)

1. Write the characteristics of laminar flow.

Ans. Characteristics of laminar flow are as follows:

1. Flow is irrotational.

2. No slip will occur at the boundary.

Each fluid layer flows separately.

2. What do you understand about the kinetic energy correction factor? 

Ans The ratio of the kinetic energy of the flow per second based on real velocity across a segment to the kinetic energy of the flow per second based on average velocity across the same section is known as the kinetic energy correction factor.

3. When will a laminar flow change to turbulent flow ?

Ans A laminar flow may change to turbulent flow when:

1. There is an increased velocity of flow.

2. There is an increased diameter of pipe.

3. The viscosity of fluid is decreased.

4. Give some examples of turbulent flow.

Ans. Some examples of turbulent flow are as follows

1. Smoke rising from a cigarette.

2. Flow over a golf ball.

3. The mixing of warm and cold air in the atmosphere.

5. Define eddy viscosity.

Ans Eddy viscosity is the viscosity that controls how momentum is transported by turbulent eddies.

6. What does the Hagen Poiseuille equation refer to ? What is Hagen Poiseuille’s formula ?

Ans. Hagen Poiseuille equation refers to loss of pressure head. 

7. Define surface loss. 

Ans. Surface loss is a loss in pressure or head that happens during pipe flow as a result of the viscosity of the fluid at the pipe’s surface.

8. What do you understand about TEL and HGL?

Ans. TEL: The definition of a total energy line (TEL) is a line that expresses the sum of the pressure head, datum head, and kinetic head of a flowing fluid in a pipe with respect to a reference line.

HGL: The line that gives the sum of the pressure head and datum head of a flowing fluid with respect to a reference line is known as a hydraulic gradient line.

9. In which cases siphon is used ?

Ans. Siphon is used in the following cases:

1. To transport water across a slope or ridge or from one reservoir to another.

2. To remove all of the water from a waterway without an outlet sluice.

10. Define a water hammer in pipes.

Ans. The pipe walls get a pounding effect from the high pressure wave. Water hammer in pipes is the term for this occurrence.

11. What are the necessary conditions for a pipe network ?

Ans. Followings are the necessary conditions for any network of pipes:

1. The amount of flow into each junction must match the amount of flow leaving the junction.

2. Each loop’s head losses must aggregate to zero algebraically.

12. What do you understand about displacement thickness?     OR What is displacement thickness ?

Ans.The distance that the solid body’s boundary should be shifted by, measured perpendicular to the boundary, in order to make up for the flow reduction caused by the creation of boundary layers is known as the displacement thickness.

13. What do you understand by shape factor?

Ans. The ratio of momentum thickness (0) to displacement thickness (δ*) is known as shape factor.

14. Define turbulent boundary layer and laminar sub layer.

Ans. Turbulent Boundary: The boundary layer is turbulent and thickens further downstream toward the transition zone. A turbulent boundary layer is what this layer of boundary is known as.

Laminar Sub Layer: This area in the boundary layer zone is next to the plate’s solid surface.

15. Explain the drag and lift. 

Ans: Drag: The component of the total force (F_R) in the direction of motion is called drag. This component is denoted by F_p.

Lift: The component of the total force (F_p) in the direction

perpendicular to the direction of motion is known as lift. This is denoted by F_L.

16. What is the average coefficient of drag?

17. Define aerofoil.

Ans. A streamlined body known as an aerofoil can be symmetrical or asymmetrical.

18. Discuss Magnus effect.

Ans A lift force is generated on a cylinder when it is spun in a uniform flow. The Magnus effect is the name for this phenomena.

19. Define impulse momentum equation.

Ans It claims that the change in momentum d(mv) in the direction of the force is equal to the impulse of force F acting on a fluid mass m in a brief period of time dt.

Mathematically,

               Fdt=d(mv)

UNIT:-04 (Impact of Jet, Impulse Turbine and Reaction Turbines)

1. What are fluid machines or hydraulic machines?

Ans. The definition of a hydraulic machine is a device that transforms hydraulic energy into mechanical energy or mechanical energy into hydraulic energy.

2. Define the term turbines.

Ans By definition, turbines are hydraulic devices that transform hydraulic energy into mechanical energy.

Example: Pelton wheel, Francis turbine, Kaplan turbine, etc.

3. Define overall efficiency.

Ans The ratio of the power present at the turbine’s shaft to the power supplied by the water entering the turbine is known as overall efficiency.

4. Define penstocks.

Ans Penstocks, which are large-diameter pipes used to transport water from storage reservoirs to the turbine, are often composed of steel or reinforced concrete.

5. What is the function of the nozzle in an impulse turbine?

Ans A nozzle is a pipe with a variable cross-sectional area that is used to control or direct the flow of fluid. It transforms the fluid’s pressure energy into kinetic energy.

6. State the function of breaking jet in Pelton wheel turbine.

Ans Water striking the runner decreases to zero when the nozzle is fully closed by the image of a spear pointing forward. However, the runner continues to revolve because of inertia. Therefore, this rotating wheel is stopped using a breaking jet.

7. Define runaway speed of turbine.

Ans. Runaway speed is the highest speed at which a turbine would operate under design head and discharge conditions but without an external load.

8. Why is the shape of the bucket of a Pelton wheel like two spoons ?

Ans. The benefit of having two spoons is that since axial forces are equal and opposite, they cancel each other out and do not exert any axial thrust on the bearings supporting the wheel shaft.

9. What is the function of the needle spear in a Pelton wheel ?

Ans The water flow through the nozzle is controlled by a moving needle spear inside the nozzle, which also offers a smooth flow with very little energy waste.

10. Why is the governing of a turbine necessary ?

Ans. Since a turbine is connected directly to an electric generator, which must run continuously under all conditions of fluctuating load, governing a turbine is vital. Only when the turbine’s speed is constant is this feasible.

11. Differentiate between impulse turbine and a reaction turbine.

Ans.

12. What do you mean by radial flow turbine?

Ans. Turbines with radial flow are ones in which the water moves in that direction. The water may flow radially either from an outer to an inner direction or vice versa.

13. Why is spiral casing of varying area employed in reaction turbines ?

Ans. In reaction turbines, spiral casing with various areas is used to maintain a constant flow velocity around the circumference.

14. What is the significance of specific speed?

Ans. An important factor in choosing the type of turbine is a specific speed. Additionally, by knowing a turbine’s precise speed, its performance can be predicted.

15. Define unit speed.

Ans. Unit speed of a turbine operating under a unit head, or a head of 1 m, is referred to as unit speed. It is denoted by N_U.

16. List the characteristic curves of a hydraulic turbine.

Ans Following are the important characteristic curves for the hydraulic turbine:

1. Main characteristic curves of constant head curves,

2. Operating characteristic curves of constant speed curves, and

3. Constant efficiency curves or iso-efficiency curves.

UNIT:-05 (Centrifugal and Reciprocating Pumps)

1. What is a centrifugal pump?

Ans A centrifugal pump is a hydraulic device that uses centrifugal force operating on fluid to transform mechanical energy into pressure energy.

2. Differentiate between volute and vortex casing of a centrifugal pumpP. 

3. What is meant by a manometric head for a centrifugal pump?

Ans. The head that a centrifugal pump must operate against is referred to as the manometric head. With the letters H.

4. Differentiate between static head and manometric head.

ANS.

5. Define manometric efficiency. 

Ans. Manometric efficiency is defined as the ratio of the head given to the liquid by the impeller to the manometric head created by the pump.

6. Define the specific speed of a centrifugal pump.

Ans. A geometrical pump’s specific speed is the rate at which it would deliver one cubic metre of liquid per second against a one-meter head. It is denied by N₂.

7. What are the advantages of model testing ?

Ans. Advantages of model testing are as follows: 

1. Model tests are affordable and practical.

2. Through model testing, the effectiveness and performance of a hydraulic machine or structure can be foreseen.

3. Model testing is necessary to learn about the safety and dependability of the parts, which cannot be precisely checked by analytical methods.

8. What is the purpose of priming a centrifugal pump?

Ans Due to the low density of air, the pump’s head is very small—if not nonexistent—and water may not be drawn in by the device. The centrifugal pump needs to be primed to avoid this issue.

9. What is NPSH ? 

Ans. The absolute pressure head at the pump’s inlet is subtracted from the combined vapour pressure and velocity heads to determine net positive suction head (NPSH).

10. What is the significance of characteristic curves?

Ans. When a pump is operating at a different flow rate, head, or speed, characteristic curves are required to forecast how the pump will behave and operate.

11. What is meant by a positive displacement pump?

Ans. Positive displacement pumps are those in which the liquid is sucked in and then is actually pushed or displaced as a result of the force applied to it by a moving element.

12. Define the term slip of reciprocating pump.

Ans. Slip is characterized as the discrepancy between the pump’s theoretical and actual discharge.

13. Define negative slip. When does it occur in a reciprocating pump ?

Ans. Negative slip is the result of the slip being negative when the pump’s actual discharge exceeds its theoretical discharge. When the delivery pipe is small, the suction pipe is long, and the pipe is moving quickly, negative slip happens.

14. Define ideal indicator diagram.

Ans. The ideal indicator diagram is the line drawn between the pressure head in the cylinder and the length of the piston’s stroke for a full crankshaft revolution.

15. What do you mean by maximum speed of a reciprocating pump? 

Ans. The maximum speed of a reciprocating pump is the speed at which liquid does not separate or the speed at which liquid separation does not occur.

16. What is the cause of acceleration ?

Ans. Water flow in the suction and delivery pipes is not uniformly velocized; it is zero at the start and finish of the stroke and greatest in the middle. The fundamental reason for acceleration is due to this.

17. What is the purpose of an air vessel fitted in the pump ?

Ans. The air vessel is used for the following purposes:

1. To obtain a consistent, endless supply of liquid.

2. To reduce the amount of energy needed to run the pump.

3. To operate the pump without separation at a high speed.

18. What will be the total % work saved by fitting the air vessel ?

Ans Single acting reciprocating pumps save 84.8% of the work, while double acting reciprocating pumps save 39.2% of the work.

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