Deemed University 2011 B.Tech Mechanical Engineering University: Lingayas University Term: V Title of the : Fluid Mechanics - Question Paper

Roll No. ..

 

Lingayas University

B.Tech. 2^nd Year (Term V)

Examination Feb 2011

Fluid Mechanics (ME - 207)

 

[Time: 3 Hours] [Max. Marks: 100]

 

Before answering the question, candidate should ensure that they have been supplied the correct and complete question paper. No complaint in this regard, will be entertained after examination.

 

Note: Attempt five questions in all. All questions carry equal marks. Question no. 1 is compulsory. Select two questions from Section B and two questions from Section C.

Section A

Q-1. Part A

Select the correct answer of the following multiple choice questions. [10x1=10]

(i) Compressibility is the reciprocal of

(a) Bulk modulus of elasticity

(b) Shear modulus of elasticity

(c) Youngs modulus of elasticity

(d) Any of the above

(ii) The point of application of the force of buoyancy on the body is known as

(a) Centre of gravity (b) Centre of buoyancy

(c) Meta centre (d) None of the above

(iii) An ice-cube is floating in glass of water. As the cube melts the water level:

(a) Remain constant (b) Rises

(c) Falls (d) None of the above

(iv) In fluid mechanics, the continuity equation is a mathematical statement embodying the principle of

(a) Conservation of momentum

(b) Conservation of mass

(c) Conservation of energy

(d) None of the above

(v) The piezometric head is the summation of

(a) Velocity head and pressure head

(b) Velocity head and elevation head

(c) Pressure head and elevation head

(d) None of the above

(vi) Which of the following is an example of laminar flow?

(a) Underground flow (b) Flow past tiny bodies

(c) Flow of oil in measuring instruments

(d) All of the above (e) None of the above

(vii) The flow in town water supply pipes is generally

(a) Laminar (b) Turbulent

(c) Transition (d) Any of the above

(viii) Loss of head at entrance to pipe is given as

(a) (b)

(c) 0.5 (d)

(ix) The condition for maximum transmission of power through a pipeline is that one-third of the available head must be consumed in friction. The corresponding efficiency of the pipeline is

(a) 33.3% (b) 66.67%

(c) 90% (d) 100%

(x) The critical value of Reynolds number at which boundary layer changes from laminar to turbulent depends on which of the following?

(a) Turbulence in ambient flow (b) Surface roughness

(c) Pressure gradient (d) Please curvature

(e) All of the above

Part B

(a) Define boundary layer and explain the fundamental causes of its existence. [5]

(b) Explain the following:

(i) Circulation (ii) Vorticity [5]

 

Section B

Q-2. (a) Discuss the expressions for total pressure and centre of pressure for an inclined plane submerged in the liquid.

(b) A solid cylinder of 200 mm diameter and 800 mm length has its base 20 mm thick and of specific gravity 6. The remaining part of the cylinder is of specific gravity 0.6. State, if it can float vertically in water. [2x10=20]

 

Q-3. (a) Discuss the various characteristics of stream function and potential function.

(b) For a 2D flow, the velocity components are . Determine (i) the acceleration components a_x and a_y (ii) the rotation of w_z. [2x10=20]

 

Q-4. (a) Gasoline (sp. gr. 0.8) is flowing upwards through a vertical pipeline which tapers from 300 mm to 150 mm diameter. A gasoline mercury differential manometer is connected between 300 mm and 150 mm pipe section to measure the rate of flow. The distance between the manometer tappings is 1 m and gauge reading is 500 mm of mercury. Find:

(i) Differential gauge reading in terms of gasoline head

(ii) Rate of flow

Neglect friction and other losses between tappings. [10]

(b) Why co-efficient of discharge of an orifice meter is much smaller than that of venturimeter? [5]

(c) Define kinetic and momentum correction factors. [5]

 

Section C

Q-5. (a) Derive an expression for the power lost in a footstep bearing.

(b) A flow of 420 lit/min of oil (sp. gr. = 0.91 and viscosity 1.24 poise) is pumped through a pipeline 75 mm diameter having a length of 62 m and whose outlet is 3 m higher than its inlet. Estimate the power required for the pump if its efficiency is 60%. [2x10=20]

Q-6. (a) What is an equivalent pipe? Explain how its length and diameter is calculated.

(b) A pipe 50 mm diameter is 6 m long and the velocity of flow of water in the pipe is 2.4 m/s. What loss of head and the corresponding power would be saved if the central 2 m length of pipe was replaced by 75 mm diameter pipe, the change of section being sudden? Take f = 0.04 for the pipes of both diameter. [2x10=20]

Q-7. (a) Discuss the phenomenon of drag on a flat plate due to laminar and turbulent boundary layers?

(b) A submarine can be assumed to have cylindrical shape with rounded nose. Assuming its length to be 50 m and diameter 5 m, determine the total power required to overcome boundary friction if it cruises at 8 m/s velocity in sea water at 20⁰C = 1030 Kg/m³, v = 10^-6 m²/s. [2x10=20]

Q-8. (a) What is the difference between isentropic and adiabatic flows?

(b) A tank fitted with convergent nozzle contains air at a temperature of 20⁰C. The diameter at the outlet of the nozzle is 25 mm. Assuming adiabatic flow, find the mass rate of flow of air through the nozzle to the atmosphere when the pressure in the tank is:

(i) 140 KN/m² (abs) (ii) 300 KN/m²

Take for air, R = 287 J/Kg K, v = 1.4

Barometric pressure = 100 KN/m². [2x10=20]