JNTU
JNTU B.Tech II FLUID MECHANICS Previous Question Paper (November/December - 2017 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
What is the difference between cohesion and adhesion?
Answer
Cohesion is the intermolecular attraction between molecules of the same substance, which is responsible for surface tension and the formation of droplets. Adhesion is the attraction between molecules of different substances, which causes fluids to wet surfaces or cling to the walls of a container.
Brief on significance of vapour pressure.
Answer
Vapour pressure is the pressure exerted by a vapour in thermodynamic equilibrium with its condensed phases at a given temperature. Its significance in fluid mechanics is primarily related to the phenomenon of cavitation.
When the local pressure of a flowing liquid drops below its vapour pressure, the liquid begins to boil or vaporize at that temperature, forming bubbles of vapour. As these bubbles are carried by the flow into regions of higher pressure, they collapse violently. This process, known as cavitation, causes:
- Surface pitting and material erosion due to high-pressure shock waves generated during bubble collapse.
- Significant noise and mechanical vibrations in hydraulic machinery such as pumps and turbines.
- Reduction in the efficiency and performance of fluid systems by disrupting the flow profile.
Understanding vapour pressure is therefore critical for the design of hydraulic systems to ensure that operating pressures remain safely above the vapour pressure threshold to prevent cavitation damage.
What is a flow net?
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If stream function exists in a flow problem, does it imply that velocity potential also exists.
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What is the main difference between a notch and a weir?
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State the assumptions used in deriving Bernoullis equation.
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Define Boundary layer thickness.
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Is the flow with in the boundary layer rotational or irrotational? Why?
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Write the laws of fluid friction.
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What are the factors influencing the frictional losses in pipe flow?
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Part B
Derive an expression for total pressure and centre of pressure for a vertically immersed surface.
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At a certain location in the flow field, pressure equals to 50 m of water column. Obtain the equivalent pressure head in terms of (i) kerosene of specific gravity 0.8 (ii) Carbon tetrachloride of specific gravity 1.5.
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What are manometers? How are manometers classified? What are the advantages of U-tube manometer over the piezometer?
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A cylindrical tank of 3 m height and 5 cm2 cross sectional area is filled with water up to a height of 2 m and remaining with oil of specific gravity 0.8. The vessel is open to atmosphere. Calculate:
i) Pressure intensity at the interface
ii) Absolute and Gauge pressure on the base of the tank in terms of water head and oil head in terms of N/m2. Take atm Pressure as 1.0132 bar.
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Explain the following:
i) Stream tube
ii) Streak lines.
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A two dimensional flow is described by the velocity components u = 5x3 and v = -15x2y. Determine the stream function, velocity and acceleration at P(x=1m and Y= 2m).
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Distinguish between:
i) Rotational flow and irrotational flow
ii) Laminar flow and turbulent flow.
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Deduce the general three dimensional equation of continuity and deduce from it the continuity equation for one dimensional frictionless flow.
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Differentiate between the Eulerian and Lagrangian method of representing fluid motion.
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An orifice meter is to be fitted into a horizontal pipe 35 cm dia, carrying oil of specific gravity 0.85 for the purpose of flow measurement. The differential head is to be indicated by a U-tube manometer containing mercury (specific gravity = 13.6). If the manometer reading is not to exceed 0.28 m when the flow is 25kg/sec, what should be the diameter of the orifice? Assume Cd = 0.62.
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What is a pitot tube? How is it is used to measure velocity of flow at any point in a pipe or channel?
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Find the discharge through a trapezoidal notch which is 1 m wide at the top and 0.4 m at the bottom and is 0.3 m in height. The head of water on the notch is 0.2 m. Assume Cd for rectangular portion is 0.62 and for triangular portion is 0.6.
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What do you mean by boundary layer separation? What is the effect of pressure gradient on boundary layer separation?
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Starting with the Navier-stokes equations of motion for two dimensional incompressible flow, obtain Prandtl’s boundary layer equation.
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What do you understand by the boundary layer? Illustrate with reference to flow over a flat plate?
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What is meant by magnus effect? Explain.
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What do you understand about Reynold’s experiments? Explain the results of Reynold’s experiments with the help of graph and represent the laminar and turbulent flow parts on the graph.
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Derive the formula for calculating for loss of head due to sudden enlargement with a neat sketch.
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Explain the total energy line and hydraulic gradient line for fluid flow through a piping system.
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The rate of flow of water through a horizontal pipe is 0.32 m3/s. The diameter of the pipe is suddenly enlarged from 225 mm to 550 mm. The pressure intensity in the smaller pipe is 12.502 N/cm2. Determine: i) loss of head due to sudden enlargement ii) pressure intensity in the large pipe iii) power lost due to enlargement.
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