JNTU
JNTU B.Tech II FLUID MECHANICS AND HYDRAULIC MACHINES Previous Question Paper (March - 2021 - R16)
Answer any five questions
All questions carry equal marks
Main
Differentiate between: (i) real fluids and ideal fluids (ii) Newtonian and non-Newtonian fluids.
Answer
(i) Real vs Ideal Fluids: An ideal fluid is defined as a fluid that is incompressible and has zero viscosity (inviscid). It does not offer any resistance to shear deformation. In contrast, a real fluid possesses both viscosity and compressibility. When in motion, real fluids offer resistance to shear stress due to internal friction, leading to energy dissipation.
(ii) Newtonian vs Non-Newtonian Fluids: A Newtonian fluid is one that obeys Newton's law of viscosity, where the shear stress is directly proportional to the rate of angular deformation (velocity gradient), expressed as τ = μ(du/dy). For these fluids, the viscosity μ remains constant regardless of the shear rate. A non-Newtonian fluid does not follow this linear relationship; its apparent viscosity changes with the applied shear rate (e.g., pseudoplastic, dilatant, or Bingham plastic fluids).
A pressure gauge consists of two cylindrical bulbs B and C each of 10 cm2 cross sectional area, which are connected by a U-tube with vertical limbs each of 0.25 cm2 cross sectional area. A red liquid of specific gravity 0.9 is filled into C and clear water is filled into B, the surface of separation being in the limb attached to C. Find the displacement of the surface of separation when the pressure on the surface C is greater than that in B by an amount equal to 1 cm head of water.
Answer
Let AB = AC = 10 cm2 be the area of bulbs and a = 0.25 cm2 be the area of the U-tube limbs. Let Δh be the displacement of the surface of separation. When pressure at C increases by 1 cm of water, the liquid level in bulb C drops by ΔhC and in bulb B rises by ΔhB.
By continuity of volume: AB × ΔhB = a × Δh and AC × ΔhC = a × Δh. Thus, ΔhB = (0.25/10)Δh = 0.025Δh and ΔhC = 0.025Δh.
The total displacement of the separation surface in the U-tube is Δh = ΔhB + ΔhC + x, where x is the movement relative to the initial level. The pressure balance equation for a pressure difference ΔP = 1 cm of water (ρwgΔhw) is:
Substituting ρred = 0.9ρw and the displacement relations:
Solving for Δh:
The displacement of the surface of separation is 1.114 cm.
Water flows through a pipe AB 1.2 m diameter at 3 m/s and then passes through a pipe BC 1.5 m diameter. At C, the pipe branches. Branch CD is 0.8 m in diameter and carries one-third of the flow in AB. The flow velocity in branch CE is 2.5 m/s. Find the volume rate of flow in AB, the velocity in BC, the velocity in CD and the diameter of CE.
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Starting with Euler’s equation of motion along a streamline, obtain Bernoulli’s equation by its integration. List all the assumptions made.
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A 30 cm diameter pipe carries water under head of 15 m with a velocity of 4 m/s. If the axis of the pipe turns through 45°, find the magnitude and direction of the resultant force at the bend.
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What do you understand by Boundary Layer? Explain the development of Boundary layer over a flat plate.
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What are the dimensionless numbers in dimensional analysis? Discuss any three of them.
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The water is flowing through a pipe having diameters 20 cm and 10 cm at sections 1 and 2 respectively. The rate of flow through pipe is 35 litres/s. The section 1 is 6 m above datum and section 2 is 4 m above datum. If the pressure at section 1 is 39.24 N/cm2, find the intensity of pressure at section 2.
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What type of turbine is Kaplan turbine? Explain how it works with a neat diagram. Discuss the importance of draft tube in reaction turbines.
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A Kaplan turbine runner is to be designed to develop 9100 kW. The net available head is 5.6 m. If the speed ratio is 2.09, flow ratio is 0.68, overall efficiency is 86% and the diameter of the boss is 1/3 the diameter of the runner. Find the diameter of the runner, its speed and the specific speed of the turbine.
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Classify and explain different types of turbines.
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Explain the term 'cavitation' and Thomas’s cavitation number. Why does cavitation occur and what are its effects?
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A centrifugal pump lifts water under a static head of 35 m of water of which 4 m is suction lift. Suction and delivery pipes are both 150 mm in diameter. The head loss in suction pipe is 0.8 m and in delivery pipe 7 m. The impeller is 380 mm in diameter and 25 mm wide at mouth and revolves at 1200 r.p.m. Its exit blade angle is 35°. If the manometer efficiency of the pump is 82 percent determine: a) the discharge through the pipe and b) the pressure at the suction and delivery branches of the pump.
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