JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II FLUID MECHANICS AND HYDRAULIC MACHINES Previous Question Paper (August/September - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Prove that pressure always acts normal to the surface.
Answer
To prove that pressure acts normal to a surface, consider a small fluid element in the shape of a wedge with unit thickness perpendicular to the plane of the paper. Let the pressure on the inclined face be p, and the pressures on the horizontal and vertical faces be px and py respectively. If the pressure were not normal to the surface, it would have a tangential component (shear stress). However, in a fluid at rest, the fluid cannot resist shear stress. If a tangential force existed, the fluid would deform continuously, contradicting the assumption of static equilibrium. By summing the forces in the x and y directions and setting them to zero, it is found that the shear stress must be zero, meaning the pressure force acts only in the direction normal to the surface.
Explain gauge pressure, absolute pressure and vacuum pressure. How will you determine absolute pressure from gauge and vacuum pressure?
Answer
Absolute pressure is the pressure measured with reference to absolute zero pressure or a complete vacuum. It represents the total pressure exerted by the fluid including the atmospheric pressure.
Gauge pressure is the pressure measured with reference to the local atmospheric pressure as the zero point. It is the pressure indicated by a standard pressure gauge, which ignores the atmospheric pressure acting on the system.
Vacuum pressure (or negative gauge pressure) is the pressure measured below the local atmospheric pressure. It represents the extent to which the pressure in a system is lower than the ambient atmospheric pressure.
The relationship between these pressures is determined as follows:
- For a system where the pressure is above atmospheric pressure: Pabs = Patm + Pgauge
- For a system where the pressure is below atmospheric pressure (vacuum): Pabs = Patm - Pvac
Here, Pabs is the absolute pressure, Patm is the local atmospheric pressure, Pgauge is the gauge pressure, and Pvac is the vacuum pressure.
Calculate the velocity gradient at a distance of 0 cm, 5 cm, 10 cm and 15 cm if the velocity profile is a parabola with a vertex 15 cm from the surface, where the velocity is 80 cm/s. Also calculate the shear stresses at these points if the fluid at these points has a viscosity of 80 × 102 Ns/m3.
Answer
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Calculate the maximum capillary rise of water to be expected between two vertical clean glass plate spaced 1 mm apart. If the water is replaced by mercury, calculate maximum capillary depression of mercury in the same space.
Answer
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The x and y components in a 2-D flow field for an incompressible fluid are expressed as u = 2xy and v = x2 - y2.
i) Show that the motion is possible.
ii) Check whether the flow is irrotational or not.
iii) Calculate velocity potential function.
Answer
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Compare steady and unsteady, uniform and non-uniform, laminar and turbulent, rotational and irrotational flows.
Answer
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Water flows at a velocity of 2 m/s through a 90 cm diameter pipe at the end of which there is a reducer connecting it to a 60 cm diameter pipe. If the gauge pressure at the entrance to the reducer is 400 kN/m2, determine the trust on the reducer assuming the loss of head in the reducer is 1.5 m of water.
Answer
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Compare venturimeter and orifice meter.
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A venturimeter is fitted to a 15 cm diameter pipeline carrying water which is inclined at 60° to the horizontal plane. The throat diameter of the venturimeter is 5 cm and is placed higher than the inlet side. The difference in pressure head between the throat and the inlet which are 0.9 m apart is equivalent of 7.5 cm of mercury. Calculate the rate of flow of water. Assume Cd = 0.98.
Answer
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A kite weighing 10 N and having an area of 1 m2 makes an angle of 10° to the horizontal when flying in a wind of 36 km/h. If the kite is held by a cord, in which the tension is 50 N, and the cord makes an angle of 45° to the horizontal, calculate the drag and lift coefficients. Assume specific weight of air as 12.0 N/m3.
Answer
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State the angular momentum theorem. Derive an expression to determine the power developed/consumed by a hydraulic machine.
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A jet of water moving at 12 m/s impinges on a concave shaped vane to deflect the jet through 120° when stationary. If the vane is moving at 5 m/s, find the angle of the jet so that there is no shock at inlet. Also determine the absolute velocity at exit in magnitude and direction and work done per unit weight of water. Assume the vane is smooth.
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Give a layout of a pumping installation and name the main accessories.
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State various types of losses which may occur in a centrifugal pump.
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