Fluid Mechanics and Hydraulics Refresher Terms

Flashcards containing 60 key practice questions and solutions on Fluid Mechanics and Hydraulics.

What properties do practical fluids possess?

Viscosity, surface tension, and compressibility.

Which characteristic is true regarding liquids?

They do not occupy a definite shape.

According to the refresher terms, how does the specific weight of a liquid behave?

It does not vary on any other planet.

Under what standard conditions is the specific weight of water equal to $1000\,\text{kg/m}^3$?

At a normal pressure of $760\,\text{mm}$, at $4^\circ\text{C}$ temperature, and at mean sea level.

Why is the specific weight of sea water greater than that of pure water?

Due to dissolved air, dissolved salts, and suspended matter.

To which class of fluids does water belong?

Newtonian fluid.

Why do fluids change volume under external pressure?

Due to compressibility.

According to the refresher terms, molecules of fluids get attracted due to what mechanism?

Adhesion.

Why do falling drops of water become spheres?

Due to surface tension.

In an open tube, how does the free surface of mercury remain?

Curved downwards.

If cohesion between fluid molecules is greater than adhesion between the fluid and glass, how does the free level of fluid in a dipped glass tube compare to the liquid surface?

Lower than the surface of liquid.

What are barometers used to measure?

Atmospheric pressure.

What are piezometers used to measure?

Pressure in water channels, pipes, etc.

What are manometers used to measure?

Difference in pressure at two points.

What are differential manometers used to measure?

Difference in pressure at two points.

What is pressure less than atmospheric pressure known as?

Suction pressure, vacuum pressure, or negative gauge pressure.

How is gauge pressure defined?

Absolute pressure $$-$ atmospheric pressure.

What parameters cause atmospheric pressure to vary?

Altitude, temperature, and weather conditions.

Why is mercury generally used in barometers?

Its vapor pressure is practically zero and the height of the barometer will be less.

Under what orientations is the total pressure force on a plane area equal to the area multiplied by the intensity of pressure at its centroid?

When the area is horizontal, vertical, or inclined.

Where is the centre of pressure located for a vertical plane immersed in a liquid?

None of these (neither centre of higher edge, centre of lower edge, nor centroid of the area).

When a body is totally or partially immersed in a fluid, what is the magnitude of the buoyant force acting on it?

Weight of the fluid displaced by the body.

Under what position of its metacentre does a floating body attain stable equilibrium?

Above the centroid.

What is the centre of buoyancy?

Centroid of the fluid displaced.

How does the water level change in a partially filled tank carried on a truck moving with constant horizontal acceleration?

It rises on the back side and falls on the front side.

For mountainous regions having a steep slope, how are liquid-carrying wagons constructed at the bottom?

Parallel to the horizontal surface.

How does the rise of liquid along the walls of a revolving cylinder compare to the depression at the axis of rotation?

It is the same as the depression of the liquid at the axis of rotation.

When a liquid rotates at constant angular velocity about a vertical axis of a rigid body, how does pressure vary?

It varies as the square of the radial distance.

When does steady flow occur in fluids?

When conditions of flow do not change with time at a point.

When is uniform flow said to occur?

When the size and shape of the cross-section in a particular length remain constant.

If velocities of fluid particles vary from point to point in magnitude and direction as well as from instant to instant, what is the flow called?

Non-uniform flow.

Through what type of pipe and flow rate does steady uniform flow occur?

A long pipe at constant rate.

Through what type of conduit does non-uniform steady flow occur?

An expanding tube at constant rate.

What law or equation does an ideal flow of a liquid obey?

Continuity equation.

What relationship is expressed by the continuity equation?

Relates mass rate of flow along a stream line.

What is the flow called in which each liquid particle has a definite path and adjacent paths do not cross each other?

Stream line flow.

What are the main assumptions of Bernoulli's equation?

Velocity of energy of liquid particle across any cross-section is uniform, no external force except gravity acts on the liquid, and there is no loss of energy while flowing.

Reynold number is the ratio of initial (inertia) force and what other property?

Viscosity.

Flow in pipes is laminar if the Reynold number is in what range?

Less than $2100$.

Flow in pipes is turbulent if the Reynold number is in what range?

More than $3000$.

Where can the hydraulic grade line lie relative to the centre line of a conduit?

It may be above or below the centre line of conduit.

Which statements are correct regarding energy lines and gradients in pipe flow?

Total energy gradient is the graphical representation of total head, vertical distance between total energy line and hydraulic grade line equals velocity head, and vertical distance between total energy line and total energy gradient represents loss of head.

What is the ratio of inertia forces to viscous forces in any flow called?

Reynold number.

What is the ratio of inertia forces to gravitational forces in any flow called?

Froude number.

What instrument is used for measuring the velocity of flow?

Pitot tube.

What parameter does a piezometer opening in pipes measure?

Static pressure.

What is hydraulic radius equal to?

Area divided by wetted perimeter.

When is the flow in an open channel said to be non-uniform?

When the free water surface is not parallel to the channel bed, or head needed to overcome frictional resistance is either less or more than the drop in channel bed elevation.

For the most economical rectangular section of a channel, how is depth maintained relative to width?

Half the width.

What geometry defines the most economical section of a triangular channel?

Right angled triangle with equal sides.

What is considered the most efficient channel section?

Semi-circular.

What phenomenon occurs in an open channel when a rapidly flowing stream abruptly changes to a slowly flowing stream causing a distinct surface rise?

Hydraulic jump.

What properties define an ideal fluid?

It is frictionless and incompressible.

What is the horizontal component of the force on a curved surface equal to?

Force on a vertical projection of the curved surface.

When an open container with water is accelerated vertically upward with uniform linear acceleration, how does bottom pressure compare to static pressure?

Greater than static pressure.

When an open container with water is accelerated vertically downward with uniform linear acceleration, how does bottom pressure compare to static pressure?

Lesser than static pressure.

Through which point does hydrostatic force act?

Centre of pressure.

What relationships govern the capillary rise of water?

Directly proportional to surface tension, inversely proportional to water density, and inversely proportional to diameter of the tube.

For stable equilibrium of a floating body, where must its metacentre be relative to its centre of gravity?

Above the centre of gravity.

The metacentric height of a body equals the distance between which two points?

The metacentre and centre of gravity.