Fluid Mechanics
What is the material derivative of mass?
zero
Based on these definitions, which of the following combinations of parameters results in a dimensionless number?
ρ V Dμ, σg D2 Δρ2 Δ, ΔP L2ρ ν2Δ22, g ∀ ρ2μ2
During a section of a piping system carrying water, it is noticed that the hydraulic grade line increases significantly. What can we say about the flow during this section? Assume no mechanical device is present to interfere with the energy of the flow. However, allow for frictional effects.
The diameter of the pipe decreases in the direction of flow., The static pressure of the fluid decreases significantly., The velocity of the fluid decreases.
Which of the following statements are true?
The expression dP=-ρ g dz describes pressure variation in all static fluids on earth., The density of a compressible fluid increases with depth.
A rectangular plate of height H and width w, is immersed vertically in water and suspended so that its top (width edge) is just at the surface. Which of the following statements is true about this scenario? (Note that all option refer to the gage pressure.)
The net force exerted by the water gage pressure on one side of the plate is 1/2ρgH^2w., The centre of the gage pressure is located at 23H23., The gage pressure at the centroid of the plate is 1/2ρgH.
The more polished a solid surface, the larger the wetting angle tends to be.
True
When a flow has a flat (constant) velocity profile, the momentum and kinetic energy flux correction factors both equal 1.0.
True
Which of the following strategies can be used to increase the resolution of the readings on a U-Tube manometer?
Use a less dense manometer fluid., Place the main manometer scale on an incline.
If a particular solid is to be classified as a fluid, its behaviour will most closely resemble.
a bingham fluid
A particular fluid, when at rest, is relatively thin. However, as one mixes it, it tends to thicken. This type of fluid is likely to be _________.
a dilatant fluid
A floating body is considered to be stable (will not capsize) if the metacenter is located __________ the centre of gravity of the body.
above
Intermolocular forces between molecules of different chemical nature is called _________.
adhesion
Water is to _________ as _________ is to atmosphere.
air, oceans
Which of the following are true characteristics of fluids?
all liquids or gases are fluids, they tend to take the shape of their container, when at rest, they experience no shear
Intermolocular forces between molecules having the same chemical nature is called _________.
cohesion
When a prototype and its model have the same 3D shape, and corresponding locations on a model and prototype/real systems have proportional velocities, shear and pressures, this is called ________.
complete similarity
When corresponding locations on a model and prototype/real systems have proportional pressures and shear, this is called ________.
dynamic similarity
A pressure transducer is a kind of _____.
electric-based pressure gauge
The energy required to compress a unit mass of a fluid to a given pressure is _________.
flow energy, P/ρ
Identical hydrometers are placed in two different fluids (A and B). In fluid A, the bottom of the hydrometer sinks to twice the depth that it does in fluid B. What can we say about the fluids?
fluid B has about twice the density of fluid A
The expression P/ρ+½V⃗ 2+gz=constant is only valid _________.
for incompressible flow, for flow with negligible friction, along a streamline, provided no mechanical device exists in the stream
Which of the following are dimensions?
force, time, length
When using a single-fluid manometer, the expression ρg(h−ho) is equivalent to ___________, where h and ho are heights of the fluid in the test and open ends of the manometer, respectively.
gage pressure
Generally speaking, what are some main difference between liquids and gases?
gases are compressible while liquids are not, liquids can have a surface while gases have no certain surface (except the surface of its container), gases are freely expanding while the surface tension and attraction between liquid molecules keeps them together and condensed
When a prototype and its model have the same 3D shape, this is called ________.
geometric similarity
As a fluid flows through a channel under viscous and irreversible conditions, the reduction in the energy grade line is understood to be ________________ loss
head
A plastic bottle (very thin wall) is filled to the brim with water, then tightly capped and placed in water of the same state. How will the filled bottle behave when released under water?
it will almost hover
When corresponding locations on a model and prototype/real systems have proportional velocities, this is called ________.
kinematic similarity
The energy required to accelerate a unit mass of a fluid from rest to a given velocity is _________.
kinetic energy
The dimension for Head is.
length
The phenomena of surface tension has implications at the interfaces between the following phases.
liquids with gases, liquids with liquids, solids with liquids
The Bernoulli Equation can be written in all of the following dimensions except ________.
m, kPa, M L2 T-2
A device which measures the fluid pressure by the height of liquid in a column is called a _____.
manometer
The form of energy that can be converted to mechanical work completely and directly by means of a mechanical device such as a turbine is called _____________ energy.
mechanical
Which of the following are units?
metres, pounds, seconds
The most important non-dimensional number applicable to fluid dynamics is the __________.
Reynolds Number.
Pressure variation in atmospheric gases with increasing elevation is complicated by the following factors:
Temperature variations, Density variations, Variations in force due to gravity, Changes in the chemical composition of the atmosphere
For a single-inlet single-outlet flow with no mechanical energy extaction (or insertion), no external heating, and frictionless flow, the RTT applied to energy becomes __________.
The Bernoulli Equation
Which of the following statements are true? Select all that apply.
The centre of bouyancy of a completely immersed body is located at the centroid of the body., The higher the centre of bouyancy on a body, the more rotational stability it will have., For an immersed object, if the centre of bouyancy is lower than the center gravity, it is never rotationally stable.
Of the following statements, which are true concerning a flat submerged plate/surface?
The centre of pressure can never be above the centroid., If the plate is horizontal, the centre of pressure coincides with the centroid., The more dense the fluid the more the separation between the centre of pressure and the centroid.
When performing dimensional analysis, which of the following principles can assist in selecting the repeating parameter?
The chosen parameters must not be able to form a dimensionless group., The chosen parameters must cover all the primary dimensions., Pick common or simple parameters rather than those involving too many dimensions.
As a liquid flows through a horizontal constant cross-section area pipe, the rate of mechanical energy loss from the liquid as it travels from the inlet to the outlet is equal to __________. Assume the pipe to be perfectly insulated with no external energy interactions such as turbines, pumps or heaters.
m˙c(Tout−Tin), m˙ρ−1 (Pin−Pout)
As a very light feather is carried about by air, time-lapse video captures the changing location of the feather. An imaginary line connecting each subsequent location of the feather is called a _________.
pathline
Under all flow conditions, these lines only grow in length, but never wiggle. Question 7Answera.%-50vector lines
pathlines
One seeks to study the motion of a light feather as it is carried about in air. The most appropriate perspective from which to analyze this scenario would be the _________.
pathlines, streaklines
Under steady flow conditions, streamlines are the same as ___________
pathlines, streaklines
Which of the following strategies can be used to maintain high heads as water is transported from its supply reservior to the location of final use.
place booster pumps along the line, ensure the water is contain in a closed channel (pipes) rather than open flow (like a canal), use as large a pipe (in diameter) as is economically feasible
The energy required to raise the height of a unit mass of a fluid to a given elevation is _________.
potential energy, gz
The quantity, 1 atm, is equal to _________.
standard atmospheric pressure, 101325 Pa
A steel ball and a foam ball, both of identical physical dimensions, are placed in the same fluid. What can we say about the bouyancy experienced by both objects.
the bouyancy on both objects will be the same
An object is rotationally stable even though the center of buoyancy is lower than the center of gravity. Why is this so ?
the metacenter of the object is relatively high, the bouyancy and weight forces on the object provides a rotation moment that is counter to any rotation imposed on the object
Vertical stability is rarely experienced by objects in fluids except when _________.
the object is located at the interface between two fluids
The centre of pressure and the centroid on a flat plate will coincide if _________.
the plate is horizontally oriented, the plate is located at very great depths
The contact angle between water and a glass surface is approximately 0º. What are the implications of this?
the water surface is pulled up as it approaches the glass surface, water naturally wets the glass surface
A liquid droplet, when placed on solid surface is observed to easily roll about, and leaves no trace on areas of the surface that it passes over. What can be concluded about this scenario?
there are relatively weak cohesive forces between the water and the surface, the wetting angle approaches 180º.
What is the material derivative of position?
total velocity
The expression P/ρ+½V⃗ 2+gz=constant is only valid _________.
under steady flow conditions, for inviscid fluids, along a streamline, under adiabatic conditions
When using a single-fluid manometer, the expression ρg(ho−h) is equivalent to ___________, where ℎ and ho are heights of the fluid in the test and open ends of the manometer, respectively.
vacuum pressure
Which head is excluded from the determination of the hydraulic grade line (HGL).
velocity
For fluids, shear stress is proportional to _________.
velocity gradient, strain rate, viscousity
rectangular plate of height ℎ and width w extends vertically from the surface of a liquid to very great depths so that ρgh≫Po. How deep will the centre of pressure be located?
yP=2h/3
A rectangular plate of height hℎ and width w extends vertically from the surface of a liquid to very shallow depths so that ρgh≪Po. How deep will the centre of pressure be located?
yP=h/2
For a space craft travelling in outer space (where there is no drag or gravitational forces acting on it), the total derivative of the momentum of a control-volume completely enclosing the spacecraft is __________.
zero
The Bernoulli equation is derived from Newton's _________________applied to a fluid particle on its streamline.
2nd law
The dimensions for mass is Force Time-squared per Length.
True
The dimensions for strain rate is inverse Time.
True
The dimensions of vorticity is the same as the dimensions for strain rate.
True
The force acting on an area due to pressure is a vector.
True
Elastics are fluids.
False
How many surfaces does a soap bubble have?
2
The expression P/ρ+½V⃗ 2+gz=constant is known as the
Bernoulli Equation
The _____ is a pressure measurement device that uses a bent, coiled or twisted hollow tube, which deflects as the pressure inside the tube is increased.
Bourdon Tube
The __________ is based on control volume analysis.
Eulerian system
Buoyancy does not contribute to the upward forces of an object resting on the surface of the earth.
False
Gases do not experience gravitational pull to Earth.
False
Pressure variation in gases is almost linear with elevation or dep
False
Solids cannot be fluids.
False
The dimensions for compressibility is Length-cubed per Temperature.
False
The dimensions for volume is cubic-metres.
False
The dimensions for weight is newtons.
False
The term "curl" and "angular velocity" have the same meaning.
False
Which of the following statements is/are true?
If an immersed object's CB is below it's CG, it is NEVER rotationally stable.
Which of the following are characteristics of pressure in a fluid?
It always acts perpendicular to the wall in contacting the fluid., If the fluid is at rest, the quantity of pressure at a point in a fluid is the same in every direction at that point., Pressure applied to a wall of a fluid-filled closed vessel becomes transmitted to all other parts of the vessel.
Which of the following statements is true about the expression dP/dz=−ρg?
It applies to both liquids and gases., Over relatively small depths or elevations (less than 10 kilometres), g can be taken as a constant., It applies to pressures at various depths underneath ocean/sea surfaces as well as to pressures in the atmosphere at various elevations., Over most ocean depths, ρ can be taken as a constant., It is the basis of operation for manometers.
Which of the following statements is TRUE regarding the Method of Repeating Variables?
It is one method used to determine the Πs for a given dimensional problem., A very important step in this method is to determine the dimensional parameters that are permitted to be in more than one Πs., This method is normally used when persons are inexperienced in knowing and applying the dimensionless groups that are common to their particular field of study.
What are common consequences of converting physical systems with several interalated dimensional parameters to systems descibed using only non-dimensional parameters?
It reduces the complexity of the system being analyzed., It enables the prediction of real system behaviour using measurements of a similar model system that may have a much different size., It highlights which variables are most impactful on a system.
The dimensions for Area Moment of Interia is __________.
Length to the fourth power
A helium balloon rising through atmosphere is an example of a floating object
True
A helium balloon rising through atmosphere is an example of an immersed object.
True
During open flow (such as in a canal) the flow energy of the fluid remains constant.
True
During steady flow, the local derivative of any field variable equals zero.
True
Elastics cannot be fluids.
True
If a pitot-static tube is placed in a stream on an unknown liquid, no other information apart from the difference of the tube liquid heights is needed to estimate the velocity of the liquid.
True
Manometer-based pressure measurement devices must involve the use of a liquid.
True
Plastics are fluids.
True
Pressure variation in liquids is almost linear with elevation or depth.
True
Rigid Bodies cannot be fluids.
True
The area that pressure acts on is a vector.
True
