Fluid Mechanics Final Exam Review

For steady incompressible internal flow in a circular pipe, the value of the Reynolds number is about __________. 2300 5600 8450 1200

2300

T/F: In laminar flow, the friction factor is a function of the Reynold number only and is independent of the roughness of the pipe surface

True

The average speed of a fluid flow through a cross-section area is defined as the ___________. average velocity angular velocity instantaneous velocity uniform velocity

average velocity

The head loss in a pipe flow is expressed as h_L = [\delta(P)]/(\rho*g). The pressure difference \delta(P) is a ______________ function of the distance traveled by the fluid.

linear

The sum of static and dynamic pressures is called the _________ pressure. atmospheric hydrostatic stagnation total

stagnation pressure

The volume of the fluid flowing through a cross-section per unit _________ is called the volume flow rate. volume area time force

time

T or F: in the given figure, to estimate the reaction forces, CV A is usually much easier to work with than CV B. (figure is the faucet picture in the book).

False

Compared with the equation of mass conservation for a fixed control volume, what is the difference of the equation of mass conservation applied to a moving or deforming volume? The absolute velocity is replaced by the moving velocity of the control surface The absolute velocity is replaced by the fluid velocity relative to the control surface The net mass flow rate through the control surface is zero The net mass flow rate through the control volume is zero

The absolute velocity is replaced by the fluid velocity relative to the control surface.

A baseball is hit out of the park for a home run. Identify the principle that can be used for analyzing the collision between the ball and the bat. dimensional similarity conservation of mass conservation of linear momentum obstruction flow

conservation of linear momentum

From the following, identify the steady flow devices in engineering applications. Turbines Diffusers Fuel tanks Nozzles

Turbines Diffusers Nozzles

For steady and single-stream flow, where 1 and 2 denote the inlet and the outlet, respectively. Select the correct equations reflecting the mass balance. (Check all that apply) m1 = constant p1*V1*A1 = p2*V2*A2 p1*V1*A1 = 0 m1 = m2

m1 = m2, p1*V1*A1 = p2*V2*A2,

The steady linear momentum equation for a single-stream system is expressed as SumF = mdot(B2*V2-B1*V1). That means the net force acting on control volume depends on the change in linear ___________ from outlet to inlet.

momentum

According to Newton's second law, an inertial coordinate system is also called an inertial ___________. incompressible frame compressible frame absolute frame reference frame

reference frame

Water is accelerated by a nozzle to an average speed of 20m/s and strikes a stationary vertical plate at a rate of 10 kg/s with a normal velocity of 20 m/s. After the strike, the water stream splatters off in all directions in the plane of the plate. Determine the force needed to prevent the plate from moving horizontally due to the water stream. 30 N 200 N 20 N 400 N

(1)(10)(20) = 200 N

The maximum velocity in a fully developed laminar pipe flow is determined to be 26 m/s. The average flow velocity is _________m/s.

13

The kinetic energy correction factor for a fully developed laminar flow is __________.

2

Choose all the correct statements about pipe entrances. Pipe inlets have a minor loss coefficient equal to \alpha regardless of their geometry. A well-rounded pipe inlet has a smaller minor loss coefficient than a sharp-edge inlet. if a reentrant pipe inlet were to be replaced by a well-rounded pipe inlet, all else being equal, the flow would have a smaller total minor loss. A well-designed reentrant pipe inlet has the smallest possible minor loss. Pipe inlets are considered major losses, not minor losses.

A well-rounded pipe inlet has a smaller minor loss coefficient than a sharp-edge inlet. if a reentrant pipe inlet were to be replaced by a well-rounded pipe inlet, all else being equal, the flow would have a smaller total minor loss.

Identify the types of fluid flow problems most often encountered in pipe flow system design. (check all that apply). Determining the pipe diameter Determining the flow rate Determining the pipe length Determining the pressure drop

Determining the pressure drop Determining the pipe diameter Determining the flow rate

The powerful technique that is introduced to properly scale model performance to prototype performance to is called _________ analysis. business process object dynamic dimensional

Dimensional analysis.

Identify examples of the mechanical system that possess some form of mechanical energy. Reaction in a lead acid battery Flow of gasoline from an underground tank into a car Water boiling in a kettle kept on the stove A brick held at a vertical position above the ground

Flow of gasoline from an underground tank into a car A brick held at a vertical position above the ground

Force on the model is less than that on the prototype.

Force scale factor < 1

Force on the model is more than that on the prototype.

Force scale factor > 1

Identify some examples of these kinds of forces (SumF_other).(check all that apply) Forces of pressure Forces at bolts Forces acting on struts Forces acting on the whole body Forces acting on cables

Forces at bolts Forces acting on struts Forces acting on cables

The model must be the same shape as the prototype.

Geometric similarity

Body force acts on each single fluid element. But if the density of the fluid in control volume is constant, the product of mass in control volume and gravitational vector represents ___________. Gravitational force acting on control volume Gravitational force acting on a fluid element Total body force acting on control volume Total body force acting on a fluid element

Gravitational force acting on control volume Total body force acting on control volume

When pressure losses are commonly expressed in terms of equivalent fluid column height, it is called the _________ loss. dynamic velocity head liquid

Head loss

The Characteristic length used in Reynolds number for a non-circular pipe is called ___________ diameter.

Hydraulic

Identify the advantages of non-dimensionalization. (check all that apply) It reduces the number of parameters in a problem. It increases the number of parameters in the problem. It eliminates some of the dependent variables in the problem. It increases the insight about the relationships between key parameters.

It increases the insight about the relationships between key parameters. It reduces the number of parameters in a problem.

What is the definition of average velocity for a fluid flow? it is defined as the maximum speed through a cross section. It is defined as the average speed through a cross section. It is defined as the summation of speeds through cross sections. It is half of the maximum velocity

It is defined as the average speed through a cross section.

The velocity at any point in the model flow must be proportional to the velocity at the corresponding point in the prototype flow.

Kinematic similarity

In fluid mechanics, Newton's second law is usually referred to as the _______ equation. conservation of energy linear momentum Bernoulli angular momentum

Linear momentum

identify the laws from which the Bernoulli equation can be obtained. (check all that apply) Second law of thermodynamics First law of thermodynamics Newton's first law Newton's second law

Newton's second law First law of thermodynamics

________ law is also referred to as the linear momentum equation. Newtons first Keplers first Newtons second Keplers second

Newtons First

Identify the law that states that the rate of change of the linear momentum of a body is equal to the net force acting on the body. Newtons first law Newtons second law Kepler's second law Kepler's third law

Newtons second law

In the Bernoulli equation flow energy is represented as.

P/p

Identify the components that sum up to form the hydraulic grade line.

Pressure head Elevation head

What are the other names for basic dimensions?(check all that apply) fundamental dimensions Non-fundamental dimensions Primary dimensions Non-primary dimensions

Primary dimensions fundamental dimensions

Identify the regions where the Bernoulli equation cannot be applied. (check all that apply) Regions of viscous flow Outside of wakes Directly downstream of bodies Close to solid walls

Regions of viscous flow Directly downstream of bodies Close to solid walls

The method of repeating variables.

Step 1: List the parameters in the problem and count their total number n. Step 2: List the primary dimensions of each of the n parameters. Step 3: Set the reduction j as the number of primary dimensions. Calculate k, the expected number of II's, k = n -j Step 4: Choose j repeating parameters. Step 5: Construct the k II's, and manipulate as necessary. Step 6: Write the final functional relationship and check your algebra.

Consider a pipe flow system. Identify the parameters that bring about a minor head loss in the system. (check all that apply). Sudden contraction of the pipe Sudden expansion of the pipe Sharp bends in a pipe Friction losses along the wall of the pipe

Sudden contraction of the pipe Sudden expansion of the pipe Sharp bends in a pipe

Identify the guidelines for choosing repeating variables. (check all that apply). Never pick parameters that are already dimensionless Always pick the dependent variable Always pick two parameters with the same dimensions The chosen repeating parameters must represent all the primary dimensions in a problem

The chosen repeating parameters must represent all the primary dimensions in a problem Never pick parameters that are already dimensionless

T/F: Dimensional analysis will generate non-dimensional parameters that help to reduce number of experiments.

True

During a steady-flow process, choose correct statements regarding the mass balance principle. The total amount of mass contained within a control volume does not change with time. The flow velocity within a control volume is the same The total rate of mass entering a control volume is equal to the total rate of mass leaving it The total rate of mass entering a control volume is a constant

The total rate of mass entering a control volume is equal to the total rate of mass leaving it The total rate of mass entering a control volume is a constant The total amount of mass contained within a control volume does not change with time.

In the Bernoulli equation kinetic energy is represented as.

V^2/2

The velocity of the fluid flowing in a pipe is maximum at or near the ____________ of the pipe. centerline entrance exit wall

centerline

In a fluid flow with curved streamlines, the fluid particle experience a corresponding __________ due to the pressure gradient developed. (check all that apply) centripetal force centripetal acceleration centrifugal acceleration centrifugal force

centripetal force centripetal acceleration

The surface force acting on a differential surface element shown in the figure is the ___________ product of a stress tensor and the unit outward normal vector.

contracted

The _________ pressure is the pressure rise when the fluid in motion is brought to a stop isentropically. dynamic hydrostatic static stagnation

dynamic

The conservation of energy principle requires that the change in the energy content of a system be ________ the net energy transfer to or from the system during a process. less than more than independent of equal to

equal to

Consider steady incompressible flow in a round pipe. In the hydrodynamically fully developed region of the flow, the flow is said to be ____________when the normalized temperature profile also remains unchanged. irrotational inviscid hydrodynamically developing flow fully developed

fully developed

The most common body force is that of _________, which exerts a downward force on every differential element of the control volume. electric nuclear magnetic gravity

gravity

In the Bernoulli equation potential energy is represented as.

gz

The region beyond the entrance region in which the velocity profile is fully developed and remains unchanged is called the

hydrodynamically fully developed region

From the following, identify the true statements about the limitations of the Bernoulli equation. (check all that apply) it is applicable for compressible flow only it assumes that there is no shaft work. it neglects viscous effects it is applicable for steady flow only

it assumes that there is no shaft work. it neglects viscous effects it is applicable for steady flow only

Accelerating systems such as aircraft during takeoff are best analyzed __________ systems fixed to the aircraft. noninertial linear noninertial coordinate inertial linear inertial coordinate

noninertial coordinate

momentum-flux correction factor, B is equal to _________ for the case of uniform flow over an inlet or outlet. zero half one infinity

one

The total angular momentum of a(n) _________ body remains constant when the net torque acting on it is zero non-harmonic harmonic oscillating rotating

rotating

During ___________ flow, the amount of momentum within the control volume remains constant. rotational steady turbulent unsteady

steady

Because atmospheric pressure acts in every direction, the pressure forces at the outlet section where the fluid is discharged as a jet at _________ velocities can be ignored. sonic subsonic hypersonic supersonic

subsonic

The important distinguishing feature of a moving or deformed control volume is that the concept of relative _______ is to be involved. current volume velocity density

velocity

The only additional force that acts on an inclined flow when compared to a horizontal flow is the __________. weight of the fluid buoyancy viscosity surface tension

weight of the fluid

From the following, identify the true statements about a control volume. (check all that apply) A control volume should have its control surface oriented tangential to the flow. A control volume should have its control surface oriented normal to the flow. A control volume should simplify the problem A control volume should be convenient to work with

A control volume should simplify the problem A control volume should be convenient to work with A control volume should have its control surface oriented normal to the flow.

All forces in the model flow scale by a constant factor to corresponding forces in the prototype flow.

Dynamic similarity

__________ equation is an approximate relation between pressure, velocity, and elevation, and is valid in regions of steady, incompressible flow where net frictional forces are negligible. Newton's Navier-Stokes Andrade's The Bernoulli

The Bernoulli

Consider steady incompressible flow in a round pipe. If the Reynolds number is 3350, the flow is most likely _________. Laminar Transitional Turbulent

Transitional Laminar = RE < 2300 Transitional = 2300 < RE < 4000 Turbulent = 4000 < RE

In a water-cooled nuclear reactor, the reactor core must be always filled with water. if the reactor converts 20 kg of water to steam every second, select the acceptable scenarios from the following. Two pumps with an output mass flow rate of 10kg/s each are to be used to keep the core full. Two pumps with output mass flow rate of 5kg/s each are to be to keep the core full A pump with an output mass flow rate of 10kg/s is to be used to keep the core full. A pump with an output mass flow rate of 20kg/s is to be used to keep the core full.

Two pumps with an output mass flow rate of 10kg/s each are to be used to keep the core full. A pump with an output mass flow rate of 20kg/s is to be used to keep the core full.

The conservation relations are also called __________ equations since any conserved quantity must balance during a process.

balance

The three primary purposes of dimensional analysis are:

• To generate nondimensional parameters that help in the design of experiments (physical and/or numerical) and in the reporting of experimental results • To obtain scaling laws so that prototype performance can be predicted from model performance • To (sometimes) predict trends in the relationship between parameters