Midterm 1 Study Terms

Question 1

what is the definition of a continuum when talking about fluids?

Answer 1

a simplification of disregarding the atomic nature of a substance (gas) and viewed as continuous (homogenous, matter with no holes)

Question 2

how does cavitation form?

Answer 2

when the pressure of a system drops below vapor pressure, bubbles form then then suddenly collapse

Question 3

What is the definition of microscopic energy?

Answer 3

energies related to molecular structure system (sum = internal energy)

Question 4

What is the definition of macroscopic energy?

Answer 4

energies a system possess as a whole with respect to some outside reference frame (kinetic, potential)

Question 5

How is a water hammer caused and what happens?

Answer 5

occurs when a valve/pump are closed/shut down suddenly
causes the water pressure to rise and fall rapidly (can damage pipes)

Question 6

What is the speed of sound and how does it work/happen?

Answer 6

FOR COMPRESSIBLE FLOW!!
happens due small disturbances propagating and causing a change in thermodynamic property of the fluid. The small disturbance also causes a slight change in local P

Question 7

what is the definition of viscosity and how is it caused?

Answer 7

a property that represents the internal resistance to a fluid to motion or the “fluidity”
caused by the cohesive forces between molecules in liquids and by the molecular collisions in gases (varies greatly with temp)

Question 8

What is the definition of drag force?

Answer 8

The force a flowing fluid exerts on a body in the flow direction
magnitude of this force depends. in part, on viscosity

Question 9

what is the definition of dynamic viscosity?

Answer 9

a measure of the force (internal resistance, force needed to make a fluid flow at a certain rate)

Question 10

what is the definition of kinematic viscosity?

Answer 10

a measure of the velocity (how fast a fluid is moving when a force is applied)

Question 11

what are some examples of non-newtonian fluids

Answer 11

bingham: behaves like solid at small shear stress, then deforms as shear stress increases
pseudoplastic: more shear applied = less viscosity
dilatant: viscosity increases with increased deformation

Question 12

what are the differences between the viscosity of a liquid vs gas

Answer 12

liquid: molecules have more energy at higher temps, can oppose the large cohesive intermolecular forces more strongly, as result, can move more freely
gas: intermolecular forces are negligible, gas molecules at high temps move randomly at higher velocities, results in more collisions per unit volume per time and therefore in greater resistance to flow

Question 13

how does surface tension work?

Answer 13

usually, liquids at material interface exert a force per unit length, at interface between liquid and gas or 2 immiscible fluids, forces develop at the interface which cause the surface to behave like a skin or “membrane”

Question 14

what are the conditions that Bernoulli’s equation is valid for?

Answer 14

inviscid fluid (viscosity = 0)
incompressible fluid
steady flow (flow along streamline)
no shaft work
no heat transfer
irrotational
small vorticity (twisting motion, curling)

Question 15

How do we describe the motion of a fluid particle

Answer 15

STREAMLINES:
traces the path of the particle
is everywhere tangent to the velocity vector
a mathematical tool to describe a velocity field

Question 16

What does HGL stand for and what does it represent?

Answer 16

Hydraulic grade line: the line that represents the sum of the static pressure and the elevation heads

Question 17

what does EGL stand for and what does it represent?

Answer 17

Energy grade line: the line that represents the total head of the fluid

Question 18

what is dynamic head?

Answer 18

the differences between the heights of EGL and HGL (v2/2g)

Question 19

when does EGL equal HGL?

Answer 19

for stationary bodies (lakes or reservoirs)

Question 20

what is the constant distance between EGL and HGL?

Answer 20

dynamic HEAD

Question 21

In an idealized bernoulli flow, how should the EGL and HGL look?

Answer 21

the EGL should be horizontal with its height remaining constant, HGL should vary depending on flow velocity varying along the flow

Question 22

for open-channel flow, how should the EGL and HGL look?

Answer 22

HGL is at the liquid free surface and EGL is a dynamic head distance above the free surface

Question 23

what is the pressure head at a pipe exit?

Answer 23

zero and thus the HGL coincides with the pipe outlet

Question 24

what happens to EGL and HGL due to frictional effects (mechanical energy loss)

Answer 24

This causes the EGL and HGL to slope downward in the direction of flow. the slope is a measure of the head loss in the pipe. A component such as a valve, that generates significant frictional effects causes a sudden drop in both EGL and HGL in that location

Question 25

what happens to EGL and HGL whenever mechanical energy is added for removed to or from the fluid (pump, turbine)?

Answer 25

A steep jump or drop occurs
A steep jump occurs when mechanical energy is added (pump)
A steep drop occurs when mechanical energy is removed (turbine)

Question 26

What happens to the gauge pressure of a fluid at locations where the HGL intersects the fluid?

Answer 26

it is ZERO
the pressure in a flow section that lies above the HGL is NEGATIVE
the pressure in a section that lies below is POSITIVE

Question 27

what is the definition of static pressure?

Answer 27

it represents the actual thermodynamic pressure of the fluid. This is the same as the pressure used in thermodynamics and property tables

Question 28

what is the definition of dynamic pressure?

Answer 28

it represents the pressure rise when the fluid in motion is brought to a stop isentropically

Question 29

what is the definition of hydrostatic pressure?

Answer 29

technically not pressure in a real sense since its value depends on the reference level selected; it accounts for the elevation effects ie fluid weight on pressure

Question 30

what is the definition of fluid kinematics

Answer 30

the study of how fluids flow and how to describe fluid motion

Question 31

what are the two distinct ways to describe fluid motion

Answer 31

lagrangian and eulerian

Question 32

how does lagrangian track a particle

Answer 32

This method follows the path of the individual objects (particles)
requires us to track the position and velocity of each individual fluid parcel and take the parcel to be of fixed identity

Question 33

how does eulerian track a particle

Answer 33

MORE COMMON METHOD
- a finite volume called a flow domain or control volume is defined through which fluid flows in and out
- instead of tracking individual fluid particles, we define field variables, functions of space and time, within the control volume

Question 34

what is an application of fluid kinematics

Answer 34

FACKIN CFDDDD (computational fluid dynamic) model to study scour around bridge piers

Question 35

what is the definition of local acceleration in relation to material acceleration

Answer 35

acceleration due to variation in velocity through time at a given location in space
describes the unsteadiness of flow

Question 36

what is the definition of convective acceleration in relation to material acceleration

Answer 36

acceleration due to change in velocity as the particle flows from one point in space to another (changes in pipe diameter)

Question 37

what is flow visualization

Answer 37

visual observations and examination of flow field features
useful not only in physical experiments but in numerical solutions as well (CFD)

Question 38

how can streamlines help with flow visualization

Answer 38

useful as indicators of the instantaneous direction of fluid motion throughout the flow field
obtained analytically by integrating equations that define lines tangent to the velocity field