Aero Engineering 315

Lesson 10

GR#1 Review

Golf ball dimple concept in action

Global Hawk

Turbine Blade CFD

Re = 25,000

Turbine Blade CFD

with Dimples

GR#1 Review Bring calculator, pencils & your brain Calculator policy: “This examination is CLOSED

BOOK/CLOSED NOTES. You are allowed a calculator, a straight edge, and an exam supplement as resource materials for this exam. However, you may not use your calculator's memory functions to store course notes, memory equations or homework solutions.”

Point breakdownMultiple choice conceptual – 65Multiple choice short work – 50Long workout – 35Total points – 150

Understanding the concepts and definitions, and being familiar with the equations we’ve used so far, are keys to success

History of Aeronautical Design

1. Sir George Cayley

2. Otto Lilienthal

3. Samuel Langley

4. Wright Brothers

a) Secretary of the Smithsonian; $50,000 US grant to develop a powered airplane; developed efficient internal combustion engine; aircraft design neglected need for control

b) First to propose separate lift & thrust mechanisms; developed basic requirements for stability and control; researched alternatives to steam power

c) Tested airfoils in wind tunnel; built and flew gliders; used wing warping and full elevator to control aircraft; first successful crewed, heavier-than-air sustained flight on Dec 17, 1903

d) The Glider Man with over 2500 flights; first successful man-carrying glider in 1891

Introduction to Aircraft Design

Why design a brand new airplane? _________________________________

Who defines the need? _________________________________

List the three steps in the design cycle: _________________________________

List the three design phases: _________________________________

to satisfy a need

the user

synthesis, analysis, decision making

conceptual, preliminary, detail

Flow Properties

List the four fundamental flow properties: _____________________________________

These four flow properties are ______ properties

P, , T are _______ quantities, while V is a _______ quantity

Units P: : T: V:

pressure, temperature, density, velocity

point

vectorscalar

lb/ft2 or N/m2

slugs/ft3 or kg/m3

°R or Kft/s or m/s

Equation of State The equation of state we use for gases is the

____________________________________ This relation applies at a _______ for gases:

The gas constant (R) for air is ___________________________

A gas that obeys the perfect gas law is called a _______________

perfect gas law: P = RT

pointat moderate temperatures and pressuresno chemical reactions or molecular breakupsvery low molecular attraction

1716 ft•lb/sl•°R or 287 N•m/kg•K

perfect gas

Hydrostatic Equation

The hydrostatic equation (______________) says that as height increases, ___________ ____________

To derive the hydrostatic equation, we must assume a ________ fluid (sum of vertical forces is zero)

If we assume = _________ (as for _________), we can integrate the hydrostatic equation to obtain the manometry equation: __________________

dP = -g dhpressure

decreases

static

constantliquids

P2 – P1 = -l g(h2-h1)

Standard Atmosphere The standard atmosphere tabulates values of

_________, ____________, and ________ at various altitudes

In deriving the standard atmosphere (three unknowns), we had only two equations: ________________________________________

To develop the third equation, we used balloon flights to measure ______________ in the atmosphere

You are flying at 32,000 ft on a standard day. What is the atmospheric pressure? _______________ Temperature? _______________

You are flying at a pressure altitude of 7.0 km. What is the atmospheric pressure? _______________ Temperature? _______________

pressure temperature density

perfect gas law and hydrostatic equation

temperatures

574.6 lb/ft2

404.8°R

41,105 N/m2

don’t know!

Standard Atmosphere You are flying at a geometric altitude of 14,000 ft, a

pressure altitude of 15,000 ft, and a temperature altitude of 16,000 ft. What is the outside air density? __________________________________________

A thermometer mounted to your aircraft measures an air temperature of 242.71 K. What is your temperature altitude? _______________

The tropopause divides the _____________ from the ______________; for several tens of thousands of feet above the tropopause, standard air temperature __________________

An altimeter is just a __________ gauge calibrated in units of __________ instead of __________

= 1195 lb/ft2 / (1716 ft•lb/sl•R • 461.7°R) = 0.001508 sl/ft3

7.0 kmtroposphere

stratosphere

remains constantpressure

pressurealtitude

More Aero Definitions Flow field: specification of _________________ in a

_________________________________ Steady flow: flow in which properties at a ________ are

invariant with respect to _______ Streamline: imaginary line (curve) where the flow is

_________ to the line at every point Flow ________ cross a streamline

Streamtube: collection of _____________ passing through a plane ____________________ to the flow direction

One-dimensional (1-D) flow: properties are __________ across the cross section of the flow and vary only in the ________ direction

A point where flow velocity slows to zero is a ____________ point; the associated streamline is a _____________ streamline

aero propertiesregion of interest

pointtime

tangentcannot

streamlinesperpendicular

constantflow

stagnationstagnation

Mass Flow Rate and theContinuity Equation

If we assume ____ flow, we can calculate mass flow rate: m = _______

If we assume ________ flow through a streamtube, then no mass is being stored (and mass is neither created nor destroyed), and m = ____________

The continuity equation is the expression of the principle of ________________________ for fluid flows

Continuity equation: _________________ For incompressible ( = const) flows, such as

_________, and air slower than __________ ____________________, the continuity equation reduces to _____________

.

.

1-DAV

steady

constant

conservation of mass

1A1V1 = 2A2V2

liquids 100 m/s or330 ft/s or 225 mph

A1V1 = A2V2

Sources of Aerodynamic Forces

__________ forces: act ________ to the surface

__________ (_________) forces: act ____________ to the surface

Pressure normal

Shear viscoustangential

Euler’s Equation, Bernoulli’s Equation Euler’s Equation (____________) assumptions:

Bernoulli’s Equation (_________________________) additional assumption:

Bernoulli’s Equation says that ________________ is constant along a ____________

P represents ________ pressure and ½v2 represents _________ pressure (__)

P + q = P0 (_______ pressure) A pitot tube measures _______ pressure

dP = -V dVFlow along a streamlineSteady flowBody forces (gravity/magnetic) negligibleInviscid (frictionless) flow

P∞ + ½V∞2 = P1 + ½V1

2

Incompressible flow ( = constant)total pressure

streamlinestatic

dynamic qtotal

total

Airspeed Measurement and ICeT I___________ airspeed: ______________

__________________________________ C___________ airspeed: corrected for

_______________________; VC = __________ e___________ airspeed: corrected for

_______________________; Ve = __________ T___________ airspeed: corrected for

_______________________; VT = ___________ Ground speed: aircraft velocity relative to the

________; VG = __________ Dynamic pressure: q = ½V2 = ½SLVe

2

Be prepared to work backwards!

ndicated what you seeon your airspeed indicatoralibrated

position error VI + VP

quivalentnon-standard pressures f•VC

ruenon-standard densities ρ

ρV SLe

ground VT + Vwind

Viscous Flow Profile (viscous) drag is composed of _______________ drag

and __________ drag V = __ at the surface of a solid object (_________ condition) Viscosity is the tendency for a fluid to resist

__________________________ Viscosity can be described as ______________________ For liquids, viscosity ___________ at higher temperatures; for

gases, viscosity ___________ at higher temps The edge of a boundary layer is considered the location

where V = ___% of the local freestream velocity _______ pressure remains constant through the boundary

layer; ________ pressure decreases toward the surface _______ effects are only important in the boundary layer;

outside the boundary layer, we can assume __________ flow

skin frictionpressure

0 no-slip

velocity discontinuitiesresistance to flow

decreasesincreases

99Static

dynamicViscous

inviscid

Viscous Flow Reynolds number, a ______________ parameter, is the ratio of

__________ forces to _________ forces (Re = ___________)

Viscous forces dominate in a _________ boundary layer; inertial forces dominate in a ___________ boundary layer

Transition: boundary layer changes from _________ to ___________; Reynolds number at the transition point is __________

As a rule of thumb, ReXcrit ≈ _________; locations where Re > ReXcrit have ___________ boundary layers

Turbulent boundary layers have ________ dV/dy at the wall, so they produce ______ skin friction drag

Boundary layer transition can be affected by: ______________________________________________________________________________________________

Pressure drag is also known as drag due to ____________; flow separation occurs when flow momentum cannot overcome an ___________ (or unfavorable) pressure gradient (dP/dx ___ 0), i.e. when dV/dy = ____

dimensionlessinertial viscousVx/

laminarturbulent

turbulentlaminar

ReXcrit500,000

turbulenthigh

more

surface roughness; freestream turbulence; aircraftvibration; heat transfer; adverse pressure gradient

separation

adverse> 0

Viscous Flow Flow separation causes a ___________ in lift and an

__________ in pressure drag Pressure drag is the result of the loss of _______

pressure in the boundary layer and thus a _______ pressure imbalance

___________ boundary layers have higher V close to the surface, and _________ separation and ___________ pressure drag

Dimples on a golf ball help transition the boundary layer to ___________, delaying __________ and reducing ________ drag

For blunt objects, skin friction drag is _____ important, pressure drag is _____ important, and ____________ BL is preferred

For streamlined objects, skin friction is _____ important, pressure drag is _____ important, and ___________ BL is preferred

reductionincrease

totaltotal

Turbulentdelay

reduce

turbulent separationpressure

less

less

more

moreturbulent

laminar

Example ProblemYou are flying at a pressure altitude of 15,000 ft. Outside air temperature is -5°F. Your indicated airspeed is 130 kts; your flight manual indicates a position error of -5 kts. At a point on the upper surface of the wing, the velocity is determined to be 300 ft/s.a) Determine the outside air density

b) Determine your true airspeed

c) Determine the static pressure acting on the upper surface of the wing

(Use perfect gas law: = 0.001531 sl/ft3)

(Incompressible, so use Bernoulli:P∞ + ½V∞

2 = Pwing + ½Vwing2 Pwing = 1178.8 lb/ft2)

(Use ICeT: VT = V∞ = 155.3 kts = 262.46 ft/s)

Final Hints

Review homework problems 1–15 Review lesson 2–7 readings – handouts are

useful! Be very familiar with your green supplemental

data package (clean copy available for GR) Know “memory” equations (handout package) If desired, review lesson slides on k: drive (k:\

campus\df\dfan\ae315\instructor folders\ McCann)

I’ll be home Sunday for last-minute questions