Aero Engineering 315 Lesson 10 GR#1 Review

Golf ball dimple concept in action Global Hawk Golf ball dimple concept in action 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 breakdown Multiple choice conceptual – 65 Multiple choice short work – 50 Long workout – 35 Total 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 Sir George Cayley Otto Lilienthal Samuel Langley Wright Brothers Secretary of the Smithsonian; $50,000 US grant to develop a powered airplane; developed efficient internal combustion engine; aircraft design neglected need for control First to propose separate lift & thrust mechanisms; developed basic requirements for stability and control; researched alternatives to steam power 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 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

pressure, temperature, density, velocity Flow Properties List the four fundamental flow properties: _____________________________________ These four flow properties are ______ properties P, r, T are _______ quantities, while V is a _______ quantity Units P: r: T: V: pressure, temperature, density, velocity point scalar vector lb/ft2 or N/m2 slugs/ft3 or kg/m3 °R or K ft/s or m/s

1716 ft•lb/sl•°R or 287 N•m/kg•K 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 = rRT point at moderate temperatures and pressures no chemical reactions or molecular breakups very 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 r = _________ (as for _________), we can integrate the hydrostatic equation to obtain the manometry equation: __________________ dP = -rg dh pressure decreases static constant liquids P2 – P1 = -rl g(h2-h1)

Standard Atmosphere pressure temperature density 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 7.0 km troposphere stratosphere remains constant 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 __________ r = 1195 lb/ft2 / (1716 ft•lb/sl•R • 461.7°R) = 0.001508 sl/ft3 7.0 km troposphere stratosphere remains constant pressure altitude pressure

More Aero Definitions aero properties region of interest point time 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 region of interest point time tangent cannot streamlines perpendicular constant flow stagnation stagnation

Mass Flow Rate and the Continuity 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 (r = const) flows, such as _________, and air slower than __________ ____________________, the continuity equation reduces to _____________ . rAV steady . constant conservation of mass r1A1V1 = r2A2V2 liquids 100 m/s or 330 ft/s or 225 mph A1V1 = A2V2

Sources of Aerodynamic Forces __________ forces: act ________ to the surface __________ (_________) forces: act ____________ to the surface Pressure normal Shear viscous tangential

Euler’s Equation, Bernoulli’s Equation dP = -rV dV Euler’s Equation (____________) assumptions: Bernoulli’s Equation (_________________________) additional assumption: Bernoulli’s Equation says that ________________ is constant along a ____________ P represents ________ pressure and ½rv2 represents _________ pressure (__) P + q = P0 (_______ pressure) A pitot tube measures _______ pressure Flow along a streamline Steady flow Body forces (gravity/magnetic) negligible Inviscid (frictionless) flow P∞ + ½rV∞2 = P1 + ½rV12 Incompressible flow (r = constant) total pressure streamline static dynamic q total total

Airspeed Measurement and ICeT ndicated what you see 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 = ½rV2 = ½rSLVe2 Be prepared to work backwards! on your airspeed indicator alibrated position error VI + DVP quivalent non-standard pressures f•VC rue non-standard densities ground VT + Vwind

Viscous Flow skin friction pressure no-slip velocity discontinuities 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 pressure no-slip velocity discontinuities resistance to flow decreases increases 99 Static dynamic Viscous inviscid

Viscous Flow dimensionless inertial viscous rVx/m laminar turbulent 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 = ____ inertial viscous rVx/m laminar turbulent laminar turbulent ReXcrit 500,000 turbulent high more surface roughness; freestream turbulence; aircraft vibration; heat transfer; adverse pressure gradient separation adverse >

Viscous Flow reduction increase total total Turbulent delay reduce 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 increase total total Turbulent delay reduce turbulent separation pressure less more turbulent more less laminar

Example Problem You 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: r = 0.001531 sl/ft3) (Use ICeT: VT = V∞ = 155.3 kts = 262.46 ft/s) (Incompressible, so use Bernoulli: P∞ + ½rV∞2 = Pwing + ½rVwing2  Pwing = 1178.8 lb/ft2)

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