Flashcards
Section One
Cards in this deck (51)
- 1Fluid variablesVelocity, vorticity, pressure
- 2Fluid propertiesDensity, viscosity (dynamic and kinematic)
- 3Dynamic viscosityμ, a measure of the resistance to flow of a fluid under an applied force
- 4Kinematic viscosityμ/ ρ, refers to the ratio of dynamic viscosity to density, essentially the measure of a fluid's inherent resistance to flow when no external force, except gravity, is acting on it
- 5Flow separationOr boundary layer separation- the detachment of a boundary layer from a surface into a wake
- 6Transitional flowA mixture of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the edges
- 7Main difference between solids and fluid in terms of internal stressIn solids, internal stress is proportional to strain (so the deformation), in fluids, internal stress is proportional to the time rate of deformation (the rate of change of deformation in time). A fluid must be in motion in order to resist a shear stress whereas a solid can simply deform and remain stationary in a deformed position.
- 8Newtonian fluidFluids (with a constant viscosity) for which the time rate of deformation is proportional to the viscous shear stress.
- 9How does viscosity vary with temperature?μ increase if T decreases and vice versa
- 10No-slip conditionFor viscous fluids, assumes that at a solid boundary, the fluid will have zero velocity relative to the boundary
- 11The region in which viscosity slows the flow is called...The boundary layer
- 12What happens to the velocity of a fluid closer/st to a solid surface/ boundary?It is forced to be zero at the surface, this is where viscous stresses are significant (high rates of deformation)
- 13Equation for shear stress at the surface or wallτ = μ (∂u/ ∂y)
- 14Skin frictionOr surface drag/ stress, is resistance derived from friction between surface and adjacent layers of fluid near a body moving through a fluid. Acts over the whole surface of an aircraft and is an important contribution to drag.
- 15Stagnation pointLocated near leading edge of aerofoil but position moves with angle of attack. Point where flow is splitting up (to move both over and under aerofoil) reducing flow velocity to zero (v = 0 and maximum pressure here)
- 16Velocity and pressure above and below aerofoilHigh pressure, low velocity below aerofoil and low pressure high velocity above aerofoil
- 17Pressure dragCaused by air particles being more compressed on front-facing surfaces and more spaced out on back surfaces- caused when layers of air separate from surface and begin to swirl (turbulent flow- streamlined wing aerofoils can reduce this)
- 181 knot1 nautical mile/ hour = 1.151 miles/hour 1.852 km/hr = 0.514 m/s
- 19Incompressible flowConstant density
- 20Mass flow rateQ = density x volume flux (flow rate) = density x velocity x cross-sectional area =ρuA
- 21Eulerian frame of referenceNot concerned about the location or velocity of any particular particle, but rather about the velocity, acceleration, etc. of whatever particle happens to be at a particular location of interest at a particular time. (i.e. using a fixed control volume)
- 22Lagrangian frame of referenceConsider elements moving with the fluid, a moving frame of reference
- 23Camber lineLine that joins midpoints of the thickness of aerofoil
- 24Chord lineLine from leading edge to trailing edge
- 25Angle of attackAngle between chord line and relative wind
- 26ChordLength of chord line
- 27Equation for lift coefficient
- 28Suction peakPoint of lowest pressure on an aerofoil, typically (not always) located just after leading edge on upper surface. Forward of this point, pressure gradient helps produce lift but after this, pressure contributes to a drag and a separation of air flowing over the wind
- 29StallSudden reduction in lift generated by an aerofoil when the critical angle of attack is reached or exceeded (after lift stops increasing with AoA). Causes a large increase in pressure drag and a loss of lift.
- 30Why does stall occur?When the angle of attack is increased beyond critical value, the suction peak (and therefore adverse pressure gradient) grows, while the separation point on the upper surface moves forward. At critical AoA, adverse pressure gradient reaches such a high value that the boundary layer instantly detaches from the leading edge. (After flow goes past suction peak, it has to recover and go through adverse conditions (pressure increases) which can lead to flow separation.)
- 31Equation for pressure coefficient
- 32Difference between cambered and symmetric aerofoil at 0° AoACamber generates lift even at 0° but symmetric does not
- 33WakeRegion downstream of aerofoil
- 34Where are viscous effects non-negligible?Boundary layer and wake
- 35Thin aerofoil stallSeparation bubble forms even at low AoA; as AoA increases, bubble grows over upper surface; bubble bursts and flow detaches. Typical of very thin aerofoil (and flat plates) with very sharp nose
- 36Leading edge stallAttached flow; as AoA increases, separation bubble flows near leading edge; bubble bursts and flow detaches. Typical of medium thickness aerofoils with sharp nose
- 37Trailing edge stallAttached flow; as AoA increases, flow starts to separate near the trailing edge; separation points moves upstream towards leading edge as AoA increases. Typical of thick aerofoils and of large leading edge radius (more benign stall than L.E. stall)
- 38Hydrostatic equation
- 39Integrated hydrostatic equationPₐ - P = ρgh
- 40Differences in hydrostatic pressure around an object give rise to...Buoyancy forces
- 41Static pressure tappingA small pressure orifice (hole) in a surface in contact with the fluid (could be at rest or in motion)- connected to pressure-sensitive elements for measurement of static pressures
- 42Total pressure(Addition of static pressure and dynamic pressure)
- 43Pitot tubeAn open-ended, right-angled tube pointing in opposition to a fluid used to measure total pressure. Connected to a manometer, the air flow is brought to rest (stagnation) at face of the tube.
- 44Equation for drag coefficient
- 45Equation for pitching moment coefficient
- 46Equation for Reynolds number
- 47Equation for Mach numberM = u/a where u is speed of flow and a is speed of sound
- 48Equation relating ratio of specific heats with speed of sounda² = γRT with γ = Cₚ/ Cᵥ = 1.4 for air
- 49Equation for specific gas constantR = R₀ / molecular weight where R₀ is universal gas constant
- 50Buckingham's RuleNo. of variables - no. of dimensions = no. of dimensionless groups
- 51Sutherland's Law
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- Undergraduate Aerodynamics Flashcards on Section One, created by Paris Hart on 09/02/2021.
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