Aero Engineering 315 Lesson 4 Flow Definitions, Continuity Equation, Compressible and Incompressible Flow

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The Standard Atmosphere Note: Refer to your green supplemental data book

The Standard Atmosphere  Standard day - atmospheric conditions correspond to the standard atmosphere table  Pressure altitude (H p ) - the standard day altitude which corresponds to a measured pressure  Temperature altitude (H T ) - the standard day altitude which corresponds to a measured temperature  Density altitude (H  )- the standard day altitude which corresponds to a measured density

Standard Atmosphere example An aircraft flying at a geometric altitude of 20,000 ft has instrument readings of P = 900 lb/ft 2 and T = 460 deg R. a.Find h P, h T, and h  to the nearest 1000 ft b.If the aircraft were flying in a standard atmosphere, what would be the relationship among h P, h T, and h  ?

Altimetry  An altimeter is just a pressure gauge calibrated in units of altitude instead of pressure  Standard atmosphere is used to calibrate gauge dial Establishes relationship between pressure and altitude  Adjustable reference pressure allows correcting for non-standard day pressure

Manometers  Devices for measuring pressure differences  Assume height difference is small - implies g is constant  Assume the fluid is liquid -  is constant hh P2P2 P1P1 + Manometry Equation Hydrostatic equation

 Define some more basic aero terms Flow field, steady flow, streamline, stream tube, one-dimensional flow  Explain the continuity equation Physical meaning Assumptions needed to use it Solve problems using the continuity equations  Define compressible and incompressible flow  Describe two ways a flow can transmit a force Overview/Outcomes

More Aero Definitions… Flow field Specification of the aero properties (P, T,  & V) in a region of interest Steady flow Properties at a point are invariant with respect to time Streamline Imaginary line where flow is tangent to the line at every point Stream tube A collection of streamlines passing through a plane perpendicular to the flow direction One-dimensional flow Properties are constant across the cross section of flow (i.e. they vary only in one direction)

Mass Flow Rate Example A garden hose with a cross sectional area of 1 in 2 has water flowing through it at a velocity of 1 ft/s. What is the mass flow rate? Assume 1-D flow Water density is 1.94 slugs/ft 3 (see your handout)

Next Lesson (5)…  Prior to Class Work homework problems through #7 Read and Read Bernoulli’s Equation handout  In Class Euler’s Equation Bernoulli’s Equation Pressure and shear forces