Post on 03-Jun-2018
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Subsonic FlowCharacteristics
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Topics Covered in thissession:
! 1 Overview! 2 Moving Airplane In Stationary Air or Moving Air
Over Stationary Airplane?
! 3 Streamlines! 4 Airflow Characteristics versus Mach Number!
5 Constant Density or Incompressible Flow
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What needs to be doneprior to class (WNTBPC)
! Read the ANA text pages 4 through 9, Bernoullisprinciple and subsonic airflow, and PilotsHandbook of Aeronautical Knowledge (PHAK) p. 2-4Airfoil Design through p.2-6 High Pressure Below.
! Watch this lecture! Create your own notes in word, save it as a .pdf
and post it in Dropbox as homework.
! This should be no more than a page of YOUR OWNversion of notes
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1. Overview! Characteristics of Subsonic airflow! Drawings of stationary vs moving airflow!
Use of streamlines as graphic and visual depictionof invisible airflow
! Subsonic airflow-! Density changes are negligible! Considered incompressible
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2. Airplane moving through stationary air, orair moving over stationary airplane?
! Airplane in flight is moving through non-moving(stationary) air.! Studying aerodynamics on the ground we must
blow moving air over a stationary airplane.
! Leonardo Da Vinci:! The action of a medium upon a body is the same
whether the body moves in the quiescent medium, orwhether the particles of the medium impinge with thesame velocity upon the quiescent body.
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3. Streamlines! Streamlines are a visible representation of an
invisible airflow
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Streamline Relationships
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4. Airflow Characteristicversus Mach number
! Mach number is defined as airflow (or aircraft)velocity divided by the local speed of sound:
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Airplane velocity vs Airflowvelocity
As Aircraft moves through the air shape causessome airflow to be faster than aircraft, some airflow
is slower compared to AIRCRAFT VELOCITY
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Mach numbers! Airflowtraveling slower than M = 1 is called
subsonic flow. Airflow traveling faster than M = 1 iscalled supersonic flow. Subsonic and supersonicflows have very different pressure, temperature, and
density characteristics.
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5. Constant Density orIncompressible Flow
! Subsonic flow:! Constant density or incompressible flow
! Symbol for air density is rho .! Air density decreases as altitude increases and vice versa.! At a constant altitude, the air density of subsonic flow is a
constant for all practical purposes.! Therefore, rho is constant in subsonic flow at a given
altitude.
! In aerodynamics, incompressible flow means thedensitydoes not change. It does NOT mean that thepressuredoes not change! Pressure in fact does changedepending on the circumstances.
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Review! 1 Overview! 2 Moving Airplane In Stationary Air or Moving Air
Over Stationary Airplane?
! 3 Streamlines! 4 Airflow Characteristics versus Mach Number!
5 Constant Density or Incompressible Flow