Subsonic Flow Characteristics

8/12/2019 Subsonic Flow Characteristics

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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

Documents

Subsonic Flow Characteristics