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Aerodynamics: some nouns
Chapter 1 Types of flow:
Uniform Flow Steady Flow Unsteady Flow
Continuum Versus Free Molecule Flow Inviscid Flow: μ Viscous Flow: μ
＝ 0 ≠ 0
Incompressible Flow: ρ=const Compressible Flow: ρ≠const
Gradient of a Scalar Field:
The gradient of p, ▽p, at given point in space is defined as a vector such that :
1.
Its magnitude is maximum rate of change of p per unit length of the coordinate space at the given point. 2.
Its direction is that of maximum rate of change of p at the given point.
Divergence of a Vector Field:
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The time rate of change of the volume will , in general , a moving fluid element of fixed mass , per unit volume of that element , is equal to the divergence of V ,denoted by▽·V .
Curl of a Vector Field:
ωis equal to one-half of the curl of V ,where the curl of V is denoted by▽×V.
Mass Flow:
The mass flow through A is the mass crossing A per second. Let denote mass flow.
Body forces:
Gravity, electromagnetic forces, or any other forces which “ act at distance “ on the fluid inside V . Surface forces:
Pressure and shear stress acting on the control surface S. The prefect gas equation of state:
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P=ρR T Chapter 2 Pathlines :
We trace the path of element A as it moves downstream form point , as given by the dished line. Such a path is defined as the pathline for element A. Streamlines:
A streamline is a curve whose tangent at any point is in the direction of the velocity at that point.
The difference between streamlines and pathlines:
In general , streamlines are different from pathlines. You can visualize a pathlines as a time-exposure photograph of a fluid element , whereas a streamline pattern is like a single frame of a motion picture of the flow. In an unsteady flow, the streamline pattern changes; hence, each ”frame” of the motion picture is different.
However ,for the case of steady flow, the magnitude and direction of the velocity vectors at all points are fixed, invariant with time. Hence, the pathlines for different fluid elements going through the same . moreover , the pathlines and streamlines are identical . therefore, in steady flow, there is on distinction between pathlines and streamlines; they are the same curves in space. Vorticity:
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We define a new quantity, vorticity , which is simply twice the angular velocity.
In a velocity field, the curl of the velocity is equal to the vorticity. The above leads to two important definitions:
1. If ≠0 at every point in a flow ,the flow is called rotational. This implies that the fluid elements have a finite angular velocity. 2. If ＝0 at every point in a flow, the flow is called irrotational. This implies that the fluid elements have no angular velocity; rather, their motion through space is a pure translation. Circulation:
The circulation is simply the negative of the line integral of velocity around a closed curve in the flow.
Stream Function:
Velocity Function:
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Chapter 3
Bornoulli’s Equation
For incompressible 、inviscid、steady、rotational flow with no body forces.
For incompressible 、inviscid、steady、irrotational flow with no body forces.
Quasi-one-dimensional continuity equation For compressible flow
For incompressible flow
Pitot-static probe
空气动力学中的动名词解释
