Turbulence lecture 4

Turbulence lecture 4 - Turbulence Lecture 4 H. Turbulent...

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Turbulence Lecture 4 H. Turbulent flows are highly dissipative; they rapidly convert Kinetic Energy into (thermal) internal energy. Much higher than laminar case. A continuous supply of energy is needed to sustain turbulence. Need more energy in pipe flow if it goes turbulent, and a laminar wing slides through air easier than a turbulent wing. Skin friction goes up. 2 1 2 f C U τ ρ = At transition, jump in C f is about an order of magnitude. This curve is basis for attempts to maintain laminar flow on airfoils. I. Turbulent flows have all of the above properties. Interlude - If the flow is compressible or variable density or if body forces are present, the vorticity equation contains additional terms () 2 2 Dp uuv Dt f ω ωω ∇ ×∇ =∇−∇ +∇+ + × ii ± ±± ± ± ± ± f ∇× ± represents non-conservative outside forces, such as magnetic fields that exert torques. 2 p ∇×∇ Is the baroclinic torque term 1
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Consider a fluid element: Here you get a CW torque (right hand rule). Also in a compressible flow you can get “dilitation”
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Turbulence lecture 4 - Turbulence Lecture 4 H. Turbulent...

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