2024-09-24 18:43:47 +00:00
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# Introduction to fluid dynamics
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## 3 main laws
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- Momentum balance
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- Mass balance
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- Energy balance
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## The continuum assumption
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Let lambda be the mean free path, L a characteristic dimension of the problem
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Kn = lambda/L
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2024-09-24 18:55:35 +00:00
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Hypothesis:
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If Kn<<1, it is possible to use a model based on the continuum hypothesis
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That hypothesis is often valid, but not always. Within this course's scope, this hypothesis is always valid.
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## Types of flows
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Three ways flows can be be split:
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### (Un)Steady flows
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Steady: flow variables do not depend on time.
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d/dt = 0
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### (In)compressible flows
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A flox can be considered incompressible is the Mach number is low enough:
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Let v be the flow velocity, c be the celerity of sound
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Approx. M = v/c <= 0.3
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### Turbulent or laminar flows
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Turbulent flows : flow variable are stochastic and vary with space and time. This happens when the Reynolds number is high enough :
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Re = rho*v*D/mu > 2500 (for a tube)
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Turbulent flows happen often but we'll find ways get around it.
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