16100lectre40_cj - When 1&gt = a u M all the waves...

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Waves in 1-D Compressible Flow Imagine we have a steady 1-D compressible flow. Then suppose a small disturbance occurs at a location o x x = . This disturbance will cause waves to propagate away from the source. Suppose that the flow velocity were u and the speed of sound a . Then 3 waves exist: (1) Downstream propagating acoustic wave : Speed: a u + This is an isentropic disturbance (and what is commonly called a sound wave). (2)Upstream propagating acoustic wave : Speed: a u Again, this is an isentropic disturbance (and is commonly called a sound wave). (3)Entropy wave : Speed: u This wave is just a change in entropy.
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Unformatted text preview: When 1 > = a u M , all the waves propagate in the downstream direction: For example, if > > a u , then When 1 < = a u M , the slow acoustic wave propagates against the stream: For example, if > > u a then In supersonic flow, this means that the presence of a disturbance cannot be felt upstream while in a subsonic flow it can be: 1 > M , , > + a u a u u Supersonic flow Waves travel only downstream , < > + a u a u u Subsonic flow Waves travel up and downstream Shock wave Disturbance not felt upstream...
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