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Basics of Fluid Mechanics, 2014a

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416 CHAPTER 11. COMPRESSIBLE FLOW ONE DIMENSIONAL<br />

It can be noted that the additional definition was introduced for the shock upstream<br />

Mach number, M sx = Us<br />

c x<br />

. The downstream prime Mach number can be expressed as<br />

M y<br />

′<br />

= U s − U y<br />

c y<br />

= U s<br />

c y<br />

− M y = M sy − M y (11.109)<br />

Similar to the previous case, an additional definition was introduced for the shock<br />

downstream Mach number, M sy . The relationship between the two new shock Mach<br />

numbers is<br />

U s<br />

c x<br />

M sx =<br />

The “upstream” stagnation temperature <strong>of</strong> the fluid is<br />

= c y U s<br />

c x c y<br />

√ (11.110)<br />

Ty<br />

M sy<br />

T x<br />

Shock Stagnation Temperature<br />

(<br />

T 0x = T x 1+ k − 1 )<br />

2<br />

M x<br />

2<br />

and the “upstream” prime stagnation pressure is<br />

(<br />

P 0x = P x 1+ k − 1 ) k<br />

k−1<br />

2<br />

M x<br />

2<br />

(11.111)<br />

(11.112)<br />

The same can be said for the “downstream” side <strong>of</strong> the shock. The difference between<br />

the stagnation temperature is in the moving coordinates<br />

T 0y − T 0x =0 (11.113)<br />

11.5.5 Shock or Wave Drag Result from a Moving Shock<br />

It can be shown that there is no shock drag<br />

in stationary shockfor more information see<br />

“Fundamentals <strong>of</strong> Compressible Flow, Potto<br />

Project, Bar-Meir any verstion”.. However,<br />

the shock or wave drag is very significant so<br />

much so that at one point it was considered<br />

the sound barrier. Consider the figure (11.15)<br />

where the stream lines are moving with the object<br />

speed. The other boundaries are stationary<br />

but the velocity at right boundary is not<br />

zero. The same arguments, as discussed before<br />

in the stationary case, are applied. What<br />

U 1 =0<br />

ρ 1<br />

A 1<br />

P 1<br />

stationary lines at the<br />

speed <strong>of</strong> the object<br />

stream lines<br />

moving<br />

object<br />

U 2 ≠0<br />

ρ 2<br />

A 2<br />

P 2<br />

Fig. -11.15. The diagram that reexplains<br />

the shock drag effect <strong>of</strong> a moving shock.

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