Fluid isentropic nozzle flow

The relatioir of velocity to pressure iir an isentropic nozzle can be expressed analytically if the fluid behaves as air ideal gas. Combination of Eqs. (6.8) and (7.3) for isentropic flow gives ... 

Why does l(Dwering the downstream pressure not cause the fluid to flow faster in the nozzle Suppose we attach an observer to a balloon and let her ride along with the fluid through the nozzle. When she gets to the nozzle throat, she observes that the downstream pressure is lower than she had anticipated fromjthe isentropic-flow equations, and she shouts back to those of us who are behind her to come faster. Figure 8.10 shows the fate of her shout. 

Section 5.6 shows a comparison of the velocities for flow through a converging nozzle, calculated by means of (a) Bernoulli s equation, assuming that air was a constant-density fluid, and (b) the equations for isentropic flow. Show the calculations in the latter case, and check your answers against those shown in Sec. 5 6. 

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