Compressible Flow through a Nozzle/Diffuser

diagram

plots

inlet velocity

u

1

(m/s)

100

outlet diameter

d

2

(m)

0.04

This Demonstration models compressible flow through a reversible nozzle/diffuser. The inlet pressure

P

1

, the exit velocity

u

2

, and the exit temperature

T

2

are calculated from mass and energy balances during air flow. Because it is reversible, the entropy change is zero. The air exits as a free jet at atmospheric pressure (

P

2

=101.3kPa

). Set the outlet diameter

d

2

and inlet velocity

u

1

with the sliders. When

d

2

<

d

1

, the device acts as a nozzle, with the inlet pressure higher than the exit pressure

(

P

1

>

P

2

)

in order to provide the energy needed to accelerate the air through the nozzle. When

d

2

>

d

1

, the device operates as a diffuser, with the exit pressure higher than the inlet pressure

(

P

1

<

P

2

)

. When "plots" is selected, the velocity or temperature is plotted as a function of outlet diameter for compressible air flow (blue) and incompressible air flow (green). Air is assumed to behave as an ideal gas and all flow is subsonic.