f20_sp - Fluids Lecture 20 Notes 1. Laval Nozzle Flows...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Fluids Lecture 20 Notes 1. Laval Nozzle Flows Reading: Anderson 10.3 Laval Nozzle Flows Subsonic ow and choking Consider a duct with a throat, connected at its inlet to a very large still air reservoir with total pressure and enthalpy p r , h r . The duct exit is now subjected to an adjustable exit static pressure p e , sometimes also called the back pressure . As p e is gradually reduced from p r , air will ow from the reservoir to the exit with a mass ow m . We first note that the stagnation conditions are known from the reservoir values all along the duct. p o p r 2 p o = p r , a = ( 1) h o = ( 1) h r , o = = o ( 1) h o ( 1) h r If we assume isentropic ow, m can be computed with the isentropic relations applied at the exit, using the known exit pressure p e and known exit area A e . M 1 2 = ( p o /p e ) 1 2 e 1 +1 p o 1 M 2 2( 1) m = e u e A e = M e 1 + 2 e A e (1) ( 1) h o The observed relation between p e and m is shown on the bottom right in the figure. As p e is reduced, m will first increase, but at some point it will level off and remain constant even if p e is reduced all the way to zero (vacuum). When m no longer increases with a reduction in p e , the duct is said to be choked . M u throat * * p p r p r 0 m . choked x x p * 1 p e p h e p < p r r large reservoir m . M a throat 1 1 p e r If we examine the various ow properties along the duct, it is evident that the onset of choking cooincides with the throat reaching M = 1 locally. This also corresponds to the 1 mass ux...
View Full Document

Page1 / 4

f20_sp - Fluids Lecture 20 Notes 1. Laval Nozzle Flows...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online