1 / 21

Gas Dynamics for Study of Nozzles@ Off-Design

Gas Dynamics for Study of Nozzles@ Off-Design. P M V Subbarao Professor Mechanical Engineering Department. Recognize the Surprises, if Any …. Ideal Convergent-Divergent Nozzle Under Design Conditions. Ideal Convergent-Divergent Nozzle with High Back Pressure. p b1< p in, but > p *.

beverlymusic
Download Presentation

Gas Dynamics for Study of Nozzles@ Off-Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gas Dynamics for Study of Nozzles@ Off-Design P M V Subbarao Professor Mechanical Engineering Department Recognize the Surprises, if Any…..

  2. Ideal Convergent-Divergent Nozzle Under Design Conditions

  3. Ideal Convergent-Divergent Nozzle with High Back Pressure pb1< pin,but > p* pthroat>p*

  4. Ideal Convergent-Divergent Nozzle with High Back Pressure • When pbis very nearly the same as pinthe flow remains subsonic throughout. • The flow in the nozzle is then similar to that in a venturi. • The local pressure drops from pin to a minimum value at the throat, pthroat , which is greater than p*. • The local pressure increases from throat to exit plane of the nozzle. • The pressure at the exit plate of the nozzle is equal to the back pressure. • This trend will continue for a particular value of back pressure.

  5. Ideal Subsonic Convergent-Divergent Nozzle with High Back Pressure At all these back pressures the exit plane pressure is equal to the back pressure. pthroat> p*

  6. Mass Flow Rate at Higher Back Pressures

  7. Mass flow rate at Variable back pressure Throat pressure with high back pressure pb

  8. Throat pressure as a function of Variable Back pressure • For a given value of high back pressure corresponding throat pressure can be calculated. • As exit area is higher than throat area throat pressure is always less than exit plane pressure. • A decreasing exit pressure produces lowering throat pressure

  9. Exit Pressure Vs Back Pressure 1 1

  10. Variation of in Mass Flow Rate 1

  11. Will this be design Back pressure only ??? Further Decrease the Back Pressure till the throat is just choked…. If not??? Define the back pressure that generates choking at throat as critical back pressure, pb.critical.

  12. Back Pressure for Choking Vs Design Back Pressure This generates choked condition at the throat. This is the back pressure which produces maximum (design) flow rate Through the nozzle. Is this back pressure same as design back pressure? If not??????

  13. Pexit =pb,critical Pthroat =p*

  14. Variation of in Throat Pressure 1 1

  15. Variation of in Mass Flow Rate 1

  16. What Next? What happens if back pressure is further reduced? Still the gas pressure at the exit plane is equal to the back pressure? Is it possible to get further lower pressure at throat !?!?!

  17. Convergent-Divergent Nozzle with Lower Back Pressure than the critical back pressure It is impossible to have a pth- < p* ??? Pthroat =p* pb< pb,critical <pin Pthroat< p*???? However there will be a location in the diverging section where pressure can reach p*.

  18. pb < pb,critical <p0 Find out another downstream location, x where p* can be achieved with lower back pressures. A=? Feasible solution Infeasible solution ? M<1 M<1

  19. Convergent-Divergent Nozzle Under Peculiar Off-Design Conditions

  20. Standing Normal Shock in Diverging Section of CD Nozzle Normal Shock : A large discontinuity M<1 M<1 M>1

More Related