Flow analysis of subsonic and supersonic nozzles

Abstract

A nozzle is a variable cross sectional area used to accelerate the flow. As the fluid flows through the nozzle, the kinetic energy of the fluid is increased at the expense of pressure energy. The main use of nozzle is to produce a jet of steam (or gas) of high velocity to produce thrust for the propulsion of rocket motors and jet engines and to drive steam or gas turbines. Nozzle has many applications in industry of turbo machinery, separation systems, the jet propulsion units, geo-environmental techniques, air conditioning, thermal ejectors, wind tunnels and many others. The present work incorporates the detail study about subsonic and supersonic nozzles. The concept of method of characteristics is used in designing of nozzle. The program is developed in the language C++, which generates the profile of both the subsonic and supersonic nozzle. To study the performance and characteristics of the nozzles, the experimentation is carried out at different back pressures. These experimental results are compared with the theoretical, isentropic one dimensional flow for variable area passages. The geometry of the nozzle is created in modeling software GAMBIT 2.4.6 and the numerical simulation is carried out in FLUENT 6.3.26. The numerical results are compared with experimental results at design and off-design conditions. The results indicate that, there is good agreement between the graph of experimental and numerical results. In both the analysis at design condition, the flow gets accelerated throughout the nozzle length. At the design condition, the phenomenon of flow through the nozzle is changed with variation in back pressure value. For very high value of back pressure, compared to design pressure, the convergent part of the nozzle accelerate the flow and the divergent part of the nozzle act as a diffuser and decelerate the flow. On further reduction in the back pressure, the shock phenomenon is observed in the divergent portion of the nozzle. This shock position shifts downward from the throat to exit of the nozzle, with the reduction of back pressure.