Computational Analysis of Bell Nozzles

Abstract

-A Bell type nozzle is most commonly used shape for rocket nozzles. This type of nozzle not only offers significant advantages in terms of size and performance over the conical nozzle but also reduces complexity compared to annular nozzles. The nozzle uses the stagnation temperature (To) and stagnation pressure (Po) generated in the combustion chamber to create thrust by accelerating the combustion gases to a high supersonic velocity. The nozzle expansion ratio was governed by the exit velocity. During flight, the jet flow is ideally expanded and adapted to the surrounding flow only during a short period. The rest of the time, the rocket engine operates in off-design conditions. The present work incorporates 2D axisymmetric flow analysis within the bell type nozzle, at design and off-design conditions, by using computational fluid dynamic software GAMBIT 2.4.6 and FLUENT 6.3.26. A computer code, with the use of the method of characteristics and stream function, is developed to define the higher efficiency nozzle contours for analysis. Simulation has been carried out separately for two different flow conditions i.e. cold and hot. Shear Stress Transport k-ω turbulence model has been chosen for flow analysis. The converged solutions captured asymmetric lambda shock in the nozzles at higher nozzle pressure ratios (NPR) for viscous flows. It also predicted aftershock and flow separation depending upon NPR. The strength of the normal shock, at Mach stem in viscous prediction, generally increases with an increase in NPR. Good agreement is observed between predicted simulation and analytical results in terms of shock structure, shock location, the size of normal shock, aftershock, and asymmetric lambda shocks.

Review Study on Thermal Characteristics of Bell Nozzle used in Supersonic Engine

“…The fluid domain with boundary conditions of the bell nozzle [50] By altering the proposed second-order diffusion solution, it is possible to arrive at a much simpler but also more limited solution to the nozzle heat-transfer issue. The aerodynamic flow in electric rotor bell systems is comparable to naturally occurring rotating annular flow.…”

“…The nozzle shape is separated into zones and boundary conditions. For the conservation equations, the second-order upwind technique was applied, and grid adaptation was employed to precisely capture flow discontinuities [50].…”

Design and Computational Analysis of an Axisymmetric Contoured Supersonic Propulsion Nozzle

“…This would lead to a supersonic expansion within the divergent section designed previously. The convergent section was produced through the application of Rao method [11]. This approach gained great success as it is the result of numerous experimental investigations.…”

Comparative study on the performance of turbulence models in flow separation of large expansion ratio nozzle

“…In 1999, Östlund [4] tested four turbulence models that based onk ω two equations and found that only the Menter's SST model was able to capture the correct type of separation during startup and shutdown, but the wall pressure downstream of the separation was significantly different from the experimental data. Baloni et al [5] used the SST -k ω turbulence model to conduct a two-dimensional steady state simulation of a bell-shaped nozzle. The numerical simulation results and analysis results are in terms of shock structure, shock position, normal shock and asymmetric lambda shock size have good consistency.…”