Abstract:

The aim of this study is to develop a stable as well as robust computational model of a convergent-divergent nozzle that can be used to further our understanding on the complex flow behaviours such as shocks, flow separation etc. The values of temperature, pressure and velocity should be made available at every section of the nozzle so as to design the nozzle shape, insulation and cooling arrangements. Based on the problem definition a model of the said nozzle is created using Solidworks. The dimensions are available as per the problem definition. This model will be imported into a CFD environment to find the solutions of interest numerically. This data needs verification or validation by experimental means. Since experimental methods are beyond the scope of this paper, only the analytical verification part using known theoretical formulations regarding 1D nozzle flow are taken .The theoretical formulae and assumptions involving .the nozzle calculations are to be therefore gathered before to be able to verify the computational values obtained from the simulation. The theoretical calculations of pressure, velocity and temperature values are performed and tabulated, which is followed extensively in this paper for verification purposes. Also if the values obtained from the simulation conform to the known values, the geometry of the model is changed to study the effects it has on the variables of interest. The results and the ensuing conclusions are as follows: With the increase of divergence angle the Mach number tends to rise and small shocks developed in the flow seem to be die out. This trend goes on with the increase of Mach number up to a limit, say beyond 20 deg of divergence angle, with still the area ratio kept constant, it has been observed that Mach number decreases very profoundly. Mass balance ensured that the simulation conforms to conservation of mass. CFD considers the factors like boundary layer effects, shock waves, radial velocity component and so on, which leads to some minor variance from theoretical results. The variation in the results of theoretical calculations and CFD are quite insignificant. It thus establishes the fact that one-dimensional simplified nozzle analysis is sufficient to predict the nozzle performance, although frequent computational domain changes can be easily computed using a CFD solver. From the study conducted to assess the variation of divergence angle to the pressure, velocity and temperature, it has been conclusively clear that as the divergence angle increases there’s a sudden rise in velocity and thus decrease in temperature and pressure. The simulation has been analytically verified using one dimensional isentropic flow equations. We also emphasize and acknowledge the need for an experimental validation to accept our results in complete face value.


Keywords: Ansys Fluent, Area ratio, de-Laval Nozzle, CFD, Numerical analysis, 1D Nozzle flow, Solidworks etc..;