Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- Turbulence Modeling Insights into Supercritical Nitrogen Mixing LayersPublication . Magalhães, Leandro; Carvalho, Francisco; Silva, A. R. R.; Barata, Jorge M MIn Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is no longer a clear distinction between a liquid and a gas phase. The non-conventional behavior of thermophysical properties makes the modeling of supercritical fluid flows a most challenging task. In the present work, a Reynolds Averaged Navier Stokes (RANS) computational method following an incompressible but variable density approach is devised on which the performance of several turbulence models is compared in conjunction with a high accuracy multi-parameter equation of state. In addition, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are validated against experimental data, making it clear that there is no trend between turbulence model complexity and the quality of the produced results. For several instances, one- and two-equation turbulence models produce similar results. Finally, considerations about the applicability of the tested turbulence models in supercritical simulations are given based on the results and the structural nature of each model.
- Turbulence Modelling on Supercritical Jet InjectionPublication . Carvalho, Francisco Miguel Marques de; Silva, André Resende Rodrigues daAs space exploration enters a new era where not only public but also private enterprises begin to flourish, financial viability becomes a preponderant factor. It is hard to estimate how far the contribution of this sector to the development of the resources available thus far will be, but the link between engineering technology and cost reduction is unquestionable. In a Liquid Rocket Engine, higher combustion efficiency comes at the cost of both the fuel and/or the oxidiser surpassing their critical points and entering the domain of supercritical fluids. While these conditions have been present in rocket engines combustion chambers for decades, they are still not fully understood and tools to properly simulate such conditions are still in the development stages. The highly non-linear behaviour of the thermophysical properties of a fluid in this regime increases the difficulty of any attempt to run numerical simulations. The ideal gas law is no longer valid and must be replaced by more accurate models. The Peng-Robinson and the Soave-Redlich-Kwong Equations of State (EoS) are compared to a reference EoS for nitrogen to gain some insight on the magnitude of error that simpler cubic Equations of State incur in the simulation results. The output of the multi-parameter EoS is obtained from the real gas library REFPROPv9.1 thus reducing computational costs while still achieving a level of accuracy that would otherwise not be possible. A similar treatment must be given to transport and caloric properties that have a significant impact on the flow structure. To deal with the incompressible but variable density conditions inside the combustion chamber, the standard time-averaging method is replaced by the Favre averaging procedure and the system of equations is closed with different turbulence models, the main focus of this study. The performance of said models, designed and calibrated to run in subcritical conditions, is then studied and their validity for the supercritical regime is assessed. Ultimately, computational results are validated against experimental data regarding the development of the mixing layer of nitrogen. Results show a good agreement with experimental data and, when compared to additional numerical studies for the same conditions, it is visible that there is no monotonic dependence between model complexity, performance and quality of results.
- Turbulence Quantification in Supercritical Nitrogen Injection: An Analysis of Turbulence ModelsPublication . Magalhães, Leandro; Carvalho, Francisco; Silva, André; Barata, Jorge M MIn Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is no longer a clear distinction between a liquid and a gas phase. The non-conventional behavior of thermophysical properties makes the modeling of supercritical fluid flows a most challenging task. In the present work, a RANS computational method following an incompressible but variable density approach is devised on which the performance of several turbulence models is compared in conjunction with a high accuracy multi-parameter equation of state. Also, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are validated against experimental data, becoming clear that there is no trend between turbulence model complexity and the quality of the produced results. For several instances, one- and two- equation turbulence models produce similar and better results than those of Large Eddy Simulation (LES). Finally, considerations about the applicability of the tested turbulence models in supercritical simulations are given based on the results and the structural nature of each model.