Application of a Real-Gas-Library Multi-Fluid-Mixing Model to Supercritical Single Injector Flow

In this paper we report on supercritical single injector computations using a new type of real gas CFD model. This Euler-Euler model is an extension to the DLR TAU CFD code. By storing fluid data in a library, we were able to decouple equation of state (EOS) accuracy from runtime performance. The library covers all fluid states effciently and robust, including gaseous, liquid, supercritical, and multiphase states. In our new multifluid mixing model, an EOS is solved for each species. Computations were carried out using a modifed Benedict-Webb-Rubin high fidelity equation of state for cryogenic oxygen, with negligible penalty in performance compared to a pure ideal gas computation. Additional species (H, H2, O, OH, H2O, H2O2) were treated as perfect gases. The immediate goal is to create a flow solver for industrial application, i.e. to support design by enabling a fast turnaround. Thus, we focus on 2D RANS modeling in this first step. The baseline model is applied to the canonical Mascotte A60 test case. The chamber pressure is well met, the flame dimensions are within the spread found among other CFD results. In accordance with experimental results, the reaction zone is very thin. Maximum OH* occurrences are correctly predicted in the shear layer, reducing in magnitude towards shoulder and flame tip. The fluid library allows to pinpoint the extent of the liquid oxygen core, the length is determined to 20 LOX injector diameters. It is found to be embedded in a gaseous oxygen shell. Within this RANS context, H2 and O2 do not coexist in a premixed form. Finally, we show that numerical OH* concentration differs significantly from OH mass fraction distributions, the latter are thus no appropriate data to compare to experiments

Supercritical Pseudo-Boiling and its Relevance for Transcritical Injection

In this paper, a new interpretation of cryogenic jet break-up in supercritical environments is introduced. It is firmly established that under these conditions a pure fluid will exhibit neither latent heat of vaporization nor surface tension. The jet undergoes a transition from a dense cryogenic fluid to an ideal gas as it mixes and blends with the surrounding warmer gas. Regarding the thermodynamic process, this transition is characterized by large changes in density and very small changes in temperature as energy is supplied. The state where density changes and the heat capacity are maximal is sometimes called `pseudo-boiling' in the literature. However, no clear definition of this process is available, its very existence debated. In this paper, the first quantitative pseudo-boiling analysis is presented. It can be shown that pseudo-boiling exists along a line which effectively structures supercritical uid states. An equation for this continuation of the coexistence line is given. Across this line, a continuous state transition can be identfied. The temperature at pseudo-boiling replaces the critical temperature as relevant parameter at supercritical pressures. By introducing a suitable definition for a supercritical uid boundary, supercritical jet break-up can be quantified thermodynamically. This suggests a novel, thermal, jet break-up mechanism. Experimental evidence from the literature is shown, further supported by CFD simulations. The pseudo-boiling effect is found to play a role for injection conditions of reduced pressures smaller than 3, and reduced temperatures lower than 1.2