Anthony Ruiz

Large-Eddy Simulation of Supercritical-Pressure Round Jets

This paper presents the numerical computation of a turbulent jet of nitrogen into nitrogen under supercritical pressure. The large-eddy simulation framework for turbulence modeling is used and real-gas effects are accounted for through a cubic equation of state and appropriate viscosity and conductivity coefficients. The purpose of this paper is to evaluate how low-pressure large-eddy simulation equations coupled with real-gas thermodynamics and transport compare with experiments. Although this approach does not take into account the impact of high density gradients and nonlinear thermodynamics on turbulence modeling, the results show reasonable agreement with available experimental data and reveal the importance of numerics for such computations. The simulations indicate a limited influence of the density ratio and the thermodynamic conditions on the jets spreading rate and pseudosimilarity behavior.

Effects of Real-Fluid Thermodynamics on High-Pressure Fuel Injection Processes

This paper first summarizes a new theoretical description that quantifies the ef fects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions. To highlight the implications and needs related to modeling, we present a series of studies using LES that focus on experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories. We extend LES studies performed previously to the Engine Combustion Network (www.sandia.gov/ECN) Spray-H and Spray-A injectors using n-heptane and n-dodecane as the respective fuels. The accompanying analysis reveals the structural characteristics associated with the inherent scalar mixing processes at conditions directly relevant to advanced Diesel engines.

Numerical Benchmark for High-Reynolds-Number Supercritical Flows with Large Density Gradients

Because of the extreme complexity of physical phenomena at high pressure, only limited data are available for solver validation at device-relevant conditions such as liquid rocket engines, gas turbines, or diesel engines. In the present study, a two-dimensional direct numerical simulation is used to establish a benchmark for supercritical flow at a high Reynolds number and high-density ratio at conditions typically encountered in liquid rocket engines. Emphasis has been placed on maintaining the flow characteristics of actual systems with simple boundary conditions, grid spacing, and geometry. Results from two different state-of-the-art codes, with markedly different numerical formalisms, are compared using this benchmark. The strong similarity between the two numerical predictions lends confidence to the physical accuracy of the results. The established database can be used for solver benchmarking and model development at conditions relevant to many propulsion and power systems.