Validation of High-Fidelity CFD Simulations for Rocket Injector Design

Abstract

Computational fluid dynamics (CFD) has the potential to improve the historical rocket injector design process by evaluating the sensitivity of performance and injector-driven thermal environments to the details of the injector geometry and key operational parameters. Methodical verification and validation efforts on a range of coaxial injector elements have shown the current production CFD capability must be improved in order to quantitatively impact the injector design process. This paper documents the status of a focused effort to compare and understand the predictive capabilities and computational requirements of a range of CFD methodologies on a set of single element injector model problems. The steady Reynolds-Average Navier-Stokes (RANS), unsteady Reynolds-Average Navier-Stokes (URANS) and three different approaches using the Large Eddy Simulation (LES) technique were used to simulate the initial model problem, a single element coaxial injector using gaseous oxygen and gaseous hydrogen propellants. While one high-fidelity LES result matches the experimental combustion chamber wall heat flux very well, there is no monotonic convergence to the data with increasing computational tool fidelity. Systematic evaluation of key flow field regions such as the flame zone, the head end recirculation zone and the downstream near wall zone has shed significant, though as of yet incomplete, light on the complex, underlying causes for the performance level of each technique.

Assumed PDF modeling in rocket combustor simulations

“…The PennState preburner test case was also subject of the work presented in [1] where a variety of approaches of di¨erent ¦delity, ranging from RANS to LES, was employed. This broad investigation showed that even the use of more time consuming LES models does not guarantee an excellent agreement with the experimental heat §ux data.…”

“…The spatial discretization was 5th order while the time integration was 3rd order accurate. From the bulk velocity, the chamber §owthrough time can be estimated to be 8.3 ms [1]. To make sure that disturbances from the initial solution are washed out of the computational domain, preceding calculations were performed over approximately two §owthrough cycles.…”

“…Together with the measured preburner and combustion chamber pressures, the properties downstream of the preburners were calculated using the NASA chemical equilibrium code CEA and are provided in [16]. This test case has recently been of great interest and was simulated by numerous research groups using a variety of modeling approaches ranging from RANS to LES of di¨erent ¦delity [1,2]. In this work, the simulations are performed as unsteady 2D axisymmetric calculations on the computational domain illustrated in Fig.…”

“…However, even the capabilities of high-¦delity approaches like LES (Large Eddy Simulation) have to be improved in order to be accurate enough, to have a quantitative in §uence on the injector design process [1].…”

Verification, Validation, and Testing of Kinetic Mechanisms of Hydrogen Combustion in Fluid-Dynamic Computations

“…For scramjets, the verification and validation can be done by directly simulating a supersonic combustion directly, while it is not yet possible to do the same by simulating combustion in rocket engines. In recent work, Tucker et al [26], the group of researchers from five research centers, made the CFD simulations of a flow in a combustion chamber. Each participant simulated the same test case using their own methodology.…”