Detached Eddy Simulation of Base Flows under Subsonic Free Stream Conditions

The present work focuses on the numerical simulation of a base flow around a generic rocket model for subsonic flow conditions. In a preliminary study the flow for two reduced geometries are investigated to obtain an optimized discretization of the flow field for a detached eddy simulation (DES). First, an inflow plane with prescribed values from a Reynolds averaged Navier-Stokes (RANS) solution is used which avoids the unsteady simulation of the model support and most of the model body. Second, the problem size is halved by exploiting the symmetry of the geometry. In both calculations an indicator is tested, which quantifies the local grid quality with respect to the turbulent kinetic energy resolved by the DES. According to this indicator the grid resolution in the first case is very good and in the second case sufficient in the regions of interest. Although the physical interpretation is limited due to the approximations made, the results indicate a strong connection between the base flow and the wake of the support

Numerical Study of Compressible Mixing Layers in Hyshot II Supersonic Combustor

The compressible mixing layers inside a supersonic combustion chamber (HyShot II combustor) are numerically studied in this paper by using the DLR TAU code. The TAU code is firstly verified by calculating supersonic mixing layers downstream of a splitter plate. Studies of numerical settings show, that the AUSMDV upwind scheme plus dual time stepping with small physical time step is stable and efficient for the calculation of unsteady supersonic mixing layers. With the aid of this numerical experience, the DES calculation of the HyShot II combustor is subsequently carried out. Different from most previous studies, overexpanded and under-expanded flow states occur simultaneously at the exit of the current jet porthole. The shock system near the injector is a combination of detached normal shock and a small three-dimensional barrel shock ended with a Mach disk. Further insight into the flow physics is conducted by visualizing instantaneous coherent structures. A new understanding of the key flow physics in the low-momentum flux-ratio jet in supersonic crossflow is schematically provided, which is helpful to future design of injection systems for scramjet applications

Injection and mixing in a scramjet combustor: DES and RANS studies

National Science Foundation of China [51006051]; EU [ACP7-GA-2008-21 1485]The low momentum flux ratio jet in the HyShot II scramjet combustor is studied by DES (Detached Eddy Simulation) and RANS (Reynolds-Averaged Navier-Stokes) methods. The flow structure near the injector, shock pattern in the symmetry plane as well as the instantaneous coherent structures are presented and explained. Further insight into the flow physics is obtained by visualizing instantaneous coherent structures. The formation of Omega-shaped vortices, which was previously observed in experiments but never well-studied numerically, is discussed in detail. A new schematic of flow physics is proposed to enhance the understanding of the low momentum flux ratio jet. Compared to the DES result, the RANS method is unable to capture the dynamics of turbulent structures. The DES method provides much detailed information about mixing patterns and a more reliable mixing efficiency than the RANS result. The RANS method over-predicts the eddy-viscosity during turbulence modeling and suppresses unsteady turbulent fluctuations by time averaging, which results in a 25% over-estimation of the mixing efficiency. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved