Jet in supersonic cross-flow

Abstract

Lateral jet injection into supersonic crossflow is a complex problem that has been studied for many years due to critical engineering applications such as trajectory-attitude control, which enables high maneuverability in the atmosphere for missiles, and increasing the fuel-air mixture quantity and combustion efficiency in hypersonic air-breathing scramjet engines. The three-dimensional flow structures resulting from the interaction of the supersonic crossflow with the injected jet, the pressure areas in the upstream and downstream regions of the jet, shock wave interactions, and flow separation and recirculation regions are among the fundamental phenomena that need to be physically characterized. In this study, the flow field resulting from the injection of a sonic jet placed on a flat plate into a supersonic flow at Mach 5 was investigated numerically in three dimensions. In the validation process of the numerical model, validation studies were carried out using OpenFOAM software, referencing the experimental study conducted by Kovar and Schülein (2006). In computational fluid dynamics (CFD) analyses, the mesh was created with the SnappyHexMesh utility of OpenFOAM, in the modeling of turbulence, the Time-Dependent Reynolds-Averaged Navier-Stokes (URANS) equations were solved using the k-omega SST model, and the data were evaluated based on time-averaged results. In this study, the effects of changes in angle of attack on flow structures, the relationships of these changes with the freestream Mach number were investigated with a comprehensive parametric analysis. As a result of the analyses, the effects of increasing angle of attack and decreasing Mach number on the penetration of the jet flow into the freestream have been identified; the physical changes occurring in shock structures and separation regions due to this situation were interpreted. The visualized flow contours reveal that the location of the separation region formed in front of the jet, the physical form of the bow shock and barrel shock, and the vortex structures developing behind the jet exhibit a systematic differentiation depending on the changing aerodynamic parameters. According to the analysis results, the increase in jet penetration resulting from increasing angle of attack and decreasing Mach number leads to the shock structure spreading over a wider region. In connection with this phenomenon, it has been observed that the structural form of the jet core undergoes expansion and a more bending in the main flow direction. Examining the distribution of high Mach regions within the flow field reveals that this parametric change leads to a more homogeneous velocity structure and minimizes the blocking effect of the jet on the supersonic cross-flow. During this process, a decrease in the intensity of the reverse pressure gradient, the fundamental mechanism starting the separation, has been observed. As a result of the weakening pressure gradient, the intensity of the separation on the boundary layer is decreased, and the separation region physically moves further upstream from the jet exit location. This demonstrates that the change in angle of attack systematically affects not only the propagation of the jet but also the stability of the boundary layer on the plate. Although the flow field in supersonic flow and lateral jet interactions has traditionally been studied using two-dimensional visualizations, advanced three-dimensional visualization methods have been used to more comprehensively analyze the three-dimensional topology of complex structures in this region. Fundamental flow phenomena such as bow shock, barrel shock, and shear layer were isolated from the complex structure of the flow field and obtained in volumetric form, due to the scalar-based methodology developed in the numerical study. The volume of the shear layer was calculated from these volumetric data, thus determining the effects of different flow conditions on the mixture volume. Two different normalization studies were conducted to enable a physically meaningful comparison of these volumetric data; this aimed to provide comparable and reliable references for similar studies in the literature. In addition, the complex vortex topologies within the flow field were systematically investigated by using the Q-criterion method, and a structural comparison was made for all study conditions. In particular, in the baseline scenario at Mach 5 and an angle of attack of 0 degree freestream, the combination of two-dimensional surface streamlines and three-dimensional iso-surfaces has been examined in detail; thanks to this approach, the characteristic aerodynamic structures in the flow field have been verified.