Numerical study of jet injection into a supersonic crossflow

Abstract

This paper is an experimental/computational analysis of the fluid dynamic mechanisms inherent from circular jet injection into a supersonic crossflow. The goal of the current research is to use numerical simulations to provide detailed descriptions of the flow physics. Three different types of two-equation turbulence models were applied to predict the fuel mixing process. In addition, two types of inflow condition for the injection nozzle were tested. One, the injector nozzle was considered as part of the computational domain. Second, inviscid choked conditions were imposed at the fuel injection exit plane. The numerical results were compared with the experimental data in terms of fuel plume penetration contours, surface pressure data, and fuel penetration heights. Results show reasonably good agreements with surface pressure measuments, however, the penetration heights are overpredicted as compared to the experimental data. Introduction The transverse jet in supersonic crossflow constitutes a very important problem in fluid dynamics that has several practical applications, such as fuel injection in scramjet combustors and thrust vector control for aerospace vehicles. The interaction of the jet with the supersonic crossflow produces a complex, threedimensional flow field. A typical underexpanded transverse jet injected into a supersonic flow is shown schematically in Fig. 1. The figure depicts the global flow features and outlines the various regions of the jet ¶ Research Scientist, Taitech, Inc., Member AIAA. 5 Aerospace Engineer, Al%IJPRSS, Senior Member AIAA. This material is a work of the U.S. Government and is not subject to copyright protection in the United States. .plume with the wake region near the plate downstream of the jet orifice. This, sketch shows a pair of counterrotating vortices generated within the jet fluid. The jet cross-section is observed to be “kidney shaped” for a jet injected transversely in either subsonic or supersonic crossflow.lg This shape is developed due to the pressure field and viscous forces acting at the periphery of the jet. Observations by other researchers indicate the presence of a vortex pair structure that dominates the downstream cross section of the jet. If the jet is highly underexpanded, a normal shock or “Mach disk” will be present within the jet at a location within a few jet diameters of the orifice. The Mach disk becomes more important as the jet injection-to-crossflow momentum flux ratio increases. These properties of a jet in a crossflow depend primarily on the effective velocity ratio, which is defined as the ratio of the momentum flux across the jet exit to the momentum flux of the crossflow over an equal area.‘,’ In addition, a horseshoe vortex region also forms near the jet exit and wraps around the injector. Figure 2 represents some other important features , associated with a perfectly expanded transverse jet in a supersonic crossflow. A three-dimensional bow shock forms ahead of the injectant stream and interacts with the approaching boundary layer, resulting in a separation bubble. This separation region is typically two to three jet diameters ahead of the jet orifice.‘*2 This shock then merges with a strong bow shock that envelopes the periphery of the jet. A barrel shock also occurs as the underexpanded jet accelerates into the crossflow. Acceleration of the jet core flow continues until a normal shock, or Mach disk forms. Another separated region is present directly downstream of the jet plume. The objective of the present work is to gain a thorough understanding of the flow fields created by a sonic transverse jet injected into a supersonic crossflow, and particularly the large scale fuel mixing process as it applies to scramjet combustion applications. Due to the