Hydrogen combustion assisted by the oxygen plasma jet (PJ) in a Mach 1.9 supersonic internal flow was numerically investigated. Mixing and combustion behavior were compared between upstream and downstream fuel injections. For hydrogen injection downstream of the PJ, only weak combustion occurred even with a relatively high electric power input because of the rapid decrease in the ignitability of the PJ plume in the downstream. In contrast, intensive combustion easily occurred for hydrogen injection upstream of the PJ, with a relatively low electric power input, and a pseudo shock wave (PSW) was formed upstream of the fuel injector. The position of the PSW strongly affected the fuel mixing with the main airflow. The mixing and combustion of the fuel were rapidly enhanced by the formation of the leading shock wave of the PSW upstream of the fuel injector. Counter-rotating vortex pairs behind the fuel jet and PJ were enlarged by the PSW formation. The enlarged vortex structure behind the PJ was the main cause of the combustion enhancement.
In the present study, flow visualizations and quantitative measurements around a NACA0012 airfoil are performed under air and CO2 operation modes. A diaphragmless shock tube system is used for a high-subsonic airfoil testing. This system has the possibility of efficient aerodynamic experiments as an intermittent wind tunnel. A point diffraction interferometry (PDI) is used for a flow measurement technique. Moreover, the comparison with numerical results by the OpenFOAM is performed. The driver tube of this shock tube is the circular cross section with a diameter of 150mm. The driven tube is the rectangular cross section with a width of 60mm and a height of 150mm. The hot gas Mach number (uniform high-subsonic flow condition) is M2 = 0.65. The angle of attack is α = 0° and 2°, and the range of the Reynolds number is Re = 1.7–7.4 × 105. The results of the present study are as follows. In the present Reynolds numbers, if the shock wave does not generate, the shock tube airfoil flows of CO2 mode showed almost the same trend as the case of air mode quantitatively. The difference of operation gas was confirmed when the shock wave generated on the airfoil surface. In the high-subsonic flow, the pressure coefficients Cp by the PDI are in relatively agreement with the CFD results. The numerical results by the OpenFOAM give useful results for the comparison with aerodynamic data. Therefore, this shock tube system with a PDI measurement technique is considered as one of useful facilities for different operational modes.
This paper describes a novel algorithm for solving flight trajectory optimization problems subject to avoidance constraints of turbulent regions detected by an airborne Doppler lidar. The algorithm adopts a second-order cone programming (SOCP) relaxation of an original non-convex problem so as to obtain the estimate of global optimum, and subsequently applies a convex quadratic programming (CQP) based on the estimate. Moreover, by adopting a travel distance as the independent variable of the dynamics, the linearization of nonlinear state equations and the reduction of the number of constraints are achieved. The algorithm is well-suited to real-time applications due to its guaranteed convergence in polynomial computational time, and is expected to provide practically useful trajectories. Through some numerical simulations of the turbulence avoidance, the fast computational speed of the algorithm as well as the reasonableness of the calculated trajectories is demonstrated.