Chinese Journal of Aeronautics最新文献

Ruled surfaces found in engineering parts are often blended with a constraint surface, like the blade surface and hub surface of a centrifugal impeller. It is significant to accurately machine these ruled surfaces in flank milling with interference-free and fairing tool path, while current models in fulfilling these goals are complex and rare. In this paper, a tool path planning method with optimal cutter locations (CLs) is proposed for 5-axis flank milling of ruled surfaces under multiple geometric constraints. To be specific, a concise three-point contact tool positioning model is firstly developed for a cylindrical cutter. Different tool orientations arise when varying the three contact positions and a tool orientation pool with acceptable cutter-surface deviation is constructed using a meta-heuristic algorithm. Fairing angular curves are derived from candidates in this pool, and then curve registration for cutter tip point on each determined tool axis is performed in respect of interference avoidance and geometric smoothness. On this basis, an adaptive interval determination model is developed for deviation control of interpolated cutter locations. This model is designed to be independent of the CL optimization process so that multiple CLs can be planned simultaneously with parallel computing technique. Finally, tests are performed on representative surfaces and the results show the method has advantages over previous meta-heuristic tool path planning approaches in both machining accuracy and computation time, and receives the best comprehensive performance compared to other multi-constrained methods when machining an impeller.

The high-temperature non-equilibrium effect is a novel and significant issue in the flows over a high Mach number (above Mach 8) air-breathing vehicle. Thus, this study attempts to investigate the high-temperature non-equilibrium flows of a curved compression two-dimensional scramjet inlet at Mach 8 to 12 utilizing the two-dimensional non-equilibrium RANS calculations. Notably, the thermochemical non-equilibrium gas model can predict the actual high-temperature flows, and the numerical results of the other four thermochemical gas models are only used for comparative analysis. Firstly, the thermochemical non-equilibrium flow fields and work performance of the inlet at Mach 8 to 12 are analyzed. Then, the influences of high-temperature non-equilibrium effects on the starting characteristics of the inlet are investigated. The results reveal that a large separation bubble caused by the cowl shock/lower wall boundary layer interaction appears upstream of the shoulder, at Mach 8. The separation zone size is smaller, and its location is closer to the downstream area while the thermal process changes from frozen to non-equilibrium and then to equilibrium. With the increase of inflow Mach number, the thermochemical non-equilibrium effects in the whole inlet flow field gradually strengthen, so their influences on the overall work performance of the high Mach number inlet are more obvious. The vibrational relaxation or thermal non-equilibrium effects can yield more visible influences on the inlet performance than the chemical non-equilibrium reactions. The inlet in the thermochemical non-equilibrium flow can restart more easily than that in the thermochemical frozen flow. This work should provide a basis for the design and starting ability prediction of the high Mach number inlet in the wide operation range.

Streamwise Body Force Model (SBFM) could be used to simulate the force of blade on the airflow, resulting in rapid propulsion-airframe integrated simulation. However, when subjected to inlet distortion, the upstream flow field of fan stage is redistributed, which causes inaccurate prediction of fan stage performance. As inspired by the upstream influence of compressor, this paper aims to present a modification strategy for SBFM method to predict the compressor performance under circumferential inlet distortion without any knowledge of compressor geometry. Based on the linearized motion equation, the Upstream Influence Model (UIM) is introduced to predict the upstream flow field redistribution. Then the theoretical Mach number at Aerodynamic Interface Plane (AIP) position is calculated and selected to determine the corresponding body force coefficients based on the functional relationship between body force coefficients and Mach number, thus the upstream influence of compressor could be accurately quantified and the Modified Streamwise Body Force Model (MSBFM) could be established. Two studied cases are calculated with different methods and the upstream flow fields are analyzed. The prediction error of MSBFM method for compressor adiabatic efficiency is less than 3%, and the calculation efficiency is improved 20 times under the condition of ensuring computing accuracy. The MSBFM method has the potential for rapid propulsion-airframe integrated simulation.