Flow, Turbulence and Combustion最新文献

Air intakes are an integral part of contemporary passenger and military aircraft engines. Their impact on aerodynamic performance across the entire flight envelope is critical to aircraft flight safety, efficiency, and manoeuvrability, especially at high Mach numbers due to shock waves. The high demand for reductions in aircraft weight and size and enhancements in durability, comfort, and thermal and radar signatures compel researchers and engineers to explore new designs and develop efficient air intakes for high-performance aircraft engines. Although a number of studies on air intake have been conducted and reported in the open literature, there is little information available in the public domain on bifurcated twin air intakes using synthetic jet. As a result, the primary goal of this research is to use computational fluid dynamics modelling to investigate the effects of synthetic jets on swirl inflow variable geometry twin air intake aerodynamic performance over a range of Reynolds numbers. Some important parameters (distortion coefficient, non-uniformity index, swirl coefficient, and static and total pressure coefficients) were investigated. Both static and total pressure recovery have been increased at all swirl numbers. A significant decrease in distortion coefficient and swirl coefficient has also been achieved, reaching a 53% reduction in the distortion coefficient and a 62% reduction in the swirl coefficient. The reduction in the non-uniformity index is achieved by 62% for the controlled flow case. The findings show that synthetic jets are effective in controlling the flow separation in the twin air intakes and enhancing aerodynamic performance.

This paper presents experimental investigations of the polyurethane foam influence on the combustion dynamics of hydrogen-air flames propagating in a channel with a sudden change in cross-section (i.e. expansion). The channel is open at both ends. Porous media of various lengths and pore size are considered. The porous inserts are placed downstream of the sudden expansion, inside the diagnostic section of dimensions 20 × 40 mm. A Schlieren visualization technique is used to monitor flame shape and propagation dynamics. Various equivalence ratios ranging from 0.3 to 1.0 are tested. The results show that depending on the equivalence ratio, porous length and pore size, the mixture can either propagate throughout the foam or be quenched. In propagating regime, it is found that the output velocity just behind the foam increases linearly with porous matrix length, indicating that the tortuous flow within the foam plays a significant role in the propagation of the flame. These results could be used both to increase the efficiency of gaseous combustion and to ensure the explosion safety of the gas equipment.

The unravelling of multilength-scale insert-generated turbulence, particularly, the induced-forcing plays critical role in the fundamental comprehension of energy formation and decay as a function of grid conformation. This study experimentally investigates the flow mechanical characteristics at Re_Dh = 4.1 × 10⁴ for a regular-grid (RG), single-square-grid (SSG) and six 2D planar space-filling square-fractal-grids (SFG) of different fractal iterations (N), thickness ratios (t_r) and blockage ratios (σ) via piezoelectric thin-film flapping velocimetry (PTFV). Thin-film’s tip-deflection (δ_rms) and voltage response (V_rms) analysis along the grids’ centreline reveals increasing flow fluctuation strength with increasing σ, t_r and decreasing N, owing to higher shedding intensity of lower frequency, larger scale energy-containing vortices from thicker first iteration bar. However, higher: energy dissipation rate, centreline mean velocity decrement rate and local deceleration experienced in the turbulence decay region of larger t_r grid, along with additional fractal scales lead to less potent flow-structure-interplay on thin-film undulation. More importantly, SSG-generated turbulence enables the generation of average (V_rms, δ_rms) and millinewton turbulence forcing F_rms that are respectively, 9× and 5× larger than RG of similar σ, and 2× larger than the best performing N = 3 SFG. Our findings disclose the importance of grid geometrical management for effective utilisation of turbulence-generating grids in engineering applications.