Un-fully developed flow effects on topology-optimized HVAC check valves: Resistance reduction and vortex analysis

In heating, ventilation, and air conditioning (HVAC) systems, due to the limitations of the building space structure, the connection distance between duct components usually cannot allow the fluid to be fully developed. In fluid dynamics, this flow state is called un-fully developed flow. Based on un-fully developed flow, this paper proposes a multi-objective topology optimization method for duct check valves with energy consumption ratio (Φ) and flow resistance (ΔP_f, Pa) as multi-objective functions, aiming to simultaneously improve performance and drag reduction efficiency. Comparative studies show that the resistance calculation error between un-fully and fully conditions can reach 52.34 %, and there are obvious differences in the optimization results. Therefore, the study of un-fully developed flow must be given high attention. The results of un-fully developed topology optimization show that the performance (ratio of reverse pressure drop (ΔP_r, Pa) to forward pressure drop (ΔP_f, Pa), Di) of the check valve is improved by 191.7 %, and the drag reduction rate reaches 64.8 %. Further analysis shows that Reynolds number (Re) has little effect on valve performance, and the fluctuation range of Di is between −0.74 % and 5.94 % (Di = 6.68–7.04). Di and ΔP_f are both proportional to the number of blades. When a set of blades is added, Di increases by 37.6 %, but the resistance increases by 218.05 %. In addition, the vortex analysis method (Q-criterion) is extended to this study to visualize the high resistance area of the system. The numerical simulation results are consistent with the experimental data. The experimental error within 10 % and the error with the simulation results less than 5 %.