Micropore jet and permeability characteristics of the canopy fabric
SUN Zhihong1, QIU Bowen1, YU Li1,2, LI Yanjun1,2, NIE Shunchen1
1. Key Laboratory of Aircraft Environment Control and Life Support of Ministry of Industry and Information Technology, College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China; 2. College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Abstract：[Objective] Parachutes are widely used in aviation, aerospace, and weapon fields as an efficient and economical aerodynamic deceleration device. The drag force of a parachute mainly comes from the pressure differential on both sides of the permeable canopy. The essence of canopy permeability is that the air flows through the fabric pores to form a jet, thus affecting the flow field around the parachute and, subsequently, the aerodynamic performance of the parachute. To study the aerodynamic performance of a parachute, the micropore jet and permeability characteristics of its canopy fabric must be thoroughly investigated.[Methods] The micromodels of fabrics with high and low porosities were established on the basis of TexGen, numerical calculation of the pore jet flow under different pressure differentials was performed using computational fluid dynamics, and the numerical permeability values were compared with the experimental values. Then, the pressure and velocity of the jet domain were analyzed. The jet domain was divided into four regions according to various velocity and pressure characteristics along the central axis of the pores. Since the quantitative analysis of the jet domain under different pressure differentials was difficult, the relative pressure differential and relative velocity without the dimension parameters were proposed. On this basis, the jet characteristic parameters were proposed along with the application of the jet theory. The parameter change rule of different fabrics under different pressure differentials was analyzed. Moreover, the factors influencing the jet parameters were studied. Finally, the Levenberg-Marquardt optimization algorithm was used to fit the influence range of the jet domain based on the single-phase exponential decay function, and the experimental results were compared with the numerical results.[Results] The numerical results of the micropore jet flow field showed that:(1) The velocity of air increased within the pore and decreased after the outflow, while the pressure changed occur inversely. The pressure gradient was concentrated in the pore. (2) The jet flow field comprised four zones:velocity increase zone, velocity decay zone, wake decay zone, and wake transition zone. The changes in the velocity and pressure gradients along the direction of air flow primarily occurred in the velocity increase and velocity decay zones. The maximum velocity value of the central axis and the minimum pressure value were located in the adjacent pore throat. The flow characteristic parameters in the wake decay zone were not affected by the influence of the pressure differential. (3) When the pressure differential exceeded 200 Pa, the flow characteristic parameters in the fabric pore and the jet domain were determined only by the fabric structure. (4) The influence range of the jet domain increased with the porosity and shares an exponential decay relationship with the air permeability.[Conclusions] In this paper, the variation law of velocity and pressure in the fabric microporous jet flow domain is studied based on the numerical results of the pore jet flow field under different pressure differentials. The jet domain calculation model suitable for the parachute fabric is established. The research method proposed in this paper is highly significant in exploring the fine-flow field structure of the permeable parachute and improving the accuracy of the flow field model of the permeable canopy.
孙志鸿, 仇博文, 余莉, 李岩军, 聂舜臣. 伞衣织物微孔射流透气特性[J]. 清华大学学报（自然科学版）, 2023, 63(3): 330-337.
SUN Zhihong, QIU Bowen, YU Li, LI Yanjun, NIE Shunchen. Micropore jet and permeability characteristics of the canopy fabric. Journal of Tsinghua University(Science and Technology), 2023, 63(3): 330-337.
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2023, Vol. 63 
