Density estimation of an ultrahigh-speed rarefied flow field based on force analysis of a pendulum sphere. (May 2023)

• Record Type: Journal Article
• Authors: Han, Ning; Cao, Jin-Wen; Meng, Xian; Liu, Hong-Li; Zhang, Shao-Hua; Huang, He-Ji
• Is Part Of: Vacuum. Volume 211(2023)
• Publication Date: 2023-05
• Subjects: Density estimation -- Pendulum sphere -- Force analysis -- Ultrahigh-speed rarefied flow; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2023.111919
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: The similarity criterion for high speed or high enthalpy rarefied reaction flows is the binary scaling law, one of which is the product of the incoming flow density and the characteristic scale of the test model in a rarefied wind tunnel should be equal to that under the flight condition. This is to ensure that the ratio between the characteristic distance of the relaxation process and the characteristic length of the body is equal. However, in a rarefied wind tunnel, it is difficult to directly measure the flow density below 10 −5 kg/m 3 using common methods due to the relatively high rarefied degree, an indirect density estimation method based on force analysis of a pendulum sphere was proposed in this study. The oscillation trajectory of the pendulum sphere under ultrahigh-speed rarefied flow conditions was recorded and the corresponding aerodynamic drag force acted on the sphere along the trajectory was analyzed, based on which the density distribution of the flow was then estimated combined with DSMC simulations. The obtained results show that in the present study, the flow is in under-expanded condition and the measured density sharply decreased from 10 −6 kg/m 3 to 10 −7 kg/m 3 at 140–170 mm from the nozzle outlet. Highlights: An indirect density measurement method for ultrahigh-speed rarefied flow filed was presented. The aerodynamic forces acting on a small pendulum sphere in a rarefied flow can be obtained quite precisely and easily by analyzing its oscillation trajectory experimentally. By comparing the obtained forces with those simulated by DSMC, the flow density as low as 10 -6 - 10 -7 kg/m 3 could be estimated which is usually hard to be measured using conventional method.