DSMC Simulation And Bridging Formulae Study On Aerodynamics Under Hypersonic Rarefied Condition

With the rapid development of space technology, more and more spacecrafts travel between the Earth and the outer space or between the outer space and other planets. The entering of a planetary atmosphere at a near-orbital velocity has been a common sense in space exploration. In the low-density regime, the aerodynamic characteristics of spacecrafts are quite different from those in the continuum regime. Therefore, establishing a platform to predict aerodynamics and aerothermodynamics in transitional flow regime has great significance on the aerospace and defense industry. The combination of DSMC(Direct Simulation Monte Carlo) simulation and bridging formulae engineering prediction is one well-established method to efficiently analyze aerodynamics characteristics in hypersonic rarefied gas flow.Firstly, the sophisticated DSMC simulation method has been studied in theoretical and applied aspects respectively. The DSMC program is employed for simple shaped bodies in hypersonic rarefied flow and the results of DSMC simulations correlate well with windtunnel data. The aerodynamic force and moment coefficients of blunt return capsule are computed using the 3-D DSMC program. The research shows that the number of triangles of surface mesh has no effect on the accuracy of the simulations results. However, when the number of simulated molecules per collision cell is less than 8, the total number of simulated molecules is one of the main factors affecting the accuracy.Then, the simulations results of ACM(Apollo Command Module) in hypersonic rarefied gas flow illustrate that rarefaction has a negative effect on aerodynamics. The lift coefficients and lift-to-drag ratio are extremely sensitive to rarefaction. In the transitional regime, the location of the center of pressure changes widely with longitudinal static instability. However, the velocity of free stream has less influence on aerodynamics. Moreover, there is a huge difference of flow structure in continuum regime from that in transitional regime. As the density of free stream decreases, the bow shock before the blunt body becomes thicker and thicker and the stable vortex wake in the wake disappears gradually.At last, after analysis of the variation of aerodynamics on the Kn. A new bridging formulae based on biological sigmoid function is purposed. The predictions of sig bridging formulae correlate well with the results of DSMC and CFD simulations and windtunnel data. The engineering estimations of new sig bridging formulae in near continuum and free molecule flow are more accurate than other global bridging formulae. In addition, for various aerodynamic geometry and different angle of attack, we see negligible to small change in accommodation parameters of new sig bridging formulae.