Multiphysics Coupled Fluid/Thermal/Structural Simulation for Hypersonic Reentry Vehicles Ala Tabiei 1 and Subramani Sockalingam 2 Abstract: The main goal of the work described in this paper was to set up a procedure for modeling a thermal protection system for a hypersonic reentry vehicle by extending earlier work done by the authors. A multiphysics framework has been setup for the simulation of hypersonic reentry vehicles using commercial codes FLUENT and LS-DYNA with user-defined programming. The computational fluid dynamics code (FLUENT) and the material thermal and structural response code (LS-DYNA) are loosely coupled to achieve the solution. The surface recession resulting from ablation in the reentry vehicle is simulated by implementing a mesh movement algorithm in LS-DYNA. The vehicle considered in the calculation is an axisymmetric vehicle flying at zero degree angle of attack. DOI: 10.1061/(ASCE)AS.1943- 5525.0000113. © 2012 American Society of Civil Engineers. CE Database subject headings: Simulation; Fluid–structure interactions; Vehicles; Thermal factors. Author keywords: Reentry simulation; Multiphysics simulation; Fluid/structure/thermal interaction of reentry vehicle. Introduction In earlier work, the surface heat flux simulation of a hypersonic reentry vehicle using the commercial computational fluid dynamics (CFD) code FLUENT was described (Sockalingam and Tabiei 2009). A thermal protection system (TPS) is used to insulate the vehicle from the high temperatures encountered during reentry. There are two types of TPSs, reusable and ablative. The former is used for less severe reentry conditions like shuttle reentry, and the latter for severe heating conditions. Ablation involves vaporization, sublimation, and oxidation resulting in phase change of the ablative material (Milos and Chen 1997). These are endo- thermic reactions that absorb the heat away from the surface of the vehicle. The ablating mass flux reacts with boundary layer gases and makes the ablative TPS more complex to simulate com- pared with the nonablative TPS. The material thermal structural response is simulated using LS-DYNA, which is a nonlinear finite element analysis (FEA) code capable of solving for the transient temperature under nonlinear boundary conditions (Hallquist 2006). The chemically reacting hypersonic flow for an axisymmetric vehicle at zero degree angle of attack is solved using FLUENT (ANSYS 2006), and the material thermal response is computed using LS-DYNA in the current work. Fluid thermal coupling between the CFD and FEA codes is achieved by loosely coupling the codes. Ablation involves material removal, and to predict surface reces- sion and hence the shape of the ablating body, a mesh movement algorithm is implemented in LS-DYNA. The algorithm is adopted from Hassan et al. (1998) and Hogan et al. (1996). The ability to predict the change in shape is achieved by coupling the fluid and thermal response codes. Computational Fluid Dynamics FLUENT, the commercial CFD code, is used to predict surface heat flux during reentry of the hypersonic vehicle. The CFD governing equations, chemical nonequilibrium model for the reacting gas, transport properties and thermal equilibrium model have been described in detail (Sockalingam and Tabiei 2009). The boundary conditions used in the CFD simulations in FLUENT and the free stream conditions for the reentry vehicle are also given in Sockalingam and Tabiei (2009). Thermal Response Simulation Governing Conduction and Surface Energy Balance Equations LS-DYNA, the general-purpose multiphysics FEA code, is used to simulate the material thermal response (Hallquist 2006). The classical heat conduction equation is used for heat transfer in the structure (Thornton 1992): ρc ∂ T ∂ t ¼ ∂ ∂ x i  k ij ∂ T ∂ x j  þ Q ð1Þ The governing surface energy balance for a nonablating surface is (Chen and Milos 1996) q w ¼ q cond þ q rad ð2Þ q w is the heat flux to the surface computed by FLUENT (ANSYS 2006) and is q w ¼ h f ðT w À T f Þ ð3Þ The local value of the convective heat transfer coefficient is given by (Candane et al. 2007) as 1 Associate Professor, Dept. of Aerospace Engineering and Engineering Mechanics, Univ. of Cincinnati, Cincinnati, OH 45221-0070, USA (corresponding author). E-mail: tabieia@ucmail.uc.edu 2 Graduate Teaching Assistant, Dept. of Mechanical Engineering, Univ. of Delaware, Newark, DE 19716; formerly, R&D Engineer, Hawthorne & York International Ltd., Phoenix, AZ 85040, USA. E-mail: sockalsi@udel.edu Note. This manuscript was submitted on February 2, 2010; approved on February 1, 2011; published online on August 12, 2011. Discussion period open until September 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Journal of Aerospace Engi- neering, Vol. 25, No. 2, April 1, 2012. ©ASCE, ISSN 0893-1321/ 2012/2-273–281/$25.00. JOURNAL OF AEROSPACE ENGINEERING © ASCE / APRIL 2012 / 273 Downloaded 23 Apr 2012 to 128.175.13.10. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org