Earl A. Thornton

Flow-thermal-structural study of aerodynamically heated leading edges

A finite element approach for integrated fluid-thermal-structural analysis of aerodynamically heated leading edges is presented. The Navier-Stokes equations for high speed compressible flow, the energy equation, and the quasi-static equilibrium equations for the leading edge are solved using a single finite element approach in one integrated, vectorized computer program called LIFTS. The fluid-thermal-structural coupling is studied for Mach 6.47 flow over a 3-inch diameter cylinder for which the flow behavior and the aerothermal loads are calibrated by experimental data. Issues of the thermal-structural response are studied for hydrogen cooled, super thermal conducting leading edges subjected to intense aerodynamic heating.

Thermally induced bending vibrations of a flexible rolled-up solar array

An analytical approach for determining the thermal-structural response of a flexible rolled-up solar array due to a sudden increase in external heating is developed. Two analyses are presented: 1) an uncoupled thermal-structural analysis that assumes the heating and temperature gradients are not affected by thermally induced motions, and 2) a coupled thermal-structural analysis that includes the effects of structural deformations on heating and temperature gradients. The analytical methods identify key parameters for understanding the static and dynamic response. A stability criterion given in nondimensional parameters establishes the conditions for thermal flutter. Key parameters for thermal flutter include the ratio of thermal and structural response times, the solar inclination angle, and the system damping. Numerical calculations are presented for the solar arrays on the Hubble Space Telescope. Unstable oscillations are possible but are unlikely to have practical importance.

Coupled flow, thermal, and structural analysis of aerodynamically heated panels

A finite-element approach for coupling flow, thermal, and structural analyses of aerodynamicaly heated panels is presented. The Navier-Stokes equations for laminar compressible flow are solved, together with the energy equation and quasistatic structural equations of the panel. Interactions between the flow, panel heat transfer, and deformations are studied for thin stainless steel panels aerodynamically heated by Mach 6.6 flow.

Thermal structures: Four decades of progress

Since the first supersonic flight in October 1947, the United States has designed, developed and flown flight vehicles within increasingly severe aerothermal environments. Over this period, major advances in engineering capabilities have occurred that will enable the design of thermal structures for high speed flight vehicles in the twenty-first century. This paper surveys progress in thermal-structures for the last four decades to provide a historical perspective for future efforts.

Application of integrated fluid-thermal structural analysis methods

Hypersonic vehicles operate in a hostile aerothermal environment which has a significant impact on their aerothermostructural performance. Significant coupling occurs between the aerodynamic flow field, structural heat transfer, and structural response creating a multidisciplinary interaction. Interfacing state-of-the-art disciplinary analysis methods is not efficient, hence interdisciplinary analysis methods integrated into a single aerothermostructural analyzer are needed. The NASA Langley Research Center is developing such methods in an analyzer called LIFTS (Langley Integrated Fluid-Thermal-Structural) analyzer. The evolution and status of LIFTS is reviewed and illustrated through applications.

Thermally Induced Dynamics of Satellite Solar Panels

Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.

THERMALLY INDUCED VIBRATIONS OF A SELF-SHADOWED SPLIT-BLANKET SOLAR ARRAY

An analytical approach is developed for investigating thermally induced vibrations of a split-blanket solar array due to self-shadowing of the central truss. Two analyses are developed: (1) cross-member shadowing of the truss longerons due to a torsional vibration of the solar array, and (2) parallelmember shadowing when the solar vector is aligned with the plane of the truss longerons. The analytical approaches identify key parameters for understanding the thermalstructural response. For parallel-member shadowing a stability analysis establishes the condition for thermal flutter. Computations are made for a solar array representative of the Space Station Freedom (SSF) design. The results show that cross-member shadowing is unlikely to cause thermally induced vibrations. Parallel-member shadowing can cause thermally induced vibrations; however, the vibrations are stable. Under normal operations the SSF solar array should not experience thermally induced vibrations.

Buckling and Quasistatic Thermal- Structural Response of Asymmetric Rolled-Up Solar Array

Analytical studies for buckling and the quasistatic thermal‐ structural response of an asymmetrical rolled-up solar array of the type used on the Hubble Space Telescope are presented. A buckling analysis assuming asymmetric loading because of geometric asymmetry establishes critical buckling forces and buckling modes. Quasistatic thermal‐ structural responses of the solar array subjected to the sudden radiation heating typical of a night‐ day orbital transition are also developed. Computations conducted for the Hubble Space Telescope show that the solar arrays were deployed with a solar blanket prestress that would induce global torsional buckling. Numerical computations for the quasistatic response show that thermally induced bending‐ torsional deformations would cause bending moments in the solar array’ s booms consistent with the local buckling failure observed by the astronauts.

A Taylor-Galerkin finite element algorithm for transient nonlinear thermal-structural analysis

A Taylor-Galerkin finite element method for solving large, nonlinear thermal-structural problems is presented. The algorithm is formulated for coupled transient and uncoupled quasistatic thermal-structural problems. Vectorizing strategies ensure computational efficiency. Two applications demonstrate the validity of the approach for analyzing transient and quasistatic thermal-structural problems.

Finite element prediction of aerothermal-structural interaction of aerodynamically heated panels

A finite element approach is used to study the aerothermal-structural interaction of aerodynamically heated panels. The Navier-Stokes equations for laminar compressible flow are solved together with the energy equation and quasi-static structural equations of the panel. Interactions between the flow, panel heat transfer and deformations are studied for a thin stainless steel panel aerodynamically heated by a Mach 6.6 flow and for a convectively cooled panel heated by a shock-boundary layer interaction.