Biju Thuruthimattam

Aeroelastic and Aerothermoelastic Behavior in Hypersonic Flow

The testing of aeroelastically and aerothermoelastically scaled wind-tunnel models in hypersonic flow is not feasible; thus, computational aeroelasticity and aerothermoelasticity are essential to the development of hypersonic vehicles. Several fundamental issues in this area are examined by performing a systematic computational study of the hypersonic aeroelastic and aerothermoelastic behavior of a three-dimensional configuration. Specifically, the flutter boundary of a low-aspect-ratio wing, representative of a fin or control surface on a hypersonic vehicle, is studied over a range of altitudes using third-order piston theory and Euler and Navier-Stokes aerodynamics. The sensitivity of the computational-fluid-dynamics-based aeroelastic analysis to grid resolution and parameters governing temporal accuracy are considered. In general, good agreement at moderate-to-high altitudes was observed for the three aerodynamic models. However, the wing flutters at unrealistic Mach numbers in the absence of aerodynamic heating. Therefore, because aerodynamic heating is an inherent feature of hypersonic flight and the aeroelastic behavior of a vehicle is sensitive to structural variations caused by heating, an aerothermoelastic methodology is developed that incorporates the heat transfer between the fluid and structure based on computational-fluid-dynamics-generated aerodynamic heating. The aerothermoelastic solution procedure is then applied to the low-aspect-ratio wing operating on a representative hypersonic trajectory. In the latter study, the sensitivity of the flutter margin to perturbations in trajectory angle of attack and Mach number is considered. Significant reductions in the flutter boundary of the heated wing are observed. The wing is also found to be susceptible to thermal buckling.

Hypersonic Aerothermoelastic Studies for Reusable Launch Vehicles

An aeroelastic and aerothermoelastic analysis of a three-dimensional low aspect ratio wing, representative of a fin on hypersonic vehicles, is carried out using piston theory, and Euler aerodynamics. Studies on grid convergence are used to determine the appropriate computational domain and resolution for this wing in hypersonic flow, using both Euler and Navier-Stokes aerodynamics. Hypersonic computational aeroelastic responses are then generated, using Euler aerodynamics in order to obtain frequency and damping characteristics for comparison with those from first and third order piston theory solutions. Results indicate that the aeroelastic behavior is comparable when using Euler and third order piston theory aerodynamics. The transonic aeroelastic behavior of the wing is also analyzed using Euler aerodynamics. The aerothermoelastic behavior of the wing, using piston theory aerodynamics, is studied by incorporating material property degradation and thermal stresses due to non-uniform temperature distributions. Results indicate that aerodynamic heating can substantially reduce aeroelastic stability. Finally, hypersonic aeroelastic behavior of a generic vehicle resembling a reusable launch vehicle is performed using piston theory. The results presented serve as a partial validation of the CFL3D code for the hypersonic flight regime.

Three-dimensional Aeroelastic and Aerothermoelastic Behavior in Hypersonic Flow

The aeroelastic and aerothermoelastic behavior of three-dimensional configurations in hypersonic flow regime are studied. The aeroelastic behavior of a low aspect ratio wing, representative of a fin or control surface on a generic hypersonic vehicle, is examined using third order piston theory, Euler and Navier-Stokes aerodynamics. The sensitivity of the aeroelastic behavior generated using Euler and Navier-Stokes aerodynamics to parameters governing temporal accuracy is also examined. Also, a refined aerothermoelastic model, which incorporates the heat transfer between the fluid and structure using CFD generated aerodynamic heating, is used to examine the aerothermoelastic behavior of the low aspect ratio wing in the hypersonic regime. Finally, the hypersonic aeroelastic behavior of a generic hypersonic vehicle with a lifting-body type fuselage and canted fins is studied using piston theory and Euler aerodynamics for the range of 2.5 M 28, at altitudes ranging from 10,000 feet to 80,000 feet. This analysis includes a study on optimal mesh selection for use with Euler aerodynamics. In addition to the aeroelastic and aerothermoelastic results presented, three time domain flutter identification techniques are compared, namely the moving block approach, the least squares curve fitting method, and a system identification technique using an Auto-Regressive model of the aeroelastic system. In general, the three methods agree well. The system identification technique, however, provided quick damping and frequency estimations with minimal response record length, and therefore oers significant reductions in computational cost. In the present case, the computational cost was reduced by 75%. The aeroelastic and aerothermoelastic results presented illustrate the applicability of the CFL3D code for the hypersonic flight regime.

Modeling Approaches to Hypersonic Aeroelasticity

The hypersonic aeroelastic problem of a double wedge airfoil typical cross-section is studied using three different unsteady aerodynamic loads: (1) third order piston theory, (2) Euler solution, and (3) unsteady Navier-Stokes aerodynamics. Computational aeroelastic response results are obtained, and compared with piston theory solutions for a variety of flight conditions. Aeroelastic behavior is studied for 7 < M < 15 at an altitude of 70,000 feet. A parametric study of offsets and wedge angles is conducted. Piston theory and Euler solutions are fairly close below the flutter boundary, and differences increase with increase in Mach number, close to the flutter boundary. Differences between viscous and inviscid aeroelastic behavior can be substantial. The results presented serve as a partial validation of the CFL3D code for the hypersonic flight regime.Copyright

Computational aeroelastic studies of a generic hypersonic vehicle

The hypersonic aeroelastic problem of a generic hypersonic vehicle having a lifting-body type fuselage and canted fins is studied using third order piston theory and Euler aerodynamics. Computational aeroelastic response results are used to obtain frequency and damping characteristics, and compared with those from piston theory solutions for a variety of flight conditions. Aeroelastic behavior is studied for the range of 2·5 < M < 28, at altitudes ranging from 10,000ft to 80,000ft. Because of the significant computational resources required, a study on optimal mesh selection was first carried out for use with Euler aerodynamics. The three dimensional flow effects captured using Euler aerodynamics was found to lead to significantly higher flutter boundaries when compared to those based on nonlinear piston theory. The results presented here illustrate some of the more important three dimensional effects that can be encountered in hypersonic aeroelasticity of complex configurations.

Aeroelastic and Aerothermoelastic Vehicle Behavior in Hypersonic Flow

The aeroelastic and aerothermoelastic behavior of three-dimensional configurations in the hypersonic flow regime are studied. The aeroelastic behavior of a low aspect ratio wing, representative of a fin or control surface on a generic hypersonic vehicle, is examined using third order piston theory, Euler and Navier-Stokes aerodynamics. The sensitivity of the aeroelastic behavior generated using Euler and Navier-Stokes aerodynamics to parameters governing temporal accuracy is also examined. Also, a refined aerothermoelastic model, which incorporates the heat transfer between the fluid and structure using CFD generated aerodynamic heating, is used to examine the aerothermoelastic behavior of the low aspect ratio wing in the hypersonic regime. Finally, the hypersonic aeroelastic behavior of a generic hypersonic vehicle with a lifting-body type fuselage and canted fins is studied using piston theory and Euler aerodynamics for the range of 2.5 M 28, at altitudes ranging from 10,000 feet to 80,000 feet. This analysis includes a study on optimal mesh selection for use with Euler aerodynamics. In addition to the aeroelastic and aerothermoelastic results presented, three time domain flutter identification techniques are compared, namely the moving block approach, the least squares curve fitting method, and a system identification technique using an Auto-Regressive model of the aeroelastic system. In general, the three methods agree well. The system identification technique, however, provided quick damping and frequency estimations with minimal response record length, and therefore oers significant reductions in computational cost. In the present case, the computational cost was reduced by 75%. The aeroelastic and aerothermoelastic results presented illustrate the applicability of the CFL3D code for the hypersonic flight regime.

Stress transfer modeling in viscoelastic polymer matrix composites

Abstract A viscoelastic analysis of a single fiber unidirectional composite model is carried out to investigate the time-dependent stress transfer between an elastic fiber and a viscoelastic matrix for loading in the axial direction. The stress state in the composite is solved at incremental time intervals to obtain the stabilized solution, and the time required to reach a stable state. The results obtained from a linear viscoelastic analysis are compared with the corresponding result obtained by using a non-linear “clock” model for the viscoelastic matrix. It is found that the non-linear analysis predicts a significantly lower stabilization time to reach the same final stress state.