The calculation code originally developed for a hypersonic nonequilibrium flow is applied to the flowfield in front of a super orbital-velocity reentry capsule. The re-entry speed is assumed to be 12km/sec. The governing equations for a chemically and thermally nonequilibrium flow consist of the full Navier-Stokes equations, including the 11 chemical species mass conservation equations and the vibrational-electronic energy conservation equation. The Park's two-temperature model is used for the chemical reaction rates. A Harten-Yee type upwind TVD scheme is used to solve the governing equations with a fractional step method. A semi-implicit scheme is introduced because of the stiffness of chemical source terms. Under a super orbital-velocity re-entry conditions, the results of numerical calculations indicate that the vibrational excitation behind a strong bow shock is prevented by nitrogen molecule dissociation. The obtained distributions of vibrational and translational temperatures and species mass fractions are essentially sufficient to yield not only the convective but also the radiative heat transfer to the capsule surface using the existing NEQAIR code.
The convective and radiative heat transfer rates are calculated over the super-orbital reentering body surface like the MUSES-C capsule. Thermally and chemically nonequilibrium 11-species (O2, N2, O, N, NO, O+2, N+2, O+, N+, NO+ and e-) air is considered using Park's two temperature model. Chemical species number densities and temperature distributions are obtained by solving the Navier-Stokes equations and the vibrational-electronic energy conservation equation, using a Harten-Yee-type upwind TVD scheme. For the isothermal wall condition the minimum grid interval is set to 1μm in order to maintain the cell Reynolds number of O(1). The radiative heat transfer rate is calculated by integrating the radiative heat transfer equation using emission and absorption coefficients that are determined by NEQAIR (Nonequilibrium Air Radiation) and SPRADIAN (Structured Package for Radiation Analysis). Those results are compared with convective heat transfer rate.
A practical and useful upwind scheme is proposed in this paper, which was obtained by reducing numerical viscosity, based on the flux splitting method by Steger and Warming. The present scheme is classified as one of Advection Upstream Splitting Method (AUSM) schemes where the conservation of total enthalpy is ensured for the steady flow. As a result of applying it to several fundamental problems and comparing their results with those of other upwind methods, the method proposed here was found to have robustness and high-resolution.
Most of earth observation satellites have a single solar array due to the requirement imposed by the optical sensor visibility. This requirement makes spacecraft configuration highly unsymmetric, which produces particular dynamic characteristics. When the actuator such as RCS thruster is used, sensitivity from the displacement force to the attitude varies depending on the control frequency. This causes the imbalance between negative torque and positive torque on the main body, in other words, rotational center shifts from the mass center of the spacecraft. In this paper, this unsymmetric characteristic is formulated, and even more bending moment and shearing force acting on the root of the solar array are formulated. And then notations for designing a structure and a controller are indicated. Given a numerical model, formulated characteristics are also shown quantitatively.
This paper discusses the effects of the joint stiffness during the contact operation to the target by the space robotic arm. The contact dynamics in low frequency domain are focused rather than the impulse dynamics in high frequency domain. The authors proposed contact/pushing based control of the target satellite for damping its rotational motion. This method is conducted as follows: 1) a cushion type damper attached to the end-effector is approached to the selected points on the target, 2) the arm softly pushes the damper to the target, 3) the contact and/or pushing force between the damper and the target causes the angular momentum of the target to decrease. The effects of the arm vibration due to joint stiffness during such a contact operation are evaluated through numerical simulations.
This paper discusses on grid folding in the Laplace system of equations of grid generation. Although it is widely believed that a grid-generation method using the Laplace system does not result grid folding due to maximum principle, we have often encountered the grid folding especially at a trailing edged of an airfoil of O-grid topology. This paper gives an explanation of the phenomenon by considering that the elliptic grid-generation equations include partly a characteristic of a steady advection-diffusion equation. A method for avoiding grid folding in the Laplace system is presented using upwind-type finite difference discretization.