Munetsugu Kaneko

Numerical Investigation of SRB Ignition Overpressure

The numerical simulation of SRB ignition overpressure was performed to clarify the mechanism of ignition overpressure (IOP) under the same conditions as a solid rocket booster (SRB) of the Space Shuttle Columbia for the STS-1 mission. Two governing equations: 1) the Euler equations and 2) the linearized Euler equations (LEE) are employed to capture pressure fluctuations without attenuating their amplitudes as much as possible. It is assumed that gas is calorically perfect and that combustion gas, whose specific heat ratio is 1.18, fills the overall computational region. Computations are carried out for the axisymmetric case, where the ground is horizontal, and for the three-dimensional case, where the ground is eiter horizontal or oblique. The time history of pressure fluctuation shows reasonable agreement with the measured data on the SRB for the STS-1 mission. Moreover, the detailed mechanism of IOP was made clear, and the merit of using an oblique wall in a launch pad was assured to reduce the effect of overpressure waves on the body of spacecraft.

Unsteady-Nonequilibrium Shock Wave / Boundary Layer Interaction with Explicit/Implicit Hybrid Approach

The flow fields of a shock tube and a nozzle starting process for both perfect gas and flow with thermochemical nonequilibrium has been simulated. This flow is produced in high enthalpy impulse facilities such as free piston shock tunnel. The governing equations are the axisymmetric, compressible Navier-Stokes equations. For the case of thermochemical nonequilibrium, Park’s two-temperature model, where air consists of 5 species, is used for defining the thermodynamic properties of air as a driven gas. The numerical scheme employed here is the hybrid scheme of explicit and implicit methods, which was developed at our laboratory, along with AUSM + to evaluate inviscid fluxes. In the present simulation, the Mach number of an incident shock wave is set at Ms = 2:6;5:3. The results clearly show the complicated shock wave/ boundary layer interaction in the part of shock tube. These suggest that the retention of gas accounts for the growth of bifurcated shock structure. The discharge of vortex from the bifurcation surpresses the magnification of size of the bifurcation.

Numerical Study of Unsteady Shock Waves in Hypersonic Nozzle Flows

The flow field with thermal and chemical nonequilibrium in a hypersonic nozzle has been simulated. This flow is produced in high enthalpy impulse facilities such as free piston shock tunnel. The objectives of this study is make clear the complicatedunsteady process of the nozzle starting. The governing equations are the axisymmetric, compressible Navier-Stokes equations. In this study, Park’s two-temperature model, where air consists of 5 species, is employed for defining the thermodynamic properties of air used as a driven gas. The numerical scheme is a hybrid scheme combining explicit and implicit methods, which were developed in our laboratory, implemented with the AUSM+ to evaluate inviscid fluxes. In the present simulation, the Mach number of an incident shock wave is set at M, = 10.0. It corresponds to a specific enthalpy, h,, of 12MJ/kg. The results clearly show the flow structures around shock waves: viscous interaction with the wall of a shock tube and the initial stage of nozzle starting process. They also suggest that the phenomenon of a nozzle melting might be associated with a flow separation a t the nozzle inlet.