This research adopts a shock tube 16 meters long and with a 9 cm bore to create a supersonic, high-temperature, and high-pressure flowfield to observe the gasification and ignition of HTPB solid fuel under different environments. Also, full-scale 3D numerical simulation is executed to enhance the comprehension of this complex phenomenon. The CFD (Computational Fluid Dynamics) code is based on the control volume method and the pre-conditioning method for solving the Navier-Stokes equations to simulate the compressible and incompressible coupling problem. In the tests, a HTPB slab is placed in the windowed-test section. Various test conditions generate different supersonic Mach numbers and environmental temperatures. In addition, the incident angles of the HTPB slab were changed relative to the incoming shock wave. Results show that as the Mach number around the slab section exceeded 1.25, the flowfield temperature achieved 1100 K, which is higher than the HTPB gasification temperature (930 K

With the development of the space shuttle and solar system exploration, hypersonic high technology in aviation will play an important role in the next-generation frontier [

In order to investigate the ignition and combustion efficiency of a supersonic combustion ramjet and simplify the components, a 16-meter shock tube was established, as shown in Figure

Shock tube dimension (a) high pressure sections (length: 290 cm, diameter: 28.5 cm), (b) convergent nozzle space (length: 10 cm, internal diameter in divergent section: 28.5 cm, internal diameter in convergent section: 9 cm), (c) test section (window:

In Figure

Uniformly spaced grids are used to cover the flow field, and the stretching transformation clusters, using the Roberts generalized stretching transformation technique, are made near the boundary layer. The shock tube is symmetrical about the centre-plane and, therefore, only the right half of the shock tube and plate-like model needs to be modelled. The multiblock grid approach is used in the present study. The total number of cells was 2 094 750 with respect to half of the 3D shock tube, as shown in Figure

Longitudinal cut view of the grid system.

The Navier-Stokes equations in integral form for an arbitrary control volume

Now two of the newer low-diffusion flux-splitting methods, AUSM+ and AUSMDV, are presented. For both methods, the inviscid interface flux

The interface quantities

The numerals in the subscripts of

For AUSM+,

For AUSMDV,

As shown later, the inclusion of

The original system of equations from the conservative variables

As indicated, the Weiss-Smith preconditioner is formed by the addition of the vector

The numerical scheme, using the preconditioning finite volume method, was introduced to solve the governing flow equations. A second-order scheme was initially applied, so the left and right states were chosen to be the cell average values on the left and right of the cell faces. In a high-resolution scheme, in order to raise the order of accuracy of upwind differencing, all that is needed is to raise the order of accuracy of the initial-value interpolation that yields the zone-boundary data. Such schemes are labelled as high-resolution schemes as opposed to Total Variation Diminishing (TVD) schemes, which completely eliminate any of those spurious oscillations when applied to one dimensional nonlinear hyperbolic conservation laws and linear hyperbolic systems. The van Leer kappa-scheme, in which the kappa number is one-third, was selected to obtain the high-resolution upwind differencing [

An optimal multistage scheme was used for the time integration, and the multistage coefficients were modified by Tai et al. [

In order to understand the velocity and temperature statute in the shock tube, the 1D shock tube theorem is applied to determine the shock speed, temperature, and action time as follows:

The history of the action time is shown in Figure

1D theorem determined result.

The time step in an unsteady simulation from the above determined 1D theorem can be set. In Figure

Pressure and temperature profile at point no. 1 and no. 2.

Snapshots of the pressure distribution in the tube.

Snapshots of the temperature distribution in the tube.

After understanding the phenomena of a full-scale shock tube, a fuel slab was placed in the test section

Pressure profile of HTPB surface at different AOA (C: length of the HTPB slab).

Figure

The reflected shock was induced in the trailing edge at

Figure

The reflected shock was also induced at the trailing edge at

It was observed that gasification exits as the shock wave moves across the HTPB. From the recovered fuel, melting was observed on the leading edge, as shown in Figure

Temperature profile of HTPB surface at different AOA (C: length of the HTPB slab).

Mach no. profile of HTPB surface at different AOA (C: length of the HTPB slab).

Iso-density contour (a)

Snapshots of shock wave (HTPB slab @

Comparison Exp. and CFD result (HTPB slab @

Mach No. distribution (HTPB slab @

Pressure measurement (HTPB slab @

Snapshots of shock wave (HTPB slab @

Mach No. distribution (HTPB slab @

Pressure measurement (point #1, HTPB slab @

Comparison before and after the action (a) without action, (b) with action.

From the numerical simulation results, the HTPB slab at an angle of attack of 7 degrees, had higher temperature and pressure in the upper surface than at 0 degrees and 10 degrees, and the flow speed of the upper and lower surfaces was kept at supersonic and contributed to gasification ignition. According to the experimental data and the numerical results, the test period was both about 3 milliseconds, and resulted in the melting of the leading edge of the tested HTPB slab. In other areas, although the gasification criterion was reached, it was unable to burn because the flow speed was too great and the test time was limited to only 3 ms in the shock tube facility.

The author is grateful to the Professor Jr-Ming Char, CAFA Shocktube Lab., NCKU Spray Lab., and the National Science Council of the Republic of China (Taiwan) for financial support under contract number NSC 97-2221-E-344-005.