Narrow Results

An experimental investigation was carried out to evaluate the fracture pressure and behaviors of ceramic materials for a dome port cover of an air breathing engine. The experiments were performed in a shock tube, which had a working section of 70 mm in diameter and a total length of 6 m in the shock tube. The response pressure transducers were used to measure expansion pressure and reflection pressure of working section near the end edge of the shock tube. Fractured specimens collected from the dump tank were investigated for the fracture phenomenon of ceramics after testing. The fracture pressure increases as a specimen thickness increases, and as the specimen diameter decreases, respectively. The driven gas pressures P₂ obtained from theory and experiment agree well. The reflection wave pressures P₅ agree well comparatively with both results of equation and experiment at low pressure of P₄, but they do not agree well at high pressure of P₄. The fracture phenomena of the plate and dome specimens at the same diameter are broken into small particles in various thicknesses, but the fracture phenomenon of the plate specimen is not broken into the particles as specimen diameter decreases.

We investigated discretization strategies of the conservation equation in volume/surface integrated average-based multi-moment method (VSIAM3) which is a numerical framework for incompressible and compressible flows based on a multi-moment concept. We investigated these strategies through the lid-driven cavity flow problem, shock tube problems, 2D explosion test and droplet splashing on a superhydrophobic substrate. We found that the use of the constrained interpolation profile-conservative semi-Lagrangian with rational function (CIP-CSLR) method as the conservation equation solver is critically important for the robustness of incompressible flow simulations using VSIAM3 and that numerical results are sensitive to discretization techniques of the divergence term in the conservation equation. Based on these results, we proposed efficient implementation techniques of VSIAM3.

This paper presents a space–time least squares finite element formulation of one dimensional transient Navier–Stokes equations (governing differential equations: GDE) for compressible flow in Eulerian frame of reference using ρ, u, T as primitive variables with C¹¹ type p-version hierarchical interpolations in space and time. Time marching procedure is utilized to compute time evolutions for all values of time. For high speed gas dynamics the C¹¹ type interpolations in space and time possess the same orders of continuity in space and time as the GDE. It is demonstrated that with this approach accurate numerical solutions of Navier–Stokes equations are possible without any assumptions or approximations. In the approach presented here SUPG, SUPG/DC, SUPG/DC/LS operators are neither used nor needed. Time evolution shows resolution of shock structure (i.e., shock speed, shock relations and shock width) to be in excellent agreement with the analytical solutions. The role of diffusion, i.e., viscosity (physical or artificial) and thermal conductivity on shock structure is demonstrated. Riemann shock tube is used as model problem. Time evolutions are reported beginning with the first time step until steady shock conditions are achieved. In this approach, when the computed error functionals become zero (computationally), the computed nonweak solutions satisfy GDE accurately.

Impulsive transient jet originating from the open end of a short driver section shock tube has been simulated numerically by solving the unsteady Navier-Stokes equation in axisymmetric form using AUSM+ scheme for a driver section pressure ratio of 10. The simulations are performed using second order central and fifth order upwind schemes with different spatial resolutions. The effect of higher order schemes and spacial resolution on the accuracy of the solution is studied in detail. It has been observed that the results obtained from the fifth order scheme with lower spacial resolution and denser grids along the free shear layer matched close with experimental smoke flow visualization.