Narrow Results

Heat and drag reduction on the nose cone is a significant issue for increasing the speed of the supersonic vehicles. In this paper, computational fluid dynamic method is applied to investigate the thermal and drag coefficient on the sharp nose cone with different cavity shapes. In order to simulate our model, the CFD method with SST turbulence model is applied to study the flow feature and temperature distribution in the vicinity of the nose body. The effect of depth and length of the cavity on the thermal characteristic of the nose cone is comprehensively investigated. In addition, the influence of the number of the cavity in the thermal performance of the main body is studied. According to our results, increasing the length of the cavity highly efficient for the reduction of the drag at Mach = 3. As the Mach number is increased to 3, the number of the cavity becomes a significant role and it is observed that case 9 with four cavities is more efficient. Obtained results also show that increasing the cavity depth declines the temperature on the main body. Our findings confirm that the main source of the expansion is the edge of the cavity.

In order to enrich the modeling of fluid flows, we investigate in this paper a coupling between two models dedicated to distinct regimes. More precisely, we focus on the influence of the Mach number as the low Mach case is known to induce theoretical and numerical issues in a compressible framework. A moving interface is introduced to separate a compressible model (Euler with source term) and its low Mach counterpart through relevant transmission conditions. A global steady state for the coupled problem is exhibited. Numerical simulations are then performed to highlight the influence of the coupling by means of a robust numerical strategy.

We determine completely the exact Riemann solutions for the system of Euler equations in a duct with discontinuous varying cross-section. The crucial point in solving the Riemann problem for hyperbolic system is the construction of the wave curves. To address the difficulty in the construction due to the nonstrict hyperbolicity of the underlying system, we introduce the L-M and R-M curves in the velocity-pressure phase plane. The behaviors of the L-M and R-M curves for six basic cases are fully analyzed. Furthermore, we observe that in certain cases the L-M and R-M curves contain the bifurcation which leads to the nonuniqueness of the Riemann solutions. Nevertheless, all possible Riemann solutions including classical as well as resonant solutions are solved in a uniform framework for any given initial data.

The thermal shock resistance of chemical vapor deposited zinc sulfide (CVD ZnS) infrared side window of high-speed vehicles with convective cooling is studied using finite volume method. The involved factors are the surface heat flux, coolant temperature, convective heat transfer coefficient, and thermal shock initial temperature. All the material properties are temperature-dependent. The study shows that convective cooling can improve the thermal up shock resistance of CVD ZnS caused by aerodynamic heating at the upper surface. On the other hand, it can also lead to thermal down shock failure at the lower surface. The critical failure time corresponding to thermal down shock failure is much less than that corresponding to thermal up shock failure. Thus, thermal down shock failure should be avoided in application. The critical thermal shock initial temperatures, below which convective cooling will not cause thermal down shock failure, for different coolants are calculated.