Zonglin Jiang

Numerical study on blast flowfields induced by supersonic projectiles discharged from shock tubes

In this paper we report on a numerical study of the blast flowfield generated by a supersonic projectile released from the open-end of a shock tube into ambient air. The Euler equations, assuming axisymmetric flows, were solved using a dispersion-controlled scheme implemented with moving boundary conditions. Two initial test cases were calculated. One of them is for validation of the numerical method and the other for verification of the moving boundary conditions. After good agreement was achieved, four further cases were calculated for examining effects of various projectile speeds and different release times of the projectile after the precursor shock wave was discharged. The present numerical study confirms that complicated transient phenomena exist in the initial stages shortly after projectile release, and that the blast flowfield is much more complex than that which can be inferred from muzzle blast studies where combustion products obscure the flow.

Concept of non-ablative thermal protection system for hypersonic vehicles

In order to reduce the shock-wave drag and aerodynamic heating of hypersonic vehicles effectively a new concept of non-ablative thermal protection system was proposed based on the idea of flowfield reconstruction. In this non-ablative thermal protection system a spike-blunt body structure and lateral jets are combined together to realize the flowfield modification. The spike transforms the bow shock into a conical shock, and the lateral jets increase the angle of conical shock wave and keep it away from the blunt body to avoid severe shock/shock interactions. Flow visualizations and pressure measurements were conducted in a hypersonic wind tunnel at Mach number 6 to demonstrate this concept. Numerical simulations were also carried out. Both experimental and numerical results demonstrate that the non-ablative thermal protection system works well for shock-wave drag reduction and thermal protection. The peak pressure at the reattachment region is reduced by 65% even under 4 deg attack angle by the lateral jet. Experimental data also show that the working pressure of lateral jets is much lower than that of forward-facing jets at the stagnation point. All the results show that the engineering application of non-ablative thermal protection system appears to be quite promising.

Wave dynamic processes induced by a supersonic projectile discharging from a shock tube

A numerical study on wave dynamic processes occurring in muzzle blast flows, which are created by a supersonic projectile released from the open-end of a shock tube into ambient air, is described in this paper. The Euler equations, assuming axisymmetric flows, are solved by using a dispersion-controlled scheme implemented with moving boundary conditions. Three test cases are simulated for examining friction effects on the muzzle flow. From numerical simulations, the wave dynamic processes, including two blast waves, two jet flows, the bow shock wave and their interactions in the muzzle blasts, are demonstrated and discussed in detail. The study shows that the major wave dynamic processes developing in the muzzle flow remain similar when the friction varies, but some wave processes, such as shock-shock interactions, shock-jet interactions and the contact surface instability, get more intensive, which result in more complex muzzle blast flows.

Forward-Running Detonation Drivers for High-Enthalpy Shock Tunnels

In order to improve the quality of driving flows generated withdetonation-driven shock tunnels operated in the forward-running mode,variousdetonation drivers with specially-designed sections were examined in this pa-per.Four configurations of the specially-designed section,three with differentco...

Reflection and focusing of toroidal shock waves from coaxial annular shock tubes

Abstract Focusing of a toroidal shock wave emitted from a coaxial annular shock tube and the resulting shock wave reflection were studied numerically with a dispersion-controlled scheme. The numerical code was first applied to prediction of a shock wave discharged from the open-end of a circular shock tube into ambient air. The numerical interferogram was constructed from the numerical result, taking three-dimensional density distribution into account, to directly compare with an experimental interferogram. Obtaining good agreement between these results, the numerical method was applied to shock waves discharged from a coaxial annular shock tube with various initial shock Mach numbers and in different configurations. It was found that intense shock focusing appears when the toroidal shock waves merge at the axis of symmetry. A somewhat unusual shock wave reflection was also observed in the case of higher shock Mach numbers.

Shocked Flows Induced by Supersonic Projectiles Moving in Tubes

A numerical study on shocked flows induced by a supersonic projectile moving in tubes is described in this paper. The dispersion-controlled scheme was adopted to solve the Euler equations implemented with moving boundary conditions. Four test cases were carried out in the present study: the first two cases are for validation of numerical algorithms and verification of moving boundary conditions, and the last two cases are for investigation into wave dynamic processes induced by the projectile moving at Mach numbers of M-p = 2.0 and 2.4, respectively, in a short time duration after the projectile was released from a shock tube into a big chamber. It was found that complex shock phenomena exist in the shocked flow, resulting from shock-wave/projectile interaction, shock-wave focusing, shock-wave reflection and shock-wave/contact-surface interactions, from which turbulence and vortices may be generated. This is a fundamental study on complex shock phenomena, and is also a useful investigation for understanding on shocked flows in the ram accelerator that may provide a highly efficient facility for launching hypersonic projectiles.

Numerical study of oblique detonation wave initiation in a stoichiometric hydrogen-air mixture

Two-dimensional, oblique detonations induced by a wedge are simulated using the reactive Euler equations with a detailed chemical reaction model. The focus of this study is on the oblique shock-to-detonation transition in a stoichiometric hydrogen-air mixture. A combustible, gas mixture at low pressure and high temperature, corresponding to the realistic, inflow conditions applied in oblique detonation wave engines, is presented in this study. At practical flight conditions, the present numerical results illustrate that oblique detonation initiation is achieved through a smooth transition from a curved shock, which differs from the abrupt transition depicted in the previous studies. The formation mechanism of this smooth transition is discussed and a quantitative analysis is carried out by defining a characteristic length for the initiation process. The dependence of the initiation length on different parameters including the wedge angle, flight Mach number, and inflow Mach number is discussed. Despite the hypothetical nature of the simulation configuration, the present numerical study uses parameters we deem relevant to practical conditions and provides important observations for which future investigations can benefit from in reaching toward a rigorous theory of the formation and self-sustenance of oblique detonation waves.

Initiation structure of oblique detonation waves behind conical shocks

The understanding of oblique detonation dynamics has both inherent basic research value for high-speed compressible reacting flow and propulsion application in hypersonic aerospace systems. In this study, the oblique detonation structures formed by semi-infinite cones are investigated numerically by solving the unsteady, two-dimensional axisymmetric Euler equations with a one-step irreversible Arrhenius reaction model. The present simulation results show that a novel wave structure, featured by two distinct points where there is close-coupling between the shock and combustion front, is depicted when either the cone angle or incident Mach number is reduced. This structure is analyzed by examining the variation of the reaction length scale and comparing the flow field with that of planar, wedge-induced oblique detonations. Further simulations are performed to study the effects of chemical length scale and activation energy, which are both found to influence the formation of this novel structure. The initiat...

Conceptual Study on Non-ablative TPS for Hypersonic Vehicles

In order to achieve efficient wave drag reduction under non-zero attack angles and avoid the severe aerodynamic heating, a new concept of the Non-ablative Thermal Protection System (NaTPS) for hypersonic vehicles was proposed based on the idea that the conical shock wave angle can be enlarged by lateral jets to push the conical shock away from the blunt body surface. In the NaTPS, a spike-blunt body structure and lateral jets are combined together to develop a new shock-reconstructing system in front of hypersonic vehicles. When the spike acts to recast the bow shock in front of a blunt body into a conical shock, the lateral jet works to protect the spike tip from overheating and push the conical shock away from the blunt body when a pitching angle exists during flight. The experimental flow visualization and the pressure measurements were conducted in a hypersonic wind tunnel for both the conceptual demonstration and CFD validation. Numerical simulations were also carried out to examine the complex flow around the NaTPS. Both experimental and numerical results show that the NaTPS works well for shock drag reduction and thermal protection. The shock/shock interaction on shoulders of the blunt body is avoided due to lateral jet injection and the peak pressure at the reattachment region is reduced by 65% under a 4° attack angle. The lateral jet could be powered either by high pressure gas stored in the tank or by the water evaporation process in which water absorbs the heat from the hot walls of the blunt noses. The jet pressure needed for producing lateral jet is much smaller than for the forward-facing jet from the stagnation point. The advantages of this concept are well demonstrated and its practical application appears promising.

Performance Tests of JF-10 High-Enthalpy Shock Tunnel with a FDC Driver

JF-10 detonation-driven high-enthalpy shock tunnel was re-built with a forward detonation cavity (FDC) driver and the experimental data from its performance tests are summarized and reported in this paper. Test-duration of high-enthalpy flows produced with the improved JF10 is found to be extended by two times under the condition that the FDC driver is about 40% shorter than the original one. The uniform pressure area of the thus-obtained hypersonic flows in a 500 mm diameter conical nozzle is about 700 mm in length and 400 mm in diameter. Incident shock wave decay in the driven section appears to be much less by comparing with the original JF-10 shock tunnel. The performance improvement of JF-10 high-enthalpy shock tunnel was demonstrated to be very successful and high quality hypervelocity flows can be generated for aero-thermochemistry experiments.