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Self-organized generation of transverse waves associated with the transverse wave instabilities at a diverging cylindrical detonation front was numerically studied by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. After solution validation, four mechanisms of the transverse wave generation were identified from numerical simulations, and referred to as the concave front focusing, the kinked front evolution, the wrinkled front evolution and the transverse wave merging, respectively. The propagation of the cylindrical detonation is maintained by the growth of the transverse waves that match the rate of increase in surface area of the detonation front to asymptotically approach a constant average number of transverse waves per unit length along the circumference of the detonation front. This cell bifurcation phenomenon of cellular detonations is discussed in detail to gain better understanding on detonation physics.

Cylindrical cellular detonation is numerically investigated by solving two-dimensional reactive Euler equations with a finite volume method on a two-dimensional self-adaptive unstructured mesh. The one-step reversible chemical reaction model is applied to simplify the control parameters of chemical reaction. Numerical results demonstrate the evolution of cellular cell splitting of cylindrical cellular detonation explored in experimentas. Split of cellular structures shows different features in the near-field and far-field from the initiation zone. Variation of the local curvature is a key factor in the behavior of cell split of cylindrical cellular detonation in propagation. Numerical results show that split of cellular structures comes from the self-organization of transverse waves corresponding to the development of small disturbances along the detonation front related to detonation instability.

In this paper, the shock pattern oscillations induced by shock/shock interactions over double-wedge geometries in hypersonic flows were studied numerically by solving 2D inviscid Euler equations for a multi-species system. Laminar viscous effects were considered in some cases. Temperature-dependent thermodynamic properties were employed in the state and energy equations for consideration of the distinct change of the thermodynamic state. It was shown that the oscillation results in high-frequency fluctuations of heating and pressure loads over wedge surfaces. In a case with a relatively lower free-stream Mach number, the shock/shock interaction structure maintains a seven-shock configuration during the entire oscillation process. On the other hand, the oscillation is accompanied by a transition between a six-shock configuration (regular interaction) and a seven-shock configuration (Mach interaction) in a case with a higher free-stream Mach number. Numerical results also indicate that the critical wedge angle for the transition from a steady to an oscillation solution is higher compared to the corresponding value in earlier numerical research in which the perfect diatomic gas model was used.

Laser performance is greatly dependent on its operating conditions due to the strong coupling among multi-physics such as gas-dynamics, chemical reaction kinetics and optics in the mixing nozzle of COIL. In this paper, 3D CFD technology is used to simulate the mixing and reactive flow of subsonic cross jet scheme at different conditions. Results obtained show that the jet penetration depth plays a dominant role in the spatial distribution of small signal gains. In the case of over-penetration, unsteady flow structures are induced by impinging between the opposing jets. The optimum spatial distribution of the chemical performance cannot be obtained even if the full penetration condition is achieved through the subsonic transverse jet mixing scheme in the COIL nozzle flow.

Arrhenius law implicates that only those molecules which possess the internal energy greater than the activation energy Ea can react. However, the internal energy will not be proportional to the gas temperature if the specific heat ratio γ and the gas constant R vary during chemical reaction processes. The varying γ may affect significantly the chemical reaction rate calculated with the Arrhenius law under the constant γ assumption, which has been widely accepted in detonation and combustion simulations for many years. In this paper, the roles of variable γ and R in Arrhenius law applications are reconsidered, and their effects on the chemical reaction rate are demonstrated by simulating one-dimensional C-J and two-dimensional cellular detonations. A new overall one-step detonation model with variable γ and R is proposed to improve the Arrhenius law. Numerical experiments demonstrate that this improved Arrhenius law works well in predicting detonation phenomena with the numerical results being in good agreement with experimental data.

A chemical oxygen iodine laser (COIL) that operates without primary buffer gas has become a new way of facilitating the compact integration of laser systems. To clarify the properties of spatial gain distribution, three-dimensional (3-D) computational fluid dynamics (CFD) technology was used to study the mixing and reactive flow in a COIL nozzle with an interleaving jet configuration in the supersonic section. The results show that the molecular iodine fraction in the secondary flow has a notable effect on the spatial distribution of the small signal gain. The rich iodine condition produces some negative gain regions along the jet trajectory, while the lean iodine condition slows down the development of the gain in the streamwise direction. It is also found that the new configuration of an interleaving jet helps form a reasonable gain field under appropriate operation conditions. (c) 2007 Elsevier Ltd. All rights reserved.

In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics (LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.

Detonation initiation resulting from the Richtmyer–Meshkov instability is investigated numerically in the configuration of the shock/spark-induced-deflagration interaction in a combustive gas mixture. Two-dimensional multi-species Navier–Stokes equations implemented with the detailed chemical reaction model are solved with the dispersion-controlled dissipative scheme. Numerical results show that the spark can create a blast wave and ignite deflagrations. Then, the deflagration waves are enhanced due to the Richtmyer–Meshkov instability, which provides detonation initiations with local environment conditions. By examining the deflagration fronts, two kinds of the initiation mechanisms are identified. One is referred to as the deflagration front acceleration with the help of the weak shock wave, occurring on the convex surfaces, and the other is the hot spot explosion deriving from the deflagration front focusing, occurring on the concave surfaces.

The spherically converging detonation wave was numerically investigated by solving the one-dimensional multi-component Euler equations in spherical coordinates with a dispersion-controlled dissipative scheme. Finite rate and detailed chemical reaction models were used and numerical solutions were obtained for both a spherical by converging detonation in a stoichiometric hydrogen-oxygen mixture and a spherically focusing shock in air. The results showed that the post-shock pressure approximately arises to the same amplitude in vicinity of the focal point for the two cases, but the post-shock temperature level mainly depends on chemical reactions and molecular dissociations of a gas mixture. While the chemical reaction heat plays an important role in the early stage of detonation wave propagation, gas dissociations dramatically affect the post-shock flow states near the focal point. The maximum pressure and temperature, non-dimensionalized by their initial value, are approximately scaled to the propagation radius over the initial detonation diameter. The post-shock pressure is proportional to the initial pressure of the detonable mixture, and the post-shock temperature is also increased with the initial pressure, but in a much lower rate than that of the post-shock pressure.

Hypersonics for the foreseeable future is the domain of space access and hypersonic flight. A hypersonic vehicle encounters an aero-thermodynamic environment characterized by strong shocks and high temperatures, and the flow in the hypersonic regime behaves quite differently from that at supersonic Mach numbers (Bertin in Hypersonic Aerothermodynamics. Washington DC, 1994; Park in Nonequilibrium Hypersonic Aerothermodynamics, Wiley, New York, 1989; Anderson in Hypersonic and High Temperature Gas Dynamics. McGraw-Hill Book Company, New York, 1989).

Pressure wave refrigerators (PWR) refrigerate the gas through periodical expansion waves. Due to its simple structure and robustness, PWR may have many potential applications if the efficiency becomes competitive with existing alternative devices. In order to improve the efficiency, the characteristics of wave propagation in a PWR are studied by experiment, numerical simulation and theoretical analysis. Based on the experimental results and numerical simulation, a simplified model is suggested, which includes the assumptions of flux-equilibrium and conservation of the free energy. This allows the independent analysis of the operation parameters and design specifics. Furthermore, the optimum operation condition can be deduced. Some considerations to improve the PWR efficiency are also given.

A detonation driven shock tunnel is useful as a ground test facility for hypersonic flow research. By attaching a convergent section ahead of the primary diaphragm in the driver section, the downstream operation mode became available to generate a high-enthalpy test flow. A 100 mm diameter shock tunnel was for the first time installed in the Laboratory of High-Temperature-Gas Dynamics (LHD), Institute of Mechanics, Chinese Academy of Sciences, and after its continuous refitments, a high performance detonation driven shock tunnel was achieved to generate high-enthalpy and high-Reynolds number test flows. A new method to burst a metal diaphragm with the downstream operation mode is discussed.

Finite-fringe interferograms produced for axisymmetric shock wave flows are analyzed by Fourier transform fringe analysis and an Abel inversion method to produce density field data for the validation of numerical models. For the Abel inversion process, we use basis functions to model phase data from axially-symmetric shock wave structure. Steady and unsteady flow problems are studied, and compared with numerical simulations. Good agreement between theoretical and experimental results is obtained when one set of basis functions is used during the inversion process, but the shock front is smeared when another is used. This is because each function in the second set of basis functions is infinitely differentiable, making them poorly-suited to the modelling of a step function as is required in the representation of a shock wave.

This paper reports on two-dimensional numerical simulation of cellular detonation wave in a \(\rm {H_2}\)/\(\rm {O_2}\)/\(\rm {Ar}\) mixture with low initial pressure using a detailed chemical reaction model and high order WENO scheme. Before the final equilibrium structure is produced, a fairly regular but still non-equilibrium mode is observed during the early stage of structure formation process. The numerically tracked detonation cells show that the cell size always adapts to the channel height such that the cell ratio is fairly independent of the grid sizes and initial and boundary conditions. During the structural evolution in a detonation cell, even as the simulated detonation wave characteristics suggest the presence of an ordinary detonation, the evolving instantaneous detonation state indicates a mainly underdriven state. As a considerable region of the gas mixture in a cell is observed to be ignited by the incident wave and transverse wave, it is further suggested that these two said waves play an essential role in the detonation propagation.

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.

An investigation into the three-dimensional propagation of the transmitted shock wave in a square cross-section chamber was described in this paper, and the work was carried out numerically by solving the Euler equations with a dispersion-controlled scheme. Computational images were constructed from the density distribution of the transmitted shock wave discharging from the open end of the square shock tube and compared directly with holographic interferograms available for CFD validation. Two cases of the transmitted shock wave propagating at different Mach numbers in the same geometry were simulated. A special shock reflection system near the corner of the square cross-section chamber was observed, consisting of four shock waves: the transmitted shock wave, two reflection shock waves and a Mach stem. A contact surface may appear in the four-shock system when the transmitted shock wave becomes stronger. Both the secondary shock wave and the primary vortex loop are three-dimensional in the present case due to the non-uniform flow expansion behind the transmitted shock.

A hypervelocity test flow is referred to a high-enthalpy flow with speeds above 5 kmps. It is necessary to generate such extreme flows on the ground to simulate the environment of atmosphere reentry. Reflected shock tunnels (RST) and shockexpansion tubes/tunnels (SET) are the major test facilities in gasdynamic laboratories that may satisfy the above request.

Hypersonic air-breathing propulsion has been a focus technology in hypersonic aviation in the past decades [1]. Three-dimensional cavity may act as the flame holder of a Scramjet engine in air-breathing hypersonic propulsion. An interesting three-dimensional cavity is “swallowtail” cavity which has a special inner shape like a swallowtail. With three-dimensional cavity in supersonic chamber, threedimensional vortexes may be organized optimally, and the exchange of mass, momentum and energy between cavity flow and supersonic flow may be enhanced to provide better performance of mixing and combustion[2]. Also, three-dimensional cavity may avoid the sharp heat release in local region of chamber and suppress the subsonic combustion oscillation induced by the cavity in a supersonic combustor. It is necessary to study the heat release distribution of a supersonic combustor with three-dimensional cavity.

A new flux splitting method named K-CUSP scheme is proposed in the paper. The major difference between K-CUSP and two traditional CUSP schemes (H-CUSP and E-CUSP) is that all kinematic quantities and all thermodynamic quantities in total enthalpy will be separately split into convective term and pressure term. The present scheme adopts the cell-face Mach number splitting method of AUSM+ scheme and the interface flux of pressure term is given a new way in the subsonic regime. Numerical solutions demonstrate that the new scheme inherits the simplicity and robustness of FVS schemes, which overcomes the shortcomings of pressure overshoot of shock wave in H-CUSP and E-CUSP schemes, but also retains the high-resolution of FDS schemes, which achieves the high accuracy of contact discontinuity and shock discontinuity.

In this study, the idealized two-dimensional detonation cells were decomposed into the primary units referred to as sub-cells. Based on the theory of oblique shock waves, an analytical formula was derived to describe the relation between the Mach number ratio through triple-shock collision and the geometric properties of the cell. By applying a modified blast wave theory, an analytical model was developed to predict the propagation of detonation waves along the cell. The calculated results show that detonation wave is, first, strengthened at the beginning of the cell after triple-shock collision, and then decays till reaching the cell end. The analytical results were compared with experimental data and previous numerical results; the agreement between them appears to be good, in general.

To improve the quality of driving flows generated with detonation-driven shock tunnels operated in the forward-running mode, various detonation drivers with specially designed sections were examined. Four configurations of the specially designed section, three with different converging angles and one with a cavity ring, were simulated by solving the Euler equations implemented with a pseudo kinetic reaction model. From the first three cases, it is observed that the reflection of detonation fronts at the converging wall results in an upstream-traveling shock wave that can increase the flow pressure that has decreased due to expansion waves, which leads to improvement of the driving flow. The configuration with a cavity ring is found to be more promising because the upstream-traveling shock wave appears stronger and the detonation front is less overdriven. Although pressure fluctuations due to shock wave focusing and shock wave reflection are observable in these detonation-drivers, they attenuate very rapidly to an acceptable level as the detonation wave propagates downstream. Based on the numerical observations, a new detonation-driven shock tunnel with a cavity ring is designed and installed for experimental investigation. Experimental results confirm the conclusion drawn from numerical simulations. The generated driving flow in this shock tunnel could maintain uniformity for as long as 4 ms. Feasibility of the proposed detonation driver for high-enthalpy shock tunnels is well demonstrated.

Accurate aerodynamic measurements in the hypersonic flow of large aircraft models in tunnels have practical significance, but pose a significant challenge. Novel aerodynamic force measurement methods have been proposed, but lack theoretical support. The forms of the force signals techniques for signal processing and calculation of aerodynamics are especially problematic. A theoretical study is conducted to investigate the dynamic properties based on models of the draw-rod system and slender rods. The results indicate that the inertia item can be neglected in the rod governing equation; further, the solutions show that the signals of each rod are a combination of aerodynamic signals (with a constant value) and sine signals, which can be verified by experimental shock tunnel results. Signal processing and aerodynamics calculation techniques are also found to be achievable via the flat part of the signals.

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...

An Nd:glass laser pulse (18 ns, 1.38 J) is focused in a tiny area of about 100-mum diam under ambient conditions to produce micro-shock waves. The laser is focused above a planar surface with a typical standoff distance of about 4 mm, The laser energy is focused inside a supersonic circular jet of carbon dioxide gas produced by a nozzle with internal diameter of 2.9 mm and external diameter of 8 mm, Nominal value of the Mach number of the jet is around 2 with the corresponding pressure ratio of 7.5 (stagnation pressure/static pressure at the exit of the nozzle), The interaction process of the micro-shock wave generated inside the supersonic jet with the plane wall is investigated using double-pulse holographic interferometry. A strong surface vortex field with subsequent generation of a side jet propagating outward along the plane wail is observed. The interaction of the micro-shock wave with the cellular structure of the supersonic jet does not seem to influence the near surface features of the flowfield. The development of the coherent structures near the nozzle exit due to the upstream propagation of pressure waves seems to be affected by the outward propagating micro-shock wave. Mach reflection is observed when the micro-shock wave interacts with the plane wall at a standoff distance of 4 mm, The Mach stem is slightly deflected, indicating strong boundary-layer and viscous effects near the wall. The interaction process is also simulated numerically using an axisymmetric transient laminar Navier-Stokes solver. Qualitative agreement between experimental and numerical results is good.

Three cases, including a two-dimensional, an axisymmetric, and a three-dimensional flowfield, were studied to demonstrate the effectiveness and reliability of a method proposed for validation of numerical solutions of complex flowfields. Images of these flowfields were first constructed from numerical solutions based on the principle of experimental flow visualization, and then compared directly with experimental interferograms. Because both experimental and numerical results are of identical physical representation, agreement between them can be evaluated effectively by examining characteristic flow structures of the flowfields as well as comparing differences in density. An efficient algorithm for three-dimensional density integration was also proposed to replace the conventional one that is computationally expensive. The study shows that reliable validation can be achieved in this way because it allows a direct comparison between numerical and experiment results without any loss of accuracy in either of them. The validation method is highly recommended for three-dimensional flowfields where quantification of images from experimental flow visualization is very difficult or impossible.

In this paper, a numerical and experimental investigation of the evolution of a transmitting shock wave and its associated primary vortex loop, which are discharged from the open end of a square cross-sectional tube, is described. The experiments were conducted in the square tube connected to a diaphragmless shock tube and the flowfield was visualized from the axial direction with diffusive holographic interferometry. The numerical simulations were carried out by solving the three-dimensional Euler equations with a dispersion-controlled scheme. The numerical results were displayed in the form of interferograms to compare them with experimental interferograms. Good agreement between the numerical and experimental results was obtained. More detailed numerical calculations were carried out, from which the three-dimensional transition of the shock wave configuration from an initial planar to a spherical shape and the development of the primary vortex loop from a square shaped to a three-dimensional structure were clearly observed and interpreted.

This paper describes a numerical and experimental study of a micro-blast wave which is produced from the source of several tens microns in dia. and propagates in the length scale of a few centimeter in diameter. The micro-blast wave was generated by focusing a Nd:Glass pulsed-laser beam in ambient air. Its propagation and reflection were visualized by using double exposure holographic interferometry and simulated numerically using the dispersion-controlled scheme to solve the Euler and Navier-Stokes equations with initial conditions of a point-source explosion specified with the Taylor similarity law. Good agreement was obtained between numerical solutions and experimental results, and this spherical micro-blast wave was shown to be a handy model of blast waves created in large scale explosions.

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.

This paper describes results of holographic interferometric observation of the evolution of shock waves and the primary vortex loop discharged from the open-end of a 40 mm × 40 mm square tube. Experiments were conducted by using the square tube connected to a 60 mm × 1500 mm diaphragmless shock tube. Holographic interferometric flow visualization viewed from the axial direction was carried out using a diffusively-reflected beam as the object beam. In order to interpret the observed three-dimensional shock-wave motion, numerical simulations were also carried out by solving the Euler equations with the dispersion-controlled scheme. The experimental interferogram was compared with numerical visualization results. The three-dimensional transition of the shock wave configuration from a planar to a spherical shape and the development of the primary vortex loop from a square shaped to the three-dimensional structure were clearly observed.

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.

Development of a large detonation-driven shock tunnel for exploring hypersonic physics is reported in this paper and its calibration results are also presented. In order to produce hypervelocity test flows with long test-duration for supersonic combustion and aerodynamic force measurement, several new techniques were proposed and investigated to improve shock tunnel performance and extend its test time. These techniques include the backwardrunning detonation driver for strong incident shock generation, the tailored interface condition for the detonation driver and the E-shaped configuration of the vacuum tank for damping wave reflections. The long-test-duration hypervelocity detonation-driven shock tunnel was developed successfully with the techniques. This shock tunnel is about 265 m in total length with a 2.5m diameter nozzle. Its performance and calibration tests were carried out and some results are presented in this paper to demonstrate its capability for duplicating hypersonic flight conditions and its reliability for heat transfer and aerodynamic force measurement study.

In the Shock Wave Journal Vol. 2, No. 4 a benchmark test for shock wave reflection over wedges was announced. International scientists who are interested in shock wave research were invited to participate. The benchmark test aimed at comparison of various advanced numerical schemes as well as experimental results. During the last three years more than twenty results, including both CFD and experiments, were collected from all over the world. Efforts contributed by these scientists made the present benchmark test reach to a standard of the state of the art of the computational fluid dynamics applied to the shock wave research. However, it was regrettable not to publish all the results collected due to limitation on the available page number.

This paper describes propagation of shock waves within circular cross-section shock tubes with a sudden area change in cross section. A dispersion-controlled scheme was used to solve the Euler equations assuming axisymmetric flows. For experimental visualizations an aspheric cylindrical test section was designed to keep collimated incident light rays parallel once they were reflected or refracted on the inner and outer surfaces of the test section. For effective comparisons with experimental results, equivalent numerical interferograms were constructed to demonstrate effectiveness of the numerical method and verify the observed shock-wave phenomena. The numerical method was used to calculate three further cases with variations of the initial shock-wave Mach number and the flow geometry to clarify the role of these parameters. Complex transient shock-wave phenomena, such as shock-wave reflection, shock/vortex interaction and shock-wave focusing were observed in these cases, and interpreted with shock wave theory. In addition, the research clearly shows that combination of CFD with experiments is effective to highlight physical phenomena in axisymmetric flows.

A multi-dimensional numerical algorithm for detonation gas dynamics is described. The algorithm consists of a dispersion-controlled shock-capturing scheme and a pseudo-kinetic chemical reaction model. One-dimensional results obtained with this algorithm appear to be in good agreement with both the experimental data and self-similar solutions of gaseous detonation. This implies that coefficients of the pseudo-kinetic reaction rate are well tuned. Results of two-dimensional detonation computations in converging chambers reveal some global features which agree with the experimental findings, and can be explained using shock wave dynamic theory. It is shown that the numerical algorithm proposed is capable of predicting the pressure, temperature, and density ratio of detonations in a way suitable for engineering applications. The algorithm can be extended to three-dimensional problems.

Force tests were conducted at the long-duration-test shock tunnel JF12, which has been designed and built in the Institute of Mechanics, Chinese Academy of Sciences. The performance tests demonstrated that this facility is capable of reproducing a flow of dry air at Mach numbers from 5 to 9 at more than 100 ms test duration. Therefore, the traditional internal strain-gauge balance was considered for the force tests use in this large impulse facility. However, when the force tests are conducted in a shock tunnel, the inertial forces lead to low-frequency vibrations of the test model and its motion cannot be addressed through digital filtering because a sufficient number of cycles cannot be found during a shock tunnel run. The post-processing of the balance signal thus becomes extremely difficult when an averaging method is employed. Therefore, the force measurement encounters many problems in an impulse facility, particularly for large and heavy models. The objective of the present study is to develop pulse-type sting balance by using a strain-gauge sensor that can be applied in the force measurement of 100 ms test time, especially for the force test of the large-scale model. Different structures of the S-series (i.e., sting shaped balances) strain-gauge balance are proposed and designed, and the measuring elements are further optimized to overcome the difficulties encountered during the measurement of aerodynamic force in a shock tunnel. In addition, the force tests were conducted using two large-scale test models in JF12 and the S-series strain-gauge balances show good performance in the force measurements during the 100 ms test time.

In order to meet the requirement for developing hypersonic vehicles, advanced hypersonic test facilities have been developed over the world for decades. Several types of facilities were developed to produce hypersonic flows, including the combustion-heated wind tunnels, the arc-heated hypersonic wind tunnels, conventional air-heated wind tunnels, heated-light-gas driven shock tunnels, free-piston driven high-enthalpy shock tunnels, and detonation-driven shock tunnels[1]. To clarify the real gas effect of hypersonic flows and the effect of test-gas contamination on supersonic combustion, the shock tunnel appears to be promising test facilities to provide hypersonic tests with pure air flows of hyper-velocity and high total temperature. However, the test-duration produced by shock tunnels is usually quite short for supersonic combustion and the large scale models of hypersonic vehicles, therefore, it becomes very difficult for hypersonic propulsion tests with hydro-carbon fuels. A research project to investigate some techniques for developing long-test duration and hype-velocity shock tunnels has been launched since 2002 in the State Key Laboratory of High-temperature Gas Dynamics, Institute of Mechanics, Chinese Academy of Sciences[2]. Research progresses has been achieved recently with numerical simulations and experiments in several aspects, and some results are summarized and reported in the paper.

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.

We propose an integrated algorithm named low dimensional simplex evolution extension (LDSEE) for expensive global optimization in which only a very limited number of function evaluations is allowed. The new algorithm accelerates an existing global optimization, low dimensional simplex evolution (LDSE), by using radial basis function (RBF) interpolation and tabu search. Different from other expensive global optimization methods, LDSEE integrates the RBF interpolation and tabu search with the LDSE algorithm rather than just calling existing global optimization algorithms as subroutines. As a result, it can keep a good balance between the model approximation and the global search. Meanwhile it is self contained. It does not rely on other GO algorithms and is very easy to use. Numerical results show that it is a competitive alternative for expensive global optimization.

Numerical simulations of the multi‐shock interactions observable around hypersonic vehicles were carried out by solving Navier‐Stokes equations with the AUSMPW scheme and the new type of the IV interaction created by two incident shock waves was investigated in detail. Numerical results show that the intersection point of the second incident shock with the bow shock plays important role on the flow pattern, peak pressures and heat fluxes. In the case of two incident shocks interacting with the bow shock at the same position, the much higher peak pressure and more severe heat transfer rate are induced than the classical IV interaction. The phenomenon is referred to as the multi‐shock interaction and higher requirements will be imposed on thermal protection systems.

In this paper, the development of a detonation-driven high enthalpy expansion tube is introduced and its performance study is reported. The facility consists of a forward detonation cavity driver, a shock tube and an expansion section. The detonation driver was specially designed to provide the facility with uniform driving flows. In performance tests, the incident shock speeds and the static wall pressures were measured. Based on the measured shock speeds, the test flow velocities was calculated by using H. Mirels’ theory, and the thermodynamic properties predicted with the Gaseq software. The results show that the velocity of the test gas flow reached to 8300m/s, the test duration is above 50Ps and the total flow enthalpy is about 40MJ/kg. The detonation-driven enthalpy expansion was demonstrated to be a very promising facility to generate high-enthalpy flows of orbital speeds for earth-reentry study. Nomenclature us = shock speed (m/s) uc = flow velocity (m/s) lm = maximum distance between shock and interface Cx = real distance between shock and interface D1 = length of the FDC driver D2 = length of the shock tube D3 = length of the expansion section d1 = diameter of the right end of the FDC driver d2 = diameter of the shock tube

The model of self-excited oscillation of chemical reaction induced by shock wave was proposed to interpret the basic mechanism of combustion oscillation in supersonic combustor. Shock dynamics method in the reactive flow was successfully applied to describe the inherent oscillation mechanism which may take important role in the supersonic combustor. The possible effect of combustion oscillation induced by the interaction of shock wave and chemical reaction on the operation of a Scramjet engine was discussed based on the combustion oscillation mechanism mentioned above.

Cylindrical detonation propagation was numerically investigated by solving the two-dimensional multi-component Euler equations implemented with a one-step chemical reaction model. The numerical results demonstrate the evolution of cellular cell bifurcation of cylindrical detonation, and indicate that new cellular cells are generated from the self-organized transverse waves. The local curvature of the cylindrical cellular detonation is found to be a critical issue in the propagation. Originating from curvature variations, the concave front on the Mach stem between two triple points is developed from the flow expansion induced by both transverse wave motion and detonation front diverging. The concave front will focus later and result in the self-organization of transverse waves from which the cellular cell bifurcation takes place. The self-organization of transverse waves is dominated by shock diverging, flow expansion and chemical reactions.

Two essential issues in detonation initiations were discussed in this paper, that is, hotspots and reaction zone acceleration. By defining the reaction zone acceleration, the hotspot and the reaction zone acceleration are identified as the primary mechanisms underlying the deflagration to detonation transition. The dominant physical process for two mechanisms is the interaction between gasdynamic non-linearity and chemical reactions that are very sensitive to temperature gradient. In the process, spontaneous waves are generated in the reaction zone, propagate with the local sound speed, decelerate suddenly in the front of the reaction zone because of the sharp temperature gradient, and develop into a pressure pulse acting to elevate the gas temperature that will further induce more intensive chemical reactions. Such a positive feedback loop supports detonation initiation and propagation.

This paper describes a numerical study on wave interactions following the emergence of 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. The numerical results show that not only does the leading shock due to the second blast overtake the projectile but also the gas behind the projectile does so when the initial pressure ratio behind and ahead of the projectile is high. Subsequently, the projectile will overtake them again. The second blast becomes tightly coupled with the first.

本文从连续介质假设的角度出发, 推导出了不同于分子运动论的体积黏性系数公式. 新理论首次从宏观上揭示了可压缩流体体积黏性的具体物理涵义, 即体积黏性系数是体积模量与弛豫时间的乘积. 以氮气为例, 分别对转动模态和振动模态下的体积黏性进行了计算和分析, 结果表明: 连续介质理论的结果略高于分子运动论的结果, 但二者的预测趋势相同; 在振动激发态下, 弛豫时间、分子碰撞数和体积黏性要比转动激发态下的高出几个数量级.

The research progress on high-enthalpy and hypersonic flows having been achieved in the Institute of Mechanics, Chinese Academy of Sciences, is reported in this paper. The paper consists of three main parts: The first part is on the techniques to develop advanced hypersonic test facilities, in which the detonation-driven shock-reflected tunnel and the detonation-driven shock-expanded tube are introduced. The shock tunnel can be used for generating hypersonic flows of a Mach number ranging from 10 to 20, and the expansion tube is applicable to simulate the flows with a speed of 7~10km/s. The second part is dedicated to the shock tunnel nozzle flow diagnosis to examine properties of the hypersonic flows thus created. The third part is on experiments and numerical simulations. The experiments include measuring the aerodynamic pitching moment and heat transfer in hypersonic flows, and the numerical work reports nozzle flow simulations and flow non-equilibrium effects on the possible experiments that may be carried out on the above-mentioned hypersonic test facilities.