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2009, 39(4): 385-386. doi: 10.6052/1000-0992-2009-4-J2009-083

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STUDIES ON AERODYNAMIC CHARACTERISTICS OF HIGH VELOCITY VEHICLE FLYING AT HIGH ALTITUDE

2009, 39(4): 387-397. doi: 10.6052/1000-0992-2009-4-J2009-040

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The effects ofviscous interference, real gas and rare gas at high altitude areof fundamental significance in the design of tomorrow high speedvehicles, such as safe flying, precision control and guidance ofvehicles. The present paper summarizes several research works ofthe author's group in the fields of computational method, flowtopology analysis, investigation from continuum flows to rarefiedgas and their applications to the studies on aerodynamiccharacteristics of typical high speed vehicles.

REASONING ON DEVELOPMENT OF AIR-BREATHING HYPERSONIC PROPULSION TECHNOLOGY

2009, 39(4): 398-405. doi: 10.6052/1000-0992-2009-4-J2009-049

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In this paper, recentprogress in the research of air-breathing hypersonic propulsiontechnology is briefly reviewed, key problems arising from Scramjetresearch are discussed, and possible methods are presented forenhancing scramjet performances, including hypersonic flowcompression with a low total pressure loss, three-dimensionalvortex generation for supersonic mixing, preheated carbon-fuelinjection, combustor optimization for combustion control,reduction of engine wet-area for lowering friction drag, andcatalyzation of dissociated high temperature gases for moreheat-release. In consideration of the thermo-efficiency of theconstant pressure cycle, the detonation process with higherthermo-efficiency is suggested to apply to the hypersonicpropulsion, relevant methods on the detonation propulsion areintroduced and related problems are discussed. It is necessary tocarry out careful reasoning on the development of hypersonicpropulsion, and to explore new concepts and technologies to drivefurther hypersonic vehicle researches.

RECENT PROGRESS ON COMPUTATIONAL AEROELASTICITY

2009, 39(4): 406-420. doi: 10.6052/1000-0992-2009-4-J2009-046

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Corresponding to thelower critical Mach number, Kuo and Tsien proposed in 1946 theconcept of upper critical Mach number. For two-dimensionalirrotational flow on a body, before the maximum of local Machnumber reaches a threshold, namely the upper critical Mach number,the irrotational supersonic flow still prevails, and only when thelocal Mach number exceeds the critical Mach number, theirrotational flow is eventually destroyed. Afterward, differentdesign techniques of supercritical airfoils were developed toaugment the drag-divergence Mach number, and the swept wings andarea rule were introduced to overcome `sonic barrier' and toreduce the peak drag near Mach 1. These achievements brought aboutthe tremendous development of aircraft industry in the lastcentury. As the advancement of computer technique andcomputational method, the solution algorithms for differentsimplified governing equations of fluiddynamics were constructed.At present, computational fluid dynamics based the Reynoldsaveraged Navier-Stokes equation have been widely applied to theevaluation of aerodynamic performances and the understanding ofcomplex flow mechanism. Aerodynamic optimization, fluid/structureinteraction and aeroacoustics et al have now become main researchdirections. To memorialize the 100 anniversary of Professor GuoYung-Huai, recent studies on computational aeroelasticity by ourresearch group were reviewed in the present paper.

KINETIC ANALYSIS OF THE FLOW PAST A FLAT PLATE AT MODERATE REYNOLDS NUMBERS

2009, 39(4): 421-425. doi: 10.6052/1000-0992-2009-4-J2009-051

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An analytical solutiongiven by Y.H. Kuo in 1953 for the incompressible flow past a flatplate at moderate Reynolds numbers was a classical work ofboundary layer theory. Many researchers, based on experimentaldata given respectively by Janour and Schaaf and Sherman, made anassessment of Kuo's formula and carried out follow-up studies fordetermining the drag coefficient around a flat plate. Kineticanalyses in the present paper show that the experimental data ofSchaaf {\&} Sherman in low subsonic situations ($0.16 < M < 0.21)$is not suitable to serve as a standard to assess an incompressibletheory when the Reynolds number ($Re$) ranges from 1 to 10,because the corresponding Knudsen numbers under the experimentalconditions are about between 0.03 and 0.3, indicating significantrarefied gas effects, while other experimental data satisfying theincompressible assumption support Kuo's formula. When rarefied gaseffects are taken into account, the drag coefficient around a flatplate in low-speed or subsonic situations may be expressed as $C_D= C_{D,c} \times C_{D,FM} /(C_{D,c} + C_{D,FM} )$, where $C_{D,c}$and $C_{D,FM} $ are the theoretical solutions at continuum andfree molecular limits, respectively. Kuo's solution for thevelocity distribution past a flat plate is in qualitativeagreement with the numerical results given by the informationpreservation (IP) method based on kinetic theory, with somedifference occurring at the leading edge where rarefied gaseffects become significant. Compared with Blasius solution to thevelocity distribution, Kuo's correction becomes important when$Re< 100$.

SCALING FOR TURBULENT BOUNDARY LAYER IN HIGH REYNOLDS NUMBER

2009, 39(4): 426-439. doi: 10.6052/1000-0992-2009-4-J2009-045

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Over the past decadethere are debates on the scaling law of the mean velocity and onwhether the flow close to a wall can be regarded as universal forzero-pressure-gradient turbulent boundary layers at high Reynoldsnumbers. The current statuses in these issues are reviewed in thepresent paper, and these arguments seem still far from conclusion.

Mhd flow in a homopolar device with annular wire electrodes

2009, 39(4): 440-449. doi: 10.6052/1000-0992-2009-4-J2009-092

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Themagnetohydrodynamic flow in a homopolar device with annular linearelectrodes is studied analytically．As the problem is linear, thesolution may be reduced to the summation of elementary solutionsobtained by matching the local solutions in two regions or thehomopolar device. The flow features of the elementary solutionsare discussed. The structure of incomplete electrodes can improvethe Hartmann boundary layer and increase the mass flux of thehomopolar. The elementary solutions are also applied to thediscussion of a homopolar device with continuous electrodes．

THE POSSIBILITY OF USING FUSION ENERGY EARLY

2009, 39(4): 450-459. doi: 10.6052/1000-0992-2009-4-J2009-048

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First, the energyproblem faced by human is briefly presented. Then some topics arediscussed, such as the approaches in applying the nuclear energy,the possibility of getting clean nuclear energy system, thefeasibility of early utilization of fusion energy and so on.Finally, the development strategy of Chinese energy industry ispresented.

DEVELOPMENT OF EXPLOSION MECHANICS IN THE INSTRUMENT MANUFACTURE

2009, 39(4): 460-466. doi: 10.6052/1000-0992-2009-4-J2009-082

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It is described inthis article how to combine explosion mechanics with other subjectknowledge for successful engineering applications, such asatomistic investigation of microcrack for dynamic macrodamage,theoretical and experimental investigation frommicro-to-macroscopic.

THEORETICAL MODELING AND TRANS-SCALE SIMULATION OF COUPLING FIELDS GENERATED BY THE EXPLOSION OF A FOCUSED HIGH POWER LASER BEAM

2009, 39(4): 467-479. doi: 10.6052/1000-0992-2009-4-J2009-052

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The study of coupledelectromagnetic and thermo-mechanical processes concerning with afocused high power laser explosion in gas medium is now becomingan important research forefront. The subject includes a series ofenergy absorption and transfer processes, such as ionization andoptical breakdown in mixture gases, the evolution and propagationof the laser supported combustion wave (LSC) and laser supporteddetonation wave (LSD) in gas-plasma.In fact, these very complex processes can be macroscopicallyconsidered as interactions between three distinct phenomena, thatis, laser scattering, high temperature as well as high speed flowin gas plasma. In the present paper, we are mainly concerned withthe coupling effects between the electromagnetic wave propagationand the thermo-mechanical flow field, that is, the couplingbetween Maxwell equations which describe the electromagnetic waveinduced by laser, Navier-Stokes or Euler equations of gasdynamics, thermodynamic Equation of State, the Saha equation ofionization balance (Saha Eq.), the evolution and propagation ofLSC/LSD waves and the recoil pressure and impulse.This research works cover three stages. In the first one, thelaser scattering in inhomogeneous mixture and laser wavepropagation is modeled based on the Maxwell-Euler equations.In the second, a numerical model for ignition and/or opticalbreakdown of combustible mixture gases under the radiation of highpower laser is presented. The electromagnetic fields of laser beampropagating through mixtures are simulated by directly solvingMaxwell equations with FDTD scheme and free-reflection boundaryconditions. The fine structures of the power density distributionnear the focus center are revealed by means of coupling numericalanalysis of Euler equation and EOS for heat diffusion andconvection, Saha equations of ionized gas in equilibrium state anddetailed chemistry mechanism. Because the dielectric propertiesare changed with thermal state of the gas mixtures during theradiation, therefore, a unified scheme are developed by combiningCIP scheme for LSC/LSD propagation with FDTD solver for Maxwellequations over the uniform grid cells. The finer structures ofpower flux near the focus have been revealed and visualized fromnumerical results, depending on the power level and incidentangles of the laser beam.In the third stage which is now underway, models and simulationtechnique will be developed and extended to more complicated flowprocesses.

TRANSITION IN WALL-BOUNDED FLOWS

2009, 39(4): 480-507. doi: 10.6052/1000-0992-2009-4-J2009-008

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In this paper, wepresent direct comparisons of experimental results on transitionin wall-bounded flows obtained by flow visualizations, hot-filmmeasurement, and particle image velocimetry, along with a briefmention of relevant theoretical progresses, based on a criticalreview of about 120 selected publications. Despite somewhatdifferent initial disturbance conditions used in experiments, theflow structures were found to be practi- cally the same. Thefollowing observed flow structures are considered to be offundamental importance in understanding transitional wall-boundedflows: the three-dimensional nonlinear wave packets calledsolitonlike coherent structures (SCSs) in boundary layer and pipeflows, the - vortex, the secondary vortex loops, and the chain ofring vortices. The dynamic processes of the formation of thesestructures and transition as newly discovered by recentexperiments include the following: (1) The sequential interactionprocesses between the-vortex and the secondary vortex loops, whichcontrol the manner by which the chain of ring vortices isperiodically introduced from the wall region into the outer regionof the boundary layer. (2) The generation of high-frequencyvortices, which is one of the key issues for understanding bothtransitional and developed turbulent boundary layers (as well asother flows), of which several explanations have been proposed buta particularly clear interpretation can be provided by theexperimental discovery of secondary vortex loops. The ignorance ofsecondary vortex loops would make the dynamic processes and flowstructures in a transitional boundary layer inconsistent withprevious discoveries. (3) The dominant role of SCSs in allturbulent bursting, which is considered as the key mechanism ofturbulent production in a low Reynoldsnumber turbulent boundarylayer. Of direct relevance to bursting is the low-speed streaks,whose formation mechanism and link to the flow structures inwall-bounded flows can be answered more clearly than before interms of the SCS dynamics. The observed SCSs and secondary vortexloops not only enable revisiting the classic story of wall-boundedflow transition, but also open a new avenue to reconstruct thepossible universal scenario for wall-bounded flow transition.

2009, 39(4): 508-510. doi: 10.6052/1000-0992-2009-4-J2009-097

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2009, 39(4): 511-512. doi: 10.6052/1000-0992-2009-4-J2009-096

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