压缩折角激波-湍流边界层干扰直接数值模拟

进行了来流Mach数2.9,24°压缩折角激波-湍流边界层干扰的直接数值模拟,在上游的平板添加扰动以激发边界层转捩到湍流.计算得到的统计结果与实验吻合,验证了结果的可靠性.分析了角部分离区附近湍能的生成,耗散及分配机制.结果显示角部区域激波与湍流边界层相互作用造成大量湍动能产生,而湍动能的主要耗散区仍在近壁.湍流输运项起到了主要的平衡机制,把湍动能由外层输运到近壁区.通过对激波后及壁面瞬时压力的分析,认为激波低频振荡并非上游扰动引起,而是由于分离泡本身不稳定振荡产生的

Direct Numerical Simulation of Shock/Turbulent Boundary Layer Interaction in a Supersonic Compression Ramp

A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9. The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition. Both the mean wall pressure and the velocity profiles agree with those of the experimental data, which validates the simulation. The turbulent kinetic energy budget in the separation region is analyzed. Results show that the turbulent production term increases fast in the separation region, while the turbulent dissipation term reaches its peak in the near-wall region. The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation. Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble, the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance, but rather the instability of separation bubble.

Performance of supersonic model combustors with staged injections of supercritical aviation kerosene

Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Supercritical kerosene of approximately 760 K was prepared and injected in the overall equivalence ratio range of 0.5-1.46. Two pairs of integrated injector/flameholder cavity modules in tandem were used to facilitate fuel-air mixing and stable combustion. For single-stage fuel injection at an upstream location, it was found that the boundary layer separation could propagate into the isolator with increasing fuel equivalence ratio due to excessive local heat release, which in turns changed the entry airflow conditions. Moving the fuel injection to a further downstream location could alleviate the problem, while it would result in a decrease in combustion efficiency due to shorter fuel residence time. With two-stage fuel injections the overall combustor performance was shown to be improved and kerosene injections at fuel rich conditions could be reached without the upstream propagation of the boundary layer separation into the isolator. Furthermore, effects of the entry Mach number and pilot hydrogen on combustion performance were also studied.

乘波飞行器低马赫数飞行状态下的气动性能研究

乘波飞行器在低马赫数飞行状态下的气动性能是近空间飞行器设计和研究人员关心的问题之一. 本文以M=3,设计飞行高度H=15 km为设计点,最大升阻比为优化目标,并通过满足一定的有效载荷容积,气动热防护和气动操纵的要求进行了工程化设计后得到的锥导乘波体为研究对象,借助数值模拟和风洞实验技术相结合的研究手段对乘波飞行器在跨声速和超声速飞行阶段的气动性能进行了探讨. 研究结果表明,乘波飞行器在该飞行阶段的气动性能与前缘所处的气动状态密切相关

基于直接数值模拟的超/高超声速湍流模型评估与改进

对来流Mach数2.25及6的平板边界层湍流进行了直接数值模拟，并通过与理论、实验及他人计算结果的对比对数值结果进行了验证。基于直接数值模拟得到的湍流数据库，对常用的湍流模型进行了先验评估。评估的湍流模型有k-e模型（包括标准k-e模型、可实现的k-e模型及低Reynolds数k-模型）、SA模型及BL模型。结果显示，可实现的k-e模型的具有较好的预测能力，而标准k-e模型预测的湍流粘性系数偏高。SA模型在边界层内层预测准确度较高，而在外层预测值偏高。对于高Mach数情况，原始的BL模型严重低估了内-外层交界位置，造成湍流粘性系数预测值偏低。作者通过修改模型系数及内-外层交界位置对BL模型进行了修改，修改后模型预测的湍流粘性系数与DNS给出的值吻合较好

Modeling study to compare the flow and heat transfer characteristics of low-power hydrogen, nitrogen and argon arc-heated thrusters

A modelling study is performed to compare the plasma °ow and heat transfer char- acteristics of low-power arc-heated thrusters (arcjets) for three di®erent propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equa- tions, which take into account the e®ects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, veloc- ity and Mach number distributions calculated within the thruster nozzle obtained with di®erent propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the °ow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appear- ing near the cathode tip; the °ow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant °ows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, speci¯c enthalpies and thermal conductivities, are di®erent, there are appreciable di®er- ences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest speci¯c impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

Numerical modeling of heat transfer and plasma flow in a low power arcjet thruster

Modeling studies are preformed to investigate the plasma and heat transfer characteristics of a low power argon arcjet thruster. Computed temperature, velocity, static pressure, and Mach number distribution in arcjet thruster under typical operating condition are presented in this paper. It shows that the performance data from numerical modeling results are basically consistent with the experimental measured values.

高超声速风洞用蓄热式加热器

本文介绍了纯净空气高超声速风洞用蓄热式加热器的结构形式、蓄热材料选择、蓄热体结构设计方案。回顾了现有文献报道的国内外蓄热式加热器的性能和特点。对多孔砖型蓄热式加热器的蓄热能力以及结构特性进行了估算，结果表明采用多孔砖型蓄热体可有效降低相同流量下蓄热体浮起危险；选用合适的蓄热材料以及蓄热体尺寸可以获得Mach 6巡航飞行的来流条件。材料和结构等工程问题是蓄热式加热器研制的主要难点。

Numerical Simulation of a Low-power Hydrazine Arcjet Thruster

A modeling study is conducted to investigate the plasma flow and heat transfer characteristics of low-power (kW class) arc-heated thrusters (arcjets) with 2:1 hydrogen/nitrogen to simulate decomposed hydrazine as the propellant. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, the Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. Typical computed results about the temperature, velocity and Mach number distributions within arcjet thruster are presented for the case with arc current of 9 A and inlet stagnant pressure of 3.3×105 Pa to show the flow and heat transfer characteristics. It is found that the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip, and the flow transition from the subsonic to supersonic regime occurs within the constrictor region. The effect of gas viscosity on the plasma flow within arcjet thruster is examined by an additional numerical test using artificially reduced values of gas viscosity. The test results show that the gas viscosity appreciably affects the plasma flow and the performance of the arcjet thruster for the cases with the hydrazine or hydrogen as the propellant. The integrated axial Lorentz force in the thruster nozzle is also calculated and compared with the thrust force of the arcjet thruster. It is found that the integrated axial Lorentz force is much smaller than the thrust force for the low-power arcjet thruster. Modeling results for the NASA 1-kW class arcjet thruster with simulated hydrazine as the propellant are found to be reasonably consistent with available experimental data.

A 2-kW COIL with a square pipe-array JSOG and nitrogen buffer gas

A 2-kW-class chemical oxygen-iodine laser (COIL) using nitrogen buffer gas has been developed and tested since industrial applications of COIL devices will require the use of nitrogen as the buffer gas. The laser, with a gain length of 11.7 cm, is energized by a square pipe-array jet-type singlet oxygen generator (SPJSOG) and employs a nozzle bank with a designed Mach number of 2.5. The SPJSOG has advantages over the traditional plate-type JSOG in that it has less requirements on basic hydrogen peroxide (BHP) pump, and more important, it has much better operational stability. The SPJSOG without a cold trap and a gas-liquid separator could provide reliable operations for a total gas flow rate up to 450 mmol/s and with a low liquid driving pressure of around 0.7 atm or even lower. The nozzle bank was specially designed for a COIL using nitrogen as the buffer gas. The cavity was designed for a Mach number of 2.5, in order to provide a gas speed and static temperature in the cavity similar to that for a traditional COIL with helium buffer gas and a Mach 2 nozzle. An output power of 2.6 kW was obtained for a chlorine flow rate of 140 mmol/s, corresponding to a chemical efficiency of 20.4%. When the chlorine flow rate was reduced to 115 mmol/s, a higher chemical efficiency of 22.7% was attained. Measurements showed that the SPJSOG during normal operation could provide a singlet oxygen yield Y greater than or equal to 55%, a chlorine utilization U greater than or equal to 85%, and a relative water vapor concentration w = [H2O]/([O-2] + [Cl-2]) less than or equal to 0.1.

Millstone Hill电离层F层等效风场的气候学研究

Neutral winds and electric fields in the ionospheric F layer play important roles in the variations of the ionosphere, and also affect the thermospheric circulation via the close coupling between the ionosphere and the thermosphere. By now, the neutral winds and electric drifts are generally observed with ground-based Fabry-Perot interferometers (FPI) and incoherent scatter radars (ISR), rockets, and satellite-borne instrument. Based on the servo theory, the ionospheric equivalent winds, which include the information of both the neutral winds and electric fields, can be derived from these characteristic parameters observed by ionosondes. This indirect derivation has potential values in climatological researches and space weather forecast. With the data set of the incoherent scatter radar observations at Millstone Hill, USA, from 1976 to 2006, we statistically analyzed the climatological variations of the vertical component of the equivalent winds (VEWs) over Millstone Hill, which are derived from the ionospheric key parameters (the peak electron number density and peak height of the F2 layer, NmF2 and hmF2) on the basis of the servo theory, Liu's method, and measurements from the ion line-of-sight velocity as well. The main results of this analysis are summarized as follows: (1) The values of VEWs over Millstone Hill during nighttime are stronger than in the daytime, and the upward drift dominates most of the day. In 1993, Hagan found that the component of the neutral winds in the magnetic meridion in daytime is weaker than during nighttime under both solar maximum and minimum conditions; he also found that the equatorward winds dominate most of the day. Both results suggest that the thermosphere in Millstone Hill is modulated by the aurorally driven high-latitude circulation cell; that is, during geomagnetic quiet periods, the average auroral activity is strong enough to drive thermospheric circulation equatorward for most of the day at Millstone Hill. Moreover, since ion drag is the strongest during daytime when F region densities are enhanced by photoionization, the wind speeds are smaller during the daytime than in the nighttime. (2) There is equinoctial symmetry in VEWs at Millstone Hill. The amplitudes and phases of VEWs in spring are quite similar to those in autumn. In contrast, the nighttime upward drift in winter is weaker than in summer and the difference becomes more significant with increasing solar activity. This solstice asymmetry indicates that, the aurorally driven circulation in the northern hemisphere at Millstone Hill latitude is weaker in winter due to arctic darkness, because the subsolar point is in the southern hemisphere. (3) The comparison of the VEWs derived from three methods, i.e., the servo theory, Liu's method, and the ISR ion line-of-sight velocity measurements, indicates that the amplitudes and main phase tendencies of these VEWs accord well with each other during nighttime hours. However, the case in the daytime is relatively worse. This daytime discrepancy can be explained in terms of the effects of photochemical processes and the choices of the servo constants. A larger servo constant gives a stronger plasma drift in daytime. Therefore, this study tells how important to choose a suitable constant for deriving VEWs at Millstone Hill.

Krytyka dziewiętnastowiecznego rozumu. Źródła i konteksty Pałuby Karola Irzykowskiego

Wydział Filologii Polskiej i Klasycznej: Instytut Filologii Polskiej

Teaching Competences and their Development Via Video-Recording

The article deals with use of case studies for professional preparation of teachers to be. One of the suitable ways to develop professional teaching competences is to apply the method of a case study. A case study means a complex and creative solution for a given teaching situation in simulated teaching conditions. It is based on interactive and situational education and decision taking. A case study improves not only professional and teaching competences for becoming teachers – it also fulfi ls the task to develop at students their auto-evaluating and auto-refl exing skills. To increase professional competences it is mandatory to do a complex analysis of the video-record for the implemented study. A complex analysis is a subject of the research project of a student grant agency at the University of West Bohemia in Pilsen.

Evolução da estrutura urbana de Viana do Castelo

Dissertação de Mestrado apresentada à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Arquitectura e Urbanismo.

Desarrollo de líneas de productos a partir del rediseño o diversificación del producto actual.

[79] hojas : ilustraciones, fotografías.