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Chien-Cheng Chang Jeng-Yu Su Sheng-Yuan Lei 《Theoretical and Computational Fluid Dynamics》1998,10(1-4):71-90
The paper is aimed at reviewing and adding some new results to our recent work on a force theory for viscous compressible
flows around a finite body. It has been proposed to analyze aerodynamic forces directly in terms of fluid elements of nonzero
vorticity and density gradient. Let ρ denote the density, u the velocity, and ω the vorticity. It is demonstrated that for largely separated flows about bluff bodies, there are two
major source elements:
R
e(x) =−?u
2∇ρ·∇ϕ and V
e(x) =−u×ω·∇ϕ,
where ϕ is an acyclic potential, generated by the solid body moving with unit velocity in the negative direction of the force
considered. In particular, under mild conditions, the (unique) choice of ϕ enforces that the elements R
e(x) and V
e(x) decay rapidly away from the body. Four kinds of finite body are considered: a circular cylinder, a sphere, a hemi sphere-cylinder,
and a delta wing of elliptic section—all in transonic-to-supersonic regimes. From an extensive numerical study carried out
for these bodies, it is found that these two elements contribute to 95% or more of the total drag or lift for all the cases
under consideration. Moreover, R
e(x) due to density gradient becomes progressively important relative to V
e(x) due to vorticity as the Mach number increases. The present method of force analysis enables effective analysis and assessment
of relative importance of aerodynamics forces, contributed from individual flow structures. The analysis could therefore be
very much useful in view of the rapid growth in numerical fluid dynamics; detailed (either local or global) flow information
is often available. The paper is dedicated to Sir James Lighthill in honor of his great contributions to aeronautics on the
occasion of the publication of his collected works.
Received 3 January 1997 and accepted 11 April 1997 相似文献
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介绍了利用辉光放电光谱法分析掺杂纳米硅薄膜,通过优化辉光光源激发参数、计算标准样品的溅射率,建立了掺杂纳米硅薄膜的定量表面分析方法。方法应用于实际掺杂纳米硅薄膜样品的分析,并将分析深度、剖析结果与表面形貌仪的结果进行了对照。试验结果表明,分析方法快速、准确,具有实际应用价值。 相似文献
4.
Kuang-Yao Lo Shih-Chieh Lo Sheng-Yuan Chu Ren-Chuan Chang Chang-Feng Yu 《Journal of Crystal Growth》2006,290(2):532-538
Reflective second harmonic generation (RSHG) is used to analyze the growth condition of poly crystal zinc oxide (ZnO) film with a c-axis orientation, grown on the Si substrate by RF magnetron sputtering technique. It elucidates physical phenomena exhibited by growing ZnO thin films. Connecting with analytical results of the characteristic parameters derived from the X-ray patterns and SEM images, the relationship between the RSHG intensity and the substrate temperature reveals that the effect of the grain boundaries is the domination of the RSHG mechanism. The inclined structures of ZnO films on the Si substrate are explained with reference to these RSHG patterns. 相似文献
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The enzymatic nitration of phenol and m-cresol catalyzed by horseradish peroxidase was studied in the presence of H2O2 and NaNO2. The results showed that the nitration products of phenol were 2-nitro and 4-nitrophenols. There was also a small amount of by-products of hydroquinone and catechol. The influences of various reaction parameters, including pH, organic solvent type, and concentrations of NaNO2 and H2O2, on the nitration products were investigated. The yields of 4-nitrophenol and 2-nitrophenol were 14% and 12%, respectively. The nitration products of m-cresol were 4-nitro-m-cresol and 6-nitro-m-cresol, and the yields of 4-nitro-m-cresol and 6-nitro-m-cresol were 19% and 30%, respectively. 相似文献
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研制了一种基于液晶取向改变的非标记液晶型免疫传感器,并用于检测赭曲霉素A(0TA).采用戊二醛交联法将OTA同定在由自组装膜修饰的玻璃肇底表面.自组装膜能诱导液晶分子垂直排列,而连接OTA抗体后则扰乱了液晶分子取向的有序排列,导致液晶分子在化学敏感膜表面的取向发生变化,使光学信号的亮度及色彩发生变化,以此实现对OTA的... 相似文献
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利用脉冲分子束技术, 在305-322 nm范围内研究了1-萘酚(1NP)的共振双光子电离(R2PI)光谱. 1NP分子存在cis和trans两种旋转异构体, 但实验中仅观测到trans异构体的电子振动跃迁光谱, 其S1←S0跃迁的(0-0)带头出现在317.90 nm(即31456 cm-1)位置. 利用光谱选律及ab initio和密度泛函(DFT)计算, 对trans异构体在S1态的振动模进行标识, 得出主要对应于对称性为a'的平面内振动模. 计算显示, cis异构体在电子基态S0的能量较trans异构体高出439 cm-1, 而第一激发能却比trans异构体的低1216 cm-1, 与之相应的实验值分别是220和274 cm-1. 计算数值与实验结果在能量变化趋势上完全一致. 共振双光子电离谱中没有观测到cis异构体的光谱信号, 其原因可归结为分子束的有效冷却效应使得处于基态的cis异构体的布居数密度相对trans异构体极低, 导致cis光谱信号太小而未能被探测到. 相似文献
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硫化银体系共振散射光谱研究及分析应用 总被引:3,自引:0,他引:3
Triton X- 1 0 0存在下 ,在碱性介质中 ,Ag 与 S2 -形成 Ag2 S微粒 ,Ag 与 S2 -反应体系的共振光散射(RLS)明显增强 ,建立了水中痕量银的测定方法。Ag 浓度在 0 .0 1 1— 6 .0 0 μg/ m L范围内具有良好的线性关系 (r=0 .9992 )。方法检出限 3.5 6 ng/ m L;相对标准偏差 0 .5 3%— 1 .97%;样品加标回收率 92 .82 %—1 0 6 .0 0 %。方法简便 ,测定体系抗干扰的效果好 ,灵敏度高。 相似文献