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91.
92.
沟槽面与光滑面湍流边界层特性比较 总被引:3,自引:0,他引:3
应用LDV技术对沟槽面及光滑面湍流边界层流速和湍流度分布进行了精细的测量,实验结果表明:与光滑面相比,沟槽面湍流边界层时均流速分布对数公式中具有较大的积分常数C值,且沟槽面湍流度最大值较小,但其出现的位置距壁面较远。另外,偏斜因子及平坦因子的分布特性区别不大,但是在近壁区内沟槽面结果波动较大。 相似文献
93.
In this paper, dimensional scaling is used to describe the turbulence structure of the velocity and temperature fields in
the inertial range and the far dissipation range as well as the intermediate transition range under locally isotropic conditions
at sufficiently large Reynolds numbers. This kind of scaling is expressed in a strictly mathematical manner employing dimensional
π -invariants analysis. It is shown that in the case of the asymptotic solutions for either the inertial range or the far
dissipation range only one π number occurs that has to be considered as a non-dimensional universal constant. This π number
may be determined theoretically or/and empirically. In the case of the transition range two π numbers occur. Consequently,
a universal function is established that has to be derived theoretically or/and empirically, too. Here, Batchelor's [7] classical
interpolation formula for the turbulence structure of the velocity field and the empirical one of Stolovitzky et al. [59],
both may serve as universal functions, are compared with the results provided by numerical solutions of Kolmogorov′s [32]
structure equation for the velocity field. It is shown that these interpolation formulae match not only the asymptotic solutions
of the inertial range and the far dissipation range, respectively, but also these numerical results in an excellent manner.
The former may be considered as necessary condition and the latter as sufficient condition. In the case of the temperature
field results of the corresponding universal function are predicted using Yaglom's [63] structure equation. These results
also match the corresponding asymptotic solutions of both the inertial range and the far dissipation range. However, in contrast
to the case of the velocity field, the predicted universal function for the temperature field may notably overshoot its asymptotic
solution for the inertial range. This overshooting occurs in the transition range and may be considered as an analogue to
the so-called Hill ‘bump’ that usually occurs in the high-wave number portion of the temperature spectrum. 相似文献
94.
The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry (2D-PIV) and three-dimensional particle image velocimetry (3D-PIV) experiments in this study. Due to the limitation of 2D-PIV configuration, the contamination generated by the strong tangential velocity in the cyclone can be registered in the axial velocity detected by 2D-PIV. Efficient methods are proposed in this work to remove this contamination. The contamination-removed 2D-PIV data agree well with 3D-PIV results. The distributions of the axial velocity are also computed by the Reynolds stress model (RSM) and verified using the PIV experimental results. Reasonable agreements are obtained. 相似文献
95.
the measurements of flow over non-uniform gravel open channel have been conducted with Laser Doppler Velocimetry (LDV). The experimental results indicate that the distribution of mean velocity agrees well with the Nikuradse's law. From the distributions of resistance coefficient, reference level and turbulence intensity, the classification of small scale roughness case is obtained.Project supported by the National Science Foundation of China 相似文献
96.
本文研究了一端弹性支撑的并列双柱和串列双圆柱在气流中自由端的振幅响应,与单圆柱相比,在小间距时,串列双圆柱中前柱的横向振幅受到较强的激励。而在大间距时,振幅受到抑制,特别当L/D=3.5和4.0时,其振幅响应仅为单柱的1/3左右,而对于后柱,则在大间距时,纵向振幅响应有所增大,而且后柱的振幅响应要比前柱的大得多,而并列双圆柱的自由端振幅基本上受到抑制,在T/D>3.0之后,干扰很快减小到接近单个圆 相似文献
97.
98.
冲击伤复合高速破片致伤的损伤特点和冲击伤防护研究 总被引:17,自引:0,他引:17
探讨了冲击伤复合高速破片致伤的损伤特点及复合材料对冲击伤的防护效果。结果表明,肢体高速破片致伤对肺冲击伤具有加重作用,加重效应主要发生在原发冲击伤部位,加重效应的机理可能与压力波引起的血流扰动有关。利用复合材料防护可减轻肺冲击伤程度,降低动物的死亡率。 相似文献
99.
Summary We study the two-dimensional instantaneous Stokes flow driven by gravity in a viscous triangular prism supported by a horizontal
rigid substrate and a vertical wall. The oblique side of the prism, inclined at an angle α with respect to the substrate,
is a fluid-air interface, where the stresses are zero and surface tension is neglected. We develop the stream function ψ in
polar coordinates (r,θ) centered at the vertex of α and split it into an inhomogeneous part, which accounts for gravity effects, and a homogeneous
part, which is expressed as a series expansion. The inhomogeneous part and the first term of the expansion may be envisioned,
respectively, as self-similar solutions of the first kind and of the second kind for r→0, each one holding in complementary α domains with a crossover at α
c
=21.47∘, which we study in some detail. The coefficients of the series are calculated by truncating the expansion and using the method
of direct collocation with a suitable set of points at the wall. The solution strictly holds for t=0, because later the free surface ceases to be a plane; nevertheless, it provides a good approximation for the early time
evolution of the fluid profile, as shown by the comparison with numerical simulations. For 0<α<45∘, the vertex angle remains constant and the edge remains strictly at rest; the transition at α
c
manifests itself through a change in the rate of growth of the curvature. The time at which the edge starts to move (waiting
time) cannot be calculated since the instantaneous solution ceases to be valid. For α>45∘, the instantaneous local solution indicates that the surface near the vertex is launched against the substrate so that the
edge starts to move immediately with a power law dependence on time t. However, due to the high value of the exponent, the vertex may seem to be at rest for some finite time even in this case.
Received 29 August 1997; accepted for publication 21 January 1998 相似文献
100.
超音速混合层的流动不稳定性较之亚音速或不可压的混合层大大减弱,为了提高混合效率,
通过数值模拟的方法分别研究了展向曲率、展向速度、来流马赫数等因素对混合效率所
起的作用. 计算结果表明:在给定展向速度的情况下,带有展向曲率的三维混合层,曲率越
大三维扰动增长率越大,而且法向的卷起范围也越大. 当展向曲率不为零时,展向速度的增
大也能有效地增强混合能力. 由流场中的高频扰动波产生的涡,在向下游发展过程中会有破
碎、拉伸,低频扰动波没有发现这一现象. 对于有展向曲率和展向速度的混合层,提高来流
马赫数时,流场中最不稳定扰动的增长率仍很大. 因此,这是一种提高混合层混合效率的新
途径. 相似文献