1，特劳哈尔数是在流体力学中讨论物理相似与模化时引入的相似准则。常用的相似准则还有雷诺数、马赫数、弗劳德数、普朗特数、埃克特数及奴塞尔数等。在考虑具有特征频率的圆周运动时使用斯特劳哈尔数。如在模型喷注噪声频谱的实验中，我们求得频谱中频谱峰的频率fp的斯特莱哈尔数为St= =0.2式中：D为模型喷口的直径；US为喷注的速度。根据相似与模化，骶特劳哈尔数为一常数，则对实际的喷注来说，喷注噪声的峰频为fp=0.2 式中：UJ和D分别为实际喷注的速度和直径。
2，斯特劳哈尔数
斯特劳哈尔数（Strouhal number）是在流体力学中讨论物理相似与模化时引入的相似准则。常用的相似准则还有雷诺数、马赫数、弗劳德数、普朗特数、埃克特数及奴塞尔数等。在考虑具有特征频率的圆周运动时使用斯特劳哈尔数。如在模型喷注噪声频谱的实验中，我们求得频谱中频谱峰的频率fp的斯特莱哈尔数为St= =0.2式中：D为模型喷口的直径；US为喷注的速度。根据相似与模化，骶特劳哈尔数为一常数，则对实际的喷注来说，喷注噪声的峰频为fp=0.2 式中：UJ和D分别为实际喷注的速度和直径。
St=fL/V
f是漩涡分离频率，L是特征长度（如水力直径），V是流体速度。
数对于大St（数量级为1），粘度主宰流体，对于小St（数量级为10^-4
或以下），高速主宰震荡。
3，Strouhal number
In dimensional analysis, the Strouhal number is a dimensionless number describing oscillating flow mechanisms. The parameter is named after Vincenc Strouhal, a Czech physicist who experimented in 1878 with wires experiencing vortex shedding and singing in the wind.[1]The Strouhal number is an integral part of the fundamentals of fluid mechanics.
The Strouhal number is often given as
where St is the dimensionless Strouhal number, f is the frequency of vortex shedding, L is the characteristic length (for example hydraulic diameter) and V is the velocity of the fluid.
For large Strouhal numbers (order of 1), viscosity dominates fluid flow, resulting in a collective oscillating movement of the fluid "plug". For low Strouhal numbers (order of 10−4and below), the high-speed, quasi steady state portion of the movement dominates the oscillation. Oscillation at
intermediate Strouhal numbers is characterized by the buildup and rapidly subsequent shedding of vortices.[2]
For spheres in uniform flow in the Reynolds number range of 800 < Re < 200,000 there co-exist two values of the Strouhal number. The lower frequency is attributed to the large-scale instability of the wake and is independent of the Reynolds number Re and is approximately equal to 0.2. The higher frequency Strouhal number is caused by small-scale instabilities from the separation of the shear layer.[3][4]
In metrology, specifically axial-flow turbine meters, the Strouhal number is used in combination with the Roshko number to give a correlation between flow rate and frequency. The advantage of this method over the freq/viscosity versus K-factor method is that it takes into account temperature effects on the meter.
f = meter frequency, U = flow rate, C = linear coefficient of expansion for the meter housin
g material
This relationship leaves Strouhal dimensionless, although a dimensionless approximation is often used for C3, resulting in units of pulses/volume (same as K-factor).
版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。
发表评论