Surface-layer similarity in turbulent circular Couette flow

1984 ◽  
Vol 144 ◽  
pp. 123-131 ◽  
Author(s):  
Martin Claussen
Keyword(s):  
Surface Layer ◽  
Angular Momentum ◽  
Free Convection ◽  
Couette Flow ◽  
Similarity Theory ◽  
Outer Region ◽  
Cylinder Wall ◽  
Curvature Effects ◽  
Circular Couette Flow ◽  
Very High

Smith & Townsend's (1982) experimental data on circular Couette flow are re-examined in the framework of surface-layer similarity theory. Surface-layer similarity of horizontally stratified shear flow is shown to have its counterpart in a narrow-gap Couette flow between concentric cylinders. Smith & Townsend's data of mean angular momentum and mean-velocity profiles in a region near a cylinder lend support to the applicability of Monin–Obukhov similarity to circular Couette flow. Only for flows of very high Reynolds numbers is a region of logarithmic variation of mean profiles found close to the cylinder wall. Because of curvature effects on the flow, the mean profiles deviate from the logarithmic profile as distance from the cylinder wall increases. For flows of sufficiently low Reynolds number, but still very high Taylor number, no logarithmic profile seems to exist; instead, profiles in the viscous region and in the outer region are connected to each other by a ‘free-convection (rotation)’ profile. From Smith & Townsend's data the velocity field is not observed to follow the prediction of ‘free-convection’ similarity; however, the ‘free-convection’ profile is found in the distribution of mean angular momentum.

scholarly journals Monin–Obukhov Similarity and Local-Free-Convection Scaling in the Atmospheric Boundary Layer Using Matched Asymptotic Expansions

2018 ◽  
Vol 75 (10) ◽  
pp. 3691-3701 ◽  
Author(s):  
Chenning Tong ◽  
Mengjie Ding
Keyword(s):  
Surface Layer ◽  
Free Convection ◽  
Asymptotic Expansions ◽  
Atmospheric Surface Layer ◽  
Similarity Theory ◽  
Potential Temperature ◽  
Matched Asymptotic Expansions ◽  
Obukhov Length ◽  
Local Free Convection ◽  
Valid Solution

The Monin–Obukhov similarity theory (MOST) is the foundation for understanding the atmospheric surface layer. It hypothesizes that nondimensional surface-layer statistics are functions of [Formula: see text] only, where z and L are the distance from the ground and the Obukhov length, respectively. In particular, it predicts that in the convective surface layer, local free convection (LFC) occurs at heights [Formula: see text] and [Formula: see text], where [Formula: see text] is the inversion height. However, as a hypothesis, MOST is based on phenomenology. In this work we derive MOST and the LFC scaling from the equations for the velocity and potential temperature variances using the method of matched asymptotic expansions. Our analysis shows that the dominance of the buoyancy and shear production in the outer ([Formula: see text]) and inner ([Formula: see text]) layers, respectively, results in a nonuniformly valid solution and a singular perturbation problem and that [Formula: see text] is the thickness of the inner layer. The inner solutions are found to be functions of [Formula: see text] only, providing a proof of MOST for the vertical velocity and potential temperature variances. Matching between the inner and outer solutions results in the LFC scaling. We then obtain the corrections to the LFC scaling near the edges of the LFC region ([Formula: see text] and [Formula: see text]). The nondimensional coefficients in the expansions are determined using measurements. The resulting composite expansions provide unified expressions for the variance profiles in the convective atmospheric surface layer and show very good agreement with the data. This work provides strong analytical support for MOST.

The Research on Computation of Researchers Certainty Factor of Bridge's Durability Evaluation Based on the Indeterminate AHP

2014 ◽  
Vol 578-579 ◽  
pp. 1469-1472
Author(s):  
Xiao Zhen Chen ◽  
Xue Jun Zhang
Keyword(s):  
Lower Bound ◽  
Similarity Theory ◽  
Research Result ◽  
Weight Coefficient ◽  
Practical Experience ◽  
Relative Importance ◽  
Certainty Factor ◽  
Average Value ◽  
Judgment Matrix ◽  
Very High

Because of fuzziness, uncertainty of structure and researchers practical experience, it is more practical to express the relative importance of indexes with interval number. Firstly, according to researchers indeterminate judgment matrix, the upper and lower bound matrixes are formed; secondly, the similarity and the differences of the upper and lower bound matrixes of the relative importance matrix from different experts is studied by using the similarity theory of vector; lastly, certainty factor of researchers according to the upper and lower bound matrixes can be calculated, and the average value is regarded as the researchers certainty factor. The certainty factors of researchers upper and lower bound matrixes are consider together, the researchers experience is fully considered and the error from indeterminate judgment matrix to indeterminate judgment matrix is avoided. The result affords basis to calculate the weight coefficient, the research result comparing with the other method showed that the computation accuracy in this paper was very high.

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

2018 ◽  
Vol 24 (5) ◽  
pp. 478-487 ◽  
Author(s):  
Jingfeng Guo ◽  
Tieshan Cao ◽  
Congqian Cheng ◽  
Xianming Meng ◽  
Jie Zhao
Keyword(s):  
Saturation Magnetization ◽  
Outer Region ◽  
Cr Content ◽  
Pyrolysis Furnace ◽  
The Matrix ◽  
Furnace Tube ◽  
Primary Carbides ◽  
The Relationship ◽  
Very High

AbstractThe magnetism and microstructure of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes after 5 years of service were investigated in this paper. The saturation magnetization of the Cr25Ni35Nb alloy tube in the thickness direction is more than 20 emu/g, and the tube becomes ferromagnetic. The inner and outer walls of Cr35Ni45Nb alloy tubes also become ferromagnetic. But the saturation magnetization of the Cr35Ni45Nb alloy tubes approaches to zero in the center zone. The primary carbides M7C3 and NbC are changed into M23C6 and G phase at the outer region of the furnace tube. However, the M23C6-type carbides were replaced by carbon-rich carbides M7C3 at the carburization zone. Cr-depleted zones are formed at the inner and outer walls of the furnace tubes owing to oxidation. Carburization and oxidation reduce the Cr content of the matrix. Accordingly, the saturation magnetization is very high at the carburization zone and Cr-depleted zone. The magnetism of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes has a high correlation with the Cr content of the matrix. Carburization and oxidation are the main reasons that make the paramagnetic ethylene pyrolysis furnace tube change to ferromagnetic.

Sign in / Sign up

Export Citation Format

Share Document