Re-Circulating Flows Associated with Two-Dimensional Steps

1980 ◽  
Vol 31 (3) ◽  
pp. 151-172 ◽  
Author(s):  
W.D. Moss ◽  
S. Baker
Keyword(s):  
Bluff Body ◽  
Accurate Determination ◽  
Mixing Layer ◽  
Separated Flow ◽  
Shear Layers ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Mean Velocity ◽  
High Turbulence

SummaryThis paper describes measurements made in the regions of separated flow associated with three simple sharpedged two-dimensional geometries, a rear-facing step, a front-facing step and a rectangular block. The use of the pulsed-wire anemometer made possible the measurement of the three components of mean velocity and turbulence; earlier techniques, such as the hot-wire anemometer, were not well suited to the accurate determination of these quantities either in regions of continually reversing flows such as the re-circulatory zone or in regions of very high turbulence such as the shear layers bounding these zones. Supplementary measurements of surface pressure and shear stresses are also presented and comparison is made between these shear layers and the plane mixing layer. The work forms the first part of an extended programme for the investigation of bluff body flows but its principal immediate value will probably help in providing data with which to test the validity of mathematical models of turbulence as applied to re-circulating flows.

scholarly journals New Equation for Predicting Pipe Friction Coefficients Using the Statistical Based Entropy Concepts

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 611
Author(s):  
Yeon-Woong Choe ◽  
Sang-Bo Sim ◽  
Yeon-Moon Choo
Keyword(s):  
Friction Coefficient ◽  
Accurate Determination ◽  
Mean Velocity ◽  
Friction Coefficients ◽  
Flow Discharge ◽  
Comparison Results ◽  
Flow Loss ◽  
Key Variables ◽  
New Equation

In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse’s experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates.

scholarly journals Two-dimensional flow nanometry of biological nanoparticles for accurate determination of their size and emission intensity

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Stephan Block ◽  
Björn Johansson Fast ◽  
Anders Lundgren ◽  
Vladimir P. Zhdanov ◽  
Fredrik Höök
Keyword(s):  
Emission Intensity ◽  
Accurate Determination ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Two Dimensional Flow

The effect of base bleed on the steady separated flow past bluff objects

1969 ◽  
Vol 39 (4) ◽  
pp. 735-752 ◽  
Author(s):  
L. G. Leal ◽  
A. Acrivos
Keyword(s):  
Bluff Body ◽  
Separated Flow ◽  
Pressure Profile ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Wake Region ◽  
Near Wake ◽  
Flow Past ◽  
Modifying Effect ◽  
Base Bleed

The modifying effect of base bleed on the steady separated flow past a two-dimensional bluff body is considered. Detailed experimental results are presented for Reynolds numbers R between 50 and 250 and for bleed coefficients b in the range 0 to 0·15. The streamline pattern near the object is found to be strongly affected by small changes in the rate of bleed, with the recirculating closed wake disappearing altogether for b > 0·15. Nevertheless, the qualitative dependence on R of the physical dimensions of the near-wake region and the associated streamwise pressure profile appear to be unaffected by base bleed.

scholarly journals Fluorescence Assay for the Determination of d-Panthenol Based on Novel Ring-Fused 2-Pyridone Derivative

2020 ◽  
Vol 21 (21) ◽  
pp. 8386
Author(s):  
Wiktor Kasprzyk ◽  
Tomasz Świergosz ◽  
Filip Koper
Keyword(s):  
Citric Acid ◽  
Nmr Spectra ◽  
Chemical Structure ◽  
Accurate Determination ◽  
Pharmaceutical Formulations ◽  
Two Dimensional ◽  
One Dimensional ◽  
Fluorescent Method ◽  
Derivatizing Agent

Herein, a novel fluorescent method for the determination of d-panthenol (DP) level in solutions with no separate hydrolysis step has been revealed based on the utilization of citric acid (CA) as a derivatizing agent. Consequently, the essential parameters of the derivatization process were established, resulting in the development of sensitive, repeatable, and accurate determination of panthenol. The method was approved, and its usefulness in characterizing the concentration of DP in pharmaceutical formulations and selectivity in the determination of DP were validated. The chemical structure of the new fluorophore formulating in the reaction in DP with CA, i.e., 6-oxo-3,4-dihydro-2H,6H-pyrido[2,1-b][1,3]oxazine-8-carboxylic acid (ODPC), was elucidated using detailed NMR experiments: one-dimensional (1H, 13C) as well as two-dimensional NMR spectra (1H-1H COSY, 1H-13C HSQC, 1H-13C HMBC, 1H-15N HSQC, 1H-15N HMBC).

Two-dimensional turbulent wakes

1967 ◽  
Vol 30 (3) ◽  
pp. 547-560 ◽  
Author(s):  
Ian S. Gartshore
Keyword(s):  
Shear Stress ◽  
Stress Reduction ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Two Dimensional ◽  
Stress Distributions ◽  
Mean Velocity ◽  
Lower Shear ◽  
Turbulent Wakes ◽  
Velocity Scale

The equations of mean motion indicate that two-dimensional turbulent wakes, when subjected to appropriately tailored adverse pressure gradients, can be self-preserving. An experimental examination of two nearly self-preserving wakes is reported here. Mean velocity, longitudinal and lateral turbulence intensity, inter-mittency and shear stress distributions have been measured and are compared with Townsend's data from the small-deficit undistorted wake. In comparison with the undistorted case, the present wakes have slightly lower turbulent intensities and significantly lower shear stresses, all quantities being non-dimensionalized by a local velocity scale taken as the maximum mean velocity deficit. A consideration of the reasons for the shear stress reduction leads to an expression from which the shear stresses in any symmetrical free equilibrium shear flow can be found. This relationship is used to calculate the rate of growth in the measured wakes, with reasonable success.

The two-dimensional mixing region

1970 ◽  
Vol 41 (2) ◽  
pp. 327-361 ◽  
Author(s):  
I. Wygnanski ◽  
H. E. Fiedler
Keyword(s):  
Velocity Profile ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Outer Part ◽  
Eddy Diffusivity ◽  
Turbulent Energy ◽  
Two Dimensional ◽  
Low Velocity ◽  
Mean Velocity ◽  
Axial Velocity Profile

The two-dimensional incompressible mixing layer was investigated by using constant-temperature, linearized hot wire anemometers. The measurements were divided into three categories: (1) the conventional average measurements; (2) time-average measurements in the turbulent and the non-turbulent zones; (3) ensemble average measurements conditioned to a specific location of the interface. The turbulent energy balance was constructed twice, once using the conventional results and again using the turbulent zone results. Some differences emerged between the two sets of results. It appears that the mixing region can be divided into two regions, one on the high velocity side which resembles the outer part of a wake and the other on the low velocity side which resembles a jet. The binding turbulent–non-turbulent interfaces seem to move independently of each other. There is a strong connexion between the instantaneous location of the interface and the axial velocity profile. Indeed the well known exponential mean velocity profile never actually exists at any given instant. In spite of the complexity of the flow the simple concepts of eddy viscosity and eddy diffusivity appear to be valid within the turbulent zone.

Measurements of Mean Velocity and Mass Exchange in a Separated Recirculating Flow

1975 ◽  
Vol 97 (3) ◽  
pp. 334-341 ◽  
Author(s):  
W. H. Schofield ◽  
T. S. Keeble
Keyword(s):  
Mass Exchange ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Separated Flow ◽  
Momentum Exchange ◽  
Mean Velocity ◽  
Mass Rate ◽  
Recirculating Flow ◽  
Exchange Processes ◽  
Exchange Data

Experimental measurements were taken in a closed, recirculating, turbulent separated flow. The experiments were made to elucidate the mass and momentum exchange mechanisms between the throughflow and the recirculating flow in a combustor that had previously been developed for burning heavy fuels without a flame tube. Mean velocity measurements are presented for the cold flow field and these are used to derive a detailed streamline pattern. The three-dimensional shear layer surface that divides the recirculating flow from the throughflow is analyzed in detail and the variation of momentum exchange coefficient along its development length is derived. Mass exchange data show that the variation of mass transport along the mixing layer is similar to the variation of momentum transport. Overall features of the exchange processes are shown to be similar to those in simple two-dimensional, nonducted mixing flows if allowance is made for the three dimensionality of the present layers. However, it is also shown that there are significant quantitative differences between the two types of flow. The overall mass exchange rate between the two flow regions was found to be one-third of the mass rate supplied to the combustor and this is a typical figure for conventional designs.

Effective Convergence Checks for Verifying Finite Element Stresses at Two-Dimensional Stress Concentrations

2016 ◽  
Vol 1 (4) ◽  
Author(s):  
G. B. Sinclair ◽  
J. R. Beisheim ◽  
P. J. Roache
Keyword(s):  
Finite Element ◽  
Error Estimation ◽  
Accurate Determination ◽  
Benchmark Problems ◽  
Two Dimensional ◽  
Stress Concentrations ◽  
Element Analysis ◽  
Stress Risers ◽  
Stress Concentration Factors

The accurate determination of stresses at two-dimensional (2D) stress risers is both an important and a challenging problem in engineering. Finite element analysis (FEA) has become the method of choice in making such determinations when new configurations with unknown stress concentrations are encountered in practice. For such FEA to be useful, discretization errors in peak stresses have to be sufficiently controlled. Convergence checks and companion error estimates offer a means of exerting such control. Here, we report some new convergence checks to this end. These checks are designed to promote conservative error estimation. They are applied to seven benchmark problems that have exact solutions for their peak stresses. Associated stress concentration factors span a range that is larger than that normally experienced in engineering. Error levels in the FEA of these peak stresses are classified in accordance with: 1–5%, satisfactory; 1/5–1%, good; and <1/5%, excellent. The present convergence checks result in 91 error assessments for the benchmark problems. For these 91, errors are assessed as being at the same level as true exact errors on 83 occasions and one level worse for the other 8. Thus, stress error estimation is largely accurate (91%) and otherwise modestly conservative (9%).

PIV Investigation of Separated and Reattached Turbulent Flows Over Ribs of Various Aspect Ratio

2014 ◽  
Author(s):  
Kathryn M. Atamanchuk ◽  
Mark F. Tachie
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Separated Flow ◽  
Particle Image Velocimetry System ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Freestream Velocity

An experimental study is undertaken to investigate the features of separated and reattached flow over surface mounted traverse ribs of varying aspect ratio (1:1, 1:2, and 1:4) in a recirculating open channel turbulent flow. A particle image velocimetry system was used to conduct the velocity measurements. Upstream conditions were kept consistent among all three test cases. The reattachment length of the separated flow was found to decrease as rib aspect ratio increased, primarily as a result of a secondary separation reattachment formation on the ribs of increased aspect ratio. Contour plots of mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds shear stresses, as well as one-dimensional profiles of streamwise mean velocity, turbulent kinetic energy and Reynolds shear stress in the recirculation and reattachment region are presented and discussed. The results show that maximum wall-normal mean velocities are approximately 40% of the approach freestream velocity. The results also indicate that the turbulence levels downstream of the block tend to decrease as the rib aspect ratio increases.

Sign in / Sign up

Export Citation Format

Share Document