Hysteresis Curve in Reproduction of Reynolds’ Color-Band Experiments

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Hidesada Kanda ◽  
Takayuki Yanagiya
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Clear Relationship ◽  
Hysteresis Curve ◽  
Pipe Flows ◽  
Critical Reynolds Numbers ◽  
Extended Analysis ◽  
First Time

This article describes the reproduction and extended analysis of Reynolds’ color-band experiment. Reynolds found two critical Reynolds numbers (Rc) in pipe flows: Rc1 of 12,830 from laminar to turbulent flow and Rc2 of 2030 from turbulent to laminar flow. Since no clear relationship has been established between them, we studied how the entrance shape affects Rc. Thus, for the first time, a hysteresis graph can be drawn by connecting the two curves of Rc1 and Rc2 such that the two Rc values lie on separate branches of the hysteresis plot.

Effects of Roughness on Turbulent Flow in Microchannels and Minichannels

2008 ◽  
Author(s):  
Timothy P. Brackbill ◽  
Satish G. Kandlikar
Keyword(s):  
Experimental Study ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Roughness Parameter ◽  
Reynolds Numbers ◽  
Turbulent Regime ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Roughness Elements ◽  
Moody Diagram

The effect of roughness ranging from smooth to 24% relative roughness on laminar flow has been examined in previous works by the authors. It was shown that using a constricted parameter, εFP, the laminar results were predicted well in the roughened channels ([1],[2],[3]). For the turbulent regime, Kandlikar et al. [1] proposed a modified Moody diagram by using the same set of constricted parameters, and using the modification of the Colebrook equation. A new roughness parameter εFP was shown to accurately portray the roughness effects encountered in laminar flow. In addition, a thorough look at defining surface roughness was given in Young et al. [4]. In this paper, the experimental study has been extended to cover the effects of different roughness features on pressure drop in turbulent flow and to verify the validity of the new parameter set in representing the resulting roughness effects. The range of relative roughness covered is from smooth to 10.38% relative roughness, with Reynolds numbers up to 15,000. It was found that using the same constricted parameters some unique characteristics were noted for turbulent flow over sawtooth roughness elements.

The stability of a stratified fluid

1967 ◽  
Vol 29 (2) ◽  
pp. 233-240
Author(s):  
J. B. Hinwood
Keyword(s):  
Turbulent Flow ◽  
Froude Number ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Stratified Flows ◽  
Rectangular Duct ◽  
Interfacial Waves ◽  
Homogeneous Flow ◽  
Critical Reynolds Numbers ◽  
The Stability

For the flow of a stably-stratified fluid in the inlet region of a rectangular duct, it is shown experimentally that the upper and lower critical Reynolds numbers are functions of the interfacial Froude number F, and that if F is large they are lower than for a homogeneous flow. In stratified flows the disturbances leading to turbulent flow sometimes arise at the interface and lead to interfacial waves, whose wavelength at breaking is equal to the conduit depth.

scholarly journals MAXIMIZATION OF FLIGHT TIME FOR AIRPLANES WITH ELECTRICAL DRIVE BY POWERPLANT OPTIMIZATION

Aviation ◽  
2007 ◽  
Vol 11 (2) ◽  
pp. 37-40
Author(s):  
Sergey Serokhvostov
Keyword(s):  
Power Plant ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Electrical Power ◽  
Reynolds Numbers ◽  
Flight Time ◽  
Electrical Drive ◽  
Electrical Power Plant

In this paper, the problem of maximizing the flight time of an airplane with an electrical power plant (AEP) by the optimization of the mass of the accumulator in cases of fixed and non‐fixed airframe is considered. Variants of high (turbulent flow) and low (laminar flow) Reynolds numbers are taken into account. Dependence of flight time on airplane parameters is obtained. The behaviour of flight time as a function of accumulator mass near the maximum is also investigated. A comparison between the results obtained and the data for the existing AEP is made. On the basis of the results obtained, the influence of aircraft parameters on flight time is analyzed.

scholarly journals Two dimensional simulation of laminar flow by three- jet in a semi-confined space

2020 ◽  
Vol 9 (1) ◽  
pp. 111-117
Author(s):  
Mohammad Mosaddeghi
Keyword(s):  
Laminar Flow ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Confined Space ◽  
Wide Range ◽  
Critical Reynolds Numbers ◽  
Dimensional Simulation ◽  
Geometric Changes

AbstractEquipment performance improvement in a wide range of working conditions is one of the major goals of aerodynamics. This goal can be achieved by the deformation of the object being examined or by using flow control techniques in active or inactive modes. In different researches, how to change the development ratio on the semi-confined space with input jet system is surveyed. In this study, two-dimensional simulation of the flow has been investigated in three-jet laminar flow in a semi-confined space. To determine the effective and optimal mixing in a laminar flow, critical Reynolds numbers were determined to distinguish when the flow in the channel from a steady-state symmetric flowformed downstream recirculation and ultimately transient flow. To better understand the flow characteristics, the simulations were changed at a fixed jet spacing (input jets distance to height of space ratio). Also, in this paper, for comparison, four jets were considered. Based on the results, it was observed that in all cases, mixing occurred in the space between three jets. Placing the jet along the walls of the semi-confined space allows the best combination, and increase in the distance between the first and third jets and reduction of the particle coefficient caused to reach the critical Reynolds number faster and, as a result, mixing in a laminar flow with geometric changes of the semi-confined space.

scholarly journals Heteroclinic path to spatially localized chaos in pipe flow

2017 ◽  
Vol 827 ◽  
Author(s):  
N. B. Budanur ◽  
B. Hof
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Unstable Manifold ◽  
Pipe Flow ◽  
Reynolds Numbers ◽  
Lower Branch ◽  
Continuous Symmetry ◽  
Saddle Node Bifurcation ◽  
Branch Solution ◽  
First Time

In shear flows at transitional Reynolds numbers, localized patches of turbulence, known as puffs, coexist with the laminar flow. Recently, Avila et al. (Phys. Rev. Lett., vol. 110, 2013, 224502) discovered two spatially localized relative periodic solutions for pipe flow, which appeared in a saddle-node bifurcation at low Reynolds number. Combining slicing methods for continuous symmetry reduction with Poincaré sections for the first time in a shear flow setting, we compute and visualize the unstable manifold of the lower-branch solution and show that it extends towards the neighbourhood of the upper-branch solution. Surprisingly, this connection even persists far above the bifurcation point and appears to mediate the first stage of the puff generation: amplification of streamwise localized fluctuations. When the state-space trajectories on the unstable manifold reach the vicinity of the upper branch, corresponding fluctuations expand in space and eventually take the usual shape of a puff.

The Steady-State and Dynamic Characteristics of a Full Circular Bearing and a Partial Arc Bearing in the Laminar and Turbulent Flow Regimes

1967 ◽  
Vol 89 (2) ◽  
pp. 143-153 ◽  
Author(s):  
F. K. Orcutt ◽  
E. B. Arwas
Keyword(s):  
Steady State ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Dynamic Characteristics ◽  
Reynolds Numbers ◽  
Operating Parameters ◽  
Design Data ◽  
Design Charts ◽  
Laminar And Turbulent Flow

The steady-state and dynamic characteristics of a full circular bearing and a centrally loaded, 100 deg, arc bearing are calculated for a range of eccentricity ratios to 0.95 and of mean Reynolds numbers to 13,300, and presented in design charts. These are compared with the measured performance of these bearings over the same ranges of the operating parameters. There is good correlation between the theoretical and test data, leading to the conclusion that the present turbulent lubrication analysis may be used to obtain general design data for self-acting bearings, operating in the superlaminar flow regime, to supplement that presently existing for laminar flow bearings.

scholarly journals Transition From the Turbulent to the Laminar Regime for Internal Convective Flow With Large Property Variations

1970 ◽  
Vol 92 (3) ◽  
pp. 506-512 ◽  
Author(s):  
C. W. Coon ◽  
H. C. Perkins
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Bulk Temperature ◽  
Heating Rates ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
High Heating ◽  
Flow Situation

The results of a primarily experimental study of the transition from turbulent flow to laminar flow as a consequence of high heating rates are presented. Results are reported for hydrodynamically fully developed, low Mach number flows of air and helium through a vertical, circular tube. The electrically heated section was 100 diameters in length; entering Reynolds numbers ranged from 1700–40,000, and maximum wall-to-bulk temperature ratios reached 4.4. As a means of predicting the occurrence of a transition from turbulent flow to laminar flow, the experimental results are compared to the acceleration parameter suggested by Moretti and Kays and to a modified form of the parameter that is appropriate to a circular tube. It is suggested that the variable property turbulent flow correlations do not provide acceptable predictions of the Nusselt number and the friction factor if the value 4μq′′G2DTcp≃1.5×10−6 based on bulk properties, is exceeded for an initially turbulent flow situation. It is further suggested that Nusselt numbers and friction factors at locations down-stream from the point xDlaminar≃(2×10−8)(Tinlet)(Reb,inlet)2TwTbmax−1 for bulk temperatures in degrees Rankine may be obtained from the laminar correlation equations even though the flow is initially turbulent.

Flow Development in a Parallel Plate Channel

1976 ◽  
Vol 98 (1) ◽  
pp. 145-154 ◽  
Author(s):  
A. Z. Szeri ◽  
C. C. Yates ◽  
S. M. Hai
Keyword(s):  
Laminar Flow ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Parallel Plate ◽  
Reynolds Numbers ◽  
Momentum Equation ◽  
Essential Difference ◽  
Eddy Viscosity Model ◽  
Asymptotic Profile ◽  
Plate Channel

The paper presents a study of the flow that occurs in a finite, parallel plate channel. The experimental work consists of velocity profile measurements upstream of and inside the channel of a belt-type apparatus. Theoretical prediction of velocity profile development is made via numerical methods in both laminar and turbulent situations. In the laminar flow case analytical solution of a linearized form of the momentum equation was also possible. Good agreement is shown between prediction and experimental results for all Reynolds numbers tested; in turbulent flow this occurs particularly when employing Reichardt’s eddy viscosity model. For laminar flow the entrance length is estimated to be 0.008–0.01 times the Reynolds number, while in turbulent flow no essential difference was found between an entrance and the corresponding asymptotic profile. Upstream from the entrance the similar laminar profiles of Sakiadis were observed experimentally.

scholarly journals Fluid friction between rotating cylinders I—Torque measurements

1936 ◽  
Vol 157 (892) ◽  
pp. 546-564 ◽  
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Centrifugal Force ◽  
Outer Cylinder ◽  
Reynolds Numbers ◽  
Stream Line ◽  
Rotating Cylinders ◽  
Torque Measurements ◽  
Critical Reynolds Numbers ◽  
The Stability

The stability of fluid contained between concentric rotating cylinders has been investigated and it has been shown that, when only the inner cylinder rotates, the flow becomes unstable when a certain Reynolds number of the flow is exceeded. When the outer cylinder only is rotated, the flow is stable so far as disturbances of the type produced in the former case are concerned, but provided the Reynolds number of the flow exceeds a certain value, turbulence sets in. The object of the present experiments was partly to measure the torque reaction between two cylinders in the two cases in order to find the effect of centrifugal force on the turbulence, and partly to find the critical Reynolds numbers for the transition from stream-line to turbulent flow. The apparatus is shown diagrammatically in fig. 1.

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