Inception of Turbulence in the Stokes Boundary Layer Over a Transpiring Wall

2002 ◽  
Vol 124 (3) ◽  
pp. 678-684 ◽  
Author(s):  
Joseph Majdalani ◽  
James Barron ◽  
William K. Van Moorhem
Keyword(s):  
Reynolds Number ◽  
Standard Deviation ◽  
Side Wall ◽  
Flow Regimes ◽  
Computer Data ◽  
Computer Data Acquisition ◽  
Onset Of Turbulence ◽  
Wall Injection ◽  
Rectangular Chamber ◽  
Hot Film

In this work, the onset of turbulence inside a rectangular chamber is investigated, with and without side-wall injection, in the presence of an oscillatory pressure gradient. Two techniques are used to define the transition from laminar to turbulent regimes: statistical analysis and flow visualization. Calibrated hot film anemometry and a computer data acquisition system are used to record and analyze acoustical flow data. Four classifications of flow regimes are reported: (a) laminar, (b) distorted laminar, (c) weakly turbulent, and (d) conditionally turbulent. Despite numerous attempts to promote turbulence, a fully turbulent flow does not develop at any of the driving frequencies tested. Statistical measurements reveal that a periodic drop in standard deviation of axial velocity fluctuations always occurs, indicating relaminarization within each cycle. Transition between flow regimes is assessed from the standard deviation of velocity data correlated as a function of the acoustic Reynolds number ReA. Under predominantly laminar conditions, the standard deviation is found to vary approximately with the square of the acoustic Reynolds number. Under turbulent conditions, the standard deviation becomes almost directly proportional to the acoustic Reynolds number. Inception of turbulence in the oscillatory flow with side-wall injection is found to be reproducible at the same critical value of ReA≅200.

The Prediction and Measurement of Incompressible Flow in a Labyrinth Seal

1989 ◽  
Vol 111 (4) ◽  
pp. 697-702 ◽  
Author(s):  
J. A. Demko ◽  
G. L. Morrison ◽  
D. L. Rhode
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Incompressible Flow ◽  
Labyrinth Seal ◽  
Substantial Effect ◽  
Navier Stokes ◽  
Computer Data ◽  
Computer Data Acquisition ◽  
Swirl Velocity ◽  
Hot Film

Predictions and measurements were obtained for incompressible flow in a labyrinth seal for Taylor numbers of 0, 7,600, and 19,000 at an axial Reynolds number near 50,000. A hot-film anemometer with computer data acquisition was used in obtaining the measurements. The computations were made using a turbulent flow Navier-Stokes finite difference code. The QUICK differencing scheme was utilized in order to diminish false diffusion. Comparison between experiments and predictions are given for the axial and swirl velocity components and turbulent kinetic energy. Also, the substantial effect of the Taylor number on the pressure distribution is presented.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

scholarly journals Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

Actuators ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 185
Author(s):  
Zuzana Antošová ◽  
Zdeněk Trávníček
Keyword(s):  
Reynolds Number ◽  
Active Control ◽  
Flow Regimes ◽  
Velocity Profiles ◽  
Synthetic Jet ◽  
Transition To Turbulence ◽  
Jet Flows ◽  
Maximal Effect ◽  
Hot Wire ◽  
Round Jet

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

A Digital Computer Data Acquisition, Display, and Analysis System for the Gamma Camera

Radiology ◽  
1970 ◽  
Vol 96 (3) ◽  
pp. 658-661 ◽  
Author(s):  
Fred P. Bruno ◽  
Valerie A. Brookeman ◽  
Clyde M. Williams
Keyword(s):  
Data Acquisition ◽  
Digital Computer ◽  
Gamma Camera ◽  
Computer Data ◽  
Computer Data Acquisition ◽  
Analysis System

Automation Of Dihydroxyaluminum Sodium Carbonate Analysis In Antacid Tablets By Energy Dispersive X-Ray Fluorescence

1990 ◽  
Vol 73 (3) ◽  
pp. 385-388
Author(s):  
Constantine A Georgiades
Keyword(s):  
Standard Deviation ◽  
Relative Standard Deviation ◽  
Sodium Carbonate ◽  
Energy Dispersive ◽  
Computer Data ◽  
X Ray ◽  
Assay Procedure ◽  
Relative Standard ◽  
Computer Data Processing

Abstract A sensitive, specific, automated energy dispersive X-ray fluorescence (EDXRF) method for determination of anhydrous dihydroxyaluminum sodium carbonate in antacid tablets has been developed. The compound was quantltated by Impact grinding, palletizing at 10 tons pressure, and monitoring the aluminum by using a rhodium anode X-ray tube, high resolution thermoelectrlcally cooled SI(LI) detector with sample spinning, and computer data processing. The assay procedure was validated with spiked laboratory-prepared samples at 100 ± 20% levels. The average recovery was 100.6% with a relative standard deviation of 1.6% (n = 14). Instrument precision was determined and found to have an average relative standard deviation of 1.0% (n = 16). In addition, analysis precision by the EDXRF method was compared to that for titration and autoanalyzer methodologies and found to be statistically comparable. The sample precision had an averaged relative standard deviation of 2.7% (n = 16) by X-ray methodology. The advantages of this EDXRF method Include Increased sample throughput with excellent precision and accuracy, no solvent usage, and automated data handling.

MHD nanofluid heat transfer between a stretching sheet and a porous surface using neural network approach

2019 ◽  
Vol 30 (06) ◽  
pp. 1950048 ◽  
Author(s):  
Yuancheng Geng ◽  
A. Hassanvand ◽  
Mostafa Monfared ◽  
Rasoul Moradi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Magnetic Parameter ◽  
Volume Fraction ◽  
Sensitivity Analyses ◽  
Integration Scheme ◽  
Group Method ◽  
Suction Parameter ◽  
Wall Injection

Magnetohydrodynamic flow of nanofluids and heat transfer between two horizontal plates in a rotating system have been examined numerically. In order to do this, the group method of data handling (GMDH)-type neural networks is used to calculate Nusselt number formulation. Results indicate that GMDH-type NN in comparison with fourth-order Runge–Kutta integration scheme provides an effective means of efficiently recognizing the patterns in data and accurately predicting a performance. Single-phase model is used in this study. Similar solution is used in order to obtain ordinary differential equation. The effects of nanoparticle volume fraction, magnetic parameter, wall injection/suction parameter and Reynolds number on Nusselt number are studied by sensitivity analyses. The results show that Nusselt number is an increasing function of Reynolds number and volume fraction of nanoparticles but it is a decreasing function of magnetic parameter. Also, it can be found that wall injection/suction parameter has no significant effect on rate of heat transfer.

Decreasing the Side Wall Contamination in Wind Tunnels

1983 ◽  
Vol 105 (4) ◽  
pp. 435-438 ◽  
Author(s):  
T. Motohashi ◽  
R. F. Blackwelder
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Three Dimensional ◽  
Side Wall ◽  
Wind Tunnels ◽  
Turbulent Fluid ◽  
Side Walls ◽  
Suction Slot

To study boundary layers in the transitional Reynolds number regime, the useful spanwise and streamwise extent of wind tunnels is often limited by turbulent fluid emanating from the side walls. Some or all of the turbulent fluid can be removed by sucking fluid out at the corners, as suggested by Amini [1]. It is shown that by optimizing the suction slot width, the side wall contamination can be dramatically decreased without a concomitant three-dimensional distortion of the laminar boundary layer.

A Numerical Investigation on the Onset of the Various Flow Regimes in a Spherical Annulus

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Lalaoua Adel ◽  
Bouabdallah Ahcene
Keyword(s):  
Reynolds Number ◽  
Flow Behavior ◽  
Flow Regimes ◽  
Skin Friction Coefficient ◽  
Formation Mechanisms ◽  
Turbulent Regime ◽  
Turbulent Transition ◽  
Inner Sphere ◽  
Spherical Couette ◽  
Laminar Turbulent Transition

The spherical Couette system, consisting of the flow in the annular gap between two concentric rotating spheres, is a convenient problem for studying the laminar–turbulent transition. Many of the transitional phenomena encountered in this flow are of fundamental relevance for the understanding of global processes in the planetary atmospheres as well as in astrophysical and geophysical motions. Furthermore, the study of spherical Couette flow (SCF) is of basic importance in the field of hydrodynamic stability. This paper focuses principally on the numerical prediction of various transitions between flow regimes in a confined spherical gap between a rotating inner sphere and a fixed outer spherical shell. The finite-volume-based computational fluid dynamics, FLUENT software package, is adopted to investigate numerically the flow of a viscous incompressible fluid in the closed spherical gap. Two important dimensionless parameters completely define the flow regimes: the Reynolds number, Re = Ω1R12/ν, for the rotation of the inner sphere and the gap width, β = (R2 − R1)/R1 = 0.1, for the geometry. The numerical calculations are carried out over a range of Reynolds number from two until 60,000. The numerical results are compared with the experimental data available in the literature, and the agreement between the two approaches is very good. The laminar–turbulent transition, the onset of different instabilities, the formation mechanisms of various structures, and the flow behavior are examined and described in detail by the pressure field, meridional streamlines, circumferential velocity, and skin friction coefficient. In addition, the velocity time series and the corresponding power spectral density are considered and analyzed over a large range of Reynolds number. Three kinds of fundamental frequencies expressed by F0, F1, and F2 are obtained corresponding to the spiral mode associated with the wavy mode (SM + WM), the wavy mode (WVF), and the chaotic fluctuation (CF), respectively. However, no sharp fundamental frequency components are observed for the turbulent regime.

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