A Boundary-Layer Theory for Transient Viscous Losses in Turbulent Flow

1970 ◽  
Vol 92 (4) ◽  
pp. 865-873 ◽  
Author(s):  
D. J. Wood ◽  
J. E. Funk
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Numerical Solutions ◽  
Transient Flow ◽  
Viscous Effects ◽  
Viscous Losses ◽  
Rapid Flow ◽  
Flow Information ◽  
Layer Velocity ◽  
Good Agreement

A laminar boundary-layer model is proposed to account for viscous losses during the transient turbulent flow of a liquid in a tube. In this model, inviscid slug flow is assumed for the core and all viscous effects are assumed to occur in the boundary layer. The transient boundary-layer velocity distribution is determined as a function of a prescribed variation in core velocity and the associated pressure gradient. Both analytical and numerical solutions are presented. This transient flow information is used to calculate local and integrated energy dissipation rates which are then combined, with one-dimensional energy analyses. The result is a prediction of the decrease in pressure-wave magnitude due to viscous dissipation, and a comparison is made with experimental data for rapid flow extinction. Good agreement between the observed and predicted results is obtained.

Frequency Response of Fluid Lines With Turbulent Flow

1974 ◽  
Vol 96 (4) ◽  
pp. 365-369 ◽  
Author(s):  
J. E. Funk ◽  
D. J. Wood
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Attenuation Factor ◽  
Simple Expression ◽  
Layer Model ◽  
Viscous Effects ◽  
Local Boundary ◽  
The Core ◽  
Layer Velocity ◽  
Single Boundary

A single boundary layer model to account for transient viscous effects is applied to small amplitude sinusoidally disturbed turbulent flow in a tube. The viscous dissipation is calculated using a transfer function relating the local boundary layer velocity gradient to the core velocity. A simple expression for the attenuation factor is derived and the analytical results are shown to be in excellent agreement with previously reported experimental data.

scholarly journals Analytic Approximate Solution for Falkner-Skan Equation

2014 ◽  
Vol 2014 ◽  
pp. 1-22 ◽  
Author(s):  
Vasile Marinca ◽  
Remus-Daniel Ene ◽  
Bogdan Marinca
Keyword(s):  
Differential Equation ◽  
Boundary Layer ◽  
Numerical Solutions ◽  
Approximate Solutions ◽  
Rapid Convergence ◽  
Boundary Layer Problem ◽  
Small Parameters ◽  
Optimal Homotopy Asymptotic Method ◽  
Good Agreement ◽  
Layer Problem

This paper deals with the Falkner-Skan nonlinear differential equation. An analytic approximate technique, namely, optimal homotopy asymptotic method (OHAM), is employed to propose a procedure to solve a boundary-layer problem. Our method does not depend upon small parameters and provides us with a convenient way to optimally control the convergence of the approximate solutions. The obtained results reveal that this procedure is very effective, simple, and accurate. A very good agreement was found between our approximate results and numerical solutions, which prove that OHAM is very efficient in practice, ensuring a very rapid convergence after only one iteration.

Oscillations of a gas in a closed tube near half the fundamental frequency

1987 ◽  
Vol 183 ◽  
pp. 147-161 ◽  
Author(s):  
R. Althaus ◽  
H. Thomann
Keyword(s):  
Boundary Layer ◽  
Fundamental Frequency ◽  
Atmospheric Pressure ◽  
Nonlinear Effects ◽  
Viscous Effects ◽  
Sinusoidal Motion ◽  
Closed Tube ◽  
Resonant Part ◽  
Theoretical Results ◽  
Good Agreement

The oscillations are driven by the sinusoidal motion of a piston at one end of the tube. Near half the fundamental frequency the first overtone, driven by nonlinear effects, becomes resonant. For small boundary-layer friction the amplitude of this resonant part is comparable with the non-resonant acoustic solution and shocks are formed. Theoretical results are compared with pressure signals measured at the closed end of the tube. The viscous effects are large for air at atmospheric pressure and the nonlinear effects remain small. Experiments with xenon, sulphurhexafluoride (SF6) and Freon RC-318 (C4F8) were therefore conducted and shocks formed as predicted. The comparison of the nonlinear theory by Keller (1975) with the experiments shows very good agreement.

Laminar Transfer From Isothermal Spanwise Strips on a Flat Plate

1960 ◽  
Vol 82 (1) ◽  
pp. 53-63 ◽  
Author(s):  
H. H. Sogin
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Air Temperature ◽  
Calculation Method ◽  
Step Function ◽  
Inert Material ◽  
Adiabatic Wall ◽  
Good Agreement

The Rubesin-Klein-Tribus method is used to calculate rates of heat transfer by forced convection from two isothermal spanwise strips in tandem. The general results are applicable to either laminar or turbulent flow. Predictions of laminar transfer are based on Eckert’s step function. In experimentation, naphthalene cast in trays is used to simulate the isothermal strips while the inert material between them simulates the adiabatic wall. The velocities range from about 40 to 90 ft/sec, and the air temperature from 72 to 88 F. The boundary layer is shown to be laminar. The theoretical and experimental results are found to be in good agreement, confirming the calculation method and Eckert’s step function. The experimentation is extended to an array of several equally spaced strips in tandem. Effects of roughness and spanwise diffusion are noted.

scholarly journals Simulation of a laminar-turbulent flow in three-dimensional aerodynamic configurations

2021 ◽  
Vol 2057 (1) ◽  
pp. 012080
Author(s):  
T V Poplavskaya ◽  
A V Boiko ◽  
K V Demyanko ◽  
S V Kirilovskiy ◽  
Y M Nechepurenko
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Prolate Spheroid ◽  
Turbulent Transition ◽  
Good Agreement ◽  
Laminar Turbulent Transition

Abstract The goal of the paper is to determine the position of the laminar-turbulent transition in the boundary layer of a prolate spheroid using the eN-method with the calibration of threshold N-factors. It is demonstrated that the predicted and experimental data on the laminarturbulent transition are in good agreement.

An Approximate Method for the Solution of a Class of Nonsimilar Laminar Boundary Layer Equations

1976 ◽  
Vol 98 (2) ◽  
pp. 292-296 ◽  
Author(s):  
G. Nath
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Approximate Method ◽  
Laminar Boundary Layer ◽  
Boundary Layer Flows ◽  
Freestream Velocity ◽  
Boundary Layer Equations ◽  
Transverse Curvature ◽  
Layer Velocity ◽  
Good Agreement

An approximate method is developed for locally nonsimilar laminar boundary layer flows. This method is applicable to several boundary layer velocity problems where the nonsimilarity stems from the freestream velocity distribution and the transverse curvature. The results are compared with those obtained by other methods and, except in the neighborhood of the point of separation, they are in good agreement.

Thermal Performance Analysis of a Rectangular Longitudinal Finned Solar Air Heater With Semicircular Absorber Plate

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Satyender Singh ◽  
Prashant Dhiman
Keyword(s):  
Thermal Performance ◽  
Numerical Solutions ◽  
Solar Air Heater ◽  
Duct Flow ◽  
Balance Equations ◽  
Absorber Plate ◽  
Ansys Fluent ◽  
Air Heater ◽  
Glass Cover ◽  
Good Agreement

Thermal performance of a single-pass single-glass cover solar air heater consisting of semicircular absorber plate finned with rectangular longitudinal fins is investigated. The analysis is carried out for different hydraulic diameters, which were obtained by varying the diameter of the duct from 0.3–0.5 m. One to five numbers of fins are considered. Reynolds number ranges from 1600–4300. Analytical solutions for energy balance equations of different elements and duct flow of the solar air heater are presented; results are compared with finite-volume methodology based numerical solutions obtained from ansys fluent commercial software, and a fairly good agreement is achieved. Moreover, analysis is extended to check the effect of double-glass cover and the recycle of the exiting air. Results revealed that the use of double-glass cover and recycle operation improves the thermal performance of solar air heater.

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

2021 ◽  
Vol 920 ◽  
Author(s):  
Nathaniel R. Bristow ◽  
Gianluca Blois ◽  
James L. Best ◽  
Kenneth T. Christensen
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Layer Structure ◽  
Boundary Layer Structure ◽  
Barchan Dunes

Abstract

scholarly journals Experimental and Numerical Buckling Analyses of Laminated Composite Plates under Temperature Effects

2010 ◽  
Vol 19 (4) ◽  
pp. 096369351001900 ◽  
Author(s):  
Emin Ergun
Keyword(s):  
Composite Plate ◽  
Numerical Solutions ◽  
Laminated Composite ◽  
Composite Plates ◽  
Buckling Load ◽  
Fibre Reinforcement ◽  
Stacking Sequence ◽  
Laminated Composite Plates ◽  
Different Temperatures ◽  
Good Agreement

The aim of this study is to investigate, experimentally and numerically, the change of critical buckling load in composite plates with different ply numbers, orientation angles, stacking sequences and boundary conditions as a function of temperature. Buckling specimens have been removed from the composite plate with glass-fibre reinforcement at [0°]i and [45°]i (i= number of ply). First, the mechanical properties of the composite material were determined at different temperatures, and after that, buckling experiments were done for those temperatures. Then, numerical solutions were obtained by modelling the specimens used in the experiment in the Ansys10 finite elements package software. The experimental and numerical results are in very good agreement with each other. It was found that the values of the buckling load at [0°] on the composite plates are higher than those of other angles. Besides, symmetrical and anti-symmetrical conditions were examined to see the effect of the stacking sequence on buckling and only numerical solutions were obtained. It is seen that the buckling load reaches the highest value when it is symmetrical in the cross-ply stacking sequence and it is anti-symmetrical in the angle-ply stacking sequence.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

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