scholarly journals OSCILLATORY BOUNDARY LAYER FLOW OVER RIPPLED BEDS

1984 ◽  
Vol 1 (19) ◽  
pp. 154 ◽  
Author(s):  
Shinji Sato ◽  
Nobuo Mimura ◽  
Akira Watanabe
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Energy Dissipation Rate ◽  
Numerical Calculations ◽  
Measured Velocity ◽  
Oscillatory Boundary Layer ◽  
Rippled Beds ◽  
Layer Flow

Characteristics of the oscillatory boundary layer flow above rippled beds were investigated through experiments and numerical calculations. Experiments were conducted in an oscillatory flow tunnel. Velocities above symmetric and asymmetric ripples were measured with split-hot-film sensors under conditions of both sinusoidal and asymmetric oscillations. The stress field in the boundary layer was evaluated based on the distributions of the measured velocity and Reynolds stress. Relations between vortex formation and turbulence were examined, and effects of the asymmetry of oscillatory main flow and of ripple form on the velocity field were discussed. Numerical calculations were carried out by integrating the Navier-Stokes equations with an implicit finite difference scheme. Formation of a lee vortex above ripples was simulated in the calculations. The bottom shear stress and the energy dissipation rate were estimated based on the results of the experiments and calculations.

An analytical solution for the Marangoni mixed convection boundary layer flow

2010 ◽  
Vol 224 (6) ◽  
pp. 1193-1202 ◽  
Author(s):  
M A Moghimi ◽  
A Kimiaeifar ◽  
M Rahimpour ◽  
G H Bagheri
Keyword(s):  
Boundary Layer ◽  
Analytical Solution ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Convection Boundary Layer ◽  
Effective Parameters ◽  
Linear Ordinary Differential Equations ◽  
Convection Boundary ◽  
Layer Flow

In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is presented. A similarity transform reduces the Navier—Stokes equations to a set of non-linear ordinary differential equations, which are solved analytically by means of the homotopy analysis method (HAM). The results obtained in this study are compared with the numerical results released in the literature. A close agreement of the two sets of results indicates the accuracy of the HAM. The method can obtain an expression that is acceptable for all values of effective parameters and is also able to control the convergence of the solution. The numerical solution of the similarity equations is developed and the results are in good agreement with the analytical results based on the HAM.

Two-dimensional global low-frequency oscillations in a separating boundary-layer flow

2008 ◽  
Vol 614 ◽  
pp. 315-327 ◽  
Author(s):  
UWE EHRENSTEIN ◽  
FRANÇOIS GALLAIRE
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Perturbation Analysis ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Low Frequency ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Optimal Perturbation ◽  
Layer Flow

A separated boundary-layer flow at the rear of a bump is considered. Two-dimensional equilibrium stationary states of the Navier–Stokes equations are determined using a nonlinear continuation procedure varying the bump height as well as the Reynolds number. A global instability analysis of the steady states is performed by computing two-dimensional temporal modes. The onset of instability is shown to be characterized by a family of modes with localized structures around the reattachment point becoming almost simultaneously unstable. The optimal perturbation analysis, by projecting the initial disturbance on the set of temporal eigenmodes, reveals that the non-normal modes are able to describe localized initial perturbations associated with the large transient energy growth. At larger time a global low-frequency oscillation is found, accompanied by a periodic regeneration of the flow perturbation inside the bubble, as the consequence of non-normal cancellation of modes. The initial condition provided by the optimal perturbation analysis is applied to Navier–Stokes time integration and is shown to trigger the nonlinear ‘flapping’ typical of separation bubbles. It is possible to follow the stationary equilibrium state on increasing the Reynolds number far beyond instability, ruling out for the present flow case the hypothesis of some authors that topological flow changes are responsible for the ‘flapping’.

scholarly journals Turbulence statistics in smooth wall oscillatory boundary layer flow

2018 ◽  
Vol 849 ◽  
pp. 192-230 ◽  
Author(s):  
Dominic A. van der A ◽  
Pietro Scandura ◽  
Tom O’Donoghue
Keyword(s):  
Boundary Layer ◽  
Normal Distribution ◽  
Boundary Layer Flow ◽  
Vertical Gradient ◽  
Streamwise Velocity ◽  
Normal Velocity ◽  
Half Cycle ◽  
Velocity Fluctuations ◽  
Oscillatory Boundary Layer ◽  
Layer Flow

Turbulence characteristics of an asymmetric oscillatory boundary layer flow are analysed through two-component laser-Doppler measurements carried out in a large oscillatory flow tunnel and direct numerical simulation (DNS). Five different Reynolds numbers, $R_{\unicode[STIX]{x1D6FF}}$, in the range 846–2057 have been investigated experimentally, where $R_{\unicode[STIX]{x1D6FF}}=\tilde{u} _{0max}\unicode[STIX]{x1D6FF}/\unicode[STIX]{x1D708}$ with $\tilde{u} _{0max}$ the maximum oscillatory velocity in the irrotational region, $\unicode[STIX]{x1D6FF}$ the Stokes length and $\unicode[STIX]{x1D708}$ the fluid kinematic viscosity. DNS has been carried out for the lowest three $R_{\unicode[STIX]{x1D6FF}}$ equal to 846, 1155 and 1475. Both experimental and numerical results show that the flow statistics increase during accelerating phases of the flow and especially at times of transition to turbulent flow. Once turbulence is fully developed, the near-wall statistics remain almost constant until the late half-cycle, with values close to those reported for steady wall-bounded flows. The higher-order statistics reach large values within a normalized wall distance of approximately $y/\unicode[STIX]{x1D6FF}=0.2$ at phases corresponding to the onset of low-speed streak breaking, because of the intermittency of the velocity fluctuations at these times. In particular, the flatness of the streamwise velocity fluctuations reaches values of the order of ten, while the flatness of the wall-normal velocity fluctuations reaches values of several hundreds. Far from the wall, at locations where the vertical gradient of the streamwise velocity is zero, the skewness is approximately zero and the flatness is approximately equal to 3, representative of a normal distribution. At lower elevations the distribution of the fluctuations deviate substantially from a normal distribution, but are found to be well described by other standard theoretical probability distributions.

scholarly journals EFFECT OF FLOW IRREGULARITY ON OSCILLATORY BOUNDARY LAYER FLOW

2014 ◽  
Vol 1 (34) ◽  
pp. 44 ◽  
Author(s):  
Mahesa Bhawanin ◽  
Tom O'Donoghue ◽  
Dominic A Van der A ◽  
Jan S. Ribberink
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Oscillatory Boundary Layer ◽  
Layer Flow

EFFECTS OF ACCELERATION SKEWNESS ON ROUGH BED OSCILLATORY BOUNDARY LAYER FLOW

2009 ◽  
Author(s):  
Dominic A. van der A ◽  
Tom O'Donoghue ◽  
Alan G. Davies ◽  
Jan S. Ribberink
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Oscillatory Boundary Layer ◽  
Rough Bed ◽  
Layer Flow
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