A Mapped Finite Difference Study of Noise Propagation in Nonuniform Ducts With Mean Flow

1987 ◽  
Vol 109 (4) ◽  
pp. 372-380 ◽  
Author(s):  
Peter E. Raad ◽  
James W. White
Keyword(s):  
Fluid Flow ◽  
Finite Difference ◽  
Primary Objective ◽  
Mean Flow ◽  
Noise Propagation ◽  
Mapping Procedure ◽  
Soft Wall ◽  
Implicit Finite Difference ◽  
The Mean ◽  
Fully Coupled

The primary objective of this work is to study noise propagation in acoustically lined variable area ducts with mean fluid flow. The method of study is numerical in nature and involves a body-fitted grid mapping procedure in conjunction with a factored-implicit finite difference technique. The mean fluid flow model used is two-dimensional, inviscid, irrotational, incompressible, and nonheat conducting. Fully-coupled solutions of the linearized gas dynamic equations are obtained for both positive and negative Mach numbers as well as for hard and soft wall conditions. The factored-implicit finite difference technqiue used did give rise to short wavelength perturbations, but these were dampened by the introduction of higher order artificial dissipation terms into the scheme. Results compared favorably with available numerical and experimental data.

Fully coupled resonant-triad interactions in a free shear layer

1994 ◽  
Vol 278 ◽  
pp. 101-121 ◽  
Author(s):  
R. Mallier ◽  
S. A. Maslowe
Keyword(s):  
Flow Direction ◽  
Mixing Layer ◽  
Adverse Pressure Gradient ◽  
Critical Layer ◽  
Free Shear Layer ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Initial Interaction ◽  
The Mean ◽  
Fully Coupled

We report the results of an investigation of the weakly nonlinear evolution of a triad of waves, each slightly amplified on a linear basis, that are superimposed on a tanh y mixing layer. The triad consists of a plane wave and a pair of oblique modes that act as a subharmonic of order 1/2. The oblique modes are inclined at approximately ±60°. to the mean flow direction and because the resonance conditions are satisfied exactly the analysis is entirely self-consistent as an asymptotic theory. The nonlinearity first occurs within the critical layer and the initial interaction is of the parametric resonance type. This produces faster than exponential growth of the oblique waves, behaviour observed recently in the experiments of Corke & Kusek (1993). The critical-layer dynamics lead subsequently to coupled integro-differential equations governing the amplitude evolution and, as first shown in related work by Goldstein & Lee (1992) on boundary layers in an adverse pressure gradient, these equations develop singularities in a finite time.

Compressible Reynolds-Averaged Navier-Stokes Analysis of Wind Turbine Turbulent Flows Using a Fully-Coupled Low-Speed Preconditioned Multigrid Solver

2014 ◽  
Author(s):  
M. S. Campobasso ◽  
M. Yan ◽  
J. Drofelnik ◽  
A. Piskopakis ◽  
M. Caboni
Keyword(s):  
Turbulence Model ◽  
Static Pressure ◽  
Navier Stokes ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Noise Propagation ◽  
Low Speed ◽  
Analysis And Design ◽  
Reynolds Averaged Navier Stokes ◽  
Fully Coupled

The high-fidelity aeromechanical analysis and design of multi-megawatt horizontal axis wind turbines can be performed by means of Reynolds-averaged Navier-Stokes codes. The compressible or incompressible formulation of the fluid equations can be used. One of the objectives of the paper is to quantify the effects of flow compressibility on the aerodynamics of large turbine rotors with particular attention to the tip region of a 82 m rotor blade featuring a relative Mach number of about 0.3 near rated conditions. Noticeable local static pressure variations due to compressibility are observed. Such variations point to the better suitability of compressible solvers for turbine aerodynamics, not only when the solver is used for direct aeroacoustic simulation of the near field noise propagation, but also when it is used to provide the surface static pressure to be used as input for acoustic analogy noise propagation codes. On the numerical side, a novel numerical approach to low-speed preconditioning of the mean flow and turbulence model equations for the fully coupled integration of the flow equations coupled to a two-equation turbulence model is presented and implemented in a compressible Navier-Stokes research code for the steady and yawed wind-induced time-dependent flows analyzed herein.

scholarly journals Route to Chaos in the Fluidic Pinball

2018 ◽  
Author(s):  
Nan Deng ◽  
Luc R. Pastur ◽  
Marek Morzyński ◽  
Bernd R. Noack
Keyword(s):  
Machine Learning ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Flow Field ◽  
Pitchfork Bifurcation ◽  
Mean Flow ◽  
Flow Configuration ◽  
The Mean ◽  
Route To Chaos ◽  
Fluid Flow Control

The fluidic pinball has been recently proposed as an attractive and effective flow configuration for exploring machine learning fluid flow control. In this contribution, we focus on the route to chaos in this system without actuation, as the Reynolds number is smoothly increased. It was found to be of the Newhouse-Ruelle-Takens kind, with a secondary pitchfork bifurcation that breaks the symmetry of the mean flow field on the route to quasi-periodicity.

scholarly journals Turbulence structure and interaction with steep breaking waves

2011 ◽  
Vol 674 ◽  
pp. 522-577 ◽  
Author(s):  
DJAMEL LAKEHAL ◽  
PETAR LIOVIC
Keyword(s):  
Fluid Flow ◽  
Water Waves ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Small Scale ◽  
Breaking Wave ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Scale Breaking ◽  
The Mean

Large-eddy and interface simulation using an interface tracking-based multi-fluid flow solver is conducted to investigate the breaking of steep water waves on a beach of constant bed slope. The present investigation focuses mainly on the ‘weak plunger’ breaking wave type and provides a detailed analysis of the two-way interaction between the mean fluid flow and the sub-modal motions, encompassing wave dynamics and turbulence. The flow is analysed from two points of views: mean to sub-modal exchange, and wave to turbulence interaction within the sub-modal range. Wave growth and propagation are due to energy transfer from the mean flow to the waves, and transport of mean momentum by these waves. The vigorous downwelling–upwelling patterns developing at the head and tail of each breaker are shown to generate both negative- and positive-signed energy exchange contributions in the thin sublayer underneath the water surface. The details of these exchange mechanisms are thoroughly discussed in this paper, together with the interplay between three-dimensional small-scale breaking associated with turbulence and the dominant two-dimensional wave motion. A conditional zonal analysis is proposed for the first time to understand the transient mechanisms of turbulent kinetic energy production, decay, diffusion and transport and their dependence and/or impact on surface wrinkling over the entire breaking process. The simulations provide a thorough picture of air–liquid coherent structures that develop over the breaking process, and link them to the transient mechanisms responsible for their local incidence.

scholarly journals Effect of T-shaped spur dike length on mean flow characteristics along a 180-degree sharp bend

2021 ◽  
Vol 69 (1) ◽  
pp. 98-107
Author(s):  
Maryam Akbari ◽  
Mohammad Vaghefi ◽  
Yee-Meng Chiew
Keyword(s):  
Secondary Flow ◽  
Flow Pattern ◽  
Maximum Velocity ◽  
Primary Objective ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Strength ◽  
Spur Dike ◽  
Sharp Bend ◽  
The Mean

AbstractAn open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study’s primary objective is to compare variations of the mean flow pattern along a 180-degree bend with a variety of T-shaped spur dike lengths. In order to do so, parameters such as streamlines, the maximum velocity distribution, and the secondary flow strength under the influence of three T-shaped spur dike lengths will be analyzed and then compared with the case where no spur dikes are implemented. The results show that with the spur dike placed at the bend apex, the mean secondary flow strength at that range increases by approximately 2.5 times. In addition, a 67% increase in the length of the wing and web of the spur dike leads to a 27% growth in the mean secondary flow strength along the bend.

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