scholarly journals Turbulence structures in non-uniform flows

2008 ◽  
Vol 31 (10) ◽  
pp. 1344-1351 ◽  
Author(s):  
Shu-Qing Yang ◽  
Alex T. Chow
Keyword(s):  
Turbulence Structures

Kinematic and Dynamic Parameters of a Liquid-Solid Pipe Flow Using DPIV∕Accelerometry

2007 ◽  
Vol 129 (11) ◽  
pp. 1415-1421 ◽  
Author(s):  
Joseph Borowsky ◽  
Timothy Wei
Keyword(s):  
Pipe Flow ◽  
Solid Phase ◽  
Fluid Phase ◽  
Central Moment ◽  
Steady Flows ◽  
Dynamic Parameters ◽  
Two Phase ◽  
Turbulence Structures ◽  
Two Phases ◽  
Flat Profile

An experimental investigation of a two-phase pipe flow was undertaken to study kinematic and dynamic parameters of the fluid and solid phases. To accomplish this, a two-color digital particle image velocimetry and accelerometry (DPIV∕DPIA) methodology was used to measure velocity and acceleration fields of the fluid phase and solid phase simultaneously. The simultaneous, two-color DPIV∕DPIA measurements provided information on the changing characteristics of two-phase flow kinematic and dynamic quantities. Analysis of kinematic terms indicated that turbulence was suppressed due to the presence of the solid phase. Dynamic considerations focused on the second and third central moments of temporal acceleration for both phases. For the condition studied, the distribution across the tube of the second central moment of acceleration indicated a higher value for the solid phase than the fluid phase; both phases had increased values near the wall. The third central moment statistic of acceleration showed a variation between the two phases with the fluid phase having an oscillatory-type profile across the tube and the solid phase having a fairly flat profile. The differences in second and third central moment profiles between the two phases are attributed to the inertia of each particle type and its response to turbulence structures. Analysis of acceleration statistics provides another approach to characterize flow fields and gives some insight into the flow structures, even for steady flows.

Comparison of LES of Steady Transitional Flow in an Idealized Stenosed Axisymmetric Artery Model With a RANS Transitional Model

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
F. P. P. Tan ◽  
N. B. Wood ◽  
G. Tabor ◽  
X. Y. Xu
Keyword(s):  
Experimental Data ◽  
Turbulence Intensity ◽  
Eddy Viscosity ◽  
Flow Analysis ◽  
Wall Turbulence ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Accurate Treatment

In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y+ less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y+ less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS in replicating the axisymmetric experimental results, although inflow conditions, which are subject to caveats, may have differed. For the eccentric stenosis, LES with Smagorinsky coefficient of 0.13 gave the closest agreement with DNS despite the known shortcomings of fixed coefficients. The relaminarization as the flow escaped the influence of the stenosis was amply demonstrated in the simulations, graphically so in the case of LES.

Large Eddy Simulation of the Wake Behind a Turning Ship

2002 ◽  
Author(s):  
Ibrahim Yavuz ◽  
Zeynep N. Cehreli ◽  
Ismail B. Celik ◽  
Shaoping Shi
Keyword(s):  
Large Eddy Simulation ◽  
Sensitivity Study ◽  
West Virginia University ◽  
Vortical Structures ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Flow Generation ◽  
Large Eddy ◽  
Unsteady Inflow ◽  
Random Flow

This study examines the dynamics of turbulent flow in the wake of a turning ship using the large eddy simulation (LES) technique. LES is applied in conjunction with a random flow generation (RFG) technique originally developed at West Virginia University to provide unsteady inflow boundary conditions. As the ship is turning, the effects of the Coriolis and centrifugal forces on vortical structures are included. The effects of the Coriolis force on the flow-field are assessed and a grid sensitivity study is performed. The predicted turbulence structures are analyzed and compared with the wake of a non-turning ship.

Turbulence structures in flows over a submerged weir

2020 ◽  
pp. 178-184
Author(s):  
Chaewoong Ban ◽  
Sung-Uk Choi
Keyword(s):  
Turbulence Structures

scholarly journals PIV Analysis of Cavitating Flow Behind Square Multi-Orifice Plates

10.29007/fhdg ◽  
2018 ◽  
Author(s):  
Zhiyong Dong ◽  
Wenqian Zhao
Keyword(s):  
Conventional Technique ◽  
Disinfection Byproducts ◽  
Cavitating Flow ◽  
Water Disinfection ◽  
Hydrodynamic Cavitation ◽  
Pathogenic Microorganisms ◽  
Turbulence Structures ◽  
Image Velocimetry ◽  
Piv Analysis ◽  
Mutagenic Effects

Currently, in water supply engineering, the conventional technique of disinfection by chlorination is used to kill pathogenic microorganisms in raw water. However, chlorine reacts with organic compounds in water and generates disinfection byproducts (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) etc. These byproducts are of carcinogenic, teratogenic and mutagenic effects, which seriously threaten human health. Hydrodynamic cavitation is a novel technique of drinking water disinfection without DBPs. Turbulence structures of cavitating flow were observed by the Particle Image Velocimetry (PIV) technique in a self-developed hydrodynamic cavitation device due to square multi- orifice plates, including effects of orifice number and orifice layout on velocity distribution, turbulence intensity and Reynolds stress, which aimed at uncovering mechanism of killing pathogenic microorganisms by hydrodynamic cavitation.

Time-Resolved PIV Measurements of Non-Reacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control

2014 ◽  
Author(s):  
Joseph Meadows ◽  
Ajay K. Agrawal
Keyword(s):  
Flow Field ◽  
Direct Injection ◽  
Combustion Noise ◽  
Reacting Flow ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Turbulence Structures ◽  
Precessing Vortex Core ◽  
Acoustic Control ◽  
Acoustic Instabilities

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry to measure the turbulent flow field in a non-reacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the Proper Orthogonal Decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core, which would ultimately affect the acoustic behavior in a favorable manner.

The Four Stage Development of Starting Turbulent Buoyant Plumes

2021 ◽  
Author(s):  
Thanh Tran ◽  
Kiran Bhaganagar
Keyword(s):  
Large Scale ◽  
Wildland Fire ◽  
Forecast Model ◽  
Vortex Identification ◽  
Buoyant Plumes ◽  
Volcanic Plumes ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Stage Development ◽  
High Reynolds

Abstract Turbulent heated and buoyant plumes have important applications in the atmosphere such as wildland fire plumes, volcanic plumes, and chemical plumes. The purpose of the study is to analyze the turbulence structures, and to understand the stages of the development of the starting turbulent plumes. For this purpose, data generated from an in-house Weather Research Forecast model coupled with Large-eddy simulation (WRF-bLES) with two-way feedback between the buoyant plume and the atmosphere developed has been used. The release of both dense gases (Co2, So2) and, buoyant gases (He, NH3, heated air) from a circular source at the bottom of the domain have been investigated. The simulations of the axisymmetric plume were performed at a high Reynolds number of 108. Vortex Identification methods were used to extract the Coherent structures and the large-scale features of the flow. The results have demonstrated that both the dense and the buoyant heated plumes with different initial characters exhibited universal characteristics and the development of the starting plumes occurred in four characteristic stages: Stage 1 is the plume acceleration stage, followed by stage 2 which corresponds to the formation of the head of the plume which grows spatially. Stage 3 is when the plume head is fully formed and the flow transitions to quasi-steady-state behavior. The final stage is the fully developed plume. The identification of the four-stage development of the plume in the neutral environment is the first step in studying the turbulent heated and buoyant plumes development in order to characterize realistic plumes and to quantify the extent of mixing at each of these stages. This work has important contributions to fundamental fluid dynamics of buoyant plumes with implications on forecasting the plume trajectory of smoke, wildland fire, and volcanic plumes.

Sign in / Sign up

Export Citation Format

Share Document