Effects of Squish Flow on Tangential Flow and Turbulence in a Diesel Engine

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Yanzhe Sun ◽  
Kai Sun ◽  
Tianyou Wang ◽  
Yufeng Li ◽  
Zhen Lu
Keyword(s):  
Diesel Engine ◽  
Turbulent Flows ◽  
Large Scale ◽  
Radial Flow ◽  
Tangential Component ◽  
Tangential Flow ◽  
Image Velocimetry ◽  
Turbulence Production ◽  
Large Scale Flow ◽  
Main Effects

Emission and fuel consumption in swirl-supported diesel engines strongly depend on the in-cylinder turbulent flows. But the physical effects of squish flow on the tangential flow and turbulence production are still far from well understood. To identify the effects of squish flow, Particle image velocimetry (PIV) experiments are performed in a motored optical diesel engine equipped with different bowls. By comparing and associating the large-scale flow and turbulent kinetic energy (k), the main effects of the squish flow are clarified. The effect of squish flow on the turbulence production in the r−θ plane lies in the axial-asymmetry of the annular distribution of radial flow and the deviation between the ensemble-averaged swirl field and rigid body swirl field. Larger squish flow could promote the swirl center to move to the cylinder axis and reduce the deformation of swirl center, which could decrease the axial-asymmetry of annular distribution of radial flow, further, that results in a lower turbulence production of the shear stress. Moreover, larger squish flow increases the radial fluctuation velocity which makes a similar contribution to k with the tangential component. The understanding of the squish flow and its correlations with tangential flow and turbulence obtained in this study is beneficial to design and optimize the in-cylinder turbulent flow.

scholarly journals Turbulent drag in a rotating frame

2016 ◽  
Vol 794 ◽  
Author(s):  
Antoine Campagne ◽  
Nathanaël Machicoane ◽  
Basile Gallet ◽  
Pierre-Philippe Cortet ◽  
Frédéric Moisy
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulence Theory ◽  
Water Tank ◽  
Wave Interactions ◽  
Turbulent Drag ◽  
Image Velocimetry ◽  
Weak Turbulence Theory ◽  
Large Scale Flow

What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$. We report a dramatic reduction in drag as ${\it\Omega}$ increases, down to values as low as 12 % of the non-rotating drag. At small Rossby number $Ro={\it\omega}/{\it\Omega}$, the decrease in the drag coefficient $K$ follows the approximate scaling law $K\sim Ro$, which is predicted in the framework of nonlinear inertial-wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction instead originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

Experimental Study of Large-Scale Flow Structures in an Aneurysm

2018 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Large Scale ◽  
Flow Structures ◽  
Pump System ◽  
Vortical Structures ◽  
Abnormal Growth ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
The Impact ◽  
Inflow Conditions ◽  
Aneurysm Model

An aneurysm is an abnormal growth in the wall of a weakened blood vessel, and can often be fatal upon rupture. Studies have shown that aneurysm shape and hemodynamics, in conjunction with other parameters, play an important role in growth and rupture. The objective of this study was to investigate the impact of varying inflow conditions on flow structures in an aneurysm. An idealized rigid sidewall aneurysm model was prepared and the Womersley number (α) and Reynolds number (Re) values were varied from 2 to 5 and 50 to 250, respectively. A ViVitro Labs pump system was used for inflow control and Particle Image Velocimetry was used for conducting velocity measurements. The results showed that the primary vortex path varied with an increase in α, while an increase in Re was correlated to the vortex strength and formation of secondary vortical structures. The evolution and decay of vortical structures were also observed to be dependent on α and Re.

Turbulent spots in a channel: large-scale flow and self-sustainability

2013 ◽  
Vol 731 ◽  
Author(s):  
Grégoire Lemoult ◽  
Jean-Luc Aider ◽  
José Eduardo Wesfreid
Keyword(s):  
Large Scale ◽  
Large Time ◽  
Rectangular Channel ◽  
Small Scale ◽  
Turbulent Spot ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Streamwise Streaks ◽  
Large Scale Flow ◽  
Scale Motion

AbstractUsing a large-time-resolved particle image velocimetry field of view, a developing turbulent spot is followed in space and time in a rectangular channel flow for more than 100 advective time units. We show that the flow can be decomposed into a large-scale motion consisting of an asymmetric quadrupole centred on the spot and a small-scale part consisting of streamwise streaks. From the temporal evolution of the energy of the streamwise and spanwise velocity perturbations, it is suggested that a self-sustaining process can occur in a turbulent spot above a given Reynolds number.

Identification and Analysis of Vortical Structures in a Ribbed Channel

2008 ◽  
Author(s):  
Lei Wang ◽  
Mirko Salewski ◽  
Bengt Sunde´n
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Large Scale ◽  
Transport Processes ◽  
Vortical Structures ◽  
Ribbed Channel ◽  
Eddy Simulation ◽  
Separated Shear Layer ◽  
Image Velocimetry ◽  
Flow Features

Vortical motions, usually called sinews and muscles of fluid motions, constitute important features of turbulent flows and form the base for large-scale transport processes. In this study, we present a variety of flow decomposition techniques to identify and analyze the vortical structures in a ribbed channel. To this end, the instantaneous velocity fields are measured by means of a two-dimensional particle image velocimetry (PIV). Firstly, the implementation of Galilean-, Reynolds- and large-eddy simulation (LES) decompositions on the instantaneous flow fields allows one to perceive the coherent vortices embedded in the separated shear layer. In addition, the proper orthogonal decomposition (POD) is employed to extract the underlying flow features out of the fluctuating velocity and vorticity fields, respectively. For velocity-based decomposition, the first two POD modes show that the shear layer is highly unstable and associated with the ‘flapping’ motion. For vorticity-based decomposition, the first two POD modes are characterized by the distinct horizontal bands which manifest the coherent structures in the shear layer. In order to interpret the flow structures in a convenient way, a linear combination of POD modes (reconstruction) is also carried out in the present study. The result shows that a large-scale, pronounced vortex is recognizable in the region downstream of rib.

scholarly journals Experimental Investigation of the Unsteady Stator/Rotor Wake Characteristics Downstream of an Axial Air Turbine

2021 ◽  
Vol 6 (3) ◽  
pp. 22
Author(s):  
Daniel Duda ◽  
Tomáš Jelínek ◽  
Petr Milčák ◽  
Martin Němec ◽  
Václav Uruba ◽  
...  
Keyword(s):  
Cross Sections ◽  
Large Scale ◽  
Field Measurements ◽  
Secondary Flows ◽  
Rotor Blades ◽  
Spatial Correlation Function ◽  
Image Velocimetry ◽  
Air Turbine ◽  
Large Scale Flow ◽  
End Wall

A feasibility study of velocity field measurements using the Particle Image Velocimetry (PIV) method in an axial air turbine model is presented. The wakes past the blades of the rotor wheel were observed using the PIV technique. Data acquisition was synchronized with the shaft rotation; thus, the wakes were phase averaged for statistical analysis. The interaction of the rotor blade wakes with the stator ones was investigated by changing the stator wheel’s angle. The measurement planes were located just behind the rotor blades, covering approximately 3 cm × 3 cm in axial × tangential directions. The spatial correlation function suggests that the resolution used is sufficient for the large-scale flow-patterns only, but not for the small ones. The scales of fluctuations correspond to the shear layer thickness at the mid-span plane but, close to the end-wall, they contain larger structures caused by the secondary flows. The length-scales of the fluctuations under off-design conditions display a dependence on the area of the stator and rotor wakes cross-sections, which, in turn, depend on their angle. The obtained experimental data are to be used for the validation of mathematical simulation results in the future.

scholarly journals Visualizing large-scale flow using synthetic aperture PIV

2019 ◽  
Vol 61 (1) ◽  
Author(s):  
Josje van Houwelingen ◽  
Ad P. C. Holten ◽  
Herman J. H. Clercx ◽  
Rudie P. J. Kunnen ◽  
Jaap Molenaar ◽  
...  
Keyword(s):  
Large Scale ◽  
Particle Image ◽  
Synthetic Aperture ◽  
Vortex Rings ◽  
Two Dimensional ◽  
Vorticity Field ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
Small Bubbles ◽  
Proof Of Principle

Abstract We discuss the application of synthetic aperture particle image velocimetry for measuring the flow around human swimmers using small bubbles as tracer. We quantify the two-dimensional projection of the velocity field in planes perpendicular to the viewing direction of an array of six cameras. With help of simulations, modelled after the experiment, we address questions about depth selectivity and occlusion in dense bubble fields. Using vortex rings in the swimming pool, we provide a proof of principle of the method. It is further illustrated by the vorticity field produced by a human swimmer. Graphic abstract

Numerical modelling of turbulent flow in a combustion tunnel

1982 ◽  
Vol 304 (1484) ◽  
pp. 303-325 ◽  
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
High Speed ◽  
Large Scale ◽  
Numerical Technique ◽  
Vortex Method ◽  
Reacting Flow ◽  
Exothermic Process ◽  
Schlieren Photography ◽  
Large Scale Flow

A numerical technique is presented for the analysis of turbulent flow associated with combustion. The technique uses Chorin’s random vortex method (r.v.m .), an algorithm capable of tracing the action of elementary turbulent eddies and their cumulative effects without imposing any restriction upon their motion. In the past, the r.v.m . has been used with success to treat non-reacting turbulent flows, revealing in particular the mechanics of large-scale flow patterns, the so-called coherent structures. Introduced here is a flame propagation algorithm , also developed by Chorin, in conjunction with volume sources modelling the mechanical effects of the exothermic process of combustion. As an illustration of its use, the technique is applied to flow in a combustion tunnel w here the flame is stabilized by a back-facing step. Solutions for both non-reacting and reacting flow fields are obtained. Although these solutions are restricted by a set of far-reaching idealizations, they nonetheless mimic quite satisfactorily the essential features of turbulent combustion in a lean propane—air mixture that were observed in the laboratory by means of high speed schlieren photography.

scholarly journals Experimental Study by Optical and Statistical Methods of Large-Scale Velocity Fluctuations in the Flow Past a Cylinder

2019 ◽  
Vol 14 (3) ◽  
pp. 5-14
Author(s):  
S. S. Abdurakipov ◽  
K. G. Dobroselsky
Keyword(s):  
Experimental Study ◽  
Turbulent Flows ◽  
Large Scale ◽  
Particle Image ◽  
Velocity Fields ◽  
Velocity Fluctuations ◽  
Flow Past ◽  
Image Velocimetry ◽  
Flow Past A Cylinder ◽  
Proper Orthogonal

Using an optical method for measuring the velocity fields Particle Image Velocimetry (PIV) and a statistical method for analyzing coherent structures in turbulent flows Proper Orthogonal Decomposition (POD), an experimental study of the spatial structure of large-scale velocity fluctuations in the precavitational and cavitational flow past a circular cylinder with a Reynolds number of 280 000 was carried out.

Turbulent Flows Over Forward Facing Steps With Surface Roughness

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Weijie Shao ◽  
Martin Agelin-Chaab
Keyword(s):  
Surface Roughness ◽  
Turbulent Flows ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Step Height ◽  
Mean Velocity ◽  
Surface Conditions ◽  
Large Scale Structures ◽  
Image Velocimetry ◽  
Proper Orthogonal

This paper reports an investigation of the effects of surface conditions of forward-facing steps (FFS) on turbulent flows. Three surface conditions including one smooth step and two rough step surfaces created using sandpapers were studied. A particle image velocimetry (PIV) technique was used to conduct velocity measurements at several locations downstream, and the statistics up to 60 step heights are reported. The step height was maintained at 6 mm, and three Reynolds numbers of Reh = 1600, 3200, and 4800, where Reh is based on the step height and freestream mean velocity, were studied. The results indicate that the reattachment length of a FFS increases with Reynolds number but decreases with increasing surface roughness. The proper orthogonal decomposition (POD) results showed the step roughness affects even the large-scale structures.

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