Separated Flows Around the Rear Window of a Simplified Car Geometry

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Mathieu Rouméas ◽  
Patrick Gilliéron ◽  
Azeddine Kourta
Keyword(s):  
Blunt Body ◽  
Wake Flow ◽  
Complex Flow ◽  
Flow Topology ◽  
Rear Window ◽  
Near Wake ◽  
Longitudinal Vortices ◽  
Simulation Based ◽  
Aerodynamic Performances ◽  
Boltzmann Method

A 3D numerical simulation based on the lattice Boltzmann method is carried out on a simplified car geometry (initially proposed by Ahmed, Ramm, and Falting, 1984, SAE Technical Paper series No. 840300) to analyze and establish a method for controlling the near-wake flow topology of a generic blunt body model. The results indicate the existence of a complex flow topology consisting of transverse and longitudinal vortices emanating from flow separations that occur on the top and the lateral edges of the slanted rear window, respectively. The topology of each structure is detailed and the numerical results are compared with the experimental results in the literature. The results presented in this paper can then be used to develop and parametrize active control solutions conducive to improving the aerodynamic performances of automobile vehicles.

scholarly journals Volumetric 3-component velocimetry measurements of the flow field on the rear window of a generic car model

2012 ◽  
Vol 16 (1) ◽  
pp. 313-320 ◽  
Author(s):  
Nabil Tounsi ◽  
Grégoire Fourrié ◽  
Hamid Oualli ◽  
Laurent Keirsbulck ◽  
Samir Hanchi ◽  
...  
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Separated Flow ◽  
Control Device ◽  
Wake Flow ◽  
Complex Flow ◽  
Rear Window ◽  
Longitudinal Vortices ◽  
Car Model ◽  
The One

Volumetric 3-component Velocimetry measurements are carried out in the flow field around the rear window of a generic car model, the so-called Ahmed body. This particular flow field is known to be highly unsteady, three dimensional and characterized by strong vortices. The volumetric velocity measurements from the present experiments provide the most comprehensive data for this flow field to date. The present study focuses on the wake flow modifications which result from using a simple flow control device, such as the one recently employed by Fourri? et al. [1]. The mean data clearly show the structure of this complex flow and confirm the drag reduction mechanism suggested by Fourri? et al. The results show that strengthening the separated flow leads to weakening the longitudinal vortices and vice versa. The present paper shows that the Volumetric 3-component Velocimetry technique is a powerful tool used for a better understanding of a threedimensional unsteady complex flow such that developing around a bluffbody.

scholarly journals Near-Wake Observations behind Azimuthally Perforated Disks With Varying Hole Layout and Porosity in Smooth Airstreams at High Reynolds Numbers

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Raf Theunissen ◽  
Robert Worboys
Keyword(s):  
Drag Coefficient ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Mean Flow ◽  
Flow Topology ◽  
Near Wake ◽  
Two Component ◽  
High Reynolds ◽  
Component Particle

Porous disks are commonly encountered in experimental studies dealing with flow through objects such as wind turbines, parachutes, and fluidic devices to regulate pressure and/or downstream turbulence. Perforations are typically staggered and only porosity is altered to attain the required disk drag coefficient, despite a documented influence of topology. Few works have reported, however, to which extent the spatial distribution of the circular perforations affect the mean flow pertaining freestanding disks, and for this reason, this work presents a first, more systematic study focused on the effect of azimuthally varying hole topology and porosity on disk drag and near-wake characteristics. An experimental study performed in airflows of negligible freestream turbulence at Reynolds numbers in the order of 105 is reported and related to the existing literature to ensure reliability. Complementary to drag measurements, near-wake surveys have been performed on a variety of perforation layouts using two-component laser Doppler velocimetry and two-component particle image velocimetry. It is shown that minor changes in perforations can cause drastic changes in near-wake flow topology and no perforation layout can be consistently associated with highest drag. Explicit empirical expressions for drag coefficient linked with the simplified topologies considered have been derived.

scholarly journals An LES Investigation of the Near-Wake Flow Topology of a Simplified Heavy Vehicle

2018 ◽  
Vol 102 (2) ◽  
pp. 389-415 ◽  
Author(s):  
Anirudh N. Rao ◽  
Jie Zhang ◽  
Guglielmo Minelli ◽  
Branislav Basara ◽  
Siniša Krajnović
Keyword(s):  
Wake Flow ◽  
Heavy Vehicle ◽  
Flow Topology ◽  
Near Wake

scholarly journals Blunt body near-wake flow field at Mach 6

1996 ◽  
Author(s):  
Thomas Horvath ◽  
Catherine McGinley ◽  
Klaus Hannemann
Keyword(s):  
Flow Field ◽  
Blunt Body ◽  
Wake Flow ◽  
Near Wake

scholarly journals Blunt body near-wake flow field at Mach 10

1997 ◽  
Author(s):  
Thomas Horvath ◽  
Klaus Hannemann ◽  
Thomas Horvath ◽  
Klaus Hannemann
Keyword(s):  
Flow Field ◽  
Blunt Body ◽  
Wake Flow ◽  
Near Wake ◽  
Mach 10

A laser-Doppler velocimetry study of ensemble-averaged characteristics of the turbulent near wake of a square cylinder

1995 ◽  
Vol 304 ◽  
pp. 285-319 ◽  
Author(s):  
D. A. Lyn ◽  
S. Einav ◽  
W. Rodi ◽  
J.-H. Park
Keyword(s):  
Circular Cylinder ◽  
Laser Doppler ◽  
Wake Flow ◽  
Shear Stresses ◽  
Square Cylinder ◽  
Base Region ◽  
Flow Topology ◽  
Near Wake ◽  
Flow Features ◽  
High Reynolds

Ensemble-averaged statistics at constant phase of the turbulent near-wake flow (Reynolds number ≈ 21400 around a square cylinder have been obtained from two-component laser-Doppler measurements. Phase was defined with reference to a signal taken from a pressure sensor located at the midpoint of a cylinder sidewall. The distinction is drawn between the near wake where the shed vortices are ‘mature’ and distinct and a base region where the vortices grow to maturity and are then shed. Differences in length and velocity scales and vortex celerities between the flow around a square cylinder and the more frequently studied flow around a circular cylinder are discussed. Scaling arguments based on the circulation discharged into the near wake are proposed to explain the differences. The relationship between flow topology and turbulence is also considered with vorticity saddles and streamline saddles being distinguished. While general agreement with previous studies of flow around a circular cylinder is found with regard to essential flow features in the near wake, some previously overlooked details are highlighted, e.g. the possibility of high Reynolds shear stresses in regions of peak vorticity, or asymmetries near the streamline saddle. The base region is examined in more detail than in previous studies, and vorticity saddles, zero-vorticity points, and streamline saddles are observed to differ in importance at different stages of the shedding process.

scholarly journals Investigation of the near-wake flow topology of a simplified heavy vehicle using PANS simulations

2018 ◽  
Vol 183 ◽  
pp. 243-272 ◽  
Author(s):  
Anirudh N. Rao ◽  
Guglielmo Minelli ◽  
Jie Zhang ◽  
Branislav Basara ◽  
Siniša Krajnović
Keyword(s):  
Wake Flow ◽  
Heavy Vehicle ◽  
Flow Topology ◽  
Near Wake

Active Control of Vortex Breakdown Phenomenon in the Wake of a Simplified Car Geometry

2006 ◽  
Author(s):  
Benjamin Lehugeur ◽  
Patrick Gillie´ron
Keyword(s):  
Lattice Boltzmann ◽  
Numerical Experiments ◽  
Recirculation Zone ◽  
Static Pressure ◽  
Vortex Breakdown ◽  
Aerodynamic Drag ◽  
Rear Window ◽  
Longitudinal Vortices ◽  
Breakdown Phenomenon ◽  
Boltzmann Method

The breakdown of longitudinal vortices originating from the rear pillars of a simplified geometry of automobile vehicles is obtained with a view to reducing aerodynamic drag. Numerical experiments are conducted on an Ahmed body according to a computation code based on the Lattice Boltzmann Method (LBM). Vortex breakdown is obtained by a continuously and uniformly blowing at the separation line prompting the formation and maintenance of the vortex. The breakdown is characterized by a sudden disintegration of the vortex core and the appearance of a recirculation zone. Numerical results obtained at several blowing velocities reveal the critical impact of the Swirl number on vortex breakdown. Moreover, breaking down the longitudinal vortices induces an increase in the static pressure at the wall of the rear window, which can bring about drag reductions close to 6%.

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