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

Rao, Anil; Minelli, Guglielmo; Zhang, Jie; Basara, Branislav; Krajnović, Siniša

doi:10.1016/j.jweia.2018.09.019

Cited by 21 publications

(10 citation statements)

References 115 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This indicates the non-existence of the front separation bubble for the coarse wall-model simulation, a theme prevalent throughout section 3.2. spanwise directions for the two cases. In line with observations found in the computational studies of Lucas et al [13], Rao et al [17], Rao et al [18] and Dalla Longa et al [19], the presented simulations resolve an instantaneously asymmetric wake that maintains its time-averaged toroidal structure and is simply tilted to a preferred side. This opposes the experimental observations made by Evrard et al [10], Perry et al [11] and Pavia et al [12], who, based on two-dimensional PIV planes, proposed that the instantaneously asymmetric wake is composed of single or multiple horseshoe vortices that, in the long time-average, coalesce into the closed toroidal structure characteristic of the time-averaged wake.…”

Section: Detection Of Wake Bimodalitysupporting

confidence: 89%

“…Most currently published work on understanding the turbulent asymmetric wake and its bimodal dynamics is experimental. It seems that only Pasquetti and Peres [16], Lucas et al [13], Rao et al [17] and Rao et al [18] have been able to naturally resolve the turbulent wake's asymmetry numerically. More importantly, Dalla Longa et al [19] present the only computational study that features bimodality and this was accomplished using fully block-structured baseline mesh sizes of 56.6 million cells suggesting that highly resolved simulations are needed to capture the dynamics responsible for forcing a bimodal switch.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simulation of wake bimodality behind squareback bluff-bodies using LES

Hesse

Morgans

2021

Preprint

View full text Add to dashboard Cite

A large eddy simulation (LES) study of the flow around a 1/4 scale squareback Ahmed body at Re H = 33, 333 is presented. The study consists of both wall-resolved (WRLES) and wall-modelled (WMLES) simulations, and investigates the bimodal switching of the wake between different horizontal positions. Within a non-dimensional time-window of 1050 convective flow units, both WR-LES and WMLES simulations, for which only the near-wall region of the turbulent boundary layer is treated in a Reynolds-averaged sense, are able to capture horizontal (spanwise) shifts in the wake's cross-stream orientation. Equilibrium wall-models in the form of Spalding's law and the log-law of the wall are successfully used. Once these wall-models are, however, applied to a very coarse nearwall WMLES mesh, in which a portion of the turbulent boundary layer's outer region dynamics is treated in a Reynolds-averaged manner as well, large-scale horizontal shifts in the wake's orientation are no longer detected. This suggests larger-scale flow structures found within the turbulent boundary layer's outer domain are responsible for generating the critical amount of flow intermittency needed to trigger a bimodal switching event. By looking at mean flow structures, instantaneous flow features and their associated turbulent kinetic energy (TKE) production, it becomes clear that the front separation bubbles just aft of the Ahmed body nose generate high levels of TKE through the shedding of large hairpin vortices. Only in the reference WRLES and (relatively) fine near-wall

show abstract

Section: Detection Of Wake Bimodalitysupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Simulation of wake bimodality behind squareback bluff-bodies using LES

Hesse

Morgans

2021

Preprint

View full text Add to dashboard Cite

show abstract

“…From now on, the state of the wake is defined as negative (N), positive (P) or transient symmetric (TS), where respectively y * p < y * p,N , y * p > y * p,P and y * p,N < y * p < y * p,P . The TS state existence has also been recently reported in the wake of similar squareback bluff bodies: through a cluster-based approach (Kaiser et al, 2014), a POD analysis (Pavia et al, 2017) and partially-averaged NavierStokes simulations (Rao et al, 2018).…”

Section: Transient Symmetric Statementioning

confidence: 74%

Adaptive control of the dynamics of a fully turbulent bimodal wake using real-time PIV

et al. 2019

View full text Add to dashboard Cite

In this study we focus on the control of the dynamics of 3D turbulent wake downstream a square-back Ahmed body (Re H = 3.9 × 10 5 ). The peculiar dynamics of such a wake are first characterized through the trajectories of the pressure barycenter over the rear part of the model as well as the recirculation barycenter in the wake. In particular it is shown that these dynamics allow the definition of three different states: the two so-called reflectional symmetry-breaking (RSB) modes and the transient symmetric (TS) mode. It was shown recently that the time-fluctuations of the pressure barycenter could be characterized as a weak chaotic system with a well-defined attractor (Varon et al, 2017). We show that the dynamics of the bimodal wake can then be forced into a stable asymmetric or symmetric state in open loop control, using tangential continuous or pulsed blowing in three different regions along the upper edge of the rear part of the model. Finally, a simple closed-loop opposition control, based on real-time identification of the wake barycenter in the PIV fields, is used to force the chaotic dynamics of the wake into a regular oscillatory motion at a well-controlled frequency. Depending on the actuation parameters, the wake dynamics can also be switched from bimodal to a new multimodal behavior. We show that this new mode also exhibits a peculiar dynamics with an up-down instead of left-right chaotic oscillations. Interestingly, the recirculation area (size of the recirculation bubble) is much

show abstract

“…Simulations which accurately capture the wake unsteadiness at high Reynolds number, and which furthermore extend over the large time scales of bi-modal switching, are very costly. Unsteady simulations of simplified bluff body flows have been performed using partially averaged Navier-Stokes (PANS), simulations (Mirzaei, Krajnović & Basara 2015;Rao et al 2018a), unsteady Reynolds-averaged Navier-Stokes simulations (Khalighi, Chen & Iaccarino 2012), detached eddy simulations and large eddy simulations (Krajnović & Davidson 2003;Serre et al 2013;Aljure et al 2014;Östh et al 2014;Rao et al 2018b), some also employing a lattice Boltzmann formulation (Roumeas et al 2009;Lucas et al 2017 The present study achieves what we believe are the first simulations of wake bi-modality, capturing both asymmetric states, for a blunt bluff body. No artificial forcing nor inlet perturbations are applied to trigger bi-modality; the flow develops naturally from a steady inlet velocity condition, with bi-modal switches occurring randomly.…”

mentioning

confidence: 66%

Simulations of the bi-modal wake past three-dimensional blunt bluff bodies

2019

View full text Add to dashboard Cite

The bi-modal behaviour of the turbulent flow past three-dimensional blunt bluff bodies is simulated using wall-resolved large eddy simulations. Bi-modality (also called bi-stability) is a phenomenon that occurs in the wakes of three-dimensional bluff bodies. It manifests as a random displacement of the wake between preferred off-centre locations. Two bluff bodies are considered in this work: a conventional square-back Ahmed body representative of road cars, and a simplified lorry, which is taller than it is wide, with its aspect ratio corresponding to a 15 % European lorry scale model. To our knowledge, this is the first time that the asymmetric bi-modal switching behaviour of the wake, observed experimentally, has been captured in simulations. The resulting unsteady flow fields are then analysed, revealing instantaneous topological changes in the wake experiencing bi-modal switching. The best-resolved case, the simplified lorry geometry, is then studied in greater detail using modal decomposition to gain insights into the energy content and the dominant frequencies of the wake flow structures associated with the asymmetric states. High-frequency snapshots of the switching sequence allow us to propose that large hairpin vortices are responsible for the triggering of the switching.

show abstract

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

Cited by 21 publications

References 115 publications

Simulation of wake bimodality behind squareback bluff-bodies using LES

Simulation of wake bimodality behind squareback bluff-bodies using LES

Adaptive control of the dynamics of a fully turbulent bimodal wake using real-time PIV

Simulations of the bi-modal wake past three-dimensional blunt bluff bodies

Contact Info

Product

Resources

About