Assessment of LES, IDDES and RANS approaches for prediction of wakes behind notchback road vehicles

He, Kan; Minelli, Guglielmo; Wang, Jiabin; Gao, Guangjun; Krajnović, Siniša

doi:10.1016/j.jweia.2021.104737

Cited by 32 publications

(4 citation statements)

References 44 publications

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“…The Improved Delayed Detached Eddy Simulation (IDDES) approach, which has been validated to capture bi-stability (Fan et al, 2020;Kang et al, 2021;and He et al, 2021b), is used in the current study. As a hybrid modeling approach, the basic principle of IDDES is to use the RANS resolution in the boundary layer to save the near-wall resolving cost while retaining the fidelity of LES in the flow separated region.…”

Section: B Numerical Methods and Mesh Constructionmentioning

confidence: 99%

Comparison of flow characteristics behind squareback bluff-bodies with and without wheels

et al. 2023

Physics of Fluids

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The wake dynamics of two referenced variations of the squareback Windsor model with and without wheels are numerically studied by performing Improved Delayed Detached Eddy Simulation (IDDES). Numerical assessments are validated against publicly available experimental data. The focus of this study is on the wake states influenced by the wheels and the thick oncoming floor boundary layer. Results show that the addition of the wheels significantly changes the aerodynamic forces, the underbody flow, and the wake topology. The wake bi-stability is also enhanced with wheels in place due to the increased curvature of lateral shear layers in the near wake. However, the bi-stable behavior is largely suppressed when immersed in a thick boundary layer. These alterations depend on the degree of interaction between the wake recirculation and the bottom flow, and such degree is strongly affected by the underbody flow momentum. The evolution of low-order flow organizations and complementary spectral analysis highlight the differences in the coherent dynamics of the wake. The finding of the present work suggests that the wake bi-stability behind the squareback body can exist not only for a simplified geometry but also for a more realistic car with wheels in real-world upstream conditions.

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Section: B Numerical Methods and Mesh Constructionmentioning

confidence: 99%

Comparison of flow characteristics behind squareback bluff-bodies with and without wheels

et al. 2023

Physics of Fluids

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“…, where D i are the computational cell sizes in three coordinate directions. The wall-adapting local eddy-viscosity (WALE) model proposed by Nicoud and Ducros (1999), which has been successfully applied to predict wakes of the hatchback Ahmed body (Krajnovi c and Davidson, 2005;Aljure et al, 2014), and symmetrybreaking modes behind the notchback Ahmed body (He et al, 2021b;2021c), is used in this work. This SGS model is based on the square of the velocity gradient tensor and accounts for the effects of the strain and rotation rates.…”

Section: B Numerical Methodsmentioning

confidence: 99%

“…The numerical accuracy of the studied flow established by the grid-independence examination has been presented in the previously published work by the same author (He et al, 2021c). In the present work, the mesh resolution is the same as the medium mesh used in He et al (2021c). The number of cells and spatial resolutions is presented in Table I.…”

Section: Streamwise Resolutionmentioning

confidence: 99%

“…Considering the wake behind the notchback configuration involving the interaction of separations and reattachment, the wake asymmetry formed behind the notchback Ahmed body (Sims-Williams et al, 2011) is selected as the studied flow. Performing LES to predict the bistable wake behind the squareback ( € Osth et al, 2014;Evstafyeva et al, 2017;Lucas et al, 2017;Dalla Longa et al, 2019) and the notchback (He et al, 2021a;2021b;2021c). Ahmed bodies has proved to be successful due to its possibility to resolve the highly turbulent flow.…”

Section: Introductionmentioning

confidence: 99%

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Blockage influence on bi-stable flows of a notchback bluff body

Minelli

et al. 2021

Physics of Fluids

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The expected flow asymmetry behind a three-dimensional notchback Ahmed body is numerically investigated using large-eddy simulations with different blockage ratios of 0%, 5%, 10%, and 20%. The focus of the study is on the natural bi-stable flow influenced by the blockage ratio. Although the wake asymmetry can be observed under the blockage ratio within 0% À 10%, the significant blockage influence on the sensitive bi-stability is indicated by the wake structures, pressure gradients, and wake dynamics achieved with the proper orthogonal decomposition. The higher blockage ratio increases the turbulence kinetic energy, velocity, and negative pressure in the near-wake region, resulting in the decrease in the asymmetry degree. The consistency of the asymmetric wake is found with blockage ratios between 0% and 5%. However, a 20% blockage ratio symmetrizes the bi-stable wake. Several existing drag corrections for the blockage influence are discussed. The wind tunnel experiment verifies the bi-stable flow with low blockage ratios and the wake symmetrization with a 20% blockage ratio.

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Flow Topology of the Bi-Stable Wake States for the DrivAer Fastback Model

Aultman,

Duan

2024

Flow Turbulence Combust

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For this work, conditional averaging and Proper Orthogonal Decomposition (POD) were used to analyze the salient three-dimensional structures in the wake of a DrivAer fastback model with smooth underbody. Conditional averaging revealed that the bi-stable structure of the wake consists of a ring-like structure with three vortex legs, which includes a vortex pair on the side associated with the bi-stability and one on the opposite side associated with the wheel vortex. POD revealed the entrainment of low-momentum fluid from the wheel wake into the vortex pair leads to an induced spanwise crossflow which drives a feedback loop for the bi-stability. The resultant bi-stable structure was dependent on the state of the wheels. With stationary wheels, the feedback mechanism is enhanced, leading to higher spanwise crossflow that breaks the ring-like vortex. A different structure was observed when the wheels rotate, wherein the ring-like structure is unbroken and pierced by the vortex pair. The feedback mechanism and resultant vortex structure are similar to those found in simplified square-back models. Given the similarity in bi-stability between realistic and simplified vehicles, the suppression of the bi-stability in realistic vehicles could initially be based on the same mechanism as that for simplified square-back models.

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Assessment of LES, IDDES and RANS approaches for prediction of wakes behind notchback road vehicles

Cited by 32 publications

References 44 publications

Comparison of flow characteristics behind squareback bluff-bodies with and without wheels

Comparison of flow characteristics behind squareback bluff-bodies with and without wheels

Blockage influence on bi-stable flows of a notchback bluff body

Flow Topology of the Bi-Stable Wake States for the DrivAer Fastback Model

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