Sensitivity analysis of hybrid methods for the flow around the ahmed body with application to passive control with rounded edges

Delassaux, Francois; Mortazavi, Iraj; Itam, Emmanuelle; Herbert, Vincent; Ribes, Charles

doi:10.1016/j.compfluid.2020.104757

Cited by 19 publications

(13 citation statements)

References 30 publications

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“…Many results in literature reach the same conclusion such as Krajnovic and Davidson in [29]. However, later in [30,31], advantages of hybrid approaches [32,33] such as Delayed Detached Eddy Simulation (DDES) [34], a zonal hybrid LES/RANS method or Partially Averaged Navier-Stokes method (PANS), a dynamic nodal hybrid DNS/RANS approach were discussed [31]. These methods have been developed quite recently and could have been an alternative to classical LES in order to save CPU time.…”

Section: Computational Set-upmentioning

confidence: 77%

Computational Analysis of Actuation Techniques Impact on the Flow Control around the Ahmed Body

Edwige

Gilotte

Mortazavi

2022

Fluids

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Active flow control with jet devices is a promising approach for vehicle aerodynamics control. In this work an extended computational study is performed comparing three different actuation strategies for active flow control around the square back Ahmed body at Reynolds number 500,000 (based on the vehicle height). Numerical simulations are run using a Large Eddy Simulation (LES) approach, well adapted to calculate the unsteady high Reynolds number flow control using periodic jet devices. computations are validated comparing to in-house experiments for uncontrolled and some controlled cases. The novelty of this investigation is mainly related to the in-depth study of the base flow and actuation approaches by an accurate LES method and their comparison to experiments. Here, several simulations are performed to estimate the effect of active controls on the flow topology and the drag reduction. Beside the continuous blowing jet, three periodic actuation techniques including periodic blowing and suction as well as the zero flux synthetic jet devices are explored. The slots are implemented discontinuously in order to achieve a better control efficiency linked to vortex generation. In this framework, spectral analyses on global aerodynamical quantities, rear pressure/drag coefficient behavior examination as well as wake structure investigations are performed in order to compare these jet actuations. As a result, shear layer variations are observed during the blowing phase, but the main flow topology change occurs with suction and synthetic jets. Rear back pressure is therefore substantially increased.

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Section: Computational Set-upmentioning

confidence: 77%

Computational Analysis of Actuation Techniques Impact on the Flow Control around the Ahmed Body

Edwige

Gilotte

Mortazavi

2022

Fluids

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“…These investigations demonstrated that rounding the roof/rear slant connection can effectively alleviate separation on the slanted surface and shift the low-pressure separation bubbles in the near-wake region away from the base, resulting in up to a 16% reduction in drag (Thacker et al 2013;Rossitto et al 2016). Delassaux et al (2021) observed that rounding the roof edges alters the flow topology in the near-wake region, resulting in a 16% reduction in drag. However, rounding of the side edge of the slant surface delays the onset of C-pillar vortices and forms larger recirculation bubbles in the wake region, leading to a 3% increase in drag (Rossitto et al 2016).…”

Section: Introductionmentioning

confidence: 89%

PIV Analysis of Wake Characteristics of Slanted-Back Ahmed Bodies: Effect of Leading-Edge Shape

Sagharichi,

Tachie

2023

Preprint

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This study experimentally investigates turbulent flow separation over a slanted-back Ahmed body with different leading-edge configurations (rounded and square) using the particle image velocimetry (PIV) technique. Reynolds number (based on free-stream velocity and body height) is \({\text{Re}}_{\text{H}}\) = 0.17 × 105. Spatiotemporal flow characteristics, including mean flow, vorticity flux, spatial two-point correlation, reverse flow area, turbulent kinetic energy budget, frequency spectra, and proper orthogonal decomposition (POD) are analyzed. The results reveal a larger recirculation region near the leading edge of the square leading-edge (SL) case, associated with higher vorticity flux compared to the rounded leading-edge (RL) case. Pulsations are observed in the wake region recirculation bubbles through phase-averaging analysis of instantaneous velocity and vorticity. The auto and cross-correlation of reverse flow areas in the SL case exhibit higher temporal correlations in the leading edge and wake region. The analysis of Kelvin-Helmholtz wavelength and frequency spectra indicates a smaller wavelength in the RL case, corresponding to a higher dominant shedding frequency than the SL case. POD reveals the formation of smaller coherent structures with smaller convective velocities, and higher shedding frequency in the wake region of the RL case.

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“…Other advanced turbulence models have also been assessed for the Ahmed body aerodynamics, such as the partially averaged Navier-Stokes, 10 the embedded LES, 11 the scale-adaptive simulation, and the stress-blended eddy simulation. 12 The realistic car geometries are generally complex such that the generation of suitable body-fitted grids is quite cumbersome and timeconsuming, even for this simplified body geometry. Using the immersed boundary method (IBM) on Cartesian grids for complex boundaries became more and more popular over the past few decades, see Refs.…”

Section: Introductionmentioning

confidence: 99%

Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics

et al. 2022

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This paper applies a recently developed immersed boundary-turbulence wall modeling approach to turbulent flows over a generic car geometry, known as the Ahmed body, under massive flow separation, within a lattice Boltzmann solver. Although the immersed boundary method combined with hierarchical Cartesian grid offers high flexibility in automatic grid generation around complex geometries, the near-wall solution is significantly deteriorated compared to the body-fitted simulation, especially when coupled to wall models for turbulent flows at high Reynolds number. Enhanced wall treatments have been proposed in the literature and validated for attached flow configurations. In this work, the Ahmed body with a slant surface of angle 35o is considered where the flow separates massively over the slant surface and the vertical base. The large eddy simulation is performed with a Reynolds stress constraint near-wall. The eddy viscosity is computed dynamically by taking into account the actually resolved Reynolds stresses. It approaches the mixing length eddy viscosity in attached boundary layers and returns to the subgrid eddy viscosity in detached boundary layers. An explicit equilibrium wall model has been also proposed to accelerate the calculation. Comparison with the no-slip boundary condition on the separated surfaces shows that the near-wall treatments with the equilibrium wall model operate reasonably well on both attached and detached boundary layers.

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Sensitivity analysis of hybrid methods for the flow around the ahmed body with application to passive control with rounded edges

Cited by 19 publications

References 30 publications

Computational Analysis of Actuation Techniques Impact on the Flow Control around the Ahmed Body

Computational Analysis of Actuation Techniques Impact on the Flow Control around the Ahmed Body

PIV Analysis of Wake Characteristics of Slanted-Back Ahmed Bodies: Effect of Leading-Edge Shape

Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics

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