Non-symmetric bi-stable flow around the Ahmed body

Meile, Walter; Ladinek, Thomas; Brenn, Günter; Reppenhagen, Aaron; Fuchs, Anton

doi:10.1016/j.ijheatfluidflow.2015.11.002

Cited by 36 publications

(25 citation statements)

References 20 publications

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“…This distribution is caused by the reattached flow on the slant surface and a large longitudinal vortex from the windward edge of the roof and the slant existing above the slant (such flow structures were sketched in Fig. 16b of Meile et al [3]). The longitudinal vortex is also shown in the present numerical result as the vortex (A) in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The wake structure becomes a fully separated flow from the leading edge of the slant. Meile et al [3] reported that the post‐critical Ahmed model with φ = 35° slant shows wake structure transition and bi‐stability of the two kinds of wake state in the crosswind condition at the yaw angle around 12°.…”

Section: Methodsmentioning

confidence: 99%

“…However, some vehicles show a great change in their aerodynamics at a certain yaw angle because their wake flow structure suddenly changes at that yaw angle [3][4][5]. Around such a critical yaw angle, the aerodynamics of the vehicle often show bi-stability [3,6] in which the two wake structures before and after the change are both stable. Additionally, in such a situation, once one stable state appears, the state may continue for a while [5], resulting in a kind of hysteresis.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Active aerodynamics control of simplified vehicle body in a crosswind condition

Nakashima

Yan

Moriuchi

et al. 2020

J. eng.

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In this study, the authors used a steady jet from a slit nozzle to control the bi-stable aerodynamics of a simple vehicle model under crosswind conditions. In general, the aerodynamic coefficients of an automobile change continuously with variations in the relative wind direction (i.e. yaw angle). However, some vehicles show a significant change in their aerodynamics at a certain yaw angle because their wake flow structure changes at that yaw angle. Furthermore, around that critical yaw angle, their aerodynamics sometimes show bi-stability in which both the wake structures before and after the change are stable. The investigated model is the famous simplified model in vehicle aerodynamic research known as the Ahmed model. Its slant angle was set at 32° as a configuration that causes bi-stability at a specific yaw angle range larger than 6°. The active aerodynamic control method was demonstrated in both the model scale wind tunnel test and computational fluid dynamics analysis. The slit jet with 18% of the main flow velocity successfully changed the wake flow structure. This showed that it is possible to improve the aerodynamic characteristics.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Active aerodynamics control of simplified vehicle body in a crosswind condition

Nakashima

Yan

Moriuchi

et al. 2020

J. eng.

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“…In the latter case, it is fundamental to ensure that the boundary layer thickness growing on the floor is small compared to the clearance h. This is usually achieved by either mounting the model on a plate, where the boundary layer origin is fixed, or by providing a suction of the boundary layer. Stationary floor has been employed in several cases in the past (e.g., [8,16,25,30,31]). The mounting solutions can be differentiated as follows: a first solution where the model is connected to the floor through pins that very often correspond to the wheels and a second where a holding strut is located above the model.…”

Section: Wind Tunnel and Modelmentioning

confidence: 99%

Active Flow Control on a Square-Back Road Vehicle

Cerutti

Sardu

Cafiero

et al. 2020

Fluids

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An experimental investigation focused on the manipulation of the wake generated by a square back car model is presented. Four continuously-blowing rectangular slot jets were mounted on the rear face of a 1:10 commercial van model. Load cell measurements evidence drag reduction for different forcing configurations, reaching a maximum of 12% for lateral and bottom jets blowing. The spectral analysis of the pressure fluctuations evidence, for all forced cases, an energy attenuation with respect to the natural case, especially close to the shedding frequency. An energy budget highlighted the most efficient forcing configurations accounting for both the drag reduction and the power required to feed the blowing system. Two main configurations are considered: the maximum drag reduction and the best compromise, yielding 5% drag reduction and a convenient energy balance. Particle Image Velocimetry (pPIV) and stereoscopic PIV (sPIV) experiments were performed allowing the three-dimensional reconstruction of the wake in the three considered configurations. Consistently with static and fluctuating pressure measurements, sPIV results reveal a dramatic change in the wake structure when the jets blow in the maximum drag reduction configuration. Conversely, the best compromise configuration reveals a wake structure similar to the natural one.

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“…To be able to understand this complex flow field, generic bodies as the Ahmed body or the SAE model are often used to study the development and impact of resulting flow structures; for instance in [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%