Control of the Reattachment Length of a Transonic 2D Backward-Facing Step Flow

Bolgar, Istvan; Scharnowski, Sven; Kähler, Christian J.

doi:10.1007/978-3-319-30602-5_30

Cited by 13 publications

(11 citation statements)

References 17 publications

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“…Such lobed mixers are particularly popular in the study of fuel injectors, as well as core-bypass mixing for jet engine noise reduction (Waitz et al 1997;Depuru Mohan et al 2015;Smith et al 1997;Mao et al 2006Mao et al , 2009McCormick and Bennett 1994;Yu and Yip 1997). Other applications have included base pressure drag reduction for projectilelike bluff bodies (Howard and Goodman 1985;Paterson et al 1989) and more recently, modifying the reattachment length within transonic and supersonic flows (Bolgar et al 2016;Schreyer and Taskin 2018).…”

Section: Fig 1 Schematic Of a Lobed Mixermentioning

confidence: 99%

Application of Lobed Mixers to Reduce Drag of Boat-Tailed Ground Vehicles

Rejniak¹,

Gatto²

2019

JAFM

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Minimising the aerodynamic drag of commercial vehicles is important economically and ecologically. This work demonstrates the effective use of lobed-mixing geometries, traditionally used to enhance flow mixing, as a viable, passive flow control method for reducing base pressure drag of boat-tailed ground vehicles. Experiments were performed on a 1/24 th-scale Heavy Goods Vehicle representative model at a Reynolds number of 2.3 × 10 5 with force and hot-wire anemometry measurements used to quantify drag and wake characteristics. Tests on a baseline (no boat-tail), an unaltered boat-tail, and lobed-mixing configurations with varying pitch and height were compared. Overall, the baseline and unaltered boat-tail exhibited good correlation to previous results. This provided confidence in the methodology adopted. Results using lobed mixers showed up to a 10.2% drag reduction with the added vorticity produced acting to fundamentally shift the nature of the wake. This is manifested principally through the generation of counter-rotating vortical structures which enhance crosswise flow entrainment into the base wake. This action is observed to limit flow entrainment towards the ground leading to a higher wake and a characteristic 'waist'. Enhanced mixing is also demonstrated. Overall, results suggest the suitability of lobed mixers as an effective means for drag reduction of boat-tailed ground vehicles.

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Section: Fig 1 Schematic Of a Lobed Mixermentioning

confidence: 99%

Application of Lobed Mixers to Reduce Drag of Boat-Tailed Ground Vehicles

Rejniak¹,

Gatto²

2019

JAFM

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“…Due to the great need for means to stabilize and reduce the reattachment length to reduce dynamic loads on the launcher, we currently investigate the influence of a convoluted trailing edge (lobes) on the wake of a generic space-launcher model in supersonic flow (see Figure 13), and analyze the techniques potential to control the separation length and dynamics. Such passive vortex generators are of particular interest [18], both due to promising results on two-dimensional backward-facing step geometries [17,19], and their simplicity and robustness [18]. Kähler et al [17,19] investigated different lobe geometries on a 2D backward-facing step in transonic flow.…”

Section: Discussionmentioning

confidence: 99%

“…Such passive vortex generators are of particular interest [18], both due to promising results on two-dimensional backward-facing step geometries [17,19], and their simplicity and robustness [18]. Kähler et al [17,19] investigated different lobe geometries on a 2D backward-facing step in transonic flow. The lobes introduce counterrotating streamwise vortices that increase turbulent mixing and create a highly threedimensional flow field with a spanwise component [17].…”

Section: Discussionmentioning

confidence: 99%

“…Kähler et al [17,19] investigated different lobe geometries on a 2D backward-facing step in transonic flow. The lobes introduce counterrotating streamwise vortices that increase turbulent mixing and create a highly threedimensional flow field with a spanwise component [17]. Behind lobe peaks, the separation is locally rather strong, but the overall separation length is significantly reduced, and the dynamic motion of the reattachment location is stabilized [17,19].…”

Section: Discussionmentioning

confidence: 99%

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Flow structure and unsteadiness in the supersonic wake of a generic space launcher

Schreyer

Stephan

Radespiel

2016

54th AIAA Aerospace Sciences Meeting

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The wake flow of a generic axisymmetric space-launcher model with and without propulsive jet is investigated. Measurements are performed at Mach 2.9 and a Reynolds number Re D = 1.3 • 10 6 based on model diameter D, and the nozzle exit velocity of the jet is at Mach 2.5. Velocity measurements in the wake flow by means of Particle Image Velocimetry and mean and unsteady wall-pressure measurements on the main-body base are performed simultaneously. This way, the evolution of the wake flow was observed along with its spectral content. In this paper, the mean flow topology and turbulence behavior of the wake is described based on PIV measurements, and the influence of the afterexpanding jet plume is discussed. For the case without propulsive jet, a large separated zone is forming downstream of the main body shoulder and the flow is reattaching downstream on the nozzle fairing. Under the influence of the jet plume, the separated region is increased and reattachment does not occur anymore. The flow is displaced away from the wall. The jet plume appears to have a stabilizing effect on the wake flow. The development of the shear layer and the magnitude of the turbulent intensities are damped, which we showed with the axial and radial components of the turbulent velocity fluctuations, as well the Reynolds shear stress evolution along the launcher afterbody.

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“…Recently, several numerical and experimental studies in the field of BFS flow over various step angles (Bayraktar 2014), control of the reattachment length of a transonic 2D BFS flow (Bolgar et al 2015), simulation of a gently curved BFS (Asgari and Tadjfar 2017), simulation of turbulent flows over a BFS by using a modified partially averaged Navier-Stokes model (Huang et al 2017), heat transfer and fluid flow characteristics of separation and reattachment flow over a BFS (Xie and Xi 2017) and high intensity turbulent flow over a BFS (de la Torre et al 2017) are conducted by scholars. For comparison between the cited works and to identify the novelty of current study, we present a summary of the cited works in Table 1.…”

Section: Introductionmentioning

confidence: 99%

On the Instability of Two Dimensional Backward-Facing Step Flow using Energy Gradient Method

Nowruzi

Nourazar

Ghassemi

2018

JAFM

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In the present paper, the energy gradient method is implemented to study the instability of 2-D laminar backward-facing step (BFS) flow under different Reynolds numbers and expansion ratios. For this purpose, six different Reynolds numbers (50 ≤ Re ≤ 1000) and two various expansion ratios of 1.9423 and 3 are considered. We compared our results of the present study with existing experimental and numerical data and good agreement is achieved. To study of fluid flow instability, we evaluated the distributions of velocity, vorticity and energy gradient function K. The results of our study show that as the expansion ratio decreases the flow becomes more stable. We also found that the origin of instability in the entire flow field is located on the separated shear layer nearby the step edge. In addition, we approved that the inflection point on the profile of velocity corresponds to the maximum of vorticity resulted to the instability.

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Control of the Reattachment Length of a Transonic 2D Backward-Facing Step Flow

Cited by 13 publications

References 17 publications

Application of Lobed Mixers to Reduce Drag of Boat-Tailed Ground Vehicles

Application of Lobed Mixers to Reduce Drag of Boat-Tailed Ground Vehicles

Flow structure and unsteadiness in the supersonic wake of a generic space launcher

On the Instability of Two Dimensional Backward-Facing Step Flow using Energy Gradient Method

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