Effect of uniform blowing/suction in a turbulent boundary layer at moderate Reynolds number

Kametani, Yukinori; Fukagata, Koji; Schlatter, Philipp

doi:10.1016/j.ijheatfluidflow.2015.05.019

Cited by 104 publications

(81 citation statements)

References 43 publications

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“…Applying the present decomposition (2.8) to drag reduction could suggest new strategies of flow control, in the same way as the FIK decomposition (1.7) has enabled significant achievements in this field (see e.g. Iwamoto et al (2005) in high-Reynolds-number channel flows, Kametani & Fukagata (2011), Kametani et al (2015 and Stroh et al (2015) in spatially-developing boundary layers, as well as Bannier et al (2015) with their extended FIK identity). Alternatively to the FIK strategy which focuses on the Reynolds shear-stress intensity, the present decomposition suggests that a flow control focusing on the turbulent kinetic-energy production level might be of interest.…”

Section: On the Relation Between The Generation Of The Turbulence-indmentioning

confidence: 86%

“…This decomposition has been extensively and successfully used in turbulent flow analysis and control, see e.g. Iwamoto et al (2005), Kametani & Fukagata (2011), Kametani et al (2015) and Stroh et al (2015), with C f ,II typically representing the effect of the turbulent fluctuations on C f whereas C f ,I has a Reynolds-number dependence similar to laminar friction. However, several issues arise.…”

Section: Introductionmentioning

confidence: 99%

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A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer

2016

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A theoretical decomposition of mean skin friction generation into physical phenomena across the whole profile of the incompressible zero-pressure-gradient smooth-flat-plate boundary layer is derived from a mean streamwise kinetic-energy budget in an absolute reference frame (in which the undisturbed fluid is not moving). The Reynolds-number dependences in the laminar and turbulent cases are investigated from direct numerical simulation datasets and Reynolds-averaged Navier-Stokes simulations, and the asymptotic trends are consistently predicted by theory. The generation of the difference between the mean friction in the turbulent and laminar cases is identified with the total production of turbulent kinetic energy (TKE) in the boundary layer, represented by the second term of the proposed decomposition of the mean skin friction coefficient. In contrast, the analysis introduced by Fukagata et al. on a streamwise momentum budget in the wall reference frame, relates the turbulence-induced excess friction to the Reynolds shear stress weighted by a linear function of the wall distance. The wall-normal distribution of the linearly-weighted Reynolds shear stress differs from the distribution of TKE production involved in the present discussion, which consequently draws different conclusions on the contribution of each layer to the mean skin friction coefficient. At low Reynolds numbers, the importance of the buffer-layer dynamics is confirmed. At high Reynolds numbers, the present decomposition quantitatively shows for the first time that the generation of the turbulence-induced excess friction is dominated by the logarithmic layer. This is caused by the well-known decay of the relative contributions of the buffer layer and wake region to TKE production with increasing Reynolds numbers. This result on mean skin friction, with a physical interpretation relying on an energy budget, is consistent with the well-established general importance of the logarithmic layer at high Reynolds numbers, contrary to the friction breakdown obtained from the approach of Fukagata et al. based on a momentum budget. The new decomposition suggests that it may be worth investigating new drag reduction strategies focusing on TKE production and on the nature of the logarithmic layer dynamics. The decomposition is finally extended to the pressure-gradient case and to channel and pipe flows.

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Section: On the Relation Between The Generation Of The Turbulence-indmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer

2016

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“…Although suction is known to lead to turbulent drag enhancement (Kametani et al 2015), it is a way to delay transition to higher Re. Indeed, homogeneous suction reduces the growth rate of the Tollmien-Schlichting waves (Reynolds & Saric 1986;Schlichting 1987), increasing the linear stability threshold in Re (Hocking 1975).…”

mentioning

confidence: 99%

Turbulence collapse in a suction boundary layer

et al. 2016

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Turbulence in the asymptotic suction boundary layer is investigated numerically at the verge of laminarisation using direct numerical simulation. Following an adiabatic protocol, the Reynolds number Re is decreased in small steps starting from a fully turbulent state until laminarisation is observed. Computations in a large numerical domain allow in principle for the possible coexistence of laminar and turbulent regions. However, contrary to other subcritical shear flows, no laminar-turbulent coexistence is observed, even near the onset of sustained turbulence. High-resolution computations suggest a critical Reynolds number Re g ≈ 270, below which turbulence collapses, based on observation times of O(10 5 ) inertial time units. During the laminarisation process, the turbulent flow fragments into a series of transient streamwise-elongated structures, whose interfaces do not display the characteristic obliqueness of classical laminar-turbulent patterns. The law of the wall, i.e. logarithmic scaling of the velocity profile, is retained down to Re g , suggesting a large-scale wall-normal transport absent in internal shear flows close to the onset. In order to test the effect of these large-scale structures on the near-wall region, an artificial volume force is added to damp spanwise and wall-normal fluctuations above y + = 100, in viscous units. Once the largest eddies have been suppressed by the forcing, and thus turbulence is confined to the near-wall region, oblique laminar-turbulent interfaces do emerge as in other wall-bounded flows, however only transiently. These results suggest that oblique stripes at the onset are a prevalent feature of internal shear flows, but will not occur in canonical boundary layers, including the spatially growing ones.

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“…the boundary layer is thickened by the control action. This is expected since the current controller imparts a positive net mass flow rate and it is known that uniform blowing increases the boundary layer thickness (Kametani & Fukagata 2011;Kametani et al 2015;Stroh et al 2016). Note that δ starts to increase before the control slot is reached, and this is due to the upstream effect of the pressure gradient induced by the actuation, as will be discussed below.…”

Section: Mean Velocity Profilesmentioning

confidence: 88%

“…They applied the FIK identity (Fukagata et al 2002) to investigate the drag reduction mechanism and concluded that the mean convection has a strong contribution in reducing the drag for UB and increasing the drag for US. More recently, Kametani et al (2015) applied UB and US in a turbulent boundary layer at moderate Reynolds number using large eddy simulations (LES). The actuation velocity had a magnitude of 0.1%U ∞ and achieved more than 10% drag reduction (or enhancement) by UB (or US).…”

Section: Introductionmentioning

confidence: 99%

Nonlinear optimal control of transition due to a pair of vortical perturbations using a receding horizon approach

Xiao

Papadakis

2018

J. Fluid Mech.

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This paper considers the nonlinear optimal control of bypass transition in a boundary layer flow subjected to a pair of free stream vortical perturbations using a receding horizon approach. The optimal control problem is solved using the Lagrange variational technique that results in a set of linearised adjoint equations, which are used to obtain the optimal wall actuation (blowing and suction from a control slot located in the transition region). The receding horizon approach enables the application of control action over a longer time period, and this allows the extraction of time-averaged statistics as well as investigation of the control effect downstream of the control slot. The results show that the controlled flow energy is initially reduced in the streamwise direction and then increased because transition still occurs. The distribution of the optimal control velocity responds to the flow activity above and upstream of the control slot. The control effect propagates downstream of the slot and the flow energy is reduced up to the exit of the computational domain. The mean drag reduction is 55% and 10% in the control region and downstream of the slot, respectively. The control mechanism is investigated by examining the second order statistics and the two-point correlations. It is found that in the upstream (left) side of the slot, the controller counteracts the near wall high speed streaks and reduces the turbulent shear stress; this is akin to opposition control in channel flow, and since the time-average control velocity is positive, it is more similar to blowingonly opposition control. In the downstream (right) side of the slot, the controller reacts to the impingement of turbulent spots that have been produced upstream and inside the boundary layer (top-bottom mechanism). The control velocity is positive and increases in the streamwise direction, and the flow behavior is similar to that of uniform blowing.

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Effect of uniform blowing/suction in a turbulent boundary layer at moderate Reynolds number

Cited by 104 publications

References 43 publications

A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer

A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer

Turbulence collapse in a suction boundary layer

Nonlinear optimal control of transition due to a pair of vortical perturbations using a receding horizon approach

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