Effect of concentrated wall suction on a turbulent boundary layer

Abstract

The effect of suction, applied through a short porous wall strip, on a low Reynolds number self-preserving turbulent boundary layer has been quantified by measuring the local wall shear stress and the main Reynolds stresses downstream of the strip. When the suction rate is sufficiently high, pseudo-relaminarization occurs almost immediately downstream of the strip. Farther downstream, transition occurs followed by a slow return to a fully turbulent self-preserving state. During relaminarization, the measured skin friction coefficient cf falls below the level corresponding to the no suction value, reaching a minimum where transition begins. An empirical cf distribution is proposed that groups together results obtained at different streamwise stations and different suction rates. Of all the measured Reynolds stresses, the longitudinal turbulence intensity recovers relatively quickly from the change in boundary conditions while the wall-normal turbulence intensity and the Reynolds shear stress are significantly affected by the suction. The Reynolds shear stress, which is negligible during relaminarization, has the slowest recovery.

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“…The distance between the AFC section and the TE covers a distance of 5δ 0 and the results have shown that even in the case of modest flow suction, the flow does not recover to that of the baseline (σ = 0) case within this distance. This is in agreement with the findings of Antonia et al, 34 who reported that for σ = −2.6 the flow requires approximately 40δ 0 to return to its original state (x = 0, σ = 0). The treated profiles partially return to their original values in the near-wall region beyond the locations m2 and m4, which agrees with the findings of Park and Choi 35 and Antonia et al, 34 where the near-wall energy content of the streamwise velocity component was shown to return to its original value in near-wall energy content of the streamwise velocity component was shown to return to its original value in a short distance.…”

“…This is in agreement with the findings of Antonia et al, 34 who reported that for σ = −2.6 the flow requires approximately 40δ 0 to return to its original state (x = 0, σ = 0). The treated profiles partially return to their original values in the near-wall region beyond the locations m2 and m4, which agrees with the findings of Park and Choi 35 and Antonia et al, 34 where the near-wall energy content of the streamwise velocity component was shown to return to its original value in near-wall energy content of the streamwise velocity component was shown to return to its original value in a short distance. The study also reported that as the turbulent structures were brought closer to the wall, the viscous dissipation increased downstream of the AFC treatment.…”

“…σ relates the momentum of the boundary layer to the momentum of the AFC. Assuming that for turbulent boundary layers the momentum thickness can be approximated as δ ≈ 10 θ, one can infer that σ = −10 is equivalent to the elimination of the boundary layer, although Antonia et al 34 reported relaminarisation at σ = −6.5.…”

“…The effect of BL injection and suction, from turbulence point of view, has already been studied by various researchers including Antonia et al, 33,34 Park and Choi…”

“…Experiments involving larger flow rates proved that total or partial relaminarisation can be achieved above a threshold value of flow suction. 34 It was also reported that below a limiting amount of flow rate, AFC has a negligible effect on the investigated BL properties.…”