Turbulent boundary layer under the control of different schemes

Abstract

This work explores experimentally the control of a turbulent boundary layer over a flat plate based on wall perturbation generated by piezo-ceramic actuators. Different schemes are investigated, including the feed-forward, the feedback, and the combined feed-forward and feedback strategies, with a view to suppressing the near-wall high-speed events and hence reducing skin friction drag. While the strategies may achieve a local maximum drag reduction slightly less than their counterpart of the open-loop control, the corresponding duty cycles are substantially reduced when compared with that of the open-loop control. The results suggest a good potential to cut down the input energy under these control strategies. The fluctuating velocity, spectra, Taylor microscale and mean energy dissipation are measured across the boundary layer with and without control and, based on the measurements, the flow mechanism behind the control is proposed.

Flat plate drag reduction using plasma-generated streamwise vortices

“…As a result, the skin friction is substantially reduced (figure 14). Interestingly, these LSSVs change little the turbulent energy dissipation (figure 24b), unlike some other techniques such as the piezo-ceramic-actuator-generated spanwise-travelling wave (Bai et al 2014;Qiao et al 2017) where the enhancement of the dissipation in the near-wall region is one of the keys for DR.…”

“…Choi et al 1998;Agostini, Touber & Leschziner 2014) or a spanwise/transverse or streamwise-travelling wave (e.g. Du et al 2002;Quadrio et al 2009;Bai et al 2014;Qiao et al 2017).…”

“…Two spanwise-aligned arrays of M4 screws, separated longitudinally by 0.015 m and placed at 0.1 m downstream of the leading edge, trip the boundary layer. A 0.2 m long end plate, inclined by 12°, is attached to the trailing edge of the plate to avoid flow separation from the leading edge (Qiao, Zhou & Wu 2017). The streamwise pressure gradient is carefully adjusted through slightly inclining the flat plate to 0.005 Pa m −1 .…”

Reynolds number effect on the response of a rough wall turbulent boundary layer to local wall suction

“…It is accordingly of quite significant interest to enhance our understanding of the dynamic response of a rough wall TBL to various perturbations with increasing Re. To date, wall suction and injection approaches have had some success in controlling of smooth wall TBLs, particularly at low and moderate Re (see Gad-el Hak & Blackwelder 1989;Myose & Blackwelder 1995;Jacobson & Reynolds 1998;Park & Choi 1999;Rathnasingham & Breuer 2003;Lockerby, Carpenter & Davies 2005;Rebbeck & Choi 2006;Segawa et al 2007;Kametani et al 2015;Bobke, Örlü & Schlatter 2016;Qiao, Zhou & Wu 2017). Antonia et al (1988) quantified the influence of wall suction, applied through a porous wall strip, on a low Reynolds number smooth wall TBL.…”

Active Control for Wall Drag Reduction: Methods, Mechanisms and Performance

“…They compared the performance of piezoelectric vibration drag reduction under different control methods, and concluded that closed-loop control could save a lot of energy. Then, they studied the drag reduction performance under different closed-loop control methods, and verified the results through wind tunnel experiments [171].…”