Turbulent Flow Control using Wall Sensing

Turbulent flow control plays a pivotal role in diverse applications such as drag reduction, mixing, heat transfer, and boundary layer and flow separation control. Although numerous active and passive methods have been explored for mitigating drag in turbulent flows, this study introduces an approach, not widely explored, that utilizes wall-sensing based on wall shear stress. We conduct a comparative analysis with the opposition control method, which uses velocity sensing at an off-wall location. The results from opposition control reveal significant drag reduction: 21.11% at Re_τ ≈ 180 and 18% at Re_τ ≈ 390. In contrast, the wall-sensing method achieves drag reductions of 10.64% at Re_τ ≈ 180 and 7.12% at Re_τ ≈ 390. This relative ineffectiveness of the wall-sensing control method is attributed to a high-frequency content of the wall shear stress data, which, if undamped, may lead to oscillations in the applied control signal. This, in turn, requires either a reduction in gain, or ‘freezing’ of the control input in time to arrive at a stable control implementation, reducing the method effectiveness as compared to an opposition control approach.