Abstract In technical applications, pumping fluids through pipes often generates turbulent flows with high Reynolds numbers, where over 90% of the pumping energy is dissipated by near-wall turbulence. Relaminarization of such flows offers significant energy savings. Streamwise traveling waves of wall blowing and suction have been shown to relaminarize turbulent pipe flow at a low friction Reynolds number (Re =110 Re τ = 110), reducing friction losses and energy consumption. This work extends the investigation to higher Reynolds numbers, demonstrating that traveling waves can trigger relaminarization up to Re =720 Re τ = 720. A parametric study is conducted at Re =180 Re τ = 180 and Re =360 Re τ = 360, examining upstream traveling waves (UTWs, c c 0) and downstream traveling waves (DTWs, c>0 c > 0) while varying amplitude a, celerity c, and wavelength λ. Consistent with channel flow studies, UTWs destabilize the flow yet can generate sublaminar drag; only low-speed UTWs with large amplitudes effectively reduce energy consumption. For DTWs, a wide range of parameters reduces drag, but significant net energy savings occur only for 0. 067U₂, ₋₀₌ a 0. 1U₂, ₋₀₌ 0. 067 U c, l a m ≲ a ≲ 0. 1 U c, lam, c U₂, ₋₀₌ c ≈ U c, lam, and 360 _ λ ≈ 360 δ ν, independent of Reynolds number. During relaminarization, the turbulent kinetic energy decays exponentially nearly to zero within 3D/u_ 3 D / u τ, while the flow accelerates to its terminal velocity over 65D/u_ <mml: math xmlns: mml="http: //www. w3. org/
Bauer et al. (Tue,) studied this question.