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 ( \(\textrm{Re}\tau =110\) ), reducing friction losses and energy consumption. This work extends the investigation to higher Reynolds numbers, demonstrating that traveling waves can trigger relaminarization up to \(\textrm{Re}\tau =720\) . A parametric study is conducted at \(\textrm{Re}\tau =180\) and \(\textrm{Re}\tau =360\) , examining upstream traveling waves (UTWs, \(c<0\) ) and downstream traveling waves (DTWs, \(c>0\) ) while varying amplitude a, celerity c, and wavelength \(\lambda \) . 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 \(0.067U_{c,lam}\lesssim a \lesssim 0.1U_\mathrm{{{c,lam}}}\) , \(c\approx U_\mathrm{{{c,lam}}}\) , and \(\lambda \approx 360\delta _\nu \) , independent of Reynolds number. During relaminarization, the turbulent kinetic energy decays exponentially nearly to zero within \(3D/u_\tau \) , while the flow accelerates to its terminal velocity over \(65D/u_\tau \) . The relaminarized flow exhibits half-vortical structures scaling in viscous units superimposed on a laminar profile, effectively reducing the pipe cross section. Within \(180\le \textrm{Re}_\tau \le 540\) , over 97% of the theoretically achievable drag reduction is realized. These scaling relations enable prediction of traveling wave-induced relaminarization at higher Reynolds numbers, offering a practical approach for energy-efficient turbulent pipe flow control.
