Cardiac-cycle inspired turbulent drag reduction
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Flows through pipes and channels are in practice almost always turbulent and the eddying motion is responsible for the major part of the encountered friction losses and pumping costs. Conversely, for pulsatile flows, in particular for aortic blood flow, turbulence levels remain surprisingly low, despite relatively large peak velocities. Indeed, in this latter case high turbulence levels are intolerable as they would damage the shear sensitive endothelial cell layer. We here show that turbulence in ordinary pipe flow is diminished if the flow is driven in a pulsatile mode that incorporates all the key features of the cardiac waveform. At Reynolds numbers comparable to aortic blood flow, turbulence is largely inhibited, whereas at much higher speeds, the turbulent drag is reduced by more than 25%. This specific operation mode is considerably more efficient when compared to steady driving, which is the status quo for virtually all fluid transport processes ranging from heating circuits to water, gas and oil pipelines.