Pipes and pipelines are central for the distribution of fluids throughout society, ranging from small diameter tubes in domestic settings to pipes in industrial plants and to large scale pipelines. The overall pumping costs surmount to billions of Euros per year and the power to overcome frictional losses encountered in these flows is responsible for a significant part of the global energy consumption.
Virtually all pipeline flows are highly turbulent. What is probably less well known is that the major part of the frictional losses in pipelines is caused by turbulence. Already at moderate speeds turbulence is responsible for a 50% drag increase while at high speeds (i.e. high Reynolds numbers) this figure can easily increases to 99% and more. If instead the fluid could be maintained in the well-ordered “laminar” motion, pumping costs would drop dramatically.
In previous research my group demonstrated that in laboratory experiments surprisingly fully turbulent pipe flows can be turned back into smooth laminar motion and here friction could be reduced by as much as 90%. Over the last 18 months we have investigated possible applications for this new technology. From discussions with oil pipeline operators it became clear that the geometrical accuracy of state of the art pipelines (in terms of smoothens, joints etc.) is insufficient to support laminar flow and hence, even if initial relaminarisation is achieved, unlike under highly controlled laboratory conditions, turbulence would quickly return thus eliminating any initial savings. We consequently adopted our control strategy applying unsteady flow forcing that effectively weakens turbulence, even though it cannot fully eliminate it. If successful, such a forcing would not amount to lower savings but due to a lower sensitivity to the pipeline imperfections could be applied in large pipeline flows. Two new setups have been constructed in our laboratory and tests are ongoing.
