Effects of Polymer Additive on Turbulent Bulk Flow: The Polymer Concentration Dependence
We report an experimental study of the effects of polymer additives on the turbulent bulk flow. Our results confirm that both the acceleration fluctuation a and the velocity fluctuation u of the flow are suppressed when the polymer additives are present a
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Abstract We report an experimental study of the effects of polymer additives on the turbulent bulk flow. Our results confirm that both the acceleration fluctuation a and the velocity fluctuation u of the flow are suppressed when the polymer additives are present and the suppression effect on a is much stronger. We further found that polymer additives enhance the anisotropy of the flow at small scales, but do not affect the anisotropy at large scale very much. These results are qualitatively in agreement with a recent theory which predicts that only scales smaller than a critical scale are affected by the polymer additives.
1 Introduction Minute amount of long-chain polymer additives can drastically change flow properties. Examples include the well-known drag reduction phenomenon in turbulent pipe/channel flows (Virk 1975) and the elastic turbulence phenomenon at low Reynolds numbers (Groisman and Steinberg 2001). The dynamics of the polymer-turbulence interaction are determined by the three control parameters, namely the Reynolds number Rk ; the Weissenberg number Wi which is the ratio H.-D. Xi (&) H. Xu E. Bodenschatz Max-Planck Institute for Dynamics and Self-Organization, D-37077 Göttingen, Germany e-mail: [email protected] H. Xu e-mail: [email protected] E. Bodenschatz e-mail: [email protected] H.-D. Xi Institute for Turbulence-Noise-Vibration Interaction and Control, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China
Y. Zhou et al. (eds.), Fluid-Structure-Sound Interactions and Control, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-3-642-40371-2_7, Springer-Verlag Berlin Heidelberg 2014
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between the polymer relaxation time sp and the smallest time scale in turbulence sg ; and the polymer concentration /. In recent years, there have been a few experimental measurements of bulk turbulence in polymer solutions (Crawford et al. 2002; Liberzon et al. 2005; Liberzon et al. 2006; Crawford et al. 2008; Liberzon et al. 2009; Ouellette et al. 2009), which shed new light on our understanding of turbulence–polymer interactions. However, experiments systematically exploring the full parameter space are still lacking. It is therefore of great importance to have experiments that fully isolate the effect of the three control parameters. In this paper, we report an experimental study on the effects of minute high-molecular weight polymers on bulk turbulence, i.e., turbulence far away from the boundaries. We studied the polymer concentration dependence of the effects of polymer additive on the flow by using the three-dimensional Lagrangian particle tracking technique (LPT) with high temporal and spatial resolutions (Ouellette et al. 2006; Xu 2008). By differentiating the measured tracer particle trajectories once and two times, we obtained the fluid velocities and accelerations, respectively. By keeping both Rk and Wi unchanged and varying solely the polymer concentration /; we studied the concentration dependence of the root-mean-square (
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