Experimental study of the interaction of near-wall flow with flexible polymers at micro-scale

• Applicant: Professor Dr.-Ing. Wolfgang Schröder
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2004 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5425080

• Final Report Year: 2007

Final Report Abstract

In conclusion, the results demonstrate that dynamic forces acting on the plain sensor structure or on pillars with polymer filaments attached to the pillar tips can be measured up to frequencies in the order of 500 − 1,000 Hz. Nonetheless, a more detailed experimental investigation of the pillar dynamics is necessary to allow a proper detection especially of the high-frequency content of the drag fluctuations. This is of major importance since the main changes of the near-wall turbulence due to the polymer interaction are expected to happen at higher frequencies. In a first feasibility study the pillar technique has successfully been applied to detect the fluctuating wall-shear stress in turbulent pipe flow. Furthermore, it has been demonstrated that the net dynamic drag acting on the polymer filament can be deduced and first studies showed changes in the spectral density of drag fluctuations acting on filament grafted pillars. To be more precise, the high frequency content of the turbulent signal was reduced compared to the plain pillar drag. Similar behavior was detected for the wall-shear stress in ocean-type polymer solution turbulent pipe flow. Again, spectral densities shift toward lower frequencies. The results of these measurements will serve as a database for the measurements of the global shear-thinning effects due to the interaction of near-wall flow with the polymer filaments attached to the pillar tips. Arrays with flexible polymer filaments have successfully been manufactured and ongoing PIV measurements of the local flow field and of the global shear field in turbulent channel flow will allow to determine the changes in the turbulence characteristics resulting from the near-wall manipulation.

Publications

• Wall shear stress imaging in turbulent flows using microstructured surfaces with flexible micropillars. Advances in Turbulence X (Eds.: Andersson HI & Krogstad PA), pp. 467-478, 2004
  Brücker Ch, Spatz J, Schröder W
  
• Feasibility study of wall shear stress imaging using microstructured surfaces with flexible micropillars. Experiments in Fluids 39(2), pp. 464 - 474, 2005
  Brücker Ch, Spatz J, Schröder W
  
• Manufacture of high-aspect ratio micro-hair sensor arrays. Journal of Micromechanics and Microengineering 15, pp. 1904-1910, 2005
  Schmitz G, Brücker Ch, Jacobs P
  
• 2006. Local High-Resolution Wall-Shear-Stress Measurements in a Turbulent Boundary Layer Using a Micro-Pillar Based Sensor Concept. 6th Euromech Fluid Mechanics Conference, KTH Mechanics, Stockholm, Sweden, June 2006
  Große, S., Brücker, C. & Schröder, W.
  
• 2006. Micro-force drag measurements of a fixed air bubble at low Re numbers using flexible micro-pillars. Proceedings of the 13th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 26-29 June 2006
  Große, S., Schröder, W. & Brücker, C.
  
• 2006. Nano-newton drag sensor based on flexible micropillars. Measurement Science and Technology, 17, 2689-2697
  Große, S., Schröder, W. & Brücker, C
  
• 2006. On experimental and numerical method to analyze wall-bounded and free shear flows. Third International Conference on Fluid Dynamics conference, Miyagi, Japan, November 2006
  Schröder, W., Brücker, C., Große, S., Gröschel, E., Bui, P., König, D. & Renze, P.
  
• 2006. Progress in Wall Shear Stress Imaging with Flexible Micro-Pillars. 12th International Symposium on Flow Visualization, Göttingen, Germany, September 2006
  Brücker, C., Große, S., Bauer, D. & Schmitz, G.
  
• 2006. Measurement of Dynamic Wall-Shear Stress using the Micro-Pillar Sensor M P S3. APS DFD07 Meeting, Salt Lake City, USA, 18-20 November, 2007
  Große, S., Brücker, C. & Schröder, W.
  
• 2007. High Resolution Wall-Shear Stress Measurements Using a Micro-Pillar Sensor M P S3. Proceedings of the 5th International Symposium on Turbulence and Shear Flow Phenomena, TU Munich, Germany, 27-29 August 2007
  Große, S. & Schröder, W.
  
• 2007. Wall-shear stress assessment in zero-pressure gradient turbulent flow using M P S3. Proceedings of the 11th European Turbulence Conference, Porto, Portugal, 25-28 June 2007
  Große, S. & Schröder, W.