title: Development of a shear stress sensor to analyse the influence of polymers on the turbulent wall shear stress.
abstract: The drag reducing effect of polymers in a channel flow is well known and it is assumed that the polymer filaments interfere with the turbulent structures in the very near-wall flow. To analyse their precise effect, a micro-pillar shear stress sensor (MPS³) measurement system is developed which allows the detection of wall shear stress at high spatial and temporal resolutions. Different manufacturing techniques for the required micro-pillars are discussed and their influence on the flow is investigated evidencing the non-intrusive character of the pillars. Subsequently, a complete calibration is presented to relate the recorded deflection to wall shear stress values and to assure the correct detection over the whole expected frequency spectrum. A feasibility study about the ability to visualize the two-dimensional wall shear stress distribution completes the discussion about the validity of MPS³. In the last step, the drag reduction of a polymer filament grafted on a micro-pillar compared to a plain pillar and the application of MPS³ in an ocean-type polymer solution are investigated. The results confirm the expected behaviour found in the literature.
authors.affiliation: Institute of Aerodynamics, RWTH Aachen University, Aachen, Germany. B.Nottebrock@aia.rwth-aachen.de
authors.forename: Bernardo
authors.initials: B
authors.lastname: Nottebrock
authors.forename: Sebastian
authors.initials: S
authors.lastname: Grosse
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schröder
mesh_terms: D002138:Calibration; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning / Q000379:methods; D017785:Photons; D010825:Physics / Q000379:methods; D011108:Polymers / Q000737:chemistry*; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
chemical_list: D004129:Dimethylpolysiloxanes; D011108:Polymers; C013830:baysilon