title: Turbulence in blood damage modeling.
abstract: OBJECTIVE
  To account for the impact of turbulence in blood damage modeling, a novel approach based on the generation of instantaneous flow fields from RANS simulations is proposed.
  
  
  METHODS
  Turbulent flow in a bileaflet mechanical heart valve was simulated using RANS-based (SST k-ω) flow solver using FLUENT 14.5. The calculated Reynolds shear stress (RSS) field is transformed into a set of divergence-free random vector fields representing turbulent velocity fluctuations using procedural noise functions. To consider the random path of the blood cells, instantaneous flow fields were computed for each time step by summation of RSS-based divergence-free random and mean velocity fields. Using those instantaneous flow fields, instantaneous pathlines and corresponding point-wise instantaneous shear stresses were calculated. For a comparison, averaged pathlines based on mean velocity field and respective viscous shear stresses together with RSS values were calculated. Finally, the blood damage index (hemolysis) was integrated along the averaged and instantaneous pathlines using a power law approach and then compared.
  
  
  RESULTS
  Using RSS in blood damage modeling without a correction factor overestimates damaging stress and thus the blood damage (hemolysis). Blood damage histograms based on both presented approaches differ.
  
  
  CONCLUSIONS
  A novel approach to calculate blood damage without using RSS as a damaging parameter is established. The results of our numerical experiment support the hypothesis that the use of RSS as a damaging parameter should be avoided.
authors.affiliation: Biofluid Mechanics Laboratory, Charité Medical University of Berlin, Berlin - Germany.|Department of Congenital Heart Disease and Pediatric Cardiology, German Heart Institute of Berlin, Berlin - Germany.
authors.forename: Leonid
authors.initials: L
authors.lastname: Goubergrits
authors.affiliation: Biofluid Mechanics Laboratory, Charité Medical University of Berlin, Berlin - Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Osman
authors.affiliation: Biofluid Mechanics Laboratory, Charité Medical University of Berlin, Berlin - Germany.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Mevert
authors.affiliation: Biofluid Mechanics Laboratory, Charité Medical University of Berlin, Berlin - Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kertzscher
authors.affiliation: Visualization and Data Analysis, Zuse Institute of Berlin, Berlin - Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Pöthkow
authors.affiliation: Visualization and Data Analysis, Zuse Institute of Berlin, Berlin - Germany.
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Hege
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology; D006350:Heart Valve Prosthesis; D006461:Hemolysis / Q000502:physiology*; D006801:Humans; D008955:Models, Cardiovascular; D015539:Platelet Activation / Q000502:physiology*; D013314:Stress, Mechanical