A refractive index-matched facility for fluid–structure interaction studies of pulsatile and oscillating flow in elastic vessels of adjustable compliance

Abstract

The flow field in the respiratory and vascular system is known to be influenced by the flexibility of the walls. However, up to now, most of the experimental biofluidic investigations have been performed in rigid models due to the complexity and necessity of optical access. In this paper, a facility and measurement techniques for studying oscillating and pulsatile flow in elastic vessels will be described. The investigated vessel models have been adapted such that fluid-mechanical and structure-mechanical characteristics represent realistic blood flows in medium blood vessels. That is, characteristic parameters, i.e., the Reynolds and Womersley number, as well as mechanical properties of the flexible wall, i.e., the Young's modulus and the material compliance, have been chosen to reasonably represent realistic flow conditions. First, a method to manufacture elastic models, which mimic the structure-mechanical properties of vascular vessels is described. The models possess a tunable compliance and are made of transparent polydimethylsiloxane. Second, the experimental setup of the flow facility will be elucidated. The flow facility allows to mimic pulsatile flow at physiologically relevant Reynolds and Womersley numbers. The precise form of the flow cycle can individually be controlled. Water/glycerine is used as flow medium for refractive index matching particle image velocimetry (PIV) measurements. The PIV recordings not only allow to assess the mean cross-sectional flow field but also further enable to simultaneously detect the movement of the flexible wall. Additionally, the local wall-shear stress can be obtained from the single-pixel line resolved near-wall flow field. To confirm the flow conditions of the oscillatory laminar flow inside the flow facility and to evaluate the ability to assess the flow field, measurements in a straight, uniform diameter, rigid Plexiglas pipe under identical conditions to those of the oscillating flow in the flexible vessel have been performed. The measurements of oscillating flow in the rigid pipe corroborate the experimentally obtained flow field and the wall-shear stress to well confirm Womersley's analytical solution and thereby evidence the quality of the flow facility and of the measurement techniques. To further study the detectability of the vessel deformation, oscillating flow at Reynolds numbers based on the non-dilated vessel diameter D and peak velocities Re D ranging from 1,000 to 1,750 and at Womersley numbers a ranging from 5 to 17.5 has been investigated in an elastic vessel.

A review of solid–fluid selection options for optical-based measurements in single-phase liquid, two-phase liquid–liquid and multiphase solid–liquid flows

“…The density of silicone rubber varies widely based on its exact composition; however, it is usually in the range of 1100-2300 kg/ m 3 . Flexibility makes silicone rubbers particularly useful for compliant models of flows through flexible structures or membrane-like tissues, e.g., in RIM models for bloodflow experiments and, as a result, have been frequently employed in such systems (Duncan et al 1990;Perktold et al 1997;Bale-Glickman et al 2003;Burgmann et al 2009;Shuib et al 2010;Yousif et al 2010;Gülan et al 2012;Pielhop et al 2012;Geoghegan et al 2012;Im et al 2013;Kefayati and Poepping 2013). Sylgard 184, manufactured by Dow Corning, has been identified as a silicone rubber of particularly interest (Duncan et al 1990;Perktold et al 1997;Hopkins et al 2000;Yousif et al 2010;Shuib et al 2010;Buchmann et al 2010Buchmann et al , 2011Geoghegan et al 2012 andKefayati andPoepping 2013).…”

“…(iii) Particle image/tracking velocimetry (PIV/PTV) and variants thereof have been covered in detail by Adrian (1986Adrian ( , 1991, Arroyo and Greated (1991), Maas et al (1993), Grant (1997) and Fu et al (2015), among others. These techniques can provide velocity information in two or three dimensions (2-D/3-D) and have been used in many RIM systems, e.g., by Northrup et al (1991), Peurrung et al (1995), Zachos et al (1996), Hopkins et al (2000), Longmire et al (2001), Bale-Glickman et al (2003), Ninomiya and Yasuda (2006), Burgmann et al (2009), Dietze et al (2009) Buchmann et al (2010, Berard et al (2013), Im et al (2013), Yagi et al (2013), Morgan et al (2013), , Krug et al (2014).…”

Fabrication of rigid and flexible refractive-index-matched flow phantoms for flow visualisation and optical flow measurements

“…Flexible phantoms that allow the study of fluid-structure interaction have been reported by several authors (Bertram and Elliott 2003;Geoghegan et al 2009;Burgmann et al 2009;Zamir 2000). Each of these studies used a different method for fabrication of the phantom.…”

“…Each of these studies used a different method for fabrication of the phantom. Burgmann et al (2009) made high-quality straight tubes, but the method is difficult to apply to more complex arterial structures. (Doyle et al 2008;Deplano et al 2007;Yagi et al 2009) present methods for the construction of aneurysm phantoms, which have more complex re-entrant geometries.…”

“…The propagation wave speed in inviscid flow c 0 is obtained using the Moens-Korteweg formula (Burgmann et al 2009;Zamir 2000) and is given as:…”