Turbulence, bubbles and drops

Roeland van der Veen

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

In this thesis, several questions related to drop impact and Taylor-Couette turbulence are answered. The deformation of a drop just before impact can cause a bubble to be entrapped. For many applications, such as inkjet printing, it is crucial to control the size of this entrapped bubble. To study the deforming drop and resulting bubble, a high-speed color interferometry method is developed to dynamically measure the air layer profile under impacting drops. Experiments and accompanying simulations and theory show a pronounced maximum in the entrapped bubble size for a certain impact velocity, caused by competing inertial and capillary effects. The liquid-air interface of a drop impacting on micropatterned surfaces is found to globally resemble the dimple that is created on smooth surfaces, except for an increased dimple height and local symmetry-breaking. To study turbulence in a highly controlled way, the Taylor-Couette system is employed, which consists of flow between two co-axial cylinders that can independently rotate. First, the design and construction of a new Taylor-Couette system with precise temperature control and excellent optical access is treated. Next, the first evidence of multiple turbulent flow states in Taylor-Couette flow is reported, at very high Reynolds number of roughly one million. These states are found to consist of stable roll structures which persist for a Taylor number of up to 1013 and beyond. Additionally, it is found that the rotation ratio of the cylinders is the main parameter that controls the transition. Rich flow phenomena, including an unexpected antisymmetrical roll state, are observed in the aforementioned new TC-setup with a larger aspect ratio. In the last chapter, several flow properties in a setup with a smaller radius ratio of 0.5 are investigated. The strength of the secondary flows in the classical turbulent regime was found to scale as theoretically predicted. Finally, it was shown that velocity profiles with a logarithmic signature are created at plume-emitting regions.
Original languageEnglish
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Lohse, Detlef , Supervisor
  • Sun, Chao , Advisor
Award date24 Mar 2016
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-4083-4
DOIs
Publication statusPublished - 24 Mar 2016

Keywords

  • IR-100006
  • METIS-316217

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    van der Veen, R. (2016). Turbulence, bubbles and drops. Enschede: Universiteit Twente. https://doi.org/10.3990/1.9789036540834