Unsteady skin-friction field estimation based on global luminescent oil-film image analysis

Taekjin Lee, Chungil Lee, Taku Nonomura, Keisuke Asai

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Abstract: A global luminescent oil-film (GLOF) image analysis method to estimate unsteady skin-friction fields in an unsteady flow field is proposed and demonstrated. A governing equation describing the dynamics of the oil film (the thin-oil-film equation) is employed for the unsteady oil-film images. The frequency response of the oil-film movement is analyzed, and a cutoff frequency is defined as a function of the oil-film thickness and the kinematic oil viscosity. The estimating skin-friction vector is defined along with a spatiotemporal weighted window and obtained by solving the overdetermined system of the thin-oil-film equation. The system can be solved by using the weighted linear least-squares method, and the time-resolved skin-friction field can be estimated. The time-resolved GLOF image analysis method is demonstrated on an experiment of a junction flow on a flat surface with a square cylinder. The GLOF images in the Kármán vortex shedding bounding the flat surface were acquired, and the time-resolved skin-friction fields were obtained. The results showed that fluctuation in the skin-friction vectors corresponds to the shedding frequency, and the vortices bounding the surface were extracted. The averaged skin-friction field is compared with the result of the previous study based on the time-independent model. The normalized skin friction from both methods showed good agreement, which indicates that the quantitative value will be obtained when a calibration process is involved in a future study. Graphic abstract: [Figure not available: see fulltext.].

Original languageEnglish
Pages (from-to)763-772
Number of pages10
JournalJournal of Visualization
Volume23
Issue number5
DOIs
Publication statusPublished - 2020 Oct 1

Keywords

  • Image-based measurement
  • Kármán vortex shedding
  • Oil film
  • Skin friction
  • Unsteady flow
  • Wall shear stress

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electrical and Electronic Engineering

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