Linear least-squares method for global luminescent oil film skin friction field analysis

Lee, Taekjin; Nonomura, Taku; Asai, Keisuke; Liu, Tianshu

doi:10.1063/1.5001388

Cited by 25 publications

(10 citation statements)

References 16 publications

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“…In the present work, OFV were carried out for a limited number of test conditions to verify the conjectures on the presence or absence of separated flow regions on the downstream side of the bumps. In contrast to oil-film methods based on luminescent oils, such as those presented in Lee et al (2018), a transparent silicone oil mixed with a black powder (black toner for laser printers) was used in the present work. The surface illumination was provided by the TSP itself, i.e., by the luminescence of the TSP surface excited by the LEDs.…”

Section: Oil-film Visualizations (Ofv)mentioning

confidence: 99%

Experimental study of bump effects on boundary-layer transition in compressible high Reynolds number flow

Costantini¹,

Risius²,

Koch³

et al. 2019

Experimental Thermal and Fluid Science

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The influence of surface bumps on boundary-layer transition was experimentally investigated in the present work. The experiments were conducted in a (quasi-) two-dimensional flow at low to high subsonic Mach numbers and chord Reynolds numbers up to 10 million in the low-turbulence Cryogenic Ludwieg-Tube Göttingen. Various streamwise pressure gradients relevant for natural laminar flow surfaces were examined. Quasi-two-dimensional bumps, with a sinusoidal shape in the streamwise direction, fixed length and three different heights, were installed on a two-dimensional flat-plate model. The model was equipped with temperature-sensitive paint for non-intrusive transition detection and with pressure taps for the measurement of the surface pressure distributions. Boundary-layer transition was shown to occur at a more upstream location with increasing bump height-to-length ratio. This was mainly due to the local adverse pressure gradient on the downstream side of the bump, which was particularly pronounced in the case of the bump with the largest height-to-length ratio, thereby inducing boundary-layer separation (as verified via oil-film visualizations). In the case of the bump with the smallest height-to-length ratio, bumpinduced transition was found to be dependent on global pressure gradient, Mach number and Reynolds number; however, the influence of these parameters on transition induced by bumps with larger height-tolength ratios was significantly reduced. The sensitivity of boundary-layer transition to the effect of the bumps was shown to be more pronounced with stronger global flow acceleration and at smaller Mach numbers.

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Section: Oil-film Visualizations (Ofv)mentioning

confidence: 99%

Experimental study of bump effects on boundary-layer transition in compressible high Reynolds number flow

Costantini¹,

Risius²,

Koch³

et al. 2019

Experimental Thermal and Fluid Science

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“…Kurita and Iijima [18] combined GLOF and local OFI methods, and Husen et al [19] used a molecular flow tagging technique that writes a pattern within the oil film. Lee et al [20] proposed a novel approach for GLOF image analysis-a linear least-squares (LLS) method solving the thin oil-film equation, which does not require arbitrary parameters.…”

Section: Introductionmentioning

confidence: 99%

Validation and uncertainty analysis of global luminescent oil-film skin-friction field measurement

Lee

Nonomura

Asai

et al. 2019

Meas. Sci. Technol.

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Results from a skin-friction-field measurement method using global luminescent oil-film images, in which the oil film covers a large portion of the surface, were examined by comparing them with those obtained from conventional hot-wire measurements. The measurement processes including calibrations, oil-film image acquisition, and image processing are explained, and error sources are analyzed. The experimental results show that the skin frictions measured by both methods in a turbulent boundary layer on a flat surface agree when the oil-film thickness is less than the height of the viscous sublayer (corresponding to an oil-film thickness of less than five wall units). The uncertainty of the measurements is presented. When the measurement conditions were optimum (illumination, exposure time, frame rate, oil height, etc), the uncertainty was approximately 3%–4%.

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“…Global skin-friction measurements can be performed via surface-based optical methods. Techniques based on the measurement of the development of an oil film applied to the surface of interest, such as Oil-Film Interferometry (OFI) [ 28 , 40 , 41 , 42 , 43 ], Particle Image Surface Flow Visualization (PISFV) [ 44 , 45 , 46 ] and the Global Luminescent Oil Film (GLOF) [ 21 , 47 , 48 ] methods, allow for the quantitative determination of the skin-friction field. As a more qualitative technique, surface oil-flow visualization can also be a useful tool for the estimation of the locations of critical points and lines (see, e.g., [ 19 , 49 ]).…”

Section: Introductionmentioning

confidence: 99%

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint

Costantini

Henne

Klein

et al. 2021

Sensors

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In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shockwave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.

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Linear least-squares method for global luminescent oil film skin friction field analysis

Cited by 25 publications

References 16 publications

Experimental study of bump effects on boundary-layer transition in compressible high Reynolds number flow

Experimental study of bump effects on boundary-layer transition in compressible high Reynolds number flow

Validation and uncertainty analysis of global luminescent oil-film skin-friction field measurement

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint

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