Application of liquid crystals to boundary- layer visualization

Klein, Enrique J.

doi:10.2514/6.1968-376

Cited by 18 publications

(6 citation statements)

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“…These include internal and external applications such as channel ows [2], turbine blade cooling [8], jet impingement cooling [5], electronic cooling, boundary layer transition on airfoils [9], and heat transfer from rotating disks [6]. Transient technique represents uniform temperature thermal boundary condition and has been used for more complex geometries, while the steadystate technique represents uniform heat ux boundary condition and is recommended for two-dimensional geometries.…”

Section: Downloaded By [Georgia Tech Library] At 09:22 17 November 2014mentioning

confidence: 99%

Liquid Crystals and Their Application in Heat Transfer Measurements

Saniei¹

2002

Heat Transfer Engineering

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Section: Downloaded By [Georgia Tech Library] At 09:22 17 November 2014mentioning

confidence: 99%

Liquid Crystals and Their Application in Heat Transfer Measurements

Saniei¹

2002

Heat Transfer Engineering

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“…Liquid crystals have been used for over thirty years as a surface-flow visualization aid, beginning with the work of Klein. 8 The viscous nature of LCs permits the surface flow direction to be determined, similarly to the use of oil flow compounds, and the "color play"-the variation in observed colors under white-light illumination-that results from the crystalline properties can, in principle, be related to important flow phenomena (boundary-layer transition, flow separation, and shock-wave passage or impingement).…”

Section: Liquid Crystals General Descriptionmentioning

confidence: 99%

Shear-stress sensitive liquid crystals for hypersonic boundary-layer transition detection

Aeschliman

Croll

Kuntz

1995

Journal of Spacecraft and Rockets

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The use of shear-stress-sensitive (SSS) liquid crystals (LCs) has been evaluated as a boundary-layer transition detection technique for hypersonic flows. Experiments were conducted at Mach 8 in the Sandia National Laboratories Hypersonic Wind lunnel using a flat-plate model at near-0-deg angle of attack over the freestream unit-Reynolds-number range (1.2-5.8) x!0 6 /ft. Standard 35-mm color photography and Super VHS color video were used to record LC color changes due to varying surface shear stress during the transition process for a range of commercial SSS liquid crystals. Visual transition data were compared with an established method using calorimetric surface heat-transfer measurements to evaluate the LC technique. It is concluded that the use of SSS LCs can be an inexpensive, safe, and easy-to-use boundary-layer transition detection method for hypersonic flows. However, a valid interpretation of the visual records requires careful attention to illumination intensity levels and uniformity and to lighting and viewing angles, some prior understanding of the general character of the flow, and the selection of the appropriate liquid crystal for the particular flow conditions. Nomenclature M = Mach number P = pressure, psia q = heat transfer rate, Btu/ft 2 • s Re = unit Reynolds number, ft" 1 T -temperature, °R t = time, s X = distance from leading edge, in. a = angle of attack, deg r = shear stress, lbf/ft 2 Subscripts c = calculated cw = cold wall i = initial conditions, t = 0 m = measured r = recovery 0 = stagnation conditions oo = freestream conditions

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“…Klein (1968) was the first to report the use of liquid crystals for flow visualization in wind-tunnel experiments. Klein applied an unencapsulated layer of liquid crystal solution to his test model, and was thus able to qualitatively study the steady-state boundary-layer temperature distributions of the model.…”

Section: Previous Applications Of Liquid Crystalsmentioning

confidence: 99%

Digital particle image thermometry: The method and implementation

Dabiri

Gharib

1991

Experiments in Fluids

123

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A computerized flow visualization technique capable of automatically quantifying the temperature field in a two-dimensional cross section of a flow field is described. The temperature sensors used are fast-response temperature-sensitive micro-encapsulated liquid crystal particles. Illuminating the flow by a thin sheet of white light, the reflected colors from the liquid-crystal particles were captured through a 3-chip video color camera and stored onto a videotape for subsequent data processing. The temperature field was obtained through an automatic color-temperature calibration scheme in HSI rather than RGB space, thus allowing for data processing of approximately one-third the time of RGB processing. The technique is finally applied to the study of a heated vortex-ring and some preliminary results are discussed.

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Application of liquid crystals to boundary- layer visualization

Cited by 18 publications

References 0 publications

Liquid Crystals and Their Application in Heat Transfer Measurements

Liquid Crystals and Their Application in Heat Transfer Measurements

Shear-stress sensitive liquid crystals for hypersonic boundary-layer transition detection

Digital particle image thermometry: The method and implementation

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