OPEN ACCESS
This paper discusses how colour is used in experimental fluid flow studies. Firstly, colour (defined scientifically by the wavelength of the light) can be used to discriminate between different channels in optical instrumentation, making it possible to measure several flow properties, simultaneously, and without any intrusion into the flow. These aspects of modern flow measurement are discussed in terms of some examples. Alternatively, the results of the flow measurement may be represented in the form of images, graphs and three-dimensional schematics with colour being used to identify and emphasise particular features that might otherwise remain concealed. The experimental results presented in the paper confirm that using colour to discriminate between sets of data has several important advantages over the older black and white or grey scale forms of representation. Not only do colours provide an excellent basis for communication through graphical and three-dimensional presentations, but the resulting clarity may also help to reveal complex forms of fluid flow behaviour. Moreover, the inherent artistic appeal of some colour representations can draw the viewer into the technical detail, helping to simplify physical phenomena in ways that would not otherwise be possible. Although the observations made on the presentation of data are illustrated with reference to a number of experimental fluid flow problems, many of the methods and observations would be applicable in other situations, where scientific or technological data needs to be presented.
colour, data presentation, experiment, fl uid fl ow measurement, graphics, images, light, understanding, wavelength
[1] Turner, J.T. & Zhang, S., Analysis, presentation, and understanding in experimental fl uid fl ow studies: an evolutionary story. J. Optics and Laser Technology. (doi: 10.1016/ j.optiastec.2009.12.002).
[2] For information on the work of Leonardo da Vinci. Available from: (a) www.efl uids.com/ efl uids/gallery/gallery_pages/da_vinci_page.htm; (b) http://en.wikipedia.org/wiki/Leonardo_ da_Vinci#Scientifi c_studies.
[3] Bertolotti, M., The History of the Laser, CRC Press, 2005.
[4] For the invention of the laser. Available from: www.bell-labs.com/history/laser/. Additionally, regarding the disputed ownership of this invention. Available from: http://www.essortment.com/all/historylaserin_rnxv.htm.
[5] Yeh, Y. & Cummins, H.Z., Localized fl uid fl ow measurements with a He–Ne laser spectrometer. Applied Physics Letters, 4, p. 176, 1964.
[6] Durst, F., Melling, A. & Whitelaw, J.H., Principles and Practice of Laser-Doppler Anemometry, Academic Press, 1976.
[7] Albrecht, H.E., Borys, M., Damaschke, N. & Tropea, C., Laser Doppler and Phase Doppler Measurement Techniques, Springer–Verlag, 2003.
[8] Adrian, R.J., Twenty years of particle image velocimetry. Experiments in Fluids, 39(2), pp. 159–169, 2005. doi:10.1007/s00348-005-0991-7
[9] For alternative methods of colour representation, the defi nition of a pixel, and information on the colour and spatial responses of the human eye. Available from: (a) http://www.klammeraffe. org/~fritsch/uni-sb/fsinfo/Papers/webdesign/webdesign.html; (b) http://en.wikipedia.org/wiki/ Color_vision; (c) http://www.stanford.edu/class/ee368b/Handouts/09-HumanPerception.pdf.
[10] Hiller, W. & Kowalewski, T.A., Simultaneous measurement of the temperature and velocity fi elds in thermal convective fl ows, in Flow Visualization IV, ed C. Veret, Hemisphere: Paris, pp. 617–622, 1987.
[11] For an informative introduction to particle image velocimetry (PIV). Available from: www.holomap.com/dpiv.htm.
[12] Papadopoulou, K.A., Shamout, M.N., Lennox, B., Mackay, D., Taylor, A.R., Turner, J.T. & Wang, X., An evaluation of acoustic refl ectometry for leakage and blockage detection. I.Mech.E. Proc., Series E, 222(6), pp. 959–966, 2008.
[13] Papadopoulou, K.A., Leakage and Blockage Detection in Pipelines Using an Acoustic Inspection Tool, PhD thesis, University of Manchester, 2008.
[14] Zhang, S., Digital imaging and optical fl ow diagnostics applied to turbulent jets with and without excitation, PhD thesis, University of Manchester, 2006.
[15] Szajner, A. & Turner, J.T., Visualisation of an aerodynamically excited free jet, in Flow Visualization IV, ed C. Veret, Hemisphere: Paris, pp. 533–539, 1987.
[16] Zhang, S. & Turner, J.T., Aerodynamic control of a free turbulent jet using helical excitation. Eighth International Symposium on Fluid Control, Measurement and Visualization (Flucome). Chengdu, China, 2005.
[17] Merzkirch, W., Flow Visualization, Academic Press: New York, 1987.