Schlieren visualisation and measurement of axisymmetric disturbances.

• Author(s) / Creator(s)

  • Flynn, M.R.
  • Onu, K.
  • Sutherland, B. R.

• Abstract. Synthetic schlieren is a new technique that allowsone easily and inexpensively to visualise density variations, such as those caused by internal waves propagating in a density stratified fluid. In the special case of twodimensional internal waves (for example, those created by an oscillating cylinder), synthetic schlieren allows one to measure non-intrusively the wave amplitudes everywhere in space and time. The technique works by measuring the apparent displacement of points in a digitised image (such as a grid of horizontal lines), which is observed by a CCD camera through the experimental test section. Synthetic schlieren is sufficiently sensitive that it can measure sub-pixel-scale disturbances. In this work, we report on the first step toward measuring fully three-dimensional disturbances. We perform laboratory experiments in which internal waves are generated in a uniformly salt-stratified fluid by a vertically oscillating sphere. Theory predicts that the resulting wave-field is in the form of two cones emanating above and below the sphere. Using inverse tomographic techniques, we exploit the axisymmetry of the wave-field to relate the apparent displacement of pixels in an image to the wave amplitudes.

• Date created

  2002

• Subjects / Keywords

  • Internal waves
  • Visualise density variations
  • Synthetic schlieren

• Type of Item

  Article (Published)

• DOI

  https://doi.org/10.7939/R3SJ1B48P

• License

  Attribution-ShareALike 4.0 International