Surface topography of jet shock cells in a hydraulic analogy

The photograph in Fig. 1 (top) shows text visualized through free surface flow, which serves as a hydraulic analogy of an underexpanded two-dimensional jet at Froude number 1.35 [analogous to Mach number (Buchanan et al. 2007)]. The text is illuminated by a halogen lamp from below a water table and used as a Fig. 1 Photograph (top) of the analogy to shock cells downstream of a nozzle at Mach number 1.35, with flow from left to right. The text below the water flow is used as a reference for surface reconstruction; time-averaged surface (bottom) topography of the shock cells of the same flow, the contours indicate the surface gradient in the flow direction, increasing from blue to red (negative to positive). The reconstructed surface from the reference image topography technique matches well with the real free surface flow