Analytic reconstruction of a two-dimensional velocity field from an observed diffusive scalar. (25th July 2019)

• Record Type: Journal Article
• Authors: Sharma, Arjun; Rypina, Irina I.; Musgrave, Ruth; Haller, George
• Is Part Of: Journal of fluid mechanics. Volume 871(2019)
• Page Start: 755
• Page End: 774
• Publication Date: 2019-07-25
• Subjects: computational methods, -- mixing and dispersion, -- ocean circulation; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2019.301
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Inverting an evolving diffusive scalar field to reconstruct the underlying velocity field is an underdetermined problem. Here we show, however, that for two-dimensional incompressible flows, this inverse problem can still be uniquely solved if high-resolution tracer measurements, as well as velocity measurements along a curve transverse to the instantaneous scalar contours, are available. Such measurements enable solving a system of partial differential equations for the velocity components by the method of characteristics. If the value of the scalar diffusivity is known, then knowledge of just one velocity component along a transverse initial curve is sufficient. These conclusions extend to the shallow-water equations and to flows with spatially dependent diffusivity. We illustrate our results on velocity reconstruction from tracer fields for planar Navier–Stokes flows and for a barotropic ocean circulation model. We also discuss the use of the proposed velocity reconstruction in oceanographic applications to extend localized velocity measurements to larger spatial domains with the help of remotely sensed scalar fields.