Characterization of non-linear internal waves using PIV/PLIF techniques

Internal waves are a fascinating physical phenomenon that play an important role in the mixing and dynamics of both atmospheric and oceanographic flows. This experimental study addresses non-linear internal waves due to their importance in shaping the circulation and distributions of heat and carbon within density stratified systems. We aim to fully understand the dynamics of internal waves by measuring the density and velocity fields using combined PLIF/PIV measurements and comparing the experimental results with the theoretical non-linear wave solution. Non-linear theory is required due to the non-negligible amplitude of the wave compared to the wavelength. A laboratory-scale apparatus was created to replicate the flow characteristics of standing internal waves in a two-layer stratified system. Experimental results are presented for configurations with a density jump of 1.1 and 1.5 σ_t (separately). The interface location, density gradient, wave amplitude and period, velocity and vorticity fields, kinetic energy, and shear strain rate are quantified at several phases in one wave cycle. The experimental results are compared with the corresponding predictions based on third-order Stokes internal-wave theory. The results showed that the 3^rd-order non-linear theory does an outstanding job of describing the internal wave flow.