Characterization of Non-linear Internal Waves Using PIV/PLIF Techniques

Internal waves are ubiquitous in the ocean. They often form regions of high temperature or salinity variability as pycnocline oscillates to wave (Phillips, 1966). can be generated either from interaction tidal currents with submarine bathymetry (Garrett and Kunze, 2007) by wind stress at ocean surface (Munk Wunsch, 1998). The current study addresses non-linear internal due their importance mixing dynamics both atmospheric oceanographic flows. Due significance this phenomena, numerous investigations have been conducted obtain satisfactory theoretical solutions for several types fluid systems. verification these models requires precise accurate experimental data. It should noted that such generally assume simple two-layer stratified system separated a sharp interface. In reality, there is gradient density interface two layers, which make analysis more challenging. To date, most studies performed using ultrasonic probes, conductivity resistance-type gauges, salinity-sensor-type given Davis Acrivos (1967),Koop Butler (1981),Michallet Barthelemy (1998) Umeyama (2002). There one recent used particle image velocimetry (PIV) technique determine Eulerian velocity field waves, but it lacks detailed measurements necessary fully understand flow (Umeyama Matsuki, 2011). work aims measuring fields, then comparing results solution. A laboratory-scale apparatus was created replicate characteristics twolayer system. An configuration presented jump 1.1 1.5 σt separately. Experiments tank (2.438 m × 50 cm cm), constructed clear acrylic sheets thickness 1.905 cm. schematic wavemaker shown Fig. 1(a) (Mohaghar et al., 2020). line diffuser (PVC) installed along middle floor fill tank. half-cylinder plunger-type create perturbation represented between layers. On each revolution drive mechanism, switch sent voltage signal external trigger port pulse generator. By precisely controlling delay following signal, generator Nd:YAG laser camera capture an targeted phase cycle. Images recorded resolution 29 MP CCD camera, (14-bits, 6600 4400 pixels). PIV measure field, fluids layers were seeded neutrallybuoyant particles. particles illuminated dual-cavity New Wave Research Gemini wavelength 532 nm, diverged into sheet. Light entering passed through nm bandpass filter. pairs processed Insight 4GTM software 32 pixel final spot size 50% overlap. sample vector case ∆ρ = 1.5σt 1(b). order visualized planar laser-induced fluorescence (PLIF) method scalar visualization. laser-fluorescing dye, Rhodamine 6G, mixed heavier layer light sheet fluoresce dye. Following procedures outlined Mohaghar (2019), dye concentration inferred digital images. only emitted equipped notch filter blocking light. PLIF 1(c). location, gradient, amplitude period, vorticity kinetic energy shear strain rate quantified phases cycle subsequently compared corresponding predictions based on third-order Stokes internal-wave theory.