Experimental study of elevation- and depression-type internal solitary waves generated by gravity collapse

• Published in: Physics of fluids (1994) Vol. 31; no. 10
• Main Authors: Du, Hui, Wei, Gang, Wang, Shao-Dong, Wang, Xin-Long
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.10.2019
• Subjects: Amplitudes; Density; Elevation; Flow velocity; Fluid dynamics; Fluids; Flumes; Gravitation; Gravitational collapse; Phase velocity; Physics; Propagation; Solitary waves; Thickness
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/1.5121556

Gravity collapse in density stratified fluids can excite internal solitary waves (ISWs), which have been studied by creating initial steplike rectangular disturbances in two-layer fluid systems in stratified fluid flumes. The observation of the elevation- and depression-type ISWs has brought detailed insights into the conditions that generate stable propagation of ISWs and the properties thereof. In this work, the results of such experiments are compared with the wave profile, phase velocity, characteristic frequency, and induced flow velocity calculated by using nonlinear theories. In addition, we analyze the capacity of nonlinear theories to accurately predict the characteristics of stable ISWs generated by gravity collapse. The results show that ISWs are generated by the evolution of the propagating vortex that develops from the vertical shear movement in the mixed-density region of the fluid. The length L and depth D of the initial steplike disturbance and the upper- and lower-layer thicknesses h1 and h2 together determine the amplitude, number, and propagation state of the ISWs that are generated. For small-amplitude elevation- and depression-type ISWs (|a/H| < 0.04, where a and H are the amplitude and total depth of the stratified fluid, respectively), the generated ISWs are consistent with the Korteweg de Vries (KdV) theory. Large-amplitude ISWs, however, tend to be consistent with the extended KdV (eKdV) or Miyata–Choi–Camassa (MCC) theories. For larger (smaller) differences |h2 − h1|, the MCC (eKdV) theory provides the best prediction of large-amplitude ISWs.