Two Fluid Model Simulations of Short and Long Wave Instabilities
Abstract: The topic of the seminar is the Two-Fluid Model (TFM) simulations of the Kelvin-Helmholtz (KH) instability and the Density Wave Instability (DWI).
The stability of the TFM has been an outstanding problem for fifty years. It has been claimed that the TFM is ill posed. The KH instability is the physical cause of the ill posed problem. While this problem has been addressed only from mathematical and numerical perspectives, the real problem is that the TFM is incomplete. Adding appropriate short wave physics turns the TFM hyperbolic-dispersive rather than elliptic and chaotic Lyapunov stable instead of ill-posed. The resulting chaotic interfacial behavior has been identified, simulated and validated experimentally.
A physical well posed TFM does not require artificial regularization. One advantage is that the TFM simulations become more accurate. To demonstrate it, a well posed TFM is used to perform simulations of the long wave DWI. The simulations are verified with the theory of Ishii and the agreement is excellent. This verification could not be performed in the past.
The capability to simulate short and long wave instabilities with the TFM opens a new window for two-phase flow research.
Bio: Prof. Bertodano has been a member of the faculty of the Purdue School of Nuclear Engineering since 1992. He has collaborated with Prof. Ishii and Prof. Ransom on the basic research of the Two-Fluid Model (TFM) and on various problems of water nuclear reactor safety.
He received his Masters degree at MIT under the supervision of Prof. Griffith and his PhD at Rensselaer Polytechnic Institute under Prof. Richard Lahey. His involvement in two-phase flow research dates back more than three decades.
The modeling of turbulence within the TFM theory posed a major CFD challenge thirty years ago. Prof. Bertodano solved it by inserting a two-phase k-epsilon turbulence model based on linear superposition of bubble induced and shear induced turbulence which captures the general trend of two-phase turbulence under a wide range of conditions. This approach has become standard practice. His current work involves TFM RANS and URANS CFD models that focus on turbulent transport of dispersed flows, and also fundamental research of TFM stability.
