Superfluid helium consists of two inter-penetrating fluids, a viscous normal fluid and an inviscid superfluid, coupled by a mutual friction. We develop a two-fluid shell model to study superfluid turbulence and investigate the energy spectra and the balance of fluxes between the two fluids in a steady state. At sufficiently low temperatures a ’bottle-neck’ develops at high wavenumbers suggestin...

The specific objectives of this project are to obtain a critical evaluation of turbulence closure models that are commonly used in the coastal ocean, and to identify ways to improve these models. Of particular interest are the MY-2.5 model (Mellor and Yamada, 1974, 1982) and the k-e model (e.g., Rodi, 1987), which involve coupled equations describing turbulent kinetic energy and turbulent scale...

Transitional pipe flow is modeled as a one-dimensional excitable and bistable medium. Models are presented in two variables, turbulence intensity and mean shear, that evolve according to established properties of transitional turbulence. A continuous model captures the essence of the puff-slug transition as a change from excitability to bistability. A discrete model, which additionally incorpor...

The goal of this research is to investigate how well various turbulence models can describe physical properties of the upper convective boundary layer of the Sun. An accurate modeling of the turbulence motions is necessary for understanding the excitation mechanisms of solar oscillation modes. We have carried out realistic numerical simulations using several different physical Large Eddy Simula...

Recent experimental investigations and physical modeling studies have indicated that turbulence behaviors within a liquid jet have considerable effects on the atomization process. For certain flow regimes, it has been observed that the liquid jet surface is highly turbulent. This turbulence characteristic plays a key role on the breakup of the liquid jet near to the injector exit. Other experim...

Recent experimental investigations and physical modeling studies have indicated that turbulence behaviors within a liquid jet have considerable effects on the atomization process. For certain flow regimes, it has been observed that the liquid jet surface is highly turbulent. This turbulence characteristic plays a key role on the breakup of the liquid jet near to the injector exit. Other experim...

Particles suspended in turbulent flows are affected by the turbulence and at the same time act back on the flow. The resulting coupling can give rise to rich variability in their dynamics. Here we report experimental results from an investigation of finite-sized buoyant spheres in turbulence. We find that even a marginal reduction in the particle's density from that of the fluid can result in s...

Atmospheric convective boundary layer (CBL) entrainment is the downward mixing of free atmospheric air into the CBL as the CBL grows. Primarily, the CBL entrainment is driven by the buoyancy production of turbulence kinetic energy (TKE) due to heating of the lower surface or cooling at the CBL top. The effects of shear-generated turbulence in the CBL are secondary. However, cases of a purely bu...

It is now generally accepted that statistical turbulence models are unlikely, ever, to enable highfidelity predictions of massively-separated flows, especially if separation occurs from curved three-dimensional surfaces. In such circumstances, even the most elaborate turbulence models are ill-equipped to capture the dynamics associated with highly-unsteady and intense large-scale motions that a...