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AbstractThe flow distribution in a condensate demineralizer vessel of a nuclear power plant is studied using the computational fluid dynamics (CFD) approach. The model simulates the flow through the packed resin bed installed in the vessel as well as the exit of flow through the porous resin retention assembly at the bottom of the vessel. The computational model is subsequently revised to assess the impact of a proposed modification to the retention assembly to enhance drainage of the vessel and minimize unwanted resin separation during resin bed regeneration. The subject model has been developed using the ANSYS ICEM CFD meshing tool and the FLUENT 6.3 CFD software as well as associated postprocessing tools. Comparisons of flow patterns in the vessel resin beds prior to and with the modification demonstrate a sharp increase in the flow rate at the end walls of the vessel, thus resulting in accelerated depletion of resin in high-velocity areas and nonuniform consumption of resin inventory. The computational results are also compared with a theoretical analysis of the basic process.

Fog simulation is a challenge due to the complex microphysical, radiative, and turbulent processes. C‐FOG (Coastal Fog) was a comprehensive experiment which aimed to improve our understanding and forecasting skill of fog in coastal areas of Atlantic Canada. An intermittent fog event, containing two fog periods occurring over the Grand Banks of Newfoundland beginning at 00:00 UTC on September 13, 2018, is investigated in this study. Our approach is to apply the Weather Research and Forecasting (WRF) model, in conjunction with a 1‐D model for the atmospheric boundary layer, PAFOG (Parameterized Fog model). Model results are evaluated against observations collected onboard the research vessel Hugh R. Sharp. We introduced an advection term to PAFOG to investigate the ability of the model to simulate the two‐level fog/stratus system and we developed a set of sensitivity experiments. Results suggest that PAFOG with the advection terms calculated from ERA5 shows a good ability to simulate intermittent fog caused by fog lifting as stratus, and by comparison, outperform results with advection terms derived from WRF simulations. Regarding the latter, in an experiment with high vertical resolution, WRF gives a delayed fog event, whereas with low vertical resolution, WRF gives descending stratus. Our results provide a possible methodology to study the detailed structure of fog/stratus using PAFOG, a sounding profile as initial conditions, and advection profiles derived from ERA5, with low computing cost. PAFOG with advection terms has ability to simulate intermittent fog/stratus system by successfully simulating TKE and radiative coolingHigh vertical resolution in WRF suggests a delayed fog onset; with lower vertical resolution, WRF can simulate descending stratusA detailed inversion structure for the initial vertical profile plays an important role in resulting in success of the PAFOG simulation PAFOG with advection terms has ability to simulate intermittent fog/stratus system by successfully simulating TKE and radiative cooling High vertical resolution in WRF suggests a delayed fog onset; with lower vertical resolution, WRF can simulate descending stratus A detailed inversion structure for the initial vertical profile plays an important role in resulting in success of the PAFOG simulation

The aim of this contribution is to present the results of laboratory experiments on the dynamics of basic self-propagating vortices generated in a large volume of fluid when a linear (P) and an angular (M) momentum are applied locally to a fluid. Using the method proposed, it is possible to generate a whole family of isolated (net vorticity is equal to zero) vortices with different values of the nondimensional parameter , which is proportional to the ratio of linear to angular momentum ( RP/M, Ris the eddy size). Typical examples include monopole ( 0), quasi monopole ( 0.1–0.3), quasi dipole ( 1), and dipole ( ∞).

Laboratory experiments dealing with Reynolds stress gradients in shear-free turbulence in homogeneous rotating fluids were conducted to better understand associated physical phenomena. The study was motivated by possible applications to the oceanic environment where such Reynolds stress gradients are ubiquitous (e.g. in the vicinity of the continental shelf break, where turbulence decays away from the boundary). The turbulence was generated by vertical oscillations of a circular shaft with O-ring surface roughness elements; the oscillation axis coincided with the axis of symmetry of the cylindrical test cell. In the absence of background rotation, the turbulence is strong in the immediate vicinity of the shaft surface and decays with the radial distance, r. The turbulence in the boundary layer is such that ur~uθ~w, where ur, uθ, w are the radial, azimuthal and vertical r.m.s. velocity components, respectively. These velocity components are found to be proportional to Sω, where S and ω are the stroke and frequency of the shaft oscillations, respectively, i.e. much the same as for the case of oscillating-grid turbulence, which has been studied extensively. When background rotation is present, the steady-state turbulent intensity close to the shaft is similar to that of the non-rotating experiments. Away from the shaft, in the central portion of the test cell, large-scale motions containing randomly distributed cyclonic and anticyclonic vortices are developed owing to small local Rossby numbers. In the vicinity of the shaft, a rectified anticyclonic flow Uθ is observed. The magnitude of Uθ is found to be proportional to the characteristic r.m.s. turbulence velocity u, but independent of the rate of background rotation. Consideration of the equations of motion shows that mean flows should not be expected if background rotation is absent. With rotation, however, the equations indicate that the turbulent stresses can initiate, further develop and then maintain a mean anticyclonic (rectified) flow around the cylinder; the azimuthal momentum equation is shown to play a critical role in the generation of the mean anticyclonic flow.

An isolated fluid mass travelling horizontally in a stratified layer is a phenomenon described alternatively as a detached gravity-current head or a strongly nonlinear solitary wave. A key feature of this flow is the transport of mass. Laboratory experiments examine the transition in time from a regime in which the flow is density driven, to one in which it is wave dominated. A simple means of creating this transitional regime, an isolated flow that exhibits both density and wave effects, is achieved by dropping a thermal into a linearly stratified layer. This transitional regime is called an ‘isolated propagating flow’. Parameters for which the transitional regime occurs are identified. Particle-tracking studies reveal the vertical flow structure. There is an upper zone that is wave dynamical, and a lower zone in which transport of mass occurs. The transported mass slowly leaks out, until the phenomenon resembles a weakly nonlinear solitary wave. The experiments mimic a thunderstorm microburst impacting a temperature inversion, which has aviation safety implications. In the ocean, cracks in the ice cap (polar leads) cause similar flows impacting the thermocline.