Seasonal variation of air quality in a city with a large river was investigated by means of numerical simulations of air movement and pollutant dispersion over inversion-capped diurnal cycles using a Reynolds-averaged Navier–Stokes (RANS) approach with algebraic turbulent flux model. The study accounts for the effects of urban heat island (UHI), terrain orography and high thermal inertia of the river body. The case mimics the real environment of the Krasnoyarsk region with the river Yenisei (Russia). Two scenarios were considered typical of the winter and summer seasons. The study is focused on the dynamics of dispersion of CO emanating mainly from road traffic, which remains fairly uniform throughout the year. The simulation starts from a mild low-altitude inversion with penetrative convection gradually developing over the daytime and attenuating during the night. The main difference between the two cases is in the temperature of the river surface relative to the ambient air. In winter, the non-freezing river acts as a source of positive thermal buoyancy, while in summer the cool river at the daytime acts in the opposite way, as a heat sink. The effect of the river-induced air circulation appears significant enough to account for the observed winter accumulation of the pollutant in the city center.

We present a numerical model suitable for simulation of shock or blast waves passing through a cloud of water droplets. The model takes into account the droplet breakup, radiation, and evaporation effects. The gas phase (a mixture of air and water vapor) is solved within an Eulerian framework with a set of compressible transport equations. The disperse phase (water droplets) is represented by a number of Lagrangian parcels of a specified size and mass distribution. The model has been verified with experimental data. The results show that for large (millimeter-sized) droplets with high Weber numbers, the breakup model is the most important part for accurate representation of the wave-droplet interaction phenomena, while for very fine droplets (1 \(\mu\)m or less), the evaporation effects are the strongest in the shockwave mitigation process. The radiative heat flux increase due to high droplet emissivity is found to be possible for an intermediate size water droplets (about 10–20 \(\mu\)m) in the case of continuous heat release.

The article presents the results of direct numerical simulation of a turbulent vortex ring with a moderate Reynolds number, interacting with the field of external turbulent fluctuations. The ring is formed by buoyancy forces from a spherically-shaped volume of elevated temperature. We consider the interaction of the ring with the field of turbulent fluctuations (of temperature and velocity) located in the form of a horizontal layer in front of the ring. The effect of separation of vortices by the sign of vorticity in a layer of fluctuations (with respect to the rotation of the ring) during the passage of the ring through this field has been found. This effect first causes the ring to slow down when the fluctuations pass outside the ring, and then to accelerate with decreasing radius when the fluctuations pass through its center. Due to buoyancy effects in the fluctuations layer, the separation of hot and cold air occurs. During the interaction with the ring, this leads to the accumulation of the reduced temperature in the core of the ring, while the increased temperature is accumulated near the axis. This temperature distribution results in a baroclinic vorticity generation leading to the reduction of the ring radius.

We present the results of Large Eddy Simulation of a turbulent jet discharging into a confined slot with the wall spacing to jet inlet width ratio = 0.1 and Re = 10⁴. The jet exhibits a meandering motion accompanied by formation of checkerboard pattern of large vortices in the mixing layer. A passive scalar transport was simulated with uniform inlet distribution of the scalar. It was found that the fluctuations of spanwise velocity component grow downstream and their maximum location is migrating from the lateral boundaries of the jet (free-shear layers) to the wall-boundary layers. Some evidence of counter-gradient turbulent scalar transport was found in the mixing layers of the jet, which may be attributed to the influence of observed large-scale checkerboard-type vortices.