Eulerian Lagrangian Computational Fluid Dynamics Research Articles

Local impact of dust storms around a suburban building in arid and semi-arid regions: numerical simulation examples from Dubai and Riyadh, Arabian Peninsula

Dust storms are common in arid and semi-arid regions, e.g., the Arabian Peninsula, where undisturbed wind can either weather the rocks and transport the grains for kilometers over the landscape or even overseas, or form dunes and ripples. We used a multiphase Eulerian–Lagrangian computational fluid dynamics model to investigate the impact of dust storms in the form of density current on a 10 × 10-m building. This numerical investigation particularly applies to the suburbs of metropolis, consisting of peripheral neighborhoods of meter-scale buildings that, as suggested by our results, can strongly affect the path of the storm before impacting the Downtown. Our results of flow-building interaction on pulsating (CASE 1) versus sustained (CASE 2, reference) and long-lived (CASE 3) storm show a strong amplification of flow dynamic pressure up to a factor of about 14 in streamwise direction and a heavy grain accumulation of about 800 kg around the building. With respect to reference sustained storm, the results show a more intense pressure amplification up to about 12 for slower (CASE 4) or coarser (CASE 5) storm, but a less intense amplification up to about 3 for more dilute storm (CASE 6) in transverse direction. Maximum grain accumulation around the building is of about 4,300 kg (55 % is on building front) for coarser storm, whereas high fog in the building rear occurs for more dilute storm. These results can be useful when assessing the impact of dust storms against buildings.

Comparison between CFD and Surface Overflow Rate Models to Predict Particulate Matter Separation in Unit Operations for Combined Sewer Overflows

AbstractModeling particulate matter (PM) separation has been a significant topic since unit operations (UOs) has been introduced for clarification of combined sewer overflows (CSOs). In contrast with surface overflow rate (SOR) model, long debated for the limits of its applicability, computational fluid dynamics (CFD) has been an emerging tool for accurately predicting hydrodynamics and PM transport in UOs. In this study an Eulerian-Lagrangian CFD model and a SOR model coupled with particle size distribution (PSD) are used to predict PM separation from three Type I settling UOs with same surface area (SA) but different inlet locations. UOs are loaded with hydraulic conditions and PM gradation measured from samples collected in the combined sewer system of the city of Cosenza, Italy. Specifically, the samples characterize the influent flow entering into a detention tank located downstream of the combined sewer system. The detention tank is used for treating the combined sewer by gravitational settling. The...

Numerical simulation of a novel energy-efficient dew-point evaporative air cooler

We present simulation results on a novel dew-point evaporative air conditioner which was designed based on a counter-flow closed-loop configuration consisting of separated working channels and product channels. The novel evaporative air conditioner is able to cool air to temperature below ambient wet-bulb temperature and approaching dew-point temperature. To investigate the performance of the evaporative air cooler under a variety of conditions, the Eulerian–Lagrangian computational fluid dynamics (CFD) model was adopted. We validated the model by comparing the temperature distributions and outlet air conditions against experimental data. The numerical model showed good agreement with the experimental findings to within±10%. Impacts due to the inlet air condition, the air flow velocity, the dimension of the airflow passages, and the product-to-working air flow ratio on the cooler performance were analyzed. Simulation results have indicated that the novel dew-point evaporative air conditioner is able to achieve a higher wet-bulb and dew-point effectiveness with lower air velocity, smaller channel height, larger length-to-height ratio, and lower product-to-working air flow ratio.

Abrasion predictions for Francis turbines based on liquid–solid two-phase fluid simulations

The runner blades and guide vanes of Francis turbines are worn by sediment in the flow. However, there are few studies about abrasion of the runner blade and guide vane for normal turbine operating conditions. This study investigated the relation between the wear rates on the surfaces of the runner blade and guide vane and the sediment concentration, and analyzed the distribution of the wear rates for normal turbine operating condition. An Eulerian–Lagrangian Computational Fluid Dynamics (CFD) procedure was used to simulate steady liquid–solid two-phase flow for various operating conditions. The Finnie model was then used to predict the abrasion. The conditions leading to abrasion in the inner flow passage components of a Francis turbine are clarified through analysis of the abrasion conditions for the runner blades and guide vanes. Field tests and simulations show that the relative wear rate on the runner blades and guide vanes increases with increasing sediment concentration, and the maximum wear on the runner blades occurs in a small opening region with the maximum increasing as the head increases. The maximum wear on the guide vanes occurs at the maximum output and the relative wear rate on the runner blades is much greater than that on the guide vanes. There is no good data, so the relative wear rates on the runner blades and the guide vanes can only be obtained numerically. Thus actual wear rates cannot be given and are beyond the scope of this paper. This paper shows the abrasion characteristics on the runner blades and guide vanes with sediment flow and provides reference data for predicting the abrasion conditions in the flow passage components of a Francis turbine.

CFD study of droplet atomisation using a binary nozzle in fluidised bed coating

An Eulerian–Lagrangian computational fluid dynamics (CFD) model was built to describe two-fluid atomisation in a tapered fluidised bed coater using the air-blast/air-assisted atomiser model. Atomisation was modelled both with and without the inclusion of the solid phase (i.e. gas–liquid and gas–solid–liquid multiphase modelling). In addition, a multi-fluid flow model (Eulerian–Eulerian framework) combined with a population balance model was used as an alternative approach for modelling the spray produced by a two-fluid nozzle. In this approach, the CFD solver couples the population balance equation along with the Navier–Stokes equations for predicting the droplet diameter and mass fraction distribution. Comparison between simulated spray pattern (gas–liquid model) and that experimentally visualised by means of UV illumination was made and a good agreement was obtained. Parametric studies were done in order to investigate the effects of operating conditions on spray cone and liquid mass fraction inside the reactor. Furthermore, comparison of time-averaged fluidised bed behaviour with the inclusion of sprays obtained by both gas–solid–liquid multiphase modelling methods is presented.

Simulation of cavitation in outward-opening piezo-type pintle injector nozzles

The onset and development of cavitation in the annular needle seat passage of piezo-driven outward-opening pintle injector nozzles used with spray-guided direct-injection gasoline engines are studied using a Eulerian-Lagrangian computational fluid dynamics cavitation model. Cavitation is formed because of the fluid acceleration taking place at the needle sealing area and it has been found to be affected by its geometric details. Various submodels for nucleation and bubble formation, further bubble growth and collapse, as well as bubble break-up and transport are incorporated into the model. Qualitative model validation is performed against experimental data reported elsewhere in large-scale nozzle replicas, showing similar cavitation patterns to be formed. These consist of vapour pockets rather than a continuous vapour film and develop transiently in a rather chaotic manner around the circumferential needle sealing area, even under stationary geometry and fixed-flowrate conditions. Further transient effects associated with the fast opening and closing of the piezo-controlled needle valve are also presented.

A tabulated chemistry approach for numerical modeling of diesel spray evaporation in a “stabilized cool flame” environment

Droplet evaporation in a “stabilized cool flame” environment leads to a homogeneous, heated air–fuel vapor mixture that can be subsequently either burnt or utilized in fuel-reforming applications for fuel cell systems. The paper investigates the locally occurring physico-chemical phenomena in an atmospheric pressure, diesel spray, stabilized cool flame reactor, utilizing a tabulated chemistry approach in conjunction with a two-phase, Eulerian–Lagrangian computational fluid dynamics code. Actual diesel oil physical properties are used to model spray evaporation in the two-phase simulations, whereas the corresponding chemistry is represented by n-heptane. A lookup table is constructed by performing a plethora of perfectly stirred reactor simulations, utilizing a semidetailed n-heptane oxidation chemical kinetics mechanism. The overall exothermicity of the preignition n-heptane oxidation chemistry and the fuel consumption rates are examined as a function of selected independent parameters, namely temperature, fuel concentration, and residence time; their influence on cool flame reactivity is thoroughly studied. It is shown that the tabulated chemistry approach allows accurate investigation of the chemical phenomena with low computational cost. The two-phase flow inside the stabilized cool flame reactor is simulated, utilizing the developed lookup table. Predictions are presented for a variety of test cases and are compared to available experimental data, with satisfactory agreement. Model validation tests indicate that prediction quality improves with increasing values of air temperature at the reactor's inlet.