The COVID-19 pandemic has generated many concerns about cross-contamination risks, particularly in hospital settings and Intensive Care Units (ICU). Virus-laden aerosols produced by infected patients can propagate throughout ventilated rooms and put medical personnel entering them at risk. Experimental results found with a schlieren optical method have shown that the air flows generated by a cough and normal breathing were modified by the oxygenation technique used, especially when using High Flow Nasal Canulae, increasing the shedding of potentially infectious airborne particles. This study also uses a 3D Computational Fluid Dynamics model based on a Lattice Boltzmann Method to simulate the air flows as well as the movement of numerous airborne particles produced by a patient’s cough within an ICU room under negative pressure. The effects of different mitigation scenarii on the amount of aerosols potentially containing SARS-CoV-2 that are extracted through the ventilation system are investigated. Numerical results indicate that adequate bed orientation and additional air treatment unit positioning can increase by 40% the number of particles extracted and decrease by 25% the amount of particles deposited on surfaces 45s after shedding. This approach could help lay the grounds for a more comprehensive way to tackle contamination risks in hospitals, as the model can be seen as a proof of concept and be adapted to any room configuration.

The COVID-19 pandemic has generated many concerns about cross-contamination risks, particularly in hospital settings and Intensive Care Units (ICU). Virus-laden aerosols produced by infected patients can propagate throughout ventilated rooms and put medical personnel entering them at risk. Experimental results found with a schlieren optical method have shown that the air flows generated by a cough and normal breathing were modified by the oxygenation technique used, especially when using High Flow Nasal Canulae, increasing the shedding of potentially infectious airborne particles. This study also uses a 3D Computer Fluid Dynamics model based on a Lattice Boltzmann Method to simulate the air flows as well as the movement of numerous airborne particles produced by a patient’s cough within an ICU room under negative pressure. The effects of different mitigation scenarii on the amount of aerosols potentially containing SARS-CoV-2 that are extracted through the ventilation system are investigated. Numerical results indicate that adequate bed orientation and additional air treatment unit positioning can increase by 40% the number of particles extracted and decrease by 25% the amount of particles deposited on surfaces 45s after shedding. This approach could help lay the grounds for a more comprehensive way to tackle contamination risks in hospitals, as the model can be seen as a proof of concept and be adapted to any room configuration.

During the Covid-19 pandemic, location of the SARS-CoV-2 infected patients inside the hospital is a major issue to prevent viral cross-transmission. The objective of this study was to evaluate the risk of contamination through aerosol by using a global approach of the multiple environmental parameters to simulate, including seasonal context. A computational fluid dynamic (CFD) simulation based on the Lattice Boltzmann Method approach was used to predict airflow on the entire floor of a private hospital in Paris. The risk of contamination outside the rooms was evaluated by using a water vapor mass fraction tracker. Finally, the air contamination was estimated by a “cough model” producing several punctual emissions of contaminated air from potentially infected patients. In a winter configuration, the simulation showed a well-balanced ventilation on the floor and especially inside the rooms. After cough emissions from COVID-positive rooms, no significant contamination was observed in the circulation area, public waiting space and nurse office. On the contrary, in a summer configuration, the temperature difference due to the impact of the sun radiation between both sides of the building created additional air transport increasing the contamination risk in neighboring rooms and public spaces. Airborne spread was limited to rooms during winter conditions. On the contrary, during summer conditions, market airflow with potentially contaminated air coming from rooms located on the side of the building exposed to solar radiation was evidenced. These observations have implications to locate infected patients inside the building and for the conception of future health care structures.

Film Cooling is a crucial technology for engine manufacturer to develop high-efficiency gas turbine engines by raising turbine entry temperature. A lot of cooling holes geometries have been studied in the past few years in tests, as well as numerical simulations. Shaped holes are nowadays a standard geometry for protecting the blades, given the performance improvement compared to cylindrical holes. Numerical correlation with physical tests is challenging due to the high sensitivity to thermal mixing and adequate boundary condition predictions. This paper is devoted to numerical simulation comparisons of the 777 shaped holes configuration of Pennsylvania State University, for an incompressible flow with a density ratio of 1.5, a blowing ratio of 1.5 and a free stream turbulence intensity of 0.5%. Two different simulations have been chosen: a state-of-the-art RANS simulation with k-e Realizable model computed with ANSYS Fluent and a high fidelity solver Lattice-Boltzmann Method computed with Simulia PowerFLOW. In order to improve the accuracy of numerical simulations against test results, this article deals with an aerothermal model of the complete test bench. This additional modeling allows to strongly improve thermal prediction and to understand initial discrepancies related to test bench environment. Results show that k-ε Realizable simulation provides a good prediction of average effectiveness, but local differences appear due to inherent RANS modeling limitations. On the other hand, LBM simulation provides excellent results for both aerodynamic and thermal quantities: tests results are very well reproduced.

Modeling of the engine behavior in windmilling conditions is an important engineering objective. The relight capability of the engine is mainly associated with the air mass flow rate that passes through the engine high pressure core in those conditions. This is one of the parameters that drive the combustion chamber volume. Predicting the engine behavior is challenging, especially early in the development process. The pressure losses along the core are distributed between the different stages of the compressors and turbines, which are operated extremely far from their design point. Engine manufacturers must anticipate with sufficient margins to ensure that the specifications are met when the engine is finally qualified in flight. This article focuses on the behavior of compressor cascades in such conditions, corresponding to high negative incidences. A recently designed high pressure compressor is studied in windmilling conditions using three complementary approaches. First, engine tests are used to obtain validated 0D data for two flight conditions. Then, state of the art Lattice-Boltzmann Method (LBM) simulations are carried out to have insight in the flow characteristics inside the compressor. They are compared to the available experimental data. Finally, a 1D model using stage by stage Euler equation for turbomachinery is used. This kind of modeling is of particular interest because it can be used early in the design process. The correlations for losses and deviation angle from the literature are modified to account for the particularity of the flow in those conditions. One shows that the three approaches give consistent results.