Numerical Investigation of Space Launch Vehicle Base Flows with Hot Plumes

The flow field around generic space launch vehicles with hot exhaust plumes is investigated numerically. Reynolds-Averaged Navier-Stokes (RANS) simulations are thermally coupled to a structure solver to allow determination of heat fluxes into and temperatures in the model structure. The obtained wall temperatures are used to accurately investigate the mechanical and thermal loads using Improved Delayed Detached Eddy Simulations (IDDES) as well as RANS. The investigated configurations feature cases both with cold air and hot hydrogen/ water vapour plumes as well as cold and hot wall temperatures. It is found that the presence of a hot plume increases the size of the recirculation region and changes the pressure distribution on the nozzle structure and thus the loads experienced by the vehicle. The same effect is observed when increasing the wall temperatures. Both RANS and IDDES approaches predict the qualitative changes between the configurations, but the reattachment location predicted by IDDES is up to 7% further upstream than that predicted by RANS. Additionally, the heat flux distribution along the nozzle and base surface is analysed and shows significant discrepancies between RANS and IDDES, especially on the nozzle surface and in the base corner.

Characteristics of sub-10 nm particle emissions from in-use commercial aircraft observed at Narita International Airport

Civil aviation is undergoing rapid growth as a result of global economic development. Characterizing ultrafine particle emissions from jet aircraft equipped with turbofan engines, which are commonly used in civil aviation, is an important issue for the assessment of the impacts of aviation on climate and on human health. Previous studies have reported that particle number emissions from jet aircraft are dominated by volatile particles (mainly sulphate and organics) with mode diameters of 10–20 nm and that non-volatile particles (mainly soot) exhibit mode diameters of ~20–60 nm, depending on the engine types and thrust conditions. However, there are significant uncertainties in measuring particles with diameters smaller than ~10 nm, especially when fresh aircraft exhaust plumes are measured near the emission sources. We conducted field observations of aerosols and carbon dioxide (CO2) near a runway of Narita International Airport, Japan, in February 2018, with specific focuses on the contributions of sub-10 nm size ranges to total and non-volatile particles. Spiked increases in particle number concentrations and CO2 were observed to be associated with wind directions from the runway, which can be attributed to diluted aircraft exhaust plumes. We estimated the particle number emission indices (EIs) for discrete take-off plumes. The median total particle number EI with diameters larger than 2.5 nm was ~60 times greater than the median non-volatile particle number EI with diameters larger than 10 nm for take-off plumes. This value can be interpreted as the difference between total particle number emissions under real-world conditions and non-volatile particle number emissions regulated by standard engine tests. More than half of particle numbers in the plumes were found in the size range smaller than ~10 nm on average for both total and non-volatile particles. The mode diameters of the size distributions of particle number EIs were found to be smaller than ~10 nm in most cases, and the peak EI values were larger than those previously reported under real-world operating conditions. This study provides new insights into the significance of sub-10 nm particles in aircraft exhaust plumes under real-world conditions, which is important in understanding aviation impacts on human health and also in developing aviation emission inventories for regional and global models.

Impact of exhaust emissions on chemical snowpack composition at Concordia Station, Antarctica

The chemistry of reactive gases inside the snowpack and in the lower atmosphere was investigated at Concordia Station (Dome C), Antarctica, from December 2012 to January 2014. Measured species included ozone, nitrogen oxides, gaseous elemental mercury (GEM), and formaldehyde, for study of photochemical reactions, surface exchange, and the seasonal cycles and atmospheric chemistry of these gases. The experiment was installed ≈1 km from the station main infrastructure inside the station clean air sector and within the station electrical power grid boundary. Ambient air was sampled continuously from inlets mounted above the surface on a 10 m meteorological tower. In addition, snowpack air was collected at 30 cm intervals to 1.2 m depth from two manifolds that had both above- and below-surface sampling inlets. Despite being in the clean air sector, over the course of the 1.2-year study, we observed on the order of 50 occasions when exhaust plumes from the camp, most notably from the power generation system, were transported to the study site. Continuous monitoring of nitrogen oxides (NOx) provided a measurement of a chemical tracer for exhaust plumes. Highly elevated levels of NOx (up to 1000 × background) and lowered ozone (down to ≈50 %), most likely from reaction of ozone with nitric oxide, were measured in air from above and within the snowpack. Within 5–15 min from observing elevated pollutant levels above the snow, rapidly increasing and long-lasting concentration enhancements were measured in snowpack air. While pollution events typically lasted only a few minutes to an hour above the snow surface, elevated NOx levels were observed in the snowpack lasting from a few days to ≈ 1 week. GEM and formaldehyde measurements were less sensitive and covered a shorter measurement period; neither of these species' data showed noticeable concentration changes during these events that were above the normal variability seen in the data. Nonetheless, the clarity of the NOx and ozone observations adds important new insight into the discussion of if and how snow photochemical experiments within reach of the power grid of polar research sites are possibly compromised by the snowpack being chemically influenced (contaminated) by gaseous and particulate emissions from the research camp activities. This question is critical for evaluating if snowpack trace chemical measurements from within the camp boundaries are representative for the vast polar ice sheets.