Flight Characteristics with Different Supercooled Large Droplet Ice Configurations

An evaluation of the effects of different ice configurations on the flight characteristics of a fixed-wing aircraft is presented. Within a joint research project of German Aerospace Center (DLR) and Brazilian aircraft manufacturer Embraer simulation models of three supercooled large droplet (SLD) ice configurations were developed for one Phenom 300 prototype. A specific flight test campaign with artificial SLD ice shapes on the aircraft was conducted to gather the relevant flight data. The simulation models for the different ice configuration were obtained by system identification, and specific results for the SLD-ice simulation models are provided. The analysis of aircraft characteristics was based on the results of these high-quality simulation models: the icing-induced changes of the flight performance characteristics evaluated by the interpretation of several parameters like thrust-to-weight ratio and specific excess power. The typical flight performance degradation was found for all ice configurations with different magnitude. The change of aircraft eigenmodes was investigated in detail by analysing the system matrix of the linearised models at a specific trim points. In addition, the diverse effects found for different ice configurations (App. C and SLD) are discussed and the change of root locus is analysed. Furthermore, ice-induced changes of the handling qualities are evaluated using numerical criteria of flying qualities standard “MIL-STD-1797 A”: no significant deterioration was found for the investigated ice configurations.

Clinical characterization of respiratory large droplet production during common airway procedures using high-speed imaging

During the COVID-19 pandemic, a significant number of healthcare workers have been infected with SARS-CoV-2. However, there remains little knowledge regarding large droplet dissemination during airway management procedures in real life settings. 12 different airway management procedures were investigated during routine clinical care. A high-speed video camera (1000 frames/second) was for imaging. Quantitative droplet characteristics as size, distance traveled, and velocity were computed. Droplets were detected in 8/12 procedures. The droplet trajectories could be divided into two distinctive patterns (type 1/2). Type 1 represented a ballistic trajectory with higher speed large droplets whereas type 2 represented a random trajectory of slower particles that persisted longer in air. The use of tracheal cannula filters reduced the amount of droplets. Respiratory droplet patterns generated during airway management procedures follow two distinctive trajectories based on the influence of aerodynamic forces. Speaking and coughing produce more droplets than non-invasive ventilation therapy confirming these behaviors as exposure risks. Even large droplets may exhibit patterns resembling the fluid dynamics smaller airborne aerosols that follow the airflow convectively and may place the healthcare provider at risk.

Antimicrobial Testing of Dry Surfaces through Large Droplet Inoculation

The Large Droplet Inoculation (LDI) protocol for testing antimicrobial coatings and treatments is simple, reproducible, and closely mimics real-world conditions at solid/air interfaces. This is an advancement of the current ISO 22196/JIS Z 2801 standard method, as it provides greater ease-of-use and more closely resembles the contamination of common surfaces. The protocol involves inoculating 100 µL droplets containing ~107 microbial cells of a test microorganism onto sets of antimicrobial-treated and untreated control sample material. The sets are protected from dust accumulation and allowed to air dry, which causes all cells within each droplet to encounter the sample surface. The surviving cells are then collected by vortexing in a collection liquid and enumerating to evaluate differences in survival on the antimicrobial-treated and untreated control samples. Overall, the LDI protocol requires 10 hours of basic microbiology over one week and provides a simple means of assessing the efficacy of various antimicrobial coatings and treatments.

Underwater Pulse-Current FCAW - Part 2: Bubble Behaviors and Waveform Optimization

Underwater pulse-current wet welding was proposed in part 1 of this two-part report. The novel technology obtained improved metal transfer and welding process stability. The main reason for droplet oversizing and long transfer cycles was found to be the deviated large droplet stage. In this part, the waveform optimization for both bubble behaviors and metal transfer were investigated. Efforts were made for shortening the duration of the deviated large droplet stage. Pulse current influences on bubble evolution was studied. It was found that two different separation modes can be adjusted by appropriately changing the current values when the bubbles are necking. Quickly reducing the welding cur-rent can sharply lower the impact force on the droplets due to intense gas flow changes inside. Under the optimized pulse current, the range of the metal transfer cycle became narrower, and droplet diameters were smaller than that of the original condition. Stable and improved metal transfer processes were achieved with a frequency of 7.52 Hz and an average droplet diameter of 2.4 mm, which was about 1.5 times the wire diameter. The optimized pulse waveform greatly improved weld formation with less spatter and a more uniform appearance.

A Numerical Investigation on the Collision Behavior of Unequal-Sized Micro-Nano Droplets

Micro-nano droplet collisions are fundamental phenomena in the applications of nanocoating, nano spray, and microfluidics. Detailed investigations of the process of the droplet collisions under higher Weber are still lacking when compared with previous research studies under a low Weber number below 120. Collision dynamics of unequal-sized micro-nano droplets are simulated by a coupled level-set and volume of fluid (CLSVOF) method with adaptive mesh refinement (AMR). The effects of the size ratio (from 0.25 to 0.75) and different initial collision velocities on the head-on collision process of two unequal-sized droplets at We = 210 are studied. Complex droplets will form the filament structure and break up with satellite droplets under higher Weber. The filament structure is easier to disengage from the complex droplet as the size ratio increases. The surface energy converting from kinetic energy increases with the size ratio, which promotes a better spreading effect. When two droplets keep the constant relative velocity, the motion tendency of the droplets after the collision is mainly dominated by the large droplet. On one hand, compared with binary equal-sized droplet collisions, a hole-like structure can be observed more clearly since the initial velocity of a large droplet decreases in the deformation process of binary unequal-sized droplets. On the other hand, the rim spreads outward as the initial velocity of the larger droplet increases, which leads to its thickening.