Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-way Eulerian Thin Film/Discrete Phase Approach Part II: Droplet Behaviour in the Chamber

Within aeroengines, bearing chambers exhibit a highly complex two-phase environment as a result of the complex air/oil interactions. The desire to operate at higher temperatures and shaft speeds requires sufficient understanding of these systems for design optimisation. Typically, bearings are used to support the radial and axial loads transmitted by the shafts, requiring oil for lubrication and cooling. These bearings are housed in bearing chambers sealed using airblown seals. Efficient scavenging systems ensure the oil is collected and returned to tank avoiding any unnecessary working of the oil. Previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) has highlighted the need for an adequate computational model that can appropriately model the oil shedding behaviour from such bearings. Oil can breakup forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. The objective of this paper is to explore the modelling capability of fully two-way coupled Eulerian thin film/discrete phase models (ETFM-DPM) applied to our simplified bearing chamber configuration. The models are created using OpenFOAM and two-way coupling is employed, enabling Lagrangian droplets to either impinge on the film surface or be removed through effects such as film stripping, splashing or edge separation. This paper focuses on the droplets, presenting statistics relating to size, velocity, impingement and residence time providing insight into solution sensitivity to operational parameters including shaft speed and oil flow rate. This extends upon our previously published work and improves bearing chamber modelling capability.

Experimental study on the effect of bionic flap parameters on airfoil aerodynamic performance

The effects of bionic flap on airfoil performance were experimentally studied to provide theoretical support for the application of the bionic flap in aeronautical engineering. Seven kinds of bionic flaps were used to study the effects of the key flap parameters, including the flap angle, length, shape, and position, at a Reynolds number of Re = 0.8 × 106. At small angle of attacks (AoAs), the drag and pitching moment increased and the lift reduced when using the bionic flap. While at high AoAs, the lift increased and the drag reduced, which improved the airfoil stall characteristics. The configuration of deflection bionic flap had the smallest initial AoA for improving the airfoil stall characteristics in the seven kinds of bionic flaps. More than eight degrees of the effective AoA range for improving lift characteristics could be achieved. The maximum lift coefficient could be increased by 3.9%. Additionally, the control mechanisms of the flap under different flow conditions (attached flow and separated flow) were deeply studied. In the attached flow, the effective camber and thickness of the basic airfoil could be changed by the flap, resulting that the flow around the airfoil was affected, which in turn affected the Cl and the slope of the lift line. In the separated flow, the flap affected the flow around the airfoil by controlling the development of the trailing edge separation vortex. These research results confirmed the aerodynamic mechanisms for the formation of double layered feathers when birds land, and provided insight into application of bionic flaps in aeronautical engineering.

Effect of Three-Dimensional Aerodynamics and Dynamic Stall on Lead–Lag Damping of an Isolated Rotor

This paper investigates three-dimensional aerodynamic effects due to radial flow on lead–lag damping of a rotor in forward flight conditions. Three-dimensional effects in this study are restricted to yawed flow aerodynamics and radial flow coupling between blade segments. These effects are included in the ONERA dynamic stall model, and lead–lag damping for an isolated torsionally stiff rotor is calculated for different forward flight conditions. This augmented aerodynamic model with three-dimensional effects and Peters–He dynamic wake model improves the correlation of lead–lag damping with experimental data at high advance ratios. The effect of modeling static lift characteristics on damping correlation is also presented. Finally, a modification to the trailing edge separation point–based static lift model for improved yawed flow modeling amenable to aeromechanical stability analysis is proposed.

A Combined Tie-Fastening Method for the Reusable Surgical Gown with Two Neck Tie Belts to Improve Wearing Comfort

The reusable surgical gowns made of slippery materials have the tendency to slip down as they are being worn. The rear neck tie(s) can sometimes loosen, and this causes the surgical gown to slip down somewhat, making the surgical staff members feel uncomfortable. If the gowns have two rear neck ties with a tendency of loosening and allowing the gowns to slip down, the surgical staff members feel more uncomfortable when there is only one tie loosening but the other tie is tethering. To fasten the neck ties of the surgical gown with two neck tie belts, we propose a simplified method of fastening the two sets of tie belts together as one tie, instead of fastening them separately. The object of this study is to evaluate this combined tying method for its ability to secure the gown and its wearing comfort. We enrolled five volunteers to evaluate the tie loosening condition of the reusable surgical gowns with two sets of rear neck tie belts after a series of upper limb motion exercises while wearing and not wearing the X-ray protective apron beneath the gown. The amount of uppermost rear neck cloth edge separation was recorded before and after the exercise. We also evaluated the wearing comfort of five enrolled operating surgeons for comparing the original and this modified tying method while wearing and not wearing the X-ray protective apron. In the results, we found that combined tying tends to have significantly more rear gown separation (0.94 cm) than separate tying (0.27 cm) after vigorous upper extremities exercise. However, during the actual performance of the surgeries, the rear neck tie(s) loosening and wearing discomfort of the combined tying method was significantly less than using the separate tying method (loosening: 0% vs. 30%) (discomfort: 0% vs. 35%) while the X-ray protective apron was not worn. For reusable surgical gowns that have two rear neck ties, we suggest the two sets of rear neck ties could be fastened together as one combined tie in routine surgical practice. With this, tying could be performed easier and faster, and wearing comfort could be improved.