A free boundary problem arising in a model for shallow water entry at small deadrise angles

A free boundary problem arising in a model for inviscid, incompressible shallow water entry at small deadrise angles is derived and analysed. The relationship between this novel free boundary problem and the well-known viscous squeeze film problem is described. An inverse method is used to construct explicit solutions for certain body profiles and to find criteria under which the splash sheet can `split'. A variational inequality formulation, conservation of certain generalized moments and the Schwarz function formulation are introduced

Drop spreading and drifting on a spatially heterogeneous film: capturing variability with asymptotics and emulation

A liquid drop spreading over a thin heterogeneous precursor film (such as an inhaled droplet on the mucus-lined wall of a lung airway) will experience perturbations in shape and location as its advancing contact line encounters regions of low or high film viscosity. Prior work on spatially one-dimensional spreading over a precursor film having a random viscosity field [Xu & Jensen 2016, Proc. Roy. Soc. A 472, 20160270] has demonstrated how viscosity fluctuations are swept into a narrow region behind the contact line, where they can impact drop dynamics. Here we investigate two-dimensional drops, seeking to understand the relationship between the statistical properties of the precursor film and those of the spreading drop. Assuming the precursor film is much thinner than the drop and viscosity fluctuations are weak, we use asymptotic methods to derive explicit predictions for the mean and variance of drop area and the drop's lateral drift. For larger film variability, we use Gaussian process emulation to estimate the variance of outcomes from a restricted set of simulations. Stochastic drift of the droplet is predicted to be greatest when the initial drop diameter is comparable to the correlation length of viscosity fluctuations.Comment: 23 pages, 5 figure

Fluid and energy deficits : hydration markers, saliva immunoglobulin A and endurance performance

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Numerical Analysis of Aerospike Engine Nozzle Performance at Various Truncation Lengths

The aerospike engine was first devised in the early 1960s where it provided new means of reaching orbit in a single stage. The paper aimes to demonstrate the viability of the technology by showcasing the increased nozzle thrust efficiency over the conventional bell nozzle. Various truncations were applied to the nozzle and each was subjected to two conditions, an over-expansion and near optimum condition. The nozzle contour was developed using the simple approximation method and was chosen to replicate that of the XRS-2200. This anchored the data, thereby validating the computational fluid dynamics (CFD) simulation. Simulations were completed for at nozzle pressure ratios (NPR) of 58 and 15. Velocity vector plots and contours were generated in which the recirculation region can be clearly identified. This region is a result of the negative thrust contribution of the base and grows increasingly negative when the truncation applied increases in addition to when the exhaust flow is over-expanded. The results demonstrate the performance gain of the full-length aerospike nozzle, , over all other truncations. At NPRs of 58 and 15 it showed 1.5% and 10.3% gain respectively in the nozzle thrust efficiency compared to . There are, many impracticalities related to the full-length aerospike including cooling on the nozzle. Therefore, provide a realistic nozzle truncation that would be implemented. Although radical design changes to the rocket will be required for the adaptation of the aerospike engines, the changes will be beneficial in the long term. By increasing the nozzle thrust efficiency compared to bell nozzles, less fuel will be required per launch. Furthermore, removing the multi-stage method currently used, overall, the rocket will have an increased reliability due to its reduced complexity

Aerodynamic Design and Exploration of a Blended Wing Body Aircraft at Subsonic Speed

Blended Wing Body (BWB) is a novel aircraft concept which provides many different aerodynamic benefits over conventional aircrafts design. This research investigated the BWB design, L/D characteristics, surface pressure distribution and span-wise lift distribution of a BWB aircraft at low to medium subsonic speeds. A BWB model was designed, manufactured and tested in a subsonic wind tunnel to validate the CFD simulation. The results gained from the investigation proved that BWB has a L/D improvement of 9.4% than conventional aircrafts and 21% increase at medium subsonic speeds (Mach 0.6) compared to lower subsonic speeds of 25 m/sec. It was found that the lift minimally increases between the two speeds; however the improvement is generated due to drag reduction. The drag reduction is accomplished due to boundary layer attachment for a longer period of time before separation occurs. It is this difference which generates the lift to drag ratio improvement