Aerodynamics of a Supersonic Projectile in Proximity to a Solid Surface

Flow around a Mach 2.4 NATO 5.56 mm projectile in close proximity to a ground plane was investigated using computational fluid dynamics for a direct numerical reproduction of live-range experiments. The numerical approach was validated against both the live-range tests and subsequent wind-tunnel experiments. A nonspinning half-model and a full, spinning projectile were examined to clarify the influence of rotation. Multiple ground clearances were tested to obtain clear trends in changes to the aerodynamic coefficients, and the three-dimensional propagation and reflection of the shock waves were considered in detail. The behavior of the flow in the near wake was also studied as ground clearance was reduced. Ground proximity was found to significantly increase the drag force acting on the projectile, as well as generate a force normal to the ground and an increased side force, when ground clearance was less than one diameter. For clearances between approximately 0.4 and 1 diameter, the pitching moment produced was nose-down. For lower clearances, a more distinct nose-up trend was produced. The generated side force was orders of magnitude lower than the normal and drag forces

Flow Field Phenomena about Lift and Downforce Generating Cambered Aerofoils in Ground Effect

A Computational Fluid Dynamics investigation was conducted to ascertain and highlight the different ways in which ground effect phenomena are present around both an upright (lift generating) and inverted (downforce generating) cambered aerofoil when in close proximity to the ground. The trends in force and flow field behaviour were observed at various ground clearances, while the angle of attack was held constant at 6 degrees. The different mechanisms by which ground effect influences the two different configurations were highlighted through observation of the pressure coefficient plots, contour maps of velocity and turbulence intensity and their effect on the normal and drag forces. The primary contributing factor to the increase in normal force for the lifting aerofoil, as the ground was approached, was a constriction and rise in pressure of the flow. For the downforce aerofoil, a significantly sped up flow increased suction and enhanced downforce. Also discussed is the observation of a reduction in lift for the upright aerofoil as its ground clearance is reduced through high and medium clearances

The validation of a three-stage screening methodology for detecting active convulsive epilepsy in population-based studies in health and demographic surveillance systems.

UNLABELLED: BACKGROUND: There are few studies on the epidemiology of epilepsy in large populations in Low and Middle Income Countries (LMIC). Most studies in these regions use two-stage population-based screening surveys, which are time-consuming and costly to implement in large populations required to generate accurate estimates. We examined the sensitivity and specificity of a three-stage cross-sectional screening methodology in detecting active convulsive epilepsy (ACE), which can be embedded within on-going census of demographic surveillance systems.We validated a three-stage cross-sectional screening methodology on a randomly selected sample of participants of a three-stage prevalence survey of epilepsy. Diagnosis of ACE by an experienced clinician was used as 'gold standard'. We further compared the expenditure of this method with the standard two-stage methodology. RESULTS: We screened 4442 subjects in the validation and identified 35 cases of ACE. Of these, 18 were identified as false negatives, most of whom (15/18) were missed in the first stage and a few (3/18) in the second stage of the three-stage screening. Overall, this methodology had a sensitivity of 48.6% and a specificity of 100%. It was 37% cheaper than a two-stage survey. CONCLUSION: This was the first study to evaluate the performance of a multi-stage screening methodology used to detect epilepsy in demographic surveillance sites. This method had poor sensitivity attributed mainly to stigma-related non-response in the first stage. This method needs to take into consideration the poor sensitivity and the savings in expenditure and time as well as validation in target populations. Our findings suggest the need for continued efforts to develop and improve case-ascertainment methods in population-based epidemiological studies of epilepsy in LMIC

Flow Field Phenomena about Lift and Downforce Generating Cambered Aerofoils in Ground Effect

A Computational Fluid Dynamics investigation was conducted to ascertain and highlight the different ways in which ground effect phenomena are present around both an upright (lift generating) and inverted (downforce generating) cambered aerofoil when in close proximity to the ground. The trends in force and flow field behaviour were observed at various ground clearances, while the angle of attack was held constant at 6 degrees. The different mechanisms by which ground effect influences the two different configurations were highlighted through observation of the pressure coefficient plots, contour maps of velocity and turbulence intensity and their effect on the normal and drag forces. The primary contributing factor to the increase in normal force for the lifting aerofoil, as the ground was approached, was a constriction and rise in pressure of the flow. For the downforce aerofoil, a significantly sped up flow increased suction and enhanced downforce. Also discussed is the observation of a reduction in lift for the upright aerofoil as its ground clearance is reduced through high and medium clearances

FLOW VISUALIZATION OF MICRO SYNTHETIC JETS

The evolution of micro synthetic jet in a still ambient has been studied numerically. Unsteady computations of incompressible laminar flow have been performed for an axisymmetric numerical formulation for an orifice diameter of 50 micrometers. The diaphragm was assumed to oscillate sinusoidally in time and parabolically in space. Vortex pair trajectories were visualized by extracting the vortex cores from the flow data. It was demonstrated that centreline jet velocity reveals the propagation of vortex rings and dynamics of its peak value corresponds to the movement of the vortex cores. Furthermore, it was shown that the location of maximum vorticity could not be used to identify the location of the core

Effect of Inverted Aerofoil Geometry on Aerodynamic Performance in Ground Effect

A two-dimensional Computational Fluid Dynamics (CFD) study was undertaken to examine the effect of various inverted (downforce generating) aerofoil geometry configurations on the ground effect phenomena seen at low ground clearances. Simulations were conducted and comparisons made between a NACA4412 aerofoil, a Tyrrell aerofoil and three modified Tyrrell aerofoils. The results indicate underwing ground effect suction is heavily influenced by the curvature on both sides of the aerofoil