Spectral and bulk properties of turbulence in the surface layer of air over the sea

Imperial Users onl

Radial pressure distributions in an air-riding face seal

International audienceNon-contacting face seals rely on high pressures induced in a thin air-film between stationary and rotating faces. They offer ultra-low leakage and very low wear compared to contacting seals in aircraft engines. Large axial and radial movements and high temperature gradients can cause excessive distortion of the sealing faces which may become amplified at large radii, high differential pressures and rotational speeds. Such distortions alter the geometry of the gap thereby affecting the seal's performance. This paper presents an extensive investigation into the air-film behaviour of a face seal under convergent and divergent engine representative coning distortions = 0.5-2 degrees, gap = 50-300 m, and operating pressure differences =70-350 kPa. The investigation approach is both numerical and experimental. Experimental tests allowed the introduction of a known distortion onto the static face of the seal. Arrays of static pressure tappings in the primary sealing gap were used to measure the radial and circumferential variations. The experimental data are used to validate a 3D CFD model of the primary leakage path. The CFD model was generated using ANSYS ICEM and solved using ANSYS FLUENT. The models were run at the full range of operating pressures and geometries. Results show that converging coning provides the largest air-film pressures and hence the largest opening force while a diverging coning provided the least. At higher pressure ratios divergent gaps exhibited expanding supersonic flow but with unexpected levels of pressure recovery within the diverging duct. The pressure loss at the entrance to the gap was observed to be significant, particularly where entry gaps are larger. This effect was partially captured by CFD. The most significant discrepancies between CFD predictions and experiments were for the converging gap cases where the increased air-film pressure causes the disc to deform under pressure resulting in the CFD model over-predicting the pressure in the gap

Radial pressure distributions in an air-riding face seal

International audienceNon-contacting face seals rely on high pressures induced in a thin air-film between stationary and rotating faces. They offer ultra-low leakage and very low wear compared to contacting seals in aircraft engines. Large axial and radial movements and high temperature gradients can cause excessive distortion of the sealing faces which may become amplified at large radii, high differential pressures and rotational speeds. Such distortions alter the geometry of the gap thereby affecting the seal's performance. This paper presents an extensive investigation into the air-film behaviour of a face seal under convergent and divergent engine representative coning distortions = 0.5-2 degrees, gap = 50-300 m, and operating pressure differences =70-350 kPa. The investigation approach is both numerical and experimental. Experimental tests allowed the introduction of a known distortion onto the static face of the seal. Arrays of static pressure tappings in the primary sealing gap were used to measure the radial and circumferential variations. The experimental data are used to validate a 3D CFD model of the primary leakage path. The CFD model was generated using ANSYS ICEM and solved using ANSYS FLUENT. The models were run at the full range of operating pressures and geometries. Results show that converging coning provides the largest air-film pressures and hence the largest opening force while a diverging coning provided the least. At higher pressure ratios divergent gaps exhibited expanding supersonic flow but with unexpected levels of pressure recovery within the diverging duct. The pressure loss at the entrance to the gap was observed to be significant, particularly where entry gaps are larger. This effect was partially captured by CFD. The most significant discrepancies between CFD predictions and experiments were for the converging gap cases where the increased air-film pressure causes the disc to deform under pressure resulting in the CFD model over-predicting the pressure in the gap

The estimation of a preference-based measure of health from the SF-36

This paper reports on the findings of a study to derive a preference-based measure of health from the SF-36 for use in economic evaluation. The SF-36 was revised into a six-dimensional health state classification called the SF-6D. A sample of 249 states defined by the SF-6D have been valued by a representative sample of 611 members of the UK general population, using standard gamble. Models are estimated for predicting health state valuations for all 18,000 states defined by the SF-6D. The econometric modelling had to cope with the hierarchical nature of the data and its skewed distribution. The recommended models have produced significant coefficients for levels of the SF-6D, which are robust across model specification. However, there are concerns with some inconsistent estimates and over prediction of the value of the poorest health states. These problems must be weighed against the rich descriptive ability of the SF-6D, and the potential application of these models to existing and future SF-36 data set

Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UV

Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterise tuneable 3fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.Comment: 5 pages, 4 figure

P4_5 The Relativistic Ionisation Speed Limit

The paper explores a possible speed limit to be enforced on relativistic vehicles so as to not expose pedestrians to ionising electromagnetic radiation; a result of Doppler shifted light from the vehicle’s headlights. A maximum speed limit of 2.89 × 108 ms-1, 0.96 times the speed of light, was established.Â

P4_4 The Solar Cell Efficiency of Superman

The paper investigates how efficiently Superman must absorb energy from the Sun's emission spectrum to be able to perform flight for 8 hours at a constant altitude. A solar cell efficiency of 656000% is calculated, which seemingly disobeys the law of conservation of energy assuming the model of Superman as a solar cell is reasonable

P4_1 Dead Sea Walking

The paper investigates the possibility of walking on the water of the Dead Sea under the assumption that salt can be added to the lake. The current salinity is not sufficient to enable a person to walk on the water. Theoretically, this feat would be achievable if the lake contained 9.71 × 1015 kg of salt. Practically, this amount of salt would not dissolve in the volume of water present in the Dead Sea

P4_2 Using the Forks: The Energy Yield of a Lightning Bolt

Lightning may be considered as a potential energy source if the yield is comparable to other renewable energy sources. The energy yield of one strike was evaluated to be 7.5×107 J, where approximately 50 strikes produce a yield equivalent to that of an average wind turbine in a year