Modelling the vibration of tyre sidewalls

This is the author's accepted manuscript of the article published in the Journal of Sound and Vibration - available at http://www.elsevier.co

Discussion of ‘On the theory of standing waves in tyres at high vehicle speeds’ by V.V. Krylov and O. Gilbert, Journal of Sound and Vibration 329 (2010) 4398-4408

This is the author's accepted manuscript of the article published in the Journal of Sound and Vibration - available at http://www.elsevier.co

Decomposition of the forces on a body moving in an incompressible fluid

The identification of separate physical features contributing to the force resultants on a moving body is useful for insight into the associated flow, and for conceptual modelling. A natural approach is to seek a component due to viscosity and an `inviscid' remainder. It is also attractive to invoke the well-known decomposition of the velocity field into irrotational and rotational parts, and apportion the force resultants accordingly. Unfortunately, this leads to coupled contributions; the resultants nominally associated with the rotational velocities depend also on the irrotational velocity field. Here, an alternative is presented, in which the inviscid resultants are split into independent `convective' and 'accelerative' components. The former are associated with the pressure field that would arise in an inviscid flow with (instantaneously) the same velocities as the real one, and with the body's velocity parameters --- angular and translational --- unchanging. The latter correspond to the pressure generated when the body accelerates from rest in quiescent fluid with its given rates of change of angular and translational velocity. They are reminiscent of the classical, `added-mass', force resultants associated with irrotational flow, but differ crucially in applying without restriction. They are also simpler than the developed expressions for the added-mass force and moment. Finally, the force resultants due to viscosity also include a contribution from pressure. Its presence is necessary because the convective and accelerative components alone are insufficient to satisfy the equations governing the pressure field, but its existence does not seem to have been widely recognised

Interpolation for de-Dopplerisation

'De-Dopplerisation' is one aspect of a problem frequently encountered in experimental acoustics: deducing an emitted source signal from received data. It is necessary when source and receiver are in relative motion, and requires interpolation of the measured signal. This introduces error. In acoustics, typical current practice is to employ linear interpolation and reduce error by over-sampling. In other applications, more advanced approaches with better performance have been developed. Associated with this work is a large body of theoretical analysis, much of which is highly specialised. Nonetheless, a simple and compact performance metric is available: the Fourier transform of the `kernel' function underlying the interpolation method. Furthermore, in the acoustics context, it is a more appropriate indicator than other, more abstract, candidates. On this basis, interpolators from three families previously identified as promising --- piecewise-polynomial, windowed-sinc, and B-spline-based --- are compared. The results show that significant improvements over linear interpolation can straightforwardly be obtained. The recommended approach is B-spline-based interpolation, which performs best irrespective of accuracy specification. Its only drawback is a pre-filtering requirement, which represents an additional implementation cost compared to other methods. If this cost is unacceptable, and aliasing errors (on re-sampling) up to approximately 1% can be tolerated, a family of piecewise-cubic interpolators provides the best alternative

Investigation of unsteady surface pressures over a two-wheeled landing-gear model

© 2016 by A. Gatto. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.Unsteady flow around deployed landing gears is a significant contributor to aircraft noise on approach. The farfield sound is largely determined by the fluctuating pressures on the gear surface, quantities that have yet to be fully characterized even for simplified representations. The current work reports axle- and wheel-surface data from a comprehensive set of measurements on a generic, two-wheel, landing-gear model. The results show the expected high levels of unsteadiness on areas exposed to large-scale separated flow, of which some (wheel rear surfaces and forward edges) can be identified from steady data, but others (wheel faces adjacent to axle wakes, flow impingements on sidewalls) cannot. The forward-edge values for the current, untripped configuration are markedly greater than previously reported measurements with artificial transition fixing. Spectral analysis highlights a further category of potentially important contributions that are not easily detected in overall rms values: high-frequency unsteadiness associated with turbulent attached, or attaching, flows. A key implication of these results is the need for accurate representation of the true, full-scale, boundary-layer state in computations and model-scale testing. Copyrigh

The influence of yaw on the unsteady surface pressures over a two-wheeled landing-gear model

Landing-gear noise is an increasing issue for transport aircraft. A key determinant of the phenomenon is the surface pressure field. Previous studies have described this field when the oncoming flow is perfectly aligned with the gear. In practice, there may be a cross-flow component; here its influence is investigated experimentally for a generic, two-wheel, landing-gear model. It is found that yaw angles as small as 5{\deg} cause significant changes in both overall flow topology and unsteady surface pressures. Most notably, on the outboard face of the leeward wheel, large-scale separation replaces predominantly attached flow behind a leading-edge separation bubble. The effect on unsteady surface pressures includes marked shifts in the content at frequencies in the audible range, implying that yaw is an important parameter for landing-gear noise, and that purely unyawed studies may not be fully representative of the problem

Noise from a Model-Scale Vertical-Axis Wind Turbine

Vertical-axis wind turbines are an attractive option for small-scale wind-power installations. In this application, noise is crucially important. To investigate the problem, measurements taken from a model-scale turbine in a wind tunnel are considered. The sound radiated by the model is clearly evident in the cross-spectra from a pair of flush-mounted microphones. Parameter studies show that, in the normal operating range, speed is the dominant factor. The main source appears to be blade self-noise, although there are also indications of blade-wake interaction in the downstream half of the rotation path. Boundary-layer trips have a significant impact, showing that laminar instability is an important contributor to the self-noise. It will remain a risk at full scale, and its absence should be ensured at the design stage. To minimize the remaining sound radiation (at a given wind speed), configurations with lower tip-speed ratio at maximum power output should be preferred to ones having higher values of this parameter

Restrictive covenants in Xanadu

Legal scholarship is naturally inclined towards explanations and justifications of contemporary law. In the case of restrictive covenants and building schemes this has led to a distorted perception of the historical record, as revealed in recorded case reports dating from the nineteenth century. It is argued that the restrictive covenant had its historical genesis not in a response to industrialisation and mass urbanisation, but in the developments of resort towns in the eighteenth and early nineteenth centuries, as a response to the needs of land developers. Furthermore, it is argued that a better historical understanding of these origins illuminates contemporary problems concerned with the adaptability of law and the potential roles of law in development