This paper reports a new method of generating two light sheets using a dye laser system and the use of this dual-plane dye laser system to analyse average helicity and energy dissipation in a turbulent swirling flow. The dualplane PIV system that was used in this study consisted of three cameras and a single frequency Nd:YAG laser, which was used to generate two parallel light sheet planes with differing wavelengths(colour). The method of generating two different light sheet wavelengths using a single laser source is an innovative and new technique. Stereoscopic PIV measurements were obtained in one plane with the use of two CCD cameras, and standard PIV measurements were obtained in the other plane with the use of one CCD camera. The light scattered by the particles on two different light sheets were separated using appropriate optical filters. The measurements obtained were used to estimate the components of the velocity gradient tensor. The tensor components were then used to determine the average vorticity components and helicity quantities of the fluid that was investigated. To determine the average turbulent kinetic energy dissipation, the continuity equation was used to infer the out-of-plane gradient of the out-of-plane velocity. From the analysis of the results, it was found that regions with high helicity were correlated with regions of high turbulent kinetic energy dissipation. Exp Fluids (2008) 45:973-986 975

This paper is concerned with the potential use of Helmholtz resonators to provide increased acoustic damping within aero gas turbine combustion systems. Experimental measurements were undertaken using a high intensity facility into which a three burner combustor sector (non-reacting) model could be incorporated. In this way the performance of various damper geometry combinations were assessed. The effect of incident noise levels was also considered along with the associated transition from linear absorption (i.e. where absorption is directly proportional to incident pressure magnitude) to nonlinear absorption (i.e. where the proportion of acoustic loss decreases with increasing noise levels). This complicates the performance comparison between different damping geometries and means care is required when relating laboratory to engine operating conditions. In addition, all the measurements were undertaken in the presence of fuel injectors and other realistic flow field features found within a combustion system and which could affect damping performance. Finally, experimental and numerical assessment was made of the noise levels at which ingestion of hot gas will occur into the resonator cavities with and without the presence of a purging flow. For the geometries investigated ingestion occurs when the fluid displacement in the neck during an acoustic cycle is approximately equal to, or greater than, the resonator neck length. The ratio of fluid displacement and neck length provides a limit for the noise levels at which hot gas is ingested into the cavity and hence the operating condition where damping performance and system mechanical integrity is significantly compromised.

The purpose of this study was to adapt wavelet analysis as a tool for discriminating speech samples taken from healthy subjects across two biological states. Speech pressure waveforms were drawn from a study on effects of hormone fluctuations across the menstrual cycle on language functions. Speech samples from the vowel portion of the syllable 'pa', taken at the low-and high-hormone phases of the menstrual cycle, were extracted for analysis. Initial analysis applied Fourier transforms to examine the fundamental and formant frequencies. Wavelet analysis was used to investigate spectral differences at a more microbehavioural level. The key finding showed that wavelet coefficients for the fundamental frequency of speech samples taken from the high-hormone phase had larger amplitudes than those from the low-hormone phase. This study provided evidence for differences in speech across the menstrual cycle that affected the vowel portion of syllables. This evidence complements existing data on the temporal features of speech that characterise the consonant portion of syllables. Wavelet analysis provides a new tool for examination of behavioural differences in speech linked to hormonal variation.

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