is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. We experimentally study the turbulent flow between two coaxial and independently rotating cylinders. We determined the scaling of the torque with Reynolds numbers at various angular velocity ratios ͑Rotation numbers͒ and the behavior of the wall shear stress when varying the Rotation number at high Reynolds numbers. We compare the curves with particle image velocimetry analysis of the mean flow and show the peculiar role of perfect counter-rotation for the emergence of organized large scale structures in the mean part of this very turbulent flow that appear in a smooth and continuous way: the transition resembles a supercritical bifurcation of the secondary mean flow.

The technique for obtaining detailed velocity fields in a wavy liquid layer in stratified air/water pipe flow is described in this paper. By combining Particle Image Velocimetry (PIV) with an interface detection technique, the velocity field is resolved in the whole liquid layer. Furthermore, since the shape of the interface is resolved at each time instance, this information is used to conditionally average the velocity field according to the wave phase, which results in phaseresolved velocity profiles. These velocities are then used to separate the wave-induced motion from the turbulenceinduced motion in the liquid layer. In this way, the turbulent wavy regime is analysed. The results of the measurements are compared to the theory of waves and turbulence.

We investigate the deformation of a linear viscoelastic compliant coating in a turbulent flow for a wide range of coating parameters. A one-way coupling model is proposed in which the turbulent surface stresses are expressed as a sum of streamwise-travelling waves with amplitudes determined from the stress spectra of the corresponding flow over a rigid wall. The analytically calculated coating deformation is analysed in terms of the root-mean-square (r.m.s.) surface displacement and the corresponding point frequency spectra. The present study systematically investigates the influence of five coating properties namely density, stiffness, thickness, viscoelasticity and compressibility. The surface displacements increase linearly with the fluid/solid density ratio. They are linearly proportional to the coating thickness for thin coatings, while they become independent of the thickness for thick coatings. Very soft coatings show resonant behaviour, but the displacement for stiffer coatings is proportional to the inverse of the shear modulus. The viscoelastic loss angle has only a significant influence when resonances occur in the coating response, while Poisson’s ratio has a minor effect for most cases. The modelled surface displacement is qualitatively compared with recent measurements on the deformation of three different coatings in a turbulent boundary-layer flow. The model predicts the order of magnitude of the surface displacement, and it captures the increase of the coating displacement with the Reynolds number and the coating softness. Finally, we propose a scaling that collapses all the experimental data for the r.m.s. of the vertical surface displacement onto a single curve.

This paper assesses the spatial resolution and accuracy of tomographic particle image velocimetry (PIV). In tomographic PIV the number of velocity vectors are of the order of the number of reconstructed particle images, and sometimes even exceeds this number when a high overlap fraction between adjacent interrogations is used. This raises the question of the actual spatial resolution of tomographic PIV in relation to the various flow scales. We use a Taylor-Couette flow of a fluid between two independently rotating cylinders and consider three flow regimes: laminar flow, Taylor vortex flow and fully turbulent flow. The laminar flow has no flow structures, and the measurement results are used to assess the measurement uncertainty and to validate the accuracy of the technique for measurements through the curved wall. In the Taylor vortex flow regime, the flow contains large-scale flow structures that are much larger than the size of the interrogation volumes and are fully resolved. The turbulent flow regime contains a range of flow scales. Measurements in the turbulent flow regime are carried out for a Reynolds number Re between 3,800 and 47,000. We use the measured torque on the cylinders to obtain an independent estimate of the energy dissipation rate and estimate of the Kolmogorov length scale. The data obtained by tomographic PIV are assessed by estimating the dissipation rate and comparing the result against the dissipation rate obtained from the measured torque. The turbulent flow data are evaluated for different sizes of the interrogation volumes and for different overlap ratios between adjacent interrogation locations. The results indicate that the turbulent flow measurements for the lowest Re could be (nearly) fully resolved. At the highest Re only a small fraction of the dissipation rate is resolved, still a reasonable estimate of the total dissipation rate could be obtained by means of using a sub-grid turbulence model. The resolution of tomographic PIV in these measurements is determined by the size of the interrogation volume. We propose a range of vector spacing for fully resolving the turbulent flow scales. It is noted that the use of a high overlap ratio, that is, 75 %, yields a substantial improvement for the estimation of the dissipation rate in comparison with data for 0 and 50 % overlap. This indicates that additional information on small-scale velocity gradients can be obtained by reducing the data spacing.

Cardiac pressure-volume relations enable quantification of intrinsic ventricular diastolic and systolic properties independent of loading conditions. The use of pressure-volume loop analysis in early stages of development could contribute to a better understanding of the relationship between hemodynamics and cardiac morphogenesis. The venous clip model is an intervention model for the chick embryo in which permanent obstruction of the right lateral vitelline vein temporarily reduces the mechanical load on the embryonic myocardium and induces a spectrum of outflow tract anomalies. We used pressure-volume loop analysis of the embryonic chick heart at stage 21 (3.5 d of incubation) to investigate whether the development of ventricular function is affected by venous clipping at stage 17, compared with normal control embryos. Steady state hemodynamic parameters demonstrated no significant differences between the venous clipped and control embryos. However, analysis of pressure-volume relations showed a significantly lower end-systolic elastance in the clipped embryos (slope of the end-systolic pressure-volume relation: 5.68 Ϯ 0.85 versus 11.76 Ϯ 2.70 mm Hg/L, p Ͻ 0.05), indicating reduced contractility. Diastolic stiffness tended to be increased in the clipped embryos (slope of end-diastolic pressure-volume relation: 2.74 Ϯ 0.56 versus 1.67 Ϯ 0.21, p ϭ 0.103), but the difference did not reach statistical significance. Animal models are required to study mechanisms of early cardiovascular development. The chick embryo has been used as a model for many decades because the embryonic chick heart resembles the developing human heart in many aspects (1,2). The intricate relationship between hemodynamics and cardiac morphogenesis has been a major study topic in this model. The venous clip model is an intervention model for the chick embryo in which permanent obstruction of the right lateral vitelline vein temporarily reduces the mechanical load on the embryonic myocardium and induces a spectrum of outflow tract anomalies (3). This model was designed to obtain insight into the effects of altered venous return patterns on cardiac morphogenesis and malformations (4).