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Two-phase bubbly flows are found in many industrial applications. These flows involve complex local phenomena that are still poorly understood. For instance, two-phase turbulence modelling is still commonly based on single-phase flow analyses. A direct numerical simulation (DNS) database is described here to improve the understanding of two-phase turbulent channel flow at a parietal Reynolds number of 127. Based on DNS results, a physical interpretation of the Reynolds stress and momentum budgets is proposed. First, surface tension is found to be the strongest force in the direction of migration so that budgets of the momentum equations suggest a significant impact of surface tension in the migration process, whereas most modelling used in industrial application does not include it. Besides, the suitability of the design of our cases to study the interaction between bubble-induced fluctuations (BIF) and single-phase turbulence (SPT) is shown. Budgets of the Reynolds stress transport equation computed from DNS reveal an interaction between SPT and BIF, revealing weaknesses in the classical way in which pseudoturbulence and perturbations to standard single-phase turbulence are modelled. An SPT reduction is shown due to changes in the diffusion because of the presence of bubbles. An increase of the redistribution leading to a more isotropic SPT has been observed as well. BIF is comprised of a turbulent (wake-induced turbulence, WIT) and a non-turbulent (wake-induced fluctuations, WIF) part which are statistically independent. WIF is related to averaged wake and potential flow, whereas WIT appears when wakes become unstable or interact with each other for high-velocity bubbles. In the present low gravity conditions, BIF is reduced to WIF only. A thorough analysis of the transport equations of the Reynolds stresses is performed in order to propose an algebraic closure for the WIF towards an innovative two-phase turbulence model.

The prediction of void fraction, which relies on interfacial force models, is a major issue in the context of boiling. The two-fluid model requires the modelling of the momentum transfer between phases. When bubbles are small (particle hypothesis), the momentum transfer is related to interfacial forces acting on bubbles. However, the splitting of these forces into drag, lift, added mass, etc., is not straightforward from the local point of view, where only the total interfacial force is defined as an integral of the constraint over the interface. For large-size bubbles, the particle hypothesis can be questioned. The momentum transfer can then be connected to the forces acting on a fluid element of the vapour phase. Based on the local and averaged formulations of the Navier–Stokes equations, a new balance equation for forces enables us to define lift, drag, added-mass and dispersion forces acting on a fluid element of the vapour phase. This equation gives a local definition for all the forces responsible for spatial distribution of bubbles and reflects the meaning usually assigned to the interfacial forces in the particle approach. Through this means, the link between the local formulation and physical phenomena is established and a new way of modelling the lift force is proposed. Furthermore, a new laminar dispersion force which relies on surface tension and pressure effects is introduced. The analysis of the budget equation on our direct numerical simulation database brings into light the large influence of this laminar dispersion force in the migration process. Different well-known physical behaviours can be modelled via this new force: the horizontal clustering of spherical bubbles in laminar flows and the oscillating trajectories of deformable bubbles.

The early detection of breast cancer is the best means to minimise disease-related mortality. Current screening techniques have limited sensitivity and specificity. Breast nipple aspirate fluid can be obtained noninvasively and contains proteins secreted from ductal and lobular epithelia. Nipple aspirate fluid proteins are breast specific and generally more concentrated than corresponding blood levels. Proteomic analysis of 1 μl of diluted nipple aspirate fluid over a 5–40 kDa range from 20 subjects with breast cancer and 13 with nondiseased breasts identified five differentially expressed proteins. The most sensitive and specific proteins were 6500 and 15 940 Da, found in 75–84% of samples from women with cancer but in only 0–9% of samples from normal women. These findings suggest that (1) differential expression of nipple aspirate fluid proteins exists between women with normal and diseased breasts, and (2) analysis of these proteins may predict the presence of breast cancer.

Unsteady flow character is evident; transient regimes may also be considered in some cases. Nowadays, N.S calculations has the advantage to give detailed information of the flow in any kind of locations. However, this big amount of information does not give indication on what geometrical modification will improve the flow characteristics and machine performances. Perform the use of good models in also a key point. Several level of approximation already exists depending on the kind of information that has to be reached.A better insight in needed, based on theoretical consideration in order to understand and identify flow mechanism is given thereafter.

A two dimensional stability analysis is introduced to study the characteristics of rotating stall in a wide radial vaneless diffuser. The prediction of the critical flow angle and propagation velocity given by a linear stability model are given and compared to existing results in literatures. The growth rate of the different competitive mode are used do try to determinate the dominant stall mode. The equations used for a weakly nonlinear analysis which focusing on a small distance from the critical condition are then proposed.

Performance characteristics of a centrifugal pump under gas-liquid mixture are presented, using a direct coupled single-stage, single-suction centrifugal pump. Both experimental and numerical simulations comparison are carried out, for three different rotational speeds and different inlet gas volume fractions, the results of which are presented, based on dimensionless coefficients from similarity laws. The numerical results show that good agreement is obtained with experimental data at nominal rotational speed for several flow coefficients. It is found that the running of the pump is near the sudden break down of the present pump when the inlet void fraction is below 7%. However, numerical results are less sensitive to rotational speed effects compared with experiment ones; the influence of decreasing rotational speed on pump performances is more and more pronounced when inlet gas void fraction increases and flow coefficient decreases. Froude number effects are taken into account in order to explain part of these differences.

The realization and the validation of a simulation in fluid mechanics require an in-depth expertise of the modelling process. However, how could the results be guaranteed if they were not accompanied by experimental measurements? On the other hand experimental measurements show some limitations. For example, PIV measurements are limited to certain viewing planes and rarely near the walls. Moreover, this type of results rarely represents instantaneous results but rather a temporal average of the flows over the measurement time. The use of measurement probes is an intrusive method that can modify the flow and which, as the previous method leads to a mean time result. The purpose of this paper is to analyse the experimental results of the SHF pump which have already been the subject of numerous publications by using the results of the CFD which were made with the computing code star CCM +. This paper includes the comparisons between calculations and measurements inside the diffuser which makes possible to comment on the usefulness and the validity of the stationary measurements despite the unsteady nature of the flow. The analysis highlights the influence of leak rates at the entrance of the diffuser and shows a significant influence of these leak rates on the creation of recirculation swirls that disturb the flow at the entrance of some diffuser channels.

The cavitating behavior of a four-blade inducer tested in the LML laboratory large test facility is considered in the present paper. Experimental investigations based on unsteady pressure measurements and records from a six-component balance mounted on the inducer shaft are performed. Spectral analysis of the signals enables to detect several characteristic frequencies related to unbalanced two-phase flow patterns. The objective of the present paper is the understanding of the physical phenomena associated to these frequencies. Therefore, wavelet decomposition, flow visualizations, and direct analysis of the high-frequency force, moment, and pressure signals are applied. Results at nominal flow rate only are considered. Not only classical unbalanced cavitation patterns, but also unexpected flow organizations are discussed.

This paper focuses on the unsteady flow behaviour inside the vaned diffuser of a radial flow pump model, operating at partial flowrates (0.387Qi, 0.584Qi and 0.766Qi where Qi is the impeller design flowrate).The effects of the leakage flows are taken into account in the analysis. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation, for several flowrates and different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-holes probe in the same experimental conditions. The unsteady numerical simulations were carried out with Star CCM+ 10.02 code with and without leakage flow. The PIV measurements showed a high unsteadiness at very low flowrate which was confirmed by the numerical calculations. In previous studies it has been shown that the global performances, as the efficiencies are in good agreement between calculations and measurements. In this paper, a joint analysis of measurements and numerical calculations is proposed to improve the understanding of the flow behaviour in a vaned diffuser.

Two-phase bubbly flows are found in many industrial applications. These flows involvecomplex local phenomena that are still poorly understood. For instance, two-phaseturbulence modeling is still commonly based on single-phase flow analyses. A directnumerical simulation (DNS) database is described here to improve the understandingof two-phase turbulent channel flow at Re et964; = 127. Based on DNS results, a physicalinterpretation of Reynolds stresses and momentum budgets is proposed. First, surfacetension is found to be the strongest force in the direction of migration so that budgets ofthe momentum equations suggest a significant impact of surface tension in the migrationprocess, whereas most modeling used in industrial application do not include it. Besides,the suitability of the design of our cases to study the interaction between bubble-induced fluctuations (BIF) and single-phase turbulence (SPT) is shown. Budgets of theReynolds stresses transport equation computed from DNS reveal an interaction betweenSPT and BIF, revealing weaknesses in the classical way in which pseudoturbulence andperturbations to standard single-phase turbulence are modeled. An SPT reduction isshown due to changes in the diffusion because of the presence of bubbles. An increaseof the redistribution leading to a more isotropic SPT has been observed as well. BIF iscomprised of a turbulent (Wake Induced Turbulence, WIT) and a non-turbulent (WakeInduced Fluctuations, WIF) part which are statistically independent. WIF is related toaveraged wake and potential flow, whereas WIT appears when wakes become unstable orinteract with each other for high-velocity bubbles. In the present low gravity conditions,BIF is reduced to WIF only. A thorough analysis of Reynolds stresses transport equationsis performed in order to propose an algebraic closure for the WIF towards an innovativetwo-phase turbulence model.