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This research explores the efficacy of a passive control strategy designed to enhance the performance of an axial hollow fan. This investigation uses a dedicated experimental setup to evaluate various aspects of the fan's performance, including characteristics, efficiency, acoustic emissions, and flow topology. The control strategy involves introducing a portion of the main flow into the hollow fan through an upstream opening in the hub. Capitalizing on centrifugal forces, this air portion is injected into the fan's periphery via an axial slot at the rotating shroud ring. Additionally, to refine the previous strategy, a centrifugal fan is incorporated into the hub to assist in directing the flow toward the hollow blades and effectively overcoming losses. The study's findings reveal that implementing this control strategy broadens the fan's operating range and shifts its optimal operating point towards higher flow rates. This improvement is accompanied by a substantial increase in the fan's power density. Furthermore, a notable reduction in sound emissions of approximately 3 dB was recorded, especially when employing the centrifugal fan in the hub. This control strategy also significantly modifies the flow topology downstream of the fan, shifting it from an axial direction to a radial one. [ABSTRACT FROM AUTHOR]

Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance. [ABSTRACT FROM AUTHOR]

Reactive rotational molding (RAM) is a process to manufacture hollow plastic articles. Comparing to rotational molding of thermoplastics, it decreases the process cycle time due to the reactivity of the system. However, the number of influent parameters is relatively high and optimization of the process is complex. During RRM, the viscosity is one of the key parameters and varies according to the polymer molecular weight due to chemical reactions. Simulation is a way to optimize this process. Prediction of the reactive flow is of great interest to optimize process conditions and wall thickness distribution of the molded part. We developed a solver based on smoothed particle hydrodynamics method. This Lagrangian meshfree method is well adapted to simulate free surface flows like those occurring in ARM. First, we validated the code comparing the simulation results to analytical Couette flow solution and experimental measurements of dam break problem. Then, we performed two-dimensional (2D) and 3D simulations to observe the influence of the change of viscosity on the flow, due to the chemical reactions. Adhesion of the polymer on the mold surface is modeled by new boundary conditions. POLYM. ENG. SCI., 53:2509-2518, 2013. 0 2013 Society of Plastics Engineers, INTRODUCTION Rotational molding is a process for manufacturing the hollow plastic parts from few centimeter to several meters (1), (2). The main advantages of this method are no residual stresses [...]

The aim of this paper is to analyze, from experimental results, the influence of the shape of the leading edge and its sharpening on the cavitating behavior of an inducer. The studied inducer is designed according to a methodology developed at LEMFI. Successive cutting and sharpening (four cuts, which modify up to 20 percent of the blade chord at the tip), were made to modify the shape of the leading edge. For the various geometries, the experimental results obtained on the LEMFI test rig are presented as follows. Noncavitating Regime: Overall performances at 1450 rpm. Cavitating Regime: (1) The development of the cavitation versus the cavitation number, (2) the description of the various cavitation pictures, and (3) the pressure fluctuations measured at the wall at 150 mm downstream of the trailing edge for various flow rates and inlet pressures. The CFD simulations carried out under CFX-Blade Gen + on this range of inducers are presented to explain certain aspects observed.

It is a known fact that incorporating textures in the contact surfaces can significantly enhance bearing performances. The purpose of this paper is to outline the effects of texture bottom profiles and contour geometries on the performances of hydrodynamic textured journal bearings. The analysis was conducted using computational approach to test eight texture shapes: rectangular, cylindrical, spherical, triangular (TR, T1, T2, T3) and chevron. The steady-state Reynolds equation for modelling the hydrodynamic behaviour of thin viscous film was solved using finite difference technique and mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. The comparison with the benchmark data shows good consistency and an enhancement in bearing performances (load carrying capacity and friction). The results clearly show that the mechanisms of wedge effect and micro-step bearing for the full/partial texturing feature are the main crucial parameters, where the convergent wedge effect present in T2 triangular texture shape can significantly enhance the load-carrying capacity, while the divergent wedge action causes a net load loss. Considering the right arrangement of textures on the contact surface, their surface contours can have a significant impact on the performance of hydrodynamic journal bearings at high eccentricity ratios. [ABSTRACT FROM AUTHOR]

Byline: D. Fedala, S. Kouidri, F. Bakir, R. Rey In this paper, a modelling of the broadband noise radiated by an axial subsonic fan is presented and validated. It is an extension of Amiet's model predicting the broadband noise generated by an isolated airfoil. Two sources are analysed, incident turbulence interaction noise and trailing edge noise. It shows the dominance of the leading edge noise. The broadband noise directivity for axial fans presents a main radiation lobe along the fan axis for both mechanisms. It was observed that the leading edge acoustic spectra feature is very sensitive to the turbulence length scale of the incident flow.

Byline: T. Bouquet, S. Kouidri, F. Bakir, R. Rey The study presented in this paper is part of the research work on forward-curved blades centrifugal fans carried out over the last few years by the 'Laboratoire d.Energetique et de Mecanique des Fluides Interne' (Lemfi - Site Paris). The objective of this study is to better understand the internal flow in this type of machine in order to be able to correlate the aeraulic and acoustic behaviours with the geometrical characteristics of the machine. Two impellers with different profiles were manufactured and tested. The aeraulic and acoustic tests were carried out on a test bench standardised ISO 5801. The 3D CFD of the flow was carried out with a commercial code based on the resolution of the Navier-Stokes equations in finite volumes. The analysis of these results confirms that a more organised flow field leads to a better acoustic performance.

In the design procedure of a counter-rotating axial-flow stage, parameters such as the angular velocity ratio and the repartition of the work performed by each rotors are to be chosen. In the present Article, three counter-rotating stages are designed to meet the same working point. These stages have different repartitions of load between the front and rear rotor, different angular velocity ratios or mean stagger angles of the blades of the front rotors. The stage global characteristics and the unsteady features of the flow between the counter-rotating rotors are measured and compared. The three systems all have satisfying overall performances at the design point. Strong differences are observed in the flow field at partial flow rates, the rear rotor reducing the hub recirculation. The behaviour at partial flow rates is thus triggered by the rear rotor characteristics. The best compromise is obtained with a repartition of the loading of 60% for the front rotor and 40% for the rear rotor, with almost equal angular velocities. [ABSTRACT FROM AUTHOR]

An experimental study on the design of counter-rotating axial-flow fans was carried out. The fans were designed using an inverse method. In particular, the system is designed to have a pure axial discharge flow. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The relative axial spacing between fans can vary from 17% to 310%. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system has a very flexible use, with a large patch of high efficient operating points in the parameter space. The increase of axial spacing causes only a small decrease of the efficiency. [ABSTRACT FROM AUTHOR]

A centrifugal fan with a high rotational velocity and compact dimension is studied numerically and experimentally in this paper. The fan consists of a shrouded impeller rotating at 34 000 r/min with a small cavity between the impeller and outer casing. The overall performance and the major flow features have been numerically and experimentally investigated. For the numerical simulation, two computational models with/without the cavity were tested. The modelling of a very-small-size cavity is generally time-consuming, compared with the outer domain. However, it has been shown that its effect can be taken into account with a simple method discussed in this study. A simple volumetric loss model coupled to a numerical modelling of the fan without the cavity gives a very interesting approximation of the global performance of the fan. In the present work, the overall performance and the major flow features of each component inside the fan were numerically investigated. The numerical results at different locations were compared with experimental ones. It is shown that the results obtained by the simplified method and the full numerical simulation both predict the global performance obtained experimentally. Furthermore, in terms of the flow restriction obtained for the centrifugal fan, new empirical coefficients accounting for the effects of the cavity were set. [ABSTRACT FROM AUTHOR]

This article presents a numerical simulation of an unsteady cavitating flow. First, the analysis was carried out for a two-dimensional (2D) venturi-type geometry, and then for a 2D blade cascade simulating an axial inducer. The main purpose of this work is to explore the local cavitation instabilities, such as alternate blade cavitation and rotating blade cavitation, which can appear in axial inducers. The numerical simulation was performed using a commercial code based on a cell-centred finite-volume method. The cavitation model used for calculations assumes a thermal equilibrium between phases. It is based on the classical conservation equations of the vapour phase and the mixture phase, with mass transfer owing to the cavitation appearing as a source and a sink term in the vapour mass fraction equation. The mass transfer rate is derived from a simplified Rayleigh-Plesset model for bubble dynamics. [ABSTRACT FROM AUTHOR]

In the current work, computational fluid dynamics (CFD) technique coupled with experimental investigations has been used in order to study the complex phenomena related to the unsteady flow in a centrifugal fan.The studied phenomena are the interactions and unsteadiness induced by the rotating blades motion relatively to the volute and their impact on the aeroacoustic behaviour of the fan. Thus, three-dimensional and two-dimensional unsteady simulations have been carried out using unsteady Reynolds averaged Navier-Stokes approach. Turbulence has been modelled with the k-ω-shear stress model and a sliding mesh technique has been applied to the interfaces in order to allow unsteady interactions between the rotating (impeller) and the stationary zones (volute casing). The overall performances predicted by the computations have been validated at different flowrates.In order to locate the flow unsteadiness and perturbations, the near field wall pressure fluctuations at different strategic points on the volute surface have been computed. In addition to this, the unsteady flow variables provided by the CFD calculations have been used as inputs in the Ffowcs Williams-Hawkings equation in order to estimate the tonal noise generated by the centrifugal fan. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found. [ABSTRACT FROM AUTHOR]

In this work, experimental and three-dimensional numerical simulations are pursued with the intent of elucidating the differences that the hub shape has on three inducer performances and on other important engineering properties in cavitating and non-cavitating regimes. Two inducers have a cylindrical hub and the third one has a conical hub. They are noted as BH inducer (big hub), SH inducer (small hub), and CH inducer (conical hub). These machines were designed with the goal to reduce the amount of cavitation and vibration, on the one hand, and to improve the overall performance, on the other hand. Both sets of experimental and numerical data suggest that the cavitating and non-cavitating performances are affected by changes in the hub shape. The hub configuration and cavitation numbers considered give rise to various cavitation structures on the suction side of the blades, characterized – at some flow rates – by recirculating flow regions and backflow vortices. The results show the relative superiority of the CH inducer through the critical cavitation coefficient of 5 per cent, even if this inducer is very unstable for all flow rates. It was also found that the BH inducer is the most stable and that for a 15 per cent head drop, the three inducers have quite the same performances. The main experimental and numerical results presented here concern the overall performances, especially the hydrodynamic mechanism of head drop and the visualization of three-dimensional flow structures. We also present the vibratory behaviour versus the flow rate and the suction pressure. The computational three-dimensional flow in non-cavitating regimes enabled us to explain the unstable and cavitating operation for off-design conditions. The numerical computation in cavitating flows is carried out using the computational fluid dynamics (CFD) software CFX-TASCFlow 2.12 , which cavitation model was validated on our BH inducer. [ABSTRACT FROM AUTHOR]

The goal of this paper is to compare the experimental performance within the cavitating regime for three axial inducers identified by the leading edge angle at the periphery of the blades,β1T = 10, 13, 15° and which will be noted as inducer 10° , inducer 13° and inducer 15° . The three-dimensional flow was analysed using the CFD code 'CFX-BladeGENRELSP +'. This enabled us to explain the unstable and cavitating operation for off-design conditions. A brief bibliographic review of the cavitating regime and the outlines of the design method for the three axial inducers that were studied are first presented. Then, for these inducers; the main results are presented: 1) Overall performance—head coefficient and critical cavitation number (5 and 15 per cent drop) vs. the flow rate; 2) Vibration behaviour vs. the flow rate and the suction pressure; and 3) CFD results, which enable us to explain the unstable experimental behaviour for these inducers. [ABSTRACT FROM AUTHOR]

Improvement in computer power and the development of numerical computational methods over the last few years have allowed the emergence of computational fluid dynamic (CFD) codes, making possible the numerical simulation of flow and energy transfer in turbomachines. To improve the efficiency of these tools, fast design software must be used. Within the framework of the optimization process of centrifugal pumps, HELIOX software was developed. It is a tool for design and performance analysis of centrifugal pumps. HELIOX allows quick design of new pumps and improvement of existing ones. HELIOX's performance analysis has been validated through many industrial cases: approximately 100 machines of different sizes and mechanical power. Heliox can be linked to quasi-and three-dimensional analysis tools; these tools enable a better understanding of physical phenomena so as to control the flow fields inside pumps. [ABSTRACT FROM AUTHOR]

This study lies within the scope of a European project, with the objective of studying and designing a tunnel boring machine able to function in continuous mode. This operating mode allows reduction of discontinuities of excavation in order to obtain greater efficiency by reducing the excavation time. The extraction of rubble is carried out by means of a hydraulic circuit composed of a set of special pumps for slurry and of a horizontal hydraulic pipe. The optimal control of the whole installation, pumps included, requires continuous assessment of the mass flow rate of the solid–liquid mixture. During this study, we aimed to develop a methodology of mass flow rate measurement to replace the existing limited method of gamma-densitometer, as the irregularities noticed during various phase measurement reduce the reliability of this technique. This paper presents a theoretical and experimental study which will make it possible to improve the accuracy of measurement carried out by the gamma-densitometer and the development of a method based on the power consumed by the engines driving the pumps. [Copyright &y& Elsevier]

Part II. Presents a study which tested a method that allows the calculation of two-dimensional unsteady flow in a blade cascade. Application of the method to axial fans and a centrifugal pump; Aeroacoustics behavior of axial fans; Impeller-volute tongue interaction in centrifugal pump; Conclusion.

Part I. Presents a study which developed an algorithm using the singularity method that permits the determination of blade to blade flow in the turbomachine rotating cascades with incompressible fluid. Complex conjugate velocity expression for a rotor-stator configuration; Application of the method to the aeroacoustic of axial fans; Application on the impeller volute tongue interaction.

Discusses the numerical stability conditions in the calculation of potential velocity fields. Precision and method of calculation; Geometrical defect at the trailing edge related to the conformal mapping; Trailing-edge geometry of a thin profile.

An opportunity to study the effects of methylmercury poisoning in humans was provided by the large outbreak in Iraq in 1971-2. In adults, poisoning resulted from the ingestion of home-made bread prepared from methylmercury-treated seed grain and there was a highly significant correlation between the amount of bread ingested and blood mercury levels. Poisoning in infants resulted either from prior exposure in utero or from suckling or both. Blood mercury levels were higher in infants and children than in adults. There was no increased incidence of congenital defects. Symptoms and signs of poisoning and histopathological changes were mainly confined to the CNS. Symptoms developed, on average, 1-2 months after exposure. In children there was mental retardation with delayed onset of speech and impaired motor, sensory and autonomic function. Severely affected children were blind and deaf. In adults, the clinical picture could be classified as 1, mild (mainly of sensory symptoms) 2, moderate (sensory symptoms accompanied by cerebellar signs) and 3, severe (gross ataxia with marked visual and hearing loss which, in some cases, progressed to akinetic mutism followed by coma). Grades 1 and 2 carried a better prognosis thant grade 3. Interference with transmission at the myoneural junction was found in 14% of patients studied. There was no evidence of peripheral nerve involvement per se and sensory symptoms may be of central origin. The clinical differences between the Iraqi and Japanese outbreaks may be a result, in part at least, of the severe, prolonged and continuous exposure which occurred in the latter outbreak. Improvement was observed among the mild and moderate group. Treatment with chelating agents, thiol resin, haemodialysis and exchange transfusion lowered blood mercury concentrations but produced no convincing clinical benefit. To be effective, treatment may need to be instituted soon after exposure. [ABSTRACT FROM PUBLISHER]

Copyright of Tropical Animal Health & Production is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The clinical and pathological features of 18 new patients with alpha heavy chain disease seen at two referral centres in Baghdad, Iraq, are described. The series included 14 males and four females ranging in age from 14 to 47 years. Almost all patients presented because of long-standing abdominal pain and diarrhoea. The tissue diagnosis and extent of the disease were established at laparotomy in most patients. Peroral jejunal biospy was used in a number of patients, mainly for follow-up. The serological abnormality was confirmed by immunoselection technique. Most of the patients had extensive thickening of the bowel wall and/or tumour masses of the small intestine and mesenteric nodes. Histopathological sections showed muscularis. Preliminary results of the treatment, including two long remissions, are reported. In general, our observations agree with those made by other authors, mostly from the Middle East and Africa. We believe that a high index of clinical suspicion, routine use of the immunoselection, and recognition of the early pathological changes may hopefully lead to the detection of more cases before the frank neoplastic phase of the disease. [ABSTRACT FROM PUBLISHER]

Hydatid cyst is rarely mentioned among the causes of pneumothorax in text-books or monographs, especially those written in English. Five examples of tension pneumothorax secondary to ruptured hydatid cyst of the lung are reported: the mechanism of this tension effect and helpful diagnostic points are discussed. We think that surgical correction is the only satisfactory treatment of tension pneumothorax due to ruptured hydatid cyst: surgery is advocated in any suspected cyst as soon as it is discovered so as to avoid any such serious complication. [ABSTRACT FROM PUBLISHER]